Experimental and theoretical study of compositional inhomogeneities in LaNi5Dx owing to temperature gradients and pressure hysteresis,investigated using spatially resolved in-situ neutron diffraction

An in-situ neutron investigation of the spatial variation in hydride composition of LaNi₅ after a single absorption pressure step was performed. Compositional inhomogeneities are formed due to the strong temperature gradients created by the rapid absorption process coupled with the pressure and temperature hysteresis of the metal–hydrogen interaction. The hydride fraction of LaNi₅ in a cylindrical cell was mapped using the ENGIN-X stress/strain instrument and quantitative phase analysis performed using the Rietveld technique. The material was observed to preferentially absorb hydrogen close to the edges of the cell where heat transfer out of the material was more efficient. This spatial variation was maintained even after thermal equilibration. The experimental results are compared to predictions of a 3D multiphysics model solved by the software package COMSOL. The good agreement achieved demonstrates the suitability of this model for optimisation of metal hydride tank systems.