2007 Volume 115 Issue 1343 Pages 434-439
Two kinds of materials, sprayed-on crocidolite and sprayed-on amosite, containing crocidolite and amosite respectively, were treated with aqueous acetic acid solution, the pH of which was adjusted with an ammonium acetate buffer at 5, in order to remove soluble components of cement. The liquids were filtrated with a membrane filter, and the residue collected as crocidolite samples and amosite samples, respectively. The Crocidolite and amosite thus obtained were heated up to 600-1300°C for 1h. Then, power X-ray diffraction (XRD) experiment, scanning electron microscopic (SEM) observation, and thermal analysis (TG/DTA) were carried out for these burned specimens in order to observe the change of the burned materials and melting behaviors together with their thermal properties. In addition, CaCO3 and CaCl2 were mixed with the respective sprayed-on asbestos and sprayed-on crocidolite, and a TG/DTA measurement was conducted on these mixtures. Based on the SEM observation and XRD experiment on the specimens used in the TG/DTA measurements, we tried to decompose the crocidolite and amosite, applying the method of low-temperature decomposition, the applicability of which was previously confirmed in the study on the case of chrysolite. The temperature of the TG/DTA measurement could be raised up to 1000°C, and it became evident that in the cases of specimens where CaCl2 was added, all the asbestos fibers had decomposed, but not in any other specimen. The crocidolite specimen became rounded in shape when it was heated up to 1000°C, and it looked as if it was densified due to burning. CaCO3 and CaCl2 were added to this burned crocidolite, and decomposition of the material after burning was examined. In a DTA thermogram, an endothermic peak was recognized, which corresponds to the formation of a melt of CaCO3-CaO-CaCl2 as summarized in the previous report. Thus it is experimentally verified that burned crocidolite decomposes at high temperatures.