Document xjge1OxpJxrVkr3Q94g4eamOb

Patented Dec. 13, 1933 2,140,222 UNITED STATES PATENT OFFICE 2,140,222 PIGMENTARY LEAD TITANATE AND METH OD FOB MAKING THE SAME Helmut Espenschied, Metnchen Township, Mid dlesex County, N. J., assignor to National Lead Company, New York, N. Y., a corporation of New Jersey Application February 23, 1937, Serial No. 127,302 15 Claims. (CL 134--67) This Invention relates to pigmentary lead titanate and to methods for Its manufacture. An object of the present Invention is a method for the production of pigments consisting of 5 essentially or comprising lead tltanate. Another object of the invention is a method for con trolling the uniformity and particle size of pig mentary lead titanate. A third object of the in vention is a method for overcoming the photo10 sensitivity and increasing the brightness of pig mentary lead titanate. These and other objects of the invention, including the products of the methods herein Set forth, will become apparent from the following description thereof: 15 Methods for the preparation of the. compound, PbTiOj, have been described but these prior art procedures because of certain inherent difficulties without exception have failed to yield a product suitable for use as a pigment. If, for instance, 20 a starting mixture of oxides of lead and titanium or oxide-forming compounds thereof were heated to a sufficiently high temperature to bring about substantially complete titanate formation the product became excessively coarse and hard, 25 lacked uniformity of particle size, was discolored and photosensitive and had a low brightness value. If, on the other hand, in order to avoid these disadvantages, the starting mixture was heated at a lower temperature the formation of 30 the titanate did not go to completion, and the product did not develop the proper degree of crystallinity or particle size. In many instances an undesirable excess of lead compounds was present in the final product. When lncorpor35 ated in a surface-coating vehicle, films prepared therefrom tended to chalk and generally lacked resistance to weathering influences. The prior art failed to find an optimum temperature at which pigmentary lead titanate could be pre40 pared free of the disadvantages of an excessively low or an excessively high calcination tempera ture. Apparently, according to my researches no such optimum temperature exists and, conse quently, the prior art investigators failed to es45 cape from the dilemma which confronted them. By means of my invention pigments consisting essentially of or comprising lead titanate can be prepared which possess uniform particle size, high tinning strength, high brightness, good color, 60 chemical and physical inertness, freedom from photosensitivity and other requisite pigment characteristics. The complete process of my invention may be broadly described as comprising the calcination 55 of an intimate and uniform mixture of a reactive titanium compound and a reactive lead com pound containing an adjusted amount of sul phuric acid or its equivalent under carefully con trolled reaction temperatures whereby titanate formation is substantially complete at a relatively 6 low temperature, and development of particle size and crystallinity is brought about at a rela tively high temperature. Thus my invention may be considered as comprising the three follow ing features: 10 (1) The preparation of the Intimate mixture of reactive titanium compound and reactive lead compound; (2) the adjustment of the content of sulphuric acid or its equivalent in the said mix ture of reactive titanium compound and reactive 15 lead compound; and (3) the control of the cal cination temperatures. When all three features are combined in a process for the preparation of lead ritanate the resultant product will be of superior pigment quality, but it will be under- 20 stood that each of these three features may be used in conjunction with a prior art method with a resulting improvement in the product obtained thereby. QC I. The preparation, of the intimate mixture of starting ingredients It is essential that the mixture of reactive ti tanium compound and reactive lead compound be extremely intimate and uniform and that the 30 components thereof be finely divided. To obtain this Intimate and uniform mixture any suitable means may be employed. I prefer, however, that the mixing should be carried out in the wet state. For example, the reactive titanium com- 35 pound and the reactive lead compound may be wet-milled together until a sufficient degree of fineness and uniformity of the components is obtained. Another very convenient method for obtaining such an intimate and uniform mixture 40 of these starting ingredients is to precipitate one or both ingredients from aqueous solution in the presence of the other. For instance, finelydivided reactive titanium compound may be sus pended in a solution of a water soluble lead salt 45 and coprecipitated with the reactive lead com pound by adding a precipitating agent, for ex ample, an alkali neutralizing agent to the sus pension. Furthermore, it is possible to conduct the wet-milling of the starting ingredients in 50 the presence of the well-known dispersing agents for titanium compounds and lead compounds, or to disperse separately the lead compound and the