Chemical and radiation crosslinked polymer electrolyte membranes prepared from radiation-grafted ETFE films for DMFC applications

To develop a highly chemically stable polymer electrolyte membrane for application in a direct methanol fuel cell (DMFC), doubly crosslinked membranes were prepared by chemical crosslinking using bifunctional monomers, such as divinylbenzene (DVB) and bis(p,p-vinyl phenyl) ethane (BVPE), and by radiation crosslinking. The membranes were prepared by grafting of m,p-methylstyrene (MeSt) and p-tert-butylstyrene (tBuSt) into poly(ethylene-co-tetrafluoroethylene) (ETFE) films and subsequent sulfonation. The effects of the DVB and BVPE crosslinkers on the grafting kinetics and the properties of the prepared membranes, such as water uptake, proton conductivity and chemical stability were investigated. Radiation crosslinking was introduced by irradiation of the ETFE base film, the grafted film or the sulfonated membrane. The membrane crosslinked by DVB and BVPE crosslinkers and post-crosslinked by γ-ray irradiation of the corresponding grafted film possessed the highest chemical stability among the prepared membranes, a significantly lower methanol permeability compared to Nafion^® membranes, and a better DMFC performance for high methanol feed concentration. Therefore, this doubly crosslinked membrane was promising for application in a DMFC where relatively high methanol concentration could be fed.     

Preparation of microporous activated carbon and its modification for arsenic removal from water

Arsenic removal from water was investigated using activated carbon. The chemical activated carbon (CAC) prepared using H₃PO₄ from jute stick largely featured micropore structure with surface functional groups, while meso- and macropore structures were mainly developed in physical activated carbon (PAC). The CAC and PAC reduced arsenic concentration to 45 and 55 μg L⁻¹, respectively, from 100 μg L⁻¹ while iron-loaded CAC reduced to 3 μg L⁻¹, which is lower than the upper permissible limit (10 μg L⁻¹). The micropore structure of CAC along with complexation affinity of iron species towards arsenic species attributed to enhanced separation of arsenic.     

Functionalization of low-dimensional honeycomb germanium with 3d transition-metal atoms

The energetics, electronic and magnetic properties of 3d transition-metal (TM) atoms adsorbed low-dimensional Ge honeycomb structures have been systematically investigated from the spin-polarized density-functional theory calculations. For the two-dimensional Ge honeycomb structure, all TM atoms considered prefer to adsorb on the hollow site of the buckled hexagon in both single-sided and double-sided adsorption cases, with binding energies ranging between 3.27 and 5.92 eV. Upon adsorption, the semimetallic 2D honeycomb Ge can change to either ferromagnetic or antiferromagnetic metals depending on both TM species and coverage density. For the one-dimensional structure, we found binding of TM atoms to hollow site of the edge hexagon yields the minimum energy state for all TM species considered and in all three AGeNRs examined which belong to different families. Depending on ribbon width, adsorbed TM species and adsorption concentration, most of the TM decorated AGeNRs can either be metals or semiconductors with ferromagnetic or antiferromagnetic spin alignment, except for Co-adsorbed ones which remain to be nonmagnetic. Interestingly, Cr or Mn adsorption can make certain AGeNRs to be half-metallic with a 100% spin-polarization at Fermi level which can be good candidates for future application in spintronic fields. Furthermore, the effect of the on-site Coulomb interaction on the stability of these half-metallic ribbons is also considered by performing L(S)DA + U calculations, and the results show that the half-metallic ground state of the Cr-adsorbed ribbons is more robust than that of the Mn-adsorbed one.     

滚动接触疲劳试验机的研究现状

滚动接触疲劳试验机主要用于研究材料在模拟工况条件下的接触疲劳性能。本文就国内外已经实际应用的滚动接触疲劳试验机的现状及接触疲劳试验基本工作原理加以介绍,并就滚动接触疲劳试验机的发展方向作了探讨。     

Modified thick thermal barrier coatings: microstructural characterization

Thick thermal barrier coatings were modified with laser glazing and phosphate based sealing treatments. Surface porosity of the sealed coatings decreased significantly in all cases. Structural analysis showed a strong preferred crystal orientation of the t′ZrO₂ phase in direction [002] in laser-glazed 25CeO₂–2.5Y₂O₃–ZrO₂ coating. In laser-glazed 22MgO–ZrO₂ coating the major phase was rhombohedral Mg₂Zr₅O₁₂. In phosphate sealed 8Y₂O₃–ZrO₂ coating the strengthening mechanism was identified as adhesive binding without chemical bonding. Coating microstructures were determined by scanning electron microscopy, energy dispersive spectroscopy, transmission electron microscopy and optical microscopy. Coatings were also characterized by X-ray diffraction, microhardness and porosity.     

Fabrication and microstructure of in situ toughened Al2O3/Fe3Al

Fe₃Al nano-particles and commercial purity Al₂O₃ powders were used as raw materials to fabricate in situ reinforced Al₂O₃/Fe₃Al nano/micro-composites. Densification and microstructure were studied. The Al₂O₃ matrix grains were characterized by platelet grains. The Fe₃Al particles inhibited the grain growth of Al₂O₃ grains and limited the densification of the composites. In Al₂O₃/Fe₃Al composites, the Fe₃Al particles were uniformly dispersed in the Al₂O₃ matrix. The major Fe₃Al micro-particles, about 1 μm in average size, existed at Al₂O₃ grain boundaries, and the Fe₃Al nano-particles were found embedded in the matrix grains. The grain size of the intragranular particles ranged from several to several hundred nanometers. The grain size and aspect ratio of Al₂O₃ platelet grains and distribution of intragranular Fe₃Al could be optimized by controlling the Fe₃Al contents and sintering process. The in situ formed Al₂O₃ platelet grains, as well as Fe₃Al dispersoids, were beneficial to the increase of the mechanical properties of alumina.     

