Advanced Materials Forum III

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Authors: Sandra G. Cruz, Penka I. Girginova, Márcia C. Neves, Petr Smolka, Robert Kusak, Madalena Caldeira, José Teixeira-Dias, Julio Pedrosa, Tito Trindade
Abstract: An overview of the chemical strategies developed in our laboratories to obtain welldefined BiVO4 particles is presented. The methods rely on the thermal treatment (including hydrothermal conditions) of aqueous solutions containing bismuth(III) cations, vanadium(V) species and organic ligands. The use of distinct polyaminocarboxylates and cyclodextrins as possible morphological modifiers was investigated. NMR spectroscopic techniques were applied to the distinct chemical baths in order to have a better insight on the nature of the solute precursors.
Authors: Ronaldo Santos da Silva, Antonio Carlos Hernandes
Abstract: We have studied the synthesis and sintering of BaTiO3 (BTO) nanometric powders produced by Pechini technique. A laser sintering procedure was applied to the BTO and its major advantage was the quickness of the processing. We have used the radiation of a CO2 laser (CW – 100 W) as the heating source. A linear rate of irradiation was applied to avoid macroscopic defects. The calcined powder at 800°C presented a single crystalline phase confirmed by the XRD and a crystallite size of 20 nm. BTO ceramics sintered at Pmax = 7.0 W/mm2 for 10 min of irradiation showed a high relative density (98 ± 1) % with an average grain size of 400 nm for a total time of sintering of 40 minutes.
Authors: Julia T. Gonçalves, Victor I. Boev, Alexey Solovyev, Carlos J.R. Silva, M.J.M. Gomes
Abstract: Transparent hybrid organic-inorganic ureasil xerogels with embedded PbS nanoparticles were prepared by exposing the xerogels doped with lead (II) nitrate to hydrogen sulphide atmosphere. Absorbance spectrum of the nonocomposites showed well defined peaks at 560 nm and 370 nm attributed to 1s(v) - 1s(c) and 1s(v) - 2p(c) exciton transitions, respectively. After four days of thermal treatment at 50 °C under argon atmosphere the obtained materials showed enhanced photoluminescence response in the near infra-red region.
Authors: Juan M. Montes, Jesus Cintas, Francicso Gomez Cuevas, José A. Rodríguez
Abstract: In this work, mechanically alloyed Al-5AlN powders have been sintered by the Electrical Resistance Sintering (E.R.S.) technique. A die of alumina-base refractory concrete has been employed. Several electric intensity currents and passage times through the compact have been tested during the consolidation process. Compacts have been mechanically characterized by their hardness distribution and by an indirect tensile test. The obtained results are compared with the corresponding values of compacts prepared with the same powders by the conventional route of cold pressing and furnace sintering. Finally, for all the electrically consolidated compacts, the final porosity, as well as the average hardness and the strength in the indirect tensile test are empirically related to the electric energy supplied during the process. This energy is a function of the electric intensity current and passage time. The aforementioned empirical relationships are useful to select the best process conditions.
Authors: Larisa Grigorjeva, Donats Millers, Witold Łojkowski, Tomas Strachowski
Abstract: Time-resolved luminescence and Furje Transformation Infrared (FTIR) absorption spectroscopy for ZnO nanocrystals prepared under different chemical reactions using microwave driven hydrothermal process was studied. OH- group stretching vibration frequency is considerably different in nanocrystals studied and in single ZnO crystal. It is shown that fractions of chemicals used in synthesis process could be found in nanopowders. Luminescence at ~2.0 eV (due to defect states in ZnO crystals and nanopowders) was suppressed in nanopowders obtained by urea method.
Authors: Stefan Köstler, Andreas Rudorfer, Roswitha Berghauser, Volker Ribitsch, Georg Jakopic
Abstract: Dispersions of colloidal particles of polycyclic aromatic hydrocarbons were obtained by nanosecond laser ablation. Aqueous suspensions of micron-sized crystals were irradiated with the second harmonic output of a Nd:YAG laser and converted into colloidal particles. Ionic and nonionic surfactants were used in the ablation process to stabilise the particles. Dispersions with good long term stability were obtained. A strong dependence of particle formation rate on laser fluence was found and the particle formation process is discussed on the basis of UV-Vis spectra and microscopic examination of the crystals.
Authors: Patricia Benito, Maria Herrero, Francisco Martin Labajos, Vicente Rives
Abstract: The synthesis and characterization of Co,Al Layered Double Hydroxides (LDHs) containing carbonate is reported. The solids have been submitted to several thermal treatments, hydrothermal and microwave-hydrothermal, modifying both the treatment time and temperature, with the main aim of studying their influence on the crystallinity of the solids and on the stabilization of divalent cobalt oxidation state. The results show that whichever the temperature and time used the only phase detected was the hydrotalcite, and that the cobalt cations keep the divalent oxidation state.
Authors: Natércia Nunes, Filomena Costa, António Maurício C. Fonseca, Isabel Neves, M.Alice Carvalho, Cristina Ribeiro
Abstract: The encapsulation of Cu(II) purine derivative complex was carried out by ion exchange of the complex from aqueous solutions into zeolite NaY. The entrapped complex was characterized by spectroscopic methods (FTIR and ICP-AES) and surface analysis (XRD). The various techniques of characterization used show that the Cu(II) complex was effectively encapsulated in the zeolite and this process does not modify the morphology and structure of the NaY zeolite. These materials have potential applications in heterogeneous catalysis in mild reaction conditions.
Authors: Lilian Marques Silva, Roberto R. Lima, Alexsander T. Carvalho, Maria Lucia Pereira Silva, Joana Catarina Madaleno, Luiz Pereira
Abstract: Films produced by plasma polymerization of ethyl ether and methyl or ethyl acetate show good adsorption characteristic for polar and non-polar organic compounds. These films when used in microchannels machined in a 3D-structure present some preconcentration of organic compounds. Therefore, the aim of this work is to investigate the physical-chemical preconcentration mechanisms on this structure. The test molecules used were n-hexane and 2-propanol. Quartz crystal microbalance and mass spectrometry were used to measure preconcentration. Two different procedures for reactant injection on the structure were used: a continuous flow during several minutes or a small amount injected on a single pulse and in a few seconds. The microchannels were also modified by the introduction of small ceramic particles for enhancement of the flow dispersion. It was possible to notice for all films a similar kinetic of retention. The main removal mechanism is adsorption. Although all films can provide the removal of the adsorbents molecules, the most important characteristic for the adsorption and/or retention is the surface condition. Thus, the retention of polar compound can be troubled if a non-polar compound was used previously. The most promising films for retention are ethyl ether and ethyl acetate when n-hexane and 2-propanol are used as test molecules. The results using n-hexane or 2-propanol point out the use of low-cost microchannels for preconcentration development.
Authors: Juras Banys, Martynas Kinka, Jan Macutkevic, Georg Völkel, Winfried Böhlmann, Venkatesan Umamaheswari, Martin Hartmann, Andreas Pöppl
Abstract: Melting-freezing dynamics of water confined in three MCM-41 materials with pore diameters of 2.0 nm, 2.5 nm and 3.7 nm was analyzed using dielectric spectroscopy method. Obtained results show, that reorientation of water molecules is strongly affected by confinement and interaction with the pore surface, which leads to the formation of highly disordered hydrogen bonded network. Defects of this network play the key role in the overall relaxation of confined water.

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