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RESEARCH REPORT N O . u -z-/^ y. nit- t RESEARCH REPORT NO. RESEARCH REPORT RESEARCH REPORT HO. 6l PHYSICAL PROPERTIES OE CGALINGA ASBESTOS. I. MORPHOLOGY AS INFERRED FROM NITROGEN ADSORPTION DATA <3- r>* UNION CARBIDE CORPORATION ax o NUCLEAR DIVISION o P.O. BOX 324, TUXEDO, NEW YORK o d X UCC 001897 RESEARCH REPORT NO. 6l PHYSICAL PROPERTIES OF CGALINGA ASBESTOS. I. MORPHOLOGY AS INFERRED FROM NITROQEN ADSORPTION DATA 37 A. , Naumann W. H. Dresher J * UNION CARBIDE CORPORATION NUCLEAR DIVISION Research Center Tuxedo, New York Issued: June 26, 196b UCC 001898 .TABLE OF CONTENTS Page I. SUMMARY AND CONCLUSIONS................................................................. 1 II. INTRODUCTION.......................................... 3 III. BACKGROUND .......tf.....#..#.......#...................... 3 IV. EXPERIMENTAL PROCEDURES 13 V. EXPERIMENTAL RESULTS 13 A. Reference Chrysotiles ...................................................... .. B. CoalInga Specimens ................................... . 1. Flake chrysotile ..............o.................. 2. Blsisd chrysotile 3. Serpentinite .................................................. 4. Products ......................................... 5. Cross-fiber .................... C* Stragsxi Chrysotile .........a........................ D. Texture Studies ................................ 15 IS 19 21 22 23 24 25 25 VT. REFERENCES.......... .................................................................... 29 -iiUCC 001899 p p P I. SUMMARY AND CONCLUSIONS 1 Surface area measurements have been made on samples that are representative of the mineral forms that make up the Coalinga asbestos ore body, and these data have been compared with data for chrysotile specimens from other sources. In general, the samples from the Coalinga deposit were of higher surface area than is usually found for natural chrysotile. Coalinga material was also less subject to variation with activation temp erature and with wet or dry opening treatments than is usually observed. Surface area values for Coalinga samples ranged from approximately 20 ms/g for a hard, dense, probably non-fibrous form of serpentine, to 80 m2/g for thin, leathery flakes of pure chrysotile. Refined and semi-refined asbestos products derived from the Coalinga deposit had areas in the range 50 to 60 m2/g. In a comparison study, a specimen of chrysotile from Stragari, Serbia, Yugoslavia, was found to have physical appearances and adsorptive properties similar to those of "Coalinga flake". The results of similar examinations made on specimens of four Canadian materials were more in line with values reported in the literature to be typical for chrysotile. The apparent surface area of the Canadian specimens was a function of activation temperature, and was increased by wet or dry mechanical opening treatments. After chemical dispersion treatment these Canadian specimens had areas approaching those of Coalinga materials, and the surface area was also in dependent of activation temperature. The adsorption properties of the Canadian specimens were Inter preted as reflecting a structure consisting of a closely packed array of tubular chrysotile fibrils with extra-fibril solid matter cementing the assemblage together. A solid made up in this way would have a well-defined pore structure and would have, as available surface, something less than the total surface of the individual fibrils. Thus, various types of open ing processes tear fibrils from the matrix in which they are imbedded and expose their true surface area. Chemical dispersion of the opened material allows a nearly pure fraction of fibrils to be obtained. The adsorptive properties of the Coalinga and Stragari chrysotile specimens were Indica tive of a much looser structure with essentially all fibril surfaces avail able for adsorption, and with voids between fibrils sufficiently large so UCC 001900 2 as to prevent capillary condensation of water between fibrils,, The adsorp tion data indicate further that the central pores of the fibrils from both the Coalinga and the Canadian specimens studied in the present investigation were not available for adsorption, and that the pore structures observed with the Canadian specimens were associated entirely with voids between fibrils, and not within fibrils. The similarities between the Coalinga materials and the Serbian chrysotile indicate that while Coalinga asbestos differs from most other chrysotile asbestos, it is not truly unique. UCC 001901 IX, INTRODUCTION Very soon after the first samples of asbestos were received from the Union Carbide deposit near Coalinga, California, it was realized that this was an unusual and perhaps a unique material In all mineralogical and chemical examinations the material was without a doubt the mineral chrysotile - the most commonly occurring asbestiform mineral The mode of its occurrence and some of Its physical properties indicated, however, that there were differences between this material and the material mined in Canada and elsewhere. In