Synthesis of carbides and carbonitrides by carbothermal reduction with oxide intermediates of low volatility

The paper summarizes recent results of lab-scale experiments on the carbothermal reduction of TiO2 and Cr2O3. In both reduction reactions, the carbon particles are consumed and the oxide particles are the precursors of the hard phase that is formed. In the case of the reduction of TiO2 the experiments were focussed on the role of Ti2O3 as an oxide intermediate and on the investigation of the effect of nitrogen on the whole reaction mechanism. Due to its instability in nitrogen-containing atmospheres, Ti2O3 does not appear as an intermediate reaction product if nitrogen is present. Nitrogen is incorporated into the solid phase as cubic TiCxOyNz is formed, its content depending on its partial pressure. Independent of the composition of the starting Cr2O3-C mixture in the reduction, Cr3C2 is the first carbide formed, hypothetically as a protective layer around the Cr2O3 particles.