Resumo em Inglês:

The purpose of this work was to analyze water sorption by polymerized acrylic resins under different pressure, temperature and time treatments. A thermo-cured acrylic resin was used as the denture base (Classico Ltda.) and ethylene glycol di-methacrylate as a cross-linking agent, with processing carried out in a water bath at 73 °C for nine hours. Forty-five samples were prepared following the criteria and dimensions of specification # 12 of the American Dental Association (ADA), using a matrix in the shape of a stainless steel disc with 50 ± 1 mm diameter and 0.5 ± 0.05 mm thickness. The control group samples were stored in distilled water for 30 days, while groups GII to GIX were placed in a polymerization device with adjustable pressure, time and temperature. An analysis of the variance of the results revealed the influence of different factors on water sorption only, with significant factors being temperature, time, pressure and the interaction between time and temperature. Other interactions exerted no significant influence on water sorption. Neither additional treatments nor the control group (GI) showed any significant difference in comparison to the averages of other treatments.

Resumo em Inglês:

Disks of a commercial alumina were fabricated by slip casting, calcination and sintering. The surfaces were machined using SiC papers (120 and 320 grit) and characterized by residual stresses measurements. The mechanical strength was determined in biaxial flexure (ball on discontinuous ring). The specimens were subjected to thermal shock conditions (cooling using a high-velocity air jet) and the critical temperature differential for crack propagation was determined. The temperature and stress distributions during air impinging were calculated using a finite element method. The value of the heat transfer coefficient was estimated by fitting the calculated temperature profiles with those measured during each test. The calculated tension for the thermal shock fracture was compared with the mechanical strength, together with the fracture features in each case. The differences were explained on the basis of the calculated stress distributions.

Resumo em Inglês:

Si3N4/SiC nanocomposite powders were obtained from a preceramic polymeric network based on poly(methylsilane) as the in situ quasi-stoichiometric SiC source. These powders were constituted of nanosized SiC particles homogeneously distributed in the Si3N4 particulate matrix. beta-SiC whiskers were grown at 1400 °C in the pores of the matrix. At 1600 °C, the alpha -> beta Si3N4 phase transition took place, but no elemental silicon from Si3N4 decomposition was detected, evidencing the protective effect of the SiC phase.

Resumo em Inglês:

Silica gel was functionalised with chloropropyl groups through the sol-gel process and then a beta-diketone was incorporated into the support. Afterwards, Eu3+ ion and its chelates of 1,10-phenantroline (phen) and 2,2'-bipyridine (bpy), red phosphors, were supported on such silica. Luminescence studies of Eu3+ bound to this new material have shown that there is an increase in the intensity of the emission when the ion is isolated by ligands in the silica matrix. The energy transfer from the ligands phen and bpy to Eu3+ ion was observed in the excitation spectra, which present new bands ascribed to the ligands and/or complex. The Eu3+-functionalised silica was characterised by TGA and FTIR. TGA analysis showed that there is a large loss of mass around 300 °C, which is ascribed to the organic part of the material. The FTIR spectra presented the vibration modes for Si-C and -CH2-. The luminescent properties of the ions surrounding the Eu3+ ion were studied. The decay curve displayed a bi-exponential behaviour, indicating that there is more than one site of Eu3+ on the surface of the silica.

Resumo em Inglês:

Thermal diffusivity and optical absorption have been investigated for porous silicon, at room temperature, using photoacoustic spectroscopy. The experimental results obtained conform well with the existing studies recently published. The value obtained for thermal diffusivity is 0.045 ± 0.002 cm²/s.The absorption onsets show energy structures, differing from the ordinary semiconductor of bulk type.

