Metal hydride hydrogen absorption

Hydrides. According to X-ray and neutron diffraction and metallographic studies of the Nb-H system,524 the H may be considered a lattice gas with phase transitions. In the a-, a -, j6-, and -phases of the system, H occupies tetrahedral interlattice positions. Whereas direct reaction between niobium metal and hydrogen occurs only after repeated activation of the metal by hydrogen absorption at ca. 7 atm and 350 °C, NbH2 is formed at temperatures as low as 22 °C in mixtures of LaNi5H6 7 and Nb.525 The extraordinary catalytic effect of the lanthanum-nickel complex is attributed to the presence of surface-absorbed atomic hydrogen species which are able to diffuse into the niobium lattice. There has been a review of the T a-H system.526... 

The cost of metal hydride storage includes cooling the water, heating, equipment necessary to create the hydrogen absorption and release, and the metal hydride itself. Table 7.5 provides the base case assumptions used in determining the total cost of metal hydride hydrogen storage. 

A number of metals have the ability to absorb hydrogen, which may be taken into solid solution or form a metallic hydride, and this absorption can provide an alternative reaction path to the desorption of H,. as gas. In the case of iron and iron alloys, both hydrogen adsorption and absorption occur simultaneously, and the latter thus gives rise to another equilibrium involving the transfer of H,<,s across the interface to form interstitial H atoms just beneath the surface ... 

Switendick was the first to apply modem electronic band theory to metal hydrides [5]. He compared the measured density of electronic states with theoretical results derived from energy band calculations in binary and pseudo-binary systems. Recently, the band structures of intermetallic hydrides including LaNi5Ht and FeTiH v have been summarized in a review article by Gupta and Schlapbach [6], All exhibit certain common features upon the absorption of hydrogen and formation of a distinct hydride phase. They are ... 

Apparently an ion-exchange resin will allow the absorption of the metal hydride species onto its surface by protonation and subsequent elimination of hydrogen (Equation 2.11). This hydrogen elimination is a reversible reaction. The metal species remains as a labile species that can be desorbed by hydrogen in a fluid-stripping medium. 

Hydrogen Weight Alloy Weight Fig. 5.7 Hydrogen absorption capacity of metal hydride alloy... 

Fernandez and Sanchez [18] investigated the kinetics of hydrogen absorption and desorption by activated magnesium powder (several cycles of hydrogen absorp-tion/desorption at 375°C) using a volumetric technique. They pointed out that for-mation/decomposition of metal hydrides comprises a number of steps taking place in series transport to the surface, dissociation, H chemisorption, surface-... 

K.S. Jung, E.Y. Lee, K.S. Lee, Catalytic effects of metal oxide on hydrogen absorption of magnesium metal hydride, J. Alloys Compd. 421 (2006) 179-184. 

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