Vaporisation studies on Sn-Te-O system by Knudsen effusion mass spectrometry: Thermodynamic properties over (SnO2+SnTe3O8) biphasic region

Abstract Vaporisation studies along the pseudo binary line of SnO2–TeO2 (SnTe3O8 + SnO2) in the Sn-Te-O system were conducted by using Knudsen effusion mass spectrometry in the temperature range 843–968 K. SnTe3O8 vaporises incongruently and TeO2(g), TeO(g), Te2(g) and O2(g) were the neutral species observed over the equilibrium vapour. Partial pressure – temperature (p-T) relations of TeO2(g), TeO(g), Te2(g) over (SnTe3O8 + SnO2) “two phase” region were determined in the temperature range 843–968 K. Partial pressures of O2(g) were calculated by considering gas phase equilibrium reactions involving this species and TeO2(g), TeO(g), Te2(g). Using the p-T relations, enthalpy changes of the following reactions were evaluated: SnTe3O8(s) ⇌ SnO2(s) + 3TeO2(g); SnTe3O8(s) + 2TeO(g) ⇌ 4TeO2(g) + 0.5 Te2(g) + SnO2(s) and 0.5Te2(g) + TeO2(g) ⇌ 2TeO(g). Subsequently, the enthalpy and Gibbs energy of formation of SnTe3O8 phase at 298.15 K were deduced as ΔfHm° = −1613.7 ± 67.8 kJ mol−1 and ΔfGm° = −1386.7 ± 67.8 kJ mol−1. Knudsen effusion mass spectrometric studies on this system are being reported for the first time.