Thermochemical study of vaporization of sodium borosilicate glass melt containing tellurium

Abstract

The vaporization behavior of sodium borosilicate glass melt with a composition of 1Na 2O-1B 2O 3-3SiO 2-0.15TeO 2 has been studied by a mass spectrometric Knudsen effusion method in the temperature range 991–1151 K. Vapor species of NaBO 2(g), Na 2(BO 2) 2(g), Te(g), Te 2(g), TeO(g) and TeO 2(g) have been identified. On the basis of the measured partial pressures of tellurium-containing vapors, the enthalpy of formation and the dissociation energy for Te 2(g) and the reaction enthalpy for 2TeO(g) → 0.5Te 2(g) + TeO 2(g) have been determined to be ΔH ° f,298(Te 2, g) = 164.8 ± 8.1 kJ mol −1 , D ° 298(Te 2) = 258.6 ± 8.1 kJ mol −1 and ΔH ° r,298 = −144.6 ± 8.3 kJ mol −1 , respectively. Chemical activities and activity coefficients of the TeO 2 and NaBO 2 components in the glass melt have also been derived. From these results it can be concluded that the vaporization of the TeO 2 and NaBO 2 components is much suppressed thermochemically.