Abstract in English:The tunable Tc region of MnSb alloy (44 - 49 % at. Sb) was analyzed using OM, VSM, DSC, XRD, EDS and XRF characterization techniques. Thermal and magnetic analysis suggests the existence of a non reported irreversible reaction on heating, compatible to a reverse peritectoid transition MnxSb ➔ Mn2Sb + Mnx'Sb.
Abstract in English:In this study, chitosan hydrogels were produced with 0, 2, 4 and 6 wt% of cellulose nanocrystals (CNC) using hexahydrate zinc nitrate (Zn(NO3)2.6H2O) as a catalyst for chitosan crosslinking reaction. CNC´s size was estimated by dynamic light scattering (DLS) and surface charge by zeta potential. Hydrogels were characterized by rotational rheometer, swelling test, uniaxial compression test, in vitro degradation, scanning electron microscopy (SEM) and microtomography. Results showed that zinc nitrate and CNC addition did not influence mechanical properties, degradation, and morphology of the hydrogels. However, zinc nitrate decreased 36.54% of the gel time and 41.37% of the swelling degree, and increased the crosslinking degree of the chitosan hydrogels, proving not only its catalytic effect but also its participation in the crosslinking reaction. Porosity was slightly reduced after addition of zinc nitrate and incorporation of CNC. In the mechanism of crosslinking reaction, a competition between CNC and zinc nitrate was observed.
Abstract in English:The development and utilization of new energy sources has been extensively studied in the world. Here, we report the development of flexible self-supported metal-free electrodes based on non-oxidized graphene multilayer (MLG) paper containing the lead iodide nanoparticles (PbI2-NPs). The PbI2-NPs was obtained and characterized by X-ray diffraction (XDR) and Raman spectroscopy. Supercapacitor containing the PbI2-NPs in MLG electrodes was fabricated by a simple method and characterized using atomic force microscopy (AFM), cyclic voltammetry (CV) and galvanostatic charge-discharge techniques. The results show a flexible supercapacitor fashion reaching capacitance values of 154 F/g with high prospects in electronic area. Energy and power densities obtained for the pure MLG supercapacitor were 3.40 µWh cm-2 and 0.73 mW cm-2, respectively. Regarding to PbI2-NPs/MLG capacitor the energy and power density obtained were 3.50 Wh kg-1 and 1.10 kW kg-1. The results herein presented open the possibility to new energy storage devices using PbI2-NPs and MLG flexible supercapacitor configuration.
Abstract in English:We evaluated solid-state sensors (MOS) manufactured using nanostructured tin oxide (SnO2) obtained by different synthesis methods for selectivity, response and repeatability at different operating temperatures and methane concentrations. In addition, Zeolite 13X pellets were placed in front of the sensors to improve CH4 selectivity in the presence of CO2. The palladium doped sensor (1.4% w/w) showed the highest sensitivity at 80 ºC (83%) and shorter response times (16 s), whereas non-doped sensors exhibited the best sensitivity (78%) and response times (14 s) for those with smaller particle size (8 nm). Zeolite 13X pellets proved to be efficient at making the sensor more selective for CH4 in the presence of CO2.
Abstract in English:Hybrid solar cells show an increasing number in researches due to its low cost and easy of production. They are composed by and organic material and a semiconductor oxide. The aim of this paper was to synthesis and characterize zinc oxide by coprecipitation and apply it in a hybrid solar cell that uses a P3HT/P3OT copolymer as charge carrier. The cell was assembled in "sandwich" form using FTO/ZnO/P3HT-P3OT as work electrode, (Pt/FTO) as conter electrode and I/I-3 redox couple as electrolyte. Through the X-ray diffractogram the formation of a single ZnO wutzite hexagonal phase was observed. The morphology obtained for the oxide was spherical. The results of photochronoamperometry showed current density values of jP3HT/P3OT =0.55 mA.cm-2 for the cell in the presence of the copolymer and the curve jxV showed an efficiency of 0.16% for the studied cell, demonstrating that the polymer was a satisfactory sensitizer.
Abstract in English:Zinc is an important chemical element in many metabolic mechanisms at low concentrations, but can be toxic when administrated in doses higher than 500 µg·g-1 or 3 mg·L-1. This metal has been detected in many aquatic environments due to several industry activities and swine manure effluents. Thus, the contaminant removal of water and wastewater has been a major challenge. Many processes are applied and evaluated in an attempt to removal zinc found in environment, such as adsorption. In the present study Fe3O4@C core-shell nanoparticles were synthesized and used to adsorb ionic zinc species in aqueous solutions. The core-shell nanoparticles exhibited excellent zinc removal capacity, with a maximum efficiency equal 65% where applied in an aqueous solution containing 10 mg·l-1 of this ionic metal.
Abstract in English:Dye-sensitized solar cells (DSSC) have received much attention as an alternative to silicon-based solar cells, due to various advantages. Zinc oxide (ZnO) is an n-type semiconductor employed as photoanode on DSSC. The decrease of charge recombination is an efficient strategy capable of improving the photovoltaic performance of the device. In this perspective, Nb2O5 was added on ZnO solar cells. The oxides were characterized by the X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR) and X-ray fluorescence (XRF). The photovoltaic parameters were obtained through J-V plots and photocronoamperometry. The results showed that the niobium oxide obtained presented orthorhombic crystal structure and DSSC with the addition of niobium oxide showed better efficiency, of 1.42% when compared the device with only ZnO.
