Particles metal hydride

One of the problems with early hydride systems was decrepitation of the alloy. Each time the metal hydride storage tank was recharged the particles would break down and eventually the particles became so small that they began to pass through the 5-p.m sintered metal filter which kept the hydride inside the tank. Addition of 0.5% manganese, which caused the decrepitation process to cease once the particles reached a size of about 10 p.m, solved this problem. 

Condensation of metal vapors followed by deposition on cooler surfaces yields metal powders as does decomposition of metal hydrides. Vacuum treatment of metal hydrides gives powders of fine particle size. Reaction of a metal haHde and molten magnesium, known as the KroU process, is used for titanium and zirconium. This results in a sponge-like product. 

By far the most important redox reaction relative to chemical stability is the reaction between an oxidizable material and oxygen from air. The particle size and any droplets have a large effect on the combustion properties. Some substances react so rapidly in air that ignition occurs spontaneously. These so called pyrophoric compounds (white phosphorus, alkali metals, metal hydrides, some metal catalysts, and fully alkylated metals and nonmetals) must be stored in the absence of air. 

Alkali metals, finely divided aluminum and magnesium particles, hydrazine, diborane, metal hydrides, and hydrogen are strong reducing agents [35]. An example of a significant problem is the possible explosive reaction between light metals and carbon tetrachloride which is itself a stable compound [57]. 

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%. 

AB5 metal hydride particles have been dispersed in a polymer matrix in order to entrap the micro and nanoparticles produced by repeated fragmentation processes of the metal phase during the... 

It was shown that the AB5/ABS composite tolerated the hydrogenation effects on metal particles, with no losses in hydrogenation kinetics. The results indicated that the compositions are suitable for metal hydride based hydrogen storage devices. 

One remark talks about nano-hydrides become in fashion now. But it is necessary to realize that nearly all the metal hydrides are nano-materials initially, definitely. In the course of hydrogenation, the compact samples of metals (or IMCs) disintegrate into small particles which have (according microscopic or surface-area measurements) micro- (and not nano-) size. However, this does not speak yet for anything. These particles are not monocrystals, but - micro-sized conglomerates of nano-sized clasters (domains). These clasters have sometimes the structure, which differs from that, indicated (defined) by X-ray or neutron... 

Duration of a cycle of HHP operation is defined as time required for reaction hydrogenation/dehydrogenation in pair hydride system. This time determines heat capacity of HHP. Duration of a cycle depends on kinetics of hydrogenation reactions, a heat transfer between the heated up and cooling environment, heat conductivities of hydride beds. Rates of reactions are proportional to a difference of dynamic pressure of hydrogen in sorbers of HHP and to constants of chemical reaction of hydrogenation. The relation of dynamic pressure is adjusted by characteristics of a heat emission in beds of metal hydride particles (the heat emission of a hydride bed depends on its effective specific heat conductivity) and connected to total factor of a heat transfer of system a sorber-heat exchanger. The modified constant of speed, as function of temperature in isobaric process [1], can characterize kinetics of sorption reactions. In HHP it is not sense to use hydrides with a low kinetics of reactions. The basic condition of an acceptability of hydride for HHP is a condition of forward rate of chemical reactions in relation to rate of a heat transmission. 

Denote the radius of a shrinking spherical particle of powder metal hydride by L(t), the radius of the shrinking hydride core by p(t). When some amount of... 

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