Document KJpZOXaBz4ob4grb1dD1jZ9w6

SEP 18 2002 4:14 PM PR TO 12145201181 P.03X20 round i the first then nally :oI of Asbestos Minerals: Nature, Occurrence, and Properties As indicated in Chapter 1 (Historical Background), the term asbestos was given to naturally occurring fibrous materials, later found to be minerals, which showed the properties of relative indestructibility and resistance to fire. That pragmatic definition could be applied to a number of minerals. Today we would Emit it to naturally occurring, commercial, fibrous minerals of the serpentine or amphibole series. Fibrous forms of other minerals, such as wollastonite, fibrous brucite, or fibrous forms of calcite or gypsum would not be included (108). Even so, a certain heterogeneity is seen in the minerals encompassed, and some difficulty is experienced in fitting the commercial names for various varieties of asbestos to chemical or mineralbgical classifications. Asbestiform minerals fall into two major subdivisions: chrysotile, which belongs to the serpentines, and the amphiboles, including crocidoEte, actinolite-tremolite, amosite, and anthophyllite (686). A large number of trade and mining terms have been applied to the asbestos minerals. For example, names that have been used for crocidolite vary greatly with the variety and location: potential crocidoEte, asteriated crocidoEte, amorphous riebeckite rock, asteriated mass-fiber riebeckite, acicular crocidoEte, griqualandite, and tiger-eye, not to mention the well known blue asbestos; the scientific mineralogical names are now the rule (686). [A3 The crystalline structure of chrysotile is that of a layer of magnesium oxide-hydroxide octahedra bonded to a layer of silicon dioxide tetrahedra in somewhat mismatched fashion that produces a curvature in 33 [RECEIVES TIME--SEP. 18-,. j 9 PM, PRINT T!ME SEP. 18. 3:25PM SEP 18 2002 4:15 PM FR TO 12145201181 P.04/20 34 2. Asbestos Minerals: Nature, Occurrence, and Properties the sheet (265,708). The sheet, consequently, tends to roll itself into a hollow tube or possibly a tight spiral (708) with the magnesium hy droxide on the outer surface. This hollow tube constitutes1'the basic fibril of chrysotile. Fibrils, bonded together, constitute fibers and the fibers in turn may be banded together to build up the macroscopic material. Theoretically any given piece of chrysotile can be successively split until the ultimate fibrils are reached, but the ease of fiberization varies with the particular ore. In contrast with the chrysotile crystal, amphiboles consist of double chains of linked silicon-oxygen tetrahedra lying parallel to the vertical crystallographic axis and bound laterally by metallic ions (Fig. 2-1). There is no tendency for such layers to roll into tubes. The Si-O bonds along the chain are much stronger than the metallic ion bonds between chains, so that the amphiboles break lengthwise with ease, giving a fibrous appearance. In the occasional incorrect use of the term "fibril" for amphiboles writers presumably are referring to assemblages of a small number of molecular aggregates. GEOLOGICAL FORMATION Although the amphiboles are major participants in rock formation, asbestiform amphiboles rarely occur in concentrated deposits that can be economically developed. Chrysotile, on the other hand, is not a common rock-forming mineral, but it does occur in a number of large scale deposits. Details of the origin of the asbestos deposits have not been completely resolved. The present account, intended as back ground to discussions of asbestos use and its biomedical effects, has been drawn from a number of reviews which should be consulted for further information and specific references (108,328,628,686,708). Chrysotile was apparently formed in fractures in serpentine rocks. These rocks were formed over geological time from the interaction of hydrothermal solution and pressure. Hot, mineralized water entered the fractures and dissolved the serpentine host. As the temperature and pressure dropped, fibrous crystals of hydrous magnesium silicate began to grow out of solution from both sides of the fissure. Where the rocks remained immobile relative to each other, the crystals continued to grow at right angles to the walls, forming what is now called the "cross-fiber" form of chrysotile. But if the rocks on either side moved laterally, the fibers were constrained towards an orientation parallel to the surfaces, to produce the "slip-fiber" form. In this form the fibers tend to be longer, but may have been physically weakened by the OE !:19 Fv 1VT T.'M: SEP. 18. 