Resumo em Inglês:

The aim of this study was to compare the in vitro wear and superficial roughness of four materials (Delton Dyract Flow, Dentsply; Filtek Flow, Vitremer, 3M ESPE) used as fissure sealant in 32 extracted human molars divided in four groups (n = 8) after abrasion with toothbrush/dentifrice. Impressions of each occlusal surface were made to analyze wear and circular specimens were prepared to analyze the roughness. Teeth and specimens were mounted in a toothbrushing machine. The replicas were observed using a SEM to determine the superficial wear. Wear: there were no statistically significant differences either between Delton and Filtek Flow or between Dyract Flow and Vitremer. Roughness: there were no statistical differences between Filtek Flow and Dyract Flow, Dyract Flow and Vitremer, Vitremer and Delton., Considering the clinical practice, if caries activity is present the use of Vitremer is suggested not only for its well known fluoride release, but it presented good roughness results.

Resumo em Inglês:

According to some estimates, world's population growth is expected about 50% over the next 50 years. Thus, one of the greatest challenges faced by Engineering is to find effective options to food storage and conservation. Some researchers have investigated how to design durable buildings for storing and conserving food. Nowadays, developing concrete with mechanical resistance for room temperatures is a parameter that can be achieved easily. On the other hand, associating it to low temperature of approximately 35 °C negative requires less empiricism, being necessary a suitable dosage method and a careful selection of the material constituents. This ongoing study involves these parameters. The presented concrete was analyzed through non-destructive tests that examines the material properties periodically and verifies its physical integrity. Concrete with and without incorporated air were studied. The results demonstrated that both are resistant to freezing.

Resumo em Inglês:

Hg based superconducting ceramics present the highest critical temperatures ever reported, particularly the phase 1223 with the highest Tc so far obtained -135 K. However, these compounds are obtained by a complex synthesis route and suffer degradation at ambient atmosphere. This disadvantage may be overcome by doping with an appropriate amount of Re. Samples of nominal composition Hg0.82Re0.18Ba2Ca2Cu3O8+δ having different oxygen contents were studied by X ray absorption and diffraction techniques. Using XANES we determined the Re valence = +7 in an octahedral distorted coordination. We determined the distances of Re-O bonds (1.85 Å and 2.10 Å) by EXAFS. XRD Rietveld fits showed segregation of two superconducting phases with distinct lattice parameters. The main phase is associated with Hg, Re-1223 with higher oxygen content, and the secondary superconducting phase is related to undoped Hg-1223.

Resumo em Inglês:

Cr3C2-Ni20Cr coatings have been used for corrosion and wear resistant applications. However, one of the shortcomings of these coatings is its low hardness, and consequent low wear resistance, for long term high temperature applications. Nanostructured coatings of many materials have exhibited higher hardness and strength compared with conventional coatings of the same material. Consequently, nanostructured coatings of other materials, including Cr3C2-Ni20Cr have been attempted to enhance overall performance. In this study the effects of high energy milling parameters on Cr3C2-25(Ni20Cr) powder characteristics as well as the microstructure and mechanical properties of nanostructured Cr3C2-25(Ni20Cr) coatings formed by high velocity oxygen fuel (HVOF) spraying have been evaluated. The average particle size and crystallite size of milled Cr3C2-25(Ni20Cr) powders decreased with increase in milling time and this decrease was more pronounced in nitrogen compared to that in hexane. This difference has been attributed to a cushioning effect in the latter medium. The coatings prepared with milled Cr3C2-25(Ni20Cr) powders had a more uniform microstructure, were harder and had higher relative fracture toughness compared with coatings prepared with as-received powders.

Resumo em Inglês:

A study was made of the variation of the magnetic properties of cobalt-based alloys using different compositions of CoFeSiB and CoFeSiBCr systems, which were produced by the melt-spinning technique and some of them subjected to a stress annealing treatment. A comparative study of core geometry and supporting material was also performed in order to obtain low noise fluxgate sensor core using amorphous magnetic ribbons of these alloys. The best alloy was a stress annealed Co67.5Fe3.5Si17.4B11.6 sample, which yielded fluxgate sensors with lower noise levels than those of commercial crystalline materials.

Resumo em Inglês:

The study of the stiffness of laterally loaded semi-rigid connections in plywood-timber beams is justified by the influence that the deformation of the connection has on the overall displacements of the structure. Semi-rigid connections are characterized by the occurrence of a slip between the connected pieces. The characterization of a connection is usually based on an isolated single connector behavior, which is described by its load-slip relationship expressed by the slip modulus, and so it is extended to the group of connectors. Although the method of analysis is well established, the concept of equivalent slip modulus, defined as the slip modulus per unit length of a connection, has not been totally explored. In this study, we focus on the experimental determination of the equivalent slip modulus for mechanically analyzing plywood-timber beams with continuous connections. The results demonstrated that the test is suitable for obtaining experimental values of the equivalent slip modulus.

