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Chen Z.,South China Normal University | Zhao R.,South China Normal University | Du P.,South China Normal University | Hu H.,South China Normal University | And 5 more authors.
Journal of Materials Chemistry A | Year: 2014

Alternative micro-sized LiNi0.5Mn1.5O4 spinels with octahedral structure (showing only one type of {111} crystal face) or chamfered polyhedral structure with extra other faces have been synthesized via a controllable method. A possible growth model, complexing-pyrolyzing- oriented, is also proposed for the formation of chamfered polyhedral LiNi 0.5Mn1.5O4 spinel based on the experimental results in this paper. The chamfered polyhedral LiNi0.5Mn 1.5O4 can provide a large capacity of 103 mA h g -1 even at a discharge rate as high as 50 C, which is far superior to that of the octahedral structure. Besides, the capacity retentions of the chamfered polyhedral composites are found to be 90.82% at 25 °C after 500 cycles and 90.00% at 55 °C after 200 cycles, which are also better than those of the octahedral composites. These results represent the first experimental evidence for lattice-plane anisotropy in LiNi0.5Mn 1.5O4 crystals. Moreover, the pseudo-sphere structure is beneficial for obtaining high volumetric energy density and excellent processability in practical applications. In short, we have revealed for the first time that, through chamfering an octahedron to a pseudo-sphere-like polyhedron rather than doping or coating, a micro-sized LiNi 0.5Mn1.5O4 spinel with good compatibility between energy/power density and cycle life can be synthesized successfully without sacrificing other properties. © 2014 the Partner Organisations.

Severac F.,Roche Holding AG | Severac F.,National Polytechnic Institute of Toulouse | Alphonse P.,Inter - University Research and Engineering Center on Materials | Esteve A.,Roche Holding AG | And 5 more authors.
Advanced Functional Materials | Year: 2012

Over the next few years, it is expected that new, energetic, multifunctional materials will be engineered. There is a need for new methods to assemble such materials from manufactured nanopowders. In this article, we demonstrate a DNA-directed assembly procedure to produce highly energetic nanocomposites by assembling Al and CuO nanoparticles into micrometer-sized particles of an Al/CuO nanocomposite, which has exquisite energetic performance in comparison with its physically mixed Al/CuO counterparts. Using 80 nm Al nanoparticles, the heat of reaction and the onset temperature are 1.8 kJ g -1 and 410 °C, respectively. This experimental achievement relies on the development of simple and reliable protocols to disperse and sort metallic and metal oxide nanopowders in aqueous solution and the establishment of specific DNA surface-modification processes for Al and CuO nanoparticles. Overall, our work, which shows that DNA can be used as a structural material to assemble Al/Al, CuO/CuO and Al/CuO composite materials, opens a route for molecular engineering of the material on the nanoscale. The fabrication of high-energy Al/CuO nanocomposites by nanoparticle DNA-directed assembly is demonstrated. The complementarity of the strands attached to the Al and CuO nanoparticles enables the assembly of micrometer-sized aggregates, which release heat upon thermal actuation, to be directed. The actuation temperature of 410°C of these materials is among the lowest published in the literature. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Suarez R.,Ingenieria | Sertucha J.,Ingenieria | Larranaga P.,Ingenieria | Lacaze J.,Inter - University Research and Engineering Center on Materials
Metallurgical and Materials Transactions B: Process Metallurgy and Materials Processing Science | Year: 2016

Appropriate nodularity in ductile iron castings is strongly associated with the presence of high enough not combined Mg dissolved in the melt to cast. However, the residual Mg which is commonly measured for production control accounts for both dissolved Mg and Mg combined as oxides and sulfides. To account for the uncertainties associated with such a control, it is quite usual to over treat the melt with the risk of porosity appearance. A new methodology based on thermal analysis has been developed in the present work so as to estimate the amount of free Mg dissolved in the melt ready for pouring. A combination of Te mixture and a new “reactive mixture” composed of sulfur plus a commercial inoculant has been prepared for this purpose. This reactive mixture is able to transform the magnesium remaining dissolved in the melt to combined forms of this element. Experiments performed both during start of production (when Mg overtreatment is usual) and during normal mass production indicate that important variations of free Mg occur without relevant changes in residual Mg content as determined by spectrometry. The method developed in the present work has shown to be highly effective to detect those melt batches where active Mg content is not high enough for guaranteeing a correct nodularity of castings. Selection of proper active Mg thresholds and a correct inoculation process are critical to avoid “false”-negative results when using this new method. © 2016 The Minerals, Metals & Materials Society and ASM International

Li R.,Shanghai University of Engineering Science | Li R.,Ecole Nationale Superieure de Chimie de Lille | Zhen Q.,Shanghai University of Engineering Science | Drache M.,Ecole Nationale Superieure de Chimie de Lille | And 3 more authors.
Solid State Ionics | Year: 2011

Using (Bi2O3)0.75(Dy2O 3)0.25 nano-powder synthesized by reverse titration co-precipitation method as raw material, dense ceramics were sintered by both Spark Plasma Sintering (SPS) and pressureless sintering. According to the predominance area diagram of Bi-O binary system, the sintering conditions under SPS were optimized. (Bi2O3)0.75(Dy 2O3)0.25 ceramics with relative density higher than 95% and an average grain size of 20 nm were sintered in only 10 min up to 500 °C. During the pressureless sintering process, the grain growth behavior of (Bi2O3)0.75(Dy2O 3)0.25 followed a parabolic trend, expressed as D 2 - D02 = Kt, and the apparent activation energy of grain growth was found to be 284 kJ mol- 1. Dense (Bi 2O3)0.75(Dy2O3) 0.25 ceramics with different grain sizes were obtained, and the effect of grain size on ion conductivity was investigated by impedance spectroscopy. It was shown that the total ion conductivity was not affected by the grain size down to 100 nm, however lower conductivity was measured for the sample with the smallest grain size (20 nm). But, although only the δ phase was evidenced by X-ray diffraction for this sample, a closer inspection by Raman spectroscopy revealed traces of α-Bi2O3. © 2011 Elsevier B.V. All rights reserved.

Berne C.,Inter - University Research and Engineering Center on Materials | Berne C.,ENSIACET | Andrieu E.,ENSIACET | Reby J.,CETIM | And 2 more authors.
Journal of the Electrochemical Society | Year: 2015

The electrochemical behavior of an α,β'-brass CuZn40Pb2 (CW617N) was studied in basic nitrate solutions with various basic pHs and nitrate ion concentrations. In all the chosen experimental conditions, corrosion at the open circuit potential proceeded by the galvanic coupling of the α and β' phases, leading to a surface dezincification of the β' phase. The study showed that the extent of the dezincification was affected by the presence of lead in the alloy but the pH was the major parameter. During polarization tests, a pseudo-passive or a passive stage followed by a breakdown was observed: corrosion phenomena mainly involved copper and zinc dissolution from the β' phase. At pH 11, a Cu2O/PbO layer was efficient in achieving passivity of the brass. At pH 12, a Cu(OH)2-rich surface layer was formed: it was not protective enough, and complete dissolution of the β' phase was observed leading to the removal of lead particles. © 2015 The Electrochemical Society.

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