Evaluation of Raman Parameters Using Visible Raman Microscopy for Soot Oxidative Reactivity

Soot crystalline structure was evaluated for four soot samples and one carbon black using Raman parameters obtained from first-order Raman spectra. For this work, different numbers of peaks from three to as many as five curves with combined Lorentzian and Gaussian bands were fitted for the spectra, and Raman parameters were compared with soot oxidative reactivity, in order to investigate the correlation between the Raman parameters and the oxidative reactivity for each curve-fitting method. Among these methods, the combination of three Lorentzian-shaped bands at about 1200 (D4), 1360 (D1), and 1580 cm(-1) (G), and one Gaussian-shaped band at about 1500 cm(-1) (D3), which is designated as 3L1G, shows the most consistent results for various Raman parameters with respect to soot oxidative reactivity; amorphous carbon fraction, crystallite size, and distribution of crystallite size are in good agreement with soot oxidative reactivity. Also, crystallite sizes from several empirical formulas using Raman spectroscopy were evaluated for the soot samples investigated, with respect to XRD results. In conclusion, a modified Knight and White's formula using the 3L1G fitting method, L-a = 4.4(A(D1)/A(G))(-1), is proposed to evaluate crystallite sizes of soot samples, which are more comparable to fringe lengths obtained by HR-TEM image analysis than to crystallite sizes by XRD.