spite of these outward differences, the micro scopic particles, as observed in the electron microscope, and the crystal structure, as observed using x-ray diffraction, indicated that structurally these two materials were identical. The mode of occurrence of the material in the deposit misled many people, including asbestos experts, for many years Even though there are small deposits of conventional cross-fiber chrysotile in the vicinity of the Coalinga deposit which, at various times, have been mined on a small scale, the main ore body was completely ignored because of its unusual appearance The ore, instead of occurring In veins with the fiber oriented perpendicular to the plane of the vein, occurs in randomly oriented matte like flakes and agglomerates in a "slip" orientation The ore is so high grade and so friable that the deposit can be mined non-selectively with a bulldozer. Early physical tests and application amenability studies indicated that there were differences between Coalinga chrysotile fiber and Canadian chrysotile fiber. When asbestos is to be used in organic polymer matrices, such as in vinyl-asbestos tile, the oil absorbency of the fiber is a criti cal factor. Comparative tests run on Coalinga dry-processed material and Canadian dry-processed material showed that nearly twice as much di-octyl phthalate could be absorbed by Coalinga asbestos as could be absorbed by Canadian asbestos. Similarly, Coalinga products showed a substantially higher kerosene absorption factor than did the comparable Canadian Group 7 grade fiber. Specific surface areas, as determined by nitrogen adsorption, were invariably higher for Coalinga fiber than for Canadian materials. Early tests of the amenability of Coalinga asbestos to vinyl-asbestos tile UCC 001902 production indicated the need for significant changes of the tile formula tion and manufacturing procedure if this material was to he used. The need for these changes was quickly correlated with the high specific surface of Coalinga asbestos. Independently, Johns-Manville personnel discovered that between one-third and one-half the amount of asbestos would be required in vinyl-asbestos tile formulations if Coalinga fiber were to be used in place of Canadian fiber. The balance of the formulation could then be m^P Up by less expensive fillers. . In view of the similarities and yet obvious differences between Coalinga chrysotile asbestos and chrysotile asbestos from other sources, fundamental studies were undertaken to explain the apparently anomalous behavior of the Coalinga asbestos. UCC 001903 {**/. taw a*Vi^ HI.. -BACKGROUND The mineral chrysotile, Mgs(OH)s SJ^Oio# has a layer structure like that of the kaolinite minerals. The structure consists of a tetrahedral silica layer and an octahedral magnesium hydroxide layer joined together into a composite sheet in which the tips of the silica tetrahedra and one of the surfaces of the octahedral layer lie in a common plane. Figure 1 is a repre sentation of the structure. In this diagram the "a^ dimension has been exaggerated in order to show the details of the structure. Pauling(3) predicted before the layer structure of chrysotile was recognized that a magnesium analog of the kaolinite minerals would have to exist as curved sheets because of a miss-match in the natural repeat distances of the individual layers. The normal repeat distance for the silica layers, 8.9 8, as found in kaolin, is smaller than the equivalent repeat distance of an octahedral magnesia sheet, 9^ 2, as found in the mineral, brucite(^). Pauling's prediction has been abundantly verified by x-ray diffraction studies and by electron microscopy^* 5~10) ,, The layers of chrysotile curve and close to form cylinders of extreme length to diameter ratio. The elec tron micrographs of Figure 2 are typical of the chrysotile crystals or fibrils that are formed in this way. Figure 2 illustrates another peculiarity of chrysotile fibrils, namely, in electron micrographs they appear hollow along some segments of their length. It was once suspected that this was an artifact resulting from changes that occurred during sample preparation or under the influence of electron beamsf^jllJ^ hut later work, particularly the end-view electron micrographs of Maser, Rice, and KLug(40), leaves little doubt about the tubular morphology of chrysotile. This permits a characterization of the fibrils in terms of an inner and an outer diameter. The length of chrysotile fibrils range from a few microns to many tens of microns. Tube diameters are subject to much less variation. Dimemsional data that have been obtained for chrysotile specimens from various sources are summarized in Table I. A narrow range of inner and outer dia meters is to be expected, for the lattice miss-match that causes curvature and tube formation gives rise to a strain-free configuration at only one unique radius of curvature. There will be strain for larger or smaller UCC 001904 6, -- Hydroxyl Oxygen Magnesium Silicon FIGURE I: CHRYSOTILE STRUCTURE (after Whittaker) UCC 001905 a. Dispersed Grade 7R Asbestos b. Dispersed