REDUCTION OF TITANIUM-DIOXIDE IN A NONEQUILIBRIUM HYDROGEN PLASMA

Plasma processing offers improved thermodynamics and kinetics over con ventional, thermal processing. In the current work, the reduction of T iO2 was investigated in a moderate-pressure (p < 46 torr) nonequilibri um hydrogen plasma at temperatures below 1273 K; the effect of plasma power, plasma pressure, time, and applied voltage on the extent of the reduction was examined. Reduction of powdered TiO2 at the surface of a packed bed has produced up to 60 pet conversion of TiO2 to Ti2O3 in only 5 minutes of plasma-specimen contact. While the plasma-assisted r eduction occurs at the surface, the reduction of TiO2 to Ti50O99 withi n the interior of the bed by diatomic hydrogen establishes a value of P-H2O that leads to the reoxidation of the Ti2O3. The continued reduct ion of the surface material by monatomic hydrogen from the plasma bala nces this oxidation process, and a steady-state condition is establish ed. When the interior of the bed is completely reduced to Ti50O99, the partial pressure of water vapor declines, and further reduction of Ti 2O3 at the surface can proceed. It is hypothesized that the reduction process involves the formation of a Magneli-like oxide between Ti2O3 a nd TiO.