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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Sulphur is one
of the most important pollutants in the atmosphere, being one of the main
elements responsible for acid rain. 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.