Microstructure and hydrogenation thermokinetics of ZrTi_(0.2)V_(1.8) alloy

摘要

The microstructures and phase composition of the pseudobinary ZrTi_(0.2)V_(1.8) alloy were examined by scan electron microscope (SEM) and X-ray diffraction (XRD). Before hydrogenation, the hypoeutectic structure accompanied with ZrV_2 + (ZrV_2 + Zr) spherical-like texture has been observed in ZrTi_(0.2)V_(1.8) and the dominant phase could be ascribed to the C15 Laves phase. Hydrogen absorption pressure-composition isotherms (P-C isotherms) and hydriding kinetics of ZrTi_(0.2)V_(1.8) 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 ± 1J 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 p-phase. The activation energy E_a of the alloy is ～ 3.6 kJ mol~(-1) for the first absorption stage and ～61.9kJ mol~(-1) for the second one.