Proposal for new indexes describing the degree of hysteresis and those applications to the ZrMn 2–H 2 systems

Abstract

For purposes of comparing the degrees of hysteresis between different alloy–hydrogen systems, three kinds of indexes have been proposed instead of the conventional hysteresis factors. The new indexes are defined in the P– T-diagram by the thermodynamic parameters being independent of measurement temperature. Each index has shown that the degrees of hysteresis for the ZrMn 2–H 2 systems increases with decreasing lattice constants. A literature review has made it clear that the hydrogen-induced volume expansion for the ZrMn 2-based alloys increases with decreasing lattice constants. These four relationships could be described in terms of hyperbolic regression expressions. Δ S/Δ H shows close hyperbolic relationships with the lattice constants both for hydrogen absorption and for desorption.