A Raman measurement scheme for accurate compositional analysis of dark-colored sample by minimizing laser-induced sample degradation: Determination of Fe3O4 concentration in sintered ores.

ABSTRACT

An effective and rapid Raman measurement scheme to determine Fe3O4 concentration in sintered ores was explored. Because sintered ores are brownish-black materials that easily absorb laser photons, accurate quantitative analysis requires obtaining an Fe3O4 peak with a high signal-to-ratio by reducing the possibility of local sample heating and degradation. For this purpose, a wide area coverage (WAC) Raman scheme with a laser-illumination diameter of 1 mm was adopted to decrease the laser power per area (LP/A) on each sample. The sintered ore sample was also wetted with water to reduce the chance of further heating by the laser. The combination of the WAC scheme and water-wetting allowed to increase the laser power during sample measurement, and the subsequent intensity (as well as the signal-to-noise ratio) of the Fe3O4 peak was elevated compared with both that measured by a Raman microscope yielding a higher LP/A and without water-wetting of the sample. In the Raman spectra of 93 real sintered ore samples measured using the proposed scheme, the ratio of Fe3O4 and Fe2O3 peak areas correlated closely (R2 = 0.94) with Fe3O4 concentration determined by titration. The demonstrated scheme is practical when Raman spectroscopy is employed for compositional analysis of dark and highly photon-absorbing samples.