Resumo em Inglês:

The surface of glassy carbon (GC) electrode has been modified by oxidation of L-cysteine. The covalent modified GC electrode with L-Cysteine has been studied, according the supporting electrolyte used. Favourable interactions between the L-cysteine film and DA enhance the current response compared to that at the Nafion GC and bare GC electrodes, achieving better performances than those other electrodes. This behaviour was as result of the adsorption of the cysteine layer film, compact and uniform formation; depending on L-cysteine solution (phosphate buffer or chloridric acid supporting electrolyte) used for modifying GC surface. In cyclic voltammetric measurements, modified electrodes can successfully separate the oxidation/reduction DA peaks in different buffer solutions, but an evident dependence in the response was obtained as function of pH and modified electrode. The modified electrode prepared with L-cysteine/HCl solution was used to obtain the calibration curve and it exhibited a stable and sensitive response to DA. The results are described and discussed in the light of the existing literature.

Resumo em Inglês:

Polyurethane adhesives made from synthetic chemicals are non-biodegradable, costly and difficult to find raw materials from local market. To avoid solid pollution problem, cost effectiveness and easy availability of raw materials, biomaterials based polyurethane adhesives are used in current industrial interest. Direct use of castor oil in polyurethane adhesive gives limited hardness. Modification on active sites of castor oil to utilize double bond of unsaturated fatty acid and carboxyl group yields new modified or activated polyols, which can be utilized for polyurethane adhesive formulation. In view of this, we have synthesized polyurethane adhesives from polyester polyols, castor oil based polyols and epoxy based polyols with Isocyanate adducts based on castor oil and trimethylolpropane. To study the effects of polyurethane adhesive strength (i.e. lap shear strength) on wood-to-wood and metal-to-metal bonding through various types of polyols, cross-linking density, isocyanate adducts and also to compare adhesive strength between wood to wood and metal to metal surface. These polyols and polyurethanes were characterized through GPC, NMR and IR-spectroscopy, gel and surface drying time. Thermal stability of PU adhesives was determined under the effect of cross-linking density (NCO/OH ratio). The NCO/OH ratio (1.5) was optimized for adhesives as the higher NCO/OH ratio (2.0) increasing cross-linking density and decreases adhesion. Lower NCO/OH ratio (1.0) provideslow cross-linking density and low strength of adhesives.

Resumo em Inglês:

A weight-based analysis was made of the translaminar Charpy impact toughness performance of conventional and advanced composite materials for aircraft fabrication. The materials were carbon-epoxy (C-Ep) and hybrid fiber-metal TiGr (Titanium-Graphite) laminates. 5 mm-thick three-point bend specimens were tested over a temperature range of -70 to 180 ºC to reproduce typical in-service conditions of supersonic jetliners. The energies required for the processes of damage initiation (Ei), damage propagation (Ep), and whole fracture (Et = Ei + Ep), were evaluated at two loading rates, namely, 2.25 and 5.52 m/s in an instrumented Charpy impact testing machine. C-Ep laminates with unidirectional fiber tapes arranged in cross-ply architecture consistently showed the best performance in terms of damage initiation toughness, whereas the hybrid fiber-metal laminate TiGr excelled in terms of propagation toughness. On the other hand, the overall performance of bi-directional fabric C-Ep laminates was very disappointing. The impact behavior of composite laminates was substantiated by a qualitative analysis of topographic aspects of fracture surfaces.

Resumo em Inglês:

Size and external and internal morphologies of nanoparticles and microparticles are very important on the design of drug devices for controlled release. Random enteric copolymers such as poly (methacrylic acid-co-ethyl acrylate) and poly (methacrylic acid-co-methyl methacrylate) were used to produce nanoparticles, which contain a model drug and could be employed as drug carriers for proteins. The solvent effect on re-dispersion of such nanoparticles was studied by Scanning Electron Microscopy (SEM) and revealed not only differences in size, but also several shapes, depending on the chemical nature of the polymer matrix and the non-solvent used. Acrylate containing copolymers in acidic aqueous dispersions lead to spheroidal particles. However for the copolymer containing methyl methacrylate, spheroidal particles collapsed in a "grenade" type morphology and besides some cubic structures are also formed. Dynamic Light Scattering (DLS) studies of the re-dispersed nanoparticles showed the strong tendency to form agglomerates not only in acidic water but also in hexane and the presence of bimodal size distributions.

