Resumo em Inglês:

Mechanical properties, morphology and nonisothermal crystallization of poly(3-hydroxybutyrate) (PHB) and blends of PHB and polystyrene (PS) were studied by tensile tests, scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). A two-phase structure composed by a PHB matrix and nearly spherical particles of PS was clearly noticed in SEM images. The presence of small amounts (0.5% to 3%) of amorphous PS affected the crystallinity of PHB, being more evident when high cooling rates were applied. The kinetics of nonisothermal crystallization was modeled according to Ozawa equation. The dependence of Ozawa parameters on temperature followed the same trend for PHB and PHB/PS blends; model parameters were found to be lower for the blends than for the neat PHB.

Resumo em Inglês:

The aim of this study was to evaluate the effect of different peak wavelengths (450nm, 468nm and 490nm) of experimental LEDs on hardness, elastic modulus, degree of conversion and temperature rise of a microhybrid resin composite – Venus® (Heraeus Kulzer). Hardness and elastic modulus were determined by nanoindentation technique (n=5), degree of conversion was measured by FTIR (n=5) and temperature rise was measured with a thermistor (n=30). Data were submitted to ANOVA and multiple comparisons tests (α=0.05). Mechanical properties and degree of conversion (p<0.001) were superior on the top surfaces of the specimens. 468nm showed the highest mechanical properties values. There was no statistical difference in the degree of conversion (p=0.51) and in temperature rise (p=0.06) among all LEDs. Hardness and elastic modulus were influenced by LED´s wavelength, whereas degree of conversion and temperature rise were not influenced.

Resumo em Inglês:

This paper discusses the influence of the flow of a fluid from the static regime to the turbulent in CO2 corrosion experienced by low carbon steel. A more comprehensive approach to CO2 corrosion implies taking the free flowing velocity and shear stress of the fluid and the surface roughness of the material into consideration. Low carbon steel samples in two different superficial finish conditions were used as the rotating cylinder electrode. The corrosion rate were determined by linear polarization at 25 °C in a 0.5 mol/L NaHCO3 solution purged with CO2 at 1 atm pressure in pH 7.5. The effect of superficial finish on CO2 corrosion in flow conditions was studied. The results obtained showed that the corrosion rate increases with flow velocity and is influenced by surface roughness.

Resumo em Inglês:

Thermal shock is one of the most severe conditions to which a refractory lining can be subjected to during its industrial application. Thus, there are several methods available for testing thermal shock damage resistance of refractories. Among them, a very common method is the quench test, which consists of quenching a hot refractory bar into water. After that a retained mechanical property is determined. Considering this, the aim of the work herein is to compare the thermal shock damage resistance between two specimen sizes among several materials. The dimensions 150 mm × 25 mm × 25 mm and 160 mm × 40 mm × 40 mm were used. The small bars are generally used for mechanical characterization in the refractory field (recommended by ASTM C1171-05). The large bars, on the other hand, are a requirement of DIN 196-1, which regards procedures for testing cement materials. Experimental results have indicated that the thermal shock damage is bigger for the large bars, as predicted by theoretical aspects. Although the size difference between the specimens was not so big, it was possible to observe the size effect using a statistical treatment. Five different castable formulations, of which three contained eutectic aggregates, were tested. The highest variation found in thermal shock damage resistance because of the size was about 15%.

Resumo em Inglês:

Environmental stress cracking (ESC) is one of the most important causes of polymer premature failure, occurring when a combination of mechanical load and an aggressive fluid is applied. The phenomenon is well know by polymer producers and product designers but its mechanisms are not very well understood. Although the ESC effects of many commercial polymers are well known, this type of failure in biopolymers were not studied yet. In the current work, the stress cracking behaviour of poly(3-hydroxybutyrate) (PHB) with 4,0 and 6,2% of hydroxyvalerate (HV) was investigated in injection-moulded bars under contact with sodium hydroxide (NaOH) solutions. The experiments were conducted using two different types of stress arrangements: (i) an ordinary tensile testing and (ii) a relaxation experiment. In both situations the injection-moulded bars were exposed to the NaOH solution and some testing conditions where varied, like the cross-head speed of the tensile test and the maximum load of the relaxation arrangement. The results showed that NaOH acted as a strong stress cracking agent for PHB, causing surface cracking and reducing significantly the mechanical properties. Catastrophic failure with an extensive surface damage was also observed by photographed and scanning electron microscopy (SEM) images. The magnitude of the effects increased with decreasing crosshead speed and increasing loading level.

