Effect of substitution on hysteresis in some high-pressure AB2 and AB5 metal hydrides

Abstract

Abstract Ti 0.95 Zr 0.05 Cr 1.2 Mn 0.8− x V x –H 2 ( x =0, 0.05 or 0.1), Ti 0.95 Zr 0.05 Cr 1.2 Mn 0.8− y Co y –H 2 ( y =0, 0.1 or 0.2) and Ce 0.8 La 0.2 Ni 5− z Co z –H 2 ( z =0, 0.5, 1.0 or 1.5) systems were studied experimentally in order to (a) find suitable alloys for high-pressure applications, and (b) gain insight into the reasons for the hysteresis and its reduction due to certain partial substitutions. A special volumetric pressure–composition isotherm (PCI) measurement technique at high pressures (up to 400 bar in this case), pressure differential scanning calorimetry (PDSC), and X-ray diffractometry (XRD) of both starting alloys and SO 2 - (or air-) poisoned high-pressure hydrides were applied. Practically hysteresis-free high-pressure alloy–hydrogen systems with good PCI plateau properties were found, e.g. Ti 0.95 Zr 0.05 Cr 1.2 Mn 0.75 V 0.05 –H 2 . Furthermore, it was shown that an intermediate hydride phase in the Ce 0.8 La 0.2 Ni 3.5 Co 1.5 –H 2 system exists, which explains the remarkably reduced hysteresis compared to the less or non-substituted systems. Finally, an experimental correlation between hysteresis and discrete unit cell volume expansion between coexisting phases was displayed. It suggests that the volume expansion is a major reason for the hysteresis, but more experimental data needs to be collected.