Raman spectroscopic characterisation of inorganic fibres and particles and their coverage by wetting agents
Inorganic fibres especially asbestos have been widely used as a raw material in the construction industries. However, asbestos is now recognised as a carcinogenic material. Therefore, asbestos removal is being widely undertaken. But the hazards increase at this stage as the material is disturbed. Dry removal was found to be an exhausting operation producing a high concentration of fibres. The spraying or injection of wetting agent into the material reduces the hazard associated with the removal process by aggregating the fibres together. The airborne concentration of fibres is then considerably reduced. Raman microspectroscopy has been shown to be a very powerful technique for the identification of micrometer-sized fibres and particles, with little or no sample preparation. Such spectra are sensitive to the composition of the material and can often be used to distinguish between similar species. Raman microscopy also provides important information about surface coverage of such materials with a spatial resolution between 2 and 4 um. Raman spectra were obtained from five asbestos reference standards in comparison with four non-fibrous analogues. The different species such as amosite, anthophyllite, chrysotile, crocidolite and tremolite gave distinct spectra. There were no very distinct differences between the spectra of asbestos fibres and their non-fibrous forms except sometimes in the v(OH) stretching region or band width in the case of tremolite. The reference spectra have been used for identification of known and unknown (industrial samples) fibres on cellulose filters. Moreover, other inorganic particles on cellulose filters have been identified. The discrimination between pure diesel and coal particles on quartz filters and the identification of gunshot residues on paper substrates were also successfully achieved. The coverage of wetting agents on the surface of inorganic fibres connected with asbestos removal operations have been also investigated. Basic laboratory experiments were undertaken. Several inorganic fibres such as man made and asbestos fibres as well as calcium silicate were wetted using different processes: spraying, dipping and capillary adsorption in order to measure the distribution of wetting agents on individual fibres. Insulation materials, usually composed of calcium silicate and asbestos fibres from asbestos removal sites, were collected and also analysed by Raman microspectroscopy. Finally, the effectiveness of suppressing dust was measured on wet industrial samples using a rotating drum tester and the data correlated with Raman measurements.