Metals, hydrogen absorbing

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. 

Analysis methods for hydrogen absorbed in the deposit have been described (65), and instmments are commercially available to detect hydrogen in metals. Several working tests have been devised that put plated specimens under strain and measure the time to failure. A method for cadmium-plated work has been described (66) as has a mechanical test method for evaluating treatments on AlSl 4340 Steel (67). Additional information on testing for hydrogen embrittlement is also available (68). 

Such binary borides (p. 145), carbides (p. 297) and nitrides (p. 417) as are formed have been referred to already. The ability of the metals to absorb molecular hydrogen has also been alluded to above. While the existence of definite hydrides of nickel and platinum is in doubt the... 

Enyo, M. Sorption of Hydrogen on and in Hydrogen-Absorbing Metals in Electrochemical Environments 30... 

Hydrogen-Absorbing Metals in Electrochemical Environments Analysis of Mass Transfer and Fluid Flow for 32 Electrochemical Processes... 

This method has been applied to analyses as different as the determination of vitamin B12 in biological tissue (using a 60Co label), and the amount of hydrogen absorbed into the lattice of a transition metal. 

A description of the trapping process may be based on the chemical potentials of the hydrogen absorbed in the metal. In the general case, the chemical potential of interstitial or diffusible hydrogen may be described by the equation... 

When hydrogen combines with the metal alloy (in granular form or particles), an exothermic reaction occurs. The gas is thus stored in these metal particles until some heat is applied to release the hydrogen and build up the pressure in the tanks. When a metal hydride absorbs hydrogen, heat is given off. A hydride cold-start heater can be developed that instantly heats an automobile s catalytic converter when the car is started to dramatically reduce overall exhaust pollution up to 80%. 

The sealed nickel—metal hydride battery has characteristics very similar to those of the sealed NiCd battery. The main difference is that the NiMH battery uses hydrogen, absorbed in a metal alloy, for the active negative material in place of the cadmium used in the NiCd battery. The NiMH batteries have a higher energy density and are considered more environmentally friendly than the NiCd battery. The sealed NiMH battery, however, does not have the very high rate capability of NiCd battery, and is less tolerant of overcharge. 

Practical use of hydrogen-absorbing metals can be classified into the... 

Figure 3.28 shows the role of hydrogen-absorbing metals in the hydrogen energy system, proposed by Kitada. ... 

Metal/hydrogen systems have been treated successfully by the assumption that, at low hydrogen concentrations, deviations from Sieverts Law result from an elastic interaction energy among the absorbed hydrogen atoms. The interaction is attractive in nature since including a hydrogen atom into an interstitial site results in a local expansion of the metal lattice. It is well known that lattice dilation exerts an attractive interaction with interstitial solute atoms. Under this... 

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