Enthalpy of mixing in 0.8[xB2O3–(1 − x)P2O5]–0.2Na2O glasses at 298 K

0.8[xB2O3–(1 − x)P2O5]–0.2Na2O (with 0 ≤ x ≤ 1) glasses have been characterized by solution calorimetry at 298 K in acid solvent. The experimental data showed a strong negative departure of the enthalpy of mixing from the ideality described by the equation (in kJ/mol): ΔH = x(1 − x)(−660.2 + 570x). The results were interpreted on the basis of the structural data. Enthalpies of mixing were consistent with sub-regular solution behaviour.