GB564060A - Improvements relating to the treatment of zirconium oxide - Google Patents

Abstract

564,060. Zirconium oxide. EVERY, C. E. (Titanium Alloy Manufacturing. Co.). Jan. 8, 1943, No. 410. Drawings to Specification. [Class 1 (iii)] Zirconium oxide for use as an opacifier is prepared by heating with molten caustic soda zirconium oxide containing a small proportion of silica or to which a small proportion of silica has been added, solidifying, leaching out soluble sodium and silicon compounds with water and acid, drying, and calcining. The silica is preferably 2-10 per cent by weight of the zirconia and must be present as such. Silicon carbide present in zirconia produced by some methods may oxidize during the treatment to produce part or all of the necessary silica. Sodium nitrate may be added to aid oxidation, and small amounts of borax. Some. zirconium oxides, for example that described in Specification 544,823, may contain all or part of the silica required. Relatively pure oxides are preferably used, for example those produced by the processes described in U.S.A. Specifications 1,351,091,2,110,733 and 2,168,603 (British Specification 535,011). The mixture of zirconia and silica is milled, preferably to finer than 325 mesh, and added to molten caustic soda, at at least 750‹ C., in the proportion of 2¢ or more parts of caustic soda to 1 of zirconia, preferably about 4:1 by weight. When reaction ceases, the melt is poured out to solidify. It is leached with water, preferably at least 4 parts to 1 of solid, and the washing repeated, finally with dilute hydrochloric acid followed by washing out of acid and acid salts. The product is dried and calcined at 600-800‹ C. The average particle size is 0.5-0.8 micron. , In examples: (1) zirconium oxide, produced by oxidation of the carboxide made from zircon in an electric furnace, and containing 0.7 per cent silicon carbide, is mixed with 5 per cent each of silica, sodium nitrate, and borax, and reacted with caustic soda at 750‹ C. for 45-60 mins. After the leaching, the product is dried at 130 and calcined at 600‹ C. ; (2) the zirconia is made by oxidation of the cyanonitride produced from zircon and contains 4-6 per cent of silica. It is mixed with sodium nitrate and borax and treated as in (1) ; (3) the initial material of (1) is treated to remove all but 0.1 per cent silica and silicon carbide and processed as in (1) except for drying at 140‹ C. Results of enamelling tests compare the opacity or reflectance of treated and untreated zirconium oxides.