Document By74ajMyX7mGyN3nMDgVLv6Gw

PLAINTIFFS I i IV I Patented Sept. 27, 1938 PLAINTIFF'S EXHIBIT WV-05736 2,131,374 UNITED STATES PATENT OFFICE 2.131,374 DOLOhniiC aiAGNRSIt'M CARBONATE COM POSITION AND METHOD OF PREPARA TION Bertrand B, Orumratd, deceased, late of Alameda, . Calif,, by Dorothy H, Crurtw&ld, ad/atolstratrti, Alameda, Calif. No Drawing. Application August 17, 1936, Serial No. 98,474 21 Claims. (C). 23--156) The Invention relates to magnesium carbonate compositions of the type suitable lor insulating purposes, and more particularly to an Improved composition of this character made from doio5 mitic material as tb source ei raw material, la which tits compounds of calcium derived from the dolomitlc material arc not removed or sep arated for the purpose of providing a final prod uct of the requisite degree of lightness, strength and Insulating properties, but remain In the Ana) produe\ and also to an improved process for producing such composition whereby the. com position hvj the property of self or hydraulically setting without shrinkage. This application Is *i i a continuation In part of the co-pen<ting appH* cation Serial No. 717,077, filed March 23, 1934. Magneslusj carbonate compositions are used In sound and heat Insulating and slmii&r prod ucts, and although they can be made directly 20 from magnesite or other sources consisting es sentially of magnesium compounds, the source of rnw material, in this country at least, is primcuiiy true dolomite or similar doiomltlc material such as doiomltlc limestones, containing both mac23 ncslum and calcium compounds, primarily in the form of carbonate*. This la so because the sup ply of doiomltlc material to this country Is much greater than that of material composed primarlly of magnesium compounds; the latter sna'd tcrial being commercially available only on the west coast of the Onited Slates in the States of California and Washington, Practically 8$*& of the magnesium carbonate compositions manu factured In this country are made from dolo"7 mitio material as the source. For use In insulating products, magnesium carbonate compositions must meet certain com mercial specifications os to weight, strength and '.nsuiaUng properties, the latter, of course, being so partially a function of the weight because the more dense the product the less porous it win be. In order to satisfy such specifications, other commercial processes 'require that the calcium compounds be eliminated In the preparation of 'i* the final magnesium carbonate composition when doiomltlc material is the source of raw material. Such elimination step obviously involves consid erable expense, and as a result increases the cost of manuiacuire of the product from doi&mltie material as the urce, lei the preparation of the magnesium car bonate composition by other processes. It is the general practice to gas an aqi.rous suspevalon of caleined dolomltlc material with carbon diox65 ide-containing gas to precipitate calcium car bonate which remains Insoluble. Magnesium carbonate also precipitates out, but the gassing Is continued to such an extent as to convert the magnesium 'Compounds to form magnesium bi carbonate which is water soluble, to thus enable 6 Ihe insoluble calcium carbonate to be separated from ihe magnesium bicarbonate solution by fil tration or other sutiabU way. Subsequently, a precipitate of basic magnesium carbonate is ob tained fay heating the solution of the magnesium ?0 Bicarbonate. la such other methods, it is necessary in order to form vhe resultant magnesium carbonate in blocks or slabs of the desired shape and size, to mold the product in suitable forms under rela- ,r` lively high mechanical pressure because the mag nesium carbonate lacks self-setting properties 1. e.. it cannot undergo a hydraulic set. This molding e-quipmeot is expensive to maintain and operate as well as to construct. Furthermore, SO because of the pressure applied during the mold ing, the product Is compacted and consequently made more dense than would occur In a corre sponding product having self-setting properties. This U another reason, why, in addition to the 23 greater weight of the calcium carBonate com pares to that of magnesium, the calcium com pounds have to be removed in. other present com mercial processes. The Invention is designed to overcome the above described problems heretofore encountered in the manufacture of magnesium carbonate compositions from dolomJtic tnaieiiat as the source, and has as objects among others, the provision of an improved: tl> Light weight, yet strong magnesium catboaate composition from dolomltic material as the source, In which substantially all ol the cal cium occurring In such source in ihe form of a compound, remains in the final composition or w product In the form of a calcium compound. <2> Composition, of the character related, hav ing seif or hydraulic setting'properties; fS> Composition, of the character related, hav ing improved insulating properties, sad which a:< can be economically produced; and U> Process for obtaining such composition from doiomltlc material. Other objects of the invention win become apparent from a peruseS of the following desenptien thereof, In general, it has been found that during gas sing of an aqueous suspension of calcined doiomuic materia), with carbon dioxide-coatnSnJng gas, calcium carbonate is first formed as a precl- 68 WV-05736 2 2,131,374 pltate. and then upon continued gassing, a preci pirate ofcoraparatlvei y thin. needie-Ukc crystals of & carbonate of magnesium is formed- If s slurry containing the precipitated calcium car' beuate and the thin, needle-Jike earbou&le of magnesium crystals Is cast or poured Into a form or mold, the composition will set In a quiescent state'without application of mechanical pressure t>'*iveto, to provide the strong, and light weight i self*ttlng product of the invention. The set ting In the mold Is enhanced by application ol heat, , In other words, it hat been found that when the described aqueous suspension of calcined dolotolilc material ts gassed with carbon dioxide* containing gas to the polul where, in addition to the Insoluble calcium, carbonate precipitate, there Is formed a carbonate of magnesium In the form of comparatively thin, needle-like erys:c> i&ls, especially crystals resulting from the reac tion of the ettrboOfcSe radical with the magnesium Ion In an aqueous vehicle, the resulting composi tion has self or hydraulic setting properties ren dering It unnecessary to mold tlie composition cs under pressure to form slabs or blocks. Thus, compacting of the material docs not obtain, which, in other methods, increases the density of the final product, thereby necessitating the re moval of the calcium compounds in order to pro30 vide a product of the requisite strength, lightness and Insulating qualities, Although the doJamitlc magnesium carbonate corc;'osltion ol the Inventloo has the property of self-setting in a quiescent stale without appHca*. tloa os pressure thereto, and lids is the manner employed by this Invention for producing the product, It will also set if pressure Is applied as In other methods and still produce a stronger prod uct than could be obtained by such other rsielhcds, 19 Inasmuch as pressure molding is necessary to pro duce a satisfactory product by other methods and because pressure may be applied to the composi tion of the invention but is not necessary, the expression ''independent ol pressure" is employed a hereinafter to describe that the composition of the invention has self-setting properties not con ditioned on pressure. The self-setting principle Is imparted to the composition by the particular nature of the car:/) bonate of magnesium crystals formed during the gassing with the carbon dioxide-comelnlng gas; one cl the important lactoxs being to avoid as much as possible transformation of the water insoluble carbonate of magnesium to the water ,*.i soluble magnesium bicarbonate by the addition of excess carbon dioxide, If this were done to a material extent, magnesium carbonate could only be obtained again by heating which de stroys the self-setting properties. The Canadian Cfl Patent No, 326,336. granted December 6, 1932, discloses the method of obtaining ft self-setting c&rbonate of magnesium where a straight mag nesium compound, such as magnesite. Is the source of raw materia), r*. re is desirable, during the gassing of the aqueous suspension of the magnesium and the calcium hydroxides which arc formed by reaction between the water and the calcined doiomltic material which, because of the calcining, consists easenfn 'tisliy of efcfciua ants macnwmm oktdeS, and es pecially during formation of the needle-like crystals of the carbonate of magnesium after the calcium carbonate is precipitated, that the reac tion bo oarttod on uudor vigorous or csccrotvc 75 agitation, either mechanical or that obtained by the gassing with the carbon dioxlde-contam ing gas or both. Such agitation 1% preferable to obtain complete reaction betwero *hj magnesium and carbonate Ions, and to fo.m as small and ss thin crystals of the carbonnte of magnesium r> as can be practically obtained because the smaller and thinner the crystals, the stronger the final product. Agitation enhances the formation tt thr desired type of crystals. It is believed that with small thin crystals there ss a greater inter - H> lacing thereof to provider firmer bonding of the calcium carbonate by the carbonate ol magne sium upon setting of the composition. Also for best results, the reaction should be so controlled, in addition to the agitation, as to n convert substantially all of the magnesium com pounds present in the reacting medium, to the described crystalline carbonate of magnesium, to thereby obtain a maximum yield of ths com paratively thin, needlc-Uke carbonate ol magne- t'l slum crystals from the nsagoesluin source. This Is so because the presence of other magnesium salts admixed with the crystalline carbonate of magnesium impairs the self-setting properties of the composition and the strength of the final product, while the presence of magnesium bi carbonate solution retards setting and Impairs strength, Another important factor In obtaining the proper type ol comparatively thin, nsedle-Uke no carbonate of magnesium crystals having selfsetting properties, is temperature control prior to the setting of the composition lo molds. At too high a temperature prior to molding, the crystals are altered or transformed, from crystals m of comparatively thin, needle-like character to comparatively fat crystals which, do rot possess satisfactory self-setting properties. Therefore, during formation of the carbonate cf magnesium crystals by the carbon dioxide-containing gas, the temperature should be controlled to avoid tills transformation. Subsequent to the precipitation of the water insoluble calcium carbonate which remains prac tically Insoluble irrespective of how long the gas- - >, sing is continued, and alter formation of the seifaettlog carbonate of magnesium needle-like crys tals In the aqueous vehicle, excess water Is re moved by decantation or any other suitable meth od: and the remaining aqueous slurry, containing ',q calcium carbonate admixed with the carbonate o! magn Mlurn crystals, is ready Jor setting. After such slurry is prepared, and during the period prior lo the step of setting thr slurry, agitation should be avoided as much ns possible because v, such agnation will Increase the density of the final product and lessen the bonding power of the carbonate of magnesium crystals during set / ring thereof. In the setting operation, the de/*"* scribed slurry U east or poured direct)y into r-a molds, which are preferably ttnperforaied; and the molds ore merely heated fur a length of time and at a temperature sufficient, to set the slurry or sludge to o firm cake. Agitation of the com position ns ths ntc;d3. Is avoided because such cs agitation will impair the wiring property of the carbonate of magnesium crystals, Kence, the setting in the molds is accomplished with the composition In a quiescent state. 'Hie composition does not shrink upon setting t> and no pressure need be applied to the composi tion. Consequently, the density of the final prod uct It governed by Use quantity of water left in the slurry which i> poured tato the molds. Dus* mg the setting, it Is believed that caibcn dioxide 76 \ 2,132,374 3 gitis evolved: and microscopic observation shows that the carbonate of magnesium crystals which were originally a!) comparatively thin or fine, necdle-Iik crystals, now consist essentially of a nfx- .2 hire of two crystal forms. Some of the needle- like crystals remain, but a new. very small crys tal appears. Such new crystal tends to cluster into grapellke groups, or to edhere to the surface of the needle-like crystals. This probably aeW counts for the great strength of the final product, which breaks with a clean or concholdal fracture Jn contradistinction to the product produced by other processes, which mushes upon being broken, thus Indicating that the product of the invention IS is bonded by virtue of Interlacing of the crystals. Because of the evolution, of the carbon dioxide and the formation of the sxew crystals. It Is be lieved that a reaction probably occurs in which some of the carbonate of magnesium is converted 23 to magnesium oxide or magnesium hydroxide, thus forming a light type of magnesium carbonate which serves as the bonding medium for the cal cium carbonate in the admixture. No pressure is required to compact or mold the composition, as the composition sets In a quies cent state, but, as previously explained, pressure molding may be employed and stall produce a superior or c special dense product for certain uses. However, such pressure molding is prefer SO ably omitted inasmuch as it would increase the density of the final product which, as previously explained, is heavier, than would otherwise be the <. by the presence of the calcium car bonate. The temperature applied to the molds 35 during the setting should not be too high nor ap plied too xajddi?, because, although the product will set, the evolution of gas would be so fast as to leave the final product full ol gas holes. Nei ther should the temperature be too low, because then the setting would, generally speaking, be too slow. A suitable temperature range is sub stantially from 63' C. to $0' C. At this tempera ture range, the setting to a hard cake will usually occur In from one to three hours: the time varying 45 of course with the temperature actually applied, and also with the character of the composition resulting from the particular dolomstlc material employed. Prefersbly. the heating of the compo sition In the molds to facilitate the setting, Is ob 30 tained by ptacing the molds In a chamber contain ing steam at the proper temperature. The composition secs normally without shrink age. which is Important, because If material shrinkage were to occur, then of course its final 66 shape could net be fixed by she mold end wasteful trimming would have to be employed to produce the desired shaped black or fiiab. Abo, by not shrinking, the density of the composition Is not Increased during the setting thereof. This Is SO important for ctmtroJUaj the finai weight of the product, as determined by the original amount of water which Is left In the slurry. Under some c.rcumsCances. slight shrinkageof the camp.-sUlon might occur, but not as much as the shrinkage cs which occurs in o'.hrr commercial processes wherein mechanical pressure molding of thr com position Is absolutely necessary to produce a sat isfactory product; It of course being understood that In the other commercial processes, where 70 doiomitic meterial Is used es the source of raw material, the calcium compounds are removed, as the molded product consists essentially of mag nesium carbonate-lnstcad of the admixture of cal cium carbonate with the. carbonate of magne 7* sium which the method allows. After having set in the molds, the blocks or slabs which are formed are self-supporting before they are dried. Blocks or slabs r. med in other commercial processes where pressure molding Is employed and which consist essentially of mas- ,i neslum carbonate without calcium carbonate, are not self-supporting, and consequently, have to be supported In frames during drying thereof. The method of the invention, therefore, eliminates the necessity of having to provide such frames in to support the molded products. Upon removal of the slabs or blocks from the molds, they are noxt dried In the usual manner heretofore em ployed for drying the mechanically molded prod uct, except that no frames are needed, /v Such drying Is accomplished usually in con ventional drying ovens, at a temperature rang ing from 10' C, to 200* C,, to remove at) un combined or free moisture not existing as water ol crystallization. Depending on the tempera* -jh lure, it will take from 24 to 72 hours for the drying. The drying, if desired, may be accom plished under atmospheric conditions, tut oven drying Is preferred because It is faster. Should the materia! tend to stick in the molds upon re- y, sncval therefrom, the molds may be first grease with any suitable substance such os petroleum grease. Even though thcie is no slsrlnkogc. of the ma terial in the molds, it may &e desirable to mil! 30 nr trim the surfaces of the dry preduct so as to provide tin attractive product no: marred with surface Imperfections. Not over 10% of the product need be removed by such milling, where as with products pioduceri by other methods 05 wherein molding under pressure is required, the amount of product removed by roill'ng runs from 30% to 40%. The milled off material is not en ds cly waste material bveause if may be used for making magnesia insulating cement. However, .jy st has less value as a cement and therefor? results ir. an economic loss. Hcr.ce, because of the lesser amount of material which need be trimmed from the block or slab cf the invention, a further economy Is effected. Because of the setting of js the product of the invention. In a quiescent state with substantially no shrinkage, the molds may ba roade cf special shape? so as to form, cone* tj>ond>ng)y shaped articles such as insulating fitting*. co Although the product cc composition of the in vention conloins calcium carbonate, in which ell or the calcium orlplr.itir.g nom the source of dclesniVe milerlal exists. It Is still light enough to permit incorporation iherewith of the usual foreign materials employed in magnesium car bonate Insulatinc products. Tor example, as bestos fiber, usually employed for reinforcing puvjsoses. may be Incorporated in the sluny con taining the calemm carbonate precipitate and eo the carbonate of magnesium crystals. Also, dia- tcmftccous earth may be Incorporeted in the slurry fn? the purposes of enabling (he product to withstand higher temperatures. Standard commercial preparations of magne* 06 slum carbonate Insulating blocks produced by olher methods contain about 85% by weight of magnesium carbonate as a bonding agent and ebout IS% by weigh; of asbestos fiber to rein force the product. Under present standard*. 70 such blocks weigh from IS to IS ibs. per cubic foot: the specific gravity, thciclore. ranges from ahoul 0.2S5 to 0.288. The psoduc: of the inven tion containing the same percentage f asbestos fiber, and In which caicuun carbonate Is not ?5 4 ,131.574 eliminated, or Is other word*, contains all of the calcium occurring In the source of dolosaltie materia!, as a carbonate, can be made to weigh about 12 to IS lbs. per cubic foot; the specific 5 gravity, hence, ranging from about 0,192 to 0.256. In addition to Ughtnoss, the dolomltle product of the invention possesses greater strength and has higher Insulating efficiency than the prod uct produced by other commercial methods even though, in such other methods, the calcium compounds kre eliminated from the source of dolonUtic materia!. For example, a block of the invention weighing about 14 ibs. per cubic foot Is stronger than a 16 lb, per cubic foot block is produced by other commercial methods involv ing mechanical pressure and from which calcium carbonate Is eliminated. Yet such block of the Invention will have about a 25% greater Insu lating efficiency. By virtue of the extremely light weight of the jomposltlon. it is highly porous, 1. s.