Isobaric and isothermal hysteresis in metal hydrides and oxides

Abstract

An analysis is presented of the thermodynamics of both isothermal and isobaric hysteresis, leading to equations for the calculation of the irreversible entropy production and the loss of free energy in hysteresis cycles of both kinds. The status of ‘apparent’ enthalpies derived from the temperature dependence of isothermal data is examined and two extreme types of behaviour are identified. An analysis of experimental data shows that the palladium–hydrogen system exhibits characteristics lying between these extremes. However, this does not seriously affect the use of either isothermal or isobaric data to derive the entropy production and free-energy loss. Existing published work on rare-earth metal–oxygen systems is also analysed, but no firm conclusions can be drawn.