GB1385020A - Solidified silica foam product and process - Google Patents

Abstract

1385020 Solidified silica foam products FIBERGLAS CANADA Ltd 29 Dec 1971 [29 Dec 1970 12 Nov 1971] 60538/71 Heading C1A [Also in Division C3] A solidified silica foam product is prepared from an aqueous solution of a sodium and/or potassium silicate containing a surface-tension depressant and optionally a filler, by foaming the solution by gas entrainment, e.g. with air, introducing into the solution before or after foaming a silicon dioxide polymer forming agent (as defined below) to make the foam rigid and water-resistant, shaping the foamed material and then hardening the shaped product in a polymerization zone under a high relative humidity of at least 80% and under conditions of temperature and, if necessary, pressure or physical containment whereby the shaped product hardens substantially free of damaging contraction or expansion. The required humidity during hardening may be provided by affecting hardening while passing the foamed material through a curing tunnel filled with saturated steam or by hardening in a mold which is either completely filled with foam material so that no moisture can escape or is only partially filled with foam material having an appropriately humidified atmosphere thereon. Contraction during hardening is avoided by maintaining the material at a temperature not more than 10‹ F. below its temperature at the entry to the polymerization zone. Expansion is avoided by use of a temperature not more than 5‹ F. above the entry temperature or by hardening in a mold which is either partially filled with foam and then pressurized or is completely filled. The silica polymer forming agents are alkali metal fluorosilicates; potassium fluoborate; calcium fluoroborate or fluorotitanate; dimetallic inorganic salts, e.g. sodium calcium borates or lithium calcium borates; alcoholates and carboxylic acid salts of polyvalent metals, e.g. tetra alkyl titanates; zinc oxide; magnesium or zinc carbonate; and generally, poly valent metal salts of weak acids having a pk A of at least 1À3, examples being calcium aluminate, tellurite, fluoride, phosphate, pyrophosphate, borate, tungstate, fumarate, maleate, malonate or succinate, magnesium phosphate, barium hypophosphate, aluminium acetate, copper acetate, cadmium tungstate and zinc, aluminium, cobalt or iron borate. Numerous surface tension depressants are given and gelling agents, e.g. triacetin, glycol, alcohols and ketones may be present. Suitable fillers, present preferably in amounts of up to 10% by weight of the final product, are carbon black, titania, diatomaceous earth, silica, burned magnesia, powdered ceramic, and fibres of glass, asbestos or magnesium silicate. The products normally have a dry density of not more than 25 lbs/cu. ft. Reference has been directed by the Comptroller to Specifications 1,334,681 and 1,334,076.