| 摘要 |
To improve the adherence of a vitreous enamel to a ferrous base, the base is coated with nickel-alkali metal oxide crystalline particles in an amount greater than 0.05 grams of dry particles per square foot of base, the enamel being applied to either the coated or uncoated side. The particles may be crystallized on a nucleus of nickelous oxide. Preferably, a nickel-lithium oxide is used, the particles containing lithium oxide in an amount from 0.5 to 12.0% by weight. The nickelous oxide nucleus may comprise 5 to 80% by weight of the particles. The sand-blasted base of steel is coated with an aqueous slurry of the particles in the following mixture, in weight per cent; the particles 5-30; silica (as diluting material) 0-40; bentonite 0-10; sodium carbonate 0-1%; sodium nitrite 0-1%; water, balance. The water is evaporated and the enamel sprayed on and fired. Examples of enamels used are (1) silica 50.8; sodium oxide 19.8; calcium oxide 5.9; aluminium oxide 5.5; boron oxide 18.8; cobalt oxide 0.5; and (2) silica 56.0; feldspar 15.0; borax 12.0; soda ash 7.0; sodium nitrite 5.0; fluorspar 5.0. Both were fired at 1580 DEG F. for 8 minutes. Nickel-alkali metal oxide crystals are prepared as follows: sodium or potassium compounds being possible alternatives to the preferred lithium compounds. A nickel compound such as nickelous nitrate is heated to about 280 DEG F. to melt the same and lithium carbonate dissolved therein. The mixture is heated to 400 DEG to 600 DEG F. for a period of 1 to 10 hours to decompose the nitrates and carbonates and to nucleate the precipitation of fine nickel-lithium oxide crystals, containing, based on the nickel oxide, 0.5 to 12% alkali metal oxide. Heating is then at 1030 DEG to 1080 DEG F. for a period of 1 to 10 hours to obtain crystal growth to the required particle size. Alternatively, the nucleation may be on nickelous oxide particles, about 5 to 80% of finely divided particles being added to the nickelous nitrate and lithium carbonate molten mixture and the same heating cycle used. In a further method, a mixture of nickelous oxide and lithium carbonate is heated to 1200 DEG to 1600 DEG F., preferably about 1480 DEG F., the lithium carbonate melting at a lower temperature so that part of the lithium oxide will be volatized, but part diffuses into the nickelous oxide to form the nickel-lithium oxide crystal structure. Particular examples are given in which 4 parts of the lithium compound are used to 96 of the nickel compound and 2 to 97.5, the rest impurities. |
