A Phenomenological Model for Interstitial Hydrogen Absorption in Niobium

A phenomenological model has been developed for hydrogen absorption in niobium. The model has nine free parameters that have a physical basis. The model provides an excellent fit to the highly accurate isotherm data by Veleckis et al. and has been cross-validated by limiting the fitting procedure to a training set. The model makes it possible to extract more information from the data than could be extracted with the computational methods available when the measurements were made. The partial molal enthalpy and partial molal entropy of hydrogen dissolution were calculated using the parameter values corresponding to the best fit to the isotherms. These quantities are consistent with those reported by Veleckis et al. Interpreting the model parameter values reveals insights into the nature of the interaction between hydrogen atoms in niobium. These insights support our previous analysis of hydrogen interactions in niobium using density functional theory calculations.