PRODUCTION OF SILICON FOR SOLAR CELLS: PRESSURE EFFECTS ON THE SiF4-Na REACTION AND ITS PRODUCTS.

Article abstract of DOI:10.1016/0025-5408(81)90012-X

The effects of the SiF//4 pressure on the SiF//4-Na reaction and its products have been studied. Constant volume batch experiments were carried out in which Na, preheated to 250 degree C, was exposed to SiF//4 at different pressures. Because of the exothermic character of the reaction, the temperature at the reaction zone peaks to a maximum that depends on the pressure of SiF//4. At SiF//4 pressure around 1 atm, the temperature maximum reaches the highest values, near the melting point of silicon (1412 degree C). Depending on the SiF//4 pressure, three distinct reaction behaviors and corresponding reaction products can be identified. The pressure range of more interest for practical application of the SiF//4-Na reaction lies between 350 and 760 torr. At these pressures, clear segregation between the Si and NaF phases is observed and the average Si particle size is 0. 2 mm.