titanium compound in aqueous mediums with or without the aid of dispersing agents, mix these 55 2 8,140,833 suspensions together and obtain the intimate and radical and an additional equivalent quantity of uniform mixture by coflocculation, if necessary reactive lead compound in excess of that required with the aid of a coagulating agent. to form lead titanate be present in the reaction Whatever be the means employed to obtain mixture prior to heating. The quantity of sul g this intimate and uniform mixture of reactive furic add and reactive lead compound should r, titanium compound and reactive lead compound, be so adjusted that the final product will contain the mixture should be free from aggregates or lead sulfate in an amount between about 5% o coarse particles of either ingredient. The beet and 25%. results are obtained when employing starting The manner of adjusting the sulfuric add con 10 mixtures having an average particle size of about tent of the reaction mixture will depend upon in 2-3 microns. In any case, particles substantially .the nature of the reactive titanium compound in excess of 6 microns are undesirable in the employed as the source of titanium. For ex starting mixture. ample, it is convenient to employ in the practice Upon this feature of the present invention de of my Invention hydrous titanium oxide hydro ls pends in a measure the completeness of the ulti lytically precipitated from sulfuric acid solutions 13 mate reaction and the time required to complete of titanium. Even after thorough washing such the said reaction, and to a lesser degree, the par hydrous titanium oxide always contains a certain ticle size of the final product. amount of combined or adsorbed sulfuric acid. If it be desired that the final product be sub- The amount of this combined or adsorbed sulfuric 20 stantially free from chalking then in preparing add will vary depending upon the hydrolysis 20 the intimate and uniform starting mixtures the conditions, physical character of the hydrous proportions of lead and titanium compounds titanium oxide and manner of washing. Gen must be carefully controlled In order that the erally speaking, the sulfuric add content of pre final product be substantially free from an excess cipitated hydrous titanium oxide tends to in 2s of either starting ingredient. If there is present crease with increasing fineness of particle size. 26 in the final product any considerable excess of Therefore, when employing hydrous titanium titanium dioxide, the product will exhibit some oxide containing combined or adsorbed sulfuric tendency to chalk; if lead oxide be in excess the acid in the practice of my Invention it is first product will tend to react with oleaginous ve- necessary to determine the quantity of sulfuric 30 hides forming soaps which render the composi add contained in the said hydrous titanium oxide so tion thick and gummy. It appears also that free. and then to adjust as by elimination, in the PbO will tend to accelerate the breakdown of well-known manner as by adding neutralizing the titanate molecule. However, if products con agents which form neutral sulfates, or by addi taining uncombined TiOs are prepared according tion of more sulfuric add in order to obtain the 35 to the present Invention they will exhibit a re desired quantity of lead sulfate in the final 35 v 'y duced tendency to chalking as compared with product. pure titanium dioxide and the preparation of I am aware that the prior art has suggested such products is within the scope of the present that a titanic acid containing the SO4 radical invention. Therefore, the proportion of reactive could be used in reactions which yield titanates. 40 titanium "compound to reactive lead compound in However, the prior art has failed to disclose the 40 the starting mixture should be so regulated that relation between lead sulfate content and the there will be present at least one molecule of TfOa pigment properties, particularly the photo for every molecule of PbO. In the event that a sensitivity of lead titanate. The prior art always substantially non-chalking pigment is desired regarded the presence of the sulfate radical as an 46 the content of free TiOa in the final product undesirable Impurity and made every effort to 45 should not substantially exceed about 2%, and eliminate it prior to or during the thermal re the content of free PbO in all cases should not action. Thus, for example, in the preparation of substantially exceed about 1%. lead titanate the prior art employed temperatures It will be understood that by the terms "re- approaching 1000 C. in order to decompose any M active lead compound" and "reactive titanium lead sulfate formed. Furthermore, as pointed w compound" I mean to include the oxides of lead out above, the sulfate radical or sulfuric acid con and titanium, including hydrous titanium oxide tent Of titanic acid hydrolytically precipitated and titanium dioxide, as well as lead and tita -from titanium sulfate solutions will vary, and nium compounds which when heated to the cal- this fact, in my opinion, accounts for the great ss cinatlon temperatures hereinafter disclosed yield variation in photosensitivity observed in prior 55 the oxides of these metals. art lead titanate. If hydrous titanium oxide from which the sul n. The adjustment of