Abstract in English:Civil construction seeks to increase the useful life of the facades of buildings. Installing a ventilated facade is one way to accomplish this due to aesthetic and technical advantages. Ceramic tiles are the main products used as the covering. To the back face of a tile, a bidirectional screen of glass fiber is adhered using epoxy resin. This set forms a composite for security reasons. During the last decade, there has been an increase in the substitution of composites of synthetic fibers with those of natural fibers. The present work compares the fire-resistant behavior of glass fiber with that of jute fiber applied to ceramics installed in ventilated facade. The following conjoint composites were produced: glazed porcelain tile, epoxy resin, glass fiber and jute fiber screens. In this work, it was verified that the jute fiber did not present advantages regarding the exposure to fire in comparison with the glass fiber.
Abstract in English:Degradation of mechanical properties and durability of reinforced concrete structures occur when they are subjected to fire situations, depending on the characteristics of the material, fire duration and the ways of fire extinguishing. Mechanical properties such as compressive strength, tensile strength and elasticity modulus are some examples of typically altered characteristics in concrete during high temperature exposure. Nevertheless, little is known about the advance of the carbonation front on fire-damaged concrete, which is a characteristic directly related to the durability of the structural system. For this purpose, the carbonation front was evaluated in specimens with characteristic strengths of 20 MPa and 35 MPa, subjected to high temperatures (200 °C, 500 ºC and 700 ºC) and different types of cooling (fast and slow). It was observed that the concrete durability is harmed by exposure to high temperatures and fast cooling. However, advance of the carbonation front was not verified in slow cooling situations.
Abstract in English:The use of firewood ash waste for the production of electric porcelain can represent an important technological and environmental alternative for the final disposal of this abundant solid waste material. This work aims to study the effect of replacing of sodium feldspar (albite) for firewood ash waste in electrical siliceous porcelain formulation. The firewood ash waste was obtained from a ceramic plant located in south-eastern Brazil (Campos dos Goytacazes-RJ). For this purpose, siliceous porcelain formulations containing up to 4.2 wt.% of firewood ash waste as a replacement for sodium feldspar were prepared. Disk specimens were pressed and fired at 1300 °C using a fast-firing cycle. The porcelain specimens were tested to determine their technical properties (linear shrinkage, water absorption, apparent porosity, apparent density, tensile strength, and electrical resistivity). The results indicated that test specimens containing up to 4.2 wt.% of firewood ash waste have high potential for use as electrical siliceous porcelain material. Thus, an alternative use of firewood ash waste is proposed, which can be converted into economic gain and also contribute for the environmental sustainability.
Abstract in English:Lanthanum gallate with partial substitutions for strontium and magnesium shows higher ionic conductivity than traditional ionic conductors such as yttria-stabilized zirconia (8YSZ), and has been considered for application as solid electrolyte and electrode in Solid Oxide Fuel Cells operating at intermediate temperatures (500-700ºC). Parallel to the development of new solid electrolytes, improvement of the already known electrolytes has been one goal. In this work, the effects of adding 8YSZ to La0.9Sr0.1Ga0.8Mg0.2O3-δ (LSGM), on the microstructure and electrical performance were investigated. Compound electrolytes consisting of up to 20 wt.% 8YSZ were prepared by solid state reactions. Sintered pellets with up to 10 wt.% 8YSZ achieved near full density after sintering at 1450ºC and reduction in the fraction of impurity phases. Addition of 8YSZ promoted grain growth to LSGM. The higher ionic conductivity was obtained for 1 wt.% 8YSZ addition with slight decrease of the apparent activation energy.
Abstract in English:Waste incorporation into clay ceramic is a worldwide accepted recycling procedure for environmentally friendly reuse of spent industrial materials. In the present work a clay ceramic from the city of Campos dos Goytacazes, Brazil, was, for the first time, investigated with different amounts, up to 10 wt%, of a solid waste generated from the “Sulfatreat” natural gas treatment process. Both the waste and the incorporated ceramic were characterized by X-ray fluorescence and X-ray diffraction as well as vibratory sieving, gas chromatography and sedimentation method. Ceramic samples were prepared by uniaxial pressing at 18 MPa and sintered at 850°C. Physical and mechanical properties of these ceramics such as linear shrinkage, apparent density, water absorption and flexural strength were evaluated. Microstructure of the incorporated ceramics was analyzed by optical microscopy. The results showed that, within the standard deviation, the linear shrinkage and apparent density of the clay ceramic were not affected by the waste incorporation. However, the water absorption is benefitted, by decreasing above 5 wt% incorporation, while the flexural strength is impaired for any incorporated amount. Porosity and larger waste particles observed in microstructure are proposed reasons for these advantages and shortcomings.
Abstract in English:The development of ceramic membranes with different geometries and compositions extends the possibilities of industrial applications, inducing advantages in terms of increased permeability, membrane area by volume module and chemical, thermal and mechanical resistance. The use of low-cost raw materials is a trend that has grown in scientific research. The aim of this work is to prepare membranes with hollow fiber geometry from alumina and residue of quartzite, by the technique of immersion precipitation in distilled water from a mixture of ceramic mass with a solution of polyethersulfone and, synthesized in temperatures of 1100 ºC to 1500 °C. The hollow fiber membranes were characterized by chemical analysis, X-ray diffraction, particle size distribution, scanning electron microscopy, apparent porosity, flexural strength and permeated water flow by the membranes. The results indicated that the sintering temperature has direct influence on the formation of the mullite phase, and the properties of apparent porosity and permeate flow. The higher the sintering temperature (1400-1500 ° C) increase the formation of the mullite phase, the lower the porosity, as well as the lower the permeate water flow in the membranes. However, there was increase in flexural strength in the hollow fiber membranes with high temperature.
