Thermodynamic activities in B2O3-SiO2 melts at 1,475 K

Eight glass samples in the B2O3-SiO2 system with compositions from 20 to 90 mol% B2O3 were prepared. The equilibrium vaporization was studied by Knudsen effusion mass spectrometry at temperature between 1,450 and 1,500 K. B2O3(g) was the most abundant boron-containing species in the vapor; no silicon-containing gaseous species were detected. Thermodynamic activities of B2O3 in the liquid were determined at 1,475 K. Thermodynamic activities of SiO2 and integral excess Gibbs energies were estimated from the thermodynamic activities of B2O3. The thermodynamic data support the results obtained by other methods indicating the existence of a miscibility gap in the metastable liquid