The Microstructure,Texture and Mechanical Properties of Friction Stir Welded Aluminum Alloy

Russian Journal of Non-Ferrous Metals - The microstructure and texture of 7075-T6 FSW weld with optimal parameters are investigated using optical microscopy, electron back scatter diffraction and...     

Polyethersulfone containing sulfonimide groups as proton exchange membrane fuel cells

In this publication a new synthesis approach of polyethersulfone containing sulfonimide groups (SI-PES), by chemical modification of sulfonated polyethersulfone (S-PES), was developed. The synthesis protocol was optimized in order to turn all the sulfonic function into sulfonimide. The effect of replacing arylsulfonic acid function with a more acidic one, i.e. aryl trifluoromethanesulfonimide, was evaluated through thermal, dynamic mechanical analysis, water uptake and conductivity. For similar ionic exchange capacity (IEC), i.e. 1.8 H⁺/dm³, at 60 °C and 95% relative humidity, the conductivity of SI-PSF is 9.5 mS/cm while that of S-PSF is only 3.5 mS/cm. However, at 60 °C the water uptake is 3 times higher for SI-PSF membranes as compare with S-PSF. An important change is observed in the slope of the conductivity and water uptake plots of SI-PES membranes, at different temperatures, depending of IEC. This could be explained by an important change in membrane morphology.     

A framework for efficient performance prediction of distributed applications in heterogeneous systems

Predicting distributed application performance is a constant challenge to researchers, with an increased difficulty when heterogeneous systems are involved. Research conducted so far is limited by application type, programming language, or targeted system. The employed models become too complex and prediction cost increases significantly. We propose dPerf, a new performance prediction tool. In dPerf, we extended existing methods from the frameworks Rose and SimGrid. New methods have also been proposed and implemented such that dPerf would perform (i) static code analysis and (ii) trace-based simulation. Based on these two phases, dPerf predicts the performance of C, C++ and Fortran applications communicating using MPI or P2PSAP. Neither one of the used frameworks was developed explicitly for performance prediction, making dPerf a novel tool. dPerf accuracy is validated by a sequential Laplace code and a parallel NAS benchmark. For a low prediction cost and a high gain, dPerf yields accurate results.     

Beyond Intercalation‐Based Li‐Ion Batteries: The State of the Art and Challenges of Electrode Materials Reacting Through Conversion Reactions (Adv. Mater. 35/2010)

Despite the imminent commercial introduction of Li‐ion batteries in electric drive vehicles and their proposed use as enablers of smart grids based on renewable energy technologies, an intensive quest for new electrode materials that bring about improvements in energy density, cycle life, cost, and safety is still underway. This Progress Report highlights the recent developments and the future prospects of the use of phases that react through conversion reactions as both positive and negative electrode materials in Li‐ion batteries. By moving beyond classical intercalation reactions, a variety of low cost compounds with gravimetric specific capacities that are two‐to‐five times larger than those attained with currently used materials, such as graphite and LiCoO₂, can be achieved. Nonetheless, several factors currently handicap the applicability of electrode materials entailing conversion reactions. These factors, together with the scientific breakthroughs that are necessary to fully assess the practicality of this concept, are reviewed in this report.     

Practical Solvent‐Free Ruthenium Trichloride‐Mediated Benzannulation Approach to Fused Functionalized Arenes

The solvent‐ and ligand‐free [2+2+2] ruthenium‐promoted cycloaddition of α,ω‐diynes and alkynes provides a facile and efficient strategy for the synthesis of substituted benzene‐derived systems. The search for the optimal reaction conditions revealed the unprecedented catalytic activity of ruthenium trichloride for benzannulation reactions and this atom‐economical process allowed the synthesis of fused arenes including dihydrobenzofurans, isoindolines, indanes in good to high yields. This practical protocol also gave rise to the preparation of pentasubstituted aromatic derivatives and was applied to the one‐gram scale synthesis of a functionalized heterocycle.

