1993 Volume 33 Issue 11 Pages 1150-1158
The in-flight reductions of Fe2O3, Cr2O3, TiO2 and Al2O3 were carried out in the Ar-H2 and Ar-CH4 plasma in order to elucidate the reduction ability of hydrogen and carbon in thermal plasma.
The Ar-H2 plasma reduces Fe2O3 and Cr2O3 to their metals. TiO2 is reduced to Ti2O3 and Ti3O5. Al2O3 is not reduced. The products contain non-spherical and spherical particles, which are quenched and cooled from gas and liquid respectively. The reaction mechanisms are explained as follows, from the experimental observations, the phase diagram calculation and the heat conduction calculation. The oxide particles in the plasma are heated quickly, and then they melt and vaporize. Fe2O3 and Cr2O3 are vaporized as a metallic state in Ar-H2 plasma. They are quenched and precipitated as non-spherical particles of their metals. TiO2 and Al2O3 are vaporized as their suboxides such as TiO, AlO and Al2O. They are precipitated as non-spherical particles and oxidized to stable oxides such as Ti2O3, Ti3O5 and Al2O3 during the cooling. The particles which are not vaporized completely are cooled from liquid phase as spherical particles. The phase diagram calculation is used to predict the quenched phase and the quenched temperature. The results of the heat conduction calculation of the particles in the plasma support this vaporizing and quenching mechanism.
The Ar-CH4 plasma reduces Fe2O3 and Cr2O3 to their metals. Chromium carbide and titanium carbide are obtained from Cr2O3 and TiO2 by this treatment. The mechanisms are induced as follows. Fe, Cr, Ti and Al are vaporized as metallic sates or the suboxides. When they are cooled, Cr and ti make their carbides and Al precipitates as Al2O3. The production of carbides makes it difficult to obtain metals by reduction of oxide with carbon.