Resumo em Inglês:

A novel mesoporous Mn - organophosphate was synthesized for the first time. It is characterized by several physicochemical techniques. Small angle X-ray diffraction analysis shows the first peak in 2.5ºwith 39 Aº pore width. Elemental analysis shows that the composition is [(C12H23N)3PO]40Mn. Scanning electron microscopic picture shows the flag morphology with 1-15 µm particle size. Thermogravimetry/Differentaial thermal analysis shows almost 80% exothermic weight loss. Nitrogen adsorption isotherm shows type III with 300 m²/g BET surface area. Fourier transform Infrared spectroscopic analysis shows that the framework vibrations are comparable to other well known silica mesoporous materials. Electron spin resonance spectroscopic analysis shows the absence of hyperfine splitting indicates the presence of Mn3+ species. Ultraviolet - visible spectroscopic analysis shows that most of the Mn is in tetrahedral co-ordination beside small square pyramidal species. A plausible synthesis mechanism also proposed.

Resumo em Inglês:

The purpose of this study was to evaluate the impact and fracture resistance of acrylic resins: a heat-polymerized resin, a high-impact resin and an experimental polymethyl methacrylate with elastomer in different proportions (10, 20, 40 and 60%). 120 specimens were fabricated and submitted to conventional heat-polymerization. For impact test, a Charpy-type impact tester was used. Fracture resistance was assessed with a 3-point bending test by using a mechanical testing machine. Ten specimens were used for each test. Fracture (MPa) and impact resistance values (J.m-1) were submitted to ANOVA - Bonferroni's test - 5% significance level. Materials with higher amount of elastomer had statistically significant differences regarding to impact resistance (p < 0.05). Fracture resistance was superior (p < 0.01) for high-resistance acrylic resin. The increase in elastomer concentration added to polymethyl methacrylate raised the impact resistance and decreased the fracture resistance. Processing the material by injection decreased its resistance to impact and fracture.

Resumo em Inglês:

Thin films of titanium were deposited onto Al2O3 substrate by hollow cathode discharge method for the formation of a ceramic-ceramic joint using indirect brazing method. An advantage of using this technique is that a relatively small amount of titanium is required for the metallization of the ceramic surface when compared with other conventional methods. Rapidly solidified brazing filler of Cu49Ag45Ce6 in the form of ribbons was used. The thickness of deposited titanium layer and the brazing temperature/time were varied. The quality of the brazed joint was evaluated through the three point bending flexural tests. The brazed joints presented high flexural resistance values up to 176 MPa showing the efficiency of the technique.

Resumo em Inglês:

Changes to the microestructure during thermal aging treatment at 610 ºC in Fe-xMo-5Ni-0.05C alloys were studied for different aging times with different Mo concentrations. The heat treatment at 610 ºC induces carbide precipitation into the metallic matrix near Fe2Mo phase. The X-ray diffraction studies revealed a more intense precipitation of α-FeMo, Fe3Mo, R(Fe63Mo37) phases and MoC, Fe2MoC carbides for the alloys containing 15 and 11% Mo, respectively. This work shows that hardness and coercive force changes are function of the molybdenum content and aging time variation. Vickers hardness and coercive force both increase with the increase of molybdenum content and reach maximum values at 4 and 1h of aging, respectively.

Resumo em Inglês:

This paper presents an experimental analysis of the pullout strength of bonded and axially loaded steel rods used as connector elements in log-concrete composite bridge decks. Static and cyclic tests were carried out to evaluate the fatigue of the connectors using two species of reforested wood, three types of commercial adhesives and three levels of wood moisture content. It was found that six failure modes (rod interface failure, timber interface failure, combined timber interface/rod interface failure, combined rod interface/timber substrate failure, rod failure, and adhesive failure) can occur in the geometry of a single test specimen. The results indicate the good performance of epoxy glued steel rod connectors for use in log-concrete composite bridge decks.