< cellular la structure, which is one of the factors contribut ing toward Us heat Insulating efficiency, S'urthermare, although the composition Is shaped, , it is not stocy or rock like In appearance as are artificial simes or natural rocks such as the original detomlUc material from which it is es sentially derived, but is chalk-like In character. In other words, compared to an artificial stone :;o or natural rock, it is relatively cashable, ar.d the material raay be readily rubbed off from the surface thereof. If, in other commercial processes emploiing doiomitlc material as the source of raw material, the calcium compounds were not removed, then the final product would weigh too much to meet commercial specifications because of the mate ria! shrinkage which occurs during the molding, and the mechanical pressure necessary to effect m molding, which mechanical pressure compacts the product. Alio, such product would be very fragile; and because of increased density im parted by the calcium carbonate, would have unsatisfactory insulating efficiency. Prom the preceding description, it Is seen that one of the Important features of the method re sides in ihv foimation. In the aqueous suspen sion of the calcined dolomltic material, of the carbonate of magnesium crystals having the ii self-setting properties, which, because of such self-setting properties, allow the calcium car bonate derived irom rhe doiomlttc material to remain m the final product without impairing its efficiency compared to products compacted by i* pressure molding and in which calcium earbonate is eliminated by necessity, The preferred process for obtaining such crystals will now be described. Dolomite, which contain.- magnesium earbontu ate and calelum carbonate In the ratio of about 40 to 60, respectively, or any other dolomltic limestone. Is first calcined In the usual manner to prepare oxides of these metals. As a result of the calcining, carton dioxide gas is evolved, oy which may be subsequently used in the process during tiie gassing operation. However, if the plant does not have calcining facilities but pur chases the calcined dolomltic material, stack gas or any other suitable carbon dioxldc-contalnmg to gas may be employed during the gassing for carbonating purposes. A comparative!? dilute aqueous suspension of magnesium and calcium hydroxides Is then pre pared by slaking and mixing the calcined dolomltTS Jc material with water, preferably Id the propor tions of about 20 parts of water by weight to I part of the calelned doiomUic material by weight, although the proportion' '-ay very widely from about 30 to 40 parts of water by weight lo 1 part of She dolomitlc material by weight. Too little 5 water impedes the reaction of the magnesium compounds in the vehicle, with the carbon di oxide-containing gas, while too much water may be impractical as it Involves the problem of sub sequent separation of the water from the slurry 10 containing the calcium carbonate and the car bonate of magnesium crystals.. Also, upon in troduction of the carbon dioxide-containing gas Into the suspension, an exothermic carbonatlon reaction occurs; and for reasons subsequently re lated, It is desirable to prevent too high a reaction temperature. Therefore, the quantity of water shovid be sufficient to absorb as much of the heaS of the gassing reaction as is practically pos sible. At the same time, It may be preferable to employ an outside cooling medium to provent too high a heat of reaction. The preferred propor tions of water arc those which permit the opti mum rate of reaction without undue creation of heat, and still provide a minimum quantity which ts to be subsequently removed. Of course, the proportions may vary in accordance with the car bon dioxide voncentratlon in the gas as well as the character of the dolomltic material. Carbon dioxide-containing gas is next intro duced Into the aqueous suspension of the mag nesium and calcium hydroxides, preferably into an open tank or vessel which contains the sus pension, The calcium hydroxide has a greater affioity for the carbon dioxide than the mag nesium hydroxide. A"* a result, the first reaction which occurs ts the precipitation of water insolu ble calcium carbonate which after once precipi tated Is not, redissolvcd upon continued gassing. After precipitation of the calcium cartonace, two major reactions occur, namely, the formation of water soluble magnesium bicarbonate and the formation of an insoluble carbonate of magnesi um. These reactions are controSicd more or leas by temperature conditions, and the length of time of gassing. If the temperature Is too low, the formation of the bicarbonate is favored. If the temperature H too high, the rate of reaction Is too slow for commercial practicability. As it is desired to produce the comparatively .,A fine or thin, needle-like carbonate of magnesium crystals having the self-setting properties, the temperature for the precipitation of the car bonate of magnesium crystals should be main tained above the point below which the formation *3 of magnesium blcatbonatc is favored, because the presence of too great a quantity of the bicarbonate in the final gassed composition retards the set ting properties of the carbonate of magnesium crystals. A statable temperature rsr.ge is be- co tween about 20* C. and 40* C,, preferably at about 30* C. Since the reaction Involved is exothermic, some cooling will probably be necessary to main tain this temperature range, depending upon Die rate of reaction and the amount cf water. In 63 order to enhance the reaction and produce small sire carbonate ol magnesium crystals for the reasons previously explained, vigorous agitation is preferable. Mechanical agitation may be em ployed. However.it is preferred to effect the arl- 70 talion through the introduction of the carbon dioxide containing gas with or without additional agiaatkm. The presence of magnesium in form other than the crystal form impairs the setting properties 7s 8,181,874 5 of the eoawsiUotti Tfccwfota, & maximum yield c! the carbonate of magnesium crystals should bo obtained. after the calcium carbonate has been precipitated. To insure this maximum yield or A complete carbonados of substantially all the magnesium In the form of thu Insoluble crystal line earbonatc precipitate, over-gassing which results In the formation of the water soluble bi carbonate is avoided as much as possible; and io the gassing Is continued until the resulting pre cipitate of the carbonate of magnesium erystftis starts to go Into solution as magnesium bicar- bonate,or. In other words, to a point not substan >tially beyond Icelpient solution of the carbonate is of magnesium crystals* At this eod point, substantially alt of the magnesium will be precipitated in the crystalline form, but upon continued or over.gass'ng a ma jor reaction.then eocurs between the carbonate 23 of magnpslum and carbonic acid to form the im- des'rdbie water soluble magnesium bicarbonate, - This end point can be determined by observa tion of the operator, and by chemical titration of selected samples because as the amount of blear- 25 bonaU increases beyond the end point, the amount of acid required to neutralize filtered Wimples from the batch Increases. By slight over- gassing or carbonating slightly beyond the end point or. In other words, until the resulting car- 50 bonate of mayneslum crystalline precipitate starts to go Into solution, substantially complete car- bonatlon Is Insured, If the gassing has been car ried out too far beyond the desired end point, and If the composition has not been excessively over- M gassed, the relatively small amount of the water soluble magnesium bicarbonate can be neutralized by the addition of agnes'*un oxide, to reprcclpl* late the desired carbonate of magnesium crystals from the magnesium bicarbonate In solution. ; i It Is to be noted that In other commercial proc esses, the aqueous suspension of the calcined dolomltlc material is completely overgassed. In other words, the gassing is carried on to convert all of the magnesium carbonate to the water sol- uble magnesium bicarbonate to permit separa tion of the calcium carbonate. Magnesium car bonate Is subsequently precipitated from the bi carbonate solution by application, of heat which in the process Is avoided, es ll destroys or Impairs the self-setting properties f the carbonate of magnesium crystals. To facilitate this over-gas sing In the other processes, gases containing rela tively high percentages of carbon dioxide are employed to enhance the formation of the biear- $5 bonate. Also, to enhance formation of the bi carbonate, the gas In such other processes Is Introduced Into a closed vessel or tank which is consequently under pressure. It Is known that the bicarbonate solution formation ts favored by X) pressure. Since over-gassing U to be avoided In the process, gases containing much lower per centages of carbon dioxide and even stack gases which contain a tow carbon dioxide content, may br employed In the ptocess. Low carbon dioxide 05 content gases cannot be employed In the other processes with practicability. Also, since over- gassing is avoided* In the process, there 1s no necessity of gassing in a closed vessel under pres sure and. as previously related, there is employed an open vessel during the gassing or carbona* tion. These facta result Sn further economy. Since the process permits the use of tow content carbon dioxide-containing ga-s, In percentages as low as S% by weight, thU enhances the desired ?g excess agitation to produce the desired type of carboaote of macaealutn crystals, because a greater volume of las has to be Introduce* to complete the react'. compared to the volume which would be required when employing a con centrated gas which In other processes has run 8 as high as 100% carbon dioxide. After the Introduction of carbon dioxide has been stopped at the desired point, the aqueous mixture containing the precipitated calcium car bonate and the carbonate of magnesium crystals, 10 is allowed ta stand, in a relatively quiescent state, for about an hour or two without application of heat which, as previously related, affects the set ting properties of the carbonate of magnesium crystals if applied prior to the sitting. JTurtng 18 this period, the precipitate settles as a slurry or sludge, and a water layer torms at the top. Such layer of water starts to collect substantially Im mediately after the gassing is completed. The small quantity of magnesium bicarbonate In sola- 20 Uon formed by the slight cvor-gasslog, is con verted to the carbonate of magnesium crystals by its own decomposition and by reaction with any existing small quantity of minute particles of magnesium hydroxide which might not have 25 reacted during the gassing. The r.cutting moss will be substantially neutral, and the precipitate will consist essentially of calcium carbonate intermixed with needle-like crystals of a carbonate of magnesium which 80 produces the set. After standin*' for the desired time to allow settling of the slurry or sludge, ex cess water which collects above the slurry or sludge map be drained, or removed in any other suitabic manner, such as by filtration; the amount S3 of water In the slurry, as controlled by the quan tity of excess water removed, determining the density of the fins! product inasmuch as the com position does not shrink cn setting. The slurry at this point is ready for me in the preparation 40 of the final product, such as heat insulating material, without further treatment except that occurring during the setting thereof, in this connection, the setting Is carried out In the man ner previously related, case being taken to avoid 45 appJIrsUofi of heat prior to the setting. Analysis under the microscope reveals that the thin or fine ?jeed:e*Iike carbonate of magnesium crystals which provide the self-setting composi tion of the Invention, will vary in sl&e from 20 to to 60 microns In length and from 2 to 5 microns tn thickness. In other processes, involving carbonation of magnesium compounds, crystals are formed but because of lack of rigorous or exces sive agitation, they are much larger in size. How- ever, such crystals are altered or transformed prior to maiding, by subsequent steps of the proc esses, such as by application of heat prior to molding. In Uve method of the Invention, the product or composition containing calcium car- on bonate intermixed with the thin, needle-like crys tals of a carbonate of magnesium., Is cast or poured directly into open molds or forms, to set, Its a quiescent state, in thr manner previously ex plained, 65 The aqueous slurry prepared os above described and containing substantially all the magnesium, as a carbonate tn the form of described crystals, and also the calcium carbonate, may be cast or poured Into the molds as such, but in view of ?o the light weight, strength, insulating properties, and totting properties of the final product, other materials desirable for Incorporation in the man ufacture of insulating materials, may be inter mixed with the slurry. Preferably, ff this Is done, ?o mmmaamm k \ e 2,131,374 such other materials are Introduced Into the i. The method of producing from dolomttic slurry prior to the removal of excess water for materia? a composition having r^lf-setting prop adjusting or controlling '.he water content, Jrv erties which turnprises carbonating under agita some cases, it might be desirable to even add tion an aqueous vehicle containing calcined dolo- r, water to such slurry where the other material mftic material to convert substantially all of the 8 absorbs In itself a lot of water. Usually, foreign magnesium centalnlng substance in such vehicle materials, such as asbestos or diatcmaccous earth, to a carbonate of magnesium In crystalline form which ail! not detract materially from the heat possessing self-setting properties, providing a Insulating properties of the final product, are Jn- desired density slurry of calcium carbonate de l eerporsted In the slurry. Upon setting, the car rived assentlaily lrom said dolomitlc material and JO bonate of magnesium serves os the bending agent sold carbonate of magnesium by. adjusting the for the foreign material incorporated therewith, water content of such slurry, casting said slurry as well os for the calcium carbonate. The slurry Into a form, and heating the slurry 1c the form to which any of the above types of foreign mate- to enhance setting of the composition. \S rials may have been added and after the water 5. The step In the method of producing a content is adjusted or controlled, Is poured Into composition deiived essentially from doiomitlc molds and allowed to set in a quiescent state in material and set Independent of application of the manner already explained. pressure thereto which comprises heating a After setting and drying, the resulting produel, formed slurry containing calcium carbonate and although containing a very high proportion of a carbonate cf magnesium in crystalline form 20 calcium carbonate. Is found to have, as was pre having self-setting properties. viously related, a higher mechanical strength and 6, The method of producing a set composition a lighter weight than the materials previously from dolemitlc materia! which comprises treat made from magnesium carbonate alone. This is ing with carbon dioxide-containing gas an aque ;-s so, even though all the calcium occurring os a ous vehicle containing the esiemed -doiomitlc ma calcium compound In the origins?. source of terial to precipitate calcium carbonate, control fioiamitlc materia), remains In the final product ling the conditio,.: oi treatment to convert sub as calcium carbonate. Although the described stantially all of the magnesium containing sub prccefs Is preferred, it may be varied, as will be stance in said veh'cle to a seif-setting carbonate j" eppareot to those skilled In thv art from the In crystalline form, sr.d heating si< a quiescent 30 tempting* of the Invention. Its accordance with slate a slurry containing both said calcium car the character of raw material employed, the con bonate and said crystalline carbonate of mag centration of tas, the amount of water Id the nesium until it sets to a firm cake. aqueous suspension, etc. Jlis only important that 1. The method of preparing insulating rrrate- .sr, aU cf the magnesium compounds In the aqueous slurry be convened to she fine, needle-like car bonate of magnesium crystals, which It has been jiiil from doiomitlc materia) as the source which comprises gassing an aqueous suspension of the calcined doloioJUc material with carbon Cloxide- found will set hydraulically to bond the calcium contatnlng gas to precipitate first calcium car carbonate and thereby provide the Improved bonate, continuing the gassing to precipitate next jo product of the invention, and that these crystals a carbonate of magnesium, cont: oiling conditions be not subsequently destroyed during further of temperature to avoid formation of magnesium step* of the process: the factors pointed out above bJcarbonate, stopping the gassing substantially facilitating obtaining the desired type of crystals. a*, the time when incipient solution of said car What is claimed is-- bonate of magnesium to the bicarbonate occurs i*. 1. A composition derived essentially from doio- to obtain substantially a maximum yield of said mftic material and having scSf-sctUQg properties comprising a slurry in which the major portion of the solid materials are calcium and magnesium compounds, the calcium compound In such slurry .*.D being calcium carbonate, end substantially all tit the magnesium In such slurry being in the form of a crystalline carbonate of magnesium having scif-setting pro)>*rtier, 2. The step Jo the method of producing from carbonate of magnesium precipitate In the form of needle-like crystals having self-setting prop erties, removing excess water, casting the result ing slurry of the calcium eaibonate end the car bonate of magnesium into a mold, applying beat 51? to such slurry in the mold while In a quiescent state to effect setting of the slurry to a firm cake Independent of application of pressure thereto, and subsequently drying said set cke, dolemitlc material a composition having self- S. The method of preparing a set composition setting properties which comprises carbonating a from dolomitic material as the source which suspension containing calcined doiomitic mate rial to convert substantially ah of the magnesium containing substance in such suspension to a comprises carbonating a relatively dilute aqueous suspension of the calcined dolomitic material to precipitate calcium carbonate, continuing the carbonate o! magnesium in crystalline form pos carbonetlon to precipitate a carbonate of mag sessing self-setting properties. nesium, maintaining the temperature of reaction 3. The method of producing from ''oiomltle above the temperature below which the forma materia? a composition having self-setting prop tion of magnesium bicarbonate Is favored and erties which comprises carbonating an aqueous below the temperature above which the reaction <>> vehicle containing calcined dolomitle material to form water Insoluble calcium carbonate and to convert substantially all of the magnesium con taining substance in such vehicle to a water in soluble carbonate of magnesium In crystalline 10 form, terminating the carbon&Uon when sub stantially all the magceslum containing sub proceeds loo slowly, terminating the earbcnallon 65 substantially at the time when Incipient solu tion of said carbonate of magnesium to the bi carbonate occurs to obtain substantially a. maxi mum yield of said carbonate of magnesium pre cipitate in the form of relatively thin ncedle11ke crystals having self-setting properties re i stance has been thus converted; and enhancing moving ekeess water to provide a slurry of the the setting by applying heat to a slurry contain desired density, prior lo any application of heal ing said calcium carbonate and said crystalline to such slurry casting it into a mold without 78: carbonate of magnesium. removing the calclxtsn carbonate therefrom Rp- 76 V, 2.133.874 7 plying heat tc such slurry in the mold while in a Quiescent state end without application of pres sure thereto to egect setting of the slurry to a ftrm cake, and subsequently drying the cake. 6 8. The method of producing from dolomitte material o composition having self-setting prop erties which comprises carbonating an aqueous suspension containing calcined dolomitic materia) to form calcium carbonate and to convert sub20 stanUally all of the magnesium substance In such suspension to a carbonate of magnesium In crys talline form possessing self-setting properties, Inh corporatlng is said carbonated suspension foreign r material ol the cius consisting of asbestos and !.