Hierarchical Nanoporous Copper Architectures via 3D Printing Technique for Highly Efficient Catalysts

Nanoporous metals represent a class of functional materials with unique bicontinuous open porous structural properties, making them ideal candidates for various catalyst applications. However, the pursuit of nanoporous properties, extremely small pores, and high surface area, results in the restriction of mass transport. Herein, a free‐standing hierarchical nanoporous Cu material, prepared by a selective laser melting 3D printing technique and a one‐step dealloying process, is presented as a highly efficient electrocatalyst for methanol oxidation. It is demonstrated that the digitally controlled hierarchical structure with macro‐ and nano‐scaled pores can be utilized for promoting and directing mass transport as well as for the enhancement of catalytic properties. This work highlights a facile, low‐cost, and alternative strategy for hierarchical nanoporous structure design that can be applied to binary, ternary, and quaternary metal alloys for various functional applications.     

Combustion synthesis of α-Si3N4 assisted by molten salt additives

Combustion synthesis (CS) of silicon nitride (Si₃N₄), assisted by molten salt additives under high N₂ pressure, is reported. The effect of salt additives (NaCl, MgCl₂, and MgCl₂?6H₂O) on the reaction temperature and the final α-Si₃N₄ content is studied. The maximum reaction temperature (T_max) decreased with an increase in the amount of the salt additives. NaCl is found to be the most suitable as it results in 57.8% α-Si₃N₄ at 30 mass% concentration. MgCl₂ is strongly hygroscopic, and MgCl₂?6H₂O decomposes at very low temperature. Therefore, they absorb heat at low temperatures, which makes it difficult to reach the ignition temperature, thereby hindering the reaction propagation. Si₃N₄ is necessary as a diluent for creating pores in the raw materials to allow effective penetration and contact of N₂ gas with the Si particles.     

Study of Electronic Structure and Defect Formation in Ti<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Ni<Subscript>1+<Emphasis Type="Italic">x</Emphasis></Subscript>Sn Half-Heusler Alloys

To investigate the electronic structure of TiNiSn-based thermoelectric materials, we systematically synthesized samples, Ti_1−x Ni_1+x Sn (−0.05 ≤ x ≤ 0.05), and performed soft-x-ray photoelectron spectroscopy (XPS) measurements. A peak with a binding energy of about 0.3 eV, not expected from the perfect crystal, was observed in the XPS spectrum, and its intensity became weaker with decreasing x. This peak indicates that defects exist in the x = 0 sample and are reduced with decreasing x. First-principles calculations using several defect models led to the conclusion that interstitial Ni defects in the half-Heusler structure consistently explain the experimental observations, including the XPS spectra and changes in lattice constants.     

Fabrication and lithium intercalation properties of epitaxial Li2RuO3 thin films

Lithium intercalation in a lithium excess layered material Li₂RuO₃ was investigated using two-dimensional model electrodes with a restricted reaction plane of (002). Li₂RuO₃ films were synthesized on Al₂O₃(0001) substrate by a pulsed laser deposition, and X-ray diffraction measurements confirmed epitaxial growth of Li₂RuO₃(002). Electrochemical characterization using cyclic voltammetry and charge/discharge measurements indicated electrochemical reactions with a discharge capacity of 200 mAh g^− 1 for the film deposited at 400 °C followed by post-annealing at 550 °C. The electrochemical activity on the (002) plane indicated three-dimensional lithium diffusion in the two-dimensional layered rocksalt structure through the lithium sites in the transition metal layer.     

Effects of grain size and dislocation density on the susceptibility to high-pressure hydrogen environment embrittlement of high-strength low-alloy steels

The tensile properties of several high-strength low-alloy steels in a 45 MPa hydrogen atmosphere at ambient temperature were examined with respect to the effects of grain size and dislocation density on hydrogen environment embrittlement. Grain size was measured using an optical microscope and dislocation density was determined by X-ray diffractometry. Both grain refinement and a reduction in dislocation density are effective in reducing the susceptibility to embrittlement. The steel that has high dislocation density or large grain size inclines to show a smooth intergranular fracture surface. Given only the grain size and dislocation density, a simple approximation of the embrittlement property of high-strength steel could be obtained. This method could be useful in selecting candidate materials in advance of the mechanical tests in high-pressure hydrogen gas.     

