Document gDraL57w9L1z4ZjEejqGaEgR3

FILE NAME: Marley (MAR) DATE: 1951 Apr DOC#: MAR027 DOCUMENT DESCRIPTION: Published Presentation from Conference . Asbestos, A Mineral of Unparalleled Properties B y M . S. B A D O L L E T * {A n nual General M eeting, Quebec City, Que., A pril, 19-51) (Transactions, Volume L I V , 1951, pp. 151-160) I ntroduction* T HE DEMAND for general knowledge on asbestos fibres has increased considerably in recent years. A few publications have printed data showing some of the physical and chemical properties . of asbestos, but in m any cases this inform ation is difficult to find and is seldom available when needed. D uring the past ten years, JohnsM anville have received many inquir ies on the physical and chemical properties of asbestos fibres. For tunately, we have had some of the inform ation in our files, and we wil lingly supplied the data. ' To help relieve this need, we have . tried to p resen t briefly in this paper some of the interesting and out standing properties of asbestos. '.Research Center, Johns-M anville Corporation, Manville, NJf. (1) F or references see end of pa per. T his inform ation was obtained over a period of years by search of the literature and by experimental in vestigations. P r o p e r t ie s o f A sbestos F ibp.es T able I (1, 2) presents, in con venient form for easy comparison, data on the principal properties of the several varieties of commercial `asbestos' -- actinolitc, am osite, anthophyllite, chrysotile, crocidolite, and tremolite. U nder each variety of fibre is a brief statem ent describ ing the properties in term s of struc ture, mineral association, origin, etc. Some of the more im portant data in Table I are expanded and presented in Table I I (3 ). S o lu b ility of A sbestos A report (4, 5) discussing the effects of acids and caustic on as bestos fibres was published in Ger m any in 1927. Be-published several times, it appears to be the only in formation available on .the subject. When, several years ago, it be came necessary to obtain technical data, not available in the literature, on the solubility of commercial grades of asbestos, tests were ar ranged following the plan adopted bv the author of the original article ('*) Samples were obtained of actino- lite from Canada amosite from Af rica, anthophyllitc from Georgia, chrysotile from Canada, crocidolite from A frica, and tremolite from California. These samples repre sented fibres obtainable in commer cial quantities. They contained some mineral im purities and thus their degree of solubility was not identical with th at of hand-pickled, highgrade crudes from these localities. The.acids used in these tests were hydrochloric, acetic, phosphoric, and sulphuric. A ll were diluted to a 25 per cent acid solution, by weight. T able II.--P hysical P roperties of Asbestos C hrysotile Specific heat B .t.u./lb./F ........ Tensile strength, Ib./sq. in........ Temp, at max. ignition loss, F...................................... Filtration properties................... Electric charge............................ Fusion point, F.................... .. Spinnability................................ Resistance to acids & alkalies Magnetite content...................... Mineral impurities present........ Flexibility............ ....................... Resistance to heat...................... Ionizable salts, micro-mhos. . .. (Relative elec, conductance) C b lo u r........................................ 0.266 80.000 100.000 1.800 Slow Pos. 2.770 Very good Poor 0-5.2 Iron, chrome. nickel, lime High Good. Brittle a t high temp. 1.82 Green, grey to white Amosite 0.193 16,000' 90,000 1.600 to 1,800 Fast Neg. 2.550 Fair Good 0 Iron Good Good. Brittle a t high temp. 1.34 Yellowishbrown Anthophyllite 0.210 4,000 & less 1,800 Medium Neg. 2,675 Poor Very good 0 Iron Poor Very good 0.58 Yellowishbrown. Some times almost white C rocidolite 0.201 100,000 300,000 1,200 Fast Neg. 2,180 Fair Good 3.0-5 9 Iron Good 0.84 Blue T remolite 0.212 1,000 8,000 1,800 Medium Neg. 2,400 Poor Good o Lime Fair to good 'A ctinolite 0.217 1,000 & less Medium Neg. 2.540 Poor Fair Lime, iron Poor ___ White Greenish MAF DEP000450 - I V' CHAPTER 1. VARIETIES AND COMPOSITION OF ASBESTOS VARIETIES There are several varieties of asbestos, differ ing considerably in composition and physical properties. The most important commercially is