Coalinga Flake Chrysotile FIG. 2 : ELECTRON MICROGRAPHS OF CHRYSOTILE. UCC 001906 8 radii which will increase with increasing departure from the ideal radius. This limits the number of layers that can be built-up into a stable cylin drical wall, and thus it controls average fibril dimensions and the distri bution of sizes around the average. Whittaker's average values of 260 2 and 110 2 for outer and inner diameters, for example, correspond to a wall 10 layers thick(^). * . TABLE I DIMENSIONAL DATA FOR CHRYSOTILE ASBESTOS Reference Inside Diameter,2 Range Average Fankuehen and Schneider(12) Noll and Kircher(7) Jagodzinski and Bagchi(l3) 130 Young and Healey(1*0 150 Whittaker(^) Kalousek and Muttart(15) 50-75 no Bates and Comer(l^) Maser, Rice, and Klug(lO) 20-190 ' 68 Jagodzinski(l7) Pundsackfl) 350 20-50 Outside Diameter,2 Range Average 195-250 120-300 260 350 175-350 260 100-500 3lO 11^-850 250 200-500 3l0 500 200-500 In view of the strain considerations, one might expect fibril diameter to be restricted to an even narrower range than is observed. It is known, however, that composition varies somewhat for chrysotile from differ ent sources and, as discussed by Roy and Roy(-*-9)^ the kind and degree of isoraorphous substitution influences the morphology of serpentines. Also, some variation in fibril diameters can arise through strain relief by the forma tion of structures more complex than simple cylinders. The "tube-within-tube" structures observed by Maser, Rice, and KLug(lO) may be cited as an example. A simple packing of fibrils to form the filaments characteristic of chrysotile should, from simple geometric considerations, lead to a material UCC 001907 9- of high surface area and high porosity. For example, a packing of hollow cylinders as depicted in Figure 3a, with outer diameters of 300 , inner diameters of 150 2, and a specific gravity of 2.56 g/cc for tube walls would lead to the following bulk properties $ Surface Area: 69 m2/g for external fibril surfaces 35 mm2/g for internal fibril surfaces 104 m2/g Total Pore Volume: 23^ for internal voids 9# for voids between fibrils 32$ Total The observed bulk properties of chrysotile seldom approach these indicated values, as is illustrated by the data of Table II. TABLE II BULK PROPERTIES OF CHRYSOTILE ASBESTOS Bugge, Kerlogue, and Westwick(20) Nagy and Bates(21) Young and Healey(1*0 Pundsack (1955)(22) Specific Surface, m2/g 14 7 10-20 Bulk specimens Product of dry mechanical opening: Product of chemical opening (Novak Process)(25) Kalousek and Muttart(^5) Noll, Kircher, and Sybertzf2^) Pundsack (l96l)(^-) 4-12 fw 30 > 50 w 10-60 17-21 - Pore Volume, $ 1-12 4-5 The rather wide range of values observed for specific surface and pore volume is not due to an Inability to measure these properties, for, in general, the measurements have been made with high precision. Rather, a range of values UCC 001908 q. idealized open structure b. Idealized closed structure (after Whittaker) flG. 3* REPRESENTATIONS OF FIBER PACKING. UCC 001909 .11 is observed because variations occur with the source, state of subdivision, and" prior treatment of the materials studied. The most reasonable interpretation for the discrepancies between potential and observed bulk properties is that at least a portion of the potential void spaces are not empty. As shown in Figure 3a, there are at least two types of void spaces in a compaction of asbestos fibrils - the intra-fibril or axial void and the inter-fibril void. Several investigators have considered the filling of these voids with condensed water or with a solid material. Evidence for a capillary condensation of water into pore spaces within chrysotile fibril compactions has been given by Pundsack^) and by Young and Healey^M. The presence of condensed water has been used to account for the variation of specific surface with temperature that is often observed with chrysotile. The question of the existence of solid material filling pore spaces must be divided into the filling of inter fibril pores and the filling of intra-fibril pores, Convincing evidence has been obtained for the presence of solid matter between fibrils. Particularly noteworthy in this regard are the electron microscope replicas of Bates and Comer(1-6) which show that troughs with sharp cusps between them appear on fracture surfaces. These may be identified as regions where asbestos fibrils have been pulled from a solid matrix. The question of the presence or absence of solid materials in the central pores of chrysotile fibrils is less well resolved, but the preponderance of evidence points to at least a partial filling of the fibril centers. Electron micrographs show that the centers of fibrils are, for the most part, of lower electron density than the fibril walls, but they also indicate that density is greater in some regions than in others. The differences may reflect regions that contain a solid filling and others where none is present. Alternatively, the fib rils may be completely filled and the differences result because of varia tions in the density of the filling. Density