Absorption of hydrogen by metals

Palladium is typical of a number of metals which unlike Pt are capable of not only adsorbing but also absorbing large quantities of hydrogen. A collection of excellent articles on various aspects of the absorption of hydrogen by metals has been published recently,to which the reader is referred for more detailed accounts of recent work. 

Burch, R. (1979) The Adsorption and Absorption of Hydrogen by Metals, in Chemical Physics of Solids and Their Surfaces, vol. 9, Chemical Society, London,... 

Hydrides. Zirconium hydride [7704-99-6] in powder form was produced by the reduction of zirconium oxide with calcium hydride in a bomb reactor. However, the workup was hazardous and many fires and explosions occurred when the calcium oxide was dissolved with hydrochloric acid to recover the hydride powder. With the ready availabiHty of zirconium metal via the KroU process, zirconium hydride can be obtained by exothermic absorption of hydrogen by pure zirconium, usually highly porous sponge. The heat of formation is 167.4 J / mol (40 kcal/mol) hydrogen absorbed. 

In addition to the surface physics and chemistry phenomena involved, a further effect may follow the interaction at the hydrogen-metal surface, that is the absorption of hydrogen by the bulk phase of the metal. This absorption leads to the formation of a solid solution within a certain, usually low, range of hydrogen concentrations. However, with several transition metals, exceeding a certain limit of hydrogen concentration results in the formation of a specific crystallographically distinct phase of the... 

In some cases, absorption of hydrogen by intermetallic compounds causes decomposition as indicated by Reaction 3. Decomposition also can lead to the formation of a new intermetallic compound, as is observed when Mg2Cu reacts with hydrogen (6) in Reaction 4. Reactions 3 and 4 take place at elevated temperatures where diffusion of the metal atoms becomes possible. 

Absorption of hydrogen by titanium metal above 400 °C gives a solid whose stoichiometry approaches TiH2, but a true dihydride does not appear to exist. This hydride has been used for the formation of glass-to-metal and ceramic-to-metal seals.1 Thermal desorption above 600 °C provides a source of very pure hydrogen.2... 

Bumasheva, V.V., and Tarasov, B.P. (1984) Influence of partial replacement of nickel or yttrium by other metals on absorption of hydrogen by compound YNi3. Zh. Neorgan. Khim., 29, No. 5, 1136-1141 (in Russian). 

Atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine), a photosynthetic inhibitor that is used in large quantities for weed control in com and sorghum, has been treated electrochemically in aqueous solution on reticulated vitreous carbon cathode in the presence of noble-metal catalysts (Stock and Bunce 2002). Elec-trocatalytic hydrogenolysis to 2-ethylamino-4-isopropylamino-s-triazine occurs in quantitative yield, and is most efficient with Pd-based catalysts. Current efficiency increases with increasing atrazine and catalyst concentration, and decreasing current density. The Authors observed a time lag between the start of the electrolysis and the appearance of the dechlorinated products, which was attributed to the absorption of hydrogen by the palladium lattice. As alternative to the electrochemical treatment, the degradation of chlorinated triazines by zero-valent-iron was already mentioned (Dombek et al. 2004). 

In 1840, V. A. Jaquelain founded a method of separating hydrogen from its admixture with methane and ethylene on the absorption of hydrogen by potassium and G. Gehlhoif used the absorption of hydrogen by the alkali metals in order to obtain the pure gas. The alkali hydrides decompose readily in moist air, and tumultuously in water. Hydrogen is liberated but without incandescence e.g. LiH+H20=Li0H- -H2+31 6 Cals. Analyses of these hydrides are in accord with the formulae LiH, NaH, KH, EbH, and CsH, and no other hydrides have been observed. 

It has many applications as a tracer, for example, to study the movement of ground waters, and to study the al sorption of hydrogen by metals and the absorption of hydrogen on metal surfaces. Many deuterated and tritiated compounds have been synthesized and studied. Some of the important physical properties of the isotopes of hydrogen are listed in Table 8-2. 

The same type of hysteresis loop which was noted in the absorption of hydrogen in palladium, where a- and yS-phases co-exist, is observed also in the absorption of hydrogen by iron (31), where now the two phases are produced by allotropy in the metal. The permeability-temperature curve shows a break at this point (Fig. 63) (5i). Indeed, wherever a phase change occurs one may look for a variation in the permeability, so that the property of permeability may be used to determine transition points. The change in permeability of nickel towards hydrogen has similarly been used to characterise the Curie point in nickel (62). 

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