Fusion product diagnostics planned for Large Helical Device deuterium experiment

Deuterium experiment on the Large Helical Device (LHD) is now being planned at the National Institute for Fusion Science. The fusion product diagnostics systems currently considered for installation on LHD are described in this paper. The systems will include a time-resolved neutron yield monitor based on neutron gas counters, a time-integrated neutron yield monitor based on activation techniques, a multicollimator scintillation detector array for diagnosing spatial distribution of neutron emission rate, 2.5 MeV neutron spectrometer, 14 MeV neutron counter, and prompt γ-ray diagnostics.     

Synthesis and characterization of polystyrene brushes for organic thin film transistors

We synthesized and characterized polystyrene brushes on a silicon wafer using surface-initiated atom transfer radical polymerization. The thickness of the polymer brush was controlled by adjusting the reaction time. We investigated monomer conversion as well as the molecular weight and density of the polymer brushes. When the monomer conversion reached 100%, the number-average molecular weight and film thickness reached 135,000 and 113 nm, respectively. The estimated densities of the synthesized polystyrene brushes were in the range 0.34-0.54 chains/nm2, high enough to be categorized in the "concentrated brush" regime. The synthesized polymer brush was used as an insulating layer in an organic thin-film transistor. Organic thin-film transistors were fabricated using pentacene as an active p-type organic semiconductor and a polystyrene brush on a SiO2 layer as a gate dielectric. The pentacene based organic thin-film transistor with the polystyrene brush exhibited a field-effect mobility microFET of 0.099 cm2/(V x s).     

Effect of Pre-strain on the Creep Strength of Ni-Based Alloys for A-USC Boilers

In order to clarify the effects of cold work on the creep rupture strengths of Ni-based alloy, the relationship between the pre-strain and the creep rupture strengths of Alloy617, Alloy263, and Ally740H was investigated. The creep rupture strength of Alloy617 increased as the pre-strain increased. The creep rupture strength of Alloy263 was roughly constant, independent of pre-strain. Meanwhile, the creep rupture strength of Alloy740H was constant with a pre-strain up to 5 %, and deceased to about one third of the initial value with a pre-strain of 7.5 % or larger. From the results of microstructure observation, the relationship between the amount of carbide in grain boundaries and the pre-strain, coordinates well with the relationship between the change in creep rupture strength and the pre-strain.     

Do Aphid Carcasses on the Backs of Larvae of Green Lacewing Work as Chemical Mimicry against Aphid-Tending Ants?

Ants attack and exclude natural enemies of aphids in ant–aphid mutualisms. However, larvae of the green lacewing, Mallada desjardinsi, prey on the cowpea aphid, Aphis craccivora, without exclusion by aphid-tending ants. Lacewing larvae are protected from ants by carrying aphid carcasses on their backs. Here, we tested whether cuticular hydrocarbons (CHCs) of aphid carcasses affected the aggressiveness of aphid-tending ants. Aphid carcasses were washed with n-hexane to remove lipids. Lacewing larvae with washed aphid carcasses were attacked by aphid-tending ants more frequently than those with untreated aphid carcasses. We measured the aggressiveness of aphid-tending ants to lacewing larvae that were either carrying a piece of cotton wool (a dummy aphid carcass) treated with CHCs from aphids or lacewing larvae, or carrying aphid carcasses. The rates of attack by ants on lacewing larvae carrying CHCs of aphids or aphid carcasses were lower than that of attack on lacewing larvae with conspecific CHCs. Chemical analysis by gas chromatography/mass spectrometry showed similarity of CHCs between aphids and aphid carcasses. These results suggest that aphid carcasses on the backs of lacewing larvae function via chemical camouflage to limit attacks by aphid-tending ants.