IMPROVEMENTS IN OR RELATING TO CERAMICS

摘要

1,217,042. Alumina. WESTERN ELECTRIC CO. Inc. 29 Feb., 1968 [27 April, 1967], No. 9857/68. Heading C1A. Alumina in the form of a thin layer is produced by first forming an alumina slip by intimately mixing together a size graded alumina, i.e. an alumina having a broad particle size range, this alumina having a minimum surface area of 12 m2/gm, a solvent, i.e. a liquid preferably organic which is volatile at temperatures only slightly elevated above the ambient, a binder, i.e. a material which retains the alumina in its cast shape after the solvent has evaporated and which is soluble in the solvent, casting the mixture on to a surface to form a layer and removing the solvent to give an unfired layer. The layer may be fired to give a ceramic product. Preferably the alumina used has a maximum surface area of 16 m2/gm. and the layer is fired for a period of time ranging from 15 mins. to 3 hours at a temperature ranging from 1425- 1550‹ C. The sovlent may be eliminated from the prefired layer by drying for several hours at room temperature. A plasticizer which is compatible with the binder may be added to the mixture and an exemplified combination is a polyvinyl butyral resin and a plasticizer consisting of a mixture of glycol and a phthalate. The solvent may be an azeotropicmixture of two organic liquids one of which is soluble in water; e.g. a mixture of ethyl alcohol and trichlorethylene. The mixture may also include a grain growth inhibitor, e.g. talc, and the alumina required for the composition may be obtained by taking an alumina having a surface area of less than 12 m2/gm. and milling it in the presence of at least a portion of the solvent and a deflocculating agent, e.g. menhaden oil. The surface on which the composition is cast may be cellulose acetate, glycol-terphthalic acid polyester, a fluo-halocarbon film, or chromium plated stainless steel. The dried prefired layer may be cut into the desired shape or shapes before firing and during such firing the shapes may be weighted down by previously fired shapes to prevent warping. The fired product preferably has a maximum grain size of about 1 micron, zero water content, and a Centre Line Average finish on at least one surface of less than 3À5 micro inches.