Absorption kinetics, hydrogen

N. Hanada, T. Ichikawa, S. Hino, H. Eujii, Hydrogen absorption kinetics of the catalyzed MgHJ by niobium oxide, J. Alloys Compd. 446-447 (2007) 67-71. 

Keywords hydrogen atoms, residual stresses, hydrogen absorption kinetics. 

And again the residual stresses change the symmetry of the task the diffusion process in the hollow cylinder obeys the law of flat symmetry. The hydrogen absorption rate increases from the side of the outer boundary. Acceleration of the process kinetics is caused by reducing the compression stresses in the radial direction, which are changed with the tensile stresses. The solution of tasks (5) and (6) is well known. Thus, it is not difficult to obtain the solution of task (4). This solution describes the hydrogen absorption kinetics from the two surfaces of the hollow cylinder at given character of the residual stresses distribution... 

The hydrogen absorption kinetics obeys the exponential law and depends on the equilibrium concentrations on the area boundaries. The latter ones is defined by the level of the residual stresses on the corresponding boundaries... 

SolubiHty of carbon dioxide in ethanolamines is affected by temperature, amine solution strength, and carbon dioxide partial pressure. Information on the performance of amines is available in the Hterature and from amine manufacturers. Values for the solubiHty of carbon dioxide and hydrogen sulfide mixtures in monoethanolamine and for the solubiHty of carbon dioxide in diethanolamine are given (36,37). SolubiHty of carbon dioxide in monoethanolamine is provided (38). The effects of catalysts have been studied to improve the activity of amines and provide absorption data for carbon dioxide in both mono- and diethanolamine solutions with and without sodium arsenite as a catalyst (39). Absorption kinetics over a range of contact times for carbon dioxide in monoethanolamine have also been investigated (40). 

Al-Soufi W, Grellmann KH, Nickel B (1991) Keto-enol tautomerization of 2-(2 -hydroxy-phenyl)benzoxazole and 2-(2 -hydroxy-4 -methylphenyl) benzoxazole in the triplet state hydrogen tunneling and isotope effects. 1. Transient absorption kinetics. J Phys Chem 95 10503-10509... 

Said this, we can let the reader to recall Fig. 1.15, where we depicted amorphous-like phase regions at grain boundaries as the pathways open for preferential diffusion of hydrogen atoms. Apparently, an alloy can benefit from some fraction of amorphous phase to improve kinetics of hydrogen absorption, but complete amorphization of crystalline lattice lowers capacity for storing hydrogen [156]. Mechanochemical activation is therefore a complex process where kinetic and thermodynamic effects must be firstly well understood, and then optimized. 

The hydrogen absorption/desorption kinetics are usually analyzed by applying the JMAK (Johnson-Mehl-Avrami-Kolmogorov) theory of phase transformations, which is based on nucleation and growth events [166-168] where a is the fraction transformed at time t or alternatively for hydrides the fraction absorbed... 

In a case of the PCX absorption curve after evacuation, the system must be heated up to a test temperature and thermally stabilized. Then by gradually increasing pressure we will observe hydrogen absorption related to a particular pressure of hydrogen. It is important that the time of visible pressure change at every step is closely connected with the kinetics of process at an applied temperature. 

Fernandez and Sanchez [18] investigated the kinetics of hydrogen absorption and desorption by activated magnesium powder (several cycles of hydrogen absorp-tion/desorption at 375°C) using a volumetric technique. They pointed out that for-mation/decomposition of metal hydrides comprises a number of steps taking place in series transport to the surface, dissociation, H chemisorption, surface-... 

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