Resumo em Inglês:

OBJECTIVE: Earlier studies on some dental materials measured roughness and/or contact angles or fluoride release separately. In the present study, five dental polymers were investigated to ascertain their contact angles, wettability, roughness, and fluoride release in dry or wet conditions. METHODS: Samples for 5 materials were prepared and stored dry or wet in deionized water pH 6.8. Samples were submitted to finishing/polishing procedures, and the measurements in Goniometer, roughness (µm) and fluoride analysis RESULTS AND CONCLUSIONS: Except for the Ariston pHc, all the materials displayed high contact angles when measured with water, showing hydrophobic characteristics. Roughness changed the contact angles, especially those of Ariston (α < 0.05). Fluoride did not modify the contact angles, but increased the roughness of the finished material.

Resumo em Inglês:

This study shows the processing of radar absorbing multilayer structures based on nonwoven substrates of polyacrylonitrile and poly (ethylene terephthalate) impregnated with a polyaniline and polyurethane mixture. Processed materials with different parameters - layer stacking and impregnated faces - were evaluated considering the incident radiation attenuation in the frequency range of 8 to 12 GHz. The results show the influence of the quantity, types and thickness of the impregnated layers. Scanning electronic microscopy observations evaluated the anchorage of the absorbing center (polyaniline) in the substrate. In a general way, the different obtained structures presented incident radiation attenuation values between 87 and 99%. This result allows its use as microwave absorbers.

Resumo em Inglês:

A variety of metallic components rely on properties that are specific to the alloy and its surface. Coatings have been extensively used to protect metallic surfaces from the aggressive effects of the environment to which it is exposed. In this investigation, the high temperature oxidation behavior of a FeCr and a FeCrY alloy coated with an aluminium based paint has been studied. The objective was to form the more resistant alumina surface layer on an aluminium free alloy. Aluminium based paint coated and uncoated specimens of the two alloys were oxidized for up to 200 hours at 1000 °C in air. The oxidized specimens were examined in a scanning electron microscope coupled to an energy dispersive system and the surfaces were analyzed by X ray diffraction analysis. The aluminium based paint coating increased the oxidation resistance of the alloys, mainly over extended periods. The FeCrY alloy coated with the Al based paint exhibited the highest oxidation resistance.

Resumo em Inglês:

Acrylic resins used for provisional prostheses should have satisfactory superficial characteristics in order to ensure gingival health and low bacterial attachment. The purpose of the present study was to evaluate the superficial roughness and contact angle after two types of polishing and the Vickers hardness of three acrylic resins (Duralay - G1, Dencrilay - G2, and Dencor - G3), all shade 66, indicated for provisional fixed prostheses. Five 20 x 3 ± 1 mm diameter discoid specimens were obtained for each group. One side of the specimens was subjected to standard polishing (pumice and whiting slurry), and the opposite side was polished with special tips. The mean roughness and contact angles of the materials were measured. The specimens were subjected to the Vickers microhardness test, which indicated that standard polishing produced a surface roughness equivalent to that of the special tips. The contact angles obtained with the standard polishing were equivalent to those observed in the special tips group. The microhardness of G1 and G3 resins showed statistical differences.

Resumo em Inglês:

Resin Transfer Molding (RTM) is a polymer composite processing technique widely used in the aeronautics and automotive sectors. This paper describes the numerical simulation of the RTM process where Darcy's law was used for the mathematical formulation of the problem. A control volume finite element method was used for the determination of pressure gradients inside the mold, and a geometric reconstruction algorithm is used for the resin flow-front determination. Permeability of the medium was considered either a constant or a two dimensional tensor. The application was validated by direct comparison with literature data and good qualitative and quantitative agreement was obtained. The finite volume method was built to be used with a two-dimensional unstructured grid, hence allowing the analysis of complex geometries. The results showed that the proposed methodology is fully capable of predicting resin flow advancement in a multi-layer (with distinct physical properties) reinforced media.

