The amount and composition of vapor pressures over a liquid or solid phase are key physical properties. With the temperature dependency of the partial pressures basic thermodynamic data can be derived such as enthalpy, entropy and Gibbs energy of the vaporization reaction as well as their partial and molar mixing values for the condensed phase. Such high precision thermodynamic data are a basis for designing new materials and predict the corrosion resistance and phase stability of new alloys for technical applications especially at high temperatures.

The vapor pressure (p_i) can be measured by the method of Knudsen Effusion Mass Spectrometry (KEMS) in a high vacuum atmosphere. Therefore, a sample is heated up in a Knudsen Cell. The crucible of the Knudsen Cell is closed with a lid which has a small orifice between 0.1 – 1 mm. At constant temperature the gas phase is in equilibrium with the sample. Due to the mean free path in vacuum, the molecules of the gas atmospheres effuse from the Knudsen Cell only stochastically. The molecules effuse out of the Knudsen Cell and will be ionized and then characterized quantitatively and qualitatively by a mass spectrometer. Thereby the equilibrium between gas phase and condensed phase will practically not be disturbed.

With the KEMS method it is possible to measure vapor pressures between 1∙10^-7 - 1 mbar. Measurements can be performed between 290 K – 3000 K.

A completely new designed experimental device is set up in our laboratory.
The aim of the project is to build up a new KEMS apparatus which exceeds the current state of the art of measuring vapor pressures in sensitivity and usability. The focus of the new KEMS-device is a user-friendly operation, compact dimensions and self-explanatory evaluation software. Special designed sample carrier will allow measuring samples highly automatical and determination of high precise thermodynamic data.