IFEG   20353
INSTITUTO DE FISICA ENRIQUE GAVIOLA
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Characterisation of pure and mixed sulphur compounds by X-ray emission spectroscopy
Autor/es:
PABLO PÉREZ; ALEJO CARRERAS; J. C. TRINCAVELLI
Lugar:
Cabo Frio, Rio de Janeiro, Brasil
Reunión:
Congreso; XI Seminario Latinoamericano de Análisis por Técnicas de Rayos X (SARX 2008); 2008
Institución organizadora:
Comité organizador SARX 2008
Resumen:
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Since its chemical reactivity depends on the oxidation state, the chemical speciation of sulphur compounds is a clue for the study of environmental contamination[1-3]. To this purpose, Kα and Kβ X-ray emission spectra of several sulphur compounds were studied. Sulphur spectrum was observed to depend on the oxidation state; for example, in the case of sodium sulphite and sodium sulphate, where the sulphur oxidation state is 4 and 6, respectively. The spectra used in the present work were measured with a scanning electron microscope LEO 1450VP equipped with a wavelength dispersive spectrometer. Because of the low statistics, the better sensitivity of Kβ peak with the oxidation state could not be used with the required accuracy. Instead, Kα peaks were introduced as a tool for chemical speciation. In order to characterise mixtures with different sulphur compounds, binary samples with different fractions of Na2SO3 and Na2SO4 were prepared, and the modifications on the spectrum were studied as a function of the SIV and SVI concentrations. The experimental spectra I(E) were processed obtaining for each mixture i the parameter ai  which minimises a function c2=S{Ii(E)-[ai IA(E)+(1-ai)IB(E)]}2, where the sum is over all the spectral channels analised and the subindexes A and B refer to each of the two compounds. A calibration curve was obtained by plotting the concentration CA of one of the compounds in the sample as a function of afor all the mixtures prepared. In addition, the dependence of the Kα peak position with the concentration of one of the compounds in the sample was studied. The calibration curve obtained in this second way can be used complementarily to the first method. Finally, the curves were tested with an “unknown” sample (i.e., a sample not used to obtain the calibration curves). The results show that this method can be used for chemical speciation in this kind of samples and could be extended to different mixtures.   Keywords: X-ray spectroscopy; sulphur oxidation states; electron probe microanalysis References: 1. PERINO E., DELUIGI M., OLSINA R., RIVEROS J., “Determination of Oxidation States of Aluminium, Silicon and Sulfur” X-Ray Spectrom., v 31, p. 115-119, 2002. 2. KAVČIČ, M., KARYDAS A., ZARKADAS CH. “Chemical state analysis of sulfur in samples of environmental interest using high resolution measurement of Ka diagram line”, Nuc. Instr. Meth. B, v. 222, p. 601-608, 2004. 3. KAVČIČ, M., DOUSSE, J.-CL., SZLACHETKO, J., CAO, W. “Chemical effects in the Kb X-ray emission spectra of sulfur”, Nuc. Instr. Meth. B, v. 260, p. 642-646, 2007.