Effect of MxO (M=Li, K, Ca) on the solubility of Ag2O in borate glass

The variation of Ag2O solubility under air atmosphere with the chemical potential of Ag was measured for the MxO–B2O3–Al2O3 system by equilibrating with Ag–Au alloy of various Ag contents at 1273 and 1373 K. It was found that in this system the regular solution model is not valid for estimating the activity coefficient over a wide composition range. The activity coefficient of Ag2O in B2O3 at infinite dilution and first-order Gibbs energy interaction coefficients of Ag2O, Al2O3, and Na2O on Ag2O were determined from the Ag2O solubility data without assuming a regular solution. The increase of the Al2O3 solubility by addition of alkali oxide suggested that the glass melts were equilibrated with 2Al2O3·9B2O3 and not Al2O3 and the activity was considered to increase by the addition of alkali oxide. A good correlation was found between the activity coefficient of Ag2O and the optical basicity.