This paper presents a new approach to tune the de/hydriding thermodynamic properties of Mg via forming reversible Mg base solid solutions in the Mg−In and Mg−In−Al systems by mechanical milling. The effect of solubility of In and Al on the reversible formation of solid solution structure and hydrogen storage properties were investigated. It is found that although the solute atoms unavoidably are rejected upon hydriding, the hydrogenated products of MgH 2 and intermediate MgIn compound could fully transform back to solid solution after dehydrogenation. In the hydriding of Mg(In, Al) ternary solid solution, Al would get dissolved into MgIn compound rather than forming free Al like the Mg(Al) binary solid solution. Therefore, the presence of In improves the dehydriding reversibility of Mg(Al) solid solution, and the reversible Al concentration could be increased up to the 8 at. %, which is just the solubility limit of Al in Mg by mechanical milling. The reversible phase transformation is responsible for the reduction in the desorption enthalpy of MgH 2 , being 12 kJ/(mol•H 2 ) reduction for the alloy Mg 0.9 In 0.1 relative to the desorption enthalpy of pure MgH 2 . Further, the hydrogen sorption kinetics of Mg(In) solid solutions are enhanced. Comparatively, both the thermodynamic destabilizing effect and the kinetic enhancing effect due to the Al dissolving are inferior to those due to the In dissolving. This work demonstrates a feasible way to improve the thermodynamics and kinetics of Mg base hydrogen storage alloys through traditional metallurgical method.

Electroplated hard chrome coating is widely used as a wear resistant coating to prolong the life of mechanical components. However, the electroplating process generates hexavalent chromium ion which is known carcinogen. Hence, there is a major effort throughout the electroplating industry to replace hard chrome coating. Composite coating has been identified as suitable materials for replacement of hard chrome coating, while deposition coating prepared using traditional co-deposition techniques have relatively low particles content, but the content of particles incorporated into a coating may fundamentally affect its properties. In the present work, Ni-W/diamond composite coatings were prepared by sediment co-electrodeposition from Ni-W plating bath, containing suspended diamond particles. This study indicates that higher diamond contents could be successfully co-deposited and uniformly distributed in the Ni-W alloy matrix. The maximum hardness of Ni-W/diamond composite coatings is found to be 2249 ± 23 Hv due to the highest diamond content of 64 wt.%. The hardness could be further enhanced up to 2647 ± 25 Hv with heat treatment at 873 K for 1 h in Ar gas, which is comparable to hard chrome coatings. Moreover, the addition of diamond particles could significantly enhance the wear resistance of the coatings.

Metal amides are promising candidates for hydrogen storage, hydrogen production, NH3 synthesis and cracking, and so on. However, the decomposition behaviors and mechanisms of metal amides remain unclear. In this study, the decomposition properties of three metal amides, including LiNH2, Mg­(NH2)2, and NaNH2, are studied by thermogravimetry, mass spectroscopy, and in situ X-ray diffraction techniques combined with density functional theory (DFT) calculations. It is found that Mg­(NH2)2, LiNH2, and NaNH2 exhibit very different metal–N and N–H bond strengths, which precipitate various formations energies of different kinds of vacancies. As a result, LiNH2 releases a major amount of NH3, with a small amount of N2 at a temperature as high as 350 °C. Mg­(NH2)2 releases NH3 and N2 synchronously at a temperature range of 300–400 °C without the emission of H2. NaNH2 synchronously releases H2, NH3, and a small amount of N2, at a narrow temperature range of 275–290 °C. Using DFT calculations, the decomposition behaviors and the corresponding decomposition mechanisms for LiNH2, Mg­(NH2)2, and NaNH2 have been well understood.

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