Reduction of titanium dioxide in a nonequilibrium hydrogen plasma

Plasma processing offers improved thermodynamics and kinetics over conventional, thermal processing. In the current work, the reduction of TiO(2) was investigated in a moderate-pressure (p < 46 torr) nonequilibrium 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 TiO(2) at the surface of a packed bed has produced up to 60 pet conversion of TiO(2) to Ti(2)O(3) in only 5 minutes of plasma-specimen contact. While the plasma-assisted reduction occurs at the surface, the reduction of TiO(2) to Ti(50)O(99) within the interior of the bed by diatomic hydrogen establishes a value of P(H2O) that leads to the reoxidation of the Ti(2)O(3). The continued reduction of the surface material by monatomic hydrogen from the plasma balances this oxidation process, and a steady-state condition is established. When the interior of the bed is completely reduced to Ti(50)O(99), the partial pressure of water vapor declines, and further reduction of Ti(2)O(3) at the surface can proceed. It is hypothesized that the reduction process involves the formation of a Magneli-like oxide between Ti(2)O(3) and TiO.