Patent GB-776275-A (GB)
Title: Improvements in or relating to the production of silica
Inventor: DAVIES STANLEY
IPC: C01B33/113
Filed: 1954-04-23
Abstract: Silica white is obtained by mixing aqueous silica gel with a liquid alcohol which contains 5 or more C atoms and is capable of forming with water an azeotropic mixture of minium boiling point and evaporating the water as a vaporous mixture with the alcohol. Preferably the alcohol has a boiling point below 200 DEG C. at atmospheric pressure, the ability to form an azeotrope containing suitably more than 20 per cent water, partial water miscibility at room temperature, and 5-9 C atoms, e.g. n-amyl, iso-amyl, or active amyl alcohols, the mixture known as technical amyl alcohol, cyclo-hexanol, n-hexyl, n-heptyl, n-octyl, or furfuryl alcohols. The gel is preferably obtained by acidifying an aqueous alkali metal silicate solution.  The gel is mixed with alcohol in excess of the amount necessary to form an azeotrope with all the water present, and the slurry is subjected to a conventional distillation, with or without stirring.  If the alcohol is only partially miscible, the evolved vapours are condensed to form two layers and the alcohol layer, after drying, recycled.  The excess alcohol may be distilled under atmospheric or reduced pressure, preferably with stirring, e.g. in a heated ball mill, or the mainly water lower layer from the condensation may be added to the silica containing excess alcohol, and the water/alcohol azeotrope again distilled, and the silica dried in an oven.  Alternatively, the slurry of the aqueous silica gel in the alcohol, heated to above the boiling point of the azeotrope, may be sprayed into a chamber through which a current of hot air passes. The evaporation may be effected preferably at atmospheric pressure. The small amount of strongly held alcohol in the silica white may be removed by ignition to red heat in the air.  The silica white may be used in amount 20-30 per cent as a reinforcing filler for natural or synthetic rubbers, e.g. GR-S or silicone rubber.  An amine, e.g. triethanolamine, cyclohexylamine, dicyclohexylamine, or hexamethylene tetramine, may be added to the rubber, or first milled with the silica white, or added during the preparation of silica white at the stage when the water is removed, but before the excess alcohol is evaporated, to reduce the vulcanization time of the rubber composition.  The silica white may also be used as a varnish flatting agent, in non-slip polishes, and for coating lamp bulbs.ALSO:Silica white for use as a rubber filler is obtained by mixing aqueous silica gel with a liquid alcohol which contains 5 or more C atoms and is capable of forming with water an azeotropic mixture of minimum boiling point and evaporating the water as a vaporous mixture with the alcohol.  Preferably the alcohol has a boiling point below 200 DEG C. at atmospheric pressure, the ability to form an azeotrope containing suitably more than 20 per cent water, partial water miscibility at room temperature, and 5-9 C atoms, e.g. n-amyl, iso-amyl, or active amyl alcohols, the mixture known as technical amyl alcohol, cyclo-hexanol, n-hexy, n-heptyl, n-octyl, or furfuryl alcohols.  The gel is preferably obtained by acidifying an aqueous alkali metal silicate solution.  The silica white may be used in amount 20-30 per cent as a reinforcing filler for natural or synthetic rubbers e.g. GR-S or silicone rubber. An amine, e.g. triethanolamine, cyclohexylamine, dicyclohexylamine, or hexamethylene tetramine, may be added to the rubber, or first milled with the silica white, or added during the preparation of silica white to reduce the vulcanization time of the rubber composition.  In examples 4, 5 and 6 compositions disclosed, include smoked sheet rubber, zinc oxide, stearic acid, sulphur, silica white, and cyclohexyl benzthiazylsulphenamide, with or without triethanolamine or tetramethyl thiuram disulphide.  The compositions are vulcanized at 141 DEG C.