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 TiO₂ 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 TiO₂ at the surface of a packed bed has produced up to 60 pct conversion of TiO₂ to Ti₂O₃ in only 5 minutes of plasma-specimen contact. While the plasma-assisted reduction occurs at the surface, the reduction of TiO₂ to Ti₅₀O₉₉ within the interior of the bed by diatomic hydrogen establishes a value of that leads to the reoxidation of the Ti₂O₃. 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 Ti₅₀O₉₉, the partial pressure of water vapor declines, and further reduction of Ti₂O₃ at the surface can proceed. It is hypothesized that the reduction process involves the formation of a Magneli-like oxide between Ti₂O₃ and TiO.