Grinding of Chrysotile in Hydrocarbons, Alcohol, and Water

Abstract

Abstract--The change of the properties of chrysotile after ball milling in organic liquids (aromatics, alcohols, silicone oils) or water was studied by gas adsorption, electron microscopy, X-ray powder diffraction, infrared spectroscopy, differential thermal analysis, zeta potential measurements, and chemical analysis. Grinding in low viscosity organic solvents leads initially to a rapid defiberization of the asbestos bundles and to a fragmentation of the isolated fibrils. Finally, amorphization and agglomeration occur causing a drastic decrease of the specific surface area of the ground material. Grinding in water brings about a defiberization, but much more slowly than in organic solvents. Moreover, prolonged grinding in water does not significantly alter the structure of chrysotile. The efficiencies of the organic solvents, considered as grinding aids that induce fracture of the fibrils, are related to the environmental stress cracking of brittle solids (Rehbinder theory). Hence, the pertinent properties of the organic liquids are their viscosity and their cohesion energy (solubility parameter). Solvents chemisorbed on the surface of the ground chrysotile reduce the surface energy of the fracture surface and prevent aggregation. Water does not react according to Rehbinder's theory, but appears to form a protective layer around the fibrils. This hypothesis was verified by dry grinding defiberized asbestos (rapid amorphization) or by disturbing the stability of the water coating by coadsorbing alcohol on the solid surface. Alternaiively, the resistance of the fibrils to fracture may be explained by Westwood's theory that grinding in water is equivalent to grinding in an alkali medium, wherein the surface charge of the chrysotile becomes negligible, and the mechanical stability of the fiber reaches a maximum.

Effects of Dry Grinding and Leaching on the Crystal Structure of Chrysotile

“…The short fibrils appeared to be cemented by shapeless, noncrystalline material. These same features were observed by Papirer and Roland (1981) for a Canadian chrysotile ground for 30 hr in toluene. These features explain the decrease in surface area and the increase in the amount of Mg that was extracted from the chrysotile surface.…”

Differences between adsorption properties of two Rhodesian chrysotile samples. Relation with the DTA features introduced by leaching and grinding

“…The crystalline network of the fibers is broken down and amorphous silico-magnesia compounds are formed upon severe dry grinding (25). We verified that chrysotile-2, heated at 600°C for 4 h in air, yields an amorphous material with the same appearance when viewed by XRD and IR.…”

The Effect of Dry Grinding on Antigorite from Mulhacen, Spain

“…Papirer and Roland (1981), Henmi and Yoshinaga (1981), Cornejo andHermosin (1988), andP6rez Rodriguez et al (1988) reported similar behavior in chrysotile, imogolite, sepiolite, and pyrophyllite, respectively. Juh~isz (1980) referred to the increase in specific surface area as the "degree of dispersivity" and its decrease the "formation of aggregates by the compaction of the fine particles.…”

“…Nevertheless, little is known of the behavior of serpentine to grinding. Papirer and Roland (1981), in a study on chrysotile, found that grinding in lowviscosity organic solvents leads to three successive and overlapping processes; rapid defiberization of the asbestos bundles followed by fragmentation of the isolated fibrils and, finally, amorphization and agglomeration resulting in a drastic decrease in the specific area.…”