ANALYSIS OF SOOT AND SOOT PRECURSORS BY UV-VISIBLE SPECTROSCOPY

Optical properties of carbon materials are importan t signatures of their structure/composition. In particular, the UV-Visibl e absorption has shown to be a very powerful diagnostic tool for investigating the structural characteristic of carbonaceous species. Recently, a reconstruction me thod of UV-Visible spectra has been developed for discriminating the contribution of different molecular weight aromatic species to the spectral properties of carb onaceous species (soot and soot precursors) deposited on quartz substrate inserted along a fuel-rich premixed ethylene flame. In this paper, this diagnostic tool was further refined and applied to soot and soot precursors deposited along a methane flame to show the reliability and sensitivity of the technique to small differences o ccurring in the molecular weight distribution and aromatic nature of the carbonaceou s species for effect of the fuel identity. The spectral properties of flame-formed carbonaceou s species deposited along a premixed methane flame and separated on a very wide molecular weight range, from 200 to 1E11u, by Size Exclusion Chromatography, wer e analyzed by on-line UV- Visible spectroscopy. According to recent studies, it was found that to different size components correspond different spectral features. The optical band gap and the UV peak position of each MW-segregated fraction were e valuated by means of a spectral reconstruction procedure, to get details on the car bon network structure in terms of sp 2 and sp 3 sites and size and stacking of the aromatic units. By comparing the results obtained for the methane f lame with those previously obtained in the ethylene flame it was shown that th e chemical environment in which soot precursor are formed, in turn depending on the fuel identity and combustion conditions, affects the internal structure of soot and the graphitization process.