Resumo em Inglês:

Nanocomposites of high-impact polypropylene resin and organosilane-functionalized nanotubes in halloysite clay were prepared with the introduction of peroxide to promote selective incorporation of the filler into the polypropylene phase of the matrix, with minor insertion into the EPR elastomeric phase, thus improving the stiffness while preserving the high toughness of the material. Silica composites were also prepared as standard filler. The effect of increasing load content on the morphological and mechanical properties of this material was evaluated by SEM and DMA. The content of the hexane-extracted fraction of these composites after processing was evaluated. Halloysite was well-dispersed in the matrix. Composites with 10% of filler and 0.5% w/w of dicumyl peroxide had increased stiffness and higher loss factor. An increase of the E’ was generated by halloysite addition, but there was a higher decrease in Tan delta. Studies using experimental planning as a tool enabled choosing appropriate amounts of DCP to obtain a high performance composite.

Resumo em Inglês:

This study presents experimental results on the behaviour of aluminium alloy metal structures and foams manufactured by lost-wax casting and using 3D printed components for internal structure definition. Results for tensile tests, metallurgical properties, surface quality and geometry tolerances were obtained and discussed. The analysis focused on development geometries, used for adjusting manufacturing parameters and prototype geometries intended for geometrical and mechanical validation. The results are indicative of the viability of the method for producing foam structures suitable for mechanical loading.

Resumo em Inglês:

Biodiesel is a fuel renewable, biodegradable and environmentally correct fuel, which can be obtained from the esterification reactions, transesterification and pyrolisis. Montmorillonite is a clay mineral of the smectite group and are of great interest for industrial processes such as catalysis and adsorption. Acid activation of clay minerals is one of the most effective methods proposed to produce active materials. In this work, montmorillonite clay was treated with H2SO4 in different concentrations (0.2 – 0.8 mol L–1), characterized by X-ray diffraction (XRD), infrared spectroscopy (FT-IR) and applied in the catalytic esterification of oleic acid. The results reveal that the clay treated with aqueous solutions 0.8 mol L–1 H2SO4 shows promising catalytic activity toward the studied reaction, with maximum conversion of oleic acid of 65% at 30 °C.

Resumo em Inglês:

Electron magnetic resonance (EMR) spectra of gadolinium-doped barium titanate (BaTiO3) have been studied at room temperature for gadolinium concentrations between 0.20 and 2.00 mol%. The results suggest that the Gd3+ ions occupy substitutional sites, replacing the Ba2+ ion, that the electron magnetic resonance linewidth increases with increasing gadolinium concentration, and that the range of the exchange interaction between Gd3+ ions is about 0.98 nm, of the same order as that of the same ion in other host lattices, such as strontium titanate (SrTiO3), strontia (SrO), quicklime (CaO), magnesia (MgO) and zircon (ZrSiO4). The fact that the electron magnetic resonance linewidth of the Gd3+ ion increases, regularly and predictably, with Gd concentration, shows that the Gd3+ ion can be used as a probe to study, rapidly and non-destructively, the crystallinity and degradation of BaTiO3.

Resumo em Inglês:

In improving the corrosion and hardness proprieties of ferritic stainless steel, the use of protective coatings becomes an interesting alternative. In this study, a carbon layer was deposited on AISI 430 by electrodeposition using N,N-dimethylformamide with the addition of an organic dopant as the electrolyte. The AISI 430 stainless steel was pretreated by anodization aiming to optimize the film anchoring. The obtained films were characterized by atomic force microscopy, by scanning electron microscopy and by optical interferometry. The microstructural characterization of the films was obtained by Raman Spectroscopy. The corrosion resistance was evaluated by open circuit potential and by potentiodynamic polarization. The friction test and the scratch test were performed to evaluate the mechanical properties. The Raman spectroscopy showed the presence of an amorphous carbon film. The films improved the corrosion resistance of stainless steel. In addition, on the wear analysis the coating showed a good adhesion on the substrate.

