Raman micro-spectroscopy identifies carbonaceous particles lying on the surface of crocidolite, amosite, and chrysotile fibers

Abstract

Micro-Raman spectroscopy has been applied on UICC (Union for International Cancer Control’s) crocidolite and amosite from South Africa and on UICC chrysotile from Canada. Under Optical Microscope (OM), the surface of the fibers was often characterized by areas, micrometric in size, appearing dark. The laser beam was successively focused on areas of the same sample showing different optical contrasts. On the bright zones, Raman spectra peculiar for crocidolite, amosite or chrysotile were recorded. When dark areas were optically identified, the laser beam was addressed onto these regions and, in the Raman patterns, in addition to the bands produced by the mineral fiber, bands ascribing to substituted carbonaceous phases were observed. These bands were lying in the 4000–1100 cm-1 spectral range. On the basis of the shape of the bands and their relative intensities, suggestions about the order-disorder of the carbonaceous particles could be proposed, and they appeared more ordered on amosite than on crocidolite and chrysotile. From the exposed data, crocidolite and amosite fibers from South Africa, and chrysotile fibers from Canada, largely used in industry in the past, are characterized by many carbonaceous micrometric particles, lying on the fiber surfaces. Based on the noxiousness of the carbon particles on human health, their presence on asbestos fibers may play a role in increasing the carcinogenic effects of the analyzed fibrous minerals.