data for massive chrysotile specimens favor the latter(-'-LA5), With either interpretation, at least a partial blocking of the central pores is indicated. Aside from the evidence for its existence, little can be said about the nature or structure of the solid materials within and between fibrils. Presumably, it can range from amorphous phases as favored by some authors(I0>l6j25), to crystalline cylindrical, segments of chrysotile arranged as suggested by Whittaker(2) (Figure 3b), There can also be a UCC 001910 .12 variation in the amount of extra-fibril solid matter present. The illustra tions of Figure 3 are idealizations to represent the extremes that are possible. Natural chrysotiles, in principle, can have structures anywhere between these extremes. It is the purpose of this report to show that chrysotile from the Coalinga asbestos ore body resembles the loose structure of Figure 3a more closely than does chrysotile from most other sources. These data will deal with the magnitude of the surface area of chrysotile specimens, an deter mined by nitrogen adsorption. Particular emphasis will be on the manner in which surface area varies with activation temperature, with wet and dry mechanical opening, and with chemical dispersion, and on the structural im plications that can be inferred from these variations. * k UCC 001911 13. XV, EXPERIMENTAL PROCEDURES Nitrogen adsorption data were obtained using a Perkin-Elmer-Shell Model 212B Sorptometer* A discussion of the principle upon which this in strument operates and of the experimental procedures employed has been given by Nelson and Eggertsenf2^). Specific surface areas were calculated from adsorption data using the conventional BET treatment(^7), The surface areas of two sets of referenced samples were measured to check the validity of the method. ' Data for the referenced adsorbents were as follows * National Bureau of Standards Reference Adsorbents Adsorbent NBS Value This Laboratory No.2 - Anatase 10.3 m2/g 10.8 m2/g No.6 - Bone Char No.8 - Silica-Alumina Catalyst 69 m2/g 550 m2/g 73 nr 7s 550+25* m2/g *DIfficulties were encountered with the activation of this sample. The material was extremely fine-grained, and contained approximately 20$ by weight volatiles,, Reference Samples from Tonawanda Laboratories, Linde Company Adsorbent Linde Value This Laboratory Cabot 'P-1 Wollaston!te 2.5 me/g 2.7 m2/g UCCND Coalinga Asbestos Silica adsorbent produced by acid leaching of Coalinga asbestos 53 515 59 I67 Davison Grade 03 silica gel 7I0 730 Samples were outgassed by heating overnight in a vacuum. Temperatures for activation were those suggested by the suppliers for the two sets of adsorbents. A temperature of 200C was used for the Linde samples, and 350C for the NBS materials. Absolute agreement was within approximately 5$ of the stated values for the NBS adsorbents, and approximately 10$ for the Linde samples. Reproducibility for a given sample was better than 5$. UCC 001912 Ik. Surface area data were obtained for chrysotile specimens in their natural state, i.ethe form in which they were received, and, in most cases for portions of the samples that had been given additional mechanical opening and chemical dispersion treatments. The chemical dispersion treat ment consisted of mechanically thrashing the samples in a Waring Blendor with a solution of an appropriate dispersing reagent such as acetic acid, aluminum chloride, or a combination of sodium aluminate and acetic acid. The resultant suspensions were centrifuged for 5 minutes at 1000 rpm. in an International Model SBV centrifuge to remove gangue particles and partially opened fiber bundles. The materials remaining in suspension were collected and dried for surface area measurements. The purpose of this treatment was to provide a source of completely defibrillated, monofilament chrysotile for examination. Purely mechanical opening was achieved either by thrashing a suspension of the materials in a Waring Blendor without dispersing re agents, or by dry grinding in a high intensity ball mill. UCC 001913 15. V. EXPERIMENTAL RESULTS A. Reference Chrysotile Samples Nitrogen adsorption data for four Canadian chrysotile specimens were consistent with literature values for chrysotile with regard to magnitude, and also with regard to the manner in which apparent surface area (l4) varied with activation temperature' , with mechanical opening, and with (22) chemical opening treatments' . TABLE I APPARENT SURFACE AREA FOR CANADIAN CHRYSOTILES Material Quebec Long Fiber - Untreated Cassiar AC - untreated Mechanically opened, dry Mechanically opened, wet Dispersed chemically Grade JR3 - untreated Dispersed chemically Grade 7TF - untreated Dispersed chemically Activation Temperature Tooc 200UC 425uc 15 18 22 19 20 22 3b 36 38 b3 43 - 51 50 49 51 30 44 52 52 50 20 25 30 45 45 44 The first two materials were essentially pure chrysotile. The first was longer fiber asbestos from the Thetford, Quebec, area supplied by Wards Natural Science Establishment. The adsorption data were obtained for fila ments pulled from a cross-fiber block