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

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 40 mol% 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 30 mol%. 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.