Structural and dielectric properties of polyvinyl alcohol/barium zirconium titanate polymer-ceramic composite

The polyvinyl alcohol (PVA)/barium zirconium titanate Ba[Zr0.1Ti0.9]O3 (BZT) polymer-ceramic composites with different volume percentage are obtained from solution mixing and hot-pressing method. Their structural and electrical properties are characterized by X-ray diffraction (XRD), Rietveld refinement, cluster modeling, scanning electron microscope and dielectric study. XRD patterns of PVA/BZT polymer-ceramics composite (with 50% volume fractions) indicate no obvious differences than the XRD patterns of pure BZT which shows that the crystal structure is still stable in the composite. The scanning electron micrograph indicates that the BZT ceramic is dispersed homogeneously in the polymer matrix without agglomeration. The dielectric permittivity (ε r) and the dielectric loss (tan δ) of the composites increase with the increase of the volume fraction of BZT ceramic. Theoretical models are employed to rationalize the dielectric behavior of the polymer composites. The dielectric properties of the composites display good stability within a wide range of temperature and frequency. The excellent dielectric properties of these polymer-ceramic composites indicate that the BZT/PVA composites can be a candidate for embedded capacitors. © 2013 Elsevier B.V.

Painéis de partículas de madeira leucena e resina poliuretana derivada de óleo de mamona

This research aimed to test particleboard with leucena (Leucaena leucocephala) wood particles and polyurethane resin castor oil based. The response variables are: modulus of rupture (MOR), internal adhesion (AI), apparent density (dap) and wood moisture content (um). The experiments were developed based on the methodological procedures of the ABNT NBR 14810:2002 standard. The particleboards were manufactured by hot-pressing at 4MPa and 90°C, using timber particles with 5% of moisture content and 10% of monocomponent and bicomponent polyurethane resin. The higher moisture content was achieved when the monocomponent polyurethane resin was used. The bicomponent polyurethane resin provided a percent increase of 43.7% and 22.7% on the modulus of rupture and apparent density, respectively, when compared to the standard limit. The internal adhesion of the panels manufactured with monocomponent resin was 2.45 times higher than the standard limit. The confidence interval between means revealed that the internal adhesion and apparent density exhibited statistical equivalence. A good correlation between the internal adhesion and apparent density was found, for this reason it was possible to estimate the internal adhesion of the panels based on the apparent density data.

Effects of high temperature plasma immersion ion implantation on wear resistance of Ti-Si-B sintered alloys

Although titanium and its alloys own good mechanical properties and excellent corrosion resistance, these materials present poor tribological properties for specific applications that require wear resistance. In order to produce wear-resistant surfaces, this work is aimed at achieving improvement of wear characteristics in Ti-Si-B alloys by means of high temperature nitrogen plasma immersion ion implantation (PIII). These alloys were produced by powder metallurgy using high energy ball milling and hot pressing. Scanning electron microscopy (SEM) and X-ray diffraction identified the presence of α-titanium, Ti6Si2B, Ti5Si3, TiB and Ti3Si phases. Wear tests were carried out with a ball-on-disk tribometer to evaluate the friction coefficient and wear rate in treated and untreated samples. The worn profiles were measured by visible light microscopy and examined by SEM in order to determine the wear rates and wear mechanisms. Ti-7.5Si-22.5B alloy presented the highest wear resistance amongst the untreated alloys produced in this work. High temperature PIII was effective to reduce the wear rate and friction coefficient of all the Ti-Si-B sintered alloys. © 2013 Elsevier B.V.

Produção e caracterização de micro e nanofibras de Poli(fluoreto de vinilideno) - PVDF obtidos pela técnica de fiação por sopro em solução

Pós-graduação em Ciência dos Materiais - FEIS

Obtenção e caracterização de filmes de PHB e de blendas de PHB com borracha natural

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Caracterização das ligas Ni-Ti-Mo, Ni-Ti-Ta e Ni-Ti-Mo-Zr obtidas por moagem de alta energia e prensagem a quente

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Preparação e caracterização de compósitos obtidos a partir de borracha natural com raspa de couro visando aplicações industriais

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

Preparo, caracterização e aplicação do compósito PTCa (Titanato de chumbo modificado com cálcio)/PEEK (Poliéter éter cetona) como sensor de radiação

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Preparação e caracterização de nanocompósitos multifuncionais obtidos com nanopartículas ferroelétricas e paramagnéticas em filmes de borracha natural: Preparación y caracterización de nanocompuestos multifuncionales obtenidos con nanopartículas ferroelétricas y paramagnéticas en películas de caucho natural