specimen. The second material was a mechanically purified product from the Cassiar, British Columbia, mine of Cassiar Asbestos Carp., Ltd. This was also a long fiber material, and was in the form of tangled filaments. The material designated "Mechanically opened, dry" consisted of filaments that had been ground to -200 mesh in a Pitchford Grinder - a high intensity vibrating ball mill. "Mechanically opened, wet" UCC 001914 16. refers to materiel that was thrashed with water in a Waring Blendoro The third and fourth asbestos types were powdery, commercial asbestos products prepared by conventional dry processing methods,, The probable source of these materials was the Thetford, Quebec, area. Both contained appreciable amounts of brucite and magnetite, and lesser amounts of other impurities. Of the two, 7TF had the greater gangue content. A BET plot of the data for untreated Cassiar AC is given in Figure 4 to give a feel for the sensitivity and resolution of the surface area method. The change in area with activation temperature for.this sample was real and measurable, even though the changes were small. The data points for each temperature fall on a straight line in accordance with BET theory. The adsorption data for the Canadian materials were in line with the generally accepted view of the morphology of natural chrysotile, namely, a closely packed array of tubular asbestos fibrils with extra-fibril solid matter cementing the assemblage together. A solid made up in this way would have a well defined capilliary pore structure, and because of the extra-fibril filling, would have something less than the total surface of the individual fibrils as available surface. In terms of this close-packed structure, the Canadian materials had a relatively low surface area when activated at 100C. because a large por tion of the fibril surfaces are made unavailable by extra-fibril solid mater ials and by water condensed in capillary pores. Apparent surface area was larger at higher activation temperatures because of the removal of the capill ary water. -An additional variation with activation temperature occurs when accessory minerals that decompose to yield products of high surface area are present* As mentioned previously, both Grade JR and 7TF contained brucite which dehydrates to MgO at 350 to 400C. This contributed to the increase in apparent surface between 200C. and 425C. for both materials. The increase in surface area with wet or dry mechanical opening is due to a liberation of individual fibrils. The effects of dry mechanical opening is shown directly by the samples of Cassiar AC where an increase in surface area was brought about by grinding. The effect is shown indirectly by the magnitudes of the areas of the four starting materials. The Quebec long fiber sample, which had received the least mechanical work, had the smallest area; while the commer cial grades 7^3 and 7TF, whose powdery appearance were indicative of drastic mechanical treatments, had the largest areas. UCC 001915 17. FIG. 4: BET plot for Cassiar chrysotile. UCC 001916 18 The products of the vet mechanical opening treatments, especially those produced in the presence of chemical dispersants, had the highest sur face areas. This is to be expected, for with the latter procedure liberated chrysotile fibrils were separated from gangue and partially opened fibril agglomerates by centrifugation. Disaggregation reached the state where essen tially all fibrils were separated from each other, and surface areas approached values which correspond to all fibril surfaces available for adsorption. B. Coalinga Specimens F. A. Mumpton and C. S. Thompson of this laboratory have shown that the Coalinga asbestos ore deposit and the serpentinite body in which it lies are composed of minerals of the serpentine group along with minor quantities of brucite and magnetite, with traces of chromite, calcite, and uvaravite garnet. They have shown further that the asbestos ore itself can be consid ered to be a mixture of four physically distinct types of material if allow ances are made for gradations between types. The basic types are; (l) thin, tough, leathery sheets of matted chrysotile; (2) brittle, plate-like and bladed fragments of green chrysotile varying in size from fractions of an inch to several inches, and also varying somewhat in color, hardness, and in brittleness; (5) hard, dense, dark colored fragments of the massive serpentinite; and (k) small, soft, flexible, pellet-like agglomerates of fibrous chrysotile varying in size from about l/V to 1" in diameter. The bulk of the chrysotile exists in this latter form. The agglomerates generally con tain appreciable quantities of both the green-bladed material and fragments of the hard, serpentinite rock. In addition to the four basic types, which occur throughout the ore body, there is at least one area of limited size where typical cross-fiber chrysotile is found. In the discussion which follows, material of Type 1 will be re ferred to as Coalinga flake chrysotile; material of Type 2 as Coalinga "bladed chrysotile; and material