N. A. Yakovleva

Effect of Mechanical Activation on the Reaction of Magnesium Hydride with Water

The effect of the parameters of mechanochemical activation of magnesium hydride and MgH2-graphite binary compositions on the parameters of materials and their hydrolytic activity has been studied. It is concluded that mechanochemical treatment increases the reactivity of magnesium hydride in its reaction with water. Graphite provides an additional activating effect during the mechanochemical treatment of MgH2. A deformation dose of 20 kJ/g was determined to be the optimum one for achieving the highest reactivity in the hydrolysis reaction with the formation of MgH2-graphite composites. As a result of the hydrolysis of such materials, up to 970–1280 mL hydrogen per composite gram is evolved in 40 min of the reaction with water without an additional change in the solution acidity.

Valence state of hydrogen in hydrides of intermetallic compounds

The experimental data on the mechanism of hydride dispersion of intermetallic compounds of the LaNi5 type and the crystal structures of hydride phases based on these compounds were analyzed. A new approach was suggested and substantiated, which allows one to consider hydride dispersion as a result of a redox process associated with the formation of Hδ− hydride ions at concentrations of hydrogen in the solid hydrideCH>-CHcr. The value ofCHcr is determined by the redox potential of the reaction Hδ++Mδ−⇌Hδ′−+Mδ′+.

Influence of aluminum and tin on the mechanism of hydrogenation of LaNi5-based intermetallides

The interaction of hydrogen with the LaNi5-based intermetallides containing different amounts of aluminum and tin was studied using the calorimetric titration technique. Based on the formal kinetic approach and X-ray diffraction data, a probable mechanism was proposed for the hydrogenation of the intermetallides in the temperature interval from 308 to 353 K. The phase of the α-solid solution in all the intermetallide—hydrogen systems is formed via similar mechanism. However, the mechanism of the β-hydride phase nucleation and growth changes dramatically when the content of the main group metal increases.

Calorimetric investigation of interactions in the LaNi4.75Al0.25−H2 and LaNi4.8Sn0.2−H2 systems

The interaction of hydrogen with intermetalic compounds LaNi4.75Al0.25 and LaNi4.8Sn0.2 has been studied in the temperature range 308–353 K by the calorimetry titration method. The mechanism of hydrogenation was investigated. It was shown that, as the temperature increases, the initial concentration of hydrogen in the metal lattice needed for β-hydride formation decreases. It was assumed that this effect is related to the concentration of Hδ+ atoms, which “oxidize” the metallic matrix according to the scheme Hδ++M0→Hδ−+M+. The enthalpy and entropy of hydrogenation for the LaNi4.75Al0.25−H2 system were calculated from thep-C-T curves and the calorimetry results. The thermodynamic parameters of the LaNi4.8Sn0.2−H2 system were obtained for the first time.

Calorimetric investigation of the interaction in the LaNi2.5Co2.4 Mn0.1−H2 system

The interaction of hydrogen with LaNi2.5Co2.4Mn0.1 was studied in a wide temperature range (308–393 K) using the technique of “calorimetric titration.” The shape of thep-C-T diagrams changes with temperature change. The values of enthalpy and entropy of hydrogenation of LaNi2.5Co2.4Mn0.1 were obtained for the first time by direct calorimetric investigations andp-C-T measurements. The volume effects of the hydrogen absorption reaction are considered, and the LaNi2.4Co2.4Mn0.1H4.9 hydride is shown to retain the CaCu5-type hexagonal structure.