Pure silicon can be obtained from Al-Si alloys by a combination of solvent refining and centrifugation. Primary silicon crystals are separated in the form of a foam after centrifugation. A vertical centrifugal separator is used which needs no more effort for further separation since each part of the high and low silicon content is divided automatically into two pieces after centrifugation. This centrifugal method does not use the density difference between two phases as in other methods, but uses the order of solidification in Al-Si alloys. How to make the Si foam, its characteristics including its density and strength, and purity of the extracted Si particles after acid leaching are reviewed.

This study describes the formation of a primary silicon network during separation of an Al‐30% Si melt and the process conditions to make bigger primary silicon crystals. As the crucible rotates in the centrifugal separation, the unfrozen aluminum‐rich phase and small silicon particles are pushed outside through the openings in the silicon network. As a result, primary silicon crystals are separated in the form of a foam after centrifugation. The recovery of the silicon ranged from 13 to 18% depending on the location in the crucible. The size of the primary silicon achieved by changing the cooling rate and quenching temperature during solidification is also measured using a quenching furnace. Primary silicon particles exhibit a coarse, plate‐like morphology, although small star‐like silicon particles are also found in the aluminum‐rich matrix. The fraction of plate silicon decreases, while the fraction of small globular silicon increases with an increasing cooling rate. The thickness of the primary silicon plate also decreases with an increasing cooling rate in the samples quenched at various temperatures during solidification.

Silicon foam and aluminium‐rich solid lump separated by centrifugation during solidification of an Al‐Si alloy, and magnified CT image of a silicon foam (background).

No abstract

The effect of insulators in a Czochralski furnace on the power consumption and the oxygen content in the melts as well as in the Si ingots was studied without considering a radiation shield. The top insulator showed better results than the other two insulators for the power consumption and Si melt temperature. The interface at the center of the melt descended in the all conditions of installing the insulators, and all interfaces were concave down. The oxygen content in the Si crystal decreased as the thickness of insulators was decreased for the top and top-side insulators, while increased for the bottom insulator.