Thermal properties and glass formation in the SiO2–B2O3–Bi2O3–ZnO quaternary system

Abstract

Lead-free glasses in the SiO2–B2O3–Bi2O3–ZnO quaternary system were studied. The glass formation region, as determined by XRD patterns of bulk samples, was limited to glasses having more than 40mol% of the glass-forming oxides SiO2 and B2O3. Crystalline phases of Zn2SiO4 (willemite) were detected in compositions of 30SiO2·10B2O3·20Bi2O3·40ZnO and 20SiO2·10B2O3·25Bi2O3·45ZnO. Glass transition temperatures (Tg), dilatometric softening points (Td) and linear coefficients of expansion in the temperatures range of 25–300°C (α25–300) were measured for subsystems along the B2O3 join of 10, 20 and 30mol%. For these subsystems, Tg ranged from 411 to 522°C, and Td ranged from 453 to 563°C, both decreasing with increasing Bi2O3 content. The measured α25–300 ranged from 53 to 95×10−7°C−1, with values increasing with increasing Bi2O3 content. The ZnO content had the opposite effect to the Bi2O3 content. It appears that Bi3+ acts as a glass-modifier in this quaternary system.