Resumo em Inglês:

This paper presents the results of an experimental investigation carried out to optimize the mix proportions of the fly ash brick by Taguchi method of parameter design. The experiments have been designed using an L9 orthogonal array with four factors and three levels each. Small quantity of cement has been mixed as binding materials. Both cement and the fly ash used are indicated as binding material and water binder ratio has been considered as one of the control factors. So the effects of water/binder ratio, fly ash, coarse sand, and stone dust on the performance characteristic are analyzed using signal-to-noise ratios and mean response data. According to the results, water/binder ratio and stone dust play the significant role on the compressive strength of the brick. Furthermore, the estimated optimum values of the process parameters are corresponding to water/binder ratio of 0.4, fly ash of 39%, coarse sand of 24%, and stone dust of 30%. The mean value of optimal strength is predicted as 166.22 kg.cm-2 with a tolerance of ± 10.97 kg.cm-2. Confirmatory experimental result obtained for the optimum conditions is 160.17 kg.cm-2.

Resumo em Inglês:

The aim of this work was to evaluate the interfacial tension from the poly(butylene terephtalate) and poly(styrene-co-acrylonitrile) (PBT/SAN) interface region using the drop retraction method. SAN filaments were sandwiched between two PBT films; the whole system was heated up to 240 °C, in a hot stage coupled to an optical microscope. The rheological parameters of the PBT/SAN system were obtained by parallel plates rheometry. An increase of the interfacial tension with the PBT molecular weight was observed with values between 0.57 and 1.06 mN/m, depending on the molecular weight. Theoretical values were calculated using the geometric-mean and harmonic-mean equations and were found to be similar to the experimental results. Viscosity measurements showed that the higher the SAN/PBT viscosity ratio, the lower the interfacial tension of these blends.

Resumo em Inglês:

The purpose of this study was to evaluate in vitro the antimicrobial activity of materials used as root canal filling in deciduous teeth by direct exposure test. The materials tested were: Guedes-Pinto, CTZ, zinc oxide eugenol, Calen®, L&C and MTA pastes. A microbial mixture was prepared with 1 mL each of pure suspension of the following microorganisms: Staphylococcus aureus, Enterococcus faecalis, Pseudomonas aeruginosa, Bacillus subtilis, Candida albicans. For the direct exposure test, sterilized paper points were contaminated with the microbial mixture suspension and placed in contact with the respective materials for 24, 48 and 72 hours. At these intervals, paper points were removed and immersed in 7 mL of Letheen broth, followed by incubation at 37 °C/48 hours. 100 µL of inoculum obtained from Letheen broth was transferred to 7 mL of BHI under identical incubation conditions. Microbial growth was evaluated by macroscopic examination of BHI broth turbidity. In conclusion, only the CTZ and MTA pastes showed antimicrobial activity.

Resumo em Inglês:

The thermodynamic compensation effect plot derived from Eyring rate process theory was applied to the thermal and UV ageing of LDPE/Carbon Black composites containing commercial carbon black (CB) and carbon black surface oxidized with nitric acid. Correlations were tested among compensation effect, electrical threshold field and volumetric electrical conductivity. Compensation plots from OIT measurements correlate with thermal and UV ageing effect on activation ΔS and ΔH values, giving a good linear correlation for all samples studied. The relative changes in dc conductivity and electrical threshold field are consistent with the OIT compensation plot, demonstrating that this analysis can be used to monitor LDPE/CB composite degradation under thermal or UV ageing. It can also be used to evaluate, quite accurately, the effect of oxidizing the surface of the CB on the electrical properties (dc conductivity and electrical threshold field) of the LDPE/CB composites.

Resumo em Inglês:

Portland cement-based materials are present in our everyday life. Over the last two decades, important developments have been made to improve their mechanical strength, mainly through microstructural design. In addition, another promising parameter still remains in the early stages of understanding: that of adhesion. Recently, interdisciplinary researchers have considered the issue of water confinement by the hydrated cementitious surfaces. It could contribute to increase the adhesion and strength in these materials. On the other hand, ionic and non-ionic chaotropic substances might be able to disorder the structure of such special water. The results presented in this paper show important effects of these chaotropic substances on the strength of cementitious materials. They highlight the role of the confined water on the adhesion, when the microstructural parameters are kept constant. More than contributing to the fundamental understanding of adhesion within cement paste, these results provide basic insights on in-situ nanotechnology.