Abstract in English:The Amazonian region of South America is known for its diversified number of plants from which food, medicine, wood and fibers have, since long time, been produced by local natives. A typical example is the guarumã (“guaruman”as suggested English spelling) scientifically identified as Ischinosiphon koem, an abundant plant found in the low lands alongside rivers of the state of Para in Brazil. Fibers extracted from the stem of the guaruman are used in ropes and baskets owing to their strength. In the present work, the possibility of applying guaruman fibers as reinforcement of polymer matrix composites is, for the first time, investigated. Amounts up to 30 vol% of continuous and aligned fibers were incorporates into epoxy matrix composites. Density measurements disclosed the guaruman to be one of the lightest natural fibers. Tensile tests indicate that the guaruman fiber addition was able to improve the composite elastic modulus. However, no significant change was found in the ultimate strength, total strain and resilience. On the other hand, a cost-effective analysis revealed a substantial reduction of ~29% in the epoxy composite price due to the incorporation of fibers. Preliminary ballistic evaluation disclosed a potential for application of guaruman epoxy composites in multilayered armor.
Abstract in English:The geopolymer binder is a relatively new class of inorganic binding material of elevated mechanical strength and good chemical properties. This can be produced using clay minerals or byproducts of the industrial processes, such as metakaolin, fly-ash and blast furnace slag. In this work, geopolymers were produced by alkaline activation of a Brazilian fly-ash with simple and compound solutions (NaOH and NaOH + Na2SiO3). The hardened specimens presented values of the mechanical strength close to 48 MPa when the activator used presented SiO2/Na2O ration close to 1.0 after 24 h of curing at 65 ºC. The increase of the temperature to 90 ºC favored the reactions of the N-A-S-H gel (geopolymer) formation and compression strength increased to values close to 90 MPa after 24 h. It has been found that physical properties, such as density and porosity, varied when different SiO2/Na2O rations was present in alkaline solutions. Time, temperature of curing and particle size of fly-ash modified the mechanical and physical proprieties of hardened inorganic binder. Was observed the diffraction phases related to zeolitic phases and carbonate new bands of absorption were related to reactions of Na2O in excess with atmospheric CO2. The variation of SiO2/Na2O modified the microstructural of the hardened specimens.
Abstract in English:Polyethylene (PE) is a polymer that has a low adhesion property, which is related to its low surface energy. However, the plasma treatment aims the modification of the surface properties without affecting the polymer structure. In this sense, the objective of this work was to prepare biocomposite films via flat extrusion with Green PE matrix and Expanded Vermiculite Clay (VMT), contents of 1, 3 and 6%. The films were treated by plasma in two different ways: Oxygen (O2) atmosphere (Condition 1); and Argon/Hydrogen (Ar/H2) atmosphere followed by a plasma treatment under O2 atmosphere (Condition 2). The results of the contact angle measurements indicated that the incorporation of VMT and the conditions used for plasma treatment increased the films wettability due to the hydrophilic character of VMT and also as a consequence of the plasma. In contrast, the XRD diffractograms indicated that there were no significant changes in the films structure.
Abstract in English:The energy absorption in ballistic tests of alumina-ultra high molecular weight polyethylene (UHMWPE) composites with 60, 80 and 90 wt% alumina submitted to gamma radiation doses of 25, 50 and 75 kGy was investigated. The ballistic tests were carried out at subsonic speed using a compressed air system. The results showed that the composite with 80% alumina irradiated with 50 kGy yields the best ballistic results. Gel content, Differential scanning calorimetry (DSC) and X-ray diffraction (XRD) results showed that this composite is the one with the highest concentration of crosslinks and the lowest volume fraction of amorphous UHMWPE. Scanning electron microscopy (SEM) images of the same composite showed a high pullout, suggesting that gamma irradiation increases the adhesion between alumina and UHMWPE.
Abstract in English:This work aims investigate the changes on tensile properties of biocomposites obtained by addition of carnauba wax and coconut fibers in a corn starch matrix. The influence of carnauba wax and coconut fibers contents on tensile strength, modulus of elasticity and elongation at break was studied using a response surface methodology. A central composite design based on three levels of carnauba wax content (0, 10 and 20 %) and coconut fibers content (0, 10 and 20 %) was elaborated. Empirical models were obtained to describe these properties as function of coconut fiber and carnauba wax contents. Optical microscopy was carried out to visualize the dispersion and interactions between coconut fibers, carnauba wax and starch matrix in the biocomposites. In presence of carnauba wax, the biocomposite became more compact and with a better interaction between the corn starch-based matrix and coconut fibers reinforcement. It was observed that tensile strength and modulus of elasticity rise with the increase in carnauba wax and coconut fiber contents. Moreover, the elongation at break increases with the addition of coconut fiber, while a decrease in the values of this property occurs with the addition of carnauba wax.
