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Abstract: We have investigated the hydrogenation and dehydrogenation properties of binary RNi5 (R: La, Pr, Nd, Sm, Gd, Tb and Dy) intermetallic compounds in the pressure range of 0.1–35 MPa and temperature range of 223–298 K. Pressure–composition isotherms demonstrated that as the atomic number of R increased in RNi5–H systems, the single pressure plateau (LaNi5) split into two plateaux (PrNi5, NdNi5, SmNi5 and GdNi5), and then into three plateaux (TbNi5 and DyNi5), indicating the presence of two hydrides ( and phases) and then three hydrides (, and phases). The and phase transitions in the TbNi5–H system corresponded, respectively, to the and transitions in the RNi5–H (R: Pr, Nd, Sm and Gd) systems having two plateaux. [Copyright &y& Elsevier]

The C14 intermetallic TiCr1.9 compound was prepared by arc melting, annealed at 1623 K in helium atmosphere for 8 h, and then quenched in water. The X-ray diffraction profiles showed that the crystal structure transformed from C14 to bcc after mechanical grinding for 18 h. The hydrogenation properties of the sample were examined by pressure–composition isotherm measurements. This sample with bcc structure reacted with hydrogen by maintaining the bcc structure. The maximum hydrogen content was found to be about 0.5 H/M at 273 K and 10 MPa, where H/M means the atomic ratio of hydrogen to metal. This hydrogen content was smaller than that of other bcc structure alloys. The sample prepared by MG consists of nanosized grains of polycrystalline TiCr1.9 and amorphous-like structure regions, judging from the bright field image and the corresponding selected area diffraction pattern. The hydrogen storage capacity is reduced due to the amorphous-like structure. [Copyright &y& Elsevier]

We investigated the pressure–composition (P–C) isotherms of several binary RNi5 (R=La, Ce, Pr, Nd, Sm and Gd) intermetallic compounds to clarify the correlation of the hydrogen storage properties between multi-plateaux. It was found that all RNi5 compounds have similar P–C isotherms with two well-separated plateaux except for CeNi5, indicating that two hydrides with compositions of RNi5H3–4 and RNi5H6–7 are formed. With increasing the atomic number of R element in the RNi5 compounds, the unit cell volume decreases due to the decrease of the radius of the R element. This influences the absolute enthalpies of dehydrogenation |ΔH| of both hydrides (β and γ) to decrease, which consequently leads to the increase of the second plateau pressure as well as the first plateau. Contrary to LaNi5–H2 system, the |ΔH| of γ hydride is smaller than that of |ΔH| of β hydride for the other systems, which indicates that the pressure gap between two plateau pressures expands with decreasing temperature. The second plateau tends to disappear with large atomic number of R element because the |ΔH| value approaches to zero. [Copyright &y& Elsevier]

Passively administered alloantiserum suppressed the in vivo growth of allografted mouse plasmacytoma X5563 with the aid of host cells, probably macrophages, but not with complement. Furthermore, it was shown that alloantiscrum probably participates in the process of tumour cell destruction in vivo as opsonin rather than as rytophilic antibody. On the other hand, administration of a decreased dose of the same whole antiserum or its fractions of γM as well as γG, or prior active immunization with living tumour cells, could induce the characteristic pattern of immunological enhancement. From concurrent studies, it was considered that enhancement might have been induced by the suppression of the development of the host's own immunity against tumour. [ABSTRACT FROM AUTHOR]

Abstract: The solution density, viscosity and conductivity of MClO4 (M = Li and Na) solutions in propylene carbonate and γ-butyrolactone are measured at the concentrations of <1.5–2.0 mol dm−3. The partial volume of the solute, derived from the density, of NaClO4 is greater than that of LiClO4 as expected. NaClO4 produces less viscous and more conductive solutions than LiClO4 throughout the examined concentration range. Notably, the conductivity of the NaClO4 solutions is 10–20% higher than that of the LiClO4 solutions at T/K = 298. The validity of the empirical cubic root law, Λ(C) = Λ 0 − AC 1/3, is examined, where Λ and Λ 0 are the molar conductivities at the molarity C and at infinite dilution. The meaning of the slope A is interpreted in the theoretical framework of the pseudolattice model. [Copyright &y& Elsevier]