- dlatomaceous earth to Impart desired properties to the final product, providing a desired density slurry by adjusting the water content, and set ting such slurry to a firm cake by applying heat thereto. xo 30, A light weight cellular chalk-ilke tomposi tion capable of use as a heat Insuluting material containing modified dolomitlc material In which substantialty all of the calcium in the original dolomitic materia) is present as calcium cs rbonate and which is bonded by a magnesium compound derived from neodie-5ikc '/stals of a carbonate of magnesium having self setting properties, said magnesium bending compound containing mag- s ncslum derived from said original riolctalttc ma terial. 15. A light weight cellular chalk-like composi tion set substantially without shrinkage inde pendent of application of pressure and capable m of use as a heat Insulating .material, containing fiber to reenforce the composition, and modified dolomitic material In which substantially all of the calcium tn the original dolotnltlc material is present as cnielum corbonale and whlehis bonded J 3 by a magnesium compound derived from needle- Jlkc ttysl9\s of a carbonate of magnesium hav ing seif-setting properties, sold magnesium bond ing compound containing magnesium derived from sa<d original dolomitic materia), 20 DOROTHT 3f. GRUKWALD, XdmfUttratriz with Che Will Annercd of Che Eitate o/ Serfrend 8. Crunufoid, Deceased. Patented July 30,1940 2,209,752 UNITED STATES PATENT OFFICE 2,205,752 MAGNESIUM CARBONATE COMPOSITION A-VD PROCESS FOR THE PREPARATION THEREOF Samuel A. Abrahams, Sao Francisco, Itufeia Lcpoa, Menl# Pare, and Louis t- CoHuagc. Paio Alto, Call*.. assignors t Plant Rubber it Asbestos Works, Sin Francisco, Call/,. a cortnsralha el CaUleraJ* No Drawing. Application Jane 5, 1938, Serial No. 212.686 2 Claims. <C?. 22--511 Our invention relates to magnesium carbenuta compositions, and more particularly to an improved magnesium carbonate. composition which has the property or sell or hydraulically setting 6 substantially without shrinkage, and also to an irnprtvcZ procex* for producing such scif-setfing com position. Isfosccriuro carbonates arc used in sound and hear insulating and similar materials, and have 10 conerally sompmrd either the heavy basic car bonate or the light basic cnrbon&te. or modifica tions of intsc materials. These basic carbonates hiii'c been prepared by various methods. One fo:m of commercial process for manufacturing 15 such baric carbonates. where dolomUte materia! is the juiurcv ol raw material and It is desired m gu--Jnct'.c calouat expounds {tom Jhe finM prodi:rl. is to calcine first the do.omUle material to form magnesium and calcium oxides which arc treated with water to prorida on aqueous suspension of magnesium and calcium hydrox ide... Such suspension ts gassed with eaibon o:oxide* containing gas, which results in a per* ntfir.cniJ:-* insoluble precipitate of calcium car55 innate, unci tin in!!Id precipitate of magnesium c:i:bor.xtc. Upon continued gassing. the mxum->;um curbonnic dissolves n the form of mng:ir'.i:nt tecurbunaie which fs nxtcr-sotublc. in u;tler to tiTt c? separation of the calcium ca:ar> bonu. si is customary commercial practice to vj ;!:? point where substantiaSly el! the masnoxihzx: n m the lorm o! the water-soluble onc- r.esiutn bicarbonate, which step enables the caiis'orn eatbonnie to be removed by filtration. 35 To obtain magnesium carbonates Iron: the water-soluble tnngcasium bicarbonate, the isf.itne.'.ium bJcarbrmaie solution is generally heated rapidly to the boiling point, which results sr the precipitation of basic magnesium carbonate. U 4l> desired, ba*ic magnesium carbonate may be prev p:.rtd horn ruafpiesllc in aubsUnthdiy the same rianne? by calcining the rnagatslte to form mag* agh no>!jo oxide; treating the magnesium oxide with y water lo thus form an aqueous suspension ol magnesium hydroxide; And gassing such susjH-r.slcn with carbon dloxlde-eor.ta1n.inc css lo form the water-soluble magnesium Bicarbonate, which resUw after initial precIpHatioo ol roag- r'tssun carbonate. SVhera dolomitlc materia! is r,o the source of raw materia.!, the magnesium bi* <a;innate solution will usually contain about 1ri lo 7'i By weight of dissolved magnesia caiculatrd as magnesium bicarbonate, Where magnct-Sie is ihe raw material, the concentration cf mn-nesJum bicarbonate will be slightly higher. In such prior methods, It was necessary In or der to form the magnesium carbonate in blocks or slabs of the desired size or shape, to mold the product under a relatively high mechanical pres sure. because the magnesium carbonate did not him; seif-scttlnff properties or could no: tmde/jp a hydraulic set. `Hus melding equipment was expensive to maintola and operate as well as to construct. Furthermore, because of the presume applied during the molding. the product was 1C compacted and consequently made more dense than would occur In a corresponding product having self-sotting Properties. This, of course, icniierefl it impractical to intermix with such prior product comparatively large quantities of 16 other heavier materials which might olheiwise have been desirable, because the increased flciv sity which JCb'.iltcd from such large Quantities produced n product having a unit weight too high lor commercial specifications. Consequent 2U ly. jhe percentages of these foreign material* which could be Included was limited. Our invention has as Us objects, among others. Ilie provision al an improved light weight self* grtUns nif!"nesium carbonate composStion hacine V> great strength ?.nd improved insulating proper ties, and which con be pioduccd by a compars- Si"f!)y cccuiernlczl proctus. Orbe," objects of invention will become appaicnt ri*om a rcajsuj; of tire fullowlng desciiption thereof. 30 In general, we have discovered that mnsne^ignj coibonate liavinp scll-setling propertias nviy Be fomipcl by decomposttfoii of a maEneslum bicar- beruuc-conuriolni: solution. Briefly, such ce- composition is eflecied by excessively agUaitng n a:i solution containing mcgncslum blcarbor-.oLc. which effects driving off of carbon dioxide, and preferably simultaneously applying a modelsie tiegrec of heaf fa expedite the driving eft ef ifte carbon dioxide. This results In the preclpuaiiori of fine necdlt-llke noimal magnesium car 4H bonate crystals having self-setting properties. Care must be taken to preclude destruction ol such norma! magnesium carbonate crystals, which would occur should tne deeompofilSioh je- 45 ocliun be conducted at loo high o Icmperaturo. Addition of active or caustic magnesium oxide, *. e., magnesium cxtde which is cot dead burnt, to the magnesium bicarbonate solution Is du- sis&ble as ft ims Mf;n round to hasten the de 5U composition icaction. Althoush such se!J>setUns normal magnesium carbonale crystals arc usually formed undermost Present ccino*.erc5a1 operating conditions as an intermediate product dutmj the decomposition reaction, theis* scif-settlne brop- ^ -v\i . r' r.,T , cities wen set recanted, and they were here tofore destroyed 1y application of heat at too high a temperature. B e durry of.such normal magnesium car bonate crystal* having self-aettmg properties t mi or poured into a form er mold. the cam- :petition will Mt in & quleue&totete without applteatfen of mechanical pressure thereto, to provae the atiteetteag product of our invention. Tbe setting hi the add is enhanced by appUcatlea et heat. In other words, we have found that ft normal magnesium <atboastc to the form ofcomparatively ttta needle-Uke e rials rtauH* laglramthodeserted decomposition at an awe- da mogMtiuza Ucarbo&ate-ccataJaBg solution. . taahytiroulle or self-setting properties rvnder- would interfere with the driving off of carbon di oxide Don the magnesium btesrfeo&atc as it de composes.and therebyImpeoc the decomposition reaction. Agitation hasbeenfound toformsmall and thla esystels which are desirable -heeaaic tee em&Ser and thinnerthecrystals, the stitmger tee ftr^1 product, tel ti prebsbly due to tee factteatwithsmall thincrystals there tia great-. er interlacing thereof to prevtte a firmer brad upon setting of the product. - As waa previously related, beat is preferably applied rimultafieously with ereesrivc agitates* to expedite the deeeaposman of tee masoe&lom bkarbonate, with consequent precipitation ofthe normal sdf-aetting tnagnwlam carbonate crystati. However, caremust be taSen teat teetern-, tn*U B&&eeemi7 to add teecompetition under X3i*? ' pressure to fora elate or bteeka. Although tea A' < products? cur ttrentlon has the property of .; sH*1 *`;, :* M:. uir-uttiag to a tlfia f pressure caltaeeat state without appheathereto, and this la the meaner *<& emptoyed by ia for predutiag the product It poreture la tas allowed to rise at any time chore tee printwheretee fineneesBe-lfce normal magwqfrim earbonate crystalswBte are formed Bsc tMr character, because then their setf-sotting pnpaHaa are datr^ed. The tempereture should not be permitted to rise mate obon r^V-A,.V. oteJU If preuan u applied as in ether m*y. 7&SV-4 * * ' soothed* heretofore koon* and still produce a At present,the proressti preferablypertmtaed mam product than has heretofore beta potSi&S> '->. stole by such ether methods. lanimwih as yea- tan molting la necessary to produce a satisfac tory product muntutma by other methods, r ** ftad la view, of the fact that pressure may he la betehee. lire etna iotrodaced dlrectiy feta tee batch presides asmltarie heating mews and also cooperates to effect agitation. Beeee.it Is preferred, although any carer writable hreUsg means,amte as heating caSs la tee vessel or ex jolted to.the produet nude by'the process of. ternal heat, say he employed Instead. It aoae fc^v'A * eur invention but Is not neoeasaty. the expres- of tee normal ^p**"111 esrimnata .crystals sl-independentofPBswreVBemployed hart- from tea-fiRt botch are left In tee cessri. sate 'iDifter to dtsHteettal the.product cfeur to. crystals sera as a seed&g means and rapedge. WBdtoa hae atlMsttty prcperties,n coadi- 4( sageredtogcrystals in sBaseosent . .. ...... * * - II; tetonUM^ii applicable to. The Idghef tte'-tempeteBe at vUteCtete-i "day ogweas *?--<* fatearbooatc-Kmtalnlas caniwwlttHtiseffected, ether ctmittHcos imaB- r2\v;r;'jdhdhas,irrwpectire ofSaw sueb magnesium M- lag teesaafc tee man rapid vriD he tee drtriag whoidte solute may bo prepared.-However. :e9 ofcarbon diaxide from teemagnesium tdcsjr-1 ftbas;nrtomlar appacebmcr-wben .dotomWe bwato. Therefore;Itispreferiedtoconduct tee ;material ls etaptoyed ti tea searce of raw mate- precreo close to the hBttsst tenperatnre^^white fc-i s*va "*. riftl tad ft.'Xs desired pounds, because under to remo<n ealtiua eoa* this eemtiUba it ts pecas- iiiwj/erttopraton the eug&etiuia teearbouete oolutioa to tbs' tteasur previously `ftlated. Fbroh may be safely eeqrioyed wttimat Imptebm the sett-rettiwpropertiesof thereystris. Suchtem perature. as mentioned above, should not he mate over tin* T. At shoot this temperature, |S$rA?:theasegwdttm tobesabstoatially.dissoivedia tee eenttoB B it fwB of the blatrbonte. when sK&Kv.-;;.'dBoadtlo*aaotertsl ts the raw material.-oawigb water idoiiifl1 esateyed to provide a boam* i#tattoa d aaa&esr&B Otat least about 1% to t% by wdghtof tee saJutiw,calculated as bam^.v;i&eriiBBWoaiboute. aiotoHooetthtsstreacih eouried withteevigorousagitation, itwfliwsBallytaketramaboutonetoraeand caie-batihorns: to drereopoee as mute as tee nuurnesfma taleartona^e as H ts oaoxmtzcti^ wractkal to deempose h^n tee mother houer oratrintu such magnesium bfentbonate B eoluUen. Ttds Is so beeausB the deeomporiUta of the nuaeAun 05- wia be mbstasUoXtyceDcetirated. However, the carfaoorieIsoulte rapid during teefirsthah hour process of oar UmtSon it epphubh* to zsnrw di of tee reaction, and teen further deoompotitlon lute triutiam. u wefl u to more cQccentntM atfabOBS wbkh obtete where aagBetite U the ia mane of nv owterisl. but cbvtoutiy \r tho aolutioci are toofilute tite would be undeslpaWe for orears at a deercashaly sJow rate. Renee. H wetfid be commerriBlly tmeeanomleat to attempt to decompose ah tee masnerium bleaibraste at tbe moderate temperature white teorid he en- cqbumtrial reescsubecauseof unncoe&sery wster jd^yed. eoapkd with vlgsrras agitation. * How S.V-.y.V-A;baht and the ermter ooal which would bo in- ever, tee magnesium bicarbonate which remains: A**'. >teved Btatirw eush water. - ' . v Vlgmeus oreme&stve aeUatiea Is Impartantin In solution in teemotherIkjuor need not be lest, becausesuch mother Uquormaybe removed from .efferiSte decomposition of Be m&cncslum blcaiv tbe crystalline magnesium carbonate preclpltat* baaite;and wehavetoandthat themore elcerotcs and used fortreatingteeorfeloM sourceef moe- teeagttatios^teemore efltectoustee decompori- nesltim oxlde-eoutalaing material from which tinV. Mecho&lcft] eritatiou by any suitable ad- the magnetism bLeartoo&te sriotion Is to be pre tattegmechanismmaybeemployed,but agitation pared. Although substantiallyail of tbe magne bythtrodudag asteeaa orstreamsof compressed sium bicarbonatecorid bedecomposed by batttn? rirtete tbo vessel In whkh the reaetiem oeem tee aagnasliimbicarbonate soteUoa. this U ob- ?,Av': /' asaHsedmlnBe.: Such vessel te pretenWy op Jwtemable forthe reasons already explained. to the atmosphere as tee reaction occurs under Instead of showing the decomposition reaction ttemph***0 eopdltteas. ahhoush it can sis be to eentinae for about cue to one and one-half utitllmfl B veesel ma4Btahd aade a vacmim, fcrgff*. tt may beeaeammhS?destraWe inremove but this is tamernmiy. Application of oressure theerystabiBenomrel magnesium carbonate pre over the vessel wouldbe UBdestreMe because this cipitate Bum tbe mother lfeuor aRrw abotd ene^ S.fiOd.762 3 half hoar, which is about the Urns when the rail of decomposition commences to slow up materially, Use operator or observer will be able to do* termlne readily the rate cl decomposition of the 6 magnesium bicarbonate as well as how much of the magnesium bicarbonate has been decom posed. by removing at regular Intervals succes sive sample filtrates of tho magnesium bicarbon ate solution, and titrating such samples with acid. 10 such m sulphuric acid. As the magnesium bi carbonate ftecosipom, leu acid it required to titrate the successive sample ?J;tales thereof. Suitable amounts of active or cau ;c magnesium oxide, Ifdesired, may be added to toe magaeslum bicarbonate solution to eld tit the decomposition thereof, to thereby hasten the reaction, but the addition of the magnesium oxide is not necessary. 3t la also desirable to take frequent successive samples from the batch as the reaction pres to resses and mske microscopic analyses of the crystals In such samples to insure that proper sett-setting crystals are being formed. The prep* e? kind of crystals win appear under the micro* scope to be substantially alt in the form of very u fine <net Jatt. needle-ltke crystals, ranging from 20 l 50 mtcrcru tn length and from 2 to 5 mi crons in thickness. When the decomposition re* action has reached the desirable point for stop* ,, ping the reaction, agitation and the application 8& of heat are terminated; and the crystals are ready for succeeding steps e? the presess. We prefer to add directly to and mix In the re action vehicle, the usual types of reenforclrtc ,, materials, irueh as asbestos fiber, in an amount SJ sufficient to provide a final Product which contains from 30% to 15% byweight of tho fiber; such product bain* generally that employed com mercially for heat Insulation. Other chemically inactive solid bodies, sueh as vermieuhto or dlatomaceous earth, may be also mixed In the re action vehicle, Kowerer. such Inert filler or re enforcing fiber may be Introduced at any suit able subsequent or prior point If so desired. When the normal magnesium carbonate pre- *5 clpltste I* tn the form of the destred crystals, and the other material is added to the reaction ve hicle. any water-soluble impurities which might be present In the precipitate Including magnesium hi carbonate, may br removed bv filtration and 60 washing, and the water content of tho mass simultaneously adjusted by removal of excess water to control the density of the final set prod uct, A suitable type of filter is an "Oliver" con tinuous rotary vacuum filter !o which removal of to excess water, nitration and washing may be done simultaneously. Xn the particular process herein described, the washing Is not necejs,'ry if after removal of excess water from the reaction ve hicle. In any suitable manner, such as bv de* to fetation, any water-sohiUe magnesium bicar bonate remaining In the slurry, which Is u .de sirable because It has been found to slow up subsequent setting, is neutralized or decomposed completely, For this purpose. we may add suffi cient matmesfum oxide to the slurry to react with substantially alt the magnesium bicarbonate therein to precipitate magnesium carbonate, Urre or any other alkali which will react with water-soluble magnesium bicarbonate to preclpl70 tele an insoluble carbonate may be employed in* tiead of the magnesium oxide; the magnesium oxide Swing preferred to lime because It does not adulterate the product and'because U. Imparts aOdltional strength to the final product. The fS addition of the neutralizing medium or washing is not necessary but the employment of either one is desirable for the reasons stated, The resulting normal magnesium carbonate slurry, after separation of the desired amount of water, Is now ready to be set. If the resultant a flurry Is not already markedly alkaline by vir tue of the addition thereto of magnesium oxide or equivalent material should washing of the siurry be omitted, we preferably Intermix wish the slurry to hasten asd also control the settles 10 of the product In the molds, and nt the same time increase the strength of the final produet, nr, excess ef an alkali having the property of consuming carbon dioxide which may be by ab- sarption. adsorption or reaction, such as pref- IS eraKy caustir or active magnesium oxide, on alkali metal hydroxide such as sodium hydroxide, or borax, for & reason to be subsequently ex plained. Other alkalies, such as lime, may also be employed, but alkalies of this type arc cot 2b preferred because they cause too much adultera tion of the final product. Id this connection, enough alkali should be added to render the slurry markedly alkaline, as the slurry has been found to set better when markedly alkaline. 