SrZrO3 powders obtained by chemical method: Synthesis, characterization and optical absorption behaviour

Strontium zirconate (SrZrO3) powders have been synthesized by the polymeric precursor method after heat treatment at different temperatures for 2 h in oxygen atmosphere. The decomposition of precursor powder was followed by thermogravimetric analysis, X-ray diffraction (XRD) and Fourier transform Raman (FT-Raman). The UV-vis absorption spectroscopy measurements suggested the presence of intermediary energy levels in the band gap of structurally disordered powders. XRD, Rietveld refinement and FT-Raman revealed that the powders are free of secondary phases and crystallizes in the orthorhombic structure. (C) 2007 Elsevier Masson SAS. All rights reserved.

Synthesis of Ba0.5Sr0.5(Ti0.80Sn0.20)O-3 prepared by the soft chemical method

Single-phase Ba0.5Sr0.5(Ti0.80Sn0.20)O-3 (BST:Sn) powders with perovskite structure were prepared by the soft chemical method. Infrared data indicates that the BST:Sn powder is carbonate free while Raman analysis has shown that the transversal (TO) and longitudinal (LO) optical modes tend to disappear with tin addition. The electron diffraction pattern of the BST:Sn powder showed an interplanar distance of 3.94 angstrom characteristic of the pseudo-cubic structure. (c) 2007 Elsevier B.V. All rights reserved.

Structural characterization of phase transition of Al2O3 nanopowders obtained by polymeric precursor method

Nanocrystalline Al(2)O(3)powders have been synthesized by the polymeric precursor method. A study of the evolution of crystalline phases of obtained powders was accomplished through X-ray diffraction, micro-Raman spectroscopy and refinement of the structures through the Rietveld method. The results obtained allow the identification of three steps on the gamma-Al2O3 to alpha-Al2O3 phase transition. The single-phase alpha-Al2O3 Powder was obtained after heat-treatment at 1050 degrees C for 2 h. A study of the morphology of the particles was accomplished through measures of crystallite size, specific surface area and transmission electronic microscopy. The particle size is closely related to gamma-Al2O3 to alpha-Al2O3 phase transition. (c) 2007 Elsevier B.V. All rights reserved.

Barium strontium titanate powders prepared by spray pyrolysis

Ultasonic spray pyrolysis (SP) has been investigated for the production of the barium strontium titanate (BST) powders from the polymeric precursors. The processing parameters, such as flux of aerosol and temperature profile inside the furnace, were optimized to obtain single phase BST. The powders were characterized by the methods of X-ray diffraction analysis, SEM, EDS and TEM. The obtained powders were submicronic, consisting of spherical, polycrystalline particles, with internal nanocrystalline structure. Crystallite size of 10 nut, calculated using Rietveld refinement, is in a good agreement with results of HRTEM. (c) 2005 Elsevier B.V. All rights reserved.

Theoretical and experimental study of disordered Ba0.45Sr0.55TiO3 photoluminescence at room temperature

Disordered and crystalline Ba0.45Sr0.55TiO3 (BST) powder processed at low temperature was synthesized by the polymeric precursor method. The single-phase perovskite structure of the ceramics was identified by the Raman and X-ray diffraction techniques. Photoluminescence at room temperature was observed only in a disordered BST sample. Increasing the calcination time intensified the photoluminescence (PL), which reached its maximum value in the sample heat treated at 300 degrees C for 30 h. This emission may be correlated with the structural disorder. Periodic ab initio quantum-mechanical calculations using the CRYSTAL98 program can yield important information regarding the electronic and structural properties of crystalline and disordered solids. The experimental and theoretical results indicate the presence of intermediary energy levels in the band gap. This is ascribed to the break in symmetry, which is responsible for visible photoluminescence in the material's disordered state at room temperature. (c) 2005 Elsevier B.V. All rights reserved.

Structural and spectroscopic characterization of Al2-xCrxO3 powders obtained by polymeric precursor method

Al2O3 and Al2-x Cr (x) O-3 (x = 0.01, 0.02 and 0.04) powders have been synthesized by the polymeric precursors method. A study of the structural evolution of crystalline phases corresponding to the obtained powders was accomplished through X-Ray Diffraction and UV-vis spectroscopy (reflectance spectra and CIEL* a*b* color data). The obtained results allow to identify the gamma-Al2O3 to alpha-Al2O3 phase transition. The single-phase alpha-Al2O3 powder was obtained after heat treatment at 1050 degrees C for 2 h. The results show that the green to red color transition and ruby luminescence lines observed for the powders of Al2-x Cr (x) O-3 are related to the gamma to alpha-Al2O3 phase transition and the temperature and time range for such transition depends on the chromium content.

