Ternary Hydrides

Mg–Ni–Cu mixtures for hydrogen storage: A kinetic study

“…On the other hand, m falls: -in the range 2.1-2.2 for pure Mg samples (in agreement with Fernandez and Sanchez [37]), according to a nucleation and growth model (A2) [36]; -between 1.24 and 1.5 (unpublished results) for binary Mg-Ni mixtures with transition metal content up to 15 wt%, according to a ''first order'' reaction model (F1) [36]. Since m gives an indication about the rate limiting step of the overall process, it can be hypothesized that in the ternary mixtures the discharging process is kinetically limited by transformations involving the Cu containing phases.…”

“…m falls in the range 0.57-0.65 (0.996 fitting correlation factor r 0.998) for all the compositions and the explored temperatures, close to m ¼ 0.60 for pure Mg (in agreement with [35]). From these m values it is possible to hypothesize that the formation of ''free MgH 2 '' takes place with a diffusion mechanism [36], with the microscopic step controlling the overall rate of the process being the diffusion of the hydrogen atoms into the Mg lattice. k 623K,FMg increases from 8.7 Â 10 À3 s À1 for pure Mg to 9 Â 10 À2 s À1 when Mg ¼ 70 wt% and even up to 8 Â 10 À1 s À1 in the mixtures with Mg ¼ 50 wt%.…”

“…m falls in the range 0.58-0.7 (0.994 r 0.998), where also the values for binary mixtures containing only ''bonded Mg'' phases (43% Mg þ 57% Cu, Mg 2 Cu molar stoichiometry, m ¼ 0.68; 45% Mg þ 55% Ni, Mg 2 Ni molar stoichiometry, m ¼ 0.62) are comprised. This suggests that also the ''bonded Mg'' phases hydrogenation could take place with a diffusion mechanism [36], with the rate limited by the migration of the hydrogen atoms into the lattices of the intermetallic phases. k 623K;BMg increases by increasing the transition metals content from 2 Â 10 À3 s À1 when Mg ¼ 70 wt% and 80 wt% up to 7 Â 10 À3 s À1 when Mg ¼ 50 wt%.…”

“…W is in very good agreement with the experimental desorbed H 2 amounts (wt%). m falls in the range 1.0-1.2, suggesting that the overall dehydrogenation process can be described with a ''geometrical contraction model (R2 ¼ contracting area)'' [36]. It should be noted that m values in the same range are also found: -for binary Mg-Cu mixtures containing only ''bonded Mg'' phases (43% Mg þ 57% Cu); -for binary Mg-Cu samples containing both ''bonded Mg'' phases and ''free Mg'' (mixtures with Cu content up to 30 wt%).…”

Magnetic Properties of Palladium and Palladium–Platinum Alloy of Various Hydrogen Content

“…[6][7][8][9][10][11][12] This is because they show such a low equilibrium pressure at ambient temperature that measurements of magnetic properties can be carried out rather easily in air or inert gas atmosphere. Other metal hydrides have in spite of their interesting properties too high equilibrium pressure to allow measurements at ambient temperature in air or inert gas atmosphere.…”