Resumo em Inglês:

Wind energy converters of small size used in isolated units to generate electrical energy must present low maintenance cost to such facilities economically viable. The aspect to be analyzed in cost reduction is the brake system, since in isolated systems the use of brake is more frequent reducing the brake pads life time. This study aims at analyzing the wear behavior of some materials used in brake pads. An organic material was analyzed comparing it with a commercial brake pad, and the sintered material was developed and tested. The materials behaviors were evaluated in both wear and friction coefficient. The sintered samples were made by powder metallurgy. The composition was compacted at 550 MPa and sintered in a furnace with controlled atmosphere to avoid oxidation. Despite the different compositions of the two types of materials, they presented a very similar wear; however, the sintered material presented a higher friction coefficient. An adjustment in the braking system of the wind generator might be proposed to use the sintered brake pad, due to its higher friction coefficient. Consequently, the braking action becomes lower, reducing the wear rate of the material.

Resumo em Inglês:

Porous titanium scaffolds are promising materials for biomedical applications such as prosthetic anchors, fillers and bone reconstruction. This study evaluated the bone/titanium interface of scaffolds with interconnected pores prepared by powder metallurgy, using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Porous scaffolds and dense samples were implanted in the tibia of rabbits, which were subsequently killed 1, 4, and 8 weeks after surgery. Initial bone neoformation was observed one week after implantation. Bone ingrowth in pores and the Ca/P ratio at the interface were remarkably enhanced at 4 and 8 weeks. The results showed that the interconnected pores of the titanium scaffolds promoted bone ingrowth, which increased over time. The powder metallurgy technique thus proved effective in producing porous scaffolds and dense titanium for biomedical applications, allowing for adequate control of pore size and porosity and promoting bone ingrowth.

Resumo em Inglês:

Double-torsion tests were carried out to ascertain whether a thin test specimen would affect the results of this test. The tests involved two test specimen sizes, one with a thickness five-fold greater than the particle size of the material and the other with a three-fold greater thickness. The width of both test specimens was ten times that of their thickness and their length was double their width. The material utilized was an alumina-based refractory castable without cement. It is important to ascertain the influence of the thickness of double-torsion test specimens when materials with a coarse microstructure are involved. Otherwise, test specimens would have to be very large, rendering the experimental procedure difficult, as in the case of the size of sintering furnaces and the size of accessories for the test. This study shows that test specimens with lower thicknesses are representative when one analyzes the calibration curve of the compliance, the length of the crack at which the break occurred (critical crack length), and the shapes of the R-curve and of the load (P) vs. displacement curves. However, the analysis of the mean values of R (R), obtained by the arithmetic average of the R values in the section of stable crack propagation and the total fracture energy (γwof), showed that these values are dependent on the size of the test specimens, indicating that this subject deserves further investigation.

Resumo em Inglês:

The crystallization kinetics of ceramics composed by Bi2O3-ZnO-Nb2O5 (BZN) was studied using non-isothermal method. The BZN samples were prepared by the polymeric precursors method. Phase evolution was evaluated by X ray diffraction and the thermal events were evaluated by differential scanning calorimetry (DSC). The crystallization of BZN occurs from 500 to 700 °C, which corresponds to a secondary event in DSC curves. The principal exothermic event in these curves is related to the decomposition of organic material and was isolated from the crystallization peak by deconvolution into two Gaussian curves. Those related to crystallization processes were evaluated in terms of crystallized fraction. Kinetic parameters were determined from Ligero (E = 242 ± 7) kJ.mol-1 and Kissinger (E = 241 ± 24) kJ.mol-1 methodologies and they are very close. The activation energy Ea = (241 ± 24) kJ.mol-1 and (242 ± 7) kJ.mol-1 (by the Kissinger and Ligero methodology, respectively), frequency factor k0 =10(13).s-1 and exponent of Avrami n = (1.3 ± 0.1) were determined. The n value indicates that the crystallization is diffusion controlled, with decreasing nucleation rate. Scanning electronic microscopy showed the presence of nanoparticulated powder.

