Chapter fifteen - Determination of phase diagrams for hydrogen-containing systems

Abstract

The high mobility of interstitially dissolved hydrogen atoms allows equilibrium to be established at relatively low temperatures making these metal–hydrogen (M–H) systems unique, in that their phase diagrams can be quite readily determined at low temperatures. This chapter concerns the experimental aspects of phase diagram determination for the M–H systems; however, some theoretical aspects of the M–H systems phase diagrams are needed because otherwise distinctions among various degrees of equilibrium vis-à-vis the resulting phase diagrams is unclear. The chapter introduces various ways to present the M–H phase equilibria, the useful rules relating the phase diagrams to the reaction enthalpy of the M–H systems, and the difference between local equilibrium and complete equilibrium in multicomponent systems. Various techniques for M–H phase diagram determinations in both open and closed systems are also discussed in the chapter.