5 le the setting operation, the slurry is east or poured directly into forms or molds which are heated for a length ot time and at & tempera* tore sufficient to set the slurry or sludge to a firm cake. Agitation of the crystals In the molds *0 Is evoided because such agitation will impair the iH1 ing of tho crystals. Hence. the settine In the molds Is accomplished with the crystals to a Quiescent state. The composition has substan tially no shrtitkage on setting and no pressure 86 need be applied to It to accomplish the settle Consequently, the density of the final product is governed by the quantity of valor left in the slurry which is poured Into tba molds. During the setting, we here found that carbon dioxide cas Is given of!: and microscopic ob*rn. tlon of the set product show's that the materlcii which was originally all comparatively thin or fine needle-like artist* now consists rwentiallv ot a mixture of two crystal forms. Some of the 45 original needle-llke crystals remain, but a new very small crystal appears. Such rrew crvsrel tends to duster Into crape-like groups, or to adhere to the surface of the tieedie-liae crystals. This probably accounts for the areai streutih of the final product, which breaks with a clean fracture, in contradistinction to the product of the prior processes, which mushes upon being broken, thus Indicating that the product of on* invention is bonded by the interlacing of the cm- to teR Because of the evolution of the earboh dioxide end the formation of the new crystals, we are led to believe that a reaction probably occurs in which lame of the carbonate of magnesium Is i converted to tight basic magnesium carbonate. The carbon dioxide-consuming alkali which ss preferably added to the slurry prior to the set ting operation, controls and hastens Use set:Inst which Is preferably conducted In an reUsert &'> chamber, not only because the senlac o-rur.* foster when the slurry is muRe markedly alkaline, but also because the consumption of some of the cm bon dioxide reduces the carbon dioxide pres sure In such chamber, end thus by the pnoeip;*- ? : of the law of mess action causes the jer.eHen to proceed faster toward the side of the set prsdivi. Also, such alkali since It consumes carbon di. oxide, controls the rate of evolution thereof nnrt precludes formation of fissures to the Interior cl ~,j 4 2,203,762 the setting product which might otherwise result from too rapid an evolution of the carton di oxide. with congruent weakjotag of the final product. For any given setting conditions, the s length ot time of the set may be regulated by the quantity ot the carbon dioxide-consuming al kali which may be odtied to the slurry; thomore alkali added within practical limits, the faster being the set. If magnesium oxide alone Is JO added, usually aa amount thereof ranging from 1% to &% by weight of magnesium carbonate, is employed; while torax alone is tasp* (r an amount usually ranging from 1% to i% by weight of magnesium carbonate. As alkali uetsl hydrox- JS Ida, such as sodfum hydroxide, being much stronger, is'employed in lesser quantities: 0.1% io 1% by wetgM of magnesium carbonate being usually luSclent, Mixtures ct the carton di oxide-consuming alkalies may, of course, be ern es ployed if so deseed. The addition of the carbon dioxide-consuming alkali, although very desirable for enhancing the set and increasing the strength of the final product, Is not essential. Although no pressure is required to compact or 85 yield the maicTlnl. pressure molding may be ?m- pioyed and ,ri:5J produce a superior product, or n jpcrial dense product fur certain purposes. How ever. suth pressure molding is preferably omitted where the final product Is intended for beat In to iulatlcm. inasmuch as H would increase the den sity, Tire temperature applied to the molds dur ing setting should not be too high or applied too rc pi clly. because although the product wilt set, the evolution of gas is so rapid as to leave the fin*) to product with pus holes. Neither should the tetri- peruturr lie too tow, because then the setting f.eiv*rnliy sinking, to? slow for practical pin** psvrs, A s'diable temperature range under atmovplie: i pressure Is substantially from 140* F. to <0 )$S` F. A) this temperature range, the setting to 8 hard coke wilt usually occur in tom one-hair to three hours, the time varying with the temptinluvc actually applied, and also with the chemical and physical character of the compos! i non. sir, well as the thickness of the moss, Pr*J- erablr. the setting U cfTected by placing the slursy Piled molds In an enclosure maintained at the desired temperature by live steam. although any ci her .nUinbJe heat may be employed instead, !x 50 n dfstrftUiB that the enclosure In which U\t set* ting is tendireted be substantially free of drafts re Die outside atmosphere because drafts might reuse evaporation of moisture end Ihh tends to cause undesirable shrinkage. 55 Thv composition seta normnJiy substantially without xhlinkage which is Important, because if H were to shrink materlslty, than of course itv final shape eoM not be fixed by the mr.td. and wasteful trimming would have to be etaployvd to c produce the detlrtcl shape block or slab. Also, by not shrinking, the density of the produc* U not lncixcsad during the setting thereof, which 1c Important for controlling the fins! weight of the pitouch as determined by the amount of warn* 5 which is in the slurry to be set. to this cotmeeH*.n. jf ihr slurry does not have the desired water conical to produce the desired density of the final product, water may to added to the slurry In an a mount neressory to produce the desired density, ; Tmir, the density of the final product may be cor,, t.toto by adjusting the water content of the sluriv ic i:o set. Under some clreyinstances, slight shrinkage of the composition might occur during setting, but not as muds ax the shrinkage whlc> 3 S cceuxs in other commercial processes wherein xwchsolcal pressure molding of ttre composition is absolutely necessary to produce a satisfactory product After having set in molds, the blocks or ?Sai>; which ere formed are sell supporting bcicic they e arc dry and while containing considerable mois ture, Blocks or slabs formed In other ccmmeicial processes where the magnesium carbonate is placed in filter molds aud pressure moltime is em ployed simultaneously with expulsion of water lu through perforations in the mdfis. are not te'f supporting: and consequently, they have to to supported in frames after they arc removed from the molds, to that they win not break during han dling prior to drying thereof, The method of our Invention, therefore, eliminates the necessity of finetag to provide frames to swpo.-t th? aoldcd product after removal from the molds. Upon removal of the slabs or blocks front the molds after selling thereof, they arc next dried 20 in the usual manner heretofore employed for dry ing Vm mechanically molded product. Such dry ing is accomplished usually ir. conventional ciry- livj ovens at a tomperatoxe cangiup from 155* F. ta 535* F.. to remove all uncombliied ot fie? water 25 not existing os water of crystallisation. Depend- leg on the temperature Bud draft, n win taka from 2 to 72 hours fur the drying. The dr.vin:. If desired, may be air shyir.c. but oven vtying Is preferred tocouse It is faster. Should the mate- 50 rial tend to Stick In the molds upen i amoral therefrom, the molds may to first phased witn any suitable substance such no petroleum sreore. Even though there Is scbsicntleHy no shrinks?: ? cf the material in the molds. It ntciy be dwimble 35 to mill or trim the variates ol the dried yrcfiwt .'pas to provide an attractive product no; hv.iito with surface tape* tec: Icrif;. Not over1ST of the product need be removed by such milling, whereat with products produced by other methods where in molding under pressure is required, the omou x*, of product removed S>y willing runs froui 2C' to 407p, The milled-off rriaterlal is not entirely waste material because 11 maybe used for mc,ki::x magnesis tnsuJfltlRBcemcr.t. Hoxvever. It hr,.* lea <3 value as veeuwnt. and iheiefOio resvits iu a.; ecaoomlc loss. Hence, because ci the Ismvt amount ot material which need be tclmir.vd Sror: the block ox slab of cur Invention. i further econ omy results. Because th- p: adust of our imeu- 50 tlon sets in a quiescent smtr substontmliy with out slulnkkge. the molds may be mode of spv;v,*J shapes so as to form contspoisdiiigiy shaped ir, > bjlathxr fittings. Standard commercial product* cf magnesium 55 carbonate UisulMlixg blocks produced by former pressure melding methods contain about 85rc by weight of magnesium carbonate as a bonding agent and stout 15C# by weight of asbe.'tcs fiber to reenforce the product. Under presrnt stand- 60 ards. such blocks weigh from 16 to s lbs. per cubic foot; the specific gravin', therefore. rit:pSng from .25 to J2S. The sitnllar product cf our Invention contetuing Uir: same percentpccs o' magnesium carbonate and asbestos fiber can i>v made to weigh uv ioa as 5 5bs. pox cubic fees, ona will overage frem 10 to 12 )hs. per cubic ;*cot; the specific gravity. Uxerffore, ranging from ,H to .IS, The product of cur invention wilt thus aver age from 35CI- to lighter than the rorre- to spending product produced by former mflSuxls; and even though irgixlcr, n is much strorper. This comparison between 65'i mogea:um <-or- hgnale biocks of oxu invention nud tho.xc hcsvio- fore produced holds teue for tuxy pivan spocifica- 2,209,708 5 Hon of materials end percentages of magnesium ceibonat? In the respective blocks. Because of tfie lightness of the product of our invention, con siderable saving in freight charges obtains. Ala, due to the low density of our product, it has a Sower heal conductivity coefficient then that of pioduel* pi educed by former methods. The heat conductivity coefficient of the product of our in* vention win run about 20% Sower than the corre* Sfl sponding product produced by former methods and containms the same percentages of Ingred;- Although the product of our * rantlon is Ulighter, it is much stronger than hart: ;lorc pro mduced products. Weight for weight, it is 50% to W% stronger; while & block of our invention, or example an a5% magnesium carbonate block weighing li lbs. per eubse foot, will be as strong or even stronger than the corresponding block SO produced by former methods and averaging 16 l 15 lbs. per cubic foot. The product of our invention because of its light weight, is highly porous, t e,, cellular in structure, which is one of the factors enabling it -- to have n high Kent insulating efficiency. Fur thermore, although the product is shaped, it is no; stony or rock-like in character as are arti ficial stones or natural rocks, but it is chalk-like in character. In other words, compared to an 30 artificial stone or natural rock. U is relatively soft c? crush&bie; the material being readily rubbed off from the surface thereof, Reference is made to our assignee's eopending applications, Bertel No. 232,698. filed June 9. 1938. 5* and Serial No. 250,663. filed March 8. 1939. con* taming related subject matter. We claim: i. The method of producing a set cagt&siuD carbonate composition which emprises decom posing magnesium bicarbonate In solution to pro vide a precipitate of a normal magnesium carbon- atc In the form of needie-Jlke crystals having se)fscltlng properties, terminating the reaction prior to conversion of said self-setting magnesium car bonate crystals to basic magnesium carbonate so that said self-setting magnesium caibonate crys tals form the final precipitate for pi eduction of the product to be set, casting a slurry containing ,. such crystals into a form prior to setting thereof, and applying hea*. to the slurry in the form to enhance setting of such slurry to a firm cake. 2. The method of producing a set magnesium casbonnte composition which comprises decorn* j. posing magnesium bicarbonate In solution by ap- plication of heat and agitation of the solution to provide a precipitate of normal magnesium car bonate In sfte^orm o! comparatively thin nctdlc- llke. cj-yat:*; Laving self-setting properties tnde- . pendenl ef application of pressus*. controlling the " temperature to avoid formation of basic mag nesium carbonate with consequent destruction of lh* self-setting properties of such precipitate, terminating the reaction p:lor to conversion of s&ld self-setting magnesium carbonate crystals to basic magnesium carbonate so that said self-set ting magnesium carbonate crystals form the fiaal precipitate for production of the product to be set, prior* to setting thereof easting a slurry eon- ,, mining such crystals into a form adapted to pro vide the shape of the final product, and applying heat to the slurry in the form to enhance setting cs sue!) slurry to a Ann cake. SAMTO. A, ABRAHAMS. ROBB? LEWON. 1/OmS I* COLLCttOS. 35 Petcnied July 30, 1940 2,209,753 UNITED STATES PATENT OFFICE 2,203,753 MAGNESIUM CARBONATE COMPOSITION AND METHOD 0F PREPARATION Sa&uil A- Abrahams, San Frmeiato. end Rubin Let s, Menlo Perk, Calif., assignors to Plant Robeer * Asbestos Worts, San Franeheo, CHf,, a corporation of CfeU/omla No Drawing, Application June 9. 1938, Serial No. 212,63 8 Claims. 1CI. 23--87) Our tnventloa relate* to magnesium carbonate compositions. and more particularly to an Im proved magnesium carbonate composition which has the property of sell or hydraulically setting with substantially no shrinkage, and also to an Unproved process for producing tush aeU-setting com position. Magnesium carbonates are used in sound and heat insulating and similar materials, and have )ii generally comprised either the heavy basic car bonate or the light baste carbonate, or modifica tions of these materials. These basV. carbonates have been prepared by various methods, a com* men method being that of gassing with carbon l.i dioxide-containing gas an aqueous suspension of magnesium hydroxide to precipitate basic mag nesium carbonate, Another lype of method is disclosed In the patent to Samuel A. Abrahams, one of the co*applicants of this application. No, 2,G2?.7i. dated January H. 1936. Briefly, the method of such patent comprise* precipitating basic magnesium carbonate from bittern* re maining as residual liquors alter crystallization of sodium chloride resulting from the ev&pora- t.*. tiea of sea water, by reaction with on aqueous solution of an alkali metal carbonate, and cre ating a certain character of precipitate by the application of heat at a temperature between 160* F., and 20G' P. In such prior methods, It was necessary Jn order to form the magnesium carbonate in blocks or slabs of the desired site and shape, to mold the product in suitable forms under a relatively high mechanical pressure, because the magnesium carri bonata did not have self-setting properties or could not undergo a hydraulic set. This mold ing equipment was expensive to maintain and operate as well as to construct. IN' 'thermore, be cause of the pressure applied during the molding. < i the product was compacted and consequently made more dense ibaa would occur In a correspending product haring self-setting prc,<erttea This, of course, rendered it Impractical to foterV mix with such prior product comparatively large jr, Quantities of other heavier material* which might have been otherwise desirable, because the In creased density which resulted from such large quantities produced a product having a unit weight too high far commercial specifications, ;u consequently, the percentages of these foreign materials winch could be Included, was limited. Our invention has as It* objects, among others, the pro*ston cf an Improved light weight seifsetting magnesium carbonate composition having ;:< great strength and improved insulating propel- ties, and which can i* produced by an economical method. Other objects of the invention will be* come apparent from a reading of the following description thereof. In general, we have discovered that if ths type a of process wherein magnesium carbonate Is pre cipitated by reaction of a magnesium compound with a carbonate salt fsuch as the particular process disclosed In the Abrahams patent men tioned previously). Is conducted so vs not to de- JO stroy the comparatively Sue magnesium carbon ate needle-like crystals which commence to form shortly after the reaction is initiated and U the reaction is so performed as to leave substantially all iho precipitated magnesium carbonate In the 16 form of the fine needle-hke crystals, such type of magnesium carbonate crystals, which form normal magnesium carbonate have sell-setting properties. Although such seif-setting normal magnesium carbonate crystals are always Tensed SO by the type of reaction mentioned, their self-set ting properties were not recognized, and they were destroyed by subsequent process steps, usu ally by the application of heat at too high a tem perature, 25 IS a slurry of such norma! magnesium carbon- ate crystals having self-setting properties is cast or poured into a form or mold, the compos!- non win *ct in a quiescent state without appllea- tion of mechanical pressure thereto, to provide SO the self-setting product of our Invention. The setting m the mold is enhanced by application of heal. In other words, w have found that a normal carboflate of magnesium in the form of comparatively thin necdle-like crystals resulting 35 from the described type of reaction, has hydraulic or seif-setting properties reuderlng it unnecessary to mold the composition under pressure to form stabs or blocks. Although the product of our in vention has the properly of self-setting In a 40 quiescent state without application of pressure (hereto, and this la the manner employed by us for producing the product, it will also set If pres sure la applied as in other methods heretofore known, and still produce a stronger product than 45 has heretofore been possible by such other meth ods.. Inasmuch as pressure molding Is necessary to produce a satisfactory product manufactured by other methods and In view of the fact that pressure may be applied to the product md<> by 0 the process of our Invention but is not necessary, the expression 'Independent ol pressure" Is em ployed hereinafter to describe that the product of our invention h#s self-setting properties not conditioned on pressure, u m 2 2,S0S,V63 In the preferred process of our Invention, we ecococjcally employ as a source of rev materials for obtaining the desired crystalline magnesium carbonate precipitate, magnesium bittern a?id a 6 concentrated 'aqueous sodium qsrboa&te solution which may be made from either soda ash or cal cined trona. If irons, which b a sutural deposit ot sodium carbonate and sodium bicarbonate. U employed, it is preferably calcined to the point 19 where substantially no sodium bicarbonate Is left. This is done to minimise as much as possible the formation of water-soluble magnesium bicarbon ate because It has been found to slow up setting, and because'ol its solubility results Id loss of a.ugii nesium.. ' .. These materials may be obtained economically on the Pacific coast; particularly tbe bittern which occurs as a by-product In the manufacture of salt from'sea water, permitted by the eUmatlc -j conditions on the Pacific coast. The reaction ia the beginning is quite similar to that disclosed in _the Abrahams patent, stoichiometric Quantities of the bittern and the alkali metal carbonate be ing employed. Although any suitable conccnd;, trations of the bittern and the alkali metal car bonate solutions may be employed, we prefer to employ solutions of these substances which ore qaite concentrated because we have found that the reaction resulting from more concentrated to solutions produces a more desirable type of crystal Insofar as self-selling properties arc concerned, The reaction is performed in an aqueous ve hicle; the total water content preferably being from 10 to 20 parts by weight to one part by :<j weight of the reacting substances. A satisfactory commercial ratio is about 15 or IS parts of water to one part of the reacting substances. It is undesirable to have too much water because of unnecessary bulk and because, as was previously <) stated, a more desirable reaction occurs when the water content Is relatively low. Too Utile water obviously impedes the rate o' reaction. Unlike the process in the Abrahams patent, the reaction herein is carried on under vigorous or V, excessive agitation. Mechanical agitation by a)>y suitable agitating mechanism may be employed, but agitation by introducing a stream or streams of compressed air into the vessel In which the re action wears. Is more desirable. Such vessel is " preferably open to the atmosphere as the reac tion occurs under atmospheric conditions, al though it can also be obtained in a vessel main tained under pressure or vacuum but this is un necessary. AgHatlOD has been found to form small and thin crystats which are desirable be cause the smaller and thinner the erysttU, the stronger the final product. This is probably duo to the fact that with small thin crystals there is a greater interlacing thereof to provide a firme- ,*, bond upon setting of the product, The process Is at present pcrferably performed In batches. When the first reseties bath H started, it is desirable to heal the batch as this has been found to facilitate and hasten the re.