5:25PV SEP 18 2002 4:15 PM FR r TO 12145201181 P.05/20 u jerries Geological Formation 35 nto a i hybasic i the :opic ively ation >uble ctical 2-1). onds ween ing a .bril" of j ' j j ! BUILD-UPOF SHICTS INTO FUNDAMENTAL FIBRILS (A) ition, it can not a large e not back- has :d for ocks. on of .tered e and licate^ -e the .nued d the ' ioved (lei to fibers v the I ] i j Fig. 2-1. Fundamental crystalline structure of asbestos minerals: (A) chrysotile; (B) amphibole (708). Reproduced with the kind permission of S. Speil. stresses. In an intermediate form, the fibers became somewhat bent in the middle as the shear progressed, with the development of a weak ness at the point of flexion. As may be expected, the fractures, and thus the veins of chrysotile, follow an erratic pattern, sometimes running independently for various distances, at other times forming a fairly .SEP. 18., 3:19PM- PRINT TIME SEP. 18. 3:25PM SEP 13 2002 4:15 PM FR TO 12145201181 P.06/20 36 2. Asbestos Minerals: Nature, Occurrence, and Properties dense network (stockwork). Sometimes the fibers were formed in a hollow space of limited dimensions to produce lenticulated masses of fibers with rather random orientation that are referred to as "mass- fiber" forms. Sedimentary rocks, in addition to igneous rocks, may have been serpentinized with a later formation of chrysotile (686). Chrysotile is found in most countries which mine asbestos, except Finland. In contrast to chrysotile deposits, the amphiboles crocidolite and amosite axe found in altered sedimentary rocks often referred to as banded ironstones. The minerals in this case seem to have been formed in situ by a chemical rearrangement and recrystallization under heat and pressure. The veins may lie in parallel bands or bedded planes. The cross-fiber form is typically found, but mass-fiber forms occur. Amosite is found largely in South Africa; some deposits are known recently in India. Crocidolite occurs in significant amounts in South Africa, China, Australia, and Bolivia. Actinolite-tremolite and anthophyllite are usually found in the mass-fiber form in pockets in either igneous or metamorphic rocks. The first pair also occur in limestone or dolomite that has undergone recrys tallization, in which case they may be associated with talc or mica. Commercial deposits of anthophyllite are found in Finland, Bulgaria, and the United States. Italy and Japan produce some tremolite. More extensive notes on the occurrence are given in the "Asbestos Fact Book" (35). . CHEMICAL CHARACTERISTICS . Attention will be given here to the more general aspects of asbestos chemistry, with some detail of those aspects that may enter into the problem of identification or into the biomedical reactions to be dis cussed in later chapters. Considerably more detail can be found else where (71,108,708,790). Chemical Composition Table 2-1 gives the ranges of gross composition of the asbestiform minerals. It will be seen that chrysotile shows less variability than the amphiboles. Crocidolite and amosite contain more silica and much more of the iron oxides, but much less magnesium oxide than chrysotile. Anthophyllite, tremolite, and actinolite also contain more silica than chrysotile but are intermediate in their content of mag- iRECElVED TIME--SEP. <8. - 2: '9PM. fOT ~!Mt_ SEP. 18.,, 3:25PM SEP 18 2002 I !i 4:15 PM FR TO 12145201181 P.07/20 >rties in a es of \assmay 686). <cept and* to as .'med t and The osite ly in Tina, i the . The crys.Tiica. jaria. More '-ook" >estos o the diselse- iform n the much than more mag- Chemical Characteristics 37 TABLE 2-1 Chemical Composition of Asbestos Types'^ SiO, AijOj Fe*Os FeO MgO CaO NatO k2o H*0 Amosite 49-53 -- -- 34-44 1-7 -- trace 0-0.4 2.5-4,5 Anthophyllite 56-58 0.5-1.5 -- 3-12 28-34 -- -- -- 1-6 Crocidolite 49-53 0-0.2 17-20 13-20 0-3 0.3-3.7 4-8.5 0-0.4 2.5-4.5 ActinoUte-Tremolite4 51-56 1.5-3 0-3 5-15 15-20 10-12 0.5-l.S 0-0.5 1.5-2.5 55-60 0-2.5 0-0.5 0-4 21-26 11-13 0-1.5 0-0.6 0.5-2.5 Chrysotile 41.8-42.0 0,1-0.5 0.2-1.3 0.1-1.6 41.8-42.8 0-0.1 0-trace 0-0.1 13.6-14.0 " Common trace elements (ppm): Ag, Ba, Ce, Co, Cr, Cu. Li, Mo. Nb, Mn. Ni, Su, Sr, Th, V, Zr. Based on superior analyses of museum quality representative fibers. " Compositions at the actinolite and tremoiite ends of a continuous series. f With kind