Microstructure and hydrogenation thermokinetics of ZrTi0.2V1.8 alloy

The microstructures and phase composition of the pseudobinary ZrTi0.2V1.8 alloy were examined by scan electron microscope (SEM) and X-ray diffraction (XRD). Before hydrogenation, the hypoeutectic structure accompanied with ZrV2 + (ZrV2 + Zr) spherical-like texture has been observed in ZrTi0.2V1.8 and the dominant phase could be ascribed to the C15 Laves phase. Hydrogen absorption pressure–composition isotherms (P–C isotherms) and hydriding kinetics of ZrTi0.2V1.8 were investigated by pressure reduction method using Sievert apparatus from 673 to 823 K. At hydrogen concentration 0.65 (H/A), the relative partial molar enthalpy and entropy calculated by Van’t Hoff equation are −60 ± 1 kJ mol−1 and −119 ± 1 J mol−1 K−1, respectively. In addition, two stages in the hydrogen absorption reaction between 673 and 823 K could be attributed to the different hydrogen absorption mechanisms including redistribution of the hydrogen atoms in the hydride phase and the diffusion of hydrogen in the β-phase. The activation energy Ea of the alloy is ∼3.6 kJ mol−1 for the first absorption stage and ∼61.9 kJ mol−1 for the second one.