Resumo em Inglês:

A series of polyurethane/PMMA simultaneous interpenetrating networks (SINs) with various hard segment contents (X) in the polyurethane phase (X = 15.5 to 36.5% in polyurethane) and wide range of polyurethane (PU) to polyacrylate (PA) ratio (PU/PA = 20:80 to 80:20) were prepared, and the damping and mechanical properties of these materials were studied. The damping of polyurethane soft phase was increased and shifted to lower temperature with increased content of PA vitreous phase. The mechanical properties were improved with increasing PA contents. The results show that PA and the polyurethane hard segment interaction play a special role in chain interpenetration density and its magnitude is revealed by the decreased dispersed domain size observed by scanning electron microscopy (SEM) and increased loss area as measured by dynamic mechanical thermal analysis (DMTA). When the weight ratio of PU/PA was 40:60, the resulting SIN materials possessed better damping properties, independent of X concentration.

Resumo em Inglês:

Biocompatible and biodegradable polymers have been studied in the last few years with good clinical success in the fixation and stabilization of bone fractures. The understanding and the control of the polymeric prosthetic degradation process and the effect of its degradation products in the organism are crucial for the success of the implant. In this present work, blends of PLLA/PHBV, obtained in several compositions by casting of solvent, obtaining samples in the form of films. The samples were characterized by the analysis of TGA, DSC, DMA and SEM. The results obtained showed that the PLLA/PHBV blends are immiscible, and present a discrete separation by microscopy. The blends obtained showed porous fracture surfaces. It is noticed that PLLA begins its degradation in a few weeks (around 2 weeks), unlike PHBV, where it was possible to observe eventual degradation up to 53 weeks. It was also observed that the blend increased its crystallinity with degradation.

Resumo em Inglês:

In this work, the application of the X-ray multiple diffraction technique using synchrotron radiation at Laboratório Nacional de Luz Síncrotron (LNLS) to study KDP phase transition induced by electric field is discussed. A Huber three-axis (omega, phi, 2theta) diffractometer mounted on a table which rotates around the incident beam allows to measure Renninger scans (RS) at the XRD station of LNLS using the adequate polarization for the experiments. Prior results indicated (080) as the best choice for the KDP primary reflection and the (440)(<img src="http:/img/fbpe/mr/v4n1/quatro.gif" alt="quatro.gif (94 bytes)"> 40) four-beam case for the secondary. Two Bragg-surface diffraction (BSD) reflections, where the secondary beam is propagated parallel to the sample surface, are involved in this multiple diffraction case. A RS interval of 3.3° around phi = 0° position was measured while the electric field was increased up to 6 kV/cm. At this value, a phase transition was observed and the secondary peaks became narrower and changed their RS position indicating possible occurrence of a metastable ferroelectric phase.

Resumo em Inglês:

The crystallization processes for the amorphous metallic alloys Fe74B17Si2Ni4Mo3 and Fe86B6Zr7Cu1 (at. %) were investigated using X-rays diffraction measurements performed in-situ during Joule-heating, with simultaneous monitoring of the electrical resistance. We determined the main structural transitions and crystalline phases formed during heating, and correlated these results to the observed resistance variations. As the annealing current is increased, the resistance shows an initial decrease due to stress relaxation, followed by a drop to a minimum value due to massive nucleation and growth of alpha-Fe nanocrystals. Further annealing causes the formation of small fractions of Fe-B, B2Zr or ZrO2, while the resistance increases due to temperature enhancement. In situ XRD measurements allowed the identification of metastable phases, as the gamma-Fe phase which occurs at high temperatures. The exothermal peaks observed in the differential scanning calorimetry (DSC) for each alloy corroborate the results. We also have performed DSC measurements with several heating rates, which allowed the determination of the Avrami exponent and crystallization activation energy for each alloy. The obtained activation energies (362 and 301 kJ/mol for Fe-B-Zr-Cu; 323 kJ/mol for Fe-B-Si-Ni-Mo) are comparable to reported values for amorphous iron alloys, while the Avrami exponent values (n = 1.0 or n = 1.2) are consistent with diffusion controlled crystallization processes with nucleation rates close to zero.