permission of International Agency for Research on Cancer. nesium oxide. [Data given by various compilers agree in broad features but may vary in detail. See, for example, the tables prepared by the Commission of the European Communities (809).] [A] The comparative composition is indicated in the three-dimensional diagrams of Fig. 2-2. The general formula for chrysotile may be written: MgjSijCVOH)*. By contrast, the chemical composition of the amphibole species is ex tremely complex. A theoretical general formula might be written as follows: (Ca,Na,Mn)2.3-(Mg/Fe,Ti,AI,Mn)5-(Si/Al)<'Os*-(OH,F)2, the elements within a parentheses being somewhat interchangeable (790). The relationships of the amphibole compositions are indicated in the three-dimensional diagrams of Fig. 2-2. A large number of minerals may be found in physical admixture with the asbestos fibers in the ores as mined. These cannot be removed by simple cleaning processes in the treatment of the ores and may affect the usefulness of the product. The exact composition of the final product may be a matter of great importance for special use. For example, magnetite intergrowths may adversely affect the operation of a trans former or other electrical equipment if present in large quantities in asbestos coverings (71). [A] Surface Characteristics The outer surface of chrysotile fibers, as mentioned earlier, consists largely of Mg(OH)* and behaves a$ such. The equilibrated pH in carbon T RECEIVED TIME^SEP. 18. 3: * 9 PM. PRINT TIME SEP. 18. 3:25PM SEP 18 2002 4:IS PM FR 38 TO 12145201181 P.08/20 2. Asbestos Minerals: Nature, Occurrence, and Properties (b) (c) Fe(ll) + Fe(lll> fig. 2-2. Schematic diagrams of three-component fields for the composition of am* phiboles. The values plotted are the relative numbers of the.ions specified expressed as percentages of their sum (790). Reproduced with the kind permission of E- J. W. Whit taker and the publishers of Acta Crystallographica. dioxide free distilled water is 10.33. The surface charge in water is positive at a pH lower than 11.8 and rises to a maximum at a pH of 3. With higher acidities the charge falls off rapidly as magnesium ions are removed and the silica surface is exposed (708). This positive charge renders chrysotile attractive to most other materials in solution which carry a negative charge. The surface of amphiboles, on the other hand, is like that of silica and carries a small negative charge in water. The specific surface area of chrysotile varies with the extent to which the fibers are pulled apart, from 4 m2/g in fibers pulled manually from a block of ore to 50 m2/g when individual fibers are separated. The specific surface area of amphiboles is lower, varying from 5 to 15 m2/g as the sample is fiberized (708). By comparison, the specific surface area of iECEiVE) "!VE it- 'Mr 3:25W SEP 18 2002 4:16 PM FR TO 12145201181 P.09/20 'ertiea i of amised as Whit- ter is ' of 3. is are harge vhid\, hand, i> /vhieh rom a . The \s/g as .rea of Chemical Characteristics 39 organic fibers varies for 0.3 m2/g for nylon to 0.98 m2/g for viscose rayon (628). As might be expected from its large specific surface area and its molecular configuration, chiysotile adsorbs gases fairly readily, particu larly those which have highly polar molecules such as water. In a liquid, adsorption can be complicated by competition between the solvent and the solute. The affinity of chrysotile for liquid organic compounds, in decreasing order, is ethanol, butanol, benzene > naphthalene > anthracene > hexane. The adsorptivity of amphiboles seems not to have been well studied (708), except for some recent papers from the National Institute of Occupational Safety and Health (287,288). Metal impurities may be associated with asbestos not only as chemi cal substitutes in the crystalline structure, but also as fragments of the host rock or as additions to the surface by various processing equip ment. Table 2-2 gives the ranges of contamination with trace metals . TABLE 2-2 Ranges of Trace Metal Contamination In Aebestoe Samples from Different Regions (524)" Type Fe<%) Cr (ppm) Co (ppm) Mn (ppm) Ni (ppm) Sc (ppm) Chrysotile Amosite Crocidolite Anthophyllxte 0.6-4.8 massive massive 2.0-4.4 317-1390 31-35 16-20 584-870 43-110 7-11 0.4-10 24-50 231-720 11800-13350 140-880 986-1060 540-1820 33-100 8-100 414-1360 0-12 0-5 0-0.6 0-5 0 With kind permission of A. Morgan and 1ARC. reported at the 1972 meeting of