the content of sulfuric acid pr its equivalent in the starting mixture furic acid has been removed, or if anhydrous titanium dioxide be employed in the practice of 0000-NLI-000018985 60 I have observed that lead titanate is extreme ly sensitive to light: it changes color from a pure light yellow to an olive-gray tint when exposed to actinic rays. The elimination of this photo sensitivity constituted a major problem in the 65 preparation of lead titanate suitable for use as a pigment. I have now found that if lead sulfate be formed, my invention as the source of titanium it will be 60 understood that in practicing this feature of my invention it will be necessary to add sufficient sulfuric acid or its equivalent as reactive sulfate radical to yield the desired content of lead sul fate. Therefore, in a process for the preparation 65 of a substantially non-chalking lead titanate pigment embodying all three features of my pres in situ, in the reaction mixture simultaneously ent invention the content and proportions of the with the formation of the lead titanate and in essential ingredients of the starting mixture will 70 amounts hereinafter to be set forth the resultant be as follows: 70 product will be substantially free from photo A reactive titanium compound such as hydrous sensitivity. titanium oxide, anhydrous titanium dioxide, or In order that lead sulfate be formed, in situ, other compound of titanium, which on heating to in the reaction mixture it is necessary that sul- the temperatures employed in the practice of my 75 furic acid or its equivalent as reactive sulfate Invention yield the dioxide of titanium; a quan- 75 8,140,223 3 tity of sulfuric acid or its equivalent sufficient, a part or all of which may be adsorbed by or combined with the hydrous titanium oxide, to yield lead sulfate in an amount between 5% and 0 about 25% in the Anal product; a reactive lead compound, such as litharge, PbO, or a com pound of lead capable of yielding PbO on heating to the temperatures employed in the practice of the invention in an amount substantially suf10 flcient to supply one molecule of PbO for every molecule of TiOa present in the reaction mixture plus an additional quantity of reactive lead com pound to supply one molecule of PbO for every molecule of H2SO4 present in the said reaction 15 mixture. If desired, in order to insure that no free PbO will be present in the final product, a slightly less amount of reactive lead compound may be employed. By the expression "sulfuric acid or its equlva20 lent" as used in this description and the expres sion "sulfuric acid" as in the claims hereof, I mean to include not only sulfuric acid, but re active sulfate compounds, for example, titanium sulfate, which yields reactive sulfate ions on 25 heating to the temperatures employed in the re action to form with the reactive lead compound, lead sulfate. When this second feature of my invention is practiced in accord with the instructions here30 lnabove given, the product quite unexpectedly does not show any substantial diminution of tinting strength due to the presence of the lead sulfate. This is most surprising since mere me chanical mixtures of lead tltanate and lead sui ts fate will show a tinting strength substantially that as would be expected from the proportions of the mixture and the tinting strength of lead tltanate and lead sulfate respectively. For exam ple, I have obtained average tinting strength 40 values of about 600 with samples of properly milled substantially pure lead tltanate PbTICb prepared according to the present invention; whereas I have obtained a tinting strength value of 530 for a sample milled under similar condi45 tions containing substantially 75% and 25% PbSO< prepared according to the methods of the present invention. Since normal lead sulfate milled under similar conditions possesses a tint ing strength of only about 70, mechanical mix50 tures of 75% PbTICh and 25% PbSOt would be expected to possess a tinting strength of only about 465. The average tinting strength for prod ucts of the present invention containing about 6 to 7% PbSOt is about 550, which shows a loss of 65 only approximately 20 points for an increase in lead sulfate content of 17 to 18%. Furthermore, the presence of lead sulfate tends to produce a product of greater whiteness. gg m. The control of the calcination temperature I have found that it is necessary, in order that lead titanate possess the best pigment properties, to exercise careful control over the temperatures of the reaction between the reactive lead com65 pound and the reactive titanium compound. Thus, I have found that the reaction temperatures should be so controlled that the lead titanate is substantially completely formed at a relatively low calcination temperature after which develop70 ment of particle size and crystallinity is effected at a relatively high calcination temperature. The lower limit of the low calcination temperatime at which tltanate formation is effected is about 500 C. and the upper limit of the higher calcination |5 temperature at which development of particle size and crystallinity is brought about is about 900* C. Preferably the first or low temperature calcination treatment is carried out at tempera tures within the range of about 500 C. to a tem perature below 750 