Harmonic structural materials of magnesium alloy AZ31B were fabricated by powder metallurgy. In the harmonic structural materials, small grains surround large grains and both of high strength and high ductility can be generated. However, there is almost no report on harmonic structural materials of magnesium alloy. AZ31B powder with average particle size of 300 µm was mechanically milled using planetary ball milling for 270 ks. Powder particles after milling possess structures with large grains surrounded by small grains. The powder was sintered using spark plasma sintering (SPS) and then subjected to forging using SPS apparatus. Forged materials exhibited tensile strength (310.5 MPa) twice that of magnesium material fabricated from initial powder (IP) associated with high ductility (22.7％) as same as IP materials. High strength magnesium alloy with superior ductility was achieved by harmonic structural design.

Pd-Cu alloys are of particular interest for use as hydrogen purification membranes, and identifying the effects of stoichiometry on hydrogen permeability is the key to exploring the possibility of improving this material. In this study, we carried out hydrogen permeation tests for Pd-51.5 mol％Cu alloy in order to understand the effects of excess Cu atoms on the hydrogen permeability of Pd-Cu alloys with B2-type crystal structure. Even though the Pd-51.5 mol％Cu alloy contained a small amount of a face-centered cubic phase, its hydrogen permeability was higher than that of practical Pd-53 mol％Cu alloy with a B2 single phase in the temperature range of 298 K to 623 K. These results were analyzed according to the consistent description of hydrogen permeation based on hydrogen chemical potential. It was found that the hydrogen solubility was improved by reducing the excess Cu atoms. On the other hand, the hydrogen diffusivity of Pd-51.5 mol％Cu alloy was still comparable to that of Pd-53 mol％Cu alloy and decreased significantly at low temperatures, just like that of the practical alloy. First-principles calculations suggested that the excess Cu atoms act as repellers and reduce the hydrogen solubility in the alloy, in a manner consistent with experimental results. It was also suggested that the excess Cu atoms reduce the apparent hydrogen diffusivity as the hydrogen atoms rarely occupy the interstitial sites around the excess Cu atoms. However, no significant differences in the hydrogen diffusivity due to the excess Cu atoms were observed in the experiment. Therefore, other factors apart from the excess Cu atoms may have inhibited the hydrogen diffusivity at low temperatures. Our findings will serve as a basis for enhancing the hydrogen permeability of Pd-Cu alloys by tuning their composition and processing.

The reactivity of Mixed sulfide (MS: mixture of nickel and cobalt sulfides) in the conventional media remains insufficient and may be further improved. The authors have developed a novel leaching method using organic aqua regia, i.e. dimethyl sulfoxide (DMSO) solutions of copper chloride (CuCl₂). In this work, the organic aqua regia was applied for the leaching of MS. Then, the recovery of Ni from the leachate was conducted by a biphasic extraction, during which commercial extractants of PC-88A were used. It was found that the extraction of Ni and Co at a given time was faster than that of conventional media, e.g. 94％ in 1 h at 393 K. One of the advantages of DMSO as a solvent is its high boiling point, which allows a high operating temperature at ambient pressure, leading to high extraction rate. The results of the biphasic extraction show that approximately 80％ of Cu remains in the leachate whereas 70％ of Ni goes to PC-88A. The leaching by organic aqua regia followed by the biphasic extraction could be a novel and attractive method to recovery Ni from MS.