the Working Conference of the Interna tional Agency for Research on Cancer (524). Other surface properties affecting biological reactions will be dis cussed in Part III. ' Chemical Reactivity The concept of asbestos as being relatively indestructible cannot be extended to the application of chemical agents, particularly in the case of chrysotile. After treatment with 1 N HC1 for 1 hour at 100C, the typical X-ray diffraction pattern of chrysotile completely disappears, but was found to be unchanged after 6% hours of treatment with 0.12 N HCI at 37C, although there was 50% decomposition, of the fibers (784). Apparently under the less drastic conditions, a sufficient number of the inner layers of the fibrils remain to continue to give the typical diffrac tion pattern. ;a!NT '1ME SEP. 18. 3:24PM SEP 18 2002 4:18 PM FR TO 12145201181 P.10/20 40 2. Asbestos Minerals: Nature, Occurrence, and Properties When croddolite was treated with 5 N HC1 at 100C, 20% was de stroyed in 3 minutes, but the reaction slowed thereafter, possibly be cause of the formation of a protective coat of polymerized silica (735). In general, the amphiboles are less affected by acids than is chrysotile; with croddolite, tremolite and anthophyllite the most resistant (Table 2-3). Amosite and actinolite apparently show an intermediate reactivity. TABLE 2-3 Solubility of Asbestos Minerals in 25% Acid and Caustic (708)a % Loss in weight, refluxing 2 hr with Type HQ CHsCOOH HsPO< HiSO, NaOH Chrysotile Croddolite Amosite Anthophyllite Actinolite Tremolite 55.69 4.38 12.84 2.66 20.31 4.77 23.42 0.91 2.63 0.60 12.28 1.99 55.18 4.37 11.67 3.16 20.19 4.99 55.75 3.69 11.35 2.73 20.38 4.58 0.99 1.35 6.97 1.22 9.52 1.80 " With kind permission of S. Spell. Amosite and actinolite are also somewhat susceptible to the action of strong alkalies, but the remaining asbestiform materials are resistant. The resistance of asbestos to reagents other than acids is good up to 100C, but decreases rapidly at higher temperatures. The following extract from the paper by Speil and Leineweber con tinues into chemisorption and chemical reaction what was said above about adsorptivity: In general, organic compositions possessing acidic functional groups dissolved in nonpolar or slightly polar solvents, such as benzene and methyl ethyl ketone [MEK], exhibit a strong tendency either to chemisorb or to slowly react with " chrysotile. Long-chain aliphatic acids, such as stearic add, oleic add, and palmitic add are chemisorbed by dry fiber. Aromatic-type acids, such as benzoic add and related compounds, are also chemisorbed as are dibasic aliphatic adds, such as adipic add. Although the unsaturated six-carbon sorbic acid appears to be chemisorbed by chrysotile, the related shorter carbon chain acrylic, crotonic adds show some evidence of slow reaction with the dry chrysotile even In nonpolar solvents and there is a tendency for the adsorbed layer to show an affinity for water. Maleic add reacts with the bulk fiber. If the fiber contains adsorbed water, the interaction of an organic add in benzene or MEK solutions differs markedly from that with the dry fiber. The long chain aliphatic adds, e.g., stearic, oleic, when dissolved in nonpolar or slightly polar solvents, show little or no tendency to sorb on fibers containing adsorbed water. Acids such as adipic, benzoic, or sorbic, which have some slight affinity for water, react with the bulk fiber structure instead of chemisorbing as they do on dry fibers. (708) JECE1YE) IP !I `9?V 'xl'll I'M,: SEP. 18. 3:24PM SEP 18 2002 4:16 PM PR I TO 12l45201181 P . 1 I <^20 erties ; det be5). In with 2-3). vity. i n 55 >7 >2 52 50 on-of stant. up to conibove* Ived tone v^ith nitic and h as i be icids jolar ater. zene hain polar ater.' ater, bers. Chemical Characteristics 41 Chrysotiie reacts with water, as suggested by the pH value 11.8 that develops in a suspension as mentioned above. It is slowly soluble under conditions of continuous extraction, even without heat. When boiling water is used, magnesium and orthosilicic add appear in increasing concentrations over the first few hours. Sea water, as may be expected, brings about decomposition of chrysotiie (304). From croddolite, 4% of the silica and 6% of the sodium are removable by extraction with water (735). ' As will be seen later, in Chapter 4 on identification, bombardment with an electron beam causes damage or even destruction of chrysotiie fibers. Some