Phase transitions of the ZrNiHx hydride

The hydrogen pressure-ZrNiHx hydride composition isotherms were determined under isoplethic experiment conditions during the desorption and sorption of hydrogen. According to the experimental data, the ZrNiHx-H2 system (0 < x < 2.229) experienced two phase transitions, hydrogenolysis with the absorption of large amounts of hydrogen and the reverse transition to the initial state. It was found that the β phase existed in the ZrNiHx-H2 system at least up to 410°C, and the region of its homogeneity was shifted toward the α solution. The homogeneity region of the γ phase at 250°C on the side depleted of hydrogen extended to the composition x = 1.50, and the temperature of its peritectoid decomposition was above 250°C. The hydrogenolysis reaction proceeded with the formation of the ɛ-ZrH3.153−x-NiZr0.7H0.3x system, which had a much higher (higher by 200–300 torr) partial hydrogen pressure over the temperature range 0–240°C, that is, was unstable with respect to the initial system.