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Knudsen Effusion Mass Spectrometry

By means of Knudsen effusion mass spectrometry (KEMS), evaporation studies can be carried out to investigate the chemical equilibrium between a condensed phase and the related gas phase. The sample to be studied by means of evaporation measurements is located in a Knudsen cell, a container with an effusion aperture – a small borehole – in its cover. The gaseous species and the condensed phase are in equilibrium: the number of molecules evaporating or subliming from the sample surface is equal to the number of molecules condensing from the gas phase. Part of the gaseous species escapes from the Knudsen cell and forms a molecular beam which can be identified and quantitatively analysed. The relationship between the mass and the type of particle is usually unambiguous. KEMS allows scientists to determine equilibrium partial pressures from approx. 10-7 Pa to 10 Pa, from room temperature to 3000 K. From these pressures, the thermodynamic data of the gas phase and the condensed phase can be calculated, for example, molecule formation energy, enthalpy of mixing, or chemical activty.

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KnudseneffusionsmassspectrometerKnudseneffusionsmassspectrometer

Specifications
• Temperature range: up to 2800 K
• Vakuum in the chamber: 10-6 -10-8 mbar
• Determination of partial pressures: 10-8 – 10 Pa
• Identification of gaseous species


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