Mechanism of ZrB2 Formation in Al–Si Alloy and Application in Si Purification

The formation of ZrB2 particles in Al–Si alloys not only improves the properties of the Al–Si alloy but also helps remove B from Si for the preparation of solar-grade Si. A thermodynamic study was performed to identify the mechanism of ZrB2 formation in Al–Si alloys. The precipitated B-bearing particles, i.e., ZrB x , were determined to be ZrB2 via electron probe microanalysis. The composition of the Al–Si alloy, which could form stable ZrB2 particles, was determined by measuring and calculating the equilibrium concentrations of Zr and B and the solubility products of ZrB2 in a Si-saturated Al–Si alloy at different temperatures. Thereafter, the segregation coefficients of B between solid Si crystals and the Si-saturated Al–Si melt with and without Zr addition were estimated thermodynamically. The mechanism whereby the B removal from Si was enhanced with Zr addition was as follows: the Zr not only reduced the concentration of B in the molten Al–Si but also significantly reduced the segregation coefficient of B between the solid Si and Si-saturated Al–Si melt.