Evaporation/condensation coefficients as determined by the multiple Knudsen effusion cell method Original Research Article

Knudsen effusion cells coupled with mass spectrometer are known to determine equilibrium pressures. We focus on the fact that a Knudsen effusion cell could work with non-equilibrium conditions. In that case, the difference between the equilibrium state and the real state can be described by introducing the concept of evaporation and condensation coefficients. We propose a new description of the Knudsen effusion cell flows in the case of two surface samples of different materials reacting by the intermediate of the gas phase. The behavior of each gaseous species on each surface are described by evaporation and condensation coefficients; for example, in the study the interaction between two surfaces, one of C and the other of Al2O3, the evaporation coefficient of Al is different for the Al2O3 surface and for the C surface. Guidelines for mass spectrometric experimental strategy are presented.