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The reaction between magnesium amide and hydride at a molar ratio of 1:2 by means of mechanical ball mining has resulted in the release of a stoichiometric amount of [H.sub.2] and the formation of magnesium nitride. Thermodynamic calculations have shown that the hydrogen release reaction of [1Mg[(N[H.sub.2]).sub.2] + 2Mg[H.sub.2] is mildly endothermic, but the low reaction enthalpy has predicted impractical operation conditions of the hydrogen uptake reaction.

Abstract: A new ternary Metal–N–H sample of Mg–Ca–N–H has been prepared by mechanical ball milling—Mg(NH2)2 and CaH2 (1:1) in a planetary ball mill machine. The structure and hydrogen desorption properties were investigated. The results show that pure H2 gas can be released during ball milling. After 72h ball milling, ∼3.8H atoms (∼3.88wt%) were found to be detached from the starting material, which is higher than most of the traditional metal hydrides. Moreover, volumetric release and soak tests on the sample collected after 12h of ball milling show that hydrogen desorption starts at a temperature around 50°C. DSC measurement on the post-12h milled sample reveals that the overall heat effect of hydrogen desorption is ∼28.2kJ/mol H2, implying that Mg–Ca–N–H system could be a potential lower temperature hydrogen storage system. In addition, the high-pressure release testing shows that 3.0wt% of hydrogen can be desorbed from the post-12h milled sample at a temperature of 380°C although 80bars of hydrogen was applied, indicating that the Mg–Ca–N–H possesses high equilibrium desorption pressure. However, recharging the sample with hydrogen is rather difficult, which may be due to the high kinetic barrier. [Copyright &y& Elsevier]

Abstract: Sintered pellets of Ce-doped Ba2In2O5 (BIC) were prepared from nanopowders. The electrical conductivities were measured using ac impedance spectroscopy under different atmospheres and temperatures. The electrical conductivity of sintered BIC was found sensitive to environmental humidity when the temperature was below 300°C. However, in the presence of hydrogen, the electrical conductivities were independent of water content in the range of 0–30vol%. The electrical conductivities of BIC were significantly affected by the presence of hydrogen in a temperature range of 100–300°C. The estimated protonic transference number and the measured open circuit voltage suggested the existence of electronic conduction. The coefficient of thermal expansion of BIC is 11.2×10−6 K−1 from 25 to 1250°C. [Copyright &y& Elsevier]

Abstract: A two-stage hydrogen release of 4.9wt.% was observed on a mixture of Mg(NH2)2 and CaH2 at 1:2 molar ratio. The H2 desorption in the temperature range from room temperature to 260°C was recyclable, which was observed by temperature-programmed-desorption (TPD), volumetric measurement and Fourier transform infrared (FT-IR). At high temperature, a ternary nitride CaMg2N2 and a solid solution of CaNH/Ca2NH, characterized by X-ray diffractometry (XRD), were formed. [Copyright &y& Elsevier]

Abstract: The dependence of chemical reaction between Mg(NH2)2 and MgH2 on the ball-milling conditions has been investigated. While the decomposition of the component Mg(NH2)2 resulted in gaseous products consisting mainly of ammonia, the mixtures of Mg(NH2)2–MgH2 prepared by ball-milling released H2 at temperatures as low as 65°C. In addition, the increase in ball-milling time can effectively suppress the ammonia evolution during the thermal treatment. The conversion of the amide and hydride to imide-like structure was demonstrated by FTIR and XRD characterization. A total amount of 4.8wt.% of H2 could be released from the investigated system. [Copyright &y& Elsevier]

A total of 7.4 wt % of hydrogen was released from the mixture of magnesium amide and magnesium hydride at a molar ratio of 1:2 by mechanical ball milling. Fourier Transform Infrared Spectroscopy (FTIR) and X-ray Diffraction (XRD) characterizations along with the amount of hydrogen released at different stages of ball milling reveal that magnesium imide was first formed in the reaction. The imide then reacted continuously with magnesium hydride and was converted to magnesium nitride and hydrogen. Thermodynamic calculation shows that the hydrogen desorption is a mild endothermic reaction with the standard enthalpy change of about 3.5 kJ/mol of H2.