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 d ue to the released enthalpy of H absorption-desorption will generate m acroscopic inhomogeneities of the alpha/beta phase proportions in meta l hydrides. We used in situ X-ray diffraction and in situ neutron diff raction respectively to study the growth of beta-LaNi5-H at the free s urface, 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 phas e while the bulk of the sample is rich in beta phase.