On mechanism of direct reduction of tantalum, hafnium, zirconium oxides

Chemical and X-ray phases analyses have been used to investigate mainly the initial stages of Ta2O5, HfO2 and ZrO2 reaction with solid carbon. The oxide reduction is accompanied by shift of the solid phase gross-composition over the low boundary of the oxide homogeneity area. According to the equilibrium diagrams of the Me-O state, α-phase (solid solution of oxygen in metal) must appear in this case, which apparently forms under conditions of given experiment too. Obviously, interaction of carbon with it conditions formation of cubic oxicarbide in the final analysis. C3O2 carbon suboxide and CO at relative high temperatures (t >= 1200-1300 deg C) are the probable gaseous products of the reaction. Supposition is made of the carbon oxide dissociation on the oxide surface, as a result of which the atomic carbon detached in the case is the reducer and oxygen is oxidant of the carbon being mixture