Process feasibility study in support of silicon material. Task I. Quarterly technical progress report (XII), June--August 1978

Abstract

Major activities during this reporting period were devoted to process system properties, chemical engineering and economic analyses. On analyses of process system properties, major activities centered on properties of silicon tetrachloride, the source material for several alternate processes under consideration for solar cell grade silicon. The following property data are reported for silicon tetrachloride: critical constants, vapor pressure, heat of vaporization, gas heat capacity, liquid heat capacity, density, surface tension, gas viscosity, liquid viscosity, gas thermal conductivity, liquid thermal conductivity, heat of formation and free energy of formation. In the viscosity investigation, a constant volume glass viscometer was fabricated and assembled for the measurement of gas viscosity values of silicon source materials from 30/sup 0/C to 350/sup 0/C. A description of the apparatus and the experimental procedure, and a discussion of the calculation of the viscosity values from the data is presented. Major activities were continued on the Union Carbide Silane Process (Case C-Revised Process) involving an improved arrangement of major process equipment and operating conditions. The preliminary process design was completed including raw material usage, utility requirements, major process equipment list and production labor for a plant to produce 1000 MT/y of solar cell gradesilicon. The silicon product is produced by pyolysis of silane in the process. Cost analysis was initiated for the completed preliminary process design for the Union Carbide Silane Process (Case C-Revised Process). In current activities, estimates are being prepared for plant investment ($million for 1000 MT/y) and product cost ($/KG Si) for the process to produce silicon by pyrolysis of silane.