| 摘要 |
A fired beryllia 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 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 so smooth as to give a reading of not more than 1.0 micro inch (Centre Line Average) when measured with a "Tallysurf" (Registered Trade Mark) tester. The coefficient of thermal expansion of the coating is sufficiently analogous to that of the beryllia film and the adherence is so firm, that after a thermal shock test in which the article is heated to 550 DEG C., cooled to 23 DEG C. in 20 minutes, immersed in liquid nitrogen at -210 DEG C., and then allowed to come to equilibrium at room temperature, no visible defects in the coating or article develop. Tantalum may be sputtered on the glazed film for production of a component for an electric circuit. The beryllia film contains at least 98% BeO 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 wt., BeO, 99.5; MgO, 0.40; Al2O3, 0.075; SiO2, 0.025. 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" (Registered Trade Mark) as a coating of uniform thickness and density. Volatile vehicle is then removed, e.g. by heated forced air drying. The green film 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 1550 DEG C., and is thereafter cleaned. The glaze frit may comprise, by weight: PbO,20-50%; SiO2,30-60% and 10-40% of other ingredients, being: 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. To this frit may be added, e.g. 2-8% kaolin based on kaolin and frit. 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. The following three frit compositions are exemplified in per cent by weight: SiO2 40.7/36.3/35.4; B2O3, 11.1/5.9/5.5; Al2O3, 3.5/4.0/4.0; PbO, 31.6/43.1/44.1; CaO, 9.8/10.4/11.0; Na2O, 1.9/-/-; K2O, 1.4/-/-; MgO, -/0.3/-. Two resulting glaze compositions are: SiO2 37.6/36.2; B2O3, 5.5/5.4; Al2O3, 6.9/4.3; PbO, 40.0/43.3; CaO, 9.7/10.8; MgO, 0.3/-. |