chrysotile, which constitutes about 95 percent of total world production. Its wide use is due to the fact that its fibers are generally strong and flexible and therefore can be applied to many uses, such as manufacture of textiles and steam packing, for which weak and brittle fibers are not adapted. Species of asbestos other than chrysotile fall in the amphibole group of minerals. The only varieties leaving significant- use are anthophyllite, tremolite. amosite, and erocidolite. Fibers of anthonhyllite and tremolite are gcnerallv weak aim brittle, and their uses are limited. Sales arc small, and only small quantities of these materials enter international trade. Amosite and erocidolite are mainiv African varieties exported to the United States and other count lies in considerable quantities for specialized uses. CHRYSOTILE ASBESTOS Chrysotile is a hydrous magnesium silicate having a composition represented by the chem ical formula S M g0'2 S i0--2II:0 . It is a fi brous form of the mineral serpentine. Antigorite.is a phity form of serpentine of no com mercial value. In recent work fehaw (5) 3 indicates that both OH, the hydroxyhradical or water of con stitution, and 1-0, the water of crystallization, are present in chrysotile. To indicate the dual nature of the water content, he writes the chemical formula (O H )sJIg0Si4O ijII-0. He claims also that in fibers from different loca tions the proportions of these- two forms in which water occurs may vary. -Thus, in Cana dian chrysotile a "renter part of.the hydration is water of crystallization, while in the Rhode sian chrysotile the hydration is due largely to the hydroxyl radical. He expresses the view that such a difference in chemical constitution may explain in part the superior electrical resistance of the Rhodesian fiber. The composition of chrysotile, however, is not rigidly fixed according to either of the for- Italicized num bers in parentheses refer to Item* In the bibliography a t the end of th is chapter. mulas given above. Minor quantities of iron, nickel, manganese, or aluminum may replace part- of tire magnesium. Such small replace ments may result- in some modifications m the physical properties of the fibers. Furthermore, these properties are influenced to some extent by the presence of impurities: but, in general, chrysotile is more constant and dependable in quality than other varieties of asbestos. Chem ical analyses of representative samples of as bestos arc "iven in Bureau of Mines Bulletin 552 (? ). AMPHIBOLE ASBESTOS The amphibole group of minerals was for merly believed to consist of anhydrous silicates of magnesium, calcium, iron, and other ele ments. However, in 1916 Schaller (2), using five exact analyses of tremolite, showed, by cal culating the molecular ratios, that water was an integral part of the composition of tremolite. and derived the formula 2CaO 5MgO S$i03II-.0, which is now the recognized composition as contrasted to the widely published formula CnO3MgO -1SO-. When X-ray studies of minerals were begun in the early 1920*s,' Schallcr's findings were confirmed, and it was further learned 'that- all amphiboles contained water of crystallization. Only in textbooks of mineralogy published since about- 1940 will the definite statement- be found: "All amphi boles contain hydroxyl.'5 The water content of amphiboles is low--only 1 or 2 percent-- whereas chrysotile contains about IS percent water. . . AMOSITE There is some doubt that amosite is a distinct mineral species. Babbitt (4) found by X-ray analysis of two amosite samples from South Africa that both were monocliuic- in crystal lization and therefore were not anthophyllites. The chemical composition of one indicated that it was probably aetinolite, and the- other was probably cummingtonite. Vermas (6) con cludes that amosite is a fibrous form of the monoclinic anq-hibole grunerite (FeMgRSi,- 0 2 (O H );. However, it seems desirable to re tain tlie name amosite in commercial usage where it serves a useful purpose. ~ Amosite may contain as high as 40 percent iron oxide, but, as it is monoclinic in crystal lization it is not a true anthophyllite, although 3 MARDEP000451 4 ASBESTOS- A MATERIALS SURVEY it is commonly classed as a high-iron antho phyllite. Amosite, unlike the true anthophyl lites. which are almost invariably weak and brittle, consists commonly of long, fairly strong fibers that have certain specialized uses. I t is mined only in Africa. ANTHOPHYLLITE The composition of anthophyllite is now gen erally expressed by the formula M<r:(.Si4On):- (0 1 !)