Abstract in English:A comparative study was conducted for three natural rubber (NR) composites: one containing raw jute fibers, one containing bleached jute fibers, and one containing cellulose nanocrystals (CNCs). The composites were prepared by adding each filler at 5 or 10 phr to the latex before chemical coagulation, and the composites were processed in a two-roll mixing mill. The mechanical, thermal, and vulcanization properties of the prepared composites were then determined. The NR stiffness increased with increasing fiber content, particularly when bleached fibers were added, as evidenced by the increased elastic moduli, maximum torques, glass transition temperature, and crosslinking density. Scanning electron microscopy showed agglomerates in the composite with 10 phr CNCs, which led to poorer mechanical performance compared to that of the bleached fiber-reinforced composite (10 phr). On the other hand, the addition of CNCs to the NR increased the cure rate index, thereby significantly advancing the optimum vulcanization time.
Abstract in English:The effect of the nitrogen content in the shielding gas and its effect on temperature distributions at the welded zone of thin sheets of duplex stainless steel have been evaluated. The duplex stainless steels have many features due to unique microstructural combination of austenite and ferrite grains. The phase balance can be easily shifted depending on the welding parameters. Two sheets were welded using pure argon and pure argon plus 2% of nitrogen as shielding gas. The thermal profile had shown that N2-supplemented shielding gas lead to higher peaks of temperature using similar welding parameters. Microstructural examination showed that the austenite phase in the weld increased with the presence of nitrogen in the shielding gas. The added nitrogen promoted primary austenite formation and slightly increases the microhardness at the solidified zone. Microhardness mapping and metallographic imaging presented information about microstructures, confirming the formation of secondary phases during thermal cycle in the temperature range 850 °C and 950 °C. Control of ferrite amounts in the welds is essential mainly to improve mechanical properties and corrosion resistance of welding zones.
Abstract in English:The objective of this work was to use tungsten and lignin as precursors to obtain a metal-organic composite tungsten-lignin (W-Lig) using different sintering temperatures. Tungsten is a refractory metal and it was selected for the composite since it is widely used for high-energy radiation shielding as it has an excellent absorption cross section for thermal neutrons. Lignin extracted from lignocelluloses biomass and it was selected to be the organic precursor for the composite due to its multiple applications. Analysis of the composite was performed after sintering processes, using a 3D optical surface profiler and measurement of the gamma radiation attenuation coefficient using cobalt source (Co-60). Metal-organic composites in ratios of W2.5%Lig and W5%Lig (in mass % of lignin) were used. The gradient of the attenuation coefficient differed when standard tungsten and the composites of W2.5%Lig and W5%Lig were compared. Therefore, the attenuation coefficient between unobstructed free radiation and the W5%Lig 90 ºC composite showed a gradient of about 43% in the two characteristic Co-60 energy peaks, with a sample thickness of 0.679 cm the calculated linear attenuation coefficient was 0.832 cm-1.
Abstract in English:In this work, compounds based on two grades of polypropylene (PP), i.e., PP H503 or PP H103 with residues of Big bag fabrics (RBB) were processed in a corrotational twin screw extruder with RBB content ranging from 10% to 50% of the weight. Then, their thermal properties were investigated through Differential Scanning Calorimetry (DSC) and Thermogravimetry (TG); mechanical by tensile and impact; thermomechanic by heat deflection temperature (HDT); and their morphology by Scanning Electron Microscopy (SEM). With the aim to add maximum RBB content without considerable damage to the properties of neat PPs, it was observed that addition of 10%, 30% and 50% of RBB did not significantly interfere in the PP matrices, being the compound PP + 30% RBB which one presented more successful properties, leading to reused compounds with higher performance and lower costs at same time.
Abstract in English:Polyethersulfone (PES) hollow fiber membranes were produced, containing 3% of two types of clay (Brasgel PA - MMT and Cloisite NA - CLNa), in order to modify the characteristics of the polyethersulfone membrane. By means of the X-ray diffraction, it was possible to observe an exfoliated and/or partially exfoliated structure in the membranes containing clay. From the analysis of contact angle, it was possible to notice an increase in the hydrophilicity of the membrane with the introduction of the clay. Through scanning electron microscopy (SEM), the morphology of the porous support of the membrane was modified with addition of clay, favoring greater uniformity of the pores and fingers. In the flow measurements with distilled water, the membranes with clay obtained the highest flows, being the greater flow with the Cloisite Na clay (~22 L/h.m2) and was in agreement with the contact angle results. In the analysis of permeation with the oily emulsion, the membrane with Brasgel PA clay in its structure presented the greatest flow (~16 L/h.m2) and the membrane with Cloisite Na presented the greatest yield (78.28%). Therefore, the clay acted by modifying both the morphology and the hydrophilicity of the polyethersulfone membrane, improving flow and yield.
Abstract in English:The aim of this work was to investigate the carbonation kinetics of lithium orthosilicate (Li4SiO4) by thermogravimetry and via thermodynamic simulations, using CO2 concentrations of 15 vol.% (typical of combustion gases) and 100 vol.%. Tests were performed in a thermogravimetric analyzer, in two sequential steps: (1) pre-treatment at 750 ºC with N2 and (2) thermal analysis, non-isothermal (at 10 ºC min-1 up to 1000 ºC) or isothermal (at 550 ºC, 600 ºC and 650 ºC). According to the non-isothermal results, the carbonation of Li4SiO4 occurs in the range of 450-746 ºC and the decarbonation above it. Also, it was possible to capture up to 24.9 wt.%CO2. The isothermal kinetics showed that an increase in temperature promotes an increase in the reaction rate. Yet, the adsorption capacity is limited by the thermodynamics at higher temperatures and the kinetics is slow at low CO2 concentrations.
