Effects of humidity on the weathering of glass

Abstract The weathering of 26 glass compositions was investigated under static conditions of 30%, 50%, 75%, 90% and 98% relative humidity (RH) at 50°C and a cycling condition between 77% and 98% RH at 50°C. The cycling condition was found to be less severe than static 98% RH. The effect of humidity level on weathering was studied and showed that water adsorption increases with time and humidity, whereas alkali generation increases with time, but not always with humidity. Significant weathering occurs for some glasses at 30% RH with the quantitative effect being almost as great as at 90% RH. Visual weathering was observed for some glasses when the level of generated alkali was less than 0.5 μg/cm 2 . Various techniques for evaluating the weathering of glass under humid conditions were investigated. Visual appearance was judged to be the best evaluation method for routine weathering tests. It represents the effect of most concern and is sufficiently precise. Electron microscopy, measurement of sorbed water and alkali generated are principally used for research studies. Weight change and haze measurement lack sensitivity and reproducibility. A standard test was defined. The conditions are 98% RH at 50°C for 12 weeks. The visual ranking system is used. The glasses were generally ranked in the same order by the various evaluation techniques.