Preparation of Y3Al5O12 : Eu phosphors by citric-gel method and their luminescent properties

By using metal nitrates as starting materials and citric acid as complexing agent, Y3Al5O12 (YAG) and Y3Al5O12:Eu (1 mol%) (YAG:Eu) powder phosphors were prepared by a citrate-gel method. The formation process of YAG and YAG:Eu were investigated by means of XRD, TG-DTA and FT-IR spectra. The purified crystalline phases of YAG and YAG:Eu were obtained at 800 degreesC. The crystalline YAG:Eu phosphors showed an orange-red emission with D-5(0)-F-7(1) (591 nm) as the most prominent group, whose intensity was dependent on the pH value of the starting solution, citric acid content and firing temperature. It has been found that the suitable pH and citric acid/metal ratio are 3 and 2 for obtaining the highest emission intensity, respectively. The emission intensity increases steadily with increasing the annealing temperature from 800 to 1200 degreesC, and nearly remains constant after 1200 degreesC. Furthermore, great differences were observed for the lifetimes and the charge transfer band of Eu3+ in crystalline and amorphous states of YAG.

Preparation and characteristics of polyimide-TiO2 nanocomposite film

A sol-gel approach has been developed to prepare polyimide-TiO2, hybrid films fi om soluble polyimides and a modified titanium precursor. The rate of the hydrolysis reaction of titanium alkoxide can be controlled by using acetic acid as a modifier. FTIR and XPS indicated that TiO2, particles were well distributed in polyimide matrixes with particle size small per than 60 nm. Polyimide hybrid films having the TiO2, component less than or equal to 10% exhibited high thermal stability, high optical transparency and good mechanical properties and possessed higher dielectric constants than correspondingly polyimides. (C) 2000 Society of Chemical Industry.

Nanocluster-containing mesoporous magnetoceramics from hyperbranched organometallic polymer precursors

Pyrolysis of hyperbranched poly[1,1'-ferrocenylene(methyl)silyne] (5) yields mesoporous, conductive, and magnetic ceramics (6). Sintering at high temperatures (1000-1200 degrees C) under nitrogen and argon converts 5 to 6N and 6A, respectively, in similar to 48-62% yields. The ceramization yields of 5 are higher than that (similar to 36%) of its linear counterpart poly[1,1'-ferrocenylene(dimethyl)silylene] (1), revealing that the hyperbranched polymer is superior to the linear one as a ceramic precursor. The ceramic products 6 are characterized by SEM, XPS, EDX, XRD, and SQUID. It is found that the ceramics are electrically conductive and possess a mesoporous architecture constructed of tortuously interconnected nanoclusters. The iron contents of 6 estimated by EDX are 36-43%, much higher than that (11%) of the ceramic 2 prepared from the linear precursor 1. The nanocrystals in 6N are mainly alpha-Fe2O3 whereas those in 6A are mainly Fe3Si. When magnetized by an external field at room temperature, 6A exhibits a high-saturation magnetization (M-s similar to 49 emu/g) and near-zero remanence and coercivity; that is, 6A is an excellent soft ferromagnetic material with an extremely low hysteresis loss.

Sintering of nanopowders of amorphous silicon nitride under ultrahigh pressure

Nanopowders of amorphous silicon nitride were densified and sintered without additives under ultrahigh pressure (1.0-5.0 GPa) between room temperature and 1600 degrees C. The powders had a mean diameter of 18 nm and contained similar to 5.0 wt% oxygen that came from air-exposure oxidation, Sintering results at different temperatures were characterized in terms of sintering density, hardness, phase structure, and grain size. It was observed that the nanopowders can be pressed to a high density (87%) even at room temperature under the high pressure. Bulk Si3N4 amorphous and crystalline ceramics (relative density: 95-98%) were obtained at temperatures slightly below the onset of crystallization (1000-1100 degrees C and above 1420 degrees C, respectively. Rapid grain growth occurred during the crystallization leading to a grain size (>160 nm) almost 1 order of magnitude greater than the starting particulate diameters, With the rise of sintering temperature, a final density was reached between 1350 and 1420 degrees C, which seemed to be independent of the pressure applied (1.0-5.0 GPa), The densification temperature observed under the high pressure is lower by 580 degrees C than that by hot isostatic pressing sintering, suggesting a significantly enhanced low-temperature sintering of the nanopowders under a high external pressure.