Abstract in English:Polystyrene (PS) is one of the most widely used polymers in the world, having a wide applicability. PS can be used in pure or modified forms, and the commercial materials most used for modifications are non-renewable and have high costs. For this reason, studies have been carried in order to evaluate renewable components application such as vegetable oils, for this purpose. In this context, different materials have been prepared from styrene (STY) and the common fatty oleic acid (FA) modified with allyl alcohol through esterification in acid catalysis. The allyl oleate (AOL) was obtained with yield of 89% (w/w) and it was submitted to a reaction with styrene at variable concentrations. The copolymers (PS-AOL) were obtained and characterized by conventional techniques. The results indicated that the copolymerization occurred. Therefore, the proposed methodology allows the compatibilization between a renewable matrix and PS for the new materials obtaining.
Abstract in English:Polypyrrole films doped with dodecylbenzenesulfonate (PPy/DBS) and with oxy-anions tungstate (PPy/DBS/TUN) and vanadate (PPy/DBS/VAN) were potentiostatically electropolymerized on aluminum alloy 1100 (AA1100). The corrosion protection of these films was evaluated by the variation of the corrosion potential (ECORR) with the immersion time and by electrochemical impedance spectroscopy (EIS) measurements in 0.05 mol L-1 NaCl and 0.05 mol L-1 HCl solutions. The EIS measurements suggest that the tungstate and the vanadate play the role of a dopant and an inhibitor. The results presented here show that PPy/DBS/TUN and PPy/DBS/VANprovide a protective effect against the corrosion of the AA1100. It was shown that the oxyanions’ inhibitory action is different depending on the electrolyte pH. In an HCl solution PPy/DBS/TUN films improve protection against aluminum alloy’s corrosion. On the other hand, in a NaCl solution, PPy/DBS/VAN films and PPy/DBS/TUN films act as inhibitor, the former being more effective.
Abstract in English:This study aims to analyze the influence of macrosegregation on microstructure evolution, and of microstructure length scale on the corrosion resistance of a Zn-5.0wt.%Mg alloy casting. The analyzed samples were taken along the length of castings unidirectionally solidified in unsteady state conditions of heat extraction. Microstructure characterization, microhardness, linear polarization and electrochemical impedance spectroscopy (EIS) tests were performed. A unique type of microstructure was observed, characterized essentially by a morphology typified by idiomorphic MgZn2 crystals in a “complex eutectic mixture” [coexistence of stable (Zn+Mg2Zn11) and metastable (Zn+MgZn2) eutectics]. The correlation between thermal and microstructural parameters, permitted experimental growth laws, correlating the evolution of the lamellar eutectic spacing with the cooling rate to be established. Vickers microhardness and electrochemical corrosion tests showed that more refined microstructures associated with higher experimental cooling rates, are related to a better set of higher hardness and corrosion resistance.
Abstract in English:Capturing carbon dioxide (CO2) from exhaust gases is an important strategy to prevent climate change. There is a great interest in developing novel CO2 sorbents. Thus, a series of polyurethane (PU) / silica xerogels functionalized with RTILs (bmim Cl and bmim TF2N) composites were prepared and characterized. PU matrix was reinforced with functionalized silica xerogels in the range of 0.5-20 wt%. PU / functionalized silica xerogels were characterized by NMR, FTIR, DSC, TGA, DMTA and FESEM. CO2 sorption capacity and reusability were assessed by the pressure-decay technique at 298.15 K and 1 bar. Results showed that the filler aggregation in PU matrix promoted the reduction of mechanical properties. However, addition of silica xerogels functionalized with RTILs in PU matrix led to increased CO2 uptake. CO2 sorption capacity tends to increase with the incorporation of silica xerogels functionalized with RTILs in PU matrix. The best CO2 sorption value was found for PU/SX-[Bmim]-[TF2N] 0.5 composite (48.5 mgCO2/g at 298.15 K and 1 bar). Moreover, the PU/SX-[Bmim]-[TF2N] 0.5 composite showed reuse capacity and higher CO2 sorption value as compared to other reported composites.
Abstract in English:Concrete is the most used material in the construction industry worldwide. Built concrete infrastructure is exposed to specific environments conditions during the asset’s life, which impose chemical and physical actions that may lead to premature deterioration. Poor concrete durability and corrosion of reinforcement bars are the primary cause of structural deterioration and reduced service life. Most concrete deterioration mechanisms are driven by transport properties, in particular, the chloride diffusion coefficient. In this paper, the effect of curing in the chloride diffusion coefficient of conventional concrete is investigated through Electrochemical Impedance Spectroscopy (EIS). Reinforced concrete samples cured for 3, 7 and 28 days were exposed to accelerated chloride testing for 300 days (40 wet-dry cycles). Results indicate that the chloride diffusion coefficient reduces significantly with curing time, evidencing that prolonged curing may decrease the likelihood of corrosion in reinforced concrete structure when combined with appropriate design and construction processes.
