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Abstract: The growth of the intermetallic layers at the interface of Ti–Ni diffusion couples was investigated under the co-effect of heat and direct current. Isothermal diffusion treatments for Ti–Ni couples were conducted at 500, 600 and 700°C for 5, 10 and 15h with and without the passage of DC current of 10A intensity. It was found that both Ti2Ni and TiNi3 layer form at the Ti–Ni interface in all couples treated by different process, but TiNi layer forms in the couples annealed above 600°C without current or at 500°C with current. The growth of the whole interfacial layer shows a parabolic relationship with time. The apparent activation energy of growth for the whole interfacial layer is 83.76kJ/mol in the couple treated by heating without a current, and it decreases to 42.11kJ/mol in the couple treated with a direct current of 10A during heating. The effect of the current on the growth of different intermetallic layers varies with its direction. [ABSTRACT FROM AUTHOR]

Abstract: The influence of additives on the reaction kinetics and microstructure refinement in LiBH4–MgH2 composites is investigated in detail. Indications of the rate-limiting processes during the reactions are obtained by comparison of the measured reaction kinetics with simulations with one specific rate-limiting process. The kinetics of the sorption reactions are derived from volumetric measurements as well as from in situ X-ray diffraction measurements. During desorption, the hydrogen is released at a constant rate, which is possibly correlated with the one-dimensional growth of MgB2 platelets. In contrast, the kinetic curves of the absorption reactions exhibit the typical shape of contracting-volume controlled kinetics. The microscopical interpretation of kinetic measurements are supported by transmission electron microscopy images confirming the formation of additive-nanostructures in the grain boundaries upon cycling. The present investigations underline the importance of the additives as nucleation substrates and the influence of microstructure on the reaction kinetics. [Copyright &y& Elsevier]