deterioration has been reported in asbestos used in electri cal insulation (686). . Although asbestos is not flammable, it is affected by heat and may need to be replaced in materials so exposed. The following changes are described by Rosato (628). The hygroscopic moisture in asbestos, as distinct from that incorporated in the molecule, is directly related to the relative humidity (R.H.) of the air with which it is in equilibrium and varies from approximately 1% by weight in air at 49% R.H. to 2.5% at 95% R.H. It is easily removed by subjecting the asbestos to a tempera ture of approximately 212F (100C), without damage to the fiber. But at higher temperatures it loses its water of crystallization and the mechan ical properties such as mechanical strength may be changed. At about 800F (427C) amphibole asbestos generally loses a considerable part of the relatively small amount of its combined water and becomes ex tremely brittle. Chrysotiie, on the other hand, loses only about 15 % and retains its flexibility. Table 2-4 gives the percentages of loss in weight versus temperatures up to 1,800? (982C). ' Further details on thermal disintegration are given in Speil and Leineweber's paper (708). TABLE 2-4 Effect of Temperature on Lose in Weight of Asbestos Fibers (628)* Temperature (F) for 2 hr 400 800 1,000 1,200 1,400 1,800 Amosite 0.23 0.98 1.16 1.39 1.43 1.53 Percentage loss in weight Anthophyilite Chrysotiie Croddolite 0.05 0.38 0.44 0.54 0.54 2.30 0.30 2.17 3.99 12.75 13.43 13.77 0.08 0.73 0.86 1.04 1.03 0.77* Tremolite 0.04 0.22 0.29 0.37 0.47 2.18 " With kind permission of Reinhold Publishing Co., New York, and C>. V. Rosato. 4 Iron changing in weight by oxidation. RECEIVED TIME--SEP. 13. 3:19PM, PRINT TIME SEP. IS. 3:24PM SEP 18 2002 4:17 PM PR TO 12145201181 P.12/20 7 42 2. Asbestos Minerals: Nature. Occurrence, and Properties PHYSICAL CHARACTERISTICS Color, Texture, and Flexibility There is a good deal of variability in the color of asbestos, particularly of chrysotile, depending upon the exact content of cations and water of crystallization as is indicated in Table 2-5 taken from Berger (71). Data given by different compilers may vary in details (e.g, in 809). TABLE 2-5 Pleoehromn and Refractive Indices of Asbestos (71)'1 Type Chrysotile Crocidolite Amosite and anthophyllite Tremolite Alpha Beta Colorless/greenish yellow; all conceivable shades as axial and intermediate colors, depending on the composition Green!Light blue Brown Yellow/coloriess Brown Green/yellow Gamma Green, yellow Refractive index 1.50-1.57 Green, light blue Light yellow/ colorless Green 1.69-1.71 1.55-1.64 1.60-1.62 " With kind permission of Chemical Publishing Co., New York. The texture of chrysotile varies from silky to quite harsh; that of crocidolite from soft to harsh. Amosite may be coarse or pliable; tremolite and anthophyllite vary from soft to harsh (328).,Harshness is linked to the flexural modulus of the fibers; those with high values being harsh and relatively stiff and giving an open, bulky, and fairly porous mass. Flexible, soft fibers tend to form stringy and denser masses. Harshness has been variously related to the water content of the fiber, fine mineral intergrowths in the bundles, and the relative proportions of two crystal lographic forms (708). The characteristics of soft and harsh chrysotile are given in Table 2-6. The important commercial property of susceptibility to spinning depends upon a combination of flexibility and length of the fiber. It is highest with the softer forms of chrysotile, fair for crocidolite and some amosites, and poor for other amphiboles. Fiber Dimensions The length of the fibers varies from very short to about 2 in. (5 cm) for chrysotile, from short to 3 in. (8 cm) for crocidolite, short to long for I ! t RECEIVED TIME ?E5. `8., 19FV PRIT TIME 5EP. *3. 