-. sometimes written TMgO-S.^iO JLO . The magnesium may be replaced in part by certain other elements, but complete replace ment-`is not possible because the anthophyllites possess only limited isomorphism. Ferrous iron may replace magnesium up to 2G.53 per cent, but such an anthophyllite would still con tain as much as 11.4S percent MgO. "When the ferrous iron content exceeds 26.53 percent, the mineral ceases to be anthophyllite, as it be comes monoclinic in crystallization whereas all anthophyllites are orthorhombic. The MfgO content, of anthophyllite is said to range from 5 to 50 percent. A series of 46 chemical analyses of anthophyllites assembled by Kabbitt (4) shows a maximum of 31.53 per cent- and a minimum of 11.4S percent. The one with the maximum MgO content contained 5.6 f>ercent FeO. The ites is very low; it CaO content of averages about anthophyl0.5 percent and rarely exceeds 2 percent. Aluminum is a more important constituent of anthophyllites than is commonly supposed. O f Babbitt's 4G tabulated analyses, 14 show more than.-10 percent ALO-, and 20 show more than 5 percent. Aluminum may replace mag nesium or silicon. TREMOLITE In tremolite the calcium may be replaced in small part by sodium. The magnesium is re- idaceaole by iron in considerable >y aluminum to a lesser degree. quantities and Also, a small part of the silicon may be replaced by alumi num. Tremolite usually consists of "gray to white silky fibers, which are for the most part weak and brittle, although libers of consider able strength and flexibility arc found at times. Roth tremolite and anthophyllite are superior to chrysotile in resistance to chemical reaction. CROCIDOLITE Crocidolite or blue asbestos belongs to the hornblende group of nmphibolcs. Its simplest chemical formula is 3X:i-0-C>Fe0`2Fe-03-lGStO_--ir-0. Considerable variation in compo sition has been noted. Sodium may be replaced by potash, ferric ami ferrous iron In- magne- mnn. Mineralogists now regard crocidolite as identical with riebeckite, being merely a fibrous form of that mineral. Crocidolite therefore bears the same relation to riebeckite that amosite bears to gruente and that chrysotile bears to massive serpentine. Blue asbestos is produced chiefly in South Africa, but substan tial quantities are now obtained in "Western Australia, and a small output is obtained in Bolivia. Except.for those in Bolivia and a recently discovered occurrence in New Quebec, Canada, no commercial deposits of blue asbes tos are known in the Western Hemisphere. In ' Bolivian blue a large part of the iron is re placed by magnesium. The magnesium con tent of African blue asbestos is somewhat lower. ERRATIC CHARACTER OF AMPHIBOLB FIBERS As may be observed from the foregoing dis cussion, the replacement ,of one element by another in varying proportions is a prevalent characteristic of the several varieties'of ainphibole asbestos. This variation in composition results in corresponding changes in their physi cal properties. These properties may also be influenced by the presence of impurities. The somewhat erratic and unpredictable physical characteristics of the amphibole fibers have a profound influence on their use. An antho phyllite from one locality may give satisfactory , service for some specific use, while one from another deposit, although appearing to be exactly the same, may be unsatisfactory. Thus, problems in amphibole asbestos procurement are much more ciiHicult- and complex than the procurement of mineral products like iron or copper, which, when pure, have constant prop erties, irrespective of the part of the world in which they may originate. IMPORTANCE OF PHYSICAL PROPERTIES The outstanding physical characteristic of asbestos is its fibrous structure. - Other im portant- fibers found in nature are those of animal origin, such as wool and silk, and those of vegetable origin, such as cotton and flax. In combustibility is one of the striking diilerenoes between asbestos and the fibrous products of animal or vegetable origin. Of perhaps equal importance is the difference in structure. Each filament of cotton, wool, or silk is of measurable and fairly constant diameter and is indivisible into liner sizes. On the other hand, fibers of chrysotile asbestos can be divided and sub divided until a fineness is attained tlMRlr^P000452 limited oulv bv the dehcaev of the machinery * * * * 'I1!....... T*.. Ch a p t e r l . v a r ie t ie s a n d c o m po sit io n ASBESTOS 5 mate, fiber size is pre.