Investigation of potassium sulphate–calcium sulphate binary system by Knudsen effusion mass spectrometry

• Thermodynamic activities of the system K2SO4–CaSO4 determined for the first time.
• New approach of ion division in Knudsen effusion mass spectrometry.
• The confirmation of the vaporisation of pure sulphates with the previous literature data.

Vaporisation studies of pure K2SO4 and mixtures of K2SO4 and CaSO4 in the quasi-binary K2SO4–CaSO4 system using Knudsen effusion mass spectrometry resulted in the determination of thermodynamic data. From the partial pressures of the gaseous species over the condensed phases it was possible to determine the sublimation enthalpyΔsubH and the thermodynamic activities of the components. The sublimation enthalpy of K2SO4 agrees very well with that of two literature sources. For the first time the experimental data of activities of K2SO4 and CaSO4 in the binary system could confirm the theoretical studies.