Processing of refractory oxides in a nonequilibrium plasma.

Abstract

This investigation focuses on the uses of non-equilibrium plasmas to enhance the chemical reactions used in metallurgical process chemistry. The main emphasis of this work was the reduction of TiO₂ and FeTiO₃ in a hydrogen plasma. The plasma was maintained in a single resonant cavity using microwave energy (2.45 GHz). The reaction was monitored for volatile species by a quadrupole mass spectrometer. The extent of reaction during hydrogen reduction experiments was performed using an external standard X-ray diffraction technique. The effect of process variables (absorbed power, chamber pressure, time of plasma solid contact, applied voltages) on the extent of the reactions and the sample temperature were investigated. An investigation into the chlorination of TiO₂ in a chlorine plasma was also performed, however, the numerous side reactions that developed during these experiments made analysis difficult. Attempts were made to identify the volatile species from the mass spectra obtained during the chlorination experiments. The reduction of fused silica as a result of contact with the plasma is also investigated. Thermodynamic calculations suggest that the reduction proceeds by the formation of silane in the plasma; metallic silicon is formed by the subsequent thermal decomposition of silane in a non-oxidizing environment. A mechanism for the formation of silane is proposed. Finally, one proposed use for this technology is presented: The production of oxygen in situ form the lunar soil. Experimental values and thermodynamic data are used to develop a plasma process flow diagram for the production of oxygen. The mining requirements, the hydrogen flow rates and the power demands for this system are compared to more conventional process under consideration for the production of lunar oxygen.