Method of preparing fumed SiO.sub.2

Details Method of preparing fumed SiO.sub.2 Method of preparing fumed SiO.sub.2

1976-09-20

1977-11-22

Cooper, Jack

Chemistry of inorganic compounds

Silicon or compound thereof

Oxygen containing

423336, 423483, 423484, C01B 3312, C01B 722

Patent

active

040596800

ABSTRACT:
Fluorosilicic acid solutions, which normally undergo decomposition when distilled, thereby creating unwanted forms of SiO.sub.2, are rendered stable during distillation by providing in the fluorosilicic acid solution an amount of HF which is at least about 10 parts of HF per 36 parts of H.sub.2 SiF.sub.6 and an amount of H.sub.2 O which is at least about 54 parts of H.sub.2 O per 36 parts of H.sub.2 SiF.sub.6. The mixture is distilled to remove any excess H.sub.2 O and excess HF that is present, without encountering formation of SiO.sub.2, until an azeotropic solution containing about 36% H.sub.2 SiF.sub.6, about 10% HF and about 54% H.sub.2 O is reached. The ternary azeotrope, being of constant quality and concentration, is more suitable for use in various processes, such as processes for making fumed SiO.sub.2, than H.sub.2 SiF.sub.6 solutions which are not of constant quality or concentration.

REFERENCES:
patent: 3110562 (1963-11-01), Hinkle
patent: 3326634 (1967-06-01), Porter et al.

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