Resumo em Inglês:

This work is focused on the development and evaluation of manufacturing methods to produce short fibers hybrid mats. Different methods were developed, including: aqueous and fluidized bed. Composites were molded to help evaluating the produced mats. The analysis showed that composites manufactured by the fluidized bed method presented the best mechanical properties.

Resumo em Inglês:

Aluminium monohydroxide, also known as aluminium oxyhydroxide (boehmite - AlO[OH]), is water insoluble but crystallises into microcrystals of various shapes. When, by X-ray diffraction, the microcrystals present a basal reflexion (d[020]) of 0.611 nm, the crystalline structure is referred to as "well-crystallised" boehmite. Natural and synthetic crystals of well-crystallised boehmite can have a plate-like shape with either a rhombic or hexagonal profile. Synthetic crystals can also be lath-like or ellipsoid in shape. The purpose of this paper is to present a method of hydrothermal synthesis using a single temperature (200 ºC) for preparing plate-like crystals of well-crystallised boehmite with ellipsoid, rhombic, hexagonal, and lath-like profiles by using different precursors. Our observations suggest that all of these shapes are stages of growth of the microcrystals of well-crystallised boehmite along the c-axis direction of the rhombic crystals.

Resumo em Inglês:

In this study mechanical properties and biocompatibility (In Vitro) of a new bone cement were investigated. A new platform technology named COOL is a variable composite of dissolved, chemically modified PMMA and different bioceramics. COOL cures at body temperature via a classical cementation reaction. Compressive strengths ranging from 3.6 ± 0.8 to 62.8 ± 1.3 MPa and bending strengths ranging from 9.9 ± 2.4 to 26.4 ± 3.0 MPa were achieved with different COOL formulations. Porosity varied between 31 and 43%. Varying the components of each formulation mechanical properties and porosity could be adjusted. In Vitro biocompatibility studies with primary human osteoblasts (pHOB) in direct contact with different COOL formulations, did not reveal any signs of toxicity. In contrast to Refobacin® R, cells incubated with COOL showed similar density, viability and ALP activity compared to control, if specimen were added immediately to the cell monolayer after preparation. In conclusion, COOL has promising mechanical properties in combination with high biocompatibility In Vitro and combines different advantages of both CPCs and PMMA cements by avoiding some of the respective shortcomings.

Resumo em Inglês:

The development of α and β-phases and the molecular orientation of injection molded disks of two isotactic polypropylene (i-PP) resins were studied by wide angle X-ray diffraction (WAXD) and pole figures. A nucleated (NPP) and non-nucleated (HPP) polymers were analyzed. The main proposal of this article was the comprehensive study of the interrelations between the processing conditions, phase contents and PP α-phase molecular orientation of injection molded PP resins. In both resins, it was observed that the α-phase was present in all regions along the thickness while the β-phase was present mainly in the external layers, decreasing from the surface to the core; however this last phase was present in a very small amount in the NPP resin. For both polymers, the orientation of the macromolecules c-axis was higher along the flow direction (RD) than along the transverse direction (TD). The b-axis of the PP α-phase molecules was oriented to the thickness direction (ND). The orientation of the c-axis along RD and b-axis along ND of the NPP samples was considerably higher than of the HPP samples, due to the NPP faster crystallization kinetics. For both polymers, the most influential processing parameters on the molecular orientation were the mold temperature and flow rate. The results indicate that, as the mold temperature increased, the characteristic molecular orientation of PP α-phase, with c-axis along RD and b-axis along ND, decreased. With increase in the flow rate an increase of the c-axis molecular orientation of the samples along RD was observed.

Resumo em Inglês:

Puducherry is a coastal region in India where the growth of Chaetomorpha antennina is very abundant on all marine concrete structures. Though the detrimental effect of this Macro algaeChaetomorpha antennina is secondary, its effect has to be ascertained. To know its effect, M20 grade concrete cubes were cast and kept in the coastal area where there is abundant growth of Chaetomorpha antennina and also laboratory simulation has been carried out. The basic mechanism by which Chaetomorpha antennina deteriorates concrete structures has been highlighted and also the detrimental effect on the algal grown concrete surface were ascertained using SEM, EDX and XRD. The result showed that there is sustainable effect by the marine algae on the concrete surface.

