GB1232102A - - Google Patents

Abstract

1,232,102. Strengthening glass. CARL-ZEISSSTIFTUNG, [trading as JENAER GLASWERK SCHOTT & GEN]. 28 June, 1968 [1 July, 1967], No. 31121/68. Heading C1M. In a process for improving the mechanical strength of glass by incorporating alkali metal ions into the glass to obtain a desired stress profile, a readily vaporizable and decomposable compound, containing the ions, is heated first to vaporize the compound and then further heated to decompose the compound, whereby the ions are deposited on the glass which is heated during deposition so that the ions diffuse into the glass by heat treatment below the softening point of the glass, the treating temperature depending on the size of the ions. Thus, if the ions to be diffused have a smaller ionic radius than the alkali metal ions in the glass, the treating temperature lies between transformation temperature and softening point; if those ions are larger than the alkali metal ions of the glass, the treatment is effected below transformation temperature. It is preferred to use an organic alkali metal compound, e.g potassium citrate, dipotassium tartrate, sodium formate. The alkali metal compound C is placed in a heated chamber B and heated to a temperature T 1 , e.g. 200‹ C. for potassium citrate. The vapours pass through a pipe D into a treatment chamber E containing a glass article F to be treated. This chamber is heated to above or below the transformation temperature of the glass, depending upon the ions to be incorporated. Using potassium citrate vapour, chamber E is heated to 600‹ C., the vapour decomposing and depositing on the surfaces of article F. An exhaust port G is provided. Vapour is passed into the chamber for 30 minutes, the temperature maintained at 600‹ C. for a further 20 minutes, whereafter the article is cooled. Other examples are given with different temperatures of operation, including the incorporation of lithium ions.