Hydride kinetics

The hydrogens within the octahedral olefin-dihydride intermediate are transferred consecutively with overall cis addition, and the rate-determining step (k9) is olefin insertion to give the alkyl- hydride. Kinetic and thermodynamic parameters for nearly all the steps of Fig. 1 have been estimated for the cyclohexene system. Because the insertion reaction is generally believed to require a cis disposition of the hydride and olefin... 

We have focused on experimental values in this work, but it is important to note two areas of group 14 hydride kinetics that are not discussed but in which we expect to see considerable progress in the near future. One is the kinetics of reactions of radicals centered on atoms of the third row and above, and the other is computational estimates of rate constants. 

G. Friedlmeier, M. Groll, Experimental analysis and modelling of the hydriding kinetics of Ni-doped and pure Mg, J. Alloys Compd. 253-254 (1997) 550-555. 

K.-E. Aguey-Zinsou, T. Nicolaisen, J.R. Ares Fernandez, T. Klassen, R. Bormann, Effect of nanosized oxides on MgH (de)hydriding kinetics, J. Alloys Compd. 434 35 (2007) 738-742. 

M. Zhu, Y. Gao, X.Z. Che, Y.Q. Yang, C.Y. Chung, Hydriding kinetics of nano-phase composite hydrogen storage alloys prepared by mechanical alloying of Mg and MmNi (CoAlMn), J. Alloys Compd. 330-332 (2002) 708-713. 

Passivation of active metals to hydrogen reaction has been recognized as an important problem in basic metal-hydrogen studies, especially in their technological application to various situations. Few investigations have addressed these difficulties. The advent of modern surface analytical techniques such as photoelectron spectroscopyy Auger electron spectroscopy, and ion spectrometry offer a tremendous opportunity to attack the passivation question. Each of these techniques is discussed with regard to their capabilities and application to hydride kinetics. 

Keywords solar-to-hydrogen conversion, photoanode, metal hydride, kinetic characteristics, equilibrium potential... 

Mintz, M. H. and Zeiri, Y. (1995) Hydriding kinetics of powders, Journal of Alloys and Compounds, 216, 159-175. 

The kinetically favored site of protonation is frequently a basic oxygen or nitrogen atom rather than a metal (see the discussion of hydride kinetic acidities below). In Equation 3.113, Ru3(CO),(,NO undergoes kinetic protonation on the nitrosyl oxygen, although the Ru-Ru bond is the thermodynamically favored site of protonation. In Equation 3.114, the kinetic site of protonation is the piperidine nitrogen, although the thermodynamic site is the iridium. -... 

Millet P, Ngameni R. (2011), Non-harmonic electro-chemical and pneumato-chemical impedance spectroscopies for analyzing the hydriding kinetics of palladium , Electrochim Acta, 56(23), 7907-7915. 

At high pressures, where n = 0 and 0 = 1, the solid surface is saturated by and the hydriding kinetics are unaltered by changes in pressure. The rate is then controlled by a process occurring within the solid and depends only on temperature, as defined by the Arrhenius term. As fixed by the pressure-independent isotherms beyond the saturation boundary indicated by P, in fig. 14, for the rate-controlling process in the solid phase is 29kJ/mol as determined by Bloch and Mintz (1981). 

Recent measurements of hydriding kinetics for plutonium power (0.2 to 0.3 m /g) by Stakebake (1992) show that the reaction is adsorption controlled at low pressures and reaction controlled at high pressures. Results for wide ranges of temperature ( — 41 to 350°C) and pressure (0.05 to 200Torr) are consistent with earlier observations by Stakebake (1981) for a powdered delta-phase alloy. In addition to confirming that the rate is independent of temperature, the combined data show three regions of pressure dependence with n = 1, j and 0 at low (< 0.5 Torr), intermediate and high (P > 7 Torr) pressures, respectively. 

From these results, a limitation of PIS analysis should be pointed out (especially when powdered samples are used, as LaNi5 considered here) the mean particle radius (at the measurement point) must be known to normalize impedance diagrams. This is because different triplet values r D dP/dC lead to similar impedance diagrams. If not, it is difficult to analyze quantitatively the hydriding kinetics. 

P. Millet, C. Decaux, R. Ngameni, and M. Guymont, Fourier-domain analysis of hydriding kinetics using pneumato-chemical impedance spectroscopy, Research Letter in Physical Chemistry, vol. 2007, Article ID 96251, 5 pages, 2007. 

Larsen and Livesay (1980) chose SmCoj as a representative compound on which to study the intrinsic hydriding kinetics of compounds of the RCoj family. The compound LaNij and several pseudobinaries were studied by Belkbir et al. (1980, 1981). All these authors analysed their data in terms of the Johnson-Mehl equation (Johnson and Mehl, 1939 Avrami, 1940)... 

Magnesium-based alloys have been projected as attractive materials for MH electrodes with specific capacity values as high as 1000 Ah/kg. However, these alloys are prone to corrosion in alkaline environment. The major problems associated with these alloys are the sluggish hydriding kinetics at room temperature and oxidation of the material under ambient environmental conditions (Figure 7.10). 

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