| 摘要 |
A fired alumina ceramic film has on at least one surface a glaze coating which does not soften below 700 DEG C. The film is not more than 0.1 inch thick and has a camber less than 0.004 inch/inch in any direction in the plane of the film. The coating is bubble free and penetrates the surface of the film and is firmly anchored thereto. The coating is uniform with a weight of 0.08-0.12 g./in.2, and is substantially free of the oxides of K and Na. The surface of the coating is free of pits and cracks and so smooth as to give a reading of not more than 1.0 micro-inch (Centre Line Average) when measured with a "Tallysurf" tester. The coefficient of thermal expansion of the coating is sufficiently analogous to that of the alumina film and the adherence is so firm, that after at least three boiling-water/icewater immersion cycles no cracking or spalling of the glaze occurs. Tantalum may be sputtered on the glazed film for production of a component for an electric circuit. The alumina film contains at least 90% alumina by weight, and may also contain, e.g., SiO2, manganese oxide and alkaline earth oxides. An example of the composition is in per cent by weight, Al2O3, 95.5; SiO2, 3.2; MgO, 1.1; CaO, 0.2. Raw material is ball milled with an organic binder, and the slip is then de-aired and applied to a smooth carrier, e.g. "Cellophane" (Trade Mark) as a coating of uniform thickness and density. It may then be stamped with score lines or holes for separation or perforation of the film after glazing. It is then fired at a maximum temperature of 3050 DEG F., and is thereafter cleaned. The glaze frit may comprise, in per cent by weight: PbO, not more than 40; SiO2, 30-60; bivalent metal oxide, e.g. alkaline earth oxide, at least 5%; B2O3, at least 3%; oxides of Na and K, not more than 5% in total; a composition exemplified is: SiO2, 40.7; B2O3, 11.1; Al2O3, 3.5; PbO, 31.6; CaO, 9.8; Na2O, 1.9; K2O, 1.4. To this frit may be added, e.g., 8% kaolin. Based on the weight of inorganic solids, 55% water, 3% glycerine and 1.5% methyl cellulose are admixed, and the whole milled to form a slip, which may be applied, e.g. by spraying. The article is then air-dried and fired in air at 1020 DEG C. |
