VAPOR PRESSURES IN THE LIQUID SYSTEM RB20-B203. DERIVED THERMODYNAMIC DATA AND A STRUCTURAL INTERPRETATION

By use of the transpiration method, the vapor pressures of the liquid system Rb2O-B2O3 between pure B2O3 and Rb2O . B2O3 were measured. The vapor over the entire composition range was an equimolar mixture of Rb2O and B2O3. Data from other sources indicate that the vapor molcule should be RbBO2. The activity of the RbBO2 in the melts showed a pronounced discontinuity at about 15 mole percent Rb2O. The activity and other thermodynamic data were compatible with a liquid structure based on Biscoe and Warrens theory, which describes the structures of alkali borate glasses. The activity of the RbBO2 in the melts and the vapor pressure of the RbBO2 above the melts could be decreased by the addition to the melt of oxygen-complexing cations.