Advanced Materials Research Vol. 976

Abstract: The stabilization of nanoparticles in solution is a challenge of major proportions, and avoiding the formation of aggregates and eventual coalescence of particles is directly linked to the conservation of its unique properties. In this work, we reported the synthesis of two hexakis-heterocyclic compounds, containing the tetrazole or 2-amino-1,3,4-thiadiazole group, respectively. The hexa-heterocyclic compounds were used in the synthesis and stabilization of Au and Ag nanoparticles. To obtain these molecules was used phosphonitrilic chloride trimer compound as core, which reacted with phenols properly substituted in the para position with either cyano or aldehyde group. The cyano group was successfully converted to the corresponding tetrazole using a 1,3-dipolar cycloaddition reaction with ammonium azide generated in situ. In the case of aldehyde derivative, it was converted to the corresponding thiosemicarbazone, which was further cyclized using FeCl₃. Compounds were characterized by RMN and IR spectroscopy. The UV-Vis spectroscopy was used for nanoparticles analysis.

Abstract: Copper and brass specimens were hot dipped aluminized using different times and temperatures conditions. Obtained coatings in a rich-aluminum matrix were characterized using microhardness test, metallographic analysis, electrochemical tests to evaluate corrosion resistance, and scanning electron microscopy/EDS analysis. Corrosion rate of hot dip aluminized copper varies according to processing parameters of molten aluminum. On the other hand, analysis and electrochemical results show that hot dipped aluminized brass increases its corrosion resistance at higher Al content within the coating.

Abstract: The treatment with mechanical vibrations during the solidification process promote microstructural changes in metallic alloys, in order to have a better understanding on this matter mechanical vibration were applied to an aluminum alloy A356, while teeming in order to evaluate the morphological changes on αAl primary phase in the solidification process. Two routes were analyzed, a cooling slope and a rotational mold. This paper shows the results of quantify the effect of mechanical vibration and the specific characteristic of casting to obtain a spherical morphology on the αAl primary, that allow to obtain thixoformable raw material.

Abstract: Influenza infection is carried out due to the virus hemagglutinin recognizes host cell surface with terminal sialic acid (SA) linked receptors SA-α-2,6-Gal for human strain. Sambucus nigra lectin has structural similarity to the viral hemagglutinin. Magnetic nanoparticles (MNP) coated with chitosan can be used as support for the study of these receptors. The goal of this study was to extract the SA-α-2,6-Gal receptors of porcine trachea for their immobilization on magnetic nanoparticles coated with chitosan. The extraction was carried out based on affinity of Sambucus nigra lectin to SA-α-2,6-Gal receptors. It was possible to immobilize up to 76% of SA-α-2,6-Gal receptors, with a molecular weight at 88.4 kDa for more representative protein. The presence of the receptors was confirmed trough FTIR analysis. Magnetic functionalized nanoparticles showed superparamagnetic properties and an average diameter around 10 nm. These results may be used to evaluate the interaction between functionalized nanoparticles and specific lectin or hemagglutinin of influenza virus as model of study virus-receptor.

Abstract: We have studied the optical properties of GaAs and Al_xGa_1-xAs thin films using low-temperature photoluminescence and Fourier transform infrared spectroscopy. The GaAs and its alloys were grown by MOCVD using solid arsenic instead of arsine, as the arsenic precursor. The gallium and aluminium precursors were trimethylgallium (TMGa) and trimethylaluminium (TMAl), respectively. Some difficulties for growing Al_xGa_1-xAs by solid-arsenic-based MOCVD system are the composition homogeneity of the layers and the oxygen and carbon incorporation during the growth process. The composition homogeneity of the films was evaluated by low-temperature photoluminescence. Infrared measurements on the samples allowed the identification of the residual impurities, which are carbon-substitutional, Ga₂O_3, molecular oxygen, humidity and two unidentified impurities. Samples grown at temperatures lower than 750°C were highly resistive, independently of the ratio V/III used; the samples grown at higher temperatures were n-type, as it was proved by Hall effect measurements.

Abstract: Several compositions of BaTiO:Nb5⁺ were made by conventional solid-state method in air atmosphere, according to the general formula BaTi_1-xNb_xO₃; (x= 0.005, 0.04, 0.08, 0.20, and 0.25). The crystal structure, microstructure, dielectric and ferroelectric properties of samples were investigated by XRD, Raman Spectroscopy, Electrical Measurements and SEM. X-ray diffraction results clearly indicated that when x ≥ 0.25 was prepared; the hexagonal phase Ba₈Ti₃Nb₄O₂₄ appeared. Electrical measurements at 1 kHz were carried out and several pellets were made, the relative permittivity was calculated. The dielectric constant of the pristine BaTiO₃ is about 7000, and the Curie temperature is ≈120°C at room temperature, decreasing to 90°C with Nb⁵⁺ addition (x = 0.005).

Abstract: Highly porous carbon nanospheres, external diameter ranging from 40 to 240 nm, have been produced from the chlorination reaction of metallocenes and derivatives at 900 °C. Their nanostructure, studied by Raman spectroscopy, consists of highly disordered graphene-like layers with size below to 6 nm. Their textural parameters showed surface area as high as 1320 m²/g and average pore width of 1.1 nm.

Abstract: It is known that magnetic, electric and optical properties of materials from mixed oxides mainly depend on the synthesis method used, therefore it is important to perform studies about the use of several synthesis routes with the purpose to understand and control the obtention of any given phase. In many of these routes it is required to control parameters such as temperature, pH, the variation of dopant concentration, etc. By this reason, in this work the effect of the method for three different synthesis routes (chemical coprecipitation, mechanosynthesis and combustion) was studied. These methods were used in the obtention of calcium manganite doped with lanthanum of theoretical stoichiometric Ca_0.3La_0.7MnO₃, using metallic minerals like precursors. The obtained powders were analyzed and characterized by X-ray diffraction (XRD), particle size analysis (PSA), scanning electron microscopy (SEM) and electron paramagnetic resonance (EPR). The crystallographic study (XRD) showed the obtention of calcium manganite doped with lanthanum with orthorrombic type structure, observed by SEM, agglomerates formed by particles with sizes smaller to one micrometer. By EPR it was found that powders obtained by chemical coprecipitation method showed magnetic behavior, in contrast with the behavior obtained by other two methods used, finding also powders with greater purity and in shorter synthesis time with regards to the ones obtained by mechanosynthesis and combustion.

Abstract: Polydiacetylenes are a type of highly conjugated polymers, and highly polar species are obtained when these polymers contain donor-acceptor azobenzene entities. In this paper the synthesis, characterization and evaluation of the dielectric constant of two polydiacetylenes containing azobenzenes as pendant groups are discussed. The Azobenzene chromophores are covalently bonded to the main chain, and their polarity is defined by an electro-donor (amine) and an electro-acceptor group (nitro or chlorine) bonded to the ends of a conjugated azobenzene structure. Both polymers were processed into plates of 1cm diameter x 0.674 mm thickness using a thermo mechanic technique. Their dielectric constants were evaluated respect to the temperature in a range of frequency of 110 MHz-1.32 GHz, from room temperature to close to their respective T_g. The dielectric constant for the polymer containing the nitro group was higher than it for polymer containing the chloride atom at all temperatures. It is discussed in terms of the ability to nitro and chloride to attract electronic density.