GB891170A - Improvements in or relating to the production of materials containing calcium silicate more especially for thermal insulation - Google Patents

Abstract

A calcium silicate hydrate is obtained by reacting an aqueous dispersion of pulverized, unset, portland cement (or cementitious substance, e.g. blast furnace slag or fuel ash having a lime to silica ratio similar to portland cement) with a solution of an alkali metal silicate or a silica sol with continuous agitation under conditions such that the final and maximum temperature is between 40 DEG and 100 DEG C., preferably 55 DEG C., and then filtering. Sodium or potassium silicate may be used. When the calcium sulphate content of the cement is low, calcium sulphate in an amount of at least 3,5% by weight of the cement is dissolved in the water in which the reaction occurs. The proportions of lime (CaO) and total silica (SiO2) in the cement and in solution are such that the calcium silicate hydrate has the formula 3(CaO).2(SiO2).x(H2O), where x is at least 10. The wet filter cake then may be moulded and heated at 175 DEG C. or more under pressure in an atmosphere of saturated steam to obtain a rigid, indurated product. Finely-divided silica, e.g. ground quartz, is added to the reaction mixture before filtration in an amount so that the calcium silicate of the rigid product has the formula (CaO)5.(SiO2)6.(H2O)y, where y is variable. Non-reactive reinforcing material, e.g. asbestos fibre, mineral or glass wool, expanded clay, perlite, vermiculite, slags or sintered fuel ash, may be included in the original dispersion of cement which is reacted with the silicate solution. In one example, cement, quartz and sodium silicate are reacted in aqueous dispersion, and the product filtered, heated in steam, dried and ground for use as an insulating filler or filter aid, and in other examples fiberized amosite asbestos and chrysotile asbestos, diatomaceous earth and slaked lime are included, and the filter cake is moulded before being heated in steam to produce moulded thermal insulating pipe sections and moulded thermal insulating wallboards.ALSO:A cementitious composition is obtained by reacting an aqueous dispersion of pulverized, unset, portland cement (or cementitious substance e.g. blast furnace slag or fuel ash having a lime to silica ratio similar to portland cement) with a solution of an alkali metal silicate or a silica sol with continuous agitation under conditions such that the final and maximum temperature is between 40 DEG and 100 DEG C., preferably 55 DEG C., and then filtering. Sodium or potassium silicate may be used. When the calcium sulphate content of the cement is low calcium sulphate in an amount of at least 3,5% by weight of the cement is dissolved in the water in which the reaction occurs. The proportions of lime (CaO) and total silica (SiO2) in the cement and in solution are such that a calcium silicate hydrate is obtained having the formula 3 3(Ca0). 2(SiO2)x(H2O) where x is at least 10. The wet filter cake then may be moulded and heated at 175 DEG C. or more under pressure in an atmosphere of saturated steam to obtain a rigid, indurated product. Finely divided silica, e.g. ground quartz, is added to the reaction mixture before filtration in an amount so that the calcium silicate of the rigid product has the formula (CaO)5.(SiO2)6.(H2O)y where y is is variable. Non-reactive reinforcing material, e.g. asbestos fibre, mineral or glass wool, expanded clay, perlite, vermiculite, slags or sintered fuel ash, may be included in the original dispersion of cement which is reacted with the silicate solution. In one example cement, quartz and sodium silicate are reacted in aqueous dispersion, and the product filtered, heated in steam, dried and ground for use as an insulating filler or filter aid, and in other examples fiberized amosite asbestos and chrysotile asbestos, diatomaceous earth and slaked lime are included, and the filter cake is moulded before being heated in steam to produce moulded thermal insulating pipe sections and moulded thermal insulating wallboards.