Analysis of the partial molar excess entropy of dilute hydrogen in liquid metals and its change at the solid-liquid transition

A systematic change in the partial molar enthalpy of mixing (Delta h(H)(-mix)) and partial molar excess entropy (Delta s(H)(-ex)) for dilute hydrogen-metal systems at the solid-liquid transition is reported. Expressions for Delta h(H)(-mix) and Delta s(H)(-ex) are derived from the Fowler model of hydrogen solubility, and the change in Delta s(H)(-ex) at melting is bounded. The theoretical bound is in agreement with measured data. A connection is made between the change in Delta s(H)(-ex) and short range order in the metal-hydrogen system. (C) 2019 Published by Elsevier Ltd on behalf of Acta Materialia Inc.