Impurity phases and their removal in Si purification with Al–Si alloy using transition metals as additives

Abstract

In order to discuss the effects of transition metals such as Zr, Hf, and Ti on the removal of impurities (B, P, Fe, Al, Ca, Ti, V, Cu, Ni, Mn, Zr, and Hf) in the purification of metallurgical-grade Si (MG-Si) with Al–Si alloy, the impurity phases formed after solidification were investigated by electron probe microanalysis (EPMA) and their removal by acid leaching was performed. EPMA investigation showed that β-Al5FeSi was the main impurity phase aside from Al in the sample without additives. However, after adding Zr, Hf, or Ti, the ZrSi2, HfSi2, or TiSi2compound dissolved in small amounts of Al was the most observed phase besides β-Al5FeSi and Al. Impurities such as V, Ni, and Mn were more likely to coexist with β-Al5FeSi when Hf or Zr was employed as the impurity getter. However, V preferentially coexisted with TiSi2 when Ti was added. The leaching results showed that the addition of Zr, Hf, or Ti significantly enhanced the extraction of B and slightly enhanced that of other impurities. The added Zr, Hf, and Ti were eliminated efficiently with the other impurities, reaching extraction ratios of 99.998%, 99.9994%, and 99.997%, respectively.