STABILITY OF THE HYDROGEN ABSORPTION AND DESORPTION PLATEAUS IN LANI5-H .3. EXPERIMENTAL-OBSERVATIONS OF COMPOSITIONAL INHOMOGENEITIES DUE TO TEMPERATURE-GRADIENTS

It has been predicted by Pens and Dantzer that temperature gradients due to the released enthalpy of H absorption-desorption will generate macroscopic inhomogeneities of the alpha/beta phase proportions in metal hydrides. We used in situ X-ray diffraction and in situ neutron diffraction respectively to study the growth of beta-LaNi5-H at the free surface, and beta-LaNi5-D in the bulk of powdered samples. It was found that a macroscopic compositional inhomogeneity does occur, and can be so severe that the free surface of the sample remains pure alpha phase while the bulk of the sample is rich in beta phase.