3:24PM SEP 1 9 2082 1 liI 4:17 PM FR TO 12145201181 P.13/20 ertles , =larly er of Data ctive lex 1.57 1.71 1.64 -1.62 iat of emo.fiked harsh nass. hness ineral ystalle are bility of the dolite TABLE 2-6 Characteristics of Soft and Harsh Chrysotile* Property Fiber bundle Feel Tenacity (flexibility) Size reduction (length) Fibrilization of bundle Surface area (equal amount of materials identically size reduced) Individual fibrils Appearance under electron microscope Individual fibrils Electron diffraction pattern Physical properties (bulk sample) Porosity Filter rates Filtrate clarity Conductivity (2.9% . suspension) Soft fiber Smooth, silky Flexible, may be bent at >90* without rupture Poor, resists fiber axis break Excellent to good, easily opened Average Canadian sample - 23 m'/g; some as high as 80 m*/g Fibrous, thin filaments moderately translucent Empty to partially filled capillary Arced reflections. disordered inteifibrii relationships High Slow Clear 22.2 ohms-1 cm*1 (x 10s) for average Arizona soft Mg leach (% NaCl equivalent) Chemical properties (bulk samples) Structural water (dry weight) CaO content 0.27 12.5-14.5% Trace to nil (Arizona soft) AljOa content Trace to minor oxide (Arizona soft) Harsh fiber Harsh, splintery Stiff, ruptures at less than 90* Good, easily broken across fiber axis Poor, tends to remain in tight bundles Average harsh = 11 m`/g; some as low as 4 m2/g Lathlike, electron-dense bundles Filled capillaries Single round or streaked reflections, ordered ! interfibril relationships Low Fast Cloudy 11.9 ohms-1 cm-1 (x 10s) for average Arizona harsh 0.10 11.0-12.5% Trace to minor oxide (Arizona harsh) Trace to nil (Arizona harsh) na) for ig for * With kind permission of International Agency for Research on'Cancer. ^RECEIVED TiME,,SSF. 13. 3:19PM, PRINT TIME SEP. 13. 3:24PM SEP 18 2002 4:17 PM FR TO 12145201181 P.14/20 44 2. Asbestos Minerals: Nature, Occurrence, and Properties actinolite and tremolite, and very short and weak for anthophyllite. Extremely long fibers, from 0.5 to 6 in. (1--15 cm), and even up to 12 in. (30 cm), occur in amosite (686). A table of percentage distributions of fiber Lengths for various types of asbestos is given in Berger's book (71). With processing of course, the fibers may be fragmented and considerably shortened in length from their original state. The individual fibril of chrysotile is the finest natural fiber known as is indicated in Table 2-7, but the dimensions of the fibers obtained in TABLE 2-7 Comparative Diameters of Fibers" Diameter Material Chrysotile fibril Chrysotile fibers Amphibole "fibril" Amphibole fibers Glass fibers Rock wool Slag fibers Flax, hemp,- etc. Cotton Wool Rayon, nylon Spider web Human hair Microns (10- mm) 0.02-0.04 0.75-1.5 0.1-0.2 1.5-4.0 1-S 4-7 3-5 12-80 10 20-28 7-7.5 7 40 "Thous" (10- in.) 0.0007-010012 0.26 0.14-0.28 0.96 0.40 0.80-1.10 0.30 1.60 " Based on data given in Berger (71). With kind permission of Chemical Publishing Co., New York. practice, and particularly of amphiboles which do not have a natural fibrillar structure, depend upon the degree of separation achieved in processing. The diameters given for other natural fibers must, of course, be given a certain latitude as well. (One could rightfully ask whose hair or what wool is meant.) Tensile Strength The tensile strength of asbestos varies considerably with the length and diameter of the constituent fibers (708):. Maximum values have been, obtained for chrysotile and crocidolite of about 60,000 kg/cm2, compared to a theoretical value of 100,000 kg/cm2 (628). These values are .RECEIVED TIME, SEP. 16. 3:19PM PRIM TIME SE: 3:24PM SEP 18 2002 4:17 PM FR TO 12145201181 P.15/20 'ropertles ihyllite. 2 in. (30 of fiber l). With derably town as lined in ) 1012 18 . 10 'ublishing i natural ieved in nust, of fully ask le length tes have i kg/cm2, alues are Physical Characteristics 45 of the same order as those given for glass fiber and carbon steel and are somewhat greater than those for cotton and rock wool. Lindell has recently given somewhat different figures (461): 450,000 lb/in.1 for chrysotile, 500,000 lb/in.1 for glass fiber, 155,000 Ib/in.* for carbon steel, 73,000-89,000 Ib/in.2 for cotton fiber, and 60,000 Ib/in.* for rock wool (Ib/in.2 -- 0.073 kg/cm2) (see also 809). When chrysotile is heated to 300C or above, the tensile strength is diminished; after 3 min at 650C the strength may be reduced to one-third. Crocidolite may be durable up to 800C (628). The tensile strength of tremolite and anthophyllite is gener ally weak. When rupture takes place, it is apparently due to failure of bonds between fibrils or molecular sandwiches, rather than disruption of those fundamental structures. Thermal Insulative Value The asbestos fiber itself does not have a low thermal conductivity, but when the fibers are separated they can trap air which has a very low conductivity and so provide insulation that, for heat flows in a constant direction, is comparable to that provided by similar materials made from other fibers. For heat loads that take place