> actios. However, care must be taken that the lempcralure of the bath is not allowed to rise at any time above the point where the fine wwdicllkc normal magnesium carbonate crystals which are formed, lose their character because then ;y their self-setting properties are destroyed. The temperature should not be permitted to rise much over 120* F,, and preferably, the temperature should be maintained between 75* P. and 80* P, In the process of the Abrahams patent referred to, the self-setting magnesium caebosate crystals arc destroyed by the high tempeiaturc applied during the later steps of the process. live steam introduced dirutSy iaio the n!t!i provides a suitable heating means and also co operate* to effect agitation, llcno., it i* p,c- & Jarred, although any other suitable heating means, such as heating colls in the vcaioi or terns] heat, may be employed icste&d. Zf setup of the magnesium carbonate crystals from the first batch are left la the vessel, such crystals iy serve os ft seeding means and expedl tc fo; ra21Ion of succeeding crystal*. thus shortening Hie liasc of reaction which is advantageous horn the view point of commercial economy, - The magnesium carbonate crystals may also be A obtained by the reaction of any other magncj::n fl compound and any other water-soluble cirbouatc ^ which are known upon reaction to precipitate substantially water-insoluble magnesium carbo nate. For example, Epsom salts o; magnesium u0 containing brines found in wells, and any other water-soluble carbonate, such as any of the alkali metal carbonates, cars be employed. When the reaction first commences, thi: batch has a comparatively thin consistency, b it as 'he Jo reaction proceeds and live fine needle-like self sawing magnesium carbonate crystals begin to form, the balch thickens. A skilled cpeialer or observer will be able co deteimlnr then sub*:aa* tlally all of the magnesium carbonate Is lit tiie vu form of the desired self-setting magnesium car bonate crystals, because when such point o-cuis. the batch has a maximum thickness, being al most gelatinous in ebnmeter. and ;,sen Immedi ately starts to thin out. This Is *nc way by which the operator can tell when the reaction is at the proper end point. . However, the most accurate and preferred way A to ascertain the proper end point of she reitc";*n fl is by taking freqaent successive samples frem V the batch as the reaction proceeds and making TM microscopic analyses of the crystals In v;ch samples. At first, when the reaction h;:s juvl been Initiated by intermixing of the reeulmt sub stances, the precipitate is not in the form of is ndl*-ISke normal macnesium casbor.ate crystals, but appears under the microscope more in the form of amorphous grapc-Ilke clusters. The f.'ic needle-like crystals term as the reaction con tinues; and successive early samples thereof show y more end more of such crystals. When the reaction is at the desired end pilot, substantially all of the magnesium carbonate pre cipitate appears under the merer, tops to be in th; form cf very fine (not fat>;needle-like crystals, ranging from 20 to 50 microns m length, end !; m 2 to 5 microns In thickness. At such end print, agitation, and the application cJ heat if applied, are terminated: and the otystsis are rerd? for succeeding steps cf the process. The i-nath of y time for tbr> reaction to be competed in the ^ first batch which is heated, although noi enusaT, A is tiruaUj* from 20 minutes to Vj hoar. For sue- H ceeding batches in which the crystal* arc formed TM by seeding In the manner explained above, the w reaction is much faster, By viituc of the presence cf small quantities cf sodium bicarbonate sometimes occurun? in commmat rourccs of the sodium carbonate or calcined trona, a small amount of water-soluble to magnesium bicarbonate Is formed in Use reac tion vehicle, which has been found i slow' up the subsequent setting, ai was previously men tioned. To neuialisv any small amount of watcr-to'.uble magnesium bicarbonate which 2,208,7fiS 3 might be formed In the reaction vehicle wad thereby preclude it from slowing up the setting of the magnesium carbonate crystals, shciid all the bicarbonate be rot washed away from such * crystals during a washing operation to be subse quently described. e may add to the reaction vehicle a quantity of caustic or active magnesium oxide, >. e.. magnesium oxide which is not dead burnt, sufficient to react with all the water-solu- 10 ble masneslum Bicarbonate to precipitate mag- nestum carbonate. This also increases the yield, lime, or an? other alkali which will react with ttfer-so!uW rttagncsfam dfcsrbwja&e to precipi tate on Insoluble carbonate, may be employed nstead o1 the magnesium otd.* i; the magnesium xlde being preferred w hmc, because It docs not adulterate the product and because it imparts additional strength to the final set product, The addition of the neutralising medium Is not neces sary. but its employment may be desirable for the reasons stated. We prefer to add directly to and mix In the reaction vehicle, the usual types oi reenforcing materials, such as asbestos fiber. In an amount sufficient ?o provide a final product which con tains from 105 to 1ft % by weight of the fiber: such produet being generally thus employed com mercially for heat insulation. Other chemically Inactive solid bodies, meb as vermlrulltc or dla30 tomacecus earth, may Oe afro mixed l.t the re action vehicle. However, such inert filler or reen/ercing fiber may be introduced at an? suit able subsequent or prior point if s- desired. , As wnn as'the end point of the reaction is ** readied. namely when substantially all of the nrormal magnesium carbonate precipitate Is in the form of tbr desired crvsUK end the other IKBterJal Is added to the reaction uehielt. water* uluble Impurities ir.eludlnz magnesium bicar bonate arc removed preferably by fllu*ai''-n and wariiinn. end the water content of the mass Is simultaneously adjusted by reniovat of excess wafer to control the density of the fins! *el s product. A suitable lype of filter continuous rotary vacuum filter is an "Oliver'1 In which re moval of excess water, filtration and washing mav be done simultaneously. The resulting magnesium carbon*'* s'uny. 50 after washing and sens ration of the desired amount of water, is now ready to he set. II the resultant slurry is not already markedly alkaline by virtue of the addition nf magnesium oxide or equivalent material to the resetsen vehicle, we ^ preferably intermix with the slurry to hveten and also control the setting of ifle product In the molds, and at thesame time increase the .strength f the final product, an excess of an alkali having the nranevty of consuming 'arben dioxide which neAn mav be by absorption, adsorption or reaction, such v preferably ematie or unive magnesium oxide, an alkali metal hydroxide such as sodium hydroxide, qt horax for a reason to t subse quently explained. Other rikasies, such as lime, rt may also be employed, but alkalies nl this lyse arc not preferred because they cause too much a dulieratinn of the final product. In this con nection enough alkali should be added to lender the slurry markedly alkaline, as the slurry has been found to set beurr when markedly *ifc*iine. To the setting operation, the slurry l* cast or ojiusd diicctly Into lorms or molds which me heated Tor a length of time and at a temperature suSclent to set the slurry or sludge to a firm cake. Agitation of the crystals in Uie molds la avoided because such agitation will impair the setting of the crystals. Hence, the setting in the molds Is accomplished with the crystals in a quiescent state. The composition has substan tially no shrinkage on setting and no pressure 5 need be applied to It to accomplish the setting. Consequently, the density of the final product is governed by the quantity of water left in the slurry which is poured. into the molds. Purine the setting, we have found that carbon dioxide gas is given off; and microscopic cb- ffiwaUon of theses product shows that the mate rial which was originally all comparatively thin or fine needle-like crystals now consists essen tially of a mixture of two crystal forms. Some 15 of the original needic-Hke crystals remain but a new, very small crystal appears. Such new crys tal tends to cluster Into grape-1ike groups, or to adhere t*, the surface of the needle-Ukc crystals. This probably accounts /or the great strength of M the final product, which breaks with a clean fracture. In contradlsunotion to the product of the prior processes. which mushes upon being broken, thus Indicating that the product of our invention is bonded by the Interlacing of the ** crystals. Because of the evolution of rise carbon dioxide and the formation of the new crystals, we are led to bgheve that a reaction probably occurs in ,, wJUrh some cJ lb? soot*} carbonate o! magne- 30 slum is converted to light basic magnesium car bonate. The carbon dioxide-consuming alkali which Ss preferably added to the slurry prior to the Betting operation, controls end hastens the , idling which is p.*c"rab!y conducted in an on- closed chamber, no; only because the setting oc curs faster when the slurry is made markedly alkaline, but al*o because the coasuawion of some of the carbon dioxide reduces the carbon ,, dioxide pro&suie m such chamber, and ihiu by the principle o! the law of mass action causes the reaction to proceed faster toward the side of the set product. Also, such alkali since il con sumes carbon dioxide, controls the rate of evoluiIon the:xof midp: ecldd<*? loir.*.* tj<xr> of fissures in the interior of the setting product, width might otherwta* result from too mpftf an evolution of the carbon dioxide, with consequent weakening of the flnAt product. For any given setting tendl.ions, the length o' time of the act may be reffu* *' lated By the quantity of the caibon dioxldecoJMUiwnp aJkeii which may be added to the slurry: the more alkali added vumn pmelicat limits, the faster being the set. If magnesium oxide alone Is added, usually an amount thereof ** ranging from 1% to S% by welcht of magnesium carbonate, la employed: while borax alone is use^ In an amount usually ranging from 1% io 2% hy weight of magnesium carbonate. An r.Skats ** metal hydroxide, surl: as sodium hydroxide, being much stronger, is employed m lesser quantities: 0.1%. to 1% by weight of magnesium carbonate being usually sufficient. Mixtures of the carbon dioxide-consuming afkahee may. of course, be employed If so desired. The addition of the carhen dioxide-consuming alkali, althnuch very de sirable for enhancing the sat and increasing the strength of the final product. 1s not essential. Although no pressure Is required to compact TO or mold the material, pressure molding may he emjrSoyed end still produce a supeiloi product, or a special dense product for certain purposes. However, such pressure molding is preferably omitted where the final product is intended for jg 4- 2,200,763 heat Insulation, Inasmuch as St would Increase the density, The temperature applied to the mold* dur.ng setting should not be too high or applied too rapidly, because although she product will ft sot, the evolution of gas is so rapid ai to leave the final product with gas holes. Neither should the -temperature be too Jo*', because then the setting Is. generally speaking, tco slow for prac tical purposes. A suitable temperature range un- 10 de.- atmospheric pressure is substantially from 140* J`, to-tas* P, At this temperature range, ths setting to a hard cake will usually occur in from & to 3 hours, the time varying with the tempera ture actually applied, and also with r e ehcmlcaj U and physical character of the cam. istuon, as well rts the thickness of the mass, Preferably, the sotting is effected by placing the slurry filled mold's in an enclosure maintained o: the de sired temperature by live steam, although any 20 other suitable heat may be employed instead. H is desirable that the enclosure in which the set ting ts conducted be substantially free of drafts to the outside atmosphere Because drafts might cause evaporation cl moisture and this tends to 29 cause unflrsir&bie shrinkage, Thi* composition sets normally substantially without shrinkage which is Important, because if ;i were to shrink materially, then of course its final shape could net bo fixed by the mold, unfl 99 wasteful trimming wpufd have to be emp/ored to produce the desired shape block or slab. Also, by not shrinking, the density of the product is not increased during the setting thereof, which ts important for controlling the final weight of M the product, as determined by the amount of wtier which is t:ithe slurry to be set. In this connection, 8?ter the previously described Alter ing and washing of tne slurry, if It floes not have the desired water content to produce the fleshed M density of the final product, water may be added to the slurry In an amount necessary to produce the desired density. Thus, the density of the final product may Be controlled by adjusting the water contrm of the slurry to be set. Under some clr46 cumstances, skghi shrinkage of the composition jnfgbt preur burin* seeing, but no: ru. much as the shrinkage which occurs In other commercial processes wherein mechanical pressure molding of the ccmposiuen is absolutely necessary to proM dues a satisfactory Product, After having <ei :n molds, the b'orks or slabs which arc formed ore self-supporting before ihc.v are flrv and while containing comIfle?able moisture. Blocks cv ?>ats formed in other com* 00 rr.erdal procwjtes vfiw* the magnesium caibonnu* is placed In filler melds and pressure mo'dlng Is employed simultaneously with expulsion of water through perforation* in the molds, are no: selfsupporting: and consequently ttiey hn.c to be 00 supported in frames after they arc removed tiom the molds, so that they will not break during handling prior to drying thereof. The methc* of our Invention, therefore, eliminates the neccssiiy of having to provide frames to support the " molded products after removal from the molds. Upon lemoval of the slabs or blocks fsom ihs molds after setting theieo!. they are next dried In the usual manner heictofoso employi'd foi d:y.. ing the mechanically molflsd product. Such fliv- mg Is Accomplished usually in ccmvcnllc:inl_ d 'ving tens at a temperature ranging from laA* P. to 395* P,, to remove all uncemblned or fret water not existIn; ns water of cystallivation. Depending on the temperature and draft. it will sake from 24 to 12 hours for the Crying. 'Hie drying, if fleshed. may be air dry!ng, Us i oien dry- ing is preferred because It is faster. Should the mats; ial tend to stick in Hie molds upon removal User*from, the molds may be first fitted with any suitable substance such as petroleum gfeSse. Even though there is sufiitanltally rso sbrmk- ugc af Ure material Irs the molds, it may be desir able to mill ortrim the stu laces *A th* di led prod uct so as to p.ovsde on attractive product not 10 marred with surface Imperfections. Not over 19% of tJ-5 pioduct need be removed by^urh milling, whtivas with products produced by oilier meth od* the wherein amount onfiopltrfomdgucutnrdeomopvreedssboyr*misilljienqgurrucntmsf from 3C% to 40%. The rnllled-ofT iv.Meilal is no entirely waste material because t may be use lor making magnesia insulating cement. Hon over. has less value as n cement, and therefore results in as economic loss Hence, because of 20 the lesser amount of materia! which need be trimmed from tb<j block oi hh of cm* 'inventton. a fuithtr economy results. Because the product of our invention sets iu a quids-'"*! slate sub stantially without shrinkage. the no!da my be 25 made of special *`/ar so os So form ruri'fjjsfHi.l- mftly shaped InsuiaU:,; fittings. Standard commercial pscducts of ma-nssium ciubonale insu'.MJnp bl.v-k* produced By former prmun* moldins methods contain a!?ou; 9$*: by 50 weight of magnesium cmbomtv at a bonding: agent and sbsut 15'! by weight of a.'besto' fiber to reenforce the product. Under piesent stand ards. su;h blocks weigh fiom 1C to 13 lbs per cubic foot: the specific gravity, ih'refOit rang }S ing fiom .2$ to .28. Use sinliar luaduv; of om* invention contaming the *amv p.vctntaco* el mfshesiam carbonate and asirsio.t fiber cur made to weigh ft\ Sow as 5 los per cubic loot, ah will average from It! tu 13 IBs. ner ctfc'c too*,: ih specific gravity, thoxefoic. lanclnj iron .14 to .19 The f>:odn;t of cur Invention v.'fii. thus average from 35'. to *5^:. lighter thitn tht ^"reaponflina piociuct procured by former method*: even though JipMo:. it Is parison helween BS*5 murh sponger. This com magnrsiiim cnrborsrtfe ."locks 4& of otn' Innnttea and those !fcrploiorr prodi/erd Isolds true lor city given speclfieMlnn of nxatcrluH and percentages of magnesium c*r'.r>,'ftio ;n the lospectjve biocki. Because of the hflht'tcj* <>( the p-o0>.;n of our invention, con^florab! saving In SO freight chxsgcs obtains. Also. Bur ta fee -aw drn'uy of oui product. H her n loxv.n Hf*: ran- ductSvity coCf?.c:e:h th^n that Oi P'OCucts yio* dueofl by former ftitthosK Tlis ht` randvetivity roefftci ent of i he product of our Invention >.v;li run u chout iowri than theconespo iflnv? product jmcdu.'cd by former metbsfls find tontaining the same rei'cenlcuos of Ingrefiicnts. Although the p.-cduct o? oui !,*. x on! Ian is It!n r, U- is much stronger thun hei'Ctotoic uicflueori 60 pj'ocurts. Weight lor vetaht. u l AO': to #xiiougci: while o block e*f oui f-,r r\- p.mwj an :>% magnesium cat fu.nr.u* u;o:fc veieh- ius )i lb', per cubic foot, will be u< tr ->*'n stiongcr than the eonc*i>i>ndinE: S:lo.-k prorixiced by forraer methods and aserar.isr. 13 to lg ju*. o$s cubic foot. The producl of our Snvention because onis 1Ight weight. l9l:'"hly povout t.cellnUn in which ss ono of toe factors enabling it mivitue. to has' a to high h ca: insulat>n% efficiency tu:theimoi e. ai- though the product Is shnorfl h i' not 'tony or rock-like in character as Ate artificial siones or natural iocks.hu; it is chalk-i:kc jr chatbete'-. In 76 2,S09,78 5 other words, compared to an artificial stone or natural rock, it Is relatively soft or crusbable; the material being readily nibbed off from the sur- face thereof. 