Preparation of Alkali-substituted β -Alumina by lmmersion in Aqueous Solution of Alkali Hydroxides

Abstract

The preparation method of alkali-substituted β -alumina from Na β -alumina, the fusion cast brick, Marsnite U, of Asahi Glass Co., was described. Since direct ion exchange of Na ion in Na β -alumina with other alkali ions using alkali aqueous solution is inhibited by a water adsorbed on the surface of Na β -alumina crystal, Na ion in β -alumina was replaced, in the first place, by (H3O)+ through the immersion of Na β -alumina in concentrated sulfuric acid. When Na β -alumina powder of 1-2mm in diameter was treated with concentrated sulfuric acid at 240 C, the replacement of Na ion by (H3O)+ was not complete because of the formation of aluminum sulfate. When Na β -alumina powder finer than 325 mesh was used, the complete replacement was obtained by 20 minutes' treatment at 240 C. On the other hand, the replacement of (H3O)+ in β -alumina by K ion and Li ion through the immersion of H β -alumina in the saturated aqueous potassium or lithium hydroxide solution, was favorable with the treatment at 240 C for 2 hours. H- and alkali-substituted β -alumina obtained by the above described exchange reaction was identified by DTA, TGA and X-ray diffractometry.