Resumo em Inglês:

Calcium sulphoaluminate cement (CSAC) is an attractive candidate for biomedical applications due to its appropriate mechanical properties and high calcium content. In vitro bioactivity and hemocompatibility of calcium sulphoaluminate cement were assessed. The cement was prepared from a mixture of calcium sulphoaluminate (CSA) clinker, gypsum and water. Cement samples were immersed in a simulated body fluid (SBF) at 37 °C for different periods of time (7, 14 and 21 days). The analyses of these samples after their immersion in SBF revealed the formation of a bonelike apatite layer on their surface. The hemolytic activity was assessed by measuring hemoglobin released from erythrocytes when they were exposed to the cement. The results showed that the cement is hemocompatible.

Resumo em Inglês:

In this work the effects of two different cyclic heat treatments (traditional route and new-designed route, named as Route 1 and Route 2, respectively) on microstructure and mechanical properties of Ti-V microalloyed steel were investigated. The results showed that the mean grain size initially decreased on execution of 1-cycle (~13.9 μm) and then remained almost constant during the subsequent cycles for Route 1. By contrast, the mean grain size decreased continuously with cyclic numbers and reached ~4.6 μm at 7-cycle for Route 2. For Route 1, with cyclic numbers UTS decreased continuously and AKU kept fluctuating due to the accumulation effect of temper softening and continuous fluctuation of RD (relative differences of grain sizes), respectively. For Route 2, the continuing decline of UTS with cyclic numbers could be ascribed to the increase of mean complex carbide size, while the AKU underwent a process of increasing and then decreasing with cyclic numbers and reached the maximum (~183 J) at 3-cycle as a result of joint influence of mean grain size and proeutectoid ferrite proportion.

Resumo em Inglês:

In the present work, the synthetic route to obtain crosslinked polyethylene (PEX) was studied using vinyltrimethoxy silane (VTMS) as crosslink agent and commercial polyethylene (HDPE and LLDPE). Materials were processed with increasing amounts of VTMS (2.5, 5.0 and 7.5 wt.%). After insertion of silane onto polymer chain in solid state, samples were molded by compression. Gel content was used to measure the extension of crosslinking. Melting temperature and degree of crystallinity were evaluated using differential scanning calorimetry (DSC). The microstructure of the starting polyethylene was correlated with the effectiveness of crosslinking and the resultant thermal and mechanical properties of the PEX. Hydroxylated liquid polybutadiene (HLPB) was employed to improve crosslink efficiency, as well as mechanical properties of the material.

Resumo em Inglês:

In this work, plasma carburizing of sintered pure iron at low temperature was investigated. Samples were carburized under a dc abnormal glow discharge in two mixed atmospheres (5%CH4 + 95%H2 and 20%CH4 + 80%H2) at 500 °C and 700 °C for 3 and 6 hours. The influence of these parameters was investigated by Scan Electron Microscopy (SEM), X-ray Diffraction (DRX), Raman spectroscopy and microhardness measurements. There is a correlation between temperature and layer morphology, and a layer of polycrystalline cementite was obtained at 500 °C and 700 °C on a ferrite substrate. Furthermore, the carburized layer thickness increased with an increase in the treatment time and the methane percentage. The topography is very dependent on the treatment temperature.

Resumo em Inglês:

The mechanical properties of aluminum alloys are strongly dependent on the thermo-mechanical process so, the strain ageing behavior of 7075 Al-alloy was investigated in this study. A set of test pieces was solution heat treated at 480 °C for 2 h, water quenched (SHTWQ) then pre-strained for 8% in tension. The test samples were aged at 140 °C for 0.5, 1, 2, 3, 4, 6, 8, 10, 12, 24, 48, 72 and 96 h in a furnace. The other set of test samples were solution heat treated at 480 °C for 2 h, quenched in sand (SHTSQ) then pre-strained for 8% in tension. They were also aged at 140 °C for same intervals. The effect of strain ageing, on the mechanical properties of Al-alloy, was investigated by mean of hardness, and tensile tests. The results shown that, the quenching rate after solution heat treatment, ageing time and temperature, as well as pre-strain, play a very important role in the precipitation-hardening associated with ageing process of the 7075 Al-alloy.

