Metal/intermetallic hydrides

In essence, metal/intermetallic hydrides of AB, AB (Laves phases), AB, and A B have not been improved to any remarkable extent since the end of the 1990s. Nevertheless, there have been some efforts directed to either improvement of synthesis or properties of metal/intermetallic hydrides particularly by application of ball milling associated with nanostructuring. Some of these more recent efforts will be briefly discussed in the following sections. 

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 ... 

Metals, intermetallic compounds, and alloys generally react with hydrogen and form mainly solid metal-hydrogen compounds (MH ). Hydrides exist as ionic, polymeric covalent, volatile covalent and metallic hydrides. Hydrogen reacts at elevated temperatrrres with many transition metals and their alloys to form hydrides. Many of the MH show large deviations from ideal stoichiometry (n= 1, 2, 3) and can exist as multiphase systems. 

In a variant of the second method described earlier the premixed metallic powders (or pulverized ingots) are milled under hydrogen atmosphere to directly form an intermetallic hydride. It can be also viewed as hydrogen alloying of metal powders and powder mixtures in hydrogen alloying mills. This method is called a reactive mechanical alloying (RMA) or mechanochemical synthesis (MCS). 

The catalytic additives that have been investigated in MgH can be roughly divided into three important groups metals/intermetallics, oxides, and chemical compounds that include hydrides. Their effect on the desorption properties of MgH will be discussed in the following sections. We are not going to discuss absorption since, as mentioned before, absorption is usually much easier than desorption. 

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