| 摘要 |
1,134,249. Coating metal oxides. BRITISH TITAN PRODUCTS CO. Ltd. 10 Aug., 1967 [25 Oct., 1966; 14 Feb., 1967], Nos. 47832/66 and 7086/67. Heading C1A. Metal oxide particles are coated by forming an aqueous solution of a hydrolysable metal salt, raising the pH until the precipitate forms, heating to redissolve the precipitate, mixing the resulting metal-containing solution with insoluble metal oxide particles, precipitating hydrous metal oxide from the solution upon the particles. In this way titanium dioxide can be coated with alumina. The metal salt preferably contains a monovalent anion, e.g. aluminium trichloride or nitrate but metal salts containing polyvalent anions, e.g. aluminium sulphate, may also be used. The initial aqueous solution conveniently contains 0À5 to 200 grams/litre of the salt. The pH is then raised to 3.8 to 5À0 by adding a watersoluble alkali. The mixture is then heated to 25‹ to 90‹ C. to redissolve the precipitate for 5 to 200 minutes. The solution may then be diluted and the insoluble metal oxide particles suspended in the solution. The pH is slowly raised to at least 5.7 over 0.25 to 10 hours. More alkali is preferably added to give a pH of at least 6.5 over 1 to 3.hours, after which the pH is adjusted to 7 to 8.5. The temperature during the pH adjustments is 10‹ to 50‹ C. The coated metal oxide may be recovered by filtration, decantation or by centrifuging. The hydrous metal oxide may alternatively be precipitated by the passage of an electric current through the suspension and the coated particles recovered by means of electrophoretic separation, or by the simultaneous mixing of the metal oxide particles, the metal containing solution and alkali. |
