THE SULFIDATION OF MANGANESE AT LOW SULFUR PRESSURES AT 700-950-DEGREES-C

The kinetics of manganese sulfidation has been studied in H2-H2S gas mixtures as a function of temperature (973-1223 K) and sulfur pressure (7 x 10(-9) to 3 x 10(-4) Pa), using a thermogravimetric technique. The sulfidation of manganese at low pressures follows the parabolic rate law similar to the behaviour at high sulfur pressures (10(-4) - 10(5) Pa), although an initial nonparabolic incubation period, longer at lower sulfur pressures, was observed. The sulfidation rate constant increased with sulfur pressure and temperature according to the following empirical equation: k(p) = const P(S2)1/n exp(-E/RT) However, in disagreement with the results at high sulfur pressures, the exponent 1/n and the activation energy changed considerably with temperature and sulfur pressure. The results are analyzed in terms of a point-defect model of the single corrosion product-MnS-and of the possibility of a doping effect of MnS by hydrogen.