Photoluminescence properties and synthesis of a PZT mesostructure obtained by the microwave-assisted hydrothermal method

Micro-cube-shaped lead zirconate titanate was synthesized using the microwave-assisted hydrothermal method. Photoluminescence and field emission scanning electron microscopy were used for monitoring the formation of mesocrystals. Based on these results, a growth mechanism was then proposed which involved nanoparticle aggregation, nanoplate self-assembly on specific architecture and the final formation of mesoscopic micro-cube-shaped lead zirconate titanate. (C) 2011 Elsevier B. V. All rights reserved.

QEXAFS and UV/Vis Simultaneous Monitoring of the TiO2-Nanoparticles Formation by Hydrolytic Sol-Gel Route

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Dependence of annealing time on structural and morphological properties of Ca(Zr0.05Ti0.95)O-3 thin films

Ca(Zr0.05Ti0.95)O-3 (CZT) thin films were prepared by the polymeric precursor method by spin-coating process. The films were deposited on Pt(1 1 1)/Ti/SiO2/Si(1 0 0) substrates and annealed at 650 degrees C for 2,4, and 6 It in oxygen atmosphere. Structure and morphology of the CZT thin films were characterized by the X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), atomic force microscopy (AFM) and field-emission scanning electron microscopy (FEG-SEM). XRD revealed that the film is free of secondary phases and crystallizes in the orthorhombic structure. The annealing time influences the grain size, lattices parameter and in the film thickness. (c) 2006 Elsevier B.V. All rights reserved.

Pearlitic reaction in Cu-10wt%Al alloy with Ag additions

The pearlitic reaction in Cu-10wt%Al alloy with additions of 4, 6, 8, and 10wt%Ag was studied using scanning electron microscopy, energy dispersive X-ray microanalysis, in situ X-ray diffractometry, and microhardness measurements. The results indicated that the presence of Ag changes the pearlitic phase microstructure and its mechanical properties, because of the influence of Ag in the pearlitic phase growth mechanism. (C) 2008 International Centre for Diffraction Data.

Gelation of siloxane-poly(oxypropylene) composites

The viscoelastic properties of siloxane-poly(oxypropylene) (PPO) nanocomposites prepared by the sol-gel process has been analyzed during gelation by dynamic rheological measurements. The changes of storage and loss moduli, complex viscosity and phase angle has been measured as a function of time showing the newtonian viscosity of the sol in the initial step of gelation, and its progressive transformation to a viscoelastic gel. The rheologic properties have been correlated to mass fractal, nearly linear growth models and percolation theory. This study, completed by quasi-elastic light scattering and Si-29 solid state nuclear magnetic resonance measurements, shows that the mechanisms of gelation of siloxane-PPO hybrids depend on the molecular weight of the polymer and on the pH of the hybrid sol. For hybrids prepared in acid medium, a polymerization involving silicon reactive species located at the extremity of the polymer chains and presenting a functionality f = 2 occurs, forming a fractal structure during the first stage of sol-gel transition. For samples prepared under neutral pH, the fractal growth is only observed for hybrids containing short polymer chains (M-w similar to 130 gmol(-1)). The fractal dimensionality determined from the change in the rheological properties, indicates that the fractal growth mechanism changes from reaction-limited to diffusion-limited aggregation when the molecular weight of the PPO increases from 130 to 4000 gmol(-1) and as catalyst conditions change from acidic to neutral. Near the gel point, these hybrid gels have the typical scaling behavior expected from percolation theory. (C) 2002 Elsevier B.V. B.V. All rights reserved.

In situ and simultaneous nanostructural and spectroscopic studies of ZnO nanoparticle and Zn-HDS formations from hydrolysis of ethanolic zinc acetate solutions induced by water

The simultaneous formation of nanometer sized zinc oxide (ZnO), and acetate zinc hydroxide double salt (Zn-HDS) is described. These phases, obtained using the sol-gel synthesis route based on zinc acetate salt in alcoholic media, were identified by direct characterization of the reaction products in solution using complementary techniques: nephelometry, in situ Small-Angle X-ray Scattering (SAXS), UV-Vis spectroscopy and Extended X-ray Absorption Fine Structures (EXAFS). In particular, the hydrolytic pathway of ethanolic zinc acetate precursor solutions promoted by addition of water with the molar ratio N = [H2O]/[Zn2+] = 0.05 was investigated in this paper. The aim was to understand the formation mechanism of ZnO colloidal suspension and to reveal the factors responsible for the formation of Zn-HDS in the final precipitates. The growth mechanism of ZnO nanoparticles is based on primary particle (radius approximate to 1.5 nm) rotation inside the primary aggregate (radius < 3.5 nm) giving rise to an epitaxial attachment of particles and then subsequent coalescence. The growth of second ZnO aggregates is not associated with the Otswald ripening, and could be associated with changes in equilibrium between solute species induced by the superficial etching of Zn-HDS particles at the advanced stage of kinetic.

