Thermodynamics of gaseous phase: Knudsen effusion method coupled with mass spectrometry
Résumé
High Temperature Mass Spectrometry (HTS) combines a vacuum vaporization reactor with a mass spectrometer. The vaporization reactor is most often a Kundsen-type effusion cell - a closed container with only a small orifice on one of the walls - in order to ensure inside the vaporization equilibrium conditions suitable for the determination of thermodynamic properties. In a conventional operation, the SMHT allows the study of "vapour" gas phases: identification of evaporating gas species, determination of their partial pressures and their formation enthalpies. In the more advanced version that we have realized in the laboratory, a multi-compartment effusion cell called a multiple cell, allows direct measurements of activities, i.e. partial pressures related to pure substances, for systems with several components since spectrometry has an analytical character. This is the only method that allows simultaneous measurements of several activities. The original NUCLIDE (1968) mass spectrometer was modified in our laboratory to adapt to different systems. The range of measurable partial pressures ranges from 10-11 to 10-4 bar, with temperatures ranging from -30°C to 2350°C in our current devices. There are several types of effusion reactors available: - Single cell reactor (T<2350°C), conventional Knudsen cell Applications: vaporization of ceramics, metals...identification of vapors, determination of equilibrium constants, enthalpy of gas molecule formation - Multiple cell reactor (T<2350°C) Applications: measurement of activities (alloys, super alloys, molten salts, oxide mixtures, complex ceramics, etc.) and partial free enthalpy determination - Single cell reactor for low temperature (-30°C