Resumo em Inglês:

Adhesion between tiles and mortars are crucial to the stability of ceramic tile systems. From the chemical point of view, weak forces such as van der Waals forces and hydrophilic interactions are expected to be developed preferably at the tiles and polymer modified Portland cement mortar interface. The main goal of this paper was to use organosilanes as primers to modify ceramic tile hydrophilic properties to improve adhesion between ceramic tiles and polymer modified mortars. Glass tile surfaces were treated with several silane derivatives bearing specific functionalities. Contact angle measurements and Fourier Transform Infrared Spectroscopy (FTIR) were used for evaluating the chemical changes on the tile surface. In addition, pull-off tests were conducted to assess the effect on adhesion properties between tile and poly(ethylene-co-vinyl acetate), EVA, modified mortar. The bond strength results have clearly shown the improvement of adherence at the tile-polymer modified mortar interface, reflecting the overall balance of silane, cement and polymer interactions.

Resumo em Inglês:

The objective of this work was to evaluate biaxial-flexural-strength (σf), Vickers hardness (HV), fracture toughness (K Ic), Young's modulus (E), Poisson's ratio (ν) and porosity (P) of two commercial glass-ceramics, Empress (E1) and Empress 2 (E2), as a function of the hot-pressing temperature. Ten disks were hot-pressed at 1065, 1070, 1075 and 1080 °C for E1; and at 910, 915, 920 and 925 °C for E2. The porosity was measured by an image analyzer software and s f was determined using the piston-on-three-balls method. K Ic and HV were determined by an indentation method. Elastic constants were determined by the pulse-echo method. For E1 samples treated at different temperatures, there were no statistical differences among the values of all evaluated properties. For E2 samples treated at different temperatures, there were no statistical differences among the values of σf, E, and ν, however HV and K Ic were significantly higher for 910 and 915 °C, respectively. Regarding P, the mean value obtained for E2 for 925 °C was significantly higher compared to other temperatures.

Resumo em Inglês:

In this work two perovskites were prepared: LaMn1-xFe xO3, and LaMn0.1-x Fe0.90Mo xO3. XRD and Mössbauer spectroscopy suggest the formation of pure phase perovskite with the incorporation of Fe and Mo in the structure. The catalytic activity of these materials was studied in two reactions with H2O2: the decomposition to O2, and the oxidation of the model organic contaminant methylene blue. The perovskite composition strongly affects the catalytic activity, while Fe decreases the H2O2 decomposition Mo strongly improves dye oxidation.

Resumo em Inglês:

The aim of this study was to investigate the influence of therapeutic dose X rays on the microhardness (MH) and degree of conversion (DC) of two different esthetic restorative dental materials. The materials were photo-activated with a LED light-curing unit using three cure-times: 5, 20 and 40 seconds. The photo-activation was carried out in two distinct periods: before and after irradiation with doses of 5, 35 and 70 Gy, from a 6 MV X rays beam. In accordance with the methodology used, it was conclude that a therapeutic dose does not have a detrimental effect on the photoinitiator molecules, because the photo-activation occurred after they were irradiated. When the irradiation was applied before photo-activation, the materials showed MH improvement, but when photo-activation was performed after irradiation, there was less improvement. However, there was no correlation between MH and DC. Thus, a therapeutic dose applied to cured material can promote linking and breaking of chain bonds in a non-linear way.

Resumo em Inglês:

Sol-gel synthesis has been investigated in order to produce stoichiometric compositions of Ba3Co2Fe24O41 (Co2Z) at lower calcination temperatures, using citric acid as quelant complex. Using this method, Co2Z ferrite could be synthesized at 950 °C, about 400 °C lower than that of conventional method. Nanocomposites (80:20% weight) of this ferrite with polychloroprene (CR) were obtained for the microwave absorption measurements by mixing, molding and curing mixtures of Ba3Co2Fe24O41 powders with polychloroprene and the additives of vulcanization. The microwave absorption measurements was carried out using the Transmission/Reflection method for the S and X-Ku bands and showed the best performance as Radar Absorber Material (RAM) in 8.0-16.0 GHz range. Thus, the material can be used by reducing the radar signature of the Brazilian Frigates' superstructures.

