Crystallizing glass seals in the system BaO/ZnO/SiO2 with high coefficients of thermal expansion

Glasses in the system BaO/ZnO/SiO2 with different BaO/ZnO ratios were melted and powdered and subsequently sieved to different grain size fractions. The powders were sintered to compact samples, then crystallized at temperatures in the range from 850 to 1000 °C and afterwards studied with respect to their phase composition and their thermal expansion behavior. In the glass with large BaO/ZnO ratio, the predominant phase was BaSi2O5. Besides, BaZn2Si2O7 occurred, which became the predominant phase in samples with small BaO/ZnO ratio. Dilatometric measurements showed a steep increase in length up to temperatures in the range from 325 to 375 °C. Then a kink was observed and at temperatures above, the coefficient of thermal expansion was somewhat smaller. The mean thermal expansion coefficients of many crystallized glasses were in the range from 12 to 14 × 10−6 K−1.