Metastable and Nanostructured Materials III

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Authors: Juan Bartolomé, F. Luis, L.M. García, F. Bartolomé, F. Petroff, C. Deranlot, F. Wilhelm, A. Rogalev, P. Bencok, N.B. Brookes
Abstract: The effect of capping with Cu, Au and Pt of an array of Co nanoparticles is revised. The magnetic surface anisotropy KS was found to be the dominant contribution to the effective anisotropy Keff of the particles. Recent X-ray Magnetic Circular Dichroism (XMCD) measurements show that there is hybridization between the 3d Co electrons and the d and 4p electrons of the capping metal. By comparison to the mechanisms which give rise to the surface anisotropy in thin films, it is argued that this hybridization governs the modification of KS, and hence, of Keff.
Authors: Jérôme Gavillet, Stéphane Getin, Etienne Quesnel, Steve Martin, Guillaume Delapierre, Karla Hiller, Joerg Nestler, Thomas Gessner, Juergen Soechtig, Guy Voirin, Lukas Buergi, Janko Auerswald, Helmut F. Knapp, Stanley Ross, Samuel Bigot, Markus Ehrat, Andreas Lieb, Marie Claire Beckers, Damien Dresse
Authors: Michelle A. Souza, Nelson M. Larocca, Edcleide Maria Araújo, Luiz Antonio Pessan
Abstract: Nanocomposites of PA6 / organoclay at different concentration were prepared via melt intercalation method using a corotating twin screw extruder. The composites were prepared with Brazilian clay that was treated with different modifiers based on quaternary ammonium salts to obtain three types of organoclays. After extrusion the mixtures were injection molded into specimens that were tested to obtain the properties of tensile strength, notched izod impact and heat deflection temperature. The structure and morphology of the nanocomposites were characterized by x-rays diffraction (XRD) and transmission electron microscopy (TEM). The results showed that the modifier “dodigen” which promoted the intermediate expansion of the bentonite clay within the three salts used for the modification of the clay affects more significantly the mechanical properties, HDT and morphology of the polyamide 6 due to the higher level of exfoliation observed in these systems compared to the others modifiers. The improvement of the properties was correlated to the level of exfoliation/intercalation obtained which depends on the process technique used, surface treatment of the Brazilian clays with organic salts and interaction between polymer and clay.
Authors: Marcos Lopes Dias, Marlon S. Santos, Felipe Rodrigues Alves, Chiaki Azuma
Abstract: Copolymerization of silicon alkoxides in alcoholic basic medium using trialkyl- or triarylchlorosilanes as terminator was investigated. Tetraethoxysilane (TEOS), phenyltriethoxysilane (PTEOS) and vinyltriethoxysilane (VTEOS) were used as monomers and triphenylchlorosilane (TPCS) and trimethylchlorosilane (TMCS) as terminator. The copolymerization of TEOS with PTEOS and VTEOS produces core-shell silica-silicone nanospherical hybrids containing large amounts of functional groups in the structure of their external layer. The structure is the result of the fast hopolymerization of TEOS in a first stage of the reaction, forming the core, followed by copolymerization of TEOS and the alkyl- or vinyl-trialkoxysilane comonomer in its last stage. The structure was confirmed by Raman and FTIR spectroscopy, wide angle X-ray scattering (WAXS) and thermogravimetry. The control of particle size is effectively made by the termination reaction and particles with average diameter between 20 and 100 nm were obtained. Introduction of other chemical functions on the surface of these nanoparticles can be carried out by common reactions with the functional surface groups. As an example, sulfonation of particles containing phenyl groups on the surface by direct sulfuric acid and chlorosulfonic acid was investigated and the results discussed.
Authors: Sylvain Pedneault, L. Roué, Jacques Huot
Abstract: In the development of metal hydrides for commercial applications, a special attention should be devoted to the ways of production. For commercial success, the raw elements of the hydrogen storage materials should be of low cost, the synthesis process should be inexpensive and easily scalable. Therefore, it is important to put some effort on the elaboration of new and more efficient means of producing metal hydrides. In this perspective, cold rolling was investigated as a new means of producing nanocrystalline materials. This technique is well-known in the industry and easily scalable. Cold rolling was performed on Mg-Ni system. The evolution of morphology, crystal structure, crystallite size, deformation, and preferred orientation was studied as a function of number of rolling passes. Cold rolling followed by a heat treatment produced the intermetallic Mg2Ni. Without heat treatment and for a large number of rolling, an amorphous phase was synthesized.
Authors: Antoine Vaichere, Daniel Rodrigo Leiva, Tomaz Toshimi Ishikawa, Walter José Botta Filho
Abstract: A good method to store hydrogen is in it atomic form in crystalline structure of metals at low pressure. Thanks to magnesium’s high hydrogen storage capacity, its low weight and its high natural abundance, it is an attractive material to develop hydrogen solid state storage. The production of Mg-based nanocomposites can enhance the kinetics of H-sorption of magnesium and the temperature of release of hydrogen. Transition metals as iron, which have important catalytic activity in hydrogen reactions with Mg, and the surface protective compound MgF2, are interesting additions for magnesium mixtures for hydrogen storage. In this work, Mg-based nanocomposites containing Fe and MgF2 were produced by reactive milling under hydrogen using the addition of FeF3, or directly MgF2 and Fe. The efficiency of centrifugal and planetary mill in MgH2 synthesis was compared. The phase evolution during different milling times (from 1 to 96 h) using the planetary was investigated. The different H-desorption behavior of selected milled mixtures was studied and associated with the different present phases in each case.
Authors: S.A. Loureiro, Daniel Fruchart, Sophie Rivoirard, Dílson S. dos Santos, L.M. Tavares
Abstract: AB2 metallic alloys provide large quantities of Laves phases when prepared using conventional thermal routes. In the present work the crystallography, hydrogenation behavior and mechanical milling (MM) effects of the pseudo-binary Zr(NbxV1-x)2 (0
Authors: Fabiana C. Gennari, Marcelo R. Esquivel
Abstract: Structure, microstructure and hydriding properties of mechanically alloyed 2Mg-Ni mixture were investigated. Two different nanocomposites were synthesized by mechanical alloying (MA) in a low-energy planetary mill, namely MN100 (100 h of milling) and MN200 (200 h of milling). The formation of nanocrystalline Mg2Ni was detected as a function of the milling time. An appropriate combination of MA plus annealing under mild conditions accomplishes the complete formation of Mg2Ni phase. The pressure-composition isotherms of the two samples reveal different hydrogen storage capacities and plateau slopes. In addition, the low temperature Mg2NiH4 (LT) formed by hydriding/cooling of MN100 h decomposes at 190 °C, whereas this hydride produced from MN200 first transforms to the high temperature Mg2NiH4 and then decomposes near 245 °C. The differences in the hydriding/dehydriding properties of MN100 and MN200 were associated with the microstructure and structure of the phases formed during MA followed by heating under argon/hydrogen.

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