Intrinsic testing of intermetallic hydrides

1 Examples of thermal and pressure cycling of classical hydrides 

In this section we will discuss the cycling studies that have been performed on LaNis. A classic example of a room temperature isotherm of LaNis from 

9 (a) Room temperature isotherm of the classical LaNis obtained at 25°C by Hydrogen Components Inc. (HCI) (F.E. Lynch), (b) Van t Hoff plot of LaNis obtained from the isotherms taken at many temperatures by C. Lundin at Denver Research Institute, University of Denver [102], Hexagonal structure in (a) from Percheron-Guegan, and co-workers [29, 72]. 

Disproportionation of intermetallics is indicated by the changes in the shape of the isotherms and associated loss in the hydrogen capacity [20]. This phenomenon may be attributed to short-range diffusion of the atoms, the thermodynamic stability of one of the elemental species from an elemental hydride, and dissociation of the non-hydride former second atom as a metal. Note that it is not necessary for all the binary intermetallic hydride to completely dissociate into elemental hydrides. Many variants of AB5 alloys have been used for hydrogen storage over the years and these hydrides were tested for intrinsic and extrinsic degradation, mainly LaNis and FeTi-type hydrides these hydrides exhibit a propensity for disproportionation. A hydride that would hydride/dehydride really well during the first few cycles may not 

Several thousand cycles were performed on classical hydrides for a prolonged time using the test method from Lambert et al. [20]. An example of LaNis 2 with no other Ni substitutions is shown in Fig. 12.11 [20]. Isotherms were taken (by removing the sample from the cycling apparatus and then attaching it to the Sievert s apparatus, after the initial 10 activation cycles, 1500, and 10000 P-T cycles. It can be seen that there is a significant loss of 

---