Silicon Material Task, part III. Low-Cost Silicon Solar Array Project. Quarterly report No. 2

Abstract

The approach to achieve solar-grade polysilicon at low-cost and high-volume is the reduction of silica with carbon in a plasma reactor. The first quarterly report covered the work performed in raw material selection, analysis and preparation, and included an initial test using a small (10 kW) dc plasma torch. This first attempt to react the silica and carbon was unsuccessful due to insufficient residence time at the reaction temperature. This factor remains the key to continued progress towards proving the feasibility of the plasma process for reduction of silica with carbon. Attempts to solve this problem has been the concerted objective of the effort to date. This continuing phase of the chemistry study concerns itself with raw material preparation and plasma tests conducted using the equipment available at the vendor's facility. Results of large (350-kW) plasma furnace test and tests conducted in a 40-kW dc plasma torch are reported. Theoretical aspects of the reaction chemistry were studied and significant information was derived from thermodynamic data generated using a computer program for the Si--O--C system.