C., and the second or higher 5 calcination temperature is carried out at tem peratures within the range of 750 C. to about 900 C. Such control of reaction temperature may be obtained in several ways; for example, the start- 10 lng mixture may be calcined in two steps where in the starting mixture is first heated at tem peratures within the lower range specified above for a period of time sufficient to combine the major portion of the starting ingredient in the 15 form of lead titanate after which the tempera ture may be raised to within the higher range specified above, and held at that point until the product has developed the desired degree of crystallinity and particle size. On the other hand, 20 the starting mixture may be heated through a gradually increasing temperature within the range of from about 500 C. to about 900 C. For this latter method for obtaining desired control of reaction temperature a rotary furnace is use- 25 ful. The starting mixture may be fed into such furnace and the rate of travel of the reaction mixture so regulated by adjustment of the rota tion speed and angle of inclination of the furnace that the said reaction mixture will remain in the 30 lower temperature zone specified above from which the product will emerge after a period of time sufficient to develop the desired degree of crystallinity and the proper particle size. The period of time at which the reaction mixture is 35 kept within the lower temperature zone may be determined by withdrawing samples from the cal cination from time to time and determining the content of unreacted starting ingredients. Gen erally, it will not be necessary to keep the reac- 40 tion mixture in the lower temperature zone until titanate formation is complete but only until a major portion of the reaction ingredients are com bined in the form of titanates. The period of time in which the reaction mixture is kept within 45 the higher temperature zone may be regulated according to the size of particle desired and the degree of crystallinity, for example, as the size of particle approaches 10~ cm., i. e,, one micron, the product will begin to show sharp X-ray dif- 50 fraction lines. Thus, the growth of particle size may be followed by means of an X-ray examina tion. The increasing sharpness of diffraction lines denotes an increase in particle size. On the other hand, the particle size determination may 55 be made by means of a microscope, whereby the size of a particle under a given magnification is compared with a scale related to that magnifi cation. Coincident with increase of particle size the product tends to become more resistant to 60 weather influences and to chalking. However, it will be understood that the particle size should not be increased to such a point that the product will be coarse. As shown by Figure No. 3 the lead titanates prepared according to the present in- 65 vention will, in general, be free from more than a trace of particles in excess of 3 microns. In any event, lead tltanate pigments prepared according to my Invention should not contain particles in excess of 5 microns. 70 The present invention avoids the pitfalls of the prior art because it separates titanate for mation, on the one hand, from development of particle size and crystallinity on the other hand. It will be appreciated that when heating at a 76 0 0 0 0 -N L I-0 0 0 0 1 8986 4 3,140,232 single elevated temperature according to the prior art, titanate formation and development of crys tallinity and growth of particle size are progress ing simultaneously. Consequently, such prior art 5 products lack the uniformity necessary for a proper pigment and no amount of milling will suffice to break down the large, hard particles formed. It will be understood, of course, that in stating that titanate formation is substantially 10 completed at the lower temperature within the specified range herein given, I mean that the ma jor portion of the lead has'been combined with titanium. Any uncombined lead compound which remains after the heating at the lower 15 temperature is promptly combined at the elevat ed temperature. Thus, the control of reactive temperature envisioned by me serves not only to produce a product of uniform particle size but one which, depending on the proportion of start20 lng ingredients, is substantially free from unre acted starting Ingredients. There is a second advantage obtained from this feature of my present invention: when the temperature of calcination is elevated much 25 above about 900 C. any lead sulfate which may be formed will tend to fuse thus causing sinter ing to take place with consequent formation of aggregated particles' which further destroy the uniformity of the product and make it coarse. 30 By controlling the reaction temperature in the manner herein described this sintering and re sulting aggregation is avoided. Having described my invention, the following examples are given for illustrative purposes only. 35 It will be understood that no undue limitations are to be drawn therefrom. Ex a mp l e n o . 