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)(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 BaCl2 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 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