Refractory Glass

Mario Moretti

Description

This is glass with an annealing temperature which is higher than that of normal glass and always not lower than 700°C.

Silica glass
This is one of the most refractory glasses known and is obtained by fusion, at over 2000°C, of very pure quartz. Its annealing temperature depends on the purity of the initial quartz and the production method and varies between 1020 and 1200°C.
Silica glass has a higher resistance to thermal changes and an optical transmission at various wavelengths than all other glass. However, its high cost and the difficulty in producing it, limits its use to few cases, like chemical laboratory objects, mercury vapour lamps and telescope mirrors.
An alternative to silica glass is glass commercially known with the name Vycor containing 96% silica and small quantities of boric acid and sodium oxide. From the perspective of mechanical resistance and resistance to thermal changes, this has the same characteristics as silica glass, but its fusion and annealing temperature is lower.

Amongst the refractory glass, we mention alumina-silicate glass and aluminate glass which have good resistance to thermal changes like the boron-silicates. Compared to these last ones, they can be used in higher temperatures and for this reason are used for the production of special coverings.