Preparation and mechanical behaviour of some chemically strengthened lithium magnesium alumino-silicate glasses

Abstract

Chemically strengthened lithium magnesium alumino-silicate glasses have been prepared by ion-exchange in sodium nitrate at 385° C, and the stress profiles of the resultant materials have been measured using the scattered light and etching technique. Unusual stress profiles have been obtained for some of the materials, with the outermost layers of the surface being in tension, rather than compression. This effect can be eliminated, however, by addition of Na₂O to the glass batch; after ion-exchange treatment, these materials exhibit the normal, relaxed stress profiles associated with many chemically strengthened glasses. The mechanical properties of the materials, both with and without Na₂O additions, have also been measured using a biaxial flexure method. The strongest glass exhibits a high strength, in the as-treated condition, of ∼ 860 MPa.