Thermal expansion of vitreous silica: Correspondence between dilatation curve and phase transitions in crystalline silica

The linear thermal expansion coefficients of fused quartz containing 3 ppm of OH produced by electrical melting of natural quartz powder were measured using an interferometric dilatometer in the temperature range 300–970 K. The data obtained show several maxima and minima, some of which correspond to the phase transitions in crystalline silica. A sharp maximum is observed at 500 K, which corresponds to the α to β transition temperature of cristobalite. Minima at 850 and 580 K correspond to low- to high-temperature phase transitions of crystalline quartz and tridymite, respectively. This correspondence was not observed in synthetic fused silica containing about 800 ppm of OH.