Alloying effect on a property of hydrogen gettering materials: An empirical formula to estimate heat of hydride formation for metals and alloys

Abstract

Getter materials are promising for the research and development of thermonuclear fusion reactors from a viewpoint of tritium handling as well as fuel and impurity control in tokamaks. Some guiding rules are indispensable in developing a getter material having suitable properties for a given process in tritium handling. In analogy to the relation between the heat of oxide formation and electronegativities of elements, we studied the change in the heat of hydride formation with metals and alloys from this viewpoint: the electronegativities of getter materials and hydrogen. We found a simple relation between them in a form of (−ΔHabs)=23s(χM−2.20)2 +3.72s−3.72, where χM and 2.20 are the electronegativities of getter material and hydrogen, and s is the stoichiometric number of hydrogen in hydride. The standard deviation from the observed values was ∼5 kcal/mol(hydride) and/or 35%. This equation was found to be valid for 70 systems which appear to form metallic hydride. An advantage of this equation can be seen in the fact that it consists of only the electronegativities of getter materials and hydrogen, and the stoichiometric number of hydrogen, both of which can be found in literature or estimated with simple assumptions. Consequently, it will be quite useful as a guiding rule to design a getter material with a given heat of hydride(tritide) formation for metals/alloys and/or heat of hydrogen(tritium) absorption.