Sloping plateaux in the pressure–composition isotherms of the titanium–hydrogen and Ti94Al6–hydrogen systems

Abstract

Pressure–composition isotherms of the titanium–hydrogen and Ti₉₄Al₆–hydrogen systems have been measured in the temperature range 673–973 K and hydrogen-concentration range (atomic ratio) 0.01–1. The plateaux of the isotherms, which correspond to the (α+β) phase region, have been found to slope upward slightly in the titanium–hydrogen system and to slope upward appreciably in the Ti₉₄Al₆–hydrogen system. The observed sloping plateaux are shown to be explicable on the basis of a lattice-gas model which incorporates in it a Gaussian distribution of energies of hydrogen in the metals with a standard deviation 0.0015 eV for the titanium–hydrogen system and 0.01 eV for the Ti₉₄Al₆–hydrogen system. Possible origins of the energy distribution are also mentioned.