Kinetics and mechanism of initial stages of carbon-thermal reduction of ZrO2

The interaction between ZrO2 and black at 1250 deg C to 1550 deg C has been investigated. Among the reaction products, we have found ZrO2 (monoclinic → tetragonal) and oxycarbide ZrCsub(x)Osub(y). It has been demonstrated that the interaction, at least in its initial stages, develops with the gaseous phase (carbon oxides) playing an active role; then it proceeds under the diffusion conditions. In the surface layer of ZrO2, there form anionic tetrahedral vacancies, surrounded by the valence unsaturated atoms. Free octahedral (or arising tetrahedral) vacancies may be filled by carbon atoms. Thus, there arises the gradient of concentration in carbon and oxygen, which is the motive force of the interaction. The incorporation of carbon leads to formation of ZrO2 and, probably, ZrO2Csub(x) first with the tetragonal and then with the cubic lattice. Further incorporation of carbon atoms in the lattice gives rise to formation of cubic oxycarbide ZrCsub(x)Osub(y)