Filmes de titânio-silício preparados por spin e dip-coating

The conditions for the preparation of luminescent materials, consisting of Eu3+ ions entrapped in a titanium matrix, in the forma of a thin film, using the sol-gel process, are described. The films were obtained from sols prepared with TEOS and TEOT, in the presence of acetylacetone as the hidrolysis-retarding agent, using the dip-coating and spin-coating techniques. The influence of these techniques on the films based on titanium and silicon are presented. The Eu3+ was used as a luminescent probe. The films have been characterized by luminescence, reflection and transmittance. The thickness of the films could be related to the preparation procedure. Transparent thin films have been prepared by dip-coating technique.

Electrical and optical characteristics of SnO2 thin films prepared by dip coating from aqueous colloidal suspensions

Starting from aqueous colloidal suspensions, undoped and Nb5+ doped SnO2 thin films have been prepared by using the dip-coating sol gel process. X-ray diffraction results show that films are polycrystalline with crystallites of average size1-4nm. Decreasing the thickness of the films and increasing the Nb5+ concentration limits the crystallite size growth during firing. Complex impedance measurements reveal capacitive and resistive effects between adjacent crystallites or grains, characteristic of electrical potential barriers. The transfer of charge throughout these barriers determines the macroscopic electrical resistance of the layer. The analysis of the optical absorption spectra shows that the samples present more than 80% of their transmittance in the visible region and the value of the band gap energy increases with decreasing crystallite size. © 1997 Chapman & Hall.

Photodesorption and electron trapping in n-type SnO2 thin films grown by dip-coating technique

Thin films of undoped and Sb-doped (2 atg%) SnO2 have been prepared by sol-gel dip-coating technique on borosilicate glasses. Variation of photoconductivity excitation with wavelength and optical absorption indicate indirect bandgap transition with energy of ≅ 3.5 eV. Conductance as function of temperature indicates two levels of capture with 39 and 81 meV as activation energies, which may be related to an Sb donor and oxygen vacancy respectively. Electron trapping by these levels are practically destroyed by UV photoexcitation (305 nm) and heating in vacuum to 200°C. Gas analysis using a mass spectrometer indicates an oxygen related level, which may not be desorbed in the simpler O2 form.

Improved Conductivity Induced by Photodesorption in SnO2 Thin Films Grown by a Sol-Gel Dip Coating Technique

Thin films of undoped and Sb-doped SnO2 have been prepared by a sol-gel dip-coating technique. For the high doping level (2-3 mol% Sb) n-type degenerate conduction is expected, however, measurements of resistance as a function of temperature show that doped samples exhibit strong electron trapping, with capture levels at 39 and 81 meV. Heating in a vacuum and irradiation with UV monochromatic light (305 nm) improve the electrical characteristics, decreasing the carrier capture at low temperature. This suggests an oxygen related level, which can be eliminated by a photodesorption process. Absorption spectral dependence indicates an indirect bandgap transition with Eg ≅ 3.5 eV. Current-voltage characteristics indicate a thermionic emission mechanism through interfacial states.

Poly(epsilon-caprolactone) nanocapsules carrying the herbicide atrazine: effect of chitosan-coating agent on physico-chemical stability and herbicide release profile

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

Bi-2212/Ag laminated tapes: Bending and joining effects

Superconducting composite Bi-2212/Ag tapes and their joints are fabricated by a combination of dip-coating and partial melt processing. The heat treated tapes have a critical current (Ic) between 8 and 26A, depending on tape thickness and the number of Bi-2212 layers. Current transmissions between 80% and 100% have been achieved through the joints of tapes. Different types of HTS joints of Bi-2212/Ag laminated tapes are made and their transport properties during winding operations are investigated. Irreversible strain values (ε irrev) for laminated tapes and their joints are determined and it is found that the degradation of Ic during tape bending depends on the type of joint.