Abstract in English:Civil construction is one segment responsible for major environmental and social impacts. Among its raw materials, Portland cement, which is produced by the burning and subsequent grinding of a composition of clays and limestones. This manufacturing process causes great environmental damage, both by the exploitation of deposits and by the process of clinkering (burning of raw materials), which emits a significant amount of CO2 in the atmosphere. Therefore, there is a need for research on materials that reduce these impacts on the environment and that can be used by civil construction to the partial replacement of cement. Thus, this research had as objective to produce settlement mortar through the partial replacement of the Portland cement by filler powder, in different proportions and to study its mechanical properties. The results show that the partial replacement of the cement by the residue has acceptable behavior in the mortar.
Abstract in English:This work aimed to produce and evaluate the ballistic behavior of niobo-phosphate glass-doped alumina composites. The niobo-phosphate glass (30% Nb2O5- 30% P2O5- 20% CaO - 20% CaF2, by mol) were added to the alumina in six different weight percentages. The composite with the highest densification, measured by the Archimedes assay, was used for the ballistic tests. X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray spectroscopy by dispersive energy (EDX) were also performed. The sintered samples were enveloped on two 1020 steel plates for the residual velocity test. The best results of densification were obtained for the niobo-phosphate glass addition of 4 wt%, which was not detected the AlPO4 phase formation. From the residual velocity test, it was observed a better energy absorption for the doped alumina, in relation to pure alumina. Therefore, it is indicated that the niobo-phosphate glass addition of 4 wt% worked properly as sintering aid for alumina, enhancing its properties and performance.
Abstract in English:Polymers such as the biocompatible polyhydroxybutyrate (PHB) and the polysaccharide chitosan (Chi), a pH-sensitive polymer, have been studied for drug delivery applications and scaffolds production. In this work, matrices of PHB and Chi were produced by compression molding (SPHB-Chi) and loaded with a broad-spectrum biocide chlorhexidine (CHX) (SPHB-Chi-CHX). The matrices were analyzed by scanning electron microscope (SEM). The SPHB-Chi capacity to absorb and deliver CHX was evaluated by UV-Vis. The antibacterial activity of the samples against S. aureus, P. aeruginosa and E. coli (most common pathogens that cause infection in several body sites) was evaluated using the disk-agar diffusion method. The CHX release results were fitted by the Power Law model. The results suggested that the morphology and the CHX delivery profile were directly related to the Chi amount in the samples and also showed that the SPHB-Chi-CHX is able to inhibit the microorganism proliferation, constituting it as a potential candidate for oral applications.
Abstract in English:The aim of this work was to study of the kinetic of Pb(II) sorption, in high lead concentration aqueous solution, by the natural hydroxyapatite (HA) and to verify whether there is a different behavior between natural and synthetic HA under different lead concentrations. Batch experiments were carried out using solutions with high lead concentration, with the objective to evaluate the effect of contact time, HA dosage and initial metal concentration on lead removal. Kinetic data were analyzed by pseudo-first and pseudo-second order models. The sorption data was then correlated with the Langmuir and Freundlich isotherm models. The PZC obtained was slightly different than those reported by other authors, who evaluated the process under low concentrations and synthetic HA as adsorbent. It was possible to identify the optimum relation between Pb(II) concentrations and mass of HA for efficiency of approximately 100% at optimum contact time. Although the results show a certain instability during the removal of lead when the concentration is much higher, the process can be considered effective. Liquid samples were analyzed by atomic absorption spectroscopy and solid samples were by X-ray diffraction and Fourier transform infrared spectroscopy.
Abstract in English:Tetracycline is used to treat various diseases in animals and humans, so its high use causes this substance to be frequently found in effluents and in potable water reservoirs, causing serious problems for human health and the environment. Many processes are applied and evaluated in an attempt to removal tetracycline found in environment, such as adsorption. The application of iron-carbon nanoparticles with core-shell structure (Fe3O4@C) as adsorbent, can be an alternative to removal of these contaminants. In the present study Fe3O4@C nanoparticles were synthesized and used to adsorb tetracycline in aqueous solutions. The core-shell characterization was performed using X-ray diffraction techniques, infrared spectroscopy, surface area, chemical analysis and morphology, and adsorption capacity through isotherms. The results indicated that Fe3O4@C nanoparticles presented good tetracycline removal capability, 73.3%, when applied an initial concentration of antibiotic of the 30 mg L-1 and 0.5 g of adsorbent.
Abstract in English:The 304L austenitic stainless steel is susceptible to mechanically induced martensitic transformation from slightly above room temperature down to cryogenic temperatures. In this work, austenitic 304L steel produced by two different thermomechanical processes, hot rolling (HR) and cold rolling and annealing (CR/A), were subjected to martensitic transformation by rolling and by tensile tests at 298 K and 155 K and the volume fraction of martensite was determined by X-ray diffraction and ferritescope measurements. The results showed that the martensitic transformation was complete for CR/A samples rolled at 155 K and that the volume fraction of martensite was larger in CR/A samples than in HR samples in all cases.
Abstract in English:In this work microfiber mats of Nile tilapia (Oreochromis niloticus) gelatin were successfully fabricated by using Solution Blow Spinning technique. The concentration and viscosity of fish gelatin solution, in acid acetic/water (80% v/v), were correleted to the morphology and diameter of the gelatin microfibers. It was found that increased solution viscosity leads to increase of fibers diameters from approximately 280 nm at viscosity ~ 0.085 Pa.s. to approximately 1195 nm at viscosity ~ 1.877 Pa.s. The TG thermograms showed similar thermal profiles for all fibrous mat gelatins with thermal stability at temperatures below 180°C. The DSC curve showed two endothermic peaks being the second one, in the range of 100-130°C, strongly influenced by the microfiber diameters. It shifts to higher temperature increasing the microfiber diameter. This behavior was associated to the diffusion of water in the microfibers. Combined DSC/TG results showed a significant influence of the microfiber diameter on the water absorption and desorption process.
