Studies of some thermodynamic aspects related to the production of silicon and ferrosilicon

Abstract: This thesis presents a fundamental study on some thermodynamic aspects regarding the silicon and ferrosilicon production. The purity requirements for silicon and ferrosilicon alloys are stringent. In order to achieve a successful and efficient refining of the silicon and ferrosilicon produced by carbothermic reduction, it is of great importance to know the phase relations in the system and to have reliable thermodynamic, kinetic and other physical data for the elements involved.The first part of the thesis includes a study of different phase relationships of the SrO-SiO2 and SiO2-SrO-Al2O3 systems. Experiments were performed to determine the phase relationships at temperatures between 1300 °C and 1625 °C in the binary system and at 1450 °C, 1500 °C and 1600 °C in the ternary system. The present result would be valuable when determining the compositions of the refining slags. A fully liquid slag would ensure favorable kinetic conditions in the refining process.The activities of some metallic elements in the silicon melt were determined in the second part of the thesis. The activities of Sr, Al, Zr and Ca in silicon were experimentally determined at temperatures that varied between 1450 °C and 1600 °C. These activities would provide useful information regarding the process temperature and the design of refining slags.The third part of the thesis covers the study of the activities in a ferrosilicon alloy. The activity coefficients for Al and Ca in FeSi50 were experimentally determined by equilibrating SiO2-Al2O3-CaO slags with ferrosilicon at 1550 °C. The activities obtained would be very useful information for the optimization of the refining process.