Incorporation of halloysite nanotubes into PVDF matrix: Nucleation of electroactive phase accompany with significant reinforcement and dimensional stability improvement

Poly(vinylidene fluoride)/halloysite nanotubes (PVDF/HNTs) nanocomposites were prepared via melt compounding. Electroactive β- and γ-phases of PVDF were nucleated by the HNTs due to electrical interaction between negatively charged surface of the HNTs and CH₂ groups of the PVDF. The ends and surface defects of the HNTs were also responsible for the formation of γ-phase, since long trans conformations with gauche defects were induced at the two regions via the formation of hydrogen bonding. In addition to nucleation of the electroactive phase, the HNTs were found to reinforce the PVDF matrix and improve its dimensional stability, as evidenced by the substantially increased tensile strength and Young’s modulus, and the remarkably decreased coefficient of thermal expansion (CTE). The improved tensile property and reduced CTE were attributed to the uniformly dispersed HNTs and good interfacial interaction between HNTs and PVDF matrix via hydrogen bonding.     

Beyond Intercalation‐Based Li‐Ion Batteries: The State of the Art and Challenges of Electrode Materials Reacting Through Conversion Reactions

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.     

Water consumption during solid state sodium borohydride hydrolysis

In this paper nickel acetate catalyzed sodium borohydride cartridges have been prepared and hydrolyzed with water for hydrogen production. Two technological solutions have been tested to increase the overall hydrogen yield, namely a porous water diffuser and a hydrophobic membrane. The first was used to improve water diffusion inside the hydride while the second to confine water inside the cartridge. The generated hydrogen flow showed a very reproducible behavior. Hydrogen promptly evolved just after water was pumped into the cartridge. After some initial peaks, a constant hydrogen flow has been recorded for the whole reaction time. The constant flow was related to the presence of the porous diffuser. The use of a hydrophobic membrane to confine the water inside the cartridge allowed to increase the overall hydrogen yield: about 6 water molecules per mol of hydride were required to complete the reaction. The reaction product was identified by XRD as Na₂B₂O₄*8H₂O. The cartridge hydrogen gravimetric content, based on water and sodium borohydride weight, was as high as 4.64%.     

Rapid synthesis of submicron crystalline barium zirconate BaZrO3 by precipitation in aqueous basic solution below 100 °C

Pure crystalline BaZrO₃ powders can be produced by precipitation in highly basic aqueous solution. The influence of several synthesis parameters is studied. At high OH^? concentration ([NaOH] = 20 mol/l), it is possible to obtain the well-crystallized stoichiometric perovskite phase at relatively low temperature (～80 °C), after a short reaction time (15 min) and without requiring any precaution to avoid the presence of CO₂. This synthesis method yields spherical particles, whose size can be controlled by changing the concentration of the Ba + Zr solution. No calcination treatment is necessary since the precipitate is crystalline. Suitable choice of the synthesis parameters ([NaOH] = 20 mol/l, [Ba + Zr] = 1 mol/l, reaction time = 15 min) yields a sub-micron precipitate with excellent densification behaviour. Corrosion tests in BaO–CuO melt show that ～98% dense BaZrO₃ obtained by sintering at 1650 °C for 13 h could be used for crucibles in the synthesis of YBa₂Cu₃O₇ superconducting single crystals.     

Isothermal and thermal cycling oxidation of hot-dip aluminide coating on flake/spheroidal graphite cast iron

Two types of cast iron, flake graphite and spheroidal graphite cast iron, with ferrite matrix and similar composition, were aluminized by hot-dipping. As-coated aluminide layer consists of the outer Al topcoat, inner Fe–Al intermetallic layer and dispersed graphite. Isothermal and thermal cycling oxidation tests of aluminized specimens have been conducted. Cast irons with aluminide coating exhibit higher oxidation resistance than without the coating. However, different graphite structure results in diverse quality of aluminide coatings. Aluminide coating on flake graphite cast iron exhibits less oxidation resistance and adhesion to the substrate.     