Resumo em Inglês:

The aim of this work was to study the micro-abrasive wear resistance of an API 5L X-70 microalloyed steel plasma nitrided under different conditions of time and temperature. Pulsed DC plasma nitriding experiments were performed under a treatment atmosphere of 10%N2 + 90%H2, at temperatures of 410, 440 and 470 °C and for nitriding times of 1, 3 and 5h. The results show that plasma nitriding performed at 440 °C and 1h led to the formation of a compound layer constituted mainly of ε-Fe2-3N nitride and a diffusion zone with large needle-like nitride, offering the highest wear resistance. The amount of γ’- Fe4N phase was found to increase with the plasma nitriding time, decreasing the wear resistance of the material.

Resumo em Inglês:

This paper describes the feasibility of using direct current electrical resistivity measurements to evaluate AISI 304 austenitic stainless steel sensitization. ASTM A262 – Practice A and double loop electrochemical potentiodynamic reactivation (DL-EPR) tests were performed to assess the degree of sensitization (DoS) qualitatively and quantitatively, and electrical resistivity (ER) was measured by the four-point direct-current potential drop method. The results indicate that the DoS increases rapidly while the ER decreases gradually in response to increasing sensitization. Thereafter, the two parameters tend to remain approximately constant. This behavior may be due to the rapid increase in the volume fraction of M23C6 precipitates over a sensitization time of 4 to 6 hours, thereafter remaining relatively constant. The ER results, which were corroborated by other techniques used in this study, confirm the promising potential of this property to monitor the sensitization phenomenon in AISI 304 steel.

Resumo em Inglês:

Thin nitride and titanium dioxide films were produced using an innovative technique called cathodic cage depositon. Uniformity, three-dimensionality and high rate deposition are some of the advantages of this technique. In this study we discuss the influences of temperature, treatment time and gaseous atmosphere on the characteristics of the deposited films. The TiN (titanium nitride) and TiO2 (titanium dioxide) films were produced using a high deposition rate of 2,5 µm/h at a work temperature and pressure of 400°C and 150 Pa respectively. EDS technique was used to identify the chemical composition of the thin film deposited, whilst Raman spectroscopy indicated the phases present confirmed by DRX analysis. The thickness of the deposited films was studied using electron microscopy scanning. The results based on the deposition parameters confirm the great efficiency and versatility of this technique, which allows a uniform three-dimensional film deposition on any material without the appearance of stress. Compared to other techniques, cathodic cage deposition enables deposition at lower temperatures and higher pressures.

Resumo em Inglês:

Aluminium (Al) samples were nitrided in 13.56 MHz radiofrequency (RF) discharge of 70:30 vol.% Ar:N2 mixture at substrate temperature of 400 °C and RF power of 300 W for different fill pressures and treatment times. The nitrided samples were then characterized for their structural and mechanical properties using x-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDS), and Vickers micro hardness testing. XRD peaks (110), (111) and (200) of aluminium nitride (AlN) and their downshift confirmed the nitride formation together with nitrogen diffusion. The metastable cubic phase (c-AlN) shows texture growth and re-orientation dependent on fill pressure and treatment time. SEM micrographs showed the surface morphology with micro-pores. EDS results showed that the nitrogen content was significantly increased with nitriding time, along with the removal of oxides. Vickers hardness of the Al surface was increased more than thrice for 30 hours nitriding.

Resumo em Inglês:

In this study, ZK60 magnesium alloy strips were produced by twin roll casting (TRC) and then subjected to warm rolling at the temperature of 300 °C and 350 °C. Rolled sheets related to different rolling reductions were prepared after sequential warm rolling with the rolling speed of 5 m/min. Microstructures, texture, hardness, tensile properties of the rolled sheets with different rolling reductions were studied experimentally. It has been found that grain refinement occurs actively during the warm rolling. Also, high density of shear bands were observed in the rolled sheets. The warm rolling sheet presents strong (0002) basal texture. In addition, the increase of the rolling reduction results in the improvement of the mechanical properties.