1 Preparation of substantially pure lead titanate-- two-step calcination About 26.5 kilograms of anhydrous titanium dioxide containing about 99.5%' TiOa and about 73.6 kilograms of fume litharge, being substan tially 100% PbO were intimately mixed with a -n sufficient quantity of water to form a slurry. This slurry was then milled in a ball mill for about one horn, to insure uniform and intimate mixing of the TlOa and PbO. The mixture was then dewatered and dried in a drying oven. After 50 drying the mixture was calcined for about two hours at a temperature of about 600 C. during which the formation of lead titanate was sub stantially complete. The temperature was then raised to 825 for about three and one-half hours. 55 After the second step the product was pulverized to render it useful as a pigment. The product had the following characteristics: ColorClear light yellow. Composition ___ PbTiOj (less than 1.0%, free 80 TiOa and less than 1.0% free PbO). Tinting strength-- 610. Oil absorption_____14. os This product was somewhat photosensitive al though in all other respects it was excellently adapted for use as a pigment. Ex a mp l e No . 2 70 Preparation of lead titanate pigment using hy drous titanium oxide containing HzSOt--twostep calcination About 88 kg. of a washed hydrous titanium ox ide slurry obtained by hydrolytic precipitation 75 from a titanium sulfate solution and containing about 30% TIOs, about 8% Hj SO< and the re mainder water was intimately and uniformly mixed by ball-milling for about one hour with about 74.0 kilograms of finely-divided litharge made up into a slurry with water. (This slight 5 deficiency of PbO over that required theoreti cally to combine with all Hj SO< and TIOj Insured the combination of all PbO and indicated the presence of a small amount of free TIOi in the final product.) The wet mixture was filtered and 10 then dried. After drying, it was heated for about two hours at about 600 C. and then for about four hours at 800 C. After calcination the prod uct was pulverized. The lead titanate pigment thus obtained pos- 15 sessed the following characteristics: ColorClear yellow to white Composition: PbTlOs About 92.0%. PbSO About 6.5%. nOaAbout 1.5%. PbO_______________ None. Tinting strength 570. Oil absorption9.7. Texture________________ Smooth. Stable against photochemical changes. 20 25 By way of contrast and comparison with the product of this example and to demonstrate the effect of my novel calcination treatment, I pre- 30 pared a lead titanate composition as 1follows: Ex a mp l e No . 2--A Although there is no teaching in the prior art as to the manner of preparing the starting mix- 35 ture and controlling the sulfuric acid content thereof, I took a starting mixture identical with that employed in the foregoing Example No. 2 and calcined it for about four and one-half hours at about 900 C. I selected this temperature, al- 40 though prior art investigators generally employed higher temperatures, because it appears to be the lowest practical temperature at which crystalline lead titanate formation will be complete in a prior art calcination treatment. After calcina- 45 tion the product was pulverized under conditions identical with those employed in pulverizing the product of Example No. 2. It had the following characteristics: ColorOlive-yellow. Composition: 50 PbTiOj____________ _____ About 92.0%. PbSO______________ ____ About 3.0%. TiOaAbout 1.5%. PbO____ _____ ____ _____ About 2.2%. Tinting strength__ _140. 55 Oil absorption_7.0 Texture_______ ______________Hard and gritty. Somewhat photosensitive. 60 It will be noted that although the same amount of sulfuric acid was present in the starting mix ture here employed as was present in the starting mixture of Example No. 2, even at 900 C. suffi cient sulfuric acid was lost, either by volatization 85 or decomposition of PbSO< to reduce the lead sulfate content to 3.0% and to leave 2.2% free PbO. The light reflectance properties of the products of Example Nos. 2 and 2--A are shown in Figure 70 No. 1. In making these determinations it was found that the product of Example No. 2--A (on Fig. 1, designated as Pigment No. 2--A) was so coarse that it would not pack sufficiently to per mit direct analysis. Therefore its reflectance 76 0000-NLI-000018987 ,8 140,233 5 properties were determined under glass which somewhat reduced Its true reflectance. However, for the sake of comparison a similar determina tion of the light-reflectance properties of the 5 product of Example No. 2 (on Fig. 1, designated as Pigment No. 2) was also made under the same glass. The light-reflectance properties of the Pigment No. 2 Is given both as directly determined and as determined under glass. The curves, Fig. 10 1 and Table A, Fig. 1, strikingly show the superior brightness of the Pigment No. 2. In order to show a comparison of the fineness and uniformity of the particles of the Pigment No. 2 and Pigment No. 2--A, photomicrographs 15 of representative portions of both products magnified 1250 times were made. These are re produced in Fig. 3. The uniformity and fineness of Pigment No. 2 as compared with the lack of uniformity and the presence of coarse particles 20 In Pigment No. 2--A Is evident. As shown by the scale In Fig. 2, Pigment No. 2 Is free from par ticles In excess of 5 microns while Pigment No. 2--A contains a considerable amount of particles as large as about 8 microns. 28 Ex a mp l e No . 