of Type 5 as Coalinga serpentinite. Surface area determinations were made for selected specimens of each of these types, for Coalinga cross-fiber chrysotile, and for a variety of products derived from the Coalinga ore body. The materials of Types 1, 2, and the Coalinga cross-fiber, occurred as large pieces and it was possible to select specimens that were essentially UCC 001917 19 pure chrysotile. The Coalinga serpentinite, while not pure serpentine, also occurred In massive' form and could be sampled readily This was not true of the agglomerates of Type 4. The variable composition, heterogeneity, and finely 'divided nature of Type 4 material made it impractical for study as a specific type. However, since the bulk of the ore exists in this form, and since processing removes most of the gangue minerals of the aggregates, the properties of the fibrous chrysotile of the agglomerates can be inferred from measurements made on gross asbestos products. 1. Flake chrysotile; Nitrogen adsorption data for the Coalinga materials differed considerably from the pattern normally found for chrysotile. This was particularly true for specimens of Coalinga flake which were of con siderably higher surface areas than has been reported for any natural chryso tile. The results for four samples selected at different times from pilot plant materials were as follows: Samples 1 2 3 4 Specific Surface 78 m2/g 81 m2/g 74 m2/g 77 m2/g The apparent surface area of Coalinga flake was independent of activation temperature: Activation Temperature 100C 200C 470C Apparent Surface Area 79 m2/g 80 m2/g 76 m2/g- Also, apparent surface area was not increased by mechanical opening and chem ical dispersion treatments. Figure 5 is a BET plot for portions of Sample 1 above. The plot includes data for untreated flake and for flake that had been pulped and opened in a Waring Blendor, both with and without chemical dispersants. Three separate methods of chemical dispersion were used. The UCC 001918 100 W P /V (Po-P) FIG. 5: BET plot forCoalinga flake chrysotile. UCC 001919 21 data points for the products of the various treatments fell on a single straight line corresponding to j8 m2/g, The values for the individual samples were as follows: Sample Strips of flake, untreated Mechanically opened flake, wet process Dispersed fiber, acetic acid as dispersant Dispersed fiber, aluminum chloride as dispersant Dispersed fiber, sodium, aluminate and hydrochloric acid as dispersant Apparent Surface Area 78m2/g 79m2/g 79m2/g 77m2/g 79m2/g These results suggest a very open structure in the natural state, with essentially ai1 fiber surfaces available for adsorption, and with inter fibril pores sufficiently large that capillary condensation of water does not occur. Wo additional surfaces were made available for adsorption by mechanical treatments nor was material of higher surface area separated as individual fibrils by any of the chemical dispersion processes. The apparent surface areas of approximately 80 m2/g for Coalinga flake as compared to approximately 50 m2/g for purified Canadian chrysotile fibrils is indicative of a somewhat smaller average fibril diameter in the Coalinga sample. 2, Bladed chrysotile. The surface area of Coalinga bladed chryso tile was lower than that of Coalinga flake, but was high compared to most non- Coalinga chrysotile specimens. Surface area of individual samples of bladed chrysotile was also more variable than for Coalinga flake. Values ranged from 25 to 1+0 m2/g. Sample Particle Size Activation Temperature Room Temp. 400C 1*01-36-1 16x20 mesh 30 m2/g 29 m2/g 1+01-36-2 16x20 mesh 37 m2/g 39 m2/g 401-36-3 16x20 mesh 30 m2/g 32 m2/g 367-38-I 367-1+1+-1A 60/80 mesh +200 mesh 26 m2/g 24 m2/g 27 m2/g - As mentioned previously, the bladed chrysotile varies somewhat in color, hard ness, and brittleness between samples. Too few samples were examined to UCC 001920 establish a firm correlation between physical properties and surface area, but there were indications that surface area was less for the harder, more brittle materials. The apparent surface area of Coalinga bladed chrysotile, like that of Coalinga flake, was independent of activation temperature. Chemical dis persion treatments, however, increased surface area appreciably. Sample 401-36-3, which had an area of 30 m2/g when sized to 16 x 20 mesh, gave an area of 58 m2/g after dispersion. Similar results were obtained with other samples. These results indicate the presence of an open structure with inter-fibril voids too large for condensation in the material, but with some extra-fibril solid material present like that of the Canadian samples to block a portion of the surfaces. 