Bi-2212/Ag tapes and laminates : effects of bending

Superconducting Bi-2212 tapes and laminates are fabricated by a combination of dip-coating and partial melt processing. The heat treated tapes have critical current densities (Jc) up to 11 kAcm -2. We investigate the degradation of critical current (Ic) during bending experiments for both single tapes and tapes with laminate structure. Although degradation of Ic is observed in both forms, the characteristics of the degradation differ. It is determined that laminated tapes perform better than single tapes when critical current is measured against bending radius, and laminated tapes tolerate a higher strain for a given reduction in critical current. It is found that increasing the number of Bi-2212 layers increases the total Ic of the laminated tape, but degradation of critical current is more pronounced during bending because of the increased total thickness of the laminate structure. It is also found that addition of silver to the Bi-2212 layers reduces critical current degradation during bending for both tapes and laminates.

Miniaturization of heterogeneous catalytic reactors: Prospects for new developments in catalysis and process engineering

This paper gives an overview of the research done since 1999 at Eindhoven University of Technology in the Netherlands in the field of miniaturization of heterogeneous catalytic reactors. It is described that different incentives exist for the development of these microstructured reaction systems. These include the need for efficient research instruments in catalyst development and screening, the need for small-scale reactor devices for hydrogen production for low-power electricity generation with fuel cells, and the recent quest for intensified processing equipment and novel process architectures (as in the fine chemicals sector). It is demonstrated that also in microreaction engineering, catalytic engineering and reactor design go hand-in-hand. This is illustrated by the design of an integrated microreactor and heat-exchanger for optimum performance of a highly exothermic catalytic reaction, viz. ammonia oxidation. It is argued that future developments in catalytic microreaction technology will depend on the availability of very active catalysts (and catalyst coating techniques) for which microreactors may become the natural housing.

Bismuth germanate films prepared by Pechini method

Bismuth germanate films were prepared by dip coating and spin coating techniques and the dependence of the luminescent properties of the samples on the resin viscosity and deposition technique was investigated. The resin used for the preparation of the films was obtained via Pechini method, employing the precursors Bi(2)O(3) and GeO(2). Citric acid and ethylene glycol were used as chelating and cross-linking agents, respectively. Results from X-ray diffraction and Raman spectroscopy indicated that the films sintered at 700 degrees C for 10 h presented the single crystalline phase Bi(4)Ge(3)O(12). SEM images of the films have shown that homogeneous flat films can be produced by the two techniques investigated. All the samples presented the typical Bi(4)Ge(3)O(12) emission band centred at 505 nm. Films with 3.1 mu m average thickness presented 80% of the luminescence intensity registered for the single crystal at the maximum wavelength. Published by Elsevier B.V.

Análise por meio de espectroscopia de emissão óptica das espécies ativas em nitretação iônica e gaiola catódica

Plasma process like ionic nitriding and cathodic cage plasma nitriding are utilized in order to become hard surface of steels. The ionic nitriding is already accepted in the industry while cathodic cage plasma nitriding process is in industrial implementation stage. Those process depend of plasma parameters like electronic and ionic temperature (Te, Ti), species density (ne, ni) and of distribution function of these species. In the present work, the plasma used to those two processes has been observed through Optical Emission Spectroscopy OES technique in order to identify presents species in the treatment ambient and relatively quantify them. So plasma of typical mixtures like N2 H2 has been monitored through in order to study evolution of those species during the process. Moreover, it has been realized a systematic study about leaks, also thought OES, that accomplish the evolution of contaminant species arising because there is flux of atmosphere to inside nitriding chamber and in what conditions the species are sufficiently reduced. Finally, to describe the physic mechanism that acts on both coating techniques ionic nitriding and cathodic cage plasma nitriding

Revestimento de sementes de milho superdoce (sh2)

A semente de milho doce é leve e rugosa. A rugosidade torna difícil a classificação das sementes quanto à forma e ao tamanho e isso dificulta a semeadura. Uma solução para esse problema seria a utilização da técnica de revestimento. Assim, este trabalho teve por objetivo avaliar diferentes materiais de enchimento, cimentantes e corantes na peletização de sementes de milho superdoce e verificar quais combinações de materiais seriam eficientes na manutenção da qualidade fisiológica das sementes após o armazenamento e que permitissem vazão e distribuição uniformes durante a semeadura. Foram então testados doze materiais de enchimento (calcários 1 e 2, caulim, carvão vegetal ativado, areia, vermiculita, fubá de milho, farinha de trigo, polvilho de mandioca, amido de milho, celite e terra de diatomáceas), dois cimentantes (goma arábica e cascorez extra) e seis corantes (tintas guache, acrílica, plástica e para tecido, corante para alimento e gelatina). As avaliações da qualidade física e fisiológica das sementes revestidas e nuas foram efetuadas por meio dos testes: teor de água, fragmentação, peso de mil sementes, volume aparente e plantabilidade, germinação, primeira contagem da germinação e emergência de plântulas em campo. O revestimento de sementes de milho superdoce proporciona homogeneidade de forma e tamanho às sementes, melhora a vazão e a distribuição dos péletes na semeadura e não compromete a emergência de plântulas em campo depois de quatro meses de armazenamento.

