Journal of Materials Science

A series of sterically encumbered, sulfonated, alternating poly(arylene ether) copolymers were synthesized so as to compare the effects of incorporating ketone and sulfone groups on the proton conductivity and performance of fuel cells of membranes prepared. Therefore, the polymers were prepared by polymerization of 4,4′-difluorobenzophenone or bis(4-fluorophenyl)sulfone with a novel monomer, 2′′,3′′,5′′,6′′-tetraphenyl-[1,1′:4′,1′′:4′′,1′′′:4′′′,1′′′′-quinquephenyl]-4,4′′′′-diol. Subsequent sulfonation and solution casting provided membranes possessing ion exchange capacities ranging from 2.1 to 2.8 mmol g−1. The water uptake of sulfonated polymers increased with increasing IEC, ranging from 68 to 146 % at 80 °C in water compared with 30 % for N117. Proton conductivities ranged between 3 and 17 mS cm−1 at 30 °C/40 % RH, and 88 and 263 mS cm−1 at 80 °C/95 % RH compared with 10 and 100 mS cm−1 for N117, respectively. The proton mobilities ranged between 76.6 × 105 cm2 V−1 S−1 and 170.4 × 105 cm2 V−1 S−1 at 80 °C, greater than that of N117. No substantial difference is observed between membrane prepared from polymers incorporating ketone and analogous membranes incorporating sulfone groups, thus inferring that ketone and sulfone groups in the polymer main chain do not appear to have any discernible difference upon membrane properties.

Na2O-SiO2 sols were prepared using silicon alkoxide and colloidal silica precursors with sodium nitrate as the salt. The experimental procedure carried out was changed depending on the precursors used. Several tests with dialysis membranes were performed in order to study the possibility of incorporating Na+-ions into the sols. These ions were introduced into silica sols contained in membranes from an exterior solution. In addition, washing tests were carried out with Na2O-SiO2 sols contained inside the membranes and with several exterior washing solutions. Resistivity of the washing solutions was measured against time. The washing solutions were changed periodically. After drying and heat-treatment, Na2O content in the gels was determined using flame photometry. The crystalline phases formed were detected by X-ray diffraction. The results show a small incorporation of alkaline ions in Na2O-SiO2 gels, even in those samples prepared through the dialysis membranes tests.

In this study, we successfully prepared NiFeCoAl0.21Ti0.21W0.04 high-entropy alloy using vacuum arc melting technique and systematically investigated the mechanical properties, microstructure, and phase composition of the alloy using an electronic universal testing machine, EBSD, SEM, EDS, and TEM technologies. The results showed that the alloy can retain good ductility (~ 38%) while having high yield strength (~ 850 MPa). The alloy presented an FCC + L12 dual-phase structure, and the L12 precipitates are a nanoscale with an average size of ~ 63 nm and are highly coherent with the FCC matrix, which ensured excellent precipitation strengthening effect and thus high strength. We have calculated the contribution of the strengthening mechanisms present in the alloy to the strength of the alloy, and the results show that precipitation strengthening dominates among all strengthening mechanisms. At the same time, the formation of annealed twins acts as a barrier to grain growth during heat treatment, which also ensures good fine-grain strengthening. In conclusion, we have obtained an excellent strength-ductility trade-off relationship by introducing a nano-precipitation phase in the alloy that is coherent with the matrix, which is expected to guide the development of higher entropy alloys with superior properties.

Graphene oxide/reduced perylene diimide radical anion hybrid (GO/rSFPDI) with high dispersibility in polar organic solvents has been flexibly developed using N,N′-diethylhexyl-1-bromo-7-pentafluorophenox-perylene diimide (SFPDI). The interaction of the GO with the SFPDI suggested the catalysis of perylene diimide (SFPDI) to reduced perylene diimide radical anion (rSFPDI). The successful preparation of GO/rSFPDI was confirmed via FT-IR, Raman, UV–Vis absorption spectrum, XRD, and SEM. Compared to the two neutral SFPDI and GO, GO/rSFPDI exhibited a novel lower energy electronic transition (max. at 700 nm) in addition to the solvatochromism and characteristics of spectral response to pH. Moreover, the fluorescence emission spectrum of GO/rSFPDI shows strong fluorescence quenching in dilute solution.