Resumo em Inglês:

There is a plethora of routes to produce hydroxyapatite(HA) and in general calcium phosphates(CP) but production usually leads to a mixture of several phases. Besides ionic contamination, most of these methods are cumbersome, restricted to small volumes of product and require a lot of thermal energy. The acid-base route eliminates foreign ions or additives and its only byproduct is water. Heterogeneous reaction drawback is that solid reactants do not easily come in contact with each other and therefore addition and stirring times become very lengthy and still the product is a mixture. The synthesis started from calcium hydroxide and phosphoric acid (PA). Ball milling was used to favor kinetics and stoichiometry. Six sets of PA addition, paddle stirring and ball milling times were used. Products were evaluated by X ray diffraction (XRD), Fourier Transform Infrared (FTIR), scanning electron microscopy (SEM), X ray fluorescence (XRF) and Ca/P ratio. Chemical analysis for calcium proceeded through oxalate precipitate and phosphorus by the phosphomolibdate technique. A set of conditions yielding high purity HA was established.

Resumo em Inglês:

This study evaluated the effect of surface sealant on the translucency of composite resin immersed in different solutions. The study involved the following materials: Charisma, Fortify and coffee, Coca-Cola®, tea and artificial saliva as solutions. Sixty-four specimens (n = 8) were manufactured and immersed in artificial saliva at 37 ± 1 °C. Samples were immersed in the solutions for three times a day and re-immersed in artificial saliva until the translucency readings. The measurements were carried out at nine times: T1 - 24 hours after specimen preparation, T2 - 24 hours after immersion in the solutions, T3 - 48 hours and T4 to T9 - 7, 14, 21, 30, 60 and 90 days, respectively, after immersion. The translucency values were measured using a JOUAN device. The results were subjected to ANOVA and Tukey's test at 5%. The surface sealant was not able to protect the composite resin against staining, the coffee showed the strongest staining action, followed by tea and regarding immersion time, a significant alteration was noted in the translucency of composite resin after 21 days.

Resumo em Inglês:

The tensile strength of metals and alloys can be considerably increased by severe plastic deformation, a consequence of the extreme grain refinement thus achieved. In the present work the deformation was performed by Equal Channel Angular Pressing and the material was an Al-4% Cu alloy. Characterization included tensile tests, and microstructural observation by optical and transmission electron microscopy. After four passes, the yield strength showed an increase of 310% over the undeformed alloy, a figure reduced to 160% by a 250 °C / 1 hour post - deformation anneal. Additionally, the alloy displayed a very low work hardening capacity, especially after the annealing heat treatment. After four deformation passes the grain size of the annealed specimens was estimated to be close to 500 nm. The tensile behaviour and the absence of work hardening were discussed in terms of the fine microstructure.

Resumo em Inglês:

The aim of this study was to synthesize and characterize the biodegradable intraocular implants based on poly (D,L-lactide-co-glycolide) (PLGA 75:25) with Cyclosporine-A (CyA) and to evaluate their in vitro drug delivery profile. Thermal analysis was conducted by using Thermogravimetry (TG) and Differential Scanning Calorimetry (DSC). Phase analysis and crystallinity of the polymer-CyA samples were assessed through X ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). Finally, microstructure and morphology of the systems were investigated by Scanning Electron Microscopy (SEM). The results showed that CyA was successfully incorporated into PLGA network with drug loading of approximately 31.6%. Also, based on FTIR and thermal analyses (TGA/DSC) no significant physical-chemical interaction was detected at the micro-nanoscale level between polymer/drug. SEM micrographs have indicated a uniform drug distribution in PLGA matrix. XRD patterns have showed that the incorporated semi-crystalline structure of CyA has not significantly altered the polymeric mainly amorphous network. In addition, the results have confirmed the chemical and biological drug stability, the drug distribution into the polymeric matrix and the possibility of cyclosporine prolonged delivery system profile.