8 Reference Is made to cur assignee's eopending applications, Serial No. 212,890, filed June 9,1938, and Serial No. 250,653 filed March 8, 1939, con taining j elll subject matter. We claim: 10 J. The tnethod of producing a set magnesium * carbonate composition which comprises effecting a reaction between a magnesium compound and a mefalUe carbonate salt to precipitate normal _ magnesium carbonate lo the form of pe*d)e-ifke |h crystals having self-setting properties, temdnai^Ing the reaction prior to conversion of said self* Vsetting msgneshun carbonate crystals to basic W magnesium earboeftte so that said seSl-seHlng magnesium carbonate crystals form the final prefid cipltale for production of the product to be set, casting a sluny containing such crystals into 8 form prior to aeuiing thereof, and applying heat to the slurry In the form to enhance setting of such slurry to a firm cake. t 2. The method or producing a set magnesium carbonate composition which comprises effecting a reaction in an aqueous vehicle under conditions of heat ar.d agitation between a maeneslum com pound and a water soluble metallic carbonate salt 98 lo precipitate normal magnesium carbonate m the form of comparatively thin needle-likc crys tals harts* eelf-soKin* properties independent of application of pressure, contro.iing the temper ature lo avoid destruction of the self-aeitlne prop erties of such precipitate, lermJ nailpg the metion prior to conversion of said self-setting magnesium carbonate crystals to basic magnesium carbonate, casting a slurry containing said self-setting mag- 5 nesium carbonate crystal* into a form prior to setting thereof, applying heat to the slurry In the form to enhance set'In* of the slurry to a firm cake, and subsequently drying the resultant cake. so 3, The method of producing a set magnesium carbonate composition which comprises effecting o reaction In an aqueous vehicle under conditions of heal and agitation between magnesium bit ters and a water soluble metallic carbonate salt is to precipitate norma! magnesium onrbor.au in the form of comparatively thin needle-like crys tals having self-setting properties independent of application of pressure, controlling the tempera ture to avoid destruction of the self-setting prop- 20 eriles of such precipitate, teiroirmtlng ihe reac tion prior to conversion of said self-setting mag nesium carbonate c'ystals to basic magnesium carbonate, washing s&Sd self-setting magnesium carbonate crystals au&slantiaUy free of impuri- 25 tics, casting a slusty containing said self-settiag magnesium carbonate crystals Into a form prior to setting thereof, applying heat to the sltury in the form to enhance setting of the slurry to a firm cake, end subseouently drying the resultant ao cake, SAMUEL A. ABRAHAMS. RUBIN LBWON. i V' t i ^tent K.. 2,*9,?5>. CERTIFICATE 0? CbaKECTCk SAffCTL i?ArfAXS, IT AL. ,ul? }0> :$u0 It ts hereby certified that errer appears in the print.* specificate numbered patent eorreetten a, felloe, ?fl5e5, f-8C tine ?2, claim 5, for the ard mailt*' re6C .~9elt<r.._. a>,, J - ** 88Sd UU,rJ fc0 ~d with tel. correction therein t-.at the am *ay vonfora Co tee recorder the ease in the e,t8at 0-fl,, Sl6ne3 and sealed this 17te t-.j of September. a. p ISaal) ?!W7 7ar. Aradale, Aettrj Cessnaloner of patent*. Patented July 30, 1940 2,209,754 UNITED STATES PATENT OFFICE 2,218.154 SELF-SET MAGNESIUM CAIIBONATE COM POSITION* AND METHOD OF EFFECTING BETTING THEREOF OjHDVft A. Abrahams. San Franche, and Rubin LeuOB, Meal Park, Calif., asslcnors to Vlant Rubber 8t Asbestos Works. 8nn Francisco. Calif., a corporation of California No Drawing, ApjtlktUon March I, 1338. Serial Kg. 295.663 18 Claims. (Cl, 18--4ft) Our invention relates i magnesium carbonate compositions, and more particularly to an tsnproved wciXM ter eSectltig setting cJ * slurr> containing magnesium carbonate prepared to possess self-setting properties and to an improved final product. This application U a continuation In part of our eo*pending application. Serial No. 212,637, filed .June 8. 1&38, In our assignee's co-pcr.ding application 10 Serial No. 2112,698, filed dune 9. 593B, we have disclosed a type of method thereby such self' setting magnesium carbonate may be prepared. f&rieSy. such type of method con*.:;rises precip itating comparatively fine oeedle-Hkc magnesium carbonate crystals in* an aqueous vehicle by re action of a magnesium compound, such as sea water bittern, with a carbonate salt, such as sodlurc carbonate. In this crystalline form, the magnesium carbonate pots-sses self-setting prop erties. Care ts taken during the reaction to pre vent total or partial destruction of such crystals after they form, which destruction would occur ahoyId the reaction be conducted at too hlsh a temperature, resulting in loss or Impairment of 25 their self-setting properties. Excessive agitation during the reaction has been found to ':peihte the fosmation cf such crystal*, and is conse quently employed. The magnesium carbonate crystais having most desirable self*setting prop 30 erties for subsequent employment In the manu facture of Insulating products, when examined undBr tire microscope, win usually range ficm about twenty (20) to fifty (SO) microns in Jenath and from about two `21 to five S) mfciuns m S3 thickness. Our assignee's co-pending application. Serial No, 212.686, filed 3uno 6. 1938, discloses another type of method whereby the described self-retting magnesium carbonate crystals r.'iy bo obtained 4fi by decompositteo of an aqueous solution of mag. noslum bicarbonate. Briefly, such decomposition ts effected by excessively nluting the mognesSuai bicarbonate solution and simultaneous*/ apply, log ftesc, M thus *hir oft oanbon dioxide, s*W> (S results In the precipitation of the sell-setting magnesium carbonate crystals. Ctue Is also taken during foimauon of the crystals to pre clude total or partial destruction thereof by too high a temperature. Addition of active or 80 raustlc magnesium oxide to the magnesium hi. carbonate solution, has been found to hasten the decomposition reaction. Such self-setting magnesium carbonate crystals may he nl formed by yassiag wills enyhon dlojade-coniolnlhB gas an aqueous vehicle con- Winins a suspension of magnesium hydroxide. In commercial practice, the magnesium hydro*" ido suspension is generally formed by treating with water ealfined magnesite (a natural oc curring magnesium carbonate) or calcined dolo- 6 mlUc material <a natural occurring mineral com posed essentially of calcium carbonate and mag nesium carbonate), In such method, the pre cipitation of the self-setting carbonate of mag nesium crystals occurs as the gassing with carbon 10 diwxlde-eontainlng gas pioceesi*. Care should be taken that the temperature of the reaction does not get too high because if St does the self-setting properties of the magnesium carbonate crystals vnold be Impaired. If not da- *5 stroyed. For best results. Use reaction ahould also be controlled to convert substantially nil <A the magnesium Jobs In Use yeacling medium to the described trystalUr.* carbonate of mayncslurn. as the presence of magnesium In a form other 80 than the fine needlc-liko crystals impairs the muInc properties Pf the product. As with le aped to the formation of such magnesium car bonate oystals by reaction of a magnesium com pound with a carbonxte salt In an aqueous ve* 26 hide, and by the decomposition of a magnesium bicarbonate solution, excessive agitation will en hance the formation thereof in the gassing meth od. A suitable temperature range for conducting SO the gassing medied is between *:xty-eight flecrets Fahrenheit i6$* F. and one hundred four decrees Fahrenheit < lor P.). preferably at about cMity-six decrees Fahrenheit tg$*y.>: theq'Mttlity of water bring preferably from fifteen <!5> 38 pasts to as high as sixty C0> parts per part of magnesium oxide, by weight. In the case where dolomltle material lx used as a source of raw material. trie Inherent lightness of the final product lasulUng fiom the self-set- id ting properties thereof, enables n slurry containJng both the calcium carbonate which Is insoluble and the self-setting magnesium rarbon&t* Crysjals, to be set as such. In vihci nwds. the enlcium carbonate need not be removed Jor the 45 production of a satisfactory light weight heat In- aulMing block, as Is required in other commercial pi essui e molding processes where dolomttic ma terial Is lha source of raw material. From the preceding, it is seen that at some 80 point during the preparation of k carbonate of magnesium by a reaction. in an aqueous itaction vehicle, which consist* essentially of tne com bination of magnesium and cutwiote Je.\y, a pre cipitate of comparatively tine or ihm needle- 88 2 2,908,764 like crystals of magnesium carbonate Is formed; and this crystalline magnesium carbonate which U s normal hydrated magnesium carbonate, be lieved to be the irlhyd?ate. has selfsetting prop> ertles. In this connection, It is desirable to ob tain relatively small needle-Ilk? crystals because these have been found to provide greater strength In the final product than that obtainable by larger crystals. Excessive agitation will produce 10 the desirable smaller crystals which for most de- . alrable self-setting properties for subsequent em ployment in the manufacture of Insulating prod ucts. will usually Rinse frem about twenty 120? to Ally <60? microns in length and frozo about 1* two 12) to five <5? m.croos In thickness, as was previously mentioned. If a slurry of such normal hydrated magnesium carbonate crystals is cast or pound Into a form or mold, the composition will set in a Quiescent SO state to provide n self.set final product: the set ting in the mold being materially expedited by application of heat The composition has sub stantially e shrinkage upon setting: ana no mcchanscal pressure need be applied thereto, as 25 ts necessary in other methods, wherein the nag- nesum carbonate is usually molded under me chanical pressure In a filter mold, simultaneously with the expulsion of water therefrom through perforations in such filter mold. As o result, the 20 density of the self-set product may be governed by the quantity of water left In the slurry which is poured into the mold, and such mold need not be perforated. The usual types of reenforcing materials. 6ueh " as asbestos or other sultable reenforcing fiber. In an amount sufficient to provide a final prod uct which contains from ter. percent. 11056 > td fifteen percent. (15%) by weight of the fiber, may be intermixed with the sferry So be set: sccft cn product being generally that employed commer cial!? for heat Insulating purposes. Other chem ically Inactive solid bodies, such as vtrwlculite or diatcmaceeus earth, may Be also mixed In the slurry. Such Inert filler or reenforcing fiber 1.1 may be mixed directly in the slurry after it is formed, or if desired, tbev may be Incorporated in the reaction vehicle in*which the aeU-settlng magnesium carbonate crystals are formed. We have found that certain conditions of alkaJO Unity ol ihe Blurry will enable control of the selling and also permit such setting to occur more expeditiously as well as impart increased strength to the final product; and, If the setting is conducted under special controlled conditions, ',*5 a superior grade product will result. Also, wo have found that the slurry before being cost into a form or mold wherein it Is to be set, may be preheated to cooperate In hastenlne the time of setting In the fon.. Our invention. <oo therefore, has &$ Its ooiecss, among ethers, the provision of improvement# ir. the product and In the marmor of obtaining setting of the de scribed self-setting magnesium carbonate crys tals. Other objects I the Invention will become re- apparent from a perusal of the following de scription thereof. In general, we have found that If the slurry of the magnesium carbonate crystals to be set Is not already markedly alkaline <1. e, alkaline 'to reserve sufficient to neutralise magnesium bicar bonate generally present in the slurry and con sume some of the carbon dioxide which is given off during the setting?, the addition of a carbon dioxide consuming alkali thereto In a quantity T5 sufficient to render the slurry markedly alkaline. will provide a control for ihe i-cttin? of the pioduct and allow sueh setting to be rxpedurd: and in addition Impart added mrongtr. to the final product. To further cxiwdiM telling I the form, the slurry may be o> cheated prior to being cast therein. Also, we have found that the set ting ts best conducted In an environment wherefn substantially no drying or dehydration of the setting mas can occur; so ibut there is very mile, if any. Joss tn weight thereof. This to helps to preclude any riirir.kaee which might tend to occur. Drying of the set product is ef fected by a separate and independent subsequent step. With respect to forms wherein a com paratively large surface area of the setting massm is exposed so that moisture can icaciJiy evape rate from such exposed area, such as open pans the Jelling to accomplish the best results should be In an enclosed chamber subiiantlalJy free of drafts to the outside atmosphere anti which 20 is moisture-laden to the point where the at mosphere under which the setting orcuts is sub stantially moisture-saturated with respect to the vapor pressure of the water In the mass being set, to preclude evaporation of moisture from 25 the setting mass. The some cfiect may bo ob tained in an pen space when forms are em ployed which enclose substantially oil of the sutface area of the setting mass, such as a tabe-i:ke form la which the setting mass is ex 3f posed only at an end of the form. In this event.' substantially no moisture can evaporate during the setting period, and such forms, there fore, provide the means for precluding drying or dehydration t,. the setting mass. &:*am can be employed at the source of heat when forms Of the latter type ore utilised hut any other #suitable heat may be employed if desired Although ft# tne steps of Che slurry before It ts cast mto the form, utilising a mark edly alkaline slurry, aid conducting the setting in cn environment wherein drying ; tho setting mass Is precluded, are employed, the step of utilizing a maikWly alkaline slimy may be omitted, and siM produce s satisfactory prod uct. Also, the step of setting the slurry without substantial dehydration in a substantially nondrying Atmosphere, may lie omnted. and still produce a good product. The step cf preheatsnc the slurry prloj to pouring U inia the form* Is desirable because it enables the setting to be conducted in a shorter time, thereby making for economy f menufueUi: r. However, sueh step may be aniUed wishout effecting the quality of the fina! product. For the production of u su perior product the setting shnnld be conducted under the described conditions wherein substan tially no drying of ihe sellins mass tan occur and the slurry is rendered markedly aJRollhe, Zn addition to effecting (he utenffty oi the final product, the markedly alkaline slurry, as pre viously pointed cut. pgrtmia expedition of the setting. Therefore, >pp cnmbttvoriOf' of this tlep end the preheetine Meg are Important in ob taining a fast set. Our improvw method of selling the slurry containin'; tJt* described srif-sethne needla-iike magnesium carbonate ciys'ais will now be de scribed in greater detail. Such magnesium car- _ bonstc h a normal hydrated magnesium carbonate, believed to be the trihydrate. which sets by conversion tc o bavie magiK'si'jm carbon ate, the conversion being enhanced ay apolicatlon of heat. Herd ofore. It was deemed neces sary t avoid application 1 hest to the raag- "5 flJiOBJS4 3 neatum carbonate crystals during the period fee- tween ti termination of the reaction by which they art formed atsd prior to the ettilae theteei la the Jenna or molds. We have now foiled 5 that heat may be applied during Oils period without weakening the final set of the prrduet In the Wotda> provided the temperature and time are below the critical point at which the normal carbrotle eommences to undergo conversion to in basic carbonate. If the preheating tempera ture ts too high, soch coavemioa will occur in a relatively short ttose. while If the tempera* Sure is low but applied over a relative)/ tone Utne, the conversioa will also occur. The skilled ,operator can readily ascertain when such ccr>- erston commences because when it does the wry starts to thKken or gel. Any preheating of the slurry before li poured Into tbs forms should, therefore, be below the botnt at which 20 incipient conversloo pr gelling occurs. Preheating of the slurry after tt is formed and before being poured Into the molds is desirable for cotntr.ertca; reasons because it enables the setting time to be materially shortened In*the *5 molds, thus resulting in economy,of miaulneuire. Tte preht&ticK should bs conducted la briny ait of the slurry to a substantially uniform tempera* lure as quickly as possible before pouring into the molds. This can be best accomplished by nfl heating relatively small batches of the slurry, and rimultancously stliring or mixing such britches la provide the uniform inc&.-porsiton of the beat, The preheating r.uy be conducted In open heated vassels if so desired: or by con 33 veying the slurry through heated screw con veyors which serve to mix the slurry as well -- aAs* wmvrj }t ASthQUgb cdnvsrsien ol the Blurry base magnesfum carbonsfe a'lft occur si dely varying temptratur&s, defending on the hsractcr of the if-settab>e normal magnesium carbonate crystals, w have found that in most ecse4 such conversion oeeurs readily at a tem perature I about one hundred thirty degrees Fahrenheit 1130* P.) to one hundred seventy degrees Fahrenheit O?0`F.h it is generally de sirable to employ m*es being preheated which talcs about ten <m to fifteen (151 minutes to bring aJ] of the slurry up to the desired pre heating temperature, it is undesirable to have conversion from the sclf-settaNe norma) hydrat ed magnesium carbonate crystals to a bnric mag nesium caiSenate. <:cur during the preheating because the entire setting should occur in the melds to provide a final product of maximum strength. As was ftreviowsJy poinied out, Ibe preheating step may be oimUed. l! so desired To hasten and alsp control the setting of the slurry containing suth crystals a-hetber tt Is or 1$ not preheated, an? at the -me time Socmtae dd tihf e strength of the final product, ve preferably trader H markedly Utallne. if It is not already m arkediy tJXollne, by addins thereto cither prior i after p-ehrfttlne it employed, or to the vehicle from which' St'ts" formed, an excess o! an alkali hiaving the property of consuming cerben diesid which may be by absorption, adsorption or rp$2k*'K ysscb ss Preferably caustic or active magnesium oxide. 1. e.. magnesium oxide which is not dead burnt, borax, or an alkali meUi hyTA dioxide such a* sodium hydroxide, or any suit able mixtures theveef. An alkali, such as lime, may alto be employed, but ts not desirable be cause i: wouM sdulierals the final product to too sres; an extent. The c*rb>n dioxlde-c^pj5 suming alkali which is added to the slurry prior to the setting is believed to enter Into a reac tion with other substances existing in the set- sJtff slurry. Fw afly glvsn sptsine conditions, the length of time of the sel may be regulated by the quantity of the carbon dioxide-consuming 6 alkali which nsty be added to the slurry: the more alkali added within practical limits,'the fester bring the set permitted, in this connec tion, the carbon dlpxnit-consttnl.ng niktilf Sho permits faster setting than would otherwise be permitted wish respect to any given slurry which docs not have the carbon 4Soside-consuming al kali therein because it allows the setting to be conducted at higher temperatures, to thereby hasten the conversion to a basic carbonate. ** It only magnesfun? oxide Is added, usually an amount thereof ranging from one percent, lift) to ten percent, (10%) by weight of magnesium carbsan in the slurry wlU suffice. Borax, fee ing a stronger alkali. is added In an amount ranging from one percent, (1%) lo two per cent. >2% i by weight of magnesium carbonate. An alkali metal hydroxide, such as sodium hy droxide, being still stronger, to employed tn an amcunt ranging from one-tenth of one percent. 