Thermodynamic modelling of the behaviour of impurities in high purity materials during their concentration for spectral and mass-spectral analysis by distilling off the base

A quasiequilibrium model for theoretical estimation of the behaviour of impurities in high purity materials during their concentration by distilling off the base through an oxide film is proposed. The model describes an open system Me-MeOm-el (Me is the base elements, el-impurity) assuming ideality of the melt, an equilibrium between the phases of the system and definite single forms of the elements in the melt and in the oxide and gaseous phases. The numerical solution of the proposed equation enables to analyze the impurities concentration kinetics in cadmium, tellurium and zinc for spectral and mass spectral analysis of these materials. The effects of a series of factors on the concentration is studied. The criteria for separation of the impurities in ones going into oxide, remaining in the melt and lost during the concentration are found. The experimental data agree fairly well with theoretical ones. (author)