Abstract: Hf7Ni10 has the same crystal structure as Zr7Ni10, which shows several unusual hydrogenation properties such as reversible hydrogenation by irreversible phase transformation and structural change caused by hydrogenation followed by dehydrogenation, and its hydrogenation properties have been unknown. The phase relation and hydrogenation properties of Hf x Zr7−x Ni10 alloys were investigated in the compositional range from Zr7Ni10 () to Hf7Ni10 (). All the samples were obtained by arc melting followed by heat treatment in vacuum. The constituent phase was identified by the combination of X-ray diffraction and microscopic analysis and hydrogenation properties were examined by differential scanning calorimetry and Sieverts’ method. No structural change from orthorhombic Cmca type to another one such as tetragonal type and orthorhombic Pbca type was observed for the addition of Hf and Hf was substituted for Zr in Zr7Ni10 in all the compositional range we examined. The lattice constant of the aimed phase decreased with an increase in Hf content. The measurements using differential scanning calorimetry indicated that the Hf-substituted alloys showed the same phase transformation as Zr7Ni10 in hydrogenation, that is the unusual phase transformation that an intermediate hydride phase appears only in dehydrogenation but not in hydrogenation. The transformation temperature decreased with an increase in Hf content. [Copyright &y& Elsevier]

Orimo et al. reported that nanostructured graphite, prepared by using the mechanical grinding under hydrogen atmosphere, contained more than 7 mass% of hydrogen whose thermal desorption spectrum (TDS) showed characteristic two peaks; one is at around 700 K and the other around 1000 K [Appl. Phys. Lett. 75 (1999) 3093; Appl. Phys. A72 (2001) 167; J. Appl. Phys. 90 (2001) 1545]. We confirmed this claim; namely, c.a. 4.5 mass% of hydrogen was detected by TDS in the desorbed gas from graphite powder mechanically ground under hydrogen in a Cr/Ni steel mortar. Yet the mechanism of hydrogenation and the physico-chemical state of adsorbed hydrogen are not known well. We found that the amount of contained hydrogen depends significantly on the grinding mortar. When a Cr steel mortar was used, we obtained 2 mass%; and when an agate mortar was used, only a trace amount of hydrogen was detected. The transmission electron microscopy and the X-ray powder diffractometry indicated that the nanostructured graphite ground in steel mortars contained a large quantity of cementite, Fe3C, to which the iron element was supplied by wearing out of mortar walls during the grinding. We examined the influence of metal particles by intentionally adding iron and nickel powder into graphite during the grinding in the metal-free agate mortar. Although in the agate mortar with metallic additives the hydrogenation did not proceed as much as in the steel mortar, the TDS spectrum showed characteristic features. The presence of catalytic metal particles seems to be a prerequisite for the hydrogenation of graphite under hydrogen by mechanical grinding. [Copyright &y& Elsevier]

A model is proposed which includes the charge transfer reaction and the formation of adsorbed hydrogen at the electrode/electrolyte interface, absorption of hydrogen into the solid-state MH electrode, recombination of adsorbed hydrogen atoms into molecular hydrogen dissolved in the electrolyte and hydrogen in the gas phase. It was found that the rate of the charge transfer reaction, as represented by the exchange current, is dependent on the partial hydrogen pressure (PH2) in a rather complex way: a positive linear dependence between log I0 and log PH2 is found at relatively low partial pressures, which subsequently passes through a maximum, turning into a negative dependence at higher partial pressures. Both the slopes of the lines and the turning points are found to be strongly dependent on the rate constants of the various reactions. The theoretical model has been verified with both switchable mirror MH thin film electrodes and multicomponent MH electrode materials, nowadays widely applied in commercial NiMH batteries. The as-deduced theoretical relationship will form the basis for the modelling of complete NiMH batteries. [Copyright &y& Elsevier]