85 <0.1%) to one percent. <ltt> by weight of mag nesium carbonate in the slurry. Magnesium ox ide has the advantage of not adulterating the product all, and, therefore, provides for great est added strength. The stronger alkalies, such 80 s borax and sodium hydroxide, however, permit faster setting. Therefore, a mixture of magne sium oxide and borax or An alkali metal hydrox ide. produces Ideal results. Such mixture >nay contain there su`- `-onees in any desirable fete- 83 portions. The upper limit of the amount of alkali rftx'eft afiotiM CW 6&ed tt rwf fikrtJco}*r)y eal. as the maximum quantity may be deter mined at the time by one skilled in the art. in -iO accordance with (be conditions, it is only Im portant that the slurry be made markedly alka line, that is. sufficient!? alkaline (o ncu-raltre any magnesium bicarbonate present, which has the unfortunate property of inhibiting the set end Ad is consequently undesirable, and provide a re serve to consume some of tlie carbon, dioxide which is evolved during setting, in the setting operation, tbe slurry is cast or paused directly inlo Imperforate forms or mollis which are hti- 60 ed lor a length of urr.e and at a temperature suf ficient to set the slurry or sludse to a firm cake. Agitation of the seii-ictrin* macaesium car bonate crystals m the mold Is avoided because suth ngieatWn sill impir the selling of the prod- ** uci. Hence, the setting in the molil t- accom plished with the crystals m a qu'eseent slate, as was previously related, the composition sett with substantially co shrinkage end ho pleasure need be applied to It (o accomplish the seinng. As n rcsu. Che dcatlty of Che final produce u. sots c.-ned by t)<e dusntlty cl wales left in the slurry which is poured into the mold. U t* io be undet- stood that the seif-settable normal hytirated *5 magnesium oarbonati* crysiahiiic precipitate Is not allowed to set in the reaction ve'ucle and that such cfto veWcJe usuafivcnnlaihs an ex cess of wotei', a desired amount of which Is Usy* jslly removed. In any suitable vrav such as by de* 70 rentatson or fillration, to dderminc the density el the final product. More water than desired >s ususlly removed when the preclprinte is sepa rated from the reaction vehicle, for example for Ihc purpose'Of washing It, but addlllonal water Je 4 2,808,764 may bp added afterwards to provide a final prod uct of the desired deadly. .During the aettiag, we have found that carbon dioxide gas la given oS: and microscopic observa 5 tion of the set product shows that the magnesium carbonate which was originally all comparatively thin or fin? needle-like crystals now consist* es sentially of a new crystal form. Some of the original needle-like crystals may remain, but a new, very small crystal appears. Such new crys tal lends to cluster into grape-llhe groups, or to adhere to the surface of tire needie-JJfce crys tals. This probably aceccnts lor the great strength of the final product which Creaks with a U dean fracture, to contradistinction to the prod uct of the prior processes wherein pressure mold ing is employed, which mushes upon being broken, thus indicating that site product of our invention Is bonded by the interlacing of the so crystals, Because of the evolution of the carbon dioxide gas and the formation of the new crystals, a re action occurs in which tlie carbonate of magne sium Is converted into a light basic magnesium US carbonate. The carbon dlcxlde-eensumlng alkali which Is preferably added lo the slurry prior to the setting operation, allows hastening and con trol of the selling which Is preferably conducted In an enclosed chamber when the molds arc of so such character as lo expose relatively large surface area of the setting mass, such as open p&n.s not only because the setting can occur faster when the slurry t* made markedly alkaline, but also because the consumption of same of the 9S carbon dioxide reduces the carbon dioxide pres sure in such setting mass, and thus by the jirin- elpis oI the law pf mass action, causes ids icaction to proceed faster toward the side of the set product. Also, such alkali since It consumes 40 carbon dioxide, controls the rate of evolution thereof and precludes formation of Assures in the interior of the setting product, which might otherwise result from too rapid ars evolution of the carbon dioxide, with consequent weakening tt of the Anal product. Although no pressure Is required to compact or mold the material, since the material sets is a quiescent state independent of pressure, pres sure molding nsay be employed and still produce a superior product, or a special dense product for certain purposes. However, such pressure molding Is preferably omitted inasmuch as It would Increase the density of the final product, wmch is undesirable where tne product is to be M employed for heat insulating purposes. Inas much as pressure molding has heretofore been necessary because the magnesium carbonate pro duced by other methods does not havo selfsetttne properties, and because pressure may be applied to the self-seltable magnesium carbonate of our invention but is not necessary, the expres sion ''Independent of pressure" is employed here inafter to describe that the magnesium carbonic of our Invention has self-setting properties not S conditioned on pressure. When picheating of the slurry is not employed and the molds are of such character as to expose a relatively large surface are# of the setting mass, the temperature applied to the molds during the 70 setting should not be too high or applied too rapidly, because, although the product will set, the evolution of gas may be so rapid as to leave the Anal product with gas holes. Neither should the temperature be too Sow, because then the set 78 ting is. generally speaking, too slow for practical purposes, A suitable temperature range under atmospheric pressure Is substantially from one hundred forty degrees Fahrenheit U<0* F,> to one hundred ninety-five degrees Fahrenheit <195' F,;. At this temperature range, the set- ling to a hard cake in molds which expose a relatively large surface area of the product will usually occur In from one-half to three iti to 3> hours, the time varying, of course, with the tomtierWuie actually applied, sod also with the 10 chemical and physical character of (he composi tion.'as well as the thickness of .the mass. Zl the slurry is preheated, and also markedly alka line. the setting in molds which expose a rela tively Urge surface ares of the product, can bi accomplished in about three to fifteen 13 to l$i minutes at a lower temperature of about on? hundred thirty degrees Fahrenheit U30' F,1 to one hundred seventy degree* Fahrenheit <170* P.i For best results, it Is important that the set- 20 ting be conducted so that substantially r.o drying or dehydration of the composition occurs during the setting thereof, as this minimizes shrinkage should the setting product have any tesideocy to shrink. For this reason, e effect the setting in 25 our improved method when the product is cast into molds which expose a relatively large sur fer? area of the product, by placing the slurryfilled molds in an enclosure or chamber main tained at the desired temperature by live moist 30 steam introduced therein under r'assur. Fur thermore. K Is important that t.n enclosure in which the setting ts conducted be free of any substantial drafts to the outside atmosphere be cause drafts might cause carrying of moisture from the product It sets, and this might cauis*ve undesirable drying which might result m shrink age. By employing !Jve steam as the heatln4j medium for effecting the setting in the moldi the region or atmosphere in which the set'isl occurs can be made moisture-saturated or over.' saturated with respect to the vapor pressure of the water in the setting material, to thereby minimize evaporation of moisture therefrom and avdd shrinkage. Under the prescribed setting 45 conditions, the slurry alter it has set in the mold and before ?J Is dried by a subsequent drying step to be. described, will weigh substantially the same as it did when firs? cast into the mold Instead of live steam as a source of heat the 50 ra effect may be obtained by using an external source of heat to heat the chamber In which 'he retting is conducted, and by introducing a spray ur other source of water into the chamber to render the atmosphere thereto moisture-laden 85 However, steam Is preferred because it penetrates the setting mass to thereby replace mote readily any moisture which might lend to be driven off because of the heat. I! molds are employed which substantiaSly completely Jacket the Hurry *ueb ns a tube-like mold wherein the slurvy is only exposed at an rnd ol the mold, then suck type of mold serve* by itself to pirelude subsist lial evaporation ol moisture during th* setting and caurcs the setting to occur under non-dryl tig conditions. Although s'.csm heat may be em ployed for heating such form or mold U is not necessary, as any other suitable kind of heat may bo utilised instead. Furthermore, tills typo of mold, partial)#ily if the sSuisy is wcheated and 70 contains the carbon dioxide-consuming alkali, allows the heat lobe applied dJicctly over a large area of the slurry, peimuting a>i extremely fast $n After havmg set in melds, the blocks or slabs 75 a,st>e,7fl4 5 which are farmed are self-auppartlne btdore they ore dry and while containing substantial)? the tame amount a! moisture as ta the Slurry before H has fat. Tb? hlooks cr slabs lorried In other 5 commercial processes where pressure molding is necessary are not self-supporting, e0(2 SuentJy have to be supported in frames alter they are remotea from the molds, w that they u'4t not break dursntf iuudlut* prior to drying thoreoA 15 Vpoa removal of the slabs or blocks Item the molds &|ter setting thereof, they arc ftc-x l dried Sr the usual manner heretofore employed for drylag the mechanicals? molded product, Such drytag is accomplished, usually, la conventional dry. tag ovens si a temperature ranging from one hun dred fifty-five degrees Fahrenheit US5* F.l to three hundred ninety-five degrees Fahrenheit (395 F,>> to remove at! UncemBlned or free water not existing as water of crystallisation, Depend*. W tag on the Umptaiusc and she or*/-, u tr.W fake Srom twenty.four to seventy-two 124 to 72) hours for the drying. The drying. If desired, may be air drying, but oven drying Is preferred because it Is faster. Should the materia! lend to stick to ** the molds uponremoval iherelram.the molds may he first greased with any suitable substance, such as petroleum greaae. Even though there Is substantially no shrink age c( the material in the moIda, St may be deslr* able to mill or trim the surfaces of the dried prodage sc as (o provfde an ett,-active prcdycl sol marred wjtrt surface imperfeciicm. ThU la par ticularly true with respect to the type of molds, each as an open pan. wherein a relatively large W surface area of the slurry is uncovered or exposed. Os the exposed area tends to leave a surface which is not smooth, Kot over ten percent. <10%> of the product need be removed by such mnijns when molds which expoke a relatively large area o* ihe slurry are employed, whereas with products produced by other methods wherein melCins <i-aer pressure is required. the amount cJ prod uct removed by milling runs from thirty percent. (SOCW to forty percent no*ui. 'file raUleo-oft material is not entirely waste material because It may be used far making magnesia insulating Cement. Koweicr, it has less value as a eemeot, and therefore results In an economic loss. Hence, because of the leaser amount of material which ;.t> need be trimmed from Ihe Block or slab of ou* invention when molds which expose a relatively targe area the slurry *re employed, a further economy- ecutitg. Bctlttit *2m P&OUCt ot fW invention sets n* a albescent state substantially sc without shrinkage, the molds may be made of special shapes so as to form correspondingly Shaped insulating fittings. Standard tcrsnmevctal products oT magnesium carbonate insulating blocks products by former so pressure molding methods contain abuut eightyfa five percent \tb%> by weight l basic magnesium carbonate at a bonding agent and about fifteen percent, * I57el by weightof asbestos fiber to rcon. ""force the'Product. ttader `present standards, c-< such blocks weigh from sixteen to eighteen pounds a6 to 18 ibs.i pev cubic foot: the specific gravity, therefore, rang!ns from twenty-five or.ehun dredths t.2? to twenty-eight one-hundredths 128X Zy adjustment of the water content of the slurry prior to casting It Into the mold, the similar product of our invention cuntslnlng the same percentages of basic magnesium carbonate and asbestos fiber can Be made to weigh as low as r.lne pounds <9 lbs.) per cubic foot, and will aver. 75 age from ten so twelve pounds <t0 to J2 fos.J per cubic foot: the specific gravity, therefore, ranging from fourteen ooe-hundredtha i.S4) to nineteen onc-hundredths i.29). The prod oct of our inven tion will, thus, avetage from thirty-five percent, 135% > tb forty-five percent. <4S%> lighter titan 5 the corresponding product produced by former methods; and even though fighter, It Is mueh stronger. Tills comparison Between eighty-five ivar-ri. <**..> magnesium rarbcnale blocks of our Invention and those hereiofcce produced is holds true for any given specification of materials atid percentages of magnesium carbonate lt the respective blocks. Because of the`lightness of the product of our tnvcntlon. considerable saving la freight Charges obtains. Also, due to the low 15 density of cur product. It has a lower bent con ductivity coefficient than that of products pro duced by former methods. The heat conduct /tty coefficient of the product of our invention a-elgh- ;p abcui len to twelve pounds tie to IZ lbs.) p<*r SO cubic loot wifi run about twenty percent. <20%t to thirty percent, <30%) lower than the product produced by farmer methods and weighing about sixteen to eighteen pounds <16 to S8 lbs.) per cubic foot, 25 Although the productofour fnvctvtion is tighter. U is much stronger than heretofore produced products. Weight for weight, u is fifty percent i50%> to one hundred percent, UC0%i stronger; while a block of our invention, for example an so eJghly^flvs percent <55%) magnesium carbonate block weighing eleven pounds <n !&sJ per cubic foot, wifi be as strong or even stronger than tha corresponding block produced by former methods and averaging sixteen to eighteen pounds < 16 to git 18 tar.) per cubic foot. As was previously related, where co'onuiic ma terial Is the source of raw material, th? calcium caibonata may be left in the slurry containing the seif-setilng magnesium carbonate crystals, <9 subseouenUy treated by our preferred method to glieci arising thereof, and still .produce a satis factory light-weighs block adapted Jo? heat in sulating purposes, in inss connection, the doio- mJtlc product resulting from the method of our invention and containing the same wi centage of asbestos fiber as occurs la tha standard com mercial magnesium fieac-losufiurng blacks pro duced by former pressure melding me;bod*, and in which calcium carbonate Js not eliminated, go can be made to weigh as low a twelve io sixteen pounds <12 to 16 lbs.> per cubic foot 'ih* specific levity, heftce, tangtaB {rota about one hundred ninety-two ooe-thoussndtHs <A32l to two hun dred fifty-six on^thpusandths l.256> >, to addt- js tton to lightness the dolcmlho product possesses greater strength and has higher insulating effi ciency than the product produced by oiber ?om* Rierctat fciethods invofvfni pressure moving, even though, in such other methods, the calcium com- go pounds are eliminated from tno source ot Solo* imtlc material. For example, a block fornved by the method of our invention, weighing about lovTtasn pounds (It fbs.J pee cubic loot, is ctronger than a sixteen pound <16 Ib.i per cubic 61 foot block produced by other commercial methods Involving tnechanlcei pressure end in which cal cium carbonate U eliminated frown the dolomlUc material. Yet such block icsuUing from our method will have about twenty-five percent. To '25%) greater insulating efficiency. The product of our invention because of Us light weight, is highly porous, i, e.. cellular in structure, which Is one o( the factors enabling ii to have s ftfgCt .'was insulating (fSetensy. Fur* 73 6 0,809,754 thermore, although the product is shaped. It is not atony or rock-like in character as are arti ficial stones or natural rocks, but is chalk-Ilk? in character. Jn other words, compared to an arti ficial stone or natural rock, It Is relatively sole or crushabie: the material being readily rubbed oft from the surface thereof. However, insofar us magnesia insulation is concerned, the final dried product of our invention is relatively hard 10 and firm or rigid, with sufficient strength and cohesive bonding power to provide a modulus of rupture (flexure strength) enabling such product to be entirely self-supporting in slabs as thin as one U> Inch and as long as three 13) feet. Such IS strength is necessary for allowing the material to be handled and applied. Not only Is the Ana) dried product self-supporting but. as previously explained, the set product prior to diylng is also seH'Suppcritng. 50 The results of our Invention are obtainable, irrespective of whether or not the composition to he set consists essentially of the sell-setting, normal hydrated magnesium carbonate crystals alone or of such magnesium carbonate crystals 25 Intermixed with other materials, Therefore. In the appended claims, the expression `'magnesium carbonate composition" includes compositions, such as the flolomitic composition described, which contain materials In addition to magnesium SO carbonate. We claim: 1. In the method of producing a self-set mag nesium carbonate composition from a Ourry con taining normal magnesium carbonate crystals 34 haring self-setting properties Independent ol ap plication of pressure, said composition being ca pable of use as a heat insulating materiel, the step of enhancing setting of such slurry by add in? ax alkali ifteitio lo consume wubev) rlJccride 40 which is evolved during the setting. 2. In the method of producing a self-set mag nesium carbonate composition from a slurry con taining normal magnesium carbonate crystals having self-setting properties independent I ap15 plication of pressure, said composition being capable of use as a heat Insulating material, the stepof enhancing setting of such slurry by adding magnesium oxide thereto lo consume carbon dioxide which is evolved during the salting. 50 3. In tiie method of producing a 6Clf-set mag nesium carbonate composition from a slurry con taining precipitated normal magnesium casbonate crystals having sell*setting properties independ ent of application ol pressure, said composition an being capable of use as a heat Insulating material, the step of Incorporating bora* w such slurry, 4. In the method of producing a self-act mag nesium carbonate composition from a slurry con taining precipitated norma! magnesium carbonate eo crystals having self-setting properties independ ent of application of pressure, said composition being capable of use as a heat insulating material, the step of incorporating an a-kali metal hy droxide in such slurry. 