Abstract in English:This work described a new magnetic material enriched with strontium as catalyst to produce babassu biodiesel. The use of magnetic materials has attracted attention due to easy and fast separation from reaction medium. Moreover, they are ecologically correct, due to they generate less discards to the environment. Techniques of analysis and characterization were carried out to check the synthesis of magnetite and strontium ferrite, besides to verify the presence of hydroxide and carbonate in the structure of the strontium oxide. The best catalytic activities presented conversions of 78.6% and 89.7% when using the catalysts SrO/Fe3O4 and SrO/SrFe2O4, respectively. Density studies of the alkali active sites were performed to elucidate the best activity for the catalyst composed with SrFe2O4.
Abstract in English:The fique is a plant typical of the Colombian Andes, from which relatively common items are fabricated. One of these is woven fabric extensively applied in sackcloths. The mechanical strength of fique fabric have motivated recent investigations on possible reinforcement of polymer matrix composites. For this purpose its thermo-mechanical behavior was unveiled. In particular, dynamic mechanical analysis (DMA) of fique fabric reinforced polyester matrix composites disclosed improved viscoelastic behavior in association with change in the glass transition temperature. The present work extends this investigation to epoxy matrix, which is one of the most employed thermoset polymer for composite matrix. Fique fabric volumetric fractions of up to 50% are for the first time incorporated into epoxy composites. It was found that these incorporations significantly increased the viscoelastic stiffness of the composite, given by the storage modulus (E’), in the temperature interval from -50 to 170°C. An accentuated softening in viscoelastic stiffness was revealed for all composites above 75°C. Peaks in both the loss modulus (E”) and tangent delta (tan δ), respectively associated with the lower and upper limits of the glass transition temperature, were shifted towards higher temperatures with increasing amount of fique fabric.
Abstract in English:The aim of this work was to study the possibility of reuse of chicken eggshell waste produced in the food manufacturing industry for processing of sustainable eggshell waste-polyester resin composite materials for use as artificial carbonaceous rocks. For this purpose, composite specimens with different eggshell waste-polyester resin compositions in different particle sizes of the eggshell waste were prepared. The technical properties (flexural strength, water absorption, apparent porosity, and bulk density), microstructural evolution, and phase analysis of the produced composite materials were investigated. The results indicated that the composite materials containing up to 65 wt.% of chicken eggshell waste with flexural strength between 31.23 and 52.06 MPa, water absorption between 0.59 and 1.37 %, apparent porosity between 0.99 and 2.28 %, and bulk density between 1.59 and 1.71 g/cm3 are highly attractive for be used as sustainable artificial carbonaceous rocks in the civil construction.
Abstract in English:The development of blends made from matrices of synthetic biodegradable polymers, and natural additives, are considered less environmentally aggressive materials. This work aimed to study the effects of gamma radiation on the properties of the thermoplastic starch (TPS)/poly(butylene adipate-co-terephthalate) (PBAT). In this work, blends of TPS/PBAT were prepared with glycerol, castor oil and TWEEN® 80, which were prepared by extrusion and then subjected to the radiation process and characterized by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results demonstrated increased thermal degradation for the F2 (composed by OM) and F3 (composed by OM and TWEEN® 80) regarding F0 (composed by glycerol) e F1 (composed by glycerol and TWEEN® 80) blends. A good blend component chemical interaction and partial miscibility for the blends F0 and F1 was observed and compared to the others. However, F2 and F3 blends did not present co-continuous phases; being that the XRD curve patterns were not altered by the gamma radiation. The tests performed demonstrated that the irradiated and non-irradiated samples did not have their properties significantly altered. Thus, it was concluded that it is feasible to replace castor oil with glycerol in TPS/PBAT blends.
Abstract in English:This study aimed at evaluating the effects of the incorporation of micro and nanoparticles of CaCO3 on the properties of poly(vinyl chloride) (PVC), intended to industrial application. The PVC compounds added with particles of different sizes were achieved in an intensive mixer. Rheological, microstructural, mechanical and thermal properties of the compounds obtained were evaluated. The rheology test showed that the compound with the addition of two-particle size plasticized faster compared than other formulations. Microstructural analysis showed a poor particle size distribution for the micro-CaCO3 charges, and the nano-CaCO3 samples have agglomerated particles. The thermal analysis showed the compound added with two particle size with higher gelation, and in the loss modulus E’ and E”, the values also were close. The analyses showed that the combination of the two-particle sizes presented superior results when compared with the micro or nano used singly.