in alternate directions, such as on a roof exposed to the sun, the moderately high density of the material combines with the low conductivity to give one of the lowest values for thermal diffusivity, the governing physical attribute under these conditions. Table 2-8 gives the relative values of thermal conduc- TABIE 2-8 Comparative Insulative Properties (437) Material Air Cork Asbestos insulation Dry clay Steel Thermal conductivity (cai cm-1 sec-1 C"` x 10*-3) 6 7-13 19-40 200 10,000-20,000 Thermal diffusivity (cm* sec"1) 0.2666 0.00X3 0.0007 0.0035 0.1282 tivity and diffusivity for typical insulating materials, as compared with those for the metal over which they may be laid. Insulative value, of course, varies inversely with thermal conductivity and diffusivity. As with most conventional materials other than polished metals, the emissivity of asbestos insulating materials for long infrared radiation at usual working temperatures is over 90% (628). If transmitted heat is to RfcnVFD TiME-SEM3._ 3:19PM. PRINT TIME SEP.18. 3:24PM SEP .18 2002 4:17 PM FR TO 12145201181 P. 18/20 46 2. Asbestos Minerals: Nature. Occurrence, and Properties be conserved or prevented from radiating to persons or surrounding objects, a layer of polished metal is needed on the surface. Other Physical Properties In Table 2-9 it will be seen that chrysotile provides less electrical insulation than do amphiboles, probably because of its high proportion TABLE 2-9 Electrical Properties of Asbestos (71) Property Chrysolites Amosite Crocidolites Anthophyllite Aqueous extract (50 g fibers, S00 cm* water) lonizable salts (equivalent % NaCl) . Electrical conductivity (10"/n cm) Electrical conductivity (IQ~*ICI cm) Dielectric constant (220V/60 cycles per sec) . fnsulating ability ((fl/cm) 15% relative humidity air, 22C; 100 V/cm) ' Specific resistance (Mfi/cm) Dry 50% Relative humidity (air) 91% Relative humidity (air) Electrical charge 0.06-0.38 120-560 0.3-1.8 33.7 1.1 X 10* 1-2100 0.01-1.0 <0.01-0.4 positive 0.04-0.08 75-160 1.3 0.01-0.06 75-125' 0.8 6.7 0.02-0.06 25-115 0.6 8.4 124 X 10" 8,000-30,000 48,000-109,000 14-1400 34-95 190,000900,000 1700-2100 <1-1360 0.6-2.3 6-19 negative * With kind permission of Chemical Publishing Co., New York. a 4 I i S-M . r RECEIVED TIME__ SEP. `9 PM FRiNT TIME SEP. >8. :24M & SEP 18 2002 4:18 PM FR TO 12145201181 P.17/20 "i operties mding metrical portion ohyllite -0.06 -115 i.6 ;.4 x 10* ,000- xooo :-21Q0 -19 Grading 47 of water-soluble materials. The marked drop with increasing relative humidity of the surrounding air is of great importance if asbestos is to be used with electrical equipment. Asbestos insulating material provides excellent sound absorption unless the fibers are densely packed. It should be remembered, how ever, that supporting structures such as studs and beams can transmit a very significant proportion of the sound incident upon a structure, particularly in the low frequencies, and so detract from the insulation provided by the asbestos. X-ray diffraction patterns and other optical properties will be taken up in connection with identification techniques to be discussed in Chapter 4. GRADING Since the reader of this text will undoubtedly come across references to the grades of asbestos, something should be said about the systems in use, as they are various and confusing. In applying the Canadian Standards Classification, as explained in Rosato's book (628), 16 oz (453 g) of the material is placed in the top of a system of three successive boxes, each containing a screen, through which it is sieved with the finest material being collected in a pan at the bottom. The screens have successive meshes of 2, 4, and 10 to the inch (to 2.5 cm). Agitation is maintained for 2 min. The greater the quantity of material left on the screen, and the higher the screen in the series, the longer the fiber and thus the better the quality (of chrysotile). The classification based on this procedure is given in Table 2-10. Other commonly used and less complicated classifications are given in Table 2-11, and in the "Asbestos Fact Book" (35). TALC A final word must be said about talc. To the mineralogist, talc is a hydrated magnesium sheet silicate consisting mainly of platelike crys tals, but also containing fibrous forms. Geological deposits of talc often coexist with other hydrated magnesium silicate minerals, some of which are fibrous (621). Tremolite is a common contaminant, anthophyllite often occurs, and chrysotile is occasionally found. Commercial talc deposits may consist of fine-grained, intimate mixtures of minerals, iRECE 1VED TIME-SEP. 18. 