Resumo em Inglês:

Single-walled carbon nanotubes, with stiffness of 1.0 TPa and strength of 60 GPa, are a natural choice for high strength materials. A problem, however, arises when experimental data are compiled. The large variability of experimental data leads to the development of numerical models denominated molecular mechanics, which is a "symbiotic" association of molecular dynamics and solid mechanics. This paper deals with molecular mechanics simulations of single-walled carbon nanotubes. To be able to evaluate the molecular mechanics model, the three major carbon nanotube configurations (armchair, zigzag and chiral) were simulated. It was proven that the carbon nanotube configuration has influence on stiffness. By varying the radius, hence the curvature, the Young's modulus changed from 0.95 TPa to 5.5 TPa, and the Poisson's ratio ranged from 0.15 to 0.29. The numerical simulations were in good agreement with those presented in the literature.

Resumo em Inglês:

The magnetic behavior and its relationship with microwave absorbing properties have been investigated for doped Z-type barium hexaferrites (Ba3Co1.3Zn0.3Cu0.4Fe 24O41)/ polychloroprene (CR) nanocomposites. Simultaneous substitutions by Co2+, Cu2+, and Zn2+ ions make possible the use of these materials as RAMs, due to the frequency dependence of µr* (permeability), responsible for the location of the hexaferrite natural resonance. The Cu2+ ions distort the crystalline field due to their electronic configuration, and this behavior results in an increase in the saturation magnetization (Ms), which improve the magnetic permeability. Similarly, the superparamagnetic contribution (associated to the nanometric size) led to the improvement of the microwave absorption.

Resumo em Inglês:

We developed a complex (amplitude and phase) modulation Diffractive Optical Element (DOE) with four phase levels, which is based in a glass substrate coated with DLC (Diamond Like Carbon) thin film as the amplitude modulator. The DLC film was deposited by magnetron reactive sputtering with a graphite target and methane gas in an optical glass surface. The glass and DLC film roughness were measured using non destructive methods, such as a high step meter, Atomic Force Microscopy and Diffuse Reflectance. Other properties, such as refractive index of both materials were measured. The DOEs were tested using 632.8 nm HeNe laser.

Resumo em Inglês:

In this work, nanocomposites were prepared by adding a small amount of single walled carbon nanotubes (SWCNTs) to an epoxy resin aiming to study the resulting mechanical, viscoelastic and thermal properties of the nanocomposites. To optimize the processing of the nanocomposites and to favor a homogeneous dispersion of the SWCNTs on the matrix, acetone was used to reduce resin viscosity, increasing diffusion of the SWCNTs in the solution. The epoxy/SWCNTs/acetone systems were also sonicated in order to minimize entanglement of the SWCNTs. The systems were characterized by Fourier transform infrared spectroscopy, Raman spectroscopy, thermogravimetry, differential scanning calorimetry and dynamic mechanical analysis. The results indicated that the addition of small amounts of SWCNTs to epoxy leads to slight structural changes in the epoxy matrix which, together with the presence of SWCNTs, may reflect on its mechanical and viscoelastic properties

Resumo em Inglês:

The aim of this article is present an overview of the promising results obtained while using carbon nanofibers based composites as catalyst support for different practical applications: hydrazine decomposition, styrene synthesis, direct oxidation of H2S into elementary sulfur and as fuel-cell electrodes. We have also discussed some prospects of the use of these new materials in total combustion of methane and in ammonia decomposition. The macroscopic carbon nanofibers based composites were prepared by the CVD method (Carbon Vapor Deposition) employing a gaseous mixture of hydrogen and ethane. The results showed a high catalytic activity and selectivity in comparison to the traditional catalysts employed in these reactions. The fact was attributed, mainly, to the morphology and the high external surface of the catalyst support.

Resumo em Inglês:

The ever growing focus on environmental issues has raised concerns about scrap tires, whose major component - vulcanized rubber - does not degrade easily. When burned, tires release toxic gases containing substantial amounts of sulfur and ammonia in addition to other pollutants. Dumped on empty city lots, tires are also a breeding ground for mosquitoes. Many proposals have been put forward to handle the disposal of scrap tires, but none of them have proved to offer a definitive solution. The study reported here investigated the production of fuel oil and activated carbon from the pyrolysis of scrap tires. The initial mass of rubber yielded approximately 46% of oil, 40% of activated carbon and 14% of gases. The resulting activated carbon displayed a specific surface area of 200 m².g-1.

