Changes in microstructure of metallurgical-grade silicon during heating for fractional melting

Abstract

Fractional melting is a good method of refining metallurgical-grade silicon. It can be used to replace the traditional Siemens process for that purpose. It is important to observe the changes in the microstructure of silicon during heating to increase the efficiency of fractional melting. The microstructures and the chemical compositions of impurity phases in heated samples were observed by using scanning electron microscopy and wavelength dispersive spectroscopy. The affinities among the various impurities were investigated using the Miedema model. Ti and Al had strong affinities with V and Ca, respectively. It is possible to use elements that have strong affinities with B and P to effectively remove B and P from the silicon matrix, which are otherwise difficult to remove because of their high segregation coefficients.