Enhanced crystallization and phase transformation of amorphous silicon nitride under high pressure

The crystallization and phase transformation of amorphous Si3N4 ceramics under high pressure (1.0-5.0 GPa) between 800 and 1700 degreesC were investigated. A greatly enhanced crystallization and alpha-beta transformation of the amorphous Si3N4 ceramics were evident under the high pressure, as characterized by that, at 5.0 GPa, the amorphous Si3N4, began to crystallize at a temperature as low as 1000 degreesC (to transform to alpha modification). The subsequent alpha-beta transformation occurred completed between 1350 and 1420 degreesC after only 20 min of pressing at 5.0 GPa. In contrast, under 0.1 MPa N-2, the identical amorphous materials were stable up to 1400 degreesC without detectable crystallization, and only a small amount of a phase was detected at 1500 degreesC. The crystallization temperature and the alpha-beta transformation temperatures are reduced by 200-350 degreesC compared to that at normal pressure. The enhanced phase transformations of the amorphous Si3N4, were discussed on the basis of thermodynamic and kinetic consideration of the effects of pressure on nucleation and growth.

CHARACTERIZATION OF A POTASSIUM-PROMOTED COBALT MOLYBDENUM ALUMINA WATER-GAS SHIFT CATALYST

A series of potassium-promoted CoMo/Al2O3 has been investigated by means of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and temperature-programmed reduction (TPR). CoMoO4 was found in the CoMo/Al2O3 catalyst by XRD and is destroyed by the presence of potassium. The reducibility of molybdenum is enhanced by potassium in the CoMoK/Al2O3 catalyst and is easier to reduce to Mo(IV) during sulfidation. In the oxidic state catalyst cobalt is increased on the surface by the addition of potassium. After sulfidation this phenomena disappeared, the distribution of cobalt remains at a constant level and is unaffected by the potassium content. The addition of potassium leads to a monotonical decrease of the molybdenum dispersion with the impregnating amount of potassium in the oxidic state catalyst but is more complicated after sulfidation. Potassium is well dispersed on the surface in both the oxidic and sulfided state. The activity in the water-gas shift reaction was correlated with the potassium content of CoMoK/Al2O3.

Effective properties of spherically anisotropic piezoelectric composites

Piezoelectric composites consisting of spherically anisotropic piezoelectric inclusions (i.e., piezoceramic material) in an infinite nonpiezoelectric matrix under a uniform electric field are theoretically investigated. Analytical solutions for the elastic displacements and the electric potentials are derived exactly. Taking account of the coupling effects of elasticity, permittivity, and piezoelectricity, formulas are derived for the effective dielectric and piezoelectric responses in the dilute limit. A piezoelectric response mechanism is revealed, in which the effective piezoelectric response vanishes irrespective of how much spherically anisotropic piezoelectric inclusions are inside. Moreover, the effective coupled responses of the piezoelectric composites show that the effective dielectric responses decrease (increase) as the inclusion elastic (piezoelectric) constants increase.

Electrochemical Synthesis of Barium Tungstate Crystallites with Different Morphologies: Effect of Electrolyte Components

Barium tungstate crystallites with different sizes and morphologies were successfully synthesized using a simple electro-chemical technique by varying the components of electrolyte solutions. XRD analysis evidenced that the as-prepared samples were a pure tetragonal-phase of BaWO4 with a scheelite structure. Scanning electron microscopy images and PL spectra of BaWO4 crystallites revealed that the presence of OH- ions and the incorporation of absolute ethanol into the electrolyte solution would have important effects on their particle sizes, morphologies, and optical properties.

Synthesis of NiWO4 nano-particles in low-temperature molten salt medium

Nickel tungstate (NiWO4) nano-particles were successfully synthesized at low temperatures by a molten salt method, and characterized by Xray diffraction (XRD), transmission electron microscopy (TEM) and ultraviolet visible spectra techniques (UV-vis), respectively. The effects of calcining temperature and salt quantity on the crystallization and development of NiWO4 crystallites were studied. Experimental results showed that the well-crystallized NiWO4 nano-particles with about 30 nm in diameter could be prepared at 270 degrees C with 6:1 mass ratio of the salt to NiWO4 precursor. XRD analysis confirmed that the product was a pure monoclinic phase of NiWO4 with wolframite structure. UV-vis spectrum revealed that NiWO4 nano-particles had good light absorption properties in both ultraviolet and visible light region. (C) 2009 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

A study on the ignition process for the catalytic partial oxidation of methane to synthesis gas by MS-TPSR technique