3 Lead titanate pigment--adjustment (elimina tion) of HiSOi--gradually increasing calcina tion temperature 30 A quantity of washed hydrous titanium oxide containing about 26 kgms. of TiOs and about 2.1 kg. of HaSO was treated with sufficient aque ous ammonia to reduce the HaSO content to about 6.25% after which the ammonium sulfate 35 formed was washed out. The hydrous titanium oxide containing the sulfuric acid was again slurried with water. Into this was gradually mixed about 72 kg. of finely-divided litharge and the whole milled for about one hour. The wet 40 mixture was then filtered and dried. After dry ing, It was then fed to a rotary furnace, the speed and temperature of which was so regulated that the reaction mixture traveled through a zone of temperature between about 500 C. to below 15 750 C. in about two hours, and through a tem perature zone of 750 C. to about 900 C. In about 4 hours. After this calcination treatment the product was pulverized for use as a pigment. The lead titanate pigment thus obtained pos- 50 sessed the following characteristics: ColorClear yellow to white. Composition: PbTlOjAbout 94.0%. ,, PbSOAbout 5%. 0 TiOaAbout 1%. PbO_________________ None. Tinting strength 570. Oil absorption11. 6(J TextureSmooth. Stable against photochemical changes. Ex a mp l e No. 4 Preparation of starting mixture by precipitation 65 method -- adjustment (addition) of HiSO* content About 20 kg. of anhydrous titanium dioxide was uniformly and evenly suspended In a solution of lead acetate containing an amount of lead, as 70 PbO, equivalent to 75 kg, by continued and thor ough agitation. When the TIOj was uniformly distributed in the lead acetate solution a sufficient quantity of concentrated aqueous solution of sodium carbonate was added thereto to preclpi7S tate an amount of lead carbonate equivalent to about 73 kgs. of PbO. The precipitated, uniform and Intimate mixture of lead carbonate and TlOz was then washed free of mother liquor. There Is present an excess of lead necessary to combine with sulfuric acid which was then added In an 5 amount sufficient to yield lead sulfate to the extent of 25% in the final product This mixture was then calcined for about 1% hours at 650 C., after which the temperature was raised to 800 C. and maintained there for 4 hours. After calcl- 10 nation the product was pulverized. The lead titanate composition thus obtained had the fol lowing characteristics: ColorYellowlsh-whlte. 15 Composition: PbTlOsAbout 74%. PbSO<-------------------------- About 25%. Free HOsLess than 1%. PbO____ .None. 20 Tinting strength 530. Oil absorption15. TextureSmooth. Stable agalhst photochemical changes. ^ Throughout this description of my Invention wherever tinting strength values are given they have been determined according to the so-called "Reynolds method", which Is described on pages 92-93 of "Physical and Chemical Examination of Paints, Varnishes, Lacquers and Colors", by H. A. Gardner, 8th ed., published by the Institute of Paint and Varnish Research. Wherever the light-reflectance data is given such data was ob tained by means of the Hardy spectrophotometer 35 described on pages 135-137 of the Physical and Chemical Examination of Paints, Varnishes, Lac quers and Colors, supra as developed by Professor T. C. Hardy, author of "Handbook of Colorlmetry", published by the Massachusetts Institute 40 of Technology, 1936. In the curves, Fig. 1, and Table A, Fig. 1, the light-reflectance data Is ex pressed according to the Hardy system. Lead titanate pigment when prepared accordlng to the present Invention is an extremely use- 45 ful material. When Incorporated into surface coating vehicles It produces extremely durable and weather resistant protective films. In fact. It can be used for any purpose where a high grade pigment material Is required, e* g.. In synthetic 60 plastics, artificial fibers, paper, rubber, etc. Although I have described the process of my Invention as relating to the preparation of lead titanate pigments consisting essentially of lead titanate and lead sulfate, the process of my 65 Invention is adapted to the preparation of com posite lead titanate pigments in which there Is present in addition to lead titanate and lead sul fate one or more inert pigment-forming mate- rials such as the extenders, barium sulfate, cal- 00 cliun sulfate, etc. For example, the extender may be added to the starting mixture prior to calcination and the process of my Invention then carried out as herein described. Or, on the other hand. If it be desired to adjust the sulfuric acid 65 content of the reaction mixture by partially elim inating combined or adsorbed sulfuric acid from hydrous titanium oxide the alkali neutralizing agent employed may be one which, with sulfuric add forms the extender such as, the oxides, hy- 70 droxldes, carbonates and the like of the alkaline earth metals. Furthermore, as pointed out above, the process of my Invention Is applicable to the preparation of pigments which contain sub stantial quantities of uncomblned titanium dl- 7S 0000-NLI-000018988 6 2, 140,232 oxide. For instance, when starting mixtures con mixture so obtained and heating said mixture taining excess amounts of reactive titanium com first at temperatures between about 500* C. and pound are calcined according to my invention to below 750 C. to form lead titanate and lead yield products comprising even as little as 5% sulfate, then heating at temperatures between 5 lead