Pós-graduação em Ciência e Tecnologia de Materiais - FC

Propriedades piezo, piroelétrica e dielétrica de compósitos cerâmica ferroelétrica/polímero dopados com polianilina

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

Síntese e caracterização de compósitos poli(fluoreto de vinilideno-trifluoretileno)/titanato de bário para uso em regeneração tecidual guiada

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Preparação e caracterização do compósito poli (fluoreto de vinilideno) / polianilina com partículas de níquel

Pós-graduação em Ciência dos Materiais - FEIS

Estudo da superfície de fibras de carbono após tratamento de implantação iônica por imersão em plasma (3IP)

In this work, plasma immersion ion implantation (PIII) treatments of carbon fibers (CFs) were performed in order to induce modifications of chemical and physical properties of the CF surface aimed to improve the performance of thermoplastic composite. The samples to be treated were immersed in nitrogen or air glow discharge plasma and pulsed at −3.0 kV for 2.0, 5.0, 10.0, and 15.0 min. After PIII processing, the specimens were characterized by atomic force microscopy (AFM), scanning electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). After CFs treatments, the CF/Polypropylene (PP) composites were produced by hot pressing method. Surface morphology of as-received CFs exhibited some scratches aligned along the fibers due to the fiber manufacturing process. After both treatments, these features became deeper, and also, a number of small particles nonuniformly distributed on the fiber surface can be observed. These particles are product of CF surface sputtering during the PIII treatment, which removes the epoxy layer that covers as-received samples. AFM analyses of CF samples treated with nitrogen depicted a large increase of the surface roughness (Rrms value approximately six times higher than that of the untreated sample). The increase of the roughness was also observed for samples treated by air PIII. Raman spectra of all samples presented the characteristic D- and G-bands at approximately 1355 and 1582 cm−1, respectively. Analysis of the surface chemical composition provided by the XPS showed that nitrogen and oxygen were incorporated onto the surface. The polar radicals formed on the surface lead to increasing of the CF surface energy. Both the modification of surface roughness and the surface oxidation contributed for the enhancement of CF adhesion to the polymeric matrix. These features were confirmed ... (Complete abstract click electronic access below)

The effect of thermal cycling on the shear bond strength of porcelain/Ti-6Al-4V interfaces

The aim of the study was to evaluate the effect of thermal cycling on the shear bond strength of the porcelain/Ti-6Al-4V interfaces prepared by two different processing routes and metallic surface conditions. Polished and SiO2 particle abraded Ti-6Al-4V alloy and Triceram bonder porcelain were used to produce the interfaces. Porcelain-to-metal specimens were processed by conventional furnace firing and hot pressing. Thermal cycling was performed in Fusayama's artificial saliva for 5000 cycles between 5 +/- 1 and 60 +/- 2 degrees C. After thermal cycling, shear bond tests were carried out by using a custom-made stainless steel apparatus. The results were analyzed using t-Student test and non-parametric Kruskal-Wallis test (p<0.01). Most of the polished-fired specimens were fractured during thermal cycling; thus, it was not possible to obtain the shear bond strength results for this group. Sandblasted-fired, polished-hot pressed, and sandblasted-hot pressed specimens presented the shear bond strength values of 76.2 +/- 15.9, 52.2 +/- 23.6, and 59.9 +/- 22.0 MPa, respectively. Statistical analysis indicated that thermal cycling affected the polished specimens processed by firing, whereas a significant difference was not observed on the other groups. (C) 2015 Elsevier Ltd. All rights reserved.

Influence of Modifications to the Pechini Method on the Electroactivity and Stability of Pt-RuOx/C Catalysts

Since electrode electroactivity and stability depend directly on the nature, morphology, and structure of the material, we have investigated how modifications to the Pechini method during the synthesis of Pt-RuOx/C electrocatalysts affected catalyst activity. The structure and stability of the resulting materials were investigated after their submission to a large number of potential scans and to constant potential for a prolonged time period in sulfuric acid 0.5 mol L-1 and methanol 0.1 mol L-1 solution. DMFC tests were accomplished using membrane electrode assemblies (MEAs) prepared by hot-pressing a pretreated Nafion 117 membrane together with the prepared Pt-RuOx anodes and a Pt cathode (from E-TEK), in order to compare the catalytic activity of the materials prepared by different methods. The stability studies demonstrated that the catalyst whose resin/carbon support mixture was agitated in a balls mill before undergoing heat-treatment was more stable than the other prepared catalysts. The catalysts synthesized with the single resin consisting of Pt and Ru and subjected to ultrasound before heat-treatment furnished the highest power density in the single fuel cell. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.011208jes]