In-situ hydrogen-induced evolution and de-/hydrogenation behaviors of the Mg93Cu7-xYx alloys with equalized LPSO and eutectic structure

Nanosizing is efficient as the dual-tuning of thermodynamics and kinetics for Mg-based hydrogen storage materials. The in-situ synthesis of nanocomposites through hydrogen-induced decomposition from long-period stacking ordered phase is proved effective to achieve active nano-sized catalysts with uniform dispersion. In this study, the Mg₉₃Cu_7-xY_x (x = 0.67, 1.33, and 2) alloys with equalized Mg–Mg₂Cu eutectic and 14H long-period stacking ordered phase of Mg₉₂Cu_3.5Y_4.5 are prepared. Its solidification path is determined as α-Mg, 14H–Mg₂Cu pair and Mg–Mg₂Cu eutectic. The increased Y/Cu atomic ratio lowers the first-cycle hydrogenation rate of the alloys due to the increased 14H–Mg₂Cu structure and reduced Mg–Mg₂Cu eutectic interfaces. After the hydrogen-induced decomposition of the long-period stacking ordered phase, MgCu₂ and YH₃ nanoparticles are in-situ formed, and the following activation process significantly accelerates. The YH₃ nanoparticles partly decompose to YH₂ at 300 °C in vacuum and Mg–Mg₂Cu-YH_x nanocomposites are in-situ formed. The nano-sized YH₂ helps catalyze H₂ dissociation and the YH_x/Mg interfaces stimulate H diffusion and the nucleation of MgH₂. Therefore, the Mg₉₃Cu₅Y₂ composite shows the fastest absorption rates. However, due to the positive effect of YH_x/Mg interfaces on H diffusion and the negative effect of YH₃ nanophases on the hydride decomposition, the minimum activation energy of 115.43 kJ mol⁻¹ is obtained for the desorption of the Mg₉₃Cu_5.67Y_1.33 hydride.     

Carbon nanotube-graphene hybrid supported platinum as an effective catalyst for hydrogen generation from hydrolysis of ammonia borane

In this study, we report the results of a kinetic study on the hydrogen (H₂) generation from the hydrolysis of ammonia borane (NH₃BH₃) catalyzed by Platinum supported on carbon nanotube-graphene hybrid material (Pt/CNT-G). Synthesized catalyst was characterized by TGA, XRD, CP-OES, TEM and SEM-EDX techniques. Characterization studies have shown that the CNT-G hybrid support material provides desired distribution of the Pt particles on the support material. The effect of various parameters such as catalyst loading, reaction temperature, effect of NaOH and the effect of NH₃BH₃ concentration are also determined. Experimental results showed that the Pt/CNT-G catalyst exhibited high catalytic activity on NH₃BH₃ hydrolysis reaction to release H₂. It has been found that Pt/CNT-G catalyst shows low activation energy of 35.34 kJ mol⁻¹ for hydrolysis reaction of NH₃BH₃. Pt/CNT-G catalyst also exhibited high catalytic activity with turnover frequency (TOF) of 135 (mol_H2/mol_cat.min). Therefore, the synthesized Pt/CNT-G catalyst is a potential candidate for enhanced H₂ generation through NH₃BH₃ hydrolysis.     

COx-free hydrogen production from ammonia on novel cobalt catalysts supported on 1D titanate nanotubes

Hydrogen storage in chemical bonds such as ammonia is an attractive alternative to physical hydrogen storage if a sustainable and efficient catalyst can be designed for the release of COx-free hydrogen on demand. This paper presents a systematic study for the design of cobalt-based catalysts, moving away from scare Ru-based systems. It demonstrates the importance of the preparation method of cobalt-based catalysts not only to tune the size of the active species and their interaction with the support but also in the promotion of active species. Cobalt supported on titanate nanotubes via an ion-exchange method leads to the incorporation of the cobalt into the crystal structure of the titanates facilitating the formation of unreducible cobalt titanate species with a detrimental effect on the reactivity, and the thermal stability of the titanate support. Considerably higher reactivities can be achieved by loading cobalt via deposition-precipitation with NaOH method, leading to the formation of reducible cobalt particles on the surface of the titanate nanorods support. In this case, the rate of reaction is inversely related to the cobalt particle size, pointing out the key effect of particle size of cobalt-based catalyst for the hydrogen production in ammonia decomposition. Although the activities reported here for cobalt-based catalysts are still below those of the state-of-the-art ruthenium counterpart systems, this work provides unique insights for the future development of sustainable catalysts for the use of ammonia as hydrogen vector.     

Nano-structures at martensite macrotwin interfaces in Ni65Al35

The atomic configurations at macrotwin interfaces between microtwinned martensite plates in Ni₆₅Al₃₅ material are investigated using transmission electron microscopy. The observed structures are interpreted in view of possible formation mechanisms for these interfaces. A distinction is made between cases in which the microtwins, originating from mutually perpendicular {110} austenite planes, enclose a final angle larger or smaller than 90°. Two different configurations, a crossing and a step type are described. Depending on the actual case, tapering, bending and tip splitting of the smaller microtwin variants are observed. The most reproducible deformations occur in a region of approximately 5–10 nm width around the interface while a variety of structural defects are observed further away from the interface. These structures and deformations are interpreted in terms of the coalescence of two separately nucleated microtwinned martensite plates and the need to accommodate remaining stresses.