The effect of the absorption of hydrogen on allotropic transformations in the rare earth metals

The purpose of the investigation was to establish the equilibrium phase diagram for pure rare earth metal-hydrogen binary systems. Pressure-composition-temperature (P-C-T) relationships for the rare earth metal-hydrogen systems with hydrogen-to-metal concentrations in the range 0–2.0 were measured at hydrogen pressures of 10−3–102 Torr and temperatures of 200–950 °C using a Sieverts apparatus. The thermodynamic functions of these systems were also determined. A partial phase diagram based on the P-C-T data and on the results of the thermal analysis is proposed for each system.