Crystallization of Pure Silicon from Molten Aluminum

Abstract

Recrystallization, that is, purification by solution of an impure material in a suitable solvent and subsequently precipitating a purer phase by evaporation of some of the solvent or by lowering the temperature of the solution, is one of the oldest chemical engineering operations. However, because of the technical problems involved, its application to metallic systems has not been generally realized. Such considerations as operating at fairly elevated temperatures with highly corrosive solutions, the associated problem of working in noncontaminating materials of construction, and the need for adequate techniques for material transfer and product recovery have greatly limited exploration in this area.

A simple thermal convection apparatus, with no moving parts, was developed to carry out the continuous recrystallization of commercial silicon from molten aluminum. At temperatures above the eutectic temperature, this process was found to produce silicon of 99.95+% purity in a single stage.

Ring is with the Lockheed Aircraft Corporation, Sunnyvale, California. R. A. Mercuri is with the Union Carbide Technical Center, Cleveland, Ohio.