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The influence of aliovalent impurities on transport properties of nonstoichiometric manganous sulphide

Mrowec S., Grzesik Z.

Bulletin of the Polish Academy of Sciences. Chemistry

2002

Vol. 50, No. 1

37-49

The influence of chromium and lithium on the manganese sulphidation kinetics has been studied as a function of temperature (973-1273 K) and sulphur activity (10(-1)-10(4)Pa) using a novel microthermogravimetric technique. It has been shown that the sulphidation of Mn-Cr and Mn-Li alloys, like that of pure manganese metal, follows strictly parabolic rate law being thus diffusion controlled. In agreement with the defect model of Mn(1-y)S it has been found that the sulphidation rate of Mn-Cr alloy is higher than that of pure manganese, the reaction rate is pressure independent and the activation energy of this process is lower. This implies that the concentration of cation vacancies in Mn(1-y)S-Cr(2)S(3) solid solution is fixed on the constant level by three-valent chromium ions substitutionally incorporated in the cation sublattice of this sulphide. In the case of Mn-Li alloy, on the other hand, the sulphidation rate is lower than that of pure manganese, and the activation energy is higher. These results can again be explained in terms of doping effect.

Corrosion of nickel aluminide in H2/H2S Gas mixtures.

Godlewska E., Żurek Z.

Inżynieria Materiałowa

1998

R. XIX, nr 4

933-936

Intermetallic compound beta-NiAl was sulphidized in H2/H2S mixtures with sulphur partial pressures raised to a -5th power Pa - 1 Pa at temperatures 1173 and 1273 K. The sulphidation runs, followed thermogravimetrically, were approximately parabolic. The calculated parabolic rate constants were very low and slightly increased with temperature and partial pressure of sulphur. The reaction products were examined by means of X-ray diffraction (XRD), energy dispersive X-ray (EDX) analyses and scanning electron microscopy (SEM). Aluminium sulphide and nickel-aluminium sulphospinel were predominant scale constituents in the applied experimental conditions. The scales were very thin and flaky. Generally two scale layers could be distinguished, the inner one was compact and outer one was discontinuous and consisted of needle-like or plate-like crystals. There was no evidence of internal sulphidation.