Resumo em Inglês:

Lead (II) sulfide (PbS) were synthesized by sonochemical method and crystals with cubic structure exhibit aggregated nanoparticles with size in the range of 50-100 nm. Commercial Poly(methyl methacrylate) (PMMA) containing the PbS nanoparticles (PbS-NP) exposed to gamma irradiation were investigated and both the viscosity-average molar mass (Mv) and degradation index (DI) values were measured. Ours results showed decreases in molar mass when the systems were gamma irradiated, i. e., random scission effects that take place in the main chain. On the other hand, DI results showed that the addition of PbS-NP at 0.3 wt% into the PMMA matrix decreased 100% the number of main chain scissions. Results about the free radical scavenger action of the PbS-NP were obtained by use of 2,2-diphenyl-1-(2,4,6-trinitrophenyl)-hydrazyl radical (DPPH) and are discussed in this study. Analysis of infrared spectra, refraction index, mechanical, and thermal properties showed influence of the PbS-NP in the physical behavior of PMMA.

Resumo em Inglês:

A characterization of the linear thermo-viscoelastic behaviour of a gap-graded bituminous mixture with SBS-polymer modified bitumen and RAP aggregates is presented in this paper. A comparison was made, in terms of their viscoelastic behaviour, between this innovative mixture and two commonly used well-graded base-course French mixtures made with pure bitumen. The materials were also compared in terms of viscous dissipated energy. Complex modulus tests on cylindrical samples were performed for each mixture. The viscoelastic behaviour of the materials was modelled using the 2S2P1D (2 springs, 2 parabolic elements, 1 dashpot) constitutive model which was developed in the Laboratory of Civil Engineering and Construction (LGCB) of the ENTPE, University of Lyon. The tests results allowed validating the time-temperature superposition principle for the studied mixtures. Experimental and modelled complex modulus (|E*|) master curves were built for each material. The gap-graded mixture was found to present higher stiffness values at low frequency/high temperature conditions, lower viscous behaviour and lower values of viscous dissipated energy compared to the conventional mixtures. Complex modulus tests were also carried out on the polymer modified bitumen of the gap-graded mixture. A link between the viscoelastic behaviour of both binder and mixture could be established thanks to the SHStS transformation developed by the ENTPE team.

Resumo em Inglês:

Recent studies involving the use of calcium aluminate cement (CAC) as a biomaterial are based on commercial products. Improvements can be attained by investigating the properties of their crystalline phases in order to better design the material's composition. Therefore, calcium aluminate phase samples immersed in simulated body fluid (SBF) solutions prepared according to Kokubo’s (KSBF) and Rigo’s (RSBF) methodology had their pH evaluated. The surfaces of these samples were analyzed by SEM, EDX and XRD techniques. The treatment with KSBF did not favor the precipitation of calcium phosphate phases on the surface of CAC phases. On the other hand, in RSBF solution, the pH value attained was higher than for the KSBF one and magnesium phosphate was identified on the surface of CA, C3A and C12A7 samples. Only for CA2, the optimal precipitation condition was attained in RSBF and a surface layer of the hydroxyapatite was detected. Based on its ability of stimulating hydroxyapatite deposition in SBF and other properties, CA2 can be eligible as the most suitable composition for biomedical purposes.

Resumo em Inglês:

Duplex Stainless Steels (DSS) have excellent corrosion resistance properties and poor wear resistance. Plasma nitriding is used to increase the surface hardness, by nitrogen diffusion into the crystal lattice, and to improve wear resistance. In this study, DSS samples were plasma nitrided at temperatures between 350 °C and 500 °C for 240 minutes under an atmosphere of 75% N2 + 25% H2 . Aparent diffusion coefficients, activation energy and pre-exponential constant were calculates using the first law of Fick for each material phase, austenite and ferrite. Nitrogen diffusion in both phases appears to be similar. The layer thickness on the alpha phase is greater than in the gama phase. Nevertheless, the difference on the layer thickness in both of the phases is small. From these results, it was proposed a model of nitrogen diffusion into a two-phase stainless steel to explain the morphology of the interface between the layer and the substrate.

