M. Bereznitsky

Experimental elucidation of the anomalous hydrogen absorption in Al-containing pseudobinary intermetallic compounds

Abstract Experimental evidence supports an explanation of the peculiar x -dependence of the hydrogen absorption in Zr(Al x Co 1− x ) 2 , Zr(Al x Fe 1− x ) 2 and LaAl x Ni 5− x in terms of two opposing trends: increasing metal–hydrogen attraction but decreasing hydrogen–hydrogen attraction. The latter factor causes a vanishing of the hydrogen absorption at high Al concentrations. Such an explanation is proposed, to the best of our knowledge, for the first time. It may give a new perspective in understanding and tailoring hydrogen absorption in intermetallic compounds.

Variation of hydriding kinetic properties in massive samples of the LaAlxNi5−x system as a function of the Al content

Abstract The hydriding kinetics of the LaAlxNi5−x (0≤x≤1.4) system was monitored for massive rectangular parallelepiped samples utilizing hydrogen pressures up to 70 atm and temperatures between 238 and 423 K. The apparent activation energies for each composition are derived from the temperature dependence of the reaction rate constants at given P/Peq ratios, where P is the applied experimental hydrogen pressure and Peq is the equilibrium pressure at a given temperature. The activation energies appear to be model-independent and indicate a minimum at x=0.25, resulting in a maximum hydriding reaction rate in the vicinity of this composition. This behavior correlates well with some bulk properties of the LaAlxNi5−x intermetallic system and the corresponding hydrides.

Pressure and temperature dependence of hydriding kinetics in massive Zr(AlxFe1−x)2 samples, x=0.2, 0.5

Abstract The hydriding kinetics of the Zr(Al x Fe 1− x ) 2 , x =0.2, 0.5, compounds was monitored for massive rectangular parallelepiped samples utilizing hydrogen pressures up to 80 atm and temperatures between 238 and 353 K (1 atm=101 325 Pa). The self-heating effects were sufficiently low under these conditions to enable approximately isothermal conditions for the kinetic experiments. The experimental data were fitted to a shrinking core model. The hydrogenations of some samples were observed in real time, utilizing a video camera and specially designed experimental system. The apparent activation energies, E a , for each compound are derived from the temperature dependence of the reaction rate constants at given P / P eq ratios, where P is the applied experimental hydrogen pressure and P eq is the equilibrium pressure at a given temperature. Combination of the present results with a previous one for Zr(Al 0.1 Fe 0.9 ) 2 indicates a minimum of E a at the x =0.2 compound. This behavior is explained in view of the atomic vibrational properties across the Zr(Al x Fe 1− x ) 2 system.