Patent GB-690888-A (GB)
Title: Compositions comprising organopolysiloxanes and silica gels
Filed: 1951-01-18
Abstract: A composition for use as a dielectric sealing material, e.g for sparking plug terminals, which will not flow after being subjected to mechanical shear, is made by replacing the water in a silica hydrogel with a water miscible organic solvent and then replacing the organic solvent with a liquid polysiloxane having a viscosity of not less than 50 cs. at 25 DEG  C., and having between 1.9 and 2.1 hydrocarbon radicals per silicon atom, at least 50 per cent of the radicals being methyl and the remainder phenyl.  The initial hydrogel has 1 to 35 per cent silica.  The composition has from 1 to 35 per cent of silica, based on the weight of the composition.  Other ingredients which may be present are aluminium, iron, copper and titanium oxides (in the form of co-gels with the silica), and suspensoids such as silica, titanium oxide, clay, kaolin, mica, talc, graphite, diatomaceous earth and Fuller's earth.  The suspensoids are preferably incorporated when making the hydrogel, being added to the sol after the silicate solution has been neutralized and before setting to the hydrogel. The siloxane may be added as a solution to the organo-gel, particularly if of high viscosity, the solvent being distilled off.  If the water-miscible solvent is not compatible with the siloxane it may first be replaced by a compatible solvent which is then replaced by the siloxane.  The siloxane may be added to the silica organo-gel and the solvent distilled off, or the solvent extracted by washing with siloxane.  The composition may be milled to improve its uniformity and more siloxane added at this stage if required for thinning.  Water-miscible solvents specified are the lower alcohols, ketones, ethers and amines.  Siloxane solvents specified are chloroform, carbon tetrachloride, toluene, benzene, ethers and petroleum ethers.  Several examples of gels according to the invention are given together with figures for penetrometer readings, bleed, flow after working, arc resistance and dielectric strength.  Comparable figures are given for a siloxane/aerogel composition.  Specification 605,036 is referred to.ALSO:A composition for use as a dielectric sealing material, e.g for sparking plug terminals, which will not flow after being subjected to mechanical shear, is made by replacing the water in a silica hydrogel with a water-imiscible organic solvent, and then replacing the solvent with a liquid polysiloxane having a viscosity not less than 50 c.s. at 25 DEG C and having between 1.9 and 2.1 hydrocarbon radicals per silicon atom, at least 50 per cent of the radicals being methyl and the remainder phenyl.  The initial hydrogel has from 1-35 per cent silica and the final composition also has from 1-35 per cent silica.  Other ingredients which may be present are aluminium, iron, copper and titanium oxides (in the form of cogels with the silica), and suspensoids such as silica, titanium oxide, clay, kaolin, mica, talc, graphite, distanaceous earth and Fuller's earth.  The suspensoids are preferably incorporated when making the hydrogel, being added to the sol after the silicate solution has been neutralized and before setting to the hydrogel.  The siloxane may be added as a solution to the organogel, particularly if of high viscosity, the solvent being distilled off.  If the water-imiscible solvent is not compatible with the siloxane it may first be replaced by a compatible solvent which is then replaced by the siloxane.  The composition may be milled to improve its uniformity and more siloxane added at this stage if required for thinning. Water-miscible solvents specified are the lower alcohols, ketones, ethers and amines.  Siloxane solvents specified are chloroform, carbon tetrachloride, toluene benzene, ethers and petroleum ethers.  Several examples of gels according to the invention are given together with figures for penetriometer readings, bleed, flow after working, arc resistance and dielectric strength.  Comparable figures are given for a siloxane/aerogel composition.  Specification 605,036, [Group IV(a)], is referred to.