3. Serpentinite, Coalinga serpentinite was of low surface area compared to Coalinga flake or bladed chrysotile. Activation Temperature 100 c. 200 C. 400 c. Apparent Surface Area 20 m2/g 24 m2/g 55 tn2/g These data were obtained for material sized to 20 x 60 mesh. The specimen was hard, brittle, and a dark blue-gray in color. X-ray diffraction showed the presence of serpentinite and brucite, Chemical analyses were as fol- lows; , Si0e MgO Fe203 32.1 $ 42,2$ 8.3$ This composition corresponds roughly to 75 per cent serpentine, 15 per cent brucite, and 10 per cent magnetite. ' The serpentinite did not respond to chemical dispersion treatments. Thrashing in a Waring KLendor reduced the particle size.but, unlike Coalinga flake and bladed chrysotiles, these treatments did not yield a suspension of colloidally-sized particles. It is probable that the Coalinga serpentinite specimen consisted chiefly of a non-fibrous form of serpentine, .This is indi cated by the failure of the material to respond to chemical dispersion UCC 001921 23 treatments. Electron micrographs of surface replicas provided more direct evidence in this regard. The replicas, which were obtained for freshly fractured surfaces, showed a layer structure like that found with clay min erals as the dominant feature. There were occasional regions showing highly disordered tubes or lathes embedded in a solid matrix, but these made up only a small portion of the total surface. The slight increase in apparent surface area between 100 and 200 is indicative of a pore network within the serpentinite. The large increase between 200 and 400 was probably due to the dehydration of the brucite of the specimen. 4, Products. Surface area data were obtained as part of the present investigation and on a service basis for a variety of pilot plant products from the Coalinga ore body. Values fell in the range 50 to 60 m2/g. The following may be considered as typical: Products by Wet Processing UCN pilot plant "JT101" UCN pilot plant "Jig Flake" TJCN pilot plant "CMS" 56, 59, 57, 6o ma/g 53, 53, 56 6i Products by Dry Processing UCN pilot plant "L-l" Johns-Manville "Red Label" Johns-Manville "Blue Label" 55 59 54, 56 m2/g The apparent surface area of the products increased by 10 to 20 m2/g with dispersion treatments. It is difficult to estimate how much of this in crease, if any, was due to changes in the chrysotile, however. The products were chiefly chrysotile, but they contained lesser amounts of other minerals such as brucite, magnetite, and the massive serpentinite. Chemical dispersion treatments remove the bulk of these gangue materials, and this alone will cause some increase in surface area. The surface area of Coalinga products will vary with activation temperature when decomposable accessory minerals such as brucite are present, but in general the concentrations of these minerals are small and the depend ence of surface area on activation temperature is also small. This is shown by the following data which were obtained for the pilot plant JT-101. UCC 001922 24 Activation Temperature 100* C. 200* C. 4oo* C. Apparent Surface Area 60 m2/g 62 ma/g 66 m2/g As mentioned previously, asbestos products prepared from the Coal inga ore body axe derived chiefly from the heterogeneous chrysotile agglomer ates that make up the bulk of the ore and, because of this, the properties of the agglomerates can be inferred from those of the products. With this as a basis, the properties of the agglomerates would be classified as being inter mediate between those of the Coalinga flake and bladed types. Pertinent properties for the three types are summarized as follows Flake Chrysotile Apparent Surface Area 70-80 m2/g Variation of Area with Activation Temperature Wo variation Variation of Area with Dispersion Treatments No variation Bladed Chrysotile 20-40 m2/g No variation Area increased Chrysotile Agglomerates (inferred from Asbestos Products) 50-60 m2/g Little,if any,variation Probably increased some. but not as much as for bladed chrysotile These results suggest that the chrysotile agglomerates may not be a distinct mineral form, but rather may be a mixture of the flake and bladed types with particle sizes so small they do not appear as such * 5. Cross-fiber. The following results were obtained for a spec: men of Coalinga cross-fiber chrysotile: - Activation Temperature 100* C. 200 C, 580* C. Apparent Surface Area 41 m2/g 45 m2/g 41 m2/g UCC 001923 25 These data were obtained for filaments approximately 1 cm. long pulled from a solid block. Again, surface area was high compared to reported values for non-Coalinga cross-fiber chrysotile, and again apparent area was not a function of activation temperature. An open structure like that of the other Coalinga chrysotiles is indicated. Thus, it appears that the open structure of Coalinga slip fiber is associated more with the locality than with the mode of occurrence of the fiber, C. Stragari Chrysotile A sample of chrysotile from Stragari, Serbia, Yugoslavia, having a physical appearance very similar to Coalinga flake was obtained through the American Museum of Natural History. Surface area data for this material were as follows: Material Untreated flakes Chemically dispersed flakes Activation Temperature 100 C. 200 C. 400 C. 100 C. Surface Area 78 ms/g 78 m2/g 80 ms/g 88 m2/g The apparent surface area of the untreated flakes was not a function of activation temperature. Some increase in area occurred with chemical dis persion, but the increase was small (10-15$) compared to Canadian chrysotiles where area is increased by a factor of two or more. It has been pointed out in the open literature that the physical appearance of Stragari chrysotile is similar to Coalinga asbestos(^8). i^e results above indicate that the material is also similar in regard to adsorption properties, and presumably also in regard to structure and morph ology. Thus, while Coalinga asbestos differs from most chrysotiles, it is not truly unique, D, Texture Studies In the discussion of the experimental observations, the Canadian chrysotile samples were described in terms of a relatively tight packing of individual fibrils with additional solid matter in Interstices between fibers. UCC 001924 Coalinga materials, particularly Coalinga flake, were described in terms of sc much looser structure with essentially all fibril surfaces available for adsorption, and with voids between fibrils sufficiently large so as to pre vent capillary condensation of water. Differences in the magnitude of surface area between dispersed Canadian samples and Coalinga flake were attributed to differing average fibril diameters. Thus, the structural interpretation for the differences between Coalinga and Canadian chrysotiles hinge on two factors (a) the presence of extra-fibril solid matter in Canadian chrysotile, and the absence of such material in Coalinga fiber; and (b) a smaller average fiber diameter for Coalinga chrysotile. A series of electron micrographs of dis persed Canadian Grade 7R3 and dispersed Coalinga flake were prepared and the external diameters of a statistical sampling of the fibrils appearing on each photographic plate were measured precisely using an optical microscope with filiar eyepiece. The results of these measurements are shown graphically in Figure 6. The fibers of the Canadian specimen were of larger average dia meters and had a greater variation in fiber size than those of the Coalinga chrysotile. Average diameter for the Canadian sample was 375 2 with a stan dard deviation between fibers of j6 2. For Coalinga flake, these values were 275 2 and 26 2, respectively. Diameter did not vary significantly along a given fiber of either material, but the greater variation was with the Cana dian sample. Surface areas calculated from the fibril dimensions were in satisfactory agreement with the nitrogen adsorption values. The fibrils of the Coalinga sample were characteristically smooth and regular 'along their entire length as would be expected for a material that contained no extra-fibril solids. The fibrils of 7R3 appeared rough and "lumpy'1 along some segments, and had bits of particulate matter adhering to them at others. The general appearance was consistent with the view that the fibrils had been broken from a solid matrix. These differences were by no means subtle, as is shown by the prints of Figure 2. Both are prints of plates used in the fibril dimension analysis, and are at the same total magnification. Figure 2b is of the Coalinga sample, and Figure 2a of dis persed 7R3. Areas showing particulate matter adhering to the fibrils of 7R3 are indicated by the arrows. A pertinent question that remains is the location and nature of the pores that give rise to the variation of apparent surface area with fll) activation temperature. Young and Healeyv took the view that the pores UCC 001925 NUMBER OF FIBRILS 27. FIBRIL DIAMETER, & FIG. 6 : Histogram of fibril diameter distribution. UCC 001926 28 were within the individual fibrils, and probably could be identified with the apparent hollow tubular structure of chrysotlle as seen on electron micrographs* Pundsack(^) interpreted water adsorption data in terms of pores of two types - one, the hollow tubes within fibrils and, the other, pores between fibers. The results of the present investigation cannot be reconciled with these interpretations. If pores within fibrils were in volved, a variation of surface area with activation temperature would be expected with all chrysotlle specimens. Hone was observed with the Coallnga flake or bladed types. It might be argued that this was because the pores of Coalinga fiber are closed,' while those of most chrysotlle specimens are open, but this argument would not apply for the results obtained with the Canadian chrysotile specimens which were given the chemical dispersion treat ment. These materials showed a variation in the natural state. If internal voids were responsible, a variation would also be observed after chemical dispersion treatments, since state of aggregation would have no effect on condensation in voids within individual fibrils* No variation was observed for dispersed products* The adsorption data indicate, therefore, that the central pores of the specimens studied in the present investigation were not available for adsorption, and that the pore structure observed for the Canadian materials was associated with voids between fibrils rather than within fibrils* UCC 001927 REFERENCES 29 1. B.E. Warren and K.W, Hering, Phys. Rev,,, 59, 925 (1942). 2, E. 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