     

Thermal conductivity of polyimide/boron nitride nanocomposite films

The thermal conductivity of polyimide/boron nitride (PI/BN) nanocomposite thin films has been studied for two sizes of BN nanofillers (40 and 120 nm) and for a wide range of content. A strong influence of BN particle size on the thermal conduction of PI has been identified. In the case of the largest nanoparticles (hexagonal‐BN), the thermal conductivity of PI/h‐BN (120 nm) increases from 0.21 W/mK (neat PI) up to 0.56 W/mK for 29.2 vol %. For the smaller nanoparticles (wurtzite‐BN), PI/w‐BN (40 nm), we observed two different behaviors. First, we see a decrease until 0.12 W/mK for 20 vol % before increasing for higher filler content. The initial phenomenon can be explained by the Kapitza theory describing the presence of an interfacial thermal resistance barrier between the nanoparticles and the polymer matrix. This is induced by the reduction in size of the nanoparticles. Modeling of the experimental results allowed us to determine the Kapitza radius a_K for both PI/h‐BN and PI/w‐BN nanocomposites. Values of a_K of 7 nm and >500 nm have been obtained for PI/h‐BN and PI/w‐BN nanocomposite films, respectively. The value obtained matches the Kapitza theory, particularly for PI/w‐BN, for which the thermal conductivity is expected to decrease compared to that of neat PI. The present work shows that it seems difficult to enhance the thermal conductivity of PI films with BN nanoparticles with a diameter <100 nm due to the presence of high interfacial thermal resistance at the BN/PI interfaces. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42461.     

Supercritical CO2 and polycarbonate based nanocomposites: A critical issue for foaming

Supercritical carbon dioxide readily induced foaming of various polymers. In that context, supercritical CO₂ was applied to carbon nanotubes based polycarbonate nanocomposites to ensure their foaming. Surprisingly, efficient foaming only occurs when low pressure is applied while at high pressure, no expansion of the samples was observed. This is related to the ability of supercritical carbon dioxide to induce crystallization of amorphous polycarbonate. Moreover, this behaviour is amplified by the presence of carbon nanotubes that act as nucleating agents for crystals birth. The thermal behaviour of the composites was analysed by DSC and DMA and was related to the foaming observations. The uniformity of the cellular structure was analysed by scanning electron microscopy (SEM). By saturating the polycarbonate nanocomposites reinforced with 1 wt% of MWNTs at 100 bar and 100 °C during 16 h, microcellular foams were generated, with a density of 0.62, a cell size ranging from 0.6 to 4 μm, and a cellular density of 4.1 × 10¹¹ cells cm⁻³. The high ability of these polymeric foams to absorb electromagnetic radiation was demonstrated at low MWNT content as the result of the high affinity of the polycarbonate matrix for MWNTs, and therefore to the good MWNTs dispersion.     

Improved stability of mesoporous carbon fuel cell catalyst support through incorporation of TiO2

The electrochemical stability of Pt deposited on mesoporous carbon, which was either applied in its unmodified state or coated with 20 wt% TiO₂, was investigated by cyclic voltammetry in N₂ purged 0.5 M sulfuric acid. XRD analysis revealed that TiO₂ was present in the anatase phase. The mean Pt particle diameter was ∼6 and ∼4 nm for mesoporous carbon with and without TiO₂, respectively. Pt supported on TiO₂ modified substrates was more stable than Pt supported on conventional mesoporous carbon when subjected to 1000 cycles in the potential range from 0.05 to 1.25 V vs. RHE. This was evident from the observation that the support with TiO₂ retained ∼53% of the electrochemically active surface area relative to the state observed after 100 cycles, whereas ∼33% of the active area remained in the case without TiO₂. The oxygen reduction mass activity was identical for both fresh samples (i.e., ). After 1000 cycles the mass activity decreased to for the case without TiO₂, whereas with TiO₂ the deactivation was minor; i.e., the mass activity after 1000 cycles was .