Resumo em Inglês:

In this work we investigated the effect of visible radiation on the electrical properties of poly[(2-methoxy-5-hexyloxy)-p-phenylenevinylene]- MH-PPV films and light emitting diodes. Complex impedance measurements of (Au or ITO)/MH-PPV/(Au or Al) samples were carried out at room temperature and exposed to white light. Over the frequency range from 100 mHz to 2 MHz, the electrical results of Au/MH-PPV/Au was dominated by the Cole-Cole approach, where the electrode influence is negligible. However, some additional influence of the interface was observed to occur when Al was used as electrode. These effects were observed under both dark and visible-light illumination conditions. A simple model based on resistor-capacitor parallel circuits was developed to represent the complex impedance of the samples, thereby separating bulk and interface contributions. We observed that the polymer electrical resistivity decreased while the dielectric constant of the polymer and the thickness of the Al/MH-PPV layer were almost constant with increasing light intensity. The decrease of the polymer layer resistance comes from a better charge injection due to a light induced dissociation of positive charge carriers at the electrode.

Resumo em Inglês:

The technique of the rotating disk was used to measure the zeta potential of planar surface of different materials, like minerals, polymeric materials, and films of paints and particles. This technique is simple and reliable from the experimental point of view. The results are discussed concerning the principles of the technique, the rheological characteristics and the applications of these materials.

Resumo em Inglês:

In order to clarify the influence of Bi-doping on oxygen diffusion in ZnO, the bulk and grain boundary oxygen diffusion coefficients were measured in Bi2O3-doped ZnO polycrystals by means of the gas-solid exchange method using the isotope 18O as the oxygen tracer. The experiments were performed on ZnO sintered samples containing 0.1, 0.3 and 0.5 mol% Bi2O3. The diffusion annealings were performed at 942, 1000 and 1092 °C, in an Ar+18O2 atmosphere under an oxygen partial pressure of 0.2 atm. After the diffusion annealings, the 18O diffusion profiles were established by secondary ion mass spectrometry (SIMS). The results show an increase in the oxygen diffusion in the Bi2O3-doped ZnO, when compared to the oxygen diffusion in the undoped ZnO polycrystal under the same experimental conditions, both in bulk and in grain-boundaries. Moreover, it was observed that the higher the Bi2O3 concentration, the higher the oxygen diffusion. These results suggest that the incorporation of Bi2O3 increases the interstitial oxygen concentration which agrees with an interstitial diffusion mechanism both in bulk and in grain-boundaries.

Resumo em Inglês:

The high temperature oxidation behavior of two ferritic stainless steels type AISI 430A and AISI 430E is examined at low oxygen pressure and high temperatures. The AISI 430A steel is ferritic up to 860 °C. Above this temperature, this steel is bi-phased: presence of austenite and ferrite phases. The 430E steel is stabilized with Nb, and is ferritic at all temperatures. The oxidation experiments were performed in a thermobalance SETARAM TGDTA 92, in the range of 850-950 °C, in Ar/H2/H2O atmosphere, under oxygen partial pressures lower than 1.3 x 10-18 atm. The microstructure and the composition of the oxide scales were analysed by scanning electronic microscopy (SEM) and energy dispersive spectroscopy (EDS). Different oxidation behaviors in AISI 430A and AISI 430E stainless steels were observed. At 850 °C, the oxidation of the 430A steel is greater than that of the 430E steel, but above 900 °C the oxidation of the 430A steels is lower than that of the 430E steel. The oxidation rate of the 430A steel shows low dependence on temperature, while the oxidation of the 430E follows an Arrhenius law, with an activation energy corresponding to the chromia scale growth.

Resumo em Inglês:

In this work, controlled reduction of perovskites supported on Al2O3 was used to prepare thermally stable nanodispersed iron catalysts based on Fe0/La2O3/Al2O3. The perovskites composites LaFe0.90Mn0.08Mo0.02O3(25, 33 and 50 wt (%)) /Al2O3 and LaFe0.90Mn0.1O3(25 wt (%)) /Al2O3 were prepared and characterized by XRD, BET, TPR, SEM and Mössbauer spectroscopy. XRD for unsupported perovskite showed the formation of a single phase perovskite structure. The Mössbauer spectra of the perovskites were fitted with hyperfine field distribution model for the perovskite. Supported perovskites on Al2O3 showed a decrease of the hyperfine field in respect to unsupported perovskite, due to decrease of particle size and dispersion of the Fe3+ specimens on the support. Also showed broaden lines and relaxation effects due to the small particle size. To produce the Fe0 catalyst, the composite perovskite(25%)/Al2O3 was reduced with H2 at 900, 1000 and 1100 °C for 1 hour. XRD data indicated the formation of Fe0 catalyst with particles sizes of ca. 35 nm. The Mössbauer spectrum showed the formation of metallic iron and doublets corresponding to species of octahedric Fe2+ and Fe3+ sites dispersed on Al2O3. These catalysts showed improved stability towards sintering even upon treatment at 1000 and 1100 °C under H2.