Nanocomposites and Nanoporous Materials VII

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Authors: Young Soon Kwon, Ji Soon Kim, Cheol Eeh Kim
Abstract: Phase transformation induced by ball-milling was studied in this work. It was found that amorphous Fe90Zr10 ribbons undergo crystallization into BCC α-Fe(Zr) under milling in an AGO-2 mill. The decomposition degree of the amorphous phase increased with increasing milling time and intensity. Analyses of samples milled at different speeds suggested that the observed crystallization is a deformation-induced process rather than a thermally induced one. In addition, the decomposition behavior of a FeSn intermetallic under ball-milling was carefully studied. Upon milling a large amount of the FeSn intermetallic decomposed into Fe5Sn3 and FeSn2, where the average grain size of the product phases stayed nearly constant with milling-time. It is suggested that the mechanically driven decomposition of FeSn results from local melting of powder particles due to high temperature pulses during ball collisions.
Authors: Byung Joo Kim, Young Seak Lee, Soo Jin Park
Abstract: In this work, we prepared porous graphite nanofibers (PCNFs) from herringbone-type graphite nanofibers, and nano-sized transition metals such as copper metal, were loaded on the PCNFs by a metal electroplating in order to prepare novel catalysts for the control of toxic gases, such as hydrogen chloride. From experimental results, PCNFs had around 2000 m2/g of a specific surface area, and it was decreased slightly after metal loading. In case of metal content, we could control them from less 3 to over 30 wt% by means of the plating time and current density applied. After the metal loading, all samples having transition metal nanoclusters showed higher efficiency of HCl removal than that of samples without metals. However we also found that some samples having excessive metal content showed a decrease in the efficiency of HCl removal. This result meant that one of key technologies was both to find optimal metal content and to remain high specific surface area of substrates.
Authors: J.S. Kim, Moo Young Huh, Jae Pyong Ahn
Abstract: Nanophase tin powder having sizes ranging from 6 to 40 nm was synthesized by the inert gas condensation method using helium as the convection gas. As-synthesized particles smaller than 8 nm were the amorphous tin oxide. As-synthesized particles larger than 10 nm can be characterized by the core-shell structure comprising inner crystalline tin core and outer amorphous tin oxide shell having a thickness of about 4 nm. Upon annealing in air, the oxidation of nanophase tin particles strongly depended on particle size. With increasing particle size, the transformation into the crystalline phases took places at a higher temperature. Calculation of the size dependent melting temperature of tin particles indicates that melting of the tin encapsulated with the amorphous tin oxide took place prior to the oxidation.
Authors: Min Hye Kim, Ji Man Kim, Young Uk Kwon
Abstract: A heterojunction structure between a cubic structured mesoporous titania thin film and polythiocyanogen inside the pores was prepared by electrodeposition technique. UV-Vis absorption and FT-IR spectra show that the electrodeposited material is polythiocyanogen and the SEM images show that polythiocyanogen is infiltrated into the pores of the mesoporous titania film. In addition, this heterojunction structure was fabricated into a photovoltaic cell and the cell performance was tested. The cell showed an overall efficiency of 0.03%.
Authors: Gil Pyo Kim, Seung Bum Yoon, Young Soo Jung, Jae Hoon Ahn, Sung Hyeon Baeck, Alan Kleiman-Schwarsctein, Eric W. Mc Farland
Abstract: Nanoparticles (Au, Pt, Ru) supported on metal oxides (TiO2, Heteropoly Acid) were prepared by PS-PVP block copolymer encapsulation method. It was confirmed by XPS analysis that the oxidation state of metal is 0 after calcination, which indicates the complete removal of polymer. Synthesized catalysts were characterized by TEM, SEM-EDS, and UV-VIS spectroscopy and it was observed that synthesis and calcination conditions, and the interaction between nanoparticle and metal oxide affected significantly the particle size of metal on the surface of metal oxide. When two different metal precursors were diffused into the core of inversed micelles, nano alloy could be synthesized and the composition of nano alloy was controlled by varying the ratio between the two metal precursors.
Authors: K.G. Kanade, Ranjit R. Hawaldar, Uttam Mulik, B.B. Kale, Dinesh Amalnerkar
Abstract: We offer sui-generis strategy for synthesis of nanosized chalcogenide semiconductors in polymer matrix by a novel polymer-inorganic solid-state reaction. In our previous report, the rationale of this strategy has been successfully established by the solid-state reaction between CdI2 and an intentionally chosen engineering thermoplastic, namely, polyphenylene sulphide (PPS). In the pursuit of this work, we explored the possibility of using other cadmium salts viz cadmium nitrate, cadmium chloride and cadmium acetate in place of cadmium iodide for the envisaged solidstate reaction with PPS. All the reactions were carried out at the melting temperature of PPS (285oC) in 1:1 and 10:1 molar ratios of polymer to cadmium salt. The resultant products were characterised by XRD, TEM-SAED and DRS. It is observed that only cadmium nitrate yielded CdS nanocrystallites (average size of 15nm) entrapped in modified polymer matrix in a competing behaviour with cadmium iodide when reacted in 10:1 molar ratio while (i) cadmium acetate leads to the formation of only cadmium oxide and (ii) cadmium chloride exhibits grossly incomplete solid state reaction yielding understated quantity of CdS when reacted with PPS.
Authors: Ranjit R. Hawaldar, A.M. Funde, D. Bhange, V. Ramaswamy, Sandesh R. Jadkar, S.D. Sathaye, Uttam Mulik, Dinesh Amalnerkar
Abstract: Herein, we report the fabrication of anthracene nanostructures and, in turn, their thin films at the air-water interface by recrystallization at the liquid-liquid interface. This method is simple, inexpensive and allows the deposition of anthracene nanoparticulate thin films on large and a variety of substrates. The virgin films were characterized by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Hot Stage Polarizing Microscopy and UV-Visible spectroscopy. Interestingly, it was found that these thin films are comprised of nanosized bushy clusters of anthracene molecules as revealed by TEM. Also, with increase in the thickness of the films, the formation of irregular microtapes was evinced by SEM. The absorption spectra reveals the presence of 2 excitonic peaks for the lowest dip sample (10 dips) whereas the spectra recorded for higher dip samples (20 dips, 30dips, 40dips) closely match with that of pure anthracene in chloroform solution. The dramatic reduction in the melting point as revealed by hot stage polarizing microscopy is the salient feature of the work.
Authors: Ji Soon Kim, Hyeong Suk Choi, Dina V. Dudina, Jeong Keun Lee, Young Soon Kwon
Abstract: An attempt was made to produce nickel aluminides with fine microstructure from nanoscale nickel and aluminum powders produced by wire electric explosion (WEE). The powders were mixed and spark plasma sintered (SPS) for simultaneous reaction and densification of the material. Various mixing methods were tested to give the best homogeneity of the nanopowders mixtures. Utrasonic pre-treatment of the powders did not result in any positive effect on mixing homogeneity. Sintered compact contained NiAl and Ni3Al phases, showed fine grain size and unexpectedly high hardness possibly due to the presence of aluminum oxide in the starting nanopowders.

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