Influence of microwave energy on structural and photoluminescent behavior of CaTiO3 powders

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Growth mechanism of octahedron-like BaMoO4 microcrystals processed in microwave-hydrothermal: Experimental observations and computational modeling

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

CuO urchin-nanostructures synthesized from a domestic hydrothermal microwave method

This letter reports the synthesis of CuO urchin-nanostructures by a simple and novel hydrothermal microwave method. The formation and growth of urchin-nanostructures is mainly affected by the addition of polyethylene glycol (PEG). The hierarchical malachite particles are uniform spheres with a diameter of 0.7-1.9 mu m. CuO urchin-nano structures were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FEG-SEM) and nitrogen adsorption (BET). The specific surface area of the CuO nanostructured microspheres was about 170.5 m(2)/g. A possible mechanism for the formation of such CuO urchin-nanostructures is proposed. (c) 2007 Elsevier Ltd. All rights reserved.

Spectrophotometric Determination of Paracetamol in Pharmaceuticals Using Microwave-Assisted Hydrolysis and a Micellar Medium

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

Spectrophotometric determination of diclofenac in pharmaceutical preparations assisted by microwave oven

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

Ground state masses and binding energies of the nucleon, hyperon and heavy baryons in a light-front model

The ground state masses and binding energies of the nucleon, lambda0, lambdac+ , lambdab0 are studied within a constituent quark QCD-inspired light-front model. The light-front Faddeev equations for the Qqq composite spin 1/2 baryons, are derived and solved numerically. The experimental data for the masses are qualitatively described by a flavor independent effective interaction.

Electrical and microstructural properties of microwave sintered SnO2-based varistors

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Asymmetrical penetration of microwave in a conducting media and determination of microwave conductivity for very thin samples using electron spin resonance

Dyson's theory of conduction electron spin resonance (CESR) has been used in the limit d less than or equal to delta (d being the thickness of the sample and delta the skin depth of the microwave field) to obtain the microwave conductivity from the (A/B) ratio of the CESR absorbed power derivative. In this work we calculate the CESR absorbed power derivative using Kaplan's approach and show that the (A/B) ratio can be enhanced if asymmetrical penetration of microwave is used, which means that the microwave field enters into the sample from one of the faces. Therefore, the determination of the microwave conductivity from the (A/B) ratio of the CESR line can be performed for thinner samples. Experimentally, asymmetrical penetration can be obtained if one of the sample's faces is covered with a thin gold layer. The determination of microwave conductivity in conducting polymers films is among the possible applications of this method. (C) 2001 Elsevier B.V. Ltd. All rights reserved.

Binding energies of excitons trapped by ionized donors in semiconductors

Using the hyperspherical adiabatic approach in a coupled-channel calculation, we present precise binding energies of excitons trapped by impurity donors in semiconductors within the effective-mass approximation. Energies for such three-body systems are presented as a function of the relative electron-hole mass sigma in the range 1 less than or equal to1/sigma less than or equal to6, where the Born-Oppenheimer approach is not efficiently applicable. The hyperspherical approach leads to precise energies using the intuitive picture of potential curves and nonadiabatic couplings in an ab initio procedure. We also present an estimation for a critical value of sigma (sigma (crit)) for which no bound state can be found. Comparisons are given with results of prior work by other authors.

Positron-helium scattering at medium energies

We present results for medium-energy elastic, inelastic [transition to He(1s2(1)s), He(1s2(1)p), He(1s3(1)s), and He(1s3(1)p) states], capture [to Ps(1s), Ps(2s), and Ps(2p) states of the positronium (Ps) atom] and total cross sections of positron-helium scattering in the close coupling approach using realistic wave functions.

SrBi2Nb2O9 thin films crystallized using a low power microwave oven

SrBi2Nb2O9 thin films were produced by the polymeric precursor method using an aqueous solution. The crystallization of the films was carried out using a domestic microwave oven by means of a SiC susceptor in order to absorb the microwave energy and rapidly transfer the heat to the film. Low microwave power and short time have been used. The films obtained are well-adhered, homogeneous and with good specularity, even when treated at 600 degreesC for 10 min. The microstructure and the structure of the films can be tuned by adjusting the crystallization conditions. Depending on the direction of the heat flux it is possible to obtain preferential oriented or polycrystalline films in the microwave oven for 10 min. The microstructure presented a polycrystalline nature with spheroid small mean grain size when the susceptor is placed above the substrate. When the susceptor is placed below the substrate, the films presented platelet grains with mean grain size around 250 nm and a 001 orientation. For comparison, films were also prepared by the conventional method at 700 degreesC for 2 h. (C) 2003 Elsevier Ltd. All rights reserved.

Analytical procedure for total mercury determination in fishes and shrimps by chronopotentiometric stripping analysis at gold film electrodes after microwave digestion

A method for the total mercury determination in fish and shrimps employing chronopotentiometric stripping analysis on gold film electrodes is described. Fish and shrimp tissues were digested using a microwave oven equipped with closed vessels. We developed a microwave heating program which decomposed all the samples employing diluted nitric acid and hydrogen peroxide. The proposed method was validated by analyzing a certified reference material and then applied for different fish species from fresh water and seawater acquired in local markets of São Paulo city, Brazil. The Brazilian legislation establishes 0.5 and 1 mg per kilogram of fish as upper limit of mercury for omnivorous and predator species, respectively. Except for blue shark tissues, the mercury content was situated below 0.5 mu g g(-1) for all the analyzed samples. The detection limit of the proposed method was calculated as 5 ng g(-1) of sample utilizing 5 minutes of electrodeposition (+300 mV vs. Ag/AgCl) on the gold electrode. (c) 2006 Elsevier Ltd. All rights reserved.

Epitaxial growth of LiNbO3 thin films in a microwave oven

Oriented LiNbO3 thin films were prepared using a polymeric precursor solution deposited on (0001) sapphire substrate by spin coating and crystallized in a microwave oven. Crystallization of the films was carried out in a domestic microwave oven. The influence of this type of heat treatment on the film orientation was analyzed by X-ray diffraction and electron channeling patterns, which revealed epitaxial growth of films crystallized at 550 and 650 degreesC for 10 min. A microstructural study indicated that the films treated at temperatures below 600 degreesC were homogeneous and dense, and the optical properties confirmed the good quality of these films. (C) 2003 Elsevier B.V. B.V. All rights reserved.