GB674324A - Improvements in or relating to graphite articles - Google Patents

Abstract

An impregnating material for graphite articles such as tubes, electrolysis, electrodes and moulds for glass articles, comprises a partially condensed organopolysiloxane having between 1 and 1.9 organic radicals (attached through carbon to silicon) per silicon atom, or a dispersion or solution of such an organopolysiloxane, e.g. in toluene. The resin is subsequently hardened by baking to render the graphite water and oxidation resistant. The partially condensed organopolysiloxane is obtained by hydrolysis and condensation of one or more compounds having the formula RxSiQ4-x where each R is an alkyl radical having, e.g. from 1 to 12 carbon atoms, or an aryl radical, e.g. phenyl, tolyl, diphenyl, and Q is halogen or alkoxy. The degree of condensation may be controlled by the time and temperature of heating. The compounds may be hydrolysed in the presence of a solvent for the condensatiin product. In examples: (1) a mixture of methylphenylsilicon dichloride and phenyl silicon trichloride was added dropwise at 25 DEG C. to a mixture of water and toluene. The resulting toluene solution was washed and the toluene distilled off under vacuum to give a liquid siloxane which was then bodied by heating to 150-170 DEG C. until a 50 per cent solution in toluene had a viscosity of 50-100 c.s.; (2) similar to (1) using in addition methyl silicon trichloride; (3) a mixture of methyl triethoxy silane and trimethylethoxysilane was added to a mixture of toluene and a 0.67 normal solution of oxalic acid at 25 DEG C. The mixture was then heated to 70 DEG C. for five hours, toluene added and the mixture washed with water until acid-free. The mixture was then distilled to remove sufficient toluene to give a 60 per cent solution of the resin; (4) similar to (3) using hydrochloric instead of oxalic acid; (5) a mixture of trimethyl ethoxysilane, phenyl silicon trichloride and methyl silicon trichloride was added to a mixture of water, toluene and isopropyl alcohol at below 25 DEG C. The mixture was refluxed for 2 hours, washed and distilled to give a 60 per cent resin solution in toluene; (6) a mixture of methyl phenyl silicon dichloride, phenyl silicon trichloride and methyl silicon trichloride was added to a mixture of water and toluene at below 30 DEG C. During the addition the water was replaced five times to remove acid, the final hydrolyzate being washed and distilled to 85-90 per cent solids. The concentrate was bodied till a 50 per cent solution had a viscosity of 120 c.p.; (7) a mixture of dimethyl silicon dichloride, phenyl silicon trichloride and methyl silicon trichloride was hydrolysed, washed and bodied as in (2) and the bodied resin diluted with toluene to give a 50 per cent solution having a viscosity of 200 c.p. Examples are given of the impregnation of graphite articles with resins described in the other examples, with subsequent drying to remove solvent and baking to cure the resin. The impregnation and baking steps may be repeated. Specification 646,023 and 646,024, [Group III], are referred to.ALSO:Graphite articles, e.g. tubes, moulds for moulding glass, and electrolysis electrodes, are impregnated with material comprising a partially condensed organopolysiloxane having from 1 to 1.9 organic radicals (attached to silicon through carbon atoms) per silicon atom, (see Group IV (a)), the siloxane finally being hardened by baking. The impregnant may be the siloxane itself, or a dispersion or solution of the siloxane in, e.g. toluene, the impregnated graphite being dried if necessary, to remove solvent, before baking. The impregnation treatment may be repeated if complete pore blocking is required. Impregnation may be assisted by evacuation before immersion in the liquid, and application of air pressure after immersion. The treated graphite is oxidation and water resistant. The graphite articles may be made by moulding a mixture of petroleum coke and a tar or pitch binder and graphitizing at above 2000 DEG C. This produces a porous graphite. Specification 646,023 and 646,024 are referred to.