Anomalous properties of chloroborosilicate glasses in the K2O–BaO–Al2O3–B2O3–SiO2–BaCl2 system

A series of chloroborosilicate glass having composition (in mol%) (100 −x)(42SiO2–30B2O3–20BaO–4K2O–4Al2O3)–xBaCl2 (where x = 0−30) has been prepared by the melt quench technique yielding transparent monolithic glasses up to x = 22.5. Structural investigation by infrared reflection and UV–vis–NIR absorption revealed the bridging action of Cl atom and decrease in non-bridging oxygens with the increase in BaCl2 content. Thermal properties (Tg, Td and Ts) were measured by the dilatometry and softening point measurement. Viscosity was calculated using the Vogel–Fulcher–Tammann equation. Elastic constants were measured by the ultrasonic method. Other mechanical properties like hardness, fracture toughness were also measured. All of the thermal and mechanical properties exhibited a similar trend of anomalous variation as a function of the BaCl2 content, showing maxima at 10 mol% and a sharp increase at 25 mol% BaCl2 content. The anomaly has been explained by the structural point of view with the help of the aforementioned spectroscopic data.