Document N2YKX064wQYgE0DmM5LdjKZ1Q

si I / THE AMERICAN MINERALOGIST, VOL. 49, JANUARY-FEBRUARY, 1964 THE CONCENTRATION AND STUDY OF THE INTERSTITIAL MATERIAL IN CHRYSOTILE ASBESTOS Edward Martinez and Joseph J. Comer, Central Research Laboratories, American Smelling and Refining Company, South Plainfield, N. J. and Sperry Rand Research Center, Sudbury, Mass. Abstract Electron microscopic studies reported in the literature have shown chrysotile asbestos to have a tubular morphology with a heretofore unidentified material filling the voids be tween fibers. This fine material is believed by some to be amorphous and by others to be crystalline. By placing chrysotile crudes in an ultrasonic field transmitted through a liquid the fine material was dispersed, making it possible to separate it from the bulk of the fiber. Electron diffraction and microscopic studies of the concentrates of the interstitial material from three samples indicate that it is amorphous and may vary in size. Introduction Electron micrographs of individual fibers of chrysotile have shown it to have a tubular morphology (Turkevich and Hillier, 1949; Bates el al., 1950). Studies with bulk specimens revealed a fine material filling the interstices between fibers (Bates and Comer, 1959); Maser el al. (1960) examined thin cross sections of chrysotile and observed material plug ging the voids. Pundsack (1956) and Kalousek and Muttart (1957) measured the densities of intact bundles of chrysotile and concluded there was a small void volume; a subsequent investigation (Pundsack, 1961) described the pore size distribution of chrysotile indicating material filling the interstices. Whitaker (1957) suggested that the fine material has the same composition and structure as the tubes but in the form of curved laths; Bates and Comer (1959) describe the interstitial material as "amorphous appearing." These studies have not resolved the difference of opinion as to whether the material filling the voids is crystalline or amorphous. The dispersion of the fine material during the fiberization of chrysotile by ultrasonic energy made it possible to obtain a concentrate of the fine material which could be examined with the electron microscope. Description of Equipment and Sample Preparation Ultrasonic unit. A Westinghouse Corporation ultrasonic cleaning system WEHH was used to fiberize the chrysotile samples. The following is a description of the generator and cleaning unit: 153 .1 ASARCO ALV 0005727 154 E. MARTINEZ AND J. J. COMER Generator Model M 2000 Frequency 20 kc nominal Power Out 1000 watts1 Power In 110 v., 20 a., 60 cps. 1 Variable from 200 to 1200 watts. Cleaning Unit Model SLA-10 Capacity 3 gal. (ll'X10'X8') Transducer Magnetostrictive Frequency 20 kc nominal Three grams of chrvsotile crudes, from which the ends had been cut to minimize contamination from wallrock material, were pulled apart with tweezers. The chrysotile was placed in a small bottle with 200 ml of methanol which was then put in the ultrasonic cleaning unit filled with water. The sample was subjected to the ultrasonic energy for 30 minutes at a power output of 1200 watts. The chrysotile was fiberized by the ultrasonic energy and the methanol became cloudy due to the dispersed colloidal material and fine chrysotile down to unit fibers. The solution was carefully decanted from the bulk of the chrysotile and then centrifuged to remove the solids consisting of a mixture of the fine material and some chrysotile fibers. . Electron microscope and diffraction. An RCA Model EMU-2D electron microscope was used. Specimens were prepared by placing drops of the diluted suspensions of fine material on grids containing collodion sub strates. Electron diffraction patterns of several areas of each specimen were obtained by the selected area diffraction technique using platinum apertures of various sizes to examine fields as small as 2 microns in diameter. Samples. Chrysotile crudes from the following Canadian mines were subjected to the ultrasonic treatment Lake Asbestos of Quebec, Black Lake, Quebec Johns-ManviHe, Asbestos, Quebec Bell, Tbetford Mines, Quebec Vimy Ridge, Quebec Cassiar, British Columbia All samples liberated an ultrafine material when subjected to ultrasonic irradiation. However, electron micrographs and diffraction patterns were obtained only on the fine material from the Lake Asbestos of Quebec and Johns-Manville chrysotile samples. Results and Discussion An electron micrograph of the fine material dispersed from a chrysotile crude by ultrasonic energy is shown in Fig. 1. The decanting and centri fuging procedure for concentration of the fine material was not com