Temperature Dependence of the Specific Heat of Borate Bismuth Glasses with the Addition of Sodium

The temperature dependences of the specific heat capacity of glasses based on bismuth and sodium borates, obtained by comparison under conditions of melt cooling into the environment, have been studied. An interpretation of the observed effects is given on the basis of the features of the molecular structure and the thermal mobility of its fragments. Viscosity changes of the melt and cooling rate strongly affects the temperature dependence of c_p, s/c_p max at temperatures above the glass transition temperature. The calculated specific heat of the melt increases with decreasing cooling rate, increasing viscosity and it approaches the values of the specific heat at the maximum corresponding to the temperature vitrification. Adding NaOH to borate glass affects the value and position of the maximum specific heat to a lesser extent than the Bi₂O₃ addition.