Electrochemical and structural characterization of heat-treated Cr3C2-NiCr coatings

The influence of heat-treatments on the electrochemical behavior of thermal spray Cr3C2-NiCr coatings prepared by high velocity oxygen fuel (HVOF) was studied in NaCl solution, at 25 degrees C, using open-circuit potential (E-OC) and electrochemical impedance spectroscopy (EIS) measurements. Coating characterization were performed before and after the heat-treatments and electrochemical tests by scanning electron microscopy, X-ray diffraction, and Auger electron spectroscopy. In addition to the changes in the original powder composition occurring during HVOF process, heat-treatment performed at 450 degrees C caused no significant changes in electrochemical response compared with untreated sample, and at 760 degrees C the main difference was the formation of a thin and defective layer of Cr2O3 at the coating surface, which increased the total impedance at the first day of immersion. Higher influence on the electrochemical was noted for samples treated at 880 degrees C, which also showed higher E-OC and total impedance, and lower corrosion current. This behavior was interpreted considering the formation of a chromium oxide layer on the coating surface, dissolution and decomposition of smaller carbide particles and their surface enrichment with Cr due to C diffusion and dissolution into the matrix, and possible Ni, Cr, and Fe diffusion to coating/substrate interface. (c) 2006 the Electrochemical Society.

An efficient microwave-assisted hydrothermal synthesis of BaZrO3 microcrystals: growth mechanism and photoluminescence emissions

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Lanthanum doped BiFeO3 powders: Syntheses and characterization

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Structure study of Bi4Ti3O12 produced via mechanochemically assisted synthesis

Nanosized bismuth titanate was prepared via high-energy ball milling process through mechanically assisted synthesis directly from their oxide mixture of Bi2O3 and TiO2. Only Bi4Ti3O12 phase was formed after 3 h of milling time. The excess of 3 wt% Bi2O3 added in the initial mixture before milling does not improve significantly the formation of Bi4Ti3O12 phase comparing to stoichiometric mixture. The formed phase was amorphized independently of the milling time, The Rietveld analysis was adopted to determine the crystal structure symmetry, amount of amorphous phase, crystallite size and microstrains. With increasing the milling time from 3 to 12 h, the particle size of formed Bi4Ti3O12 did not reduced significantly. That was confirmed by SEM and TEM analysis. The particle size was less than 20 nm and show strong tendency to agglomeration. The electron diffraction pattern indicates that Bi4Ti3O12 crystalline powder is embedded in an amorphous phase of bismuth titanate. Phase composition and atom ratio in BIT ceramics were determined by X-ray diffraction and EDS analysis. (c) 2007 Elsevier Ltd. All rights reserved.

Well-Alloyed PtFe/C Nanocatalysts of Controlled Composition and Same Particle Size: Oxygen Reduction and Methanol Tolerance

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Corrosion and Wear Studies of Cr3C2NiCr-HVOF Coatings Sprayed on AA7050 T7 Under Cooling

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Thermal Behavior of Sr(II) and Ba(II)-Diclofenac Complexes in Solid State: Study of the Dehydration and Thermal Decomposition

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Study of the thermal behavior of Al(III) and In(III)-diclofenac complexes in solid state

The Al and In-diclofenac compounds were prepared. Thermogravimetry (TG) and X-ray diffraction powder patterns were used to characterize these compounds. Details concerning the dehydration and thermal decomposition as well as data of kinetic parameters have been described here. The kinetic studies of these stages were evaluated from several heating rates with mass sample of 2 and 5 mg in open crucibles under nitrogen atmosphere. The results of the present study improve the knowledge on these compounds including their dehydration and thermal stability. The obtained data leads to a dependence on the sample mass, which results in two kinetic behavior patterns.

Thermal behavior studies of solid state compounds of 4-dimethylaminocinnamylidenepyruvate with alkali earth metals, except beryllium and radium

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)