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

Abstract

A series of chloroborosilicate glass having composition (in mol%) (100−x)(42SiO 2-30B 2 O 3-20BaO-4K 2 O-4Al 2 O 3)-xBaCl 2 (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 BaCl 2 content. Thermal properties (T g , T d and T s) 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 BaCl 2 content, showing maxima at 10 mol% and a sharp increase at 25 mol% BaCl 2 content. The anomaly has been explained by the structural point of view with the help of the aforementioned spectroscopic data.