Mass Spectrometric Studies of Non-Equilibrium Vaporizations in Knudsen Cells: a Way to the Determination of the Nature of Kinetic Processes

摘要

Non-equilibrium vaporizations in Knudsen cells occur when the net rate of vaporization at the surface of the sample is slower than the rate of effusion. In such a situation, the description of the molecular flow exchanges in an effusion cell according to the Motzfeldt equation allows the determination of the evaporation coefficients from different pressure determinations of the same sample performed with different cell geometries. Further, the chemical signification of the value of the evaporation coefficients was not very often explained. Different thermodynamic analyses are presented on experimental results in order to explain the origin of retarded vaporizations of Al_2O_3 , SiO_2, A1N , BN and mixtures Si-SiO_2 as well as amorphous SiO.