Hydrogen accumulators

But numerous papers published during rece t decades showed that hydrogen can be a very useful alloying element for production of new materials (such as hydrogen accumulators, neutron absorbers, etc.) or new technologies for alloy processing with improved treatment parameters as well as with the improved final properties of the alloys. ... 

The above discussion has assumed that the crack is loaded in mode 1 (the crack opening mode, with a tensile stress normal to the plane of the crack). Hydrogen has relatively little effect in modes II or III, as these generate shear stresses at the crack tip, rather than tensile stresses, and the shear behaviour of steels is relatively little affected by hydrogen, presumably because dilation of the lattice at the crack tip (which does not occur in modes II and III) is required for hydrogen accumulation. 

Hydrogen accumulates in the head space of the anaerobic fermentor. 

The biogeochemical fluxes and exposure pathways of various macro- and microelements are different from those shown for Tropical Rain Forest ecosystems. The chemical composition of leaves of tree species in Mangrove Forest ecosystems is connected with higher content of Mg, Cl and S-SO4- and lesser content of K and Si as compared to the leaves of trees from Tropical Rain Forest ecosystems. The content of A1 is 3-4 times higher than that of Si and this can be related to the values of hydrogenic accumulation of these elements in soils (Figure 3). 

The heat of hydrogenation of one carbon-carbon double bond of allene is 41 kcal mol-1, whereas that of an ordinary alkene is around 29 kcal mol-1. Thus the cumulated double bond of allene liberates 12 kcal mol-1 more than that of a simple alkene on hydrogenation. Accumulation of two carbon-carbon double bonds imparts an extra reactivity to allene, making it a remarkably active component participating in a variety of cycloaddition reactions as a two-carbon unit. 

A heterogeneous hydrogen-accumulating system containing porous Ti with 0.4 wt% Ni combined with high-purity Ti chips was tested for methane activation.588 Methane conversion to C1-C4 hydrocarbons reached a value of 20% with 50-55% of ethylene at 450° C and 10 atm. The hydrogen formed was accumulated as TiH2. 

Figure 1. Hydrogen accumulation as a function of time on a stoichiometric, metal-free SrTiOs crystal in 20M NaOH (41)...

Shortly after realization of preparative syntheses of fullerenes their high chemical activity was proved and fullerene hydrides were obtained (Goldshleger and Moravskii 1997). The methods of synthesis of fullerene hydrides have been intensively developing because these hydrides are considered to be the base compounds for the development of fullerene chemistry, possess a potential for the use as hydrogen accumulators. The... 

The C60H36 hydride contains 4.76 mass% of hydrogen. It can be used as hydrogen accumulator because in the temperature of 400-600 K the hydrogenation-dehydrogenation cycles are thermodynamically allowable. The thermodynamic parameters and equilibrium hydrogen pressures for the reaction... 

The research into the processes of their reversible reaction with hydrogen is of interest in connection with the development of systems for hydrogen accumulation and storage. The high potential for practical applications of fullerenes will promote the progress in this field of studies. This will inevitably result in the development of materials of new types and generations. 

TABLE 3. Metallic and organic hydrides as hydrogen accumulators... 

Thus, from Eq. (12.61) and taking uk as positive when the stress is tensile and negative when it is compressive, one sees that hydrogen accumulates in regions of compressive stress. The stress need not be externally applied. 

So far, corrosion has not come into the picture except as it stimulates the H+ + e —> Hads electronation reaction and is therefore responsible for the hydrogen accumulation inside the metal. Now consider a metal that is simultaneously being corroded and some parts of which are subjected to a tensile stress. The permeating hydrogen will tend to initiate a crack in the region where the stress is great by the mechanism described in the previous section, and the electrolytic solution (the corrosive environment) comes into contact with the inside of the crack (Fig. 12.77). 

Tarasov B.P. Hydrogen accumulation in carbon nanostructures, In Fullerenes and fullerenelike structures . 2000. Minsk BGU. P. 113-120. 

Keywords hydrogen accumulator, hydrated methane, polymorphism, phase transition, nanostructure of ice, modeling... 

SOME LESSONS OF THE CHEMISTRY OF METAL HYDRIDES IN THE LIGHT OF PROBLEMS OF HYDROGEN ACCUMULATION... 

Hydrogenolysis is, of course, the very regrettable process with reference to hydrogen accumulation problems. This effect makes the manipulations of the hydride properties by the variation of IMCs (within the framework of the given R-M metallic system) impossible. 

At the same time, we believe that the available now lessons of the chemistry of transition metal hydrides make it possible to avoid some mistakes in another field of inorganic chemistry related with hydrogen accumulation. 

Therefore layered InSe and GaSe crystals are rather promising for hydrogen energetic as operating elements in systems for hydrogen accumulation [4, 5], The concentration of hydrogen in them can reach values x = 3+4, where x is the amount of introduced atoms per one formula unit of the crystal bulk. 

Tarasov, B.P., Fokin, V.N., Borisov, D.N., Gusachenko, E.I., Klyamkin, S.N., Yakovleva, N.A., and Shilkin, S.P. (2004) Metal hydride hydrogen accumulators on the basis of alloys of magnesium and rare-earth metals with nickel. J. Altern. Energy and Ecology (ISJAEE), No. 1, 47-52 (in Russian). 

In recent years we are pinning our hopes on carbon nanomaterials, such as fullerenes, carbon nanofibers and carbon nanotubes for the use as hydrogen-accumulating matrixes. 

Nevertheless, as it seems to us, the high hydrogen capacity of new carbon nanomaterials is actual. In addition, it is essential that carbon nanotubes (CNTs) are inert in the environment and the heat of H2 adsorption on CNTs is considerably lower than the heat of metal hydrides formation. This allows one to look forward to a possibility of the use of carbon nanomaterials in the actual systems for hydrogen accumulation. 

V.A Kolatchev, R.E. Shalin, A.A. Ilyin (1995) Alloys - Hydrogen Accumulators, Reference Book, Metallurgy, Moscow. 

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