GB1338631A - Refractory laminates and their preparation - Google Patents

Abstract

1338631 Refractory shell moulds E I DU PONT DE NEMOURS & CO 28 May 1971 [25 June 1970 (11)] 18004/71 Heading B5A Refractory layered articles, e.g. shell moulds for casting metals, are formed by alternately dipping a support structure, e.g. a disposable pattern into a bath to form a positively or negatively charged coating thereon and then contacting the coating while still wet with an oppositely charged setting agent until the desired thickness has been built up. The first coating may be (a) a sol of positively charged colloidal inorganic particles, (b) a sol of negatively charged colloidal inorganic particles or (c) a solution of an alkaline ionic silicate. The setting agent may be for (a): negatively charged colloidal inorganic particles, an alkaline ionic silicate, a monofunctional organic acid or salt having an anionic portion containing at least one C 6 -C 24 alkyl group, an organic or inorganic base, a polyfunctional organic or inorganic acid or salt or a polymer latex containing an anionic surfactant and for (b) or (c) positively charged inorganic colloidal particles, a non-polymeric nitrogen-containing cationic organic compound, an organic polymer latex stabilized with a cationic surfactant, a basic aluminium salt of formula Al x (OH) y A z , where x = 1-8, y = 1-20, z = 1-4 and A is an acid anion or a polycationic organic substance. The coated structure is preferably stuccoed with refractory grain during dipping. In a preferred embodiment, one dip bath comprises a slurry of particulate refractory in a sol of negatively charged colloidal silica and the other comprises a slurry of particulate refractory in a sol of positively charged particles composed of a silica core coated with a metaloxygen compound, e.g. alumina.