The ignition processes for the catalytic partial oxidation of methane (POM) to synthesis gas over oxidic nickel catalyst (NiO/Al2O3), reduced nickel catalyst (Ni-0/Al2O3), and Pt-promoted oxidic nickel catalyst (Pt-NiO/Al2O3) were studied by the temperature-programmed surface reaction (TPSR) technique. The complete oxidation of methane usually took place on the NiO catalyst during the CH4/O-2 reaction, even with a pre-reduced nickel catalyst, and Ni-0 is inevitably first oxidized to NiO if the temperature is below the ignition temperature. It is above a certain temperature that Ni-0 is formed again, which leads to the start of the POM. The POM can be initiated at a much lower temperature on a Pt-NiO catalyst because of Pt promotion of the reduction of NiO. The POM in a fluidized bed can be easily initiated due to the addition of Pt.

Women Potters: Transforming Traditions

Vincentelli, Moira, Women Potters: Transforming Traditions (London: A and C Black, 2003) RAE2008

Facetas de Porcelana VS Facetas de Resina Composta

Projeto de Pós-Graduação/Dissertação apresentado à Universidade Fernando Pessoa como parte dos requisitos para obtenção do grau de Mestre em Medicina Dentária

Qual a eficácia clínica do sistema CEREC com os seus diferentes materiais para reabilitação em prótese fixa e sobre implantes?

Projeto de Pós-Graduação/Dissertação apresentado à Universidade Fernando Pessoa como parte dos requisitos para obtenção do grau de Mestre em Medicina Dentária

Photoelectrocatalysis: Principles, nanoemitter applications and routes to bio-inspired systems

An overview on processes that are relevant in light-induced fuel generation, such as water photoelectrolysis or carbon dioxide reduction, is given. Considered processes encompass the photophysics of light absorption, excitation energy transfer to catalytically active sites and interfacial reactions at the catalyst/solution phase boundary. The two major routes envisaged for realization of photoelectrocatalytic systems, e.g. bio-inspired single photon catalysis and multiple photon inorganic or hybrid tandem cells, are outlined. For development of efficient tandem cell structures that are based on non-oxidic semiconductors, stabilization strategies are presented. Physical surface passivation is described using the recently introduced nanoemitter concept which is also applicable in photovoltaic (solid state or electrochemical) solar cells and first results with p-Si and p-InP thin films are presented. Solar-to-hydrogen efficiencies reach 12.1% for homoepitaxial InP thin films covered with Rh nanoislands. In the pursuit to develop biologically inspired systems, enzyme adsorption onto electrochemically nanostructured silicon surfaces is presented and tapping mode atomic force microscopy images of heterodimeric enzymes are shown. An outlook towards future envisaged systems is given. © 2010 The Royal Society of Chemistry.

Phase II Archaeological Excavations at 99 Main Street, 18AP21 (Sign of the Whale), Annapolis, Maryland

Historical Annapolis Foundation (HAF) conducted terrestrial archaeological investigations at site 18AP21 in the city of Annapolis, Maryland. Excavations were carried out at this National Register site ostensibly as a Phase II project to evaluate the site and assess the need for further work. The site is at 99 Main Street in the center of downtown Annapolis, near the Annapolis waterfront. The project was carried out as part of the advanced work for the Annapolis History Center project, to be built in the adjoining buildings of 99 Main and 196 Green Streets. The buildings are the property of the Historic Annapolis Foundation and located in Maryland Research Unit 7. The excavations were undertaken by HAF, and funded by HAFF. The work was conducted for HAF and MHT, who holds an archaeological easement on the property. This preliminary phase of work included stratigraphic excavation of two testpit units. These two units revealed that the site of the existing 99 Main Street building was the location of three previous constructions. The current building at 99 Main Street, built in 1791, was preceded by an earlier brick dwelling, evidenced by a stout pier of bricks, which was attached to a wooden-sided structure that stood on a foundation of brick and stone. Ceramics indicate that these buildings date to the early-middle of the 18th century. A third structure of post-in-ground construction, evidenced by recovery of burned posts and wood fragments, likely existed prior to these, but evidence was scant. These excavations reveal that the site of 18AP21 holds potential for understanding Annapolis's early cultural developments, especially in the area of initial settlement and the origins of waterfront commerce. The assemblage of artifacts recovered includes a broad sample of common 18th century pottery such as creamware and Chinese export porcelain, and also includes some early colonial types such as tin-glazed earthenware and various red-bodied slipwares. The excavations do not provide conclusive evidence of the construction sequence. Consultation with MHT representatives indicates that further work at the site will likely be needed before modifications to the floor of the building can progress.