Resumo em Inglês:

Textile industrial wastewaters have significant quantities of dyes. Adsorption processes using industrials rejects may help in the treatment of these effluents. In this context, uptake of Reactive Blue 5G dye by babassu coconut shell activated carbon was studied with upstream flow fixed-bed experiments. First, the minimum flow rate that minimizes the diffusion effects of 4 mL/min was chosen within the range investigated (2-10 mL/min). Then, the breakthrough curves were obtained for this flow rate for different initial dye concentrations (13.15102.0 mg/L) and temperature of 30 °C. The mass retained until bed saturation in each experiment was used to obtain the dynamic isotherms, which showed a favorable dye uptake behavior with a maximum adsorption capacity of 12.9 mg.g-1. The irreversible model fitted the experimental data well when compared to Langmuir and Freundlich models. A LDF model simulated the experimental breakthrough curves, and the bed axial dispersion and mass transfer coefficients were estimated.

Resumo em Inglês:

Natural fibers from macadamia nut shell, dried coconut shell endocarp, unripe coconut mesocarp, sugarcane bagasse and pine wood residue were used to prepare activated carbon fibers (ACF) with potential application for removing microcystins. The ACF from pine wood and sugar cane bagasse were used to remove [D-Leucine¹]MCYST-LR from water. After 10 minutes of contact time, more than 98% of toxin was removed by the ACF. The microcystin adsorption monolayer, q m, in the ACF recovered 200 and 161 µg.mg-1, with the Langmuir adsorption constant, K L, of 2.33 and 1.23 L.mg-1. Adsorption of [D-Leucine¹]MCYST-LR in continuous process was studied for a fixed-bed ACF prepared from coconut shell and sugar cane bagasse and for two commercial activated carbon samples from treatment water plants of two Brazilian hemodialysis centers. Saturation of the beds occurred after 80 to 320 minutes, and the adsorption capacity for that toxin varied from 4.11 to 12.82 µg.mg-1.

Resumo em Inglês:

Currently, the most used polymer for asphalt binder modification is the thermoplastic elastomer styrene butadiene styrene (SBS) and aromatic oil is commonly added to the mixtures to improve their compatibly. This paper proposes the use of oil shale from sedimentary rock as a compatibilizer agent for polymer-modified asphalt binder (PMB). PMBs were produced by mixing a bitumen with a linear SBS copolymer (3.5% (w.w-1)) using two oil shale contents (2 and 4%) and petroleum aromatic oil to evaluate comparatively the effect of the compatibilizer agent on the SBS PMB properties. The rheological characteristics of the SBS PMBs were analyzed in a dynamic shear rheometer (DSR) and the morphology accessed by fluorescence optical microscopy. The viscoelastic behavior of the samples corroborated the results for the classical properties and varied according to the sample morphology and composition. The results indicate that the aromatic and shale oils have similar effects on the microstructure, storage stability and viscoelastic behavior of the PMBs. Thus, shale oil could be successfully used as a compatibilizer agent without loss of properties or could even replace the aromatic oil. Following the Superpave methodology it was observed that the linear- and radial-SBS PMBs and linear-SBS PMB with 2% of shale oil can be used up to 70 °C, and the linear-SBS PMBs with 4% of shale oil or 2% of aromatic oil can be used only up to 64 °C.

Resumo em Inglês:

Spent anodes, denominated butts in the aluminum industry, are recycled as part of the raw material used to produce new anodes. The fragmentation of the butt generates some sodium-rich powder, which is captured and included in the recycled material. This paper evaluates the influence of sodium content on anode reactivity. Six formulations with 0 to 25% butt powder were used. An average increase of 48 ppm of sodium from one to another formulation caused average increments of 3.38 and 2.72% for air and CO2 reactivity, respectively. The quality-related figures varied from 1.34 to 1.12 for CO2 and from 1.10 to 0.62 for air, showing quality loss in higher sodium content and higher impact on air reactivity. The Fischer formula predicted a carbon specific consumption of - 48.47 kg.t-1 Al for baked carbon anodes with 127 ppm to 367 ppm of sodium content, showing that the sodium can cause relevant carbon losses and increase costs of the aluminum production.