GB1249365A - Ion exchange strengthening of glasses with lithium vapour - Google Patents

Abstract

1,249,365. Strengthening glass. ANCHOR HOCKING CORP. 11 Dec., 1968 [11 Dec., 1967], No. 58971/68. Heading C1M. An article of a glass containing replaceable Na and/or K ions may be chemically tempered by heating to at least its annealing point, exposing to vapours of at least one lithium compound which will volatilize without decomposition, so as to exchange Na and/or K ions for Li, terminating the exposure to Li-compound vapour, and cooling to a temperature below the annealing point and at least below 800‹ F. in the substantial absence of the vapour. Examples of glasses used are given. The lithium compound may be LiF, LiCl, LiBr, LiI, LiNH 2 (in the absence of water vapour) and/or Li 2 SO 4 . Preferably the exposure is for 1-60 minutes at temperatures corresponding to glass viscosities of 10<SP>10.0</SP>-10<SP>12.6</SP> poises. For soda-lime glasses this is preferably 25-150‹ F. above the annealing point. The exposure may be carried out in a tube 3 heated by coils 4, the glass articles, in this case rods 1, being supported on refractory supports 2. The tube is heated to, e.g., 1100‹ F., and then a boat 8 containing Li compound 9 introduced to carry out the exposure. Alternatively the Li compound may be placed in the tube with the articles and heated simultaneously, exposure of the article to the compound's vapour being substantially prevented by a circulating atmosphere. Sheets, fibres or glass bottles or containers may also be treated by the process of the invention. Sub-atmospheric pressure may be employed in the treatment chamber. In an example (Example 5) glass rods were treated with LiNH 2 while dry N 3 was used to sweep out any water vapour, the treated rods having a brown coloration. Reference has been directed by the Comptroller to Specification 786,951.