Chemical Durability Improvement and Static Fatigue of Glasses.
Annual rept. no. 1. 1 Apr 78-28 Feb 79,
RENSSELAER POLYTECHNIC INST TROY N Y DEPT OF MATERIALS ENGINEERING
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The Surface layer of heat-treated borosilicate glasses exhibited lower HF etching rate compared with the bulk. The chemical analysis of the same glass indicated an excess Al2O3 concentration in the surface layer. The low HF etching rate was attributed to the lowering of the immiscibility dome by the excess Al2O3 and the consequent shift of the composition. A prolonged heat-treatment of glasses produced a surface stress layer. This surface stress was found to change its sign when the glass was heat-treated in wet atmosphere. The surface stress was attributed to the different water content in the surface layer from that in the bulk. Chemical durability, especially the etching rate of a glass in hot NaOH solution was found to be reduced by coating the glass with Zr alcoxide. The Zr compound appears to deposit on the etched surface continuously protecting the glass. Direct confirmation of the stress corrosion, i.e., the stress- accelerated reaction of glass with aqueous solution was attempted. Preliminary investigation showed that reactions are accelerated by tensile stress and retarded by compressive stress. Author
- Ceramics, Refractories and Glass