Resumo em Inglês:

The aim of this study was to determine the effect of variations in indentation load and time on the Knoop and Vickers hardness numbers (KHN and VHN) for enamel and dentin. Twenty molar teeth were divided into twenty enamel and twenty dentin specimens. Each specimen was tested using a Knoop or Vickers microhardness tester at different loads and times. The difference in hardness between the groups was analyzed with two-way ANOVA followed by a Tukey test. The results revealed that a difference of indentation time did not influence the microhardness number of enamel and dentin. The KHN values of enamel and the VHN values of dentin were affected by variation of test loads. Therefore, the tooth hardness number for different loads may not be acceptable for comparison.

Resumo em Inglês:

The use of cone and plate rotational rheology to characterize the flow properties of concentrated dispersion and extrusion methods to determine the rheological properties of pastes have become established rheometric techniques. Direct comparison between the results obtained from the two techniques has not previously been demonstrated. In this article the results of such a comparison using established experimental methods and associated analysis are reported. It is found that for most samples investigated the difference in the calculated values of shear stress at a shear rate of 5/s is <10%. Data for a series of slurries, composed of various solid fractions of lime waste, are reported over a shear rate of 0-10/s. The computed results for two techniques are shown to be, within the experimental error, identical over this shear rate range.

Resumo em Inglês:

Due to the complexity of controlling parameters in carburization, there has been relatively little work on process variables during the surface hardening process. This work focuses on the effects of the carburizing temperature and time on the mechanical properties of mild steel carburized with activated carbon, at 850, 900 and 950 ºC, soaked at the carburizing temperature for 15 and 30 minutes, quenched in oil, tempered at 550 ºC and held for 60 minutes. Prior carburization process, standard test samples were prepared from the as received specimen for tensile and impact tests. After carburization process, the test samples were subjected to the standard test and from the data obtained, ultimate tensile strength, engineering strain, impact strength, Youngs' moduli were calculated. The case and core hardness of the carburized tempered samples were measured. It was observed that the mechanical properties of mild steels were found to be strongly influenced by the process of carburization, carburizing temperature and soaking time at carburizing temperature. It was concluded that the optimum combination of mechanical properties is achieved at the carburizing temperature of 900 ºC followed by oil quenching and tempering at 550 ºC.

Resumo em Inglês:

Scrap tires are not considered harmful waste, but their stocking and disposal are a potential health and environmental risk. Properly controlled calcinations at high temperatures make tire combustion an interesting alternative due to its high calorific power, comparable to that of fuel-oil. Consequently, using them as an alternative combustible material in cement kilns makes it possible to give it a valuable use. However, it remains to be assured whether the impurities added to the clinker through these fuels do not affect its structure or properties.This paper shows the studies carried out on different clinkers under laboratory conditions with different levels of addition of scrap tire ashes, added by partially replacing traditional fuel in cement kilns.

Resumo em Inglês:

In this work, the degradation kinetics of calcium polyphosphate bioceramic was studied. Liquid state31P nuclear magnetic resonance (NMR), X-ray diffraction (XRD) and scanning electron microscope (SEM) were used to characterize the product. The in vitro degradation test was carried out at 37 ºC for up to 48 hours for both the simulation solution and the extreme solution. The ion concentrations were measured and analyzed by establishing a mathematical model referring to the chemical reaction kinetics. The results indicated that the degradability of calcium polyphosphate increased with the decrease of pH value, and the sample showed a rapid loss of ion concentration within the initial period of immersion followed by a slower loss ratio. The relationship between ion concentration and the degradation time coincided with Boxlucas model.

