A study of thermodynamic characteristics of the Zn_2P_2O_7-M_4P_2O_7(M=Li and Na)Systems by differential scanning calorimetry

摘要

Glasses, crystals, and melts in the Zn_2P_2O_7-M_4P_2O_7 (M = Li and Na) systems are studied by differ-ential scanning calorimetry (DSC). Temperature dependences of the heat capacity and the enthalpies of melting of Zn_2P_2O_7 and Na_2ZnP_2O_7 crystals are determined. The thermodynamic characteristics obtained are used for calculating the liquidus curve for the Zn_2P_2O_7-Na_2ZnP_2O_7 subsystem on the basis of the Schr~ider relationship with due regard for the temperature dependences of the enthalpy of melting for components and the nonideal behavior of melts. Reasoning from the Hruby empirical formula, the inference is drawn that the crystallization ability of lithium-zinc phosphate glasses is higher than that of sodium-zinc phosphate glasses. The radius of cooperative motion in the glass transition range for glasses in the Zn_2P_2O_7-Na_4P_2O_7 system is estimated in the framework of the phenomenological thermokinetic fluctuation theory. It is assumed that an increase in the radius with an increase in the alkali oxide content is associated with an increase in the ionicity of bonds.