Outstanding features favour the application of polymers and polymer composites in low-temperature technology. The booming hydrogen technology is a challenge for these materials, which are considered as seals and bearings in cryogenic pumps. In the present study, three types of thermoplastics, i.e., polyetheretherketone (PEEK), polyetherimide (PEI) and polyamide 6,6 (PA6,6), and one epoxy were considered as matrix materials. Micron-sized fillers, i.e., short carbon fibres, graphite flakes, and PTFE powders, were incorporated into these polymers together with nano-sized TiO2 particles. Optimised compositions of each matrix were selected from our previous works at room temperature in order to be studied at very low temperature conditions. In particular, frictional tests were carried out with polymer composite pins against polished steel surfaces under constant load over a certain distance in liquid hydrogen and liquid nitrogen. Afterwards, worn surfaces were analysed by using scanning electron microscopy (SEM). It was found out that the tribological properties in liquid hydrogen are dominated by the matrix materials, in particular thermoplastics perform generally slightly better than thermosetting resins.

The principles of continuum mechanics can be extended to porous solids only if the effective moduli are known. Although the effective bulk modulus has already been determined by approximating the geometry of a porous solid to be a hollow sphere, bounds could only be established for the other moduli. This problem of indeterminacy of the moduli is solved in this study using a particular model from the variation of the effective Poisson's ratio. In addition to this, the results are extended for the hollow sphere to real geometry by introducing a porositydependent factor. These results are compared with experimental data and the agreement is found to be good. As the effective Poisson's ratio cannot be determined accurately using experiments, the derived equation is verified using finite element analysis.

The behaviour of the conduction electrons in the eighth group elements was deduced from the results of experiments on vacuum-deposited films, by combining measurements of the electrical resistivity with thickness determinations and optical investigations. The mean free path of the electrons, their concentration, their effective mass, and the proportion of them specularly reflected at the film surfaces (known as the scattering parameter) were calculated by solving a system consisting of the Sondheimer equation for the size-dependence of the film conductivity, the known formulae giving the mean free path at the Fermi level and the plasma wavelength of the electron gas, and the Dingle relation for the scattering parameter in the spectral region of the anomalous skin effect. The data thus obtained are in reasonable agreement with the generally accepted band structure of the transition metals.

α-Iron-dispersed carbon was synthesized, through pressure pyrolysis of divinylbenzene-vinylferrocene above 750°C, and by reduction of magnetite-dispersed carbon. Divinylbenzenevinylferrocene copolymer was pyrolysed at 125 MPa above 750°C to yield carbons dispersed with α-iron accompanied by cementite. Magnetite in the carbon matrix was reduced to α-iron after heat treatments at 500°C in a flow of hydrogen. Carbons synthesized by the pressure pyrolysis of divinylbenzene-vinylferrocene at 800°C and 125 MPa contained iron-compound particles up to 200 nm, whereas the median diameter of α-iron particles in the carbon matrix after reduction treatments was 20 nm. α-Iron-dispersed carbon had a Curie temperature of 770°C. The saturation magnetization of iron-dispersed carbon increased with increasing the pyrolysis temperature of divinylbenzene-vinylferrocene copolymer, and reached a constant value of 183 e.m.u.g−1 at 800°C. The saturation magnetization of α-iron-dispersed carbon after the reduction treatment revealed practically the theoretical value of α-iron. Carbons finely dispersed with only α-iron particles were synthesized successfully by reduction of magnetitedispersed carbons.

Solar energy, as an endless clean energy, has great prospects for the use of water vapor from sewage purification and seawater desalination. Local heating of surface water has shown to maximize the energy efficiency of steam generation. Therefore, at first, the material is required to have a good ability of photo-thermal conversion. Among the photo-thermal converting materials, MXenes are arising candidates for effective photo-thermal conversion, which have shown excellent photo-thermal conversion efficiency and have been attempted for photo-thermal distillation. Although a high photo-thermal conversion efficiency has been realized, however, it is more challenging to prepare photo-thermal evaporating materials with rapid water transport capacity and generating solar steam. In this work, a photo-thermal distillation device was reported by combining a chitosan aerogel with a bio-inspired wood-like oriented porous structure prepared by directional freezing method, and Ti3C2Tx two-dimensional nanosheets coated with polyethyleneimine sprayed on the surface. The ordered microporous structure can quickly transport moisture from the bottom up to the evaporation surface by capillary force. The coating of Ti3C2Tx coated with polyethyleneimine on the evaporation surface has a strong ability to capture sunlight. The evaporation rate reaches 3.99 kg m−2 h−1 under the optical power density of 3000 W m−2 and the efficiency reaches 90%, indicating the broad application prospects as a photo-thermal conversion material for efficiently producing clean fresh water.