Study of the dielectric and ferroelectric properties of chemically processed BaxSr1-xTiO3 thin films

Polycrystalline BaxSr1-xTiO3 (x = 0.4 and 0.8) thin films with a perovskite structure were prepared by the polymeric precursor method on a platinum-coated silicon substrate. High-quality thin films with uniform composition and thickness were successfully produced by dip-coating and spin-coating techniques. The resulting thin films prepared by dip and spin-coating showed a well-developed dense polycrystalline structure with uniform grain size distribution. The metal-BST-metal structure of the thin films displays good dielectric and ferroelectric properties. The ferroelectric nature to BaxSr1-xTiO3 (x = 0.8) thin film, indicated by butterfly-shaped C-V curves and confirmed by the hysteresis curve, showed 2P(r) = 5.0 muC/cm(2) and E-c = 20 kV/cm. The capacitance-frequency curve reveals that the dielectric constant may reach a value of up to 794 at 1 kHz. on the other hand, the BaxSr1-xTiO3 (x = 0.4) thin films had paraelectric nature and dielectric constant and the dissipation factor at a frequency of 100 kHz were 680 and 0.01, respectively, for film annealed at 700 degreesC. In addition, an examination of the film's I-V curve at room temperature revealed the presence of two conduction regions in the BaxSr1-xTiO3 (x = 0.4 and 0.8) thin films, showing ohmic-like behavior at low voltage and a Schottky-emission or Poole-Frenkel mechanism at high voltage. (C) 2001 Elsevier B.V. B.V. All rights reserved.

Piezoelectric effect in composite polyurethane-ferroelectric ceramics

Flexible and free-standing films of piezoelectric composites made up of lead zirconate titanate (PZT) ceramic powder dispersed in a castor oil-based polyurethane (PU) matrix were obtained by spin coating and characterized as materials for sensor applications. The piezoelectric coefficients d 31 and d 33 were measured with the usual technique. The piezoelectric charge constant d 33 yields values up to ≤24 pC/N, even at lower PZT content (33 vol%). Some desirable properties like piezoelectricity, flexibility and good mechanical resistance show this new material to be a good alternative for use as sensors and actuators.

Structural and surface morphology characterizations of oriented LiNbO3 thin films grown by polymeric precursor method

Polymeric precursor solution was used to deposit LiNbO3 thin films by dip coating on sapphire substrates. The effects of processing variables, such as heat treatment conditions and number of deposited layers, on crystallinity and morphology of the final films were investigated. X-ray diffraction patterns show the oriented growth of the films. The rocking curves, obtained around the (006) LiNbO3 peak, revealed that the shape peak and the FWHM value were influenced by the processing variables. According to these parameters, some films presented very homogeneous dense and smooth surfaces, as shown by the SEM and AFM studies.

Oxygen related defects excitation and photoconductivity dependence of SnO2 sol-gel films with several light sources

Since oxygen vacancies act as donors in SnO2, the electrical properties are related to deviation from stoichiometric composition. Depending on stoichiometry SnO2 can be highly insulating or may exhibit fairly high n-type conductivity. Since bandgap transitions are in the ultraviolet range, its photoconductivity is strongly dependent on the excitation source. We have measured variation of photoconductivity excitation with wavelength for tin dioxide grown by dip-coating sol-gel technique using several light sources: tungsten lamp, xenon, mercury and deuterium, and present selected results. The main band is obtained in the range 3-4eV according to light source spectrum in the ultraviolet range. The presence of oxygen in the cryostat also affects the spectrum since electron-hole pairs react with adsorbed oxygen specimens. © 1999 OPA (Overseas Publishers Association) N.V. Published by license under the Gordon and Breach Science Publishers imprint.