Metal-Hydrogen System Under Extended p, T Conditions

Abstract

The preceding chapters have dealt with the properties of hydrogen in metals or metal hydrides under ordinary conditions of p, T. In this chapter, we try to extend the range of our discussion and treat binary M-H systems over the entire composition range, including elemental hydrogen, over much wider ranges of p, T. Recent progress in high-pressure technology has allowed the study of M-H systems under very high hydrogen pressures, in consequence making it possible not only to dissolve a larger amount of hydrogen but also to retain it in solution at higher temperatures. This opens the possibility of the common end member, hydrogen, being approached on the phase diagram of M-H systems via routes of high temperatures. Even more can be expected at sufficiently high pressures: elemental hydrogen is expected to become metallic and form alloys with many other elements. Thus, it is believed that there is a compelling reason to try, at this time, to describe the thermodynamical properties of the M-H system over the entire range of composition, under extended p, T conditions, even though, by necessity, the content will be rather preliminary at this stage.