Thermochemistry of nuclear waste glasses: an experimental determination

As part of a systematic study of the chemical stability of borosilicate gla sses, we show that the Gibbs free energy of formation of a glass can be det ermined experimentally from a comprehensive, consistent set of measurements . For a sodium borosilicate glass with 14.2 mol% Na2O and 18.4 mol% B2O3, t he relative enthalpy and entropy have been determined from heat capacities measured from 13 to 1480 K by adiabatic, differential scanning and drop cal orimetry, the enthalpy of formation has been obtained from solution calorim etry at 970 K, whereas the configurational entropy of the glass has been de rived from viscosity measurements through the Adam-Gibbs configurational en tropy theory. The structural and thermochemical implications of the results are discussed in terms of short-range order and mixing of BO3 and BO4 unit s. (C) 2001 Published by Elsevier Science B.V.