Resumo em Inglês:

Electrodeposition of polypyrrole films on aluminum from aqueous solutions containing p-toluene sulfonic acid and pyrrole was performed by cyclic voltammetry and galvanostatic technique. The influence of applied current density on the morphology of the films was studied by Scanning Electron Microscopy. The films displayed a cauliflower-like structure consisting of micro-spherical grains. This structure is related to dopand intercalation in the polymeric chain. Films deposited at higher current density were more susceptible to the formation of pores and defects along the polymeric chain than films deposited at lower current density. These pores allow the penetration of aggressive species, thereby favoring the corrosion process.

Resumo em Inglês:

Zinc based or doped ceramics have shown to be capable of increasing osteoblasts proliferation, biomineralization and bone formation. However, studies regarding the biological applications processes in ZnAl2O4 ceramic films are very scarce. For this reason, the objective of this in vitro study was to investigate the response of osteoblasts cells cultured onto ZnAl2O4 films. Our results showed a good biological response related to attachment and viability, with good cell morphology attached to the semi-spherical grains of the ceramic and the analysis of mineral-like tissue showed a high quantity of mineral deposited and organized as tiny spherical-like nodules attached to nanostructure surface of ZnAl2O4 material films. Based in our results, ZnAl2O4 films stimulated the bioactivity of osteoblasts cells and provide a microenvironment that favors cell differentiation and mineralization processes, suggesting their potential use as osteoconductive coating onto currently orthopedic and dental implants.

Resumo em Inglês:

The aim of this work was to study the influence of calcium carbonate nanoparticles in both tensile and impact mechanical properties of a polypropylene homopolymer. Four compositions of PP/CaCO3 nanocomposites were prepared in a co-rotational twin screw extruder machine with calcium carbonate content of 3, 5, 7 and 10 wt. (%) The tests included SEM analyzes together with EDS analyzer and FTIR spectroscopy for calcium carbonate, tensile and impact tests for PP and the nanocomposites. The results showed an increase in PP elastic modulus and a little increase in yield stress. Brittle-to-ductile transition temperature was reduced and the impact resistance increased with the addition of nanoparticles. From the stress-strain curves we determined the occurrence of debonding process before yielding leading to stress softening. Debonding stress was determined from stress-strain curves corresponding to stress in 1% strain. We concluded that the tensile properties depend on the surface contact area of nanoparticles and on their dispersion. Finally we believe that the toughening was due to the formation of diffuse shear because of debonding process.

Resumo em Inglês:

The aim of this work was to study the influence of calcium carbonate nanoparticles in crystallization process of polypropylene. Four compositions of PP/CaCO3 nanocomposites were prepared in a co-rotational twin screw extruder machine with calcium carbonate content of 3, 5, 7 and 10 wt. (%). The tests included SEM analyzes for calcium carbonate, differential scanning calorimetry (DSC) and wide angle X-ray diffraction (WAXD) for the nanocomposites. The results showed an increase in PP crystallization temperature and crystallinity degree, and a reduction in spherullites size. The formation of PP β phase was confirmed by DSC and WAXD results. Finally from DSC analyses under isothermal conditions it was confirmed that calcium carbonate nanoparticles have a nucleation effect in polypropylene crystallization process by reducing the half crystallization time and increasing the kinetic constant (k).

Resumo em Inglês:

Ni1-xZn xFe2O4 (x = 0 to 1) nanoparticles of size less than 9 nm were prepared by a chemical coprecipitation method which could be used for ferrofluid preparation. XRD, VSM and DTA-TG (STA) were used to study the effect of variation in Zn substitution and its influence on particle size, magnetic properties such as M S, H C and Curie temperature, as well as on the water content. ICP was used to estimate Ni, Zn and Fe concentrations. The average crystallite size (DaveXR) of the particles was found to decrease from 8.95 to 6.92 nm with increasing zinc substitution. The lattice constant (a o) increased with increasing zinc substitution. The specific saturation magnetization (M S) of the particles was measured at room temperature. Magnetic parameters such as M S, Hc, and Mr were found to decrease with increasing zinc substitution. Estimation of the water content, which varies the Zn concentration, plays a vital role for the correct determination of cation contents. The Curie temperature was found to decrease with increasing zinc substitution.