KINETIC-STUDY OF THE REDUCTION BY HYDROGEN OF COBALT SPINEL OXIDES WITH LOW CHROMIUM CONTENT

The reduction of Co3-xCr(x)O4 spinel oxides (0 less-than-or-equal-to x less-than-or-equal-to 0,5) by hydrogen, at 250-degrees-C, has been investigated in conditions of chemical control as a function of chromium content, x, in various conditions of prereactional treatment. The reaction involves cobaltous oxide CoO - pure or Cr substituted - as a transient phase. The rate of the reduction of CoO to metal with respect to the spinel reduction was observed to be strongly modified by slight changes in the pre-reactional and reactional protocole. A change of the kinetic regime from linear type to parabolic type was found to occur gradually with increasing Cr content over a limited x range. This and the related decrease of the reaction rate may be a consequence of the limited solubility of Cr in CoO.