-umably (lie size of the ult iinatc molecule or crystal lattice of ashesIos. In other words, liberization is a cleavage- process, and cleavage in minerals is defined as a tend ency to split in a certain direction, that is, to separate along and between layers of molecules. With respect to use. fiber size is important, and the size will depend upon the decree oi fihenzation attained in millinir. Fibers ob tained from dilieront deposits vary in the case with which they may be fiberized. 11ms. two samples of chrysotilc asbestos, given exactly the. sane mill treatment, may furnish products differing considerably in liber diameter, be cause oiic of them separates or fiberizes- more easily than the other. Such differences may have great pisictieal importance because an asbestos that is difficult to iiberize may require such intense milling to reduce tbe fibers to de sirable fineness that they may be broken into un desirable short lengths. Ease or difficulty of fiberization is therefore an important prop erty of asbestos. The use to which a chrysotile asbestos may be applied is governed largely by fiber length. The longest fibers command the highest prices and the shorter grades progressively lower prices. Apparently, therefore, primary at tention must be given to milling processes that will separate the fibers from the parent rock and will fiberize them adequately with a mini mum of fiber breakage. The heat resistance of asbestos is important in many applications. Some users of asbestos confuse nonflammability with refractoriness. ^Nevertheless, many substances that will not burn will melt or decompose at relatively low temperatures. The fireproof property of as bestos is one of its chief assets: but, although unburnable, it will decompose and lose its es sential physical properties at. moderately high temperatures. Some students of the subject have conceived the idea that asbestos is a highly refractory substance by reading the statement made by Cirkel (1) that it can with- stnnd temperatures of 2,000 to ",000 F. easily, while some varieties can be subjected to a temperature of aTOO0 F. with no apparent visible effects. With due respect to Dr. Cirkel, who wrote a splendid pioneer volume on a mineral of which little was known at that time, lie was in error regarding the heat resistance of chrysotile. lirainlenherger and coworkers (o), who have made a comprehensive study of temperature effects on chrysotile at the Minoralogieal Insti tute of the University of Zurich, state that the so-called adsorbed water of chrysotile is driven off at about 300 C. Between 5303 and 000 G. all of the water of crystallization is driven off, and the mineral gradually alters to olivine. Accompanying this dehydration is a pro nounced change in physical properties. At 100 C. there is a notable deterioration in fiber quality; and above 550 C., with more or less complete dehydration, chrysotile is completely decomposed. The amphibole varieties of as bestos will withstand somewhat higher temper atures than chrysotile. However, crocidolite, although having a low water content, is easily fused into a black magnetic mass. BIBLIOGRAPHY 1. Cirkel, F ritz. Chrysotile Asbestos: Its Occurrence, Exploitation, Mining, ami l.Ves. Canada Dept. Minos, Mines Branch, 2d ed., 1910, p. 00. 2. Schat.ler, IV. T. The Chemical Composition of Tremolite. Minerslogical Notes, Series 3. Geol. Surrey Bull. CIO, 1910, pp. 133-130. 3. B kashkxdercer. E.. E pcreciit, IV.. axd N iooli, F . The Serpentine Minerals and Their Synthesis. II (trans. by Frank Riordan, Jr.). Heir. Chim. Acta. vol. 30.1917, pp. 0-14. 4. R akeitt, -Toiix C. A New Study of the Anthopliyllite Series. Am. Mineral., vol. S3, May-June 194S, pp. 203-323. 3. S iiaw , Mvotr. C. The Asbestos Content of Asbestos Textiles. New Jersey Ceram. Res. Sts., Rutgers Univ., Mar. 27, 15)30, 7 pp. 0. Vekmas, F. II. S. The Amphibole Asbestos of South Africa (with discussion). Trans, and Proe. Geol. Soe. South Africa, vol. 53, 1932. pp. 199-232. 7. B owles, Oliver. The Asbestos Industry. Bureau of Mines Bull. 332, 1933, p. S. MARDEP000453