3:19PM, PRINT TIME__ SEP. ^S. 3:24PM SEP 18 2002 4:18 PM FR TO I 214520118 1 P.18/20 43 2. Asbestos Minerals Nature. Occurrence, and Properties TABLE 2-10 Classification of Some Types of Chrysotile Asbestos According to Groups (628)" Group No. 1, Crude No. 1 Group No. 2, Crude No. 2 Standard designation of grades Crude Asbestos Consists basically of crude J in. and longer staple Consists basically of crude i in. to J in. staple Milled Asbestos Guaranteed minimum shipping test6 Group No. 3 (spinning fibers) 3D 3Z Group No. 4 (shingle fibers) 4D 4Z Group No. 5 (paper fibers) 5D 5R Group No. 6 (waste) 6D ' Group No. 7 (shorts or refuse) 7D 7W Group No. 7 (floats)' 7RF 7TF Group No. 8 (sand and gravel) - 8S 8T Group No. 9 9T 10.5- 3.9- 1.3- 0.3 0 -8 -6 -2 0 -7 -6 -3 0 - 1.5- 9.5- 5 0 - 0.5-10.5- 5 0-0 -10 - 6 0 _0 -7 -9 0 - 0 - 5 -11 0-0-0-16 No test No test Less than 50 lb per ft3 loose measure Less than 75 lb per ft6 loose measure More than 75 lb per ft* loose measure * With kind permission of Reinhold Publishing Co., New York, and D. V. Rosato. 6 Ounces remaining on successive screens and in pan from standard agitation of 16 ounces. ' The suffix "F" designates "floats" in the case of the 7R and 7T grades. including the fibrous, that are very difficult to separate in the mining and milling processes. Talc, it has been said, is a word used in industry to refer to a property rather than a mineral species. The mineral talc is soft and may be reduced to fine particles with high surface areas, good sorption characteristics, and low frictional resis tance, but mineralogical analyses of commercial talcs rarely show pure composition. In 51 common "talcs" analyzed at Mount Sinai, the talc ,C.!VED TIME . SEP. iS.*_A --3: ..:9P..M 5R!NT "iME 3ED.',8. 3:24PM SEP 18 2002 18 PM FR TO 12145201181 P.19/20 opertie* j i tti st f I Rosato. ion of 16 mining idustry th high l resisw pure the talc Grading 49 mineral content averaged 51%. The asbestos content, in particular, mayrange as high as 87%. However, the talc used in Britain, which comes from Italy^is much purer. The contaminants Ni, Cr, and Co are also much higher in the talcs used in the United States. As will be seen in Part II, persons exposed to talc may show evidence TABLE 2-11 Various Other Classifications of Asbestos (628)" Type , Characteristics Crude 1 AAA AA A AC AK AS AX Northern British Columbia (the Cassair Asbestos Grades) Basically, a crude i in. and longer staple Extra long textile fiber Long textile fiber Textile fiber Long shingle fiber Medium long shingle fiber Shingle fiber Short shingle fiber . African Chxysotile From mines in the Shabani district of Rhodesia C and Gl Long, crude textile fiber C and G2 Textile fiber C and G3 Long shingle fiber C and G4 Shingle fiber C and G5 Short shingle fiber or paper stock From the Mashaba district of Rhodesia ' VRAJ-2 VRAJ-3 VRaJ-4 Textile fiber Long shingle fiber Shingle fiber Grade 4 Grade 3 Grade 2 Grade 1 Group 1 D3 Group 2 Dll GW Australian Chrysolite 2 in. and longer fibers 1 in. to 2 in. fibers i in. to 1 in. fibers 1 in. to 1 in. fibers African Amosite Produced from hand-selecied long fiber at Penge Mine only Long, more than 3 in. in length Produced at Penge from "run-ofrmine" fiber after longest had been hand-selected f in. to less than 3 in. From Waltevreden Mine RECEIVED TIME--SEP. 18., 3:19PM, PRINT TIME SEP. 13. 3:24PM 4:18 PM FR TO 12145201181 P.20/20 50 2. Asbestos Minerals: Nataie, Occurrence, and Properties TABLE 2-11 Continued Grade 1 2 3 Type Textile Long shingle Shingle 4 Short shingle and paper stock 5 Paper stock Russian Chrysotile Texture Hard (coagulated) Hard Semihard Hard Semihard Soft Hard Semihard Soft Hard Mark according to U.S.S.R. Standard January 1,1952 J-l J-2 / P-2 J-3 PJ-3 P-3 M-3 ;-4 P-4 M-4 J-5 ' With kind permission of Reinhold Publishing Co., New York, and D. V. Rosato. of clinical effects, notably pulmonary fibrosis closely resembling that produced by exposure to asbestos dust. These effects could be due to the contaminating asbestos, but the fibrous form of the talc itself may also play some part. Even the platelike crystals can be taken up by tissue phagocytes and are thus potentially reactive (327), ? RECEIVED'T!ME"SE3. '3.'' 3:19PM R!N7 TIME"Sr. >8. 3:23PffrflL page.20 **