Formation of beta-nickel hydroxide plate-like structures under mild conditions and their optical properties

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Crystallization of ZrF4-LaF3-AlF3 glasses

0.7125ZrF4-0.2375(1 - xLaF3 • xLnF3)-0.05AIF3 with x = 0.01, 0.02 and 0.03 for Ln = Er and x = 0.03 for Ln = Pr, Nd glasses were studied by differential thermal analysis (DTA), X-ray diffraction and optical spectroscopy. Avrami parameters (Ec and n) were obtained from DTA curves. With La3+ substitution a decrease in the stability against crystallization was observed. This decrease follows the order Er3+ > Nd3+ ≈ Pr3+ for 3% molar substitution. n values suggest an interface controlled growth mechanism with grain edge nucleation abler saturation. Two crystalline polymorphs of the LaZr3F15 phase were identified. With the substitution of 3 mol% of Pr3+, Nd3+ or Er3+ for La3+ only the crystallization of the rhombohedral α-LnZr3F15 phase was observed. An increase in Ω6 Judd's intensity parameter occurs with crystallization and also an increase in the 1.04 μm peak emission cross-section for Nd3+ 4I3/2 state suggesting the potential application of these glass ceramics in optical amplification devices. © 1997 Elsevier Science B.V.

An ultrafiltration membrane, prepared with MSU-type mesoporous silica: Preparation and specific filtration behavior

We report preparation and the singular filtration properties of an ultrafiltration membrane made with MSU-type mesoporous silica that exhibits cylindrical pores aligned mostly normal to the support. This membrane supported on tubular commercial macroporous alumina supports was prepared by the interfacial growth mechanism between stable silica-surfactant hybrid micelles made of the association of silica oligomers with polyethyleneoxide-based (PEO) surfactants and sodium fluoride, a well-known silica condensation catalyst. It appears that the combined effect of the silica nature of the membrane, whose surface charge can be easily adjusted by changing the pH and the non-connected cylindrical shape of the pores provides a new behavior in the retention properties, as proved by the filtration of polyoxyethylene polymers (PEO) with different molecular weights. Depending on the filtration conditions, a rejection rate of 80 % and a steep cut-off at 2,000 Da can be obtained or, on the reverse, polymers three times bigger than the pore diameter can diffuse through the membrane. This new filtration mechanism, which opens up new modes of separation modes, is explained in the light of both topology of the porous network and pH-dependent interactions between PEO polymers and silica porous media. © 2005 Elsevier B.V. All rights reserved.

Estudo do crescimento e caracterização de nanofitas do sistema ITO

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Fotoluminescência e mecanismo de crescimento em titanatos nanoestruturados

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Reduced graphene oxide multilayers for gas and liquid phases chemical sensing

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Zinc blende versus wurtzite ZnS nanoparticles: control of the phase and optical properties by tetrabutylammonium hydroxide

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

The modification of structural and optical properties of nano- and submicron ZnO powders by variation of solvothermal syntheses conditions

Nano- (30-60 nm) and submicron (100-350 nm) ZnO particles were synthesized using solvothermal method at 200 degrees C from an ethanolic solution of zinc acetate dihydrate, applying different reaction conditions, i.e., pH value of precursor and time of the reaction. The X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), UV-vis diffuse reflectance (DR), Raman spectroscopy, and photoluminescence (PL) spectroscopy have been employed for characterization of synthesized ZnO powders. It was shown that the structural, morphological, and optical properties are largely determined by reaction conditions during solvothermal synthesis. The particle crystallinity improves with the decrease of pH value and/or the increase of time of the reaction. The Raman and PL spectra analyses indicate that the oxygen interstitials are dominant intrinsic defects in solvothermally synthesized ZnO powders. It was observed that concentration of defects in wurtzite ZnO crystal lattices slightly changes with the variation of pH value of the precursor and time of the solvothermal reaction. The correlation between structural ordering and defect structure of particles and corresponding growth processes was discussed.

Is the meander growth in the Brazil Current system off Southeast Brazil due to baroclinic instability?

Temporally-growing frontal meandering and occasional eddy-shedding is observed in the Brazil Current (BC) as it flows adjacent to the Brazilian Coast. No study of the dynamics of this phenomenon has been conducted to date in the region between 22 degrees S and 25 degrees S. Within this latitude range, the flow over the intermediate continental slope is marked by a current inversion at a depth that is associated with the Intermediate Western Boundary Current (IWBC). A time series analysis of 10-current-meter mooring data was used to describe a mean vertical profile for the BC-IWBC jet and a typical meander vertical structure. The latter was obtained by an empirical orthogonal function (EOF) analysis that showed a single mode explaining 82% of the total variance. This mode structure decayed sharply with depth, revealing that the meandering is much more vigorous within the BC domain than it is in the IWBC region. As the spectral analysis of the mode amplitude time series revealed no significant periods, we searched for dominant wavelengths. This search was done via a spatial EOF analysis on 51 thermal front patterns derived from digitized AVHRR images. Four modes were statistically significant at the 95% confidence level. Modes 3 and 4, which together explained 18% of the total variance, are associated with 266 and 338-km vorticity waves, respectively. With this new information derived from the data, the [Johns, W.E., 1988. One-dimensional baroclinically unstable waves on the Gulf Stream potential vorticity gradient near Cape Hatteras. Dyn. Atmos. Oceans 11, 323-350] one-dimensional quasi-geostrophic model was applied to the interpolated mean BC-IWBC jet. The results indicated that the BC system is indeed baroclinically unstable and that the wavelengths depicted in the thermal front analysis are associated with the most unstable waves produced by the model. Growth rates were about 0.06 (0.05) days(-1) for the 266-km (338-km) wave. Moreover, phase speeds for these waves were low compared to the surface BC velocity and may account for remarks in the literature about growing standing or stationary meanders off southeast Brazil. The theoretical vertical structure modes associated with these waves resembled very closely to the one obtained for the current-meter mooring EOF analysis. We interpret this agreement as a confirmation that baroclinic instability is an important mechanism in meander growth in the BC system. (C) 2008 Elsevier B.V. All rights reserved.