A GENERAL-MODEL FOR PARTITIONING OF GASES BETWEEN A METAL AND ITS PLASMA ENVIRONMENT

When a metal or an alloy is exposed to a pure diatomic gas such as nit rogen, the concentration of the species in the material can be predict ed from Sieverts law. However, such calculations cannot be used to und erstand processes in which the gas phase near the metal contains excit ed molecules, atoms, ions, and electrons, in addition to the diatomic gases. The presence of plasma leads to species concentrations in the m etal that are much higher than the values predicted by the Sieverts la w. At present, there is no unified theoretical model to understand the partition of nitrogen, oxygen, and hydrogen between a metal and its p lasma environment. In this work, a theoretical. model has been develop ed to understand the enhanced solubility of gases in metals exposed to plasma environment. The model has been applied to explain several dif ferent sets of independent experimental results available in the liter ature. The analysis of the data shows that the enhanced solubilities c an be explained on the basis of superequilibrium concentration of atom ic species near the metal surface. Both the enhanced solubilities and the maximum species concentrations predicted by the model are in good agreement with the independent experimental data for various systems.