heat-resistant glass[′hēt ri‚zis·tənt ′glas]
glass capable of withstanding sharp drops in temperature (thermal shocks) without shattering. Heatresistant glass includes all glass possessing a low coefficient of thermal expansion a. Quartz glass has the greatest heat resistance of all and will not shatter even when the change in temperature is as much as 1000°C (α = 5.67 × 10–7 1/°C at 500°C). Borosilicate and certain other kinds of glass are also heat-resistant. Ordinary glass (window, container) is resistant to changes of up to 80°–100°C. The heat resistance of glass depends not only on the glass’s chemical composition but also on the intensity of heat emission at the surface of the article, the quality of the surface, and the dimensions of the article. Heat resistance can be increased by tempering, fire-polishing, or chemically treating the glass to remove defects from the glass surface. Laboratory glassware, radio tubes, and water gauges for steam boilers are made of heat-resistant glass.