titanates such products, compared to pure 750 c. and about 900 c. to obtain a product of 5 titanium dioxide, will exhibit a reduced tendency uniform particle size free from more than a to chalk. They will, however, chalk somewhat trace of particles in excess of 5 microns. more than the other products prepared accord 5. Process for the preparation of a pigment ing to my invention which consist essentially of comprising lead titanate which comprises mix 10 lead titanate, or of lead titanate and lead sulfate. ing until a uniform and Intimate mixture sub- 10 The aforegoing description has been given for stantially free from particles in excess of 5 clearness of understanding and no undue limi microns is obtained, litharge, water, hydrous ti tations should be deduced therefrom, but the ap tanium oxide and sulfuric acid, the amount of pended claims should be construed as broadly as litharge being not more than 1 mol PbO for IS possible in view of the prior art. . every mol of TIOj and H2SO4 and the amount of 15 I claim: sulfuric acid being such that the product ob 1. Process for the preparation of a pigment tained on heat-treating the said mixture will which comprises mixing until a uniform and inti contact between about 5% and about 25% of lead mate, very finely-divided mixture Is obtained, sulfate by weight, drying the mixture so obtained 20 pigment-forming materials containing a "reac and heating the said mixture first at temperatures 20 tive lead compound" and a "reactive titanium between about 500 C. and below 750 C. to form compound", the amount of said "reactive lead lead titanate and lead sulfate, then heating at compound" being not more than one mol PbO temperatures between 750 C. and about 900 C. for every mol TIOj, then heating said mixture to obtain a product of uniform particle size free 25 at a temperature sufficient to form lead titanate from more than a trace of particles in excess of 5 25 but not sufficient appreciably to develop crystal microns. line properties until formation'of lead titanate 6. In a process of preparing a pigment com is substantially complete and thereafter heating prising lead titanate, the steps which consist In at a higher temperature to develop crystalline heating an intimate, very finely-divided and uni SO properties. form mixture of a "reactive lead compound" and 30 2. Process for the preparation of a pigment comprising lead titanate which comprises mixing until a uniform and Intimate, very finely-divided mixture Is obtained, a "reactive lead compound" 35 and a "reactive titanium compound", the amount of said "reactive lead compound" being not more than one mol PbO for every mol TIOj , heating the said mixture first at temperatures between about 500 C. and below 750 C. to form lead "reactive titanium compound" first at tempera tures between about 500 C. and about 750 C. to form lead titanate, then heating at temperatures between 750 C. and about 900 C. to obtain a product of uniform particle size free from more 35 than a trace of particles in excess of 5 microns. 7. In a process of preparing a pigment com prising lead titanate, the steps which consist In heating an Intimate, very finely-divided and 40 titanate, then heating at temperatures between 750 C. and about 200 C. to obtain a product of uniform particle size free from, more than a trace of particles In excess of 5 microns. 3. Process for the preparation of a pigment 45 comprising lead titanate which comprises mix ing until a uniform and intimate, very finelydivided mixture Is obtained, a "reactive lead compound", water, a "reactive titanium com pound" and sulfuric add, the amount of said 55 "reactive lead compound" being not more than one mol PbO for every mol TIOj and H2SO4 and the amount of sulfuric acid being such that the product obtained on heat-treating the said mix ture will contain between about 5% and about 55 25% of lead sulfate by weight driving the mix ture so obtained and heating the said mixture first at temperatures between about 500 C. and below 750* C. to form lead titanate and lead sul fate, then heating at temperatures between 40 750 C. and about 900 C. to obtain a product of uniform particle size free from more than a trace of particles In excess of 5 microns. 4. Process for the preparation of a pigment comprising lead titanate which comprises mix es ing until a uniform and Intimate, very finely divided mixture Is obtained, a "reactive lead uniform mixture of a "reactive lead compound" 40 and "reactive titanium compound", containing not more than 1 mol PbO for every mol TIOj first at temperatures between about 500 C. and about 750 C. to form lead titanate, then heating at temperatures between 750 C. and about 900 C. 45 to obtain a product of uniform particle size free from more than a trace of particles in excess of 5 microns. 8. In a process of preparing a pigment com prising lead titanate, the steps which consists In heating an intimate, very finely-divided and uniform mixture of a "reactive lead compound", water, a "reactive titanium compound" and sul furic acid, containing not more than one mol PbO for every mol of TIOj and H2SO4 and an 55 amount of sulfuric acid such that the product ob tained on heat-treating the said mixture will con tain about 5% and about 25% of lead sulfate by weight, first at temperatures between about 500 C. and about 750 C. to form lead titanate, 80 then heating at temperatures between 750 C. and about 900 C. to obtain a product of uniform particles size free from more than a trace of particles in excess of 5 microns. 