A STUDY OF HEAT-DEGRADED CHRYSOTILE, AMOSITE AND CROCIDOLITE BY X-RAY-DIFFRACTION

The effect of heat on the three major asbestos minerals, chrysotile, amosite and crocidolite, has been studied over the range 100-900 degrees C by X-ray powder diffraction. In the case of the amphibole asbestos minerals, oxy-amphiboles are formed at relatively low temperatures (400-500 degrees C) accompanied by shifts in the positions of certain diffraction lines. At higher temperatures the oxy-amphiboles break down completely into various iron oxide, silica and silicate phases. Chrysotile asbestos is unaffected by heat up to 500 degrees C but above this temperature is transformed to forsterite: above 800 degrees C the transformation is rapid. Quantitative estimates, based on X-ray diffraction, of the 'asbestos' content of the heat-treated samples provides information on the rate at which the breakdown of asbestos occurs at different temperatures. For crocidolite and chrysotile the relationship between percentage remaining 'asbestos' and heat treatment is much as would be predicted but for amosite there is an apparent increase in 'asbestos' content to over 100% around 700 degrees C. This coincides with the formation of oxy-amosite.