Algorithm for blinds control based on the optimization of blind tilt angle using a genetic algorithm and fuzzy logic

This paper presents the calculation of the power of solar rays that pass through the window of an observed room and their impact on warming up and lighting of the room. The calculations were performed using a mathematical model that takes into account the geographical position of the object, time zone, orientation of windows, day of the year, and current time. This paper also includes the calculation of geometry of the solar radiation and its intensity, artificial light and cooling/heating demands. Based on data from above, the optimization of blind tilt angle was performed to achieve the best possible brightness of the room and energy savings when heating or cooling, depending on ambient temperature. Optimization was performed using a genetic algorithm and fuzzy logic. After an analysis of the results obtained from optimization of the blind tilt angle, an algorithm for blinds control was developed in order to achieve energy savings and comfort in the observed room. Based on the derived conclusions, an UML diagram was made that describes the algorithm for determining optimal blind tilt angle.     

Effects of pyrolysis temperature on the chemical composition of refined softwood and hardwood lignins

The current study uses nuclear magnetic resonance, Fourier-transform infrared spectroscopy and Raman spectroscopy to investigate the evolution of refined softwood and hardwood lignins under various pyrolytic exposures. Little chemical change occurred at pyrolysis temperatures of 250 and 300 °C, whereas significant mass loss and chemical change was observed at 400 and 500 °C. These losses were mainly attributed to evolution of methoxyl, hydroxyl, and propyl groups. Mass loss plateaued following pyrolysis at 500 °C, but rearrangements continued to occur at higher temperatures, resulting in char that became increasingly polyaromatic in nature. Following brief pyrolytic exposures at 500 and 600 °C, the refined hardwood and softwood lignins yielded coal-like products. Lignin pyrolyzed at higher temperatures yielded chars with greater order, similar in composition to coke. These coal and coke-like products are called “lignin-based carbon” (LBC). The polyaromatic nature of the LBC after high temperature pyrolysis was perceived as the result of radical formation and recombination, leading to fused aromatic structures, which occurs more readily at higher temperatures.     

Thermal performance of artificially roughened solar air heaters

Artificially roughened solar air heaters have been analysed (Prasad and Saini, 1988) for fully developed turbulent flow and found to perform better both quantitatively and qualitatively compared to the smooth ones under the same operating conditions. Optimal thermo-hydraulic performance of such solar air heaters has been analysed (Prasad and Saini, 1991) and investigated (Prasad and Verma, 2000) for the maximum heat transfer and minimum pressure drop.This paper represents the experimental results on heat transfer and thereby thermal performance of artificially roughened solar air heaters for fully developed turbulent flow data collected under actual outdoor conditions. Such solar air heaters have been found to give considerably high value of collector heat removal factor (F_R), collector efficiency factor (F′) and thermal efficiency (η_th) as compared to the corresponding values of those of smooth collectors. In the range of the operating parameters investigated, the ratio of the respective values of the parameters F_R, F′ and η_th for the roughened collectors to the smooth collectors have been found to be 1.786, 1.806 and 1.842 respectively.     

Discontinuous Galerkin approximation of two-phase flows in heterogeneous porous media with discontinuous capillary pressures

We design and investigate a sequential discontinuous Galerkin method to approximate two-phase immiscible incompressible flows in heterogeneous porous media with discontinuous capillary pressures. The nonlinear interface conditions are enforced weakly through an adequate design of the penalties on interelement jumps of the pressure and the saturation. An accurate reconstruction of the total velocity is considered in the Raviart–Thomas(–Nédélec) finite element spaces, together with diffusivity-dependent weighted averages to cope with degeneracies in the saturation equation and with media heterogeneities. The proposed method is assessed on one-dimensional test cases exhibiting rough solutions, degeneracies, and capillary barriers. Stable and accurate solutions are obtained without limiters.     

Porous graphene networks as high performance anode materials for lithium ion batteries

Porous graphene obtained by chemical vapor deposition (CVD) using porous MgO sheets as template is demonstrated to exhibit a high reversible capacity (1723 mAh g^-1), excellent high-rate capability and cycling stability for Li-ion batteries. The simple CVD approach offers a new way for large-scale production of porous graphene materials for energy storage.