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Abstract

Mass spectrometric analysis of gaseous phase above Na₂O.4 SiO₂; K₂O.4 SiO₂ and Na₂O.K₂O.8 SiO₂ melts was used to identify the species observed and to determine their partial pressure values. The principal species observed were the corresponding alkaline species and oxygen. The temperature dependence of sodium and kalium partial pressures was established and corresponding vaporization enthalpy values were calculated by second law treatment of those vapor data. The average value of sodium vaporization enthalpy in binary melt amounts of ΔH_T⁰ = 315 ± 10 kJ mol^-1 being in a good agreement with the data published previously. The vaporization enthalpy of potassium ΔH_T⁰ = 142 ± 8 kJ mol^-1 is considerably lower with comparison to sodium and does not change if potassium evaporates from binary K₂O.4 SiO₂ or ternary Na₂O.K₂O.8 SiO₂ melts respectively.