The influence of hot pressing on high density fibreboards, when the panels are used for overlaying

Um conjunto de painéis de fibras de alta densidade, colados com uma resina de melamina/ureia-formaldeído, foi submetido a operações de prensagem a quente, de modo a estudar a influência desta operação nas propriedades do substrato. Usou-se uma prensa de pratos, a uma pressão que permitisse um contacto firme entre os painéis e os pratos da prensa. Foi desenvolvido um plano experimental para três temperaturas diferentes de 95, 180 e 210 º C e dois tempos de prensagem, de 22 e 35 segundos, para cada uma delas. Os painéis foram fabricados com fibras de pinho (Pinus pinaster) a uma densidade média de 930 kg/m3 e espessura média de 6,7 mm De acordo com os resultados obtidos, as operações de pós-fabrico dos painéis de alta densidade resultaram numa ligeira melhoria do módulo de elasticidade, da tensão de rotura à flexão estática e da resistência interna dos painéis usados como substrato. Observou-se também uma ligeira diminuição da humidade de equilíbrio e espessura dos painéis, bem como um aumento da densidade e do inchamento, com o aumento da temperatura e tempo de prensagem.ct A series of high density fiberboard (HDF) panels, bonded with melamine/urea-formaldehyde (MUF), were exposed to a post manufacture hot pressing at various temperatures and pressing durations using a hot press and just enough pressure to ensure firm contact between the panel and the press platens. The experimental plan was developed for three different temperatures of 95, 180 and 210ºC and two different pressing times, of 22 and 35 seconds. The panels were made with pine fibers (pinus pinaster) at a target density of 930 kg/m3 and target thickness of 6.7 mm. The results indicated that the pos-manufacture hot-pressing of the exterior HDF panels resulted in a slightly improvement of the modulus of elasticity (MOE), bending strength and internal bonding (IB) of the panels used as substrates. A reduction in moisture content and thickness as well as an increase in density and thickness swelling was also noticed with an increase in the temperature and pressing timeinfo:eu-repo/semantics/publishedVersio

Synthesis and Electrical Properties of PZT/BaFe12O19 Multiferroic Ceramics

Multiferroic ceramics, based on the ferroelectric and ferrimagnetic phases of the Pb(Zr0.65Ti0.35)O3 (PZT) and BaFe12O19 (BaM) systems, respectively, were obtained from the conventional ceramic method. The electrical properties have been investigated in a wide temperature and frequency range. The influence of the magnetic phase on the ferroelectric and dielectric properties of the ferroelectrics phases have been taken into account. The phase transition characteristics shown to be strongly affected by the amount of the BaM phase, while the dielectric properties revealed to be directly dominated by the presence of conductive effects related to the charge transport mechanisms associated to the magnetic phase.FAPEMIG (00199-09 and 00342-10)CNPq (555496/2009-0 and 301730/2009-1)CAPES (4684/11-7

Dielectric tunability in (1-x)[Pb(Mg 1/3Nb 2/3)O 3]-xPbTiO 3 ceramics for tunable devices application

The dielectric properties of the 0.65[Pb(Mg 1/3Nb 2/3)O 3]-0.35PbTiO 3 ferroelectric ceramic composition were investigated viewing the capability to be used for tunable microwave applications. The dielectric response has been studied for three selected temperatures (300 K, 370 K and 400 K), below the paraelectric- ferroelectric phase transition temperature, as a function of the applied 'bias' electric field. The obtained dielectric tunability was found to be around 60 %, under an electric field of 19 kV/cm, which makes the studied ceramic composition an excellent candidate for application in the electro-electronic industry, as tunable devices. © 2010 IEEE

Investigation on dielectric response of PMN ceramics around paraelectric-ferroelectric diffuse phase transition

The dielectric properties of relaxor ferroelectric lead magnesium niobate Pb(Mg(1/3)Nb(2/3))O(3) (PMN) ceramics have been investigated. These studies were conducted taking into account the characterisations of the complex dielectric permittivity (real and imaginary parts) as a function of temperature and frequency in a wide interval. on the other hand, the dc 'bias' electrical field dependence of the real dielectric permittivity (C-V characterisations) has been analysed around the paraelectric-ferroelectric diffuse phase transition. Results obtained at room temperature (paraelectric phase) showed a typical behaviour of conventional dielectric materials, while measurements performed at 200 K (ferroelectric phase) evidenced an anomalous behaviour for frequencies up to 100 kHz. Such observed anomalies were characterised by two asymmetrical peaks on sweep-up and sweep-down, at -15 and +18 kV cm(-1) respectively.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES

Structural phase transitions of PbZr0.52Ti0.48O3 ceramic: An infrared spectroscopy study

The recent discovery of a ferroelectric monoclinic phase in the PbZr1-xTixO3 (PZT) system attained the attention of several researchers due to the possibility of understanding the relationships between structural features and piezoelectric properties. The nature of the monoclinic phase in some PZT compositions remains controversial and unclear. In this work, structural phase transitions of PbZr0.52Ti0.48O3 ceramic were investigated by infrared spectroscopy as a function of temperature. Studies were centered on nu(1)-stretching modes and corresponding half width Wi as a function of temperature. The occurrence of the anomalies in the infrared spectra as a function of temperature suggests the following monoclinic ( LT) -> monoclinic ( HT) -> tetragonal phase transition were observed at 183 K and at 263 K

Features of dielectric response in PMN-PT ferroelectric ceramics

In this paper, electrical and structural properties were reported for pyrochlore free (1-x)[Pb(Mg1/3Nb2/3)O-3] - xPbTiO(3) (PMN-PT) (with 35 mol% PbTiO3) ceramics obtained from fine powders. Dielectric studies were focused on the investigation of the complex dielectric permittivity (epsilon '-i epsilon '') as a function of frequency and temperature. The effects of the dc applied electric field on dielectric response were also investigated. Results revealed a field dependence dielectric anomaly in the dielectric permittivity curves (epsilon(T)) in the low dc electric field region, which in turn prevails in the whole analysed frequency interval. To the best of our knowledge, these properties for the PMN-PT ceramic system have not been reported before as in this work. The results were analysed within the framework of the current models found in the literature

Evaluating the residual stress in PbTiO3 thin films prepared by a polymeric chemical method

We report a study of residual stress in PbTiO3 (PT) thin films prepared on Si substrates by a polymeric chemical method. The E(1TO) frequency was used to evaluate the residual stress through an empirical equation available for bulk PT. We find that the residual stress in PT films increases as the film thickness decreases and conclude that it originates essentially from the contributions of extrinsic and intrinsic factors. Polarized Raman experiments showed that the PT films prepared by a polymeric chemical method are somewhat a-domain (polar axis c parallel to the substrate) oriented