Surface vs. Bulk Chemistry of Pyrolytic Carbon Blacks by SIMS and Raman Spectroscopy

The chemical nature, especially with respect to the surface, of carbon blacks obtained by pyrolysis of used tyres (CBP) is very important for their use as reinforcing filler in rubbers. Both SIMS and Raman spectroscopy were used to investigate the surface and bulk chemistry of CBP obtained by vacuum pyrolysis of used tyres and of commercial robber-grade carbon blacks. Secondary ion mass spectrometry shows, in very good agreement with earlier ESCA investigations, the formation of carbonaceous deposits on the CBP surface during the pyrolysis. A decrease of the pyrolysis pressure significantly reduces the amount of carbonaceous deposits on the CBP surface. The SIMS technique allows one to discriminate between aliphatic and small aromatic compounds, which is very difficult to achieve by ESCA for materials such as carbon blacks. Raman spectroscopy provides information about the degree of structural order in the bulk of carbon black. The Raman spectra of commercial carbon blacks depend on their particle size (surface area) and their structure. Only small differences were found between the Raman spectra of CBP and the commercial carbon black grades initially present in the tyre. Furthermore, the pyrolysis conditions had no significant influence on the Raman spectra. Therefore, the carbon black bulk portion did not change during the pyrolysis. (C) 1997 by John Wiley & Sons, Ltd.