Experimental investigation and thermodynamic assessment of Nd–H and Nd–Ni–H systems

Abstract

A coupled experimental investigation and thermodynamic study of the Nd–Ni–H system have been carried out and the self-consistent thermodynamic database on this system has been obtained. High pressure differential scanning calorimetry (HP-DSC) is used to determine the temperature of reaction NdNi5H3↔NdNi5+1.5H2 in the pressure range of 3.01–11.01MPa H2. The thermodynamic functions for Nd–H system are developed based on the critical assessment of the equilibrium pressure PH2 over sample at 600–800°C, invariant reaction temperatures and hydrogen solubilities in Nd. Two sets of thermodynamic functions for Nd–Ni–H system are provided because two sets of models for NdNi5, NdNi5H3 and NdNi5H6 are adopted. The NdNi5, NdNi5H3 and NdNi5H6 are modeled as separated phases in parameter set 1 and described as a single phase in parameter set 2. The calculated decomposition temperatures of NdNi5H3 and NdNi5Ni6 at different pressures agree well with the experimental data. However, the thermodynamic description of parameter set 1 is recommended through comparing the calculated pressure–temperature–composition (PCT) curves with the experimental results. In addition, the obtained thermodynamic database of Nd–Ni–H system is applied to analyze the hydriding process of Nd–Ni alloys.