pletely effective in eliminating all of the chrysotile fibers, but it was ASARCO ALV 0005728 INTERSTITIAL MATERIAL IN ASBESTOS 155 possible with the electron microscope to select a field containing only the fine material. A study of the electron diffraction patterns indicated that the fine material is not crystalline. The fine amorphous material fills the interstices between fibers so it is logical to assume that it may have an effect on both the physical and chemical properties of a given fiber. Study of the electron micrographs of the amorphous material indicated an apparent difference in the size of the particles. The fine material obtained from the Asbestos, Quebec, 3 Fig. 1. Electron micrograph of dispersed fine material from chrysotile crude, Black Lake, Quebec. sample appeared to be smaller in size compared to the one shown in Fig. 1. Whether this is due to lack of dispersion in the coarser material is not known. Only three samples from two sources were submitted for observa tion with the electron microscope so definite conclusions are not possible. However, this may be a real difference. If so, the size of the amorphous particles may be the reason chrysotile varies in harshness or softness of fiber depending on the source (Cirkel, 1910; Soboleff and Tatarinoff, 1933). Further study of samples from many sources will be required to verify this hypothesis. .1 ASARCO ALV 0005729 156 E. MARTINEZ AND J. J. COMER A surface property such as the zeta potential may be influenced by the amorphous material. The effect of pH on the zeta potentials of chrysotile has been studied using two techniques. Pundsack (1955) meas ured the turbidities of standardized chrysotile suspensions in which the pH had been adjusted by the additions of sodium hydroxide or hydro chloric acid. The chrysotile had been finely ground and the suspensions allowed to settle for forty minutes. Minimum turbidity was obtained at a pH of 10.1 and this was called the isoelectric pH, with the zeta poten tial being positive at lower pH's and negative in more alkaline solutions. Martinez and Zucker (1960) obtained an isoelectric pH of 11.8 using streaming potential measurements with chrysotile samples that were not extensively ground. The zeta potential investigations were run on chrysotile crudes ob tained from two sources in Quebec. However, the difference in results may possibly be due to the amount of grinding required; the turbidity procedure involved a severe grinding of the sample which would liberate the amorphous material. It is conceivable that the turbidity measure ments were made on a system containing a higher concentration of the amorphous material than in the original crude since the fine amorphous particles would stay in suspension, whereas the coarser chrysotile fibers would settle out. Acknowledgments The authors wish to express appreciation to Mr. C. A. Forbes, New Products Laboratories, Westinghouse Corporation who arranged for the use of the ultrasonic equipment. Thanks are also due to Mr. Larry Townsend of ASARCO who did much of the laboratory work. References Bates, T. F. and J. J. Comer (1959) Further observations on the morphology of chryso tile and halloysite, Proc. Sixlk Nat. Conf. Clays Clay Minerals, Pergamon Press, N. Y., N. Y., 237-248. --------- L. B. Sand and J. F. Mink (1950) The tubular crystals of chrysotile asbestos. Science 111, 512-513. Ciekel, F. (1910) Chrysotile-asbestos, its occurrence, exploitation, milling and uses. Canada Deft. Mines, Mines Branch. Kalodsek, G. L. and L. E. Muttart (1957) Studies on the chrysotile and antigorite components of serpentine. Am. Mineral. 42, 1-22. Martinez, E. and G. L. Zucker, (1960) Asbestos ore body minerals studied by zeta po tential measurements. Jour. Phys. Cham. 64, 924-926. Maser, M., R. V. Rice and H. P. Kiug (1960) Chrysotile morphology. Am. Mineral. 45, 680-688. Pdndsack, F. L. (1955) The properties of asbestos. I. The colloidal and surface chemistry of chrysotile, Jour. Phys. Chem. 59, 892-895. ASARCO ALV 0005730 INTERSTITIAL MATERIAL IN ASBESTOS 157 --------- (1956) The properties of asbestos. II. The density and structure of chrysotile. Jour. Phys. Chem. 60, 361-364. --r------ (1961) The pore structure of chrysotile asbestos, Jour. Pkys. Chem. 65, 30-33. Soboleff, X. D. and M. V. Tatarinoff (1933) The cause of brittleness in chrysotile asbestos. Econ. Cent, 28, 171-177. Turkevich, J. and J. Hiluer (1949) Electron microscopy of colloidal systems. Anal. Chem. 21, 475-485. Whitaker, E. J. VV. (1957) The structure of chrysotile. Ada Crysl. 10, 149-156. Manuscript received, May 16, 1963; accepted for publication, October 24, 1963. .( ASARCO ALV 0005731