9. In a process of preparing a pigment compris- 45 ing lead titanate, the steps which consist In heat compound", water, a "reactive titanium com ing an intimate, very finely-divided and uniform pound" and sulfuric add, the amount of said mixture of a "reactive lead compound", water, a "reactive lead compound" being not more than "reactive titanium compound" and sulfuric add 70 one mol PbO for every mol. TIOj and H2SO4 and containing not more than one mol PbO for every 70 the amount of sulfuric add being such that the mol TIOj and H2SO4 and an amount of sulfuric product obtained by heat-treating the said mix acid such that the product obtained on heat- ture will contain between about 5% and about treating the said mixture will contain about be 25% of lead sulfate based on the wdght of lead tween 5% and about 25% of lead sulfate based on 75 titanate present in the said product, drying the the weight of lead titanate present in the said 76 0000-NLI-000018989 ,9 140,333 7 product, first at temperatures between about 500 C. and about 750 C. to form leskl tltanate, then heating at temperatures between 750 C. and about 900 C. to obtain a product of uniform 5 particle size free from more than a trace of particles In excess of 5 microns. 10 In a process of preparing a pigment com prising lead tltanate, the steps which consist in heating an Intimate and uniform mixture sub10 stantially free from particles In excess of 5 microns of litharge, water, hydrous titanium oxide and sulfuric acid containing not more than one mol PbO for every mol TlOa and H2SO4 and an amount of sulfuric acid such that the product IS obtained on heat-treating the said mixture will contain about between 5% and about 25% of lead sulfate based on the weight of lead titanate pres ent in the said product, first at temperatures be tween about 500 C. and about 750 C. to form 20 lead titanate, then heating at temperatures be tween 750 C. and about 900 C. to obtain a product of uniform particle size free from more than a trace of particles in excess of 5 microns. 11. As a new composition of matter, a pigment 2g substantially Identical with a product obtained according to the process of claim 1, said pigment consisting of substantially pure lead titanate of uniform particle size, being free from more than a trace of particles in excess of 5 microns, having 30 high brightness, a clear light yellow color, and a tinting strength of about 600 as determined by the Reynolds method. 12. As a new composition of matter, a pigment substantially identical with a product obtained 35 according to the process of claim 1, said pigment consisting of substantially pure lead titanate and titanium dioxide of uniform particle size, being free from more than a trace of particles In excess of 5 microns, having a high brightness, a clear 4U light yellow to white color and a tinting strength of at least 600 as determined by the Reynolds method. 13. As a new composition of matter, a pigment substantially Identical with a product obtained according to the process of claim 3, said pigment consisting essentially of lead tltanate and lead sulfate, the amount of lead sulfate being between about 5% and about 25% by weight containing an amount of lead compounds other than the tl- 5 tanate and sulfate not substantially greater than 1% and an amount of titanium dioxide not sub stantially more than 2%, substantially uniform in particle size and containing not more than a trace of particles in excess of 5 microns, substan- 10 tially free from photosensitivity and adapted to form when Incorporated Into film-forming ve hicles substantially non-chalking surface-coating compositions. 14. As a new composition of matter, a pigment 15 substantially identical with a product obtained according to the process of claim 3, said pigment consisting essentially of lead titanate, lead sulfate and titanium dioxide, the amount of lead sulfate being between about 5% and 25% by weight con- 20 tainlng an amount of lead compounds other than the tltanate and sulfate not substantially greater than 1%, substantially uniform in particle size and containing not more than a trace of particles in excess of 5 microns, substantially free from 25 photosensitivity and adapted to form when in corporated into film-forming vehicles substan tially non-chalking, surface-coating compositions. 15. As a new composition of matter, a pigment substantially identical with a product obtained 30 according to the process of claim 4, said pigment consisting essentially of lead titanate, lead sul fate and titanium dioxide, the amount of lead sulfate being between about 5% and about 25% by weight based on the content of lead tltanate 3J containing an amount of lead compounds other than the titanate and sulfate not substantially greater than 1%, substantially uniform in particle size and containing not more than a trace of particles in excess of 5 microns, substantially free 40 from potosensitivity and adapted to form when Incorporated into film-forming vehicles substan tially non-chalking surface-coating compositions. HELMUT ESPENSCHIED. 0000-NLI-000018990