The strength of fused quartz in water vapour

Abstract

The effect of water vapour on the strength of fused quartz has been investigated by measuring the bending strength S , at 20 and 40 °C, of microscope cover slides in varying humidities ( p / p 0 ) relative to the bending strength in vacuo S 0 , and correlating this with the adsorption of water vapour on crushed slides at the same p / p 0 and temperatures. S / S 0 was found to vary with p / p 0 in the anomalous way previously observed for soda-lime glass. While an overall reduction in strength of about one-third occurred, a restoration in strength at intermediate pressures was observed at 20 °C. This restoration was not observed at 40 °C. These phenomena, combined with the reversible and irreversible nature of the adsorption of water vapour on the surface of the powder at the same p / p 0 , provided a means of interpreting the surface reactions between water and fused quartz. A model of these reactions is proposed which led to a prediction that a delay in failure with a further reduction in strength should be observed if the time of load application is increased from a few minutes to a number of hours. Subsequent experiments confirmed this prediction.