05 5. A molded light weight cellular chalk-like but substantially rigid end self-supporting basic magnesium carbonate composition capable cl use as a heat insulating materia) and self-set sub stantially without shrinkage independent ol ap ?0 plication of pressure from normal magnesium carbonate crystals having srlfvsuulng properties, said composition being strengthened by the prod uct resulting from ihc addition thereto of a car bon dioxide-consuming alkali. G. A molded tight weight cellular chalk-like but substantially rigid and self-supporting basic magnesium earbonatc composition capable of use heat Insulating material and seif-sot sub stantially without shrinkage independent of ap plication of pressure from normal magaosium carbonate crystals having seU-settlng properties, said composition being strengthened by the prod uct resulting from the addition thereto of the magnesium oxide- I. A molded light alight celhilar chalk-like 10 but substantially rigid ami self-supporting basic magnesium carbonate composition capable of use es a heatinsulating materia! aed'self-setsubstan tially without shriekMe independent of applica tion of pressure from normal magnesium car bonate crystals haying self-setting properties, ss'd composition being strengthened by the prod uct resulting from the addition thereto of bora*. & A molded light Weight cellular ehalk-Uke but substantially rigid and self-supporting basic 29 magnesium cutixmata composition capable of use as a heat insulating material and seif-set sub stantially without shrinkage independent of ap plication of pressure from normal magnesium csibonate crystals having self-setting properties, fcj said composition being strengthened by the prod uct resulting from the addition thereto of an al kali metal hydroxide, 9. A magnesium carbonate composition capable for the p*epsration ol heat Insulating material SO and having self-setting properties independent of Duplication of pressure comprising a seif-settable slurry containing neodJe-iike crystals of normal magnesium carbonate having self-settlng properties, said slurry also ham 3 sufficient alkali added 95 thereto to neutralize any oagriisluiu bicarbonate which may occur therein and consume carbon dioxide which Is evolved during setting of the slurry, 10. The method of producing a self-set mag nesium carbonate composition which comprises forming in a rescuer, vehicle a precipitate of norma! magnesium cai boosts in the form of ntedis-llke crystals having self-setting properties, without allosing setting ut such precipitate In the 45 reaction vehicle removing from the reaction ve hicle a slurry containing such precipitate. Incor porating a carbon dioxide-consuming aiksti in s&td precipitate to allow the subsequent setting thereof to be expedited, effecting the setting by 50 applying heat to the slurry, and drying the re sultant product, II. The method of producing a self-set molded magnesium carbonate composition which com prises foiming in a reaction vehicle a precipuat* r,s o( normal magnesium carbonate in the fora or r.tedle-UHe crystals having sell-sewing properties, without allowing setting of such precipitate in the reaction vehicle rtmovfag from the reaction vehicle a slurry containing such precipitate. In 60' corporating a carboh Cloxidc-consumleg alkali to allow the subsequent setting to be expedited, elthei' before or after the incorporation of said carbon dioxidc-consusfcing tYstll preheating said 05 slurry to cooperate in expediting the setting cast. In? the preheated slurry into a form adapted to shape said composition, effecting the sawing by applying heat to the slurry >a the form, and dry ing the resultant product. TO 52. In the method or setting a magnesium car bonate composition by application of heat to a slurry containing normal magnesium carbonate m the form of needle->ifce crystals having selfwumg propcrtlea: the step of expediting the set- 75 3.206.764 7 ting by preheating the slurry prior to effecting setting thereof. 13. in the method of producing a$elf*t mold ed magnesium carbonate composition by appllca* 5 tion of heat to a slurry In a form adapted to shape the composition and which contains normal mag nesium carbonate In the form of needle-tike crys tals hating self-selling properties; the steps of expediting the setting by preheating the slurry 10 prior to casting 1c into said form, and either be fore or alter such preheating Incorporating a car bon dioxide-consuming alkali. 14. A basic magnesium carbonate composition 6e!f-$M independent of application of pressure by conversion from normal magnesium carbonate crystals having self-setting properties, said com position being strengthened by the product re sulting from the addition thereto of a carbon dioxide-consuming aUcall, 20 15. A molded light weight cellular ehalk-ltke but substantially rigid and seif'Supporting basic magnesium carbonate heat insulating composition reenforced by asbestos fiber, self-set Independent of application o! pressure without shrinkage by 25 conversion from normal magnesium carbonate crystals having seif-setting properties: said com* position being characterized by the absence of fissures resulting from the incorporation therein of a carbon dioMdc-coosumine alkali. 16, The method of producing a seif-set basic magnesium carbonate composition capable o' use as a heat insulating matenal which comprises *> forming in an atjueous reaction vehicle a predpl* late of normal magnesium carbonate In the form of ncedie-Jike crystals having xelf-xclllng prop erties, without allowing setting of such precipi tate in the reaction vehicle removing from there- w actors vehicle a slurry containingsuchprecipitate. Adding sufficient alkali to oeutrahze any mag nesium bicarbonate which may occur and to con* same carbon dioxide which Is evolved during the setting, either before or after the addition of aalrt 16 alkali preheating the slurry to cooperate fn ex pediting the setting, casting the preheated slurry into a form adapted to shape said composition, effecting the setting by applying heat to the slur ry In the form while simultaneously precluding cn evaporation of substantial amounts of moisture from the setting slurry to minimize shrinkage during the setting, end eh ylng the resultant prod uct. SAMUEL A. ABRAHAMS. Ho RU3XN LEWON. patent so. 2,205,?5h. SAKU5L A. *uly 30, IjilO. It Is hereby certified that error appears tz the printed specifIcetier, of the above cjshared patent re<?uSrln5 correction as fellas: first ,!*, *lne 10, foi "2112/693" read -212.658-; d that the aaid Let- ters Fatw.t showId be read with this correction therein that the ease r.ay eanfam to the record of the case Jn the Patent Office. Signed and sealed tMa 17th dey of "epce.ti&er, *- D. 15*80. (Seal) Henry Van Arsdele, Acting Coststasior.er of Patent ii;' *: *\ v \i ^SkfenUd Jftn.,l!> 1944 2,339,041 KT<'.--.,: fe'- < * UNITED 3TATES PATENT OFFICE .,. * d '* r ' /;tv'.;/ . * **' 8^a^^GNii^^OiiONATa COM- .POSITION AND METHOD FOfi TBEPABINQ . , THE;flAMS:*- > .vu * 5*nt&A&raJumi, Bedwbdd - CS!y, SsUs lawfcfr'XBo Alto;in41<wda U Coilonge, San Mate^Cettatyi'Calif* Mitrm'lA'riant Bob ber A AitectoB'Werks, San Trarietieo, Calif* a corporation f California , NoDrawiar ' AspUcattCFa January tl, Ml, ' Setfs? No. **/ . i ciaimi. Out Invention relates to nimodua carbonate eaafHWftleas, pajaeuitrlj. to'-aOta* proved method for enhancing the getting proper- aqueous solution cl magnesium bicarbonate In the manner disclosed in our assignee'sPatentNo, 2,303.163.' Our Invention has ae its objects, tie* oS magnesium carbonate prepaid to possess among others, the provision of a method for pro* self-BtUtog properties and to so jraproved fiat! A meting with minimum cam the formation of the product.' 1 \" desired relatively small, fine magnesium carbon A* Is disclosed la our assignee1* Halted State* ate crystals, particularly with respect to the de Patent* Km, 2,209:132, 2^03,163, end 3,203,154. composition method of Patent No. 2,SOB,769, and a)] dated July 50, JWO a Mlf-wtetog magnesium the Provision ol an Improved final product re- carbonate caapfestUenadapted for use u a acund 10 suiting from such method. Other objects of our or heatInsulating materialmar be prepared from various'asuraa of materials: such as fey reaction Invention'will become apparent from a perusal of the following description thereof. In an aqueous vehicle of a magncahim'compeund, We have found that *unUsrm formation of the tu&h ib tea witotbRtera, with a carbonate salt desired relatively fine, self-settable normal mag- such astodhun carbonate; by;decomposition of 13 netium carbonate crystals may be obtained with :an aqueouj aolution of magnesium,bicarbonate: minimum care by causing precipitation of such r and by siaaini with carbon. dioxide-containing crystals m the aqueous reaction vehicle in the tuts aqueous vahicJe containing'a suspension presence of any suitable'colloidal dispersion of of magnesium hydroxide.'In the case where any suitable bentonite clay. The bentonite dotdmttic materia) is used as.the source of raw 30 may be added to the aqueous reaction vehicle material, u Is disclosed In Patent No. 2.303,154, either before formation of the selfsettable crys ' the inherent lightness of the final product result talline magnesium carbonate precipitate or Just ing from the eif-ttiag properties thereof, en after formation of such precipitate commences, ables the slurry containing both the calcium car- "but it Is more desirable to add the bentonite prior ,be&ste which la'insoluble end: the self-setting tS to the formation ol such crystals in order to in magnesium carbonate crystals to be set as such. sure that the major part of such crystalline pre Such self-setting magnesium carbonate exists cipitate occurs in the presence &f bentonite so In the fora of very fine, small crystals, and la a normal hydrated magnesium carbonate, believed that the'bentonite may be readily effective. Ex cept for the addition of the bentonite, the pro- to be the trt-hydrate. As Is pointed out ta the SC ceduzei for obtaining such aelf-settable crystals patents referred to, it Is desirable to obtain are the same as those described la the'prevtous- relatively email emulate because sash crystals ly mentioned patents, wherein precipitation of have been found to provide greater strength la such crystals Is effected under excessive or vig the final product than that obtainable by larger orous agnation, and the temperature Is saala- . crystals; and to enhance the formation ot rela $5 toiaW below the point at which tilt self-setting tively fisc, small ejystels. cere must be taken to properties ot such crystals would be destroyed 'maintain proper temperature conditions because or impaired. With respect to the decomposi It the temperature of the reaction vehicle should ,'be too high,'the relatively floe,7 small crystals tion method ol Patent No. 2,209.1W In which the employment of bentonite is particularly *p- 1'would be either totally or partially destroyed* re- 40 pHcabto, it is desirable to maintain the tempera 'suiting la Sms or impairment of their etlNset* ture dose to the highest temperature which may ting properties. Also, excessive agitation is de be alely employed without impairing the eelt- sirable during formation of the crystals, as it has .setting properties ef the crystals, However, such : been found that excessive agitation promotes the temperature should not be much over' one fcua- formation of the desirable amaller'crystais. - 45 drod twenty degrees Fahrenheit U* P.j; al The chemistry ot mar&eftium carbonate Is Quite though if care Is taken, a temperature as Ugh as peculiar inasmuch as it la capable of undergoing one hundred forty degrees Fahrenheit (MO* T.i many transformations during preparation there may be employed In such decomposition method of. Therefore, to obtain the desirea relatively The bentonite insures or promotes formation fine, smell seli-setteble magnesium carbonate 60 of the desired relatively ftae, small crystals by crystals, treat can must be observed is th prep- Inhibiting the growth thereof, and causes such ' aratlon thereof,*which Is sometimes bumhsome crystals to be more unilortn in sire, Hence, such ' In' commercial manufacture' of such crystals. bentonjte materially improves the'Steal product This Is especially so with respect to the prepara . *>y providing increased strength resulting from tion of loch crystal by decompuftfes bf an A3 th? fact tbai the fcrrsiajg wil} a be of the de^ 2,33 sired relatively fine and mail substantially uot- torm size. This insures against formation of al ternate hard and salt spots In the final set prod uct, .which'might otherwise obtain should the crystals not he all ol substantially the same rel atively-small size when the slurry containing them is rejected to setting conditions. ' . The character of the colloidal suspension or dispersion of the bentonite Is net cntteaJ, as any 'df the well-inown wiieSdaTdispersions thereof may be employed, bet Stla preferred to utilize an aqueous dispersion-because of the aqueous char acter* of the* reaction vehicles. A suitable well' known dispersion which we have found extreme' ly satisfactory is formed -by treating about one ; (1) part by weight of bentonite with about sev enteen U7> parts by weight of hot water at a temperature of about one hundred twenty-five degrees Fahrenheit*. U2S* F.) to two hundred twelve decree* .Fahrenheit (212' F.l, and thor oughly dispersing *tbe bentonite to the water to 'fortn colloidal suspension.Agitation may be 'employed to disperse the' bentonite but we pref erably subject the suspension to a colloidal mill such product being generally that employed com mercially for heat Insulating purposes. Other chemically Jnaottve solid bodies such os verml- eullte or dlatomacem earth, may be also mixed i in the slurry. Such Inert flile' or reenforcing fiber may be mixed directly In the slurry alter ft Is formed, or if desired, they may be incorporated ' in the reaction vehicle in which the self-setting * magnesium carbonate crystals ere formed. lQ After the sclf-scttable magnesium carbonate slurry containing the fine crystal promoting ben tonite is formed in the reaction vehicle, the pro cedure for setting the product is preferably that outlined in Patent No. 2,20&.75, startle at lino .i 65 column 2. page 2 of the specification thereof, which brings out the steps of preferably pre heating the slurry to shorten the time of set ting* preferably adding a carbon dioxide-con suming alXall to the slurry to ecn.'.uir.e eaibon Ct dioxide as conversion from the normal to the baste carbonate occurs during the sotting and thereby increases the sirenpth of the final prod uct; casting the slurry Inlo c form or mold adapted to shape the ccnipo*liion: electing the 23 setting independent of application yf pressure by so as'to obtain more uniform dispersion. In thU connection. It is preferred to treat the aqueous bentonite suspension with'any gultable.peptUing agent to facilitate the dispersion. Alkalies are generally most frequently employed commercial ly as peptizing -agents for the bentonite. Any suitable alkali wlU do, hut'we'prefer.*to utilize sodium carbonate as the peptizing agent, to an amount about one-tenth per cent <0.1ft) by 3fl applying heat to the slurry In the In; us while maintaining 16 in a quiescent state, and simul taneously precluding evaporation o' substantial amounts of moisture from Use .totting blurry to minimize shrinkage; and drying the resultant profiuct. Except for the inert ased strength which bentonite imparts to the final product, the ben tonite will have no adverse effect on the various steps employed lor setting the product . weight of the amount of bentonite in the sus 35 Tpe resultant set basic mojnesiuw raiUonktft pension. . .. The minimum amount of bentonite to be added to the reaction vehicle is not particularly critical but should be suSetent to promote with ease the product, even though containing bentonite, pos sesses all the characteristics outlined In the speci fication of Patent No. 2.209.754. storting at line 75 column 2, of page 4. namely ft is relatively formation of the desired uniform relatively email, fine magnesium carbonate seif-scttable crystals. Usually about one half per cent <Hft> to about two and oae-half per cent <&&%) by *0 light weight, rigid, end sclf-supjtomg. Inter* r.ally, it is cellular in structure: wvd it has. a chaik-Hke appearance. Wbrn the preferred quantity of bentonite previously ruined Is m* weight f bentonite with reference to the calcu lated amount of normal magnesium carbonate trl-hydrate preelpitable to the reaction vehicle. wlU suffice; and enough of the aqueous benton ite dispersion should be employed to provide the desired amount of bentonite, The. maximum amount ct bentonite Is governed solely by prac tical considerations, as excessive quantities of fi 6u ployed and the set. final dried insulating product is made to contain about fifteen per cent <l5ft> by weight of asbestos fiber, the pcc\*nlage of bentonite therein h about s'.x-tenths of one per ccni <0.6ft> to about three per cent <8ft> by welgh6 of the final prociucu Such small quantity will not materially affect the specific iu avny val ues ol the products noted In Parent Ho. 2209.754. bentonite have so adverse efleet on the selfeeUtog properties* of the magnesium carbonate . crystals, We liave employed with satisfactory Employment of the bentonite to produce the results of our Invention may be either In a reac tion vehicle In which the self-setting precipitate results, as much as five per cent (5ft> by weight of bentonite wHh reference to the calculated amount of magnesium carbonate trl-hydrata pre* &a consists essentially of normal hydrated magnesi um carbonate crystals alcne, or of s-ich crystals intermixed with other materials, ruch as calcium . . dpttabie to the reaction vehicle. . However. If quantities of benIonite amounting to more than five per cent (5ft) by weight of the calculated amount of magnesium carbonate trt-hydrate are employed, it usually becomes very difficult to filter the resuHant slurry because of the colloidal nature thereof imparted to It by the bentonite suspension. Also, the addition of larger quantities of bentonite may be undesirable because of too great an adulteration of the final product. Hence, the upper limit of the amount of'bentonite suspension that may be added is determined by these practical factors. The usual types of reenforcing material*, such carbonate which may remain when dolomltic material Is employed as the source of raw mate* rial. Therefore. In the appended claims, the ex pression "macncslum carbonate ctreposition" in cludes composition*, such as the dolomUlc com position referred to. which eon lain materials in addition to magnesium carbonate. w we claim: !. In the method of producing a self-stt magneslum carbonate composition eapuwte ol use as a heat Insulating material wherein a precipitate of self*cettable normal magnesium envbonete 70 crystals Is formeMn an aqueous rcoction vehicle: as asbestos or other suitable reenforcing'fiber, . to an amount sufficient to provide a Anal prod the step* of causing formation of such precipitate la the presence of a coiloId?-l bentonite dUporsion uct which contains from tea per cent <lGft> to to promote relatively sma!3 and fine crystals for fifteen'per cent (15ft> by weight of the fiber increasing the strength of the*final product. . may be intermixed with the slurry to be set; 75 2, The method of producing a set magnesium 2,sse,04i - 3 carbonate composition which comprises forming application of best and agitation of the solution in an aqueous reaction vehicle a precipitate of to provide a precipitate of normal magnesium normal magnesium carbonate in the form of crys- carbonate in the form of crystals havles selftala having self-setting properties, causing for- setting properties, causing formation of suchpremetton of such precipitate in the presence of a 5 eipUate in the presence of a colloidal bentonite 'colloidal bentonite dispersion to promote relative- dispersion to prornete relatively small and fine Jy small and fine crystals, casting a slurry con- crystals, casting a slurry containing suoh precipi* . tatnlng such .precipitate and bentonite into a tate and bentonite Into a form adapted to provide ' .form adapted 'to provide the shape of the final the shape of the final product, and applying-heat product, and applying heat to the slurry in the 10 to the slurry in the form to enhance setting of such slurry to a firm cake. SAMUEL A. ABRAHAMS. RUBIN LEWON. LOUIS L. COLLONGE. '/