Abstract: Highly pure silicon is produced by refining impure silicon to remove deleterious impurities by contacting a melt of the impure silicon with a reacitve gas which comprises a gaseous halogen compound mixed with steam, hydrogen or a stem/hydrogen mixture.

Abstract: A material resistant to high temperature melts of metal and salt which comprises a composite material containing silicon nitride, silicon oxynitride, silicon dioxide and silicon prepared by(a) suspending silicon powder in SiO.sub.2 sol to form a pourable mass,(b) molding a workpiece from said mass,(c) hardening the molded workpiece, and(d) nitriding the hardened workpiece in a nitrogen atmosphere to form silicon nitride and silicon oxynitride to a degree that SiO.sub.2 and elemental silicon remain detectable in the nitrided workpiece,is useful as the material of construction for crucibles and tools for confining, handling and treating melts of metals or salts.

Abstract: In the process wherein a titanium-containing material is subjected to react with sulphuric acid to form a solid reaction mass from which the titanium values are recovered in solution by digestion with water or dilute sulphuric acid leaving behind a reaction residue and the reaction residue is thereafter treated to recover at least part of the titanium contained therein, the improvement wherein the treatment of the reaction residue is effected by contacting with sulphuric acid of a concentration greater than 86% a mixture by weight comprising about 5 to 95% of the reaction residue and 95 to 5% of a slag having a TiO.sub.2 content 60% by weight and a Ti(III) content of about 5 to 40% by weight, and thereafter eventually adding water, steam or dilute sulphuric acid to the mass to start the reaction.