Resumo em Inglês:

Aragonite is a metastable polymorph of calcium carbonate found in mollusk’s shells, appearing in tiles and prismatic columns, cemented in a protein matrix - mainly proteins - that acts as a framework on which the aragonite is nucleated forming nacre, besides selecting the morphology of the nucleated cristaline phase. The presence of the mineralyzing organic matrix may affect osteoinductive properties of biogenic aragonite, hypothesis tested by combinated tests, comparing viability and bioactivity of biomineralizated aragonite and nacre. Bioactivity was observed by deposition of Ca-P (presumably calcium phosphate) on the surface of samples immersed in Simulated Body Fluid; biocompatibility was verified by adhesion with VERO cells; cytotoxicity and alkaline phosphatase activity assays were performed with human adipose stem cells (hASC). Samples were characterized by scanning electron microscopy and X-ray diffraction. Both materials showed similar behaviour on bioactivity assay; in contrast, exhibited different behaviours in the presence of hASC.

Resumo em Inglês:

Structured materials composed of α-Al2O3 spheres covered with a porous and thin layer of MgAl2O4 or ZnAl2O4 were obtained. The innovative coating method developed consists in the formation of a precursor gel of MgAl2O4 or ZnAl2O4 by citrate-nitrate combustion method. The alumina spheres are submerged in this gel and then submitted to a drying process in vacuum and to calcinations with N2 and N2/O2. SEM results showed that a very rough and porous layer uniformly covers the spheres. The thickness of the layer reaches the maximum value of 16 µm in the sample coated with two layers of ZnAl2O4. XRD results confirmed the MgAl2O4 or ZnAl2O4 spinel formation in the layered material. The structured materials were used as Pt catalysts supports, showing a good catalytic activity in the n-butane dehydrogenation reaction.

Resumo em Inglês:

Novel structures of Y3Al5O12: Eu3+ (denoted as YAG: Eu3+ for short) nanobelts were fabricated by calcination of the electrospun PVP/[Y(NO3)3+Eu(NO3)3+Al(NO3)3] composite nanobelts. X-ray powder diffraction (XRD) analysis showed that YAG: Eu3+ nanobelts were cubic in structure with space group Ia3d. Fourier transform infrared spectroscopy (FTIR) analysis manifested that pure YAG: Eu3+ nanobelts were formed at 900 °C. Scanning electron microscope (SEM) analysis indicated that the YAG: Eu3+ nanobelts have coarse surface. The width and thickness of YAG: Eu3+ nanobelts were ca. 3.25 µm and ca. 220 nm, respectively. Fluorescence spectra analysis revealed that YAG: Eu3+ nanobelts emitted the main strong emission centering at 592 nm under the ultraviolet excitation of 235 nm, which was attributed to 5D0→7F1 of Eu3+, and the optimum doping molar concentration of Eu3+ ions was 5%. CIE analysis demonstrated that the emitting colors of YAG: Eu3+ nanobelts could be tuned by adjusting doping concentration of Eu3+. The possible formation mechanism of YAG: Eu3+ nanobelts was also proposed.

Resumo em Inglês:

The H2S corrosion resistance of API 5L X80 steel and its welded joint (WJ) were evaluated using the weight loss method in a 5%wt brine solution and different corrosive environments based on a sodium thiosulphate solution (10–3 and 10–2 mol/l). The weight loss method, scanning electron microscopy (SEM) and X-ray diffraction analysis (XRD) were applied to measure the effects of different H2S concentrations and pH (3 and 5) on the corrosion process and formation of corrosion product films. The results showed that the obtained corrosion rate and corrosion product films for both API 5L X80 steel and its submerged arc welding (SAW) WJ depend on the pH, H2S concentration and metal surface microstructural characteristics. The corrosion product film consists of two layers with different morphologies. The heat affected zone (HAZ) shows severe localized corrosion attack relative to the base metal (BM) and weld metal (WM), which is attributed to the microstructural characteristics of this region.

Resumo em Inglês:

This paper provides a literature review and analysis of the various influencing aspects related to the use of recycled aggregates, sourced from construction and demolition waste, on the chloride ion penetration of concrete. A statistical analysis on the effect of incorporating increasing amounts of recycled aggregates of different type, size, and class on the chloride ion migration and total charge passed of concrete is also presented. The paper also presents the relationship between these properties and the corresponding compressive strength. The results show strong correlations between these parameters, which are independent of other aspects related to recycled aggregate use and made it possible obtaining a relationship between the values acquired via NT Build 492 and ASTM C1202.