Abstract in English:In this manuscript, the electromagnetic wave absorption properties of sustainable porous carbon composites were evaluated over the X-band frequency range (8.2 - 12.4 GHz). The porous carbon material was made from the byproduct of cellulose production and was used as additive on the development of radar absorbing material (RAM) composites. These porous carbon materials have different characteristics, such as porosity size (180 µm < Ø1 < 250 µm and 425 µm < Ø2 < 500 µm) and particle size (ϕ1 < 250 µm and 250 µm < ϕ2 < 425 µm). Composite materials were also studied as frequency selective surface (FSS) structures. It was shown how complex permittivity and reflection loss (RL) can be manipulated over the frequency range using FSS structure. While regular RAM presented RL of 19 dB at ~11.8 GHz, FSS structure presented a RL of 19 dB shifted to 12.4 GHz regarding the same carbon porous material (with particles between 250 and 425 µm and porosity between 180 and 250 µm). It was demonstrated here the potential use of sustainable porous carbon as RAM, and how FSS structure can be used to tune the frequency of the RL maximum peak.
Abstract in English:The population increase, urbanization and climatic change adversely affect the agricultural production have prompted actions to improve the means of production without affecting the environment. One of the actions to make the production of food more efficient and sustainable is the use of plastics in protection of crops, soils and packaging, for example. Therefore, the aim of this work was to develop flat extruded mulch films of poly (butylene adipate-co-terephthalate)/2.5 and 5.0% sugar cane residue/2.0% carnauba wax for application in soil cover and characterize them as to their chemical structure, morphology and transmittance. The FTIR results suggest that there was no chemical interaction between the components of the mulch films. SEM images and optical microscopy showed that the polymer matrix was able to cover sugarcane residues and that the carnauba wax dispersed well in the PBAT matrix. In addition, carnauba wax addition increased the transmittance of these mulch films.
Abstract in English:Firearms threat has always been a matter of personal concern, especially to soldiers in armed conflicts as well as police officers and civilians involved with public security. A multilayered armor system (MAS) is intended to personal protection against high kinetic energy ammunition, such as that used in rifles. MAS layers are normally composed of a front ceramic followed by a layer that must show both high impact resistance and low weight. Usually, synthetic fiber fabrics, such as aramid in Kevlar® and ultra-high molecular weight polyethylene (UHMWP) in Dyneema® are commonly used as the second layer. Currently, composites reinforced with natural fibers are also being considered as second MAS layer due to their good performance associated with the advantages of being cheaper and environmentally friendly. The fique is a relatively unknown natural fiber extracted from leaves of a plant native of South American Andes. In the present work, fique fibers and fique fabrics incorporated in polyester composite plates with volume fraction of 10, 20 and 30% were ballistic tested. The calculated projectile loss of energy indicated a relatively large energy dissipation by the composite. The tested specimens were statistically treated by the Weibull analysis and were examined by scanning electron microscopy.
Abstract in English:A comparative investigation on the firing behavior of a natural kaolinitic clay from Campos dos Goytacazes, Brazil, and its specific clay fraction was performed. The clay fraction, equivalent diameter less than 2 µm, was separated from the precursor clay by a sedimentation method. Chemical analysis, X-ray diffraction (XRD) and scanning electron microscopy were used to characterize the unfired materials. Thermoanalysis and dilatometry were applied to follow the structural transformations. The firing behavior was studied by water absorption and XRD of samples fired in the temperature range from 400 to 1100°C. Differences were found between the natural kaolinitic clay and its clay fraction. The absence of quartz and smaller particles of the clay fraction result in a comparatively lower temperature for structural consolidation associated with reduced open porosity. This can be attributed to solid state sintering alone, in contrast to a higher temperature liquid phase sintering needed for complete consolidation of the natural kaolinitic clay.
Abstract in English:Ferrites nanoparticles of Ni1-xZnxFe2O4 ferrites with x varying between 0 and 1, in steps of 0.2, were obtained by solution combustion synthesis (SCS) and dispersed in oil paint at the concentrations of 10, 20, 30 and 40% by ferrite weight of ferrite, with the aim of producing electromagnetic wave absorbing composites, in the X band (8-12 GHz). The ferrite powders obtained were characterized by X-ray diffraction (XRD), and to determine to mean crystallite size, crystallographic phases, as well as lattice parameters, was used the Rietveld method. The XRD results revealed the majority presence of the spinel cubic ferrite phase for all stoichiometries with crystallite size between 44 and 81 nm. The composites were characterized by the rectangular waveguide transmission line method to measure the absorption of the electromagnetic wave in the X band. The nanocomposites with 40% of NiFe2O4 and Ni0.8Zn0.2Fe2O4 presented the highest electromagnetic wave absorption performance.
Abstract in English:With technological advances in the several areas of knowledge, the constant search for materials with characteristics that meet certain applications has been growing, especially in the chemical and petrochemical industries, where materials capable of withstanding the conditions of corrosion in aggressive environments are required. The aim of this paper was to analyze the influence of the alloy element molybdenum on the microstructure and the resistance to corrosion of two duplex stainless steels identified as A (with molybdenum) and B (without molybdenum), after solution-treated under the following conditions: heating at 1100ºC for 30, 120 and 240 minutes. The steels were characterized by SEM, EDS, DRX and microhardness. The rise in solution treatment time fostered an increase in the volumetric fraction of the ferrite phase, in both steels. The solution treatment at 1100ºC for 120 minutes, for steels A and B, provided good resistance to pit corrosion, as well as the development of a passivating film in the solution of lithium chloride (120,000 ppm of chloride ions).
Abstract in English:Concern for sustainable development has provided significant improvements in the development of biodegradable materials. This work aims to evaluate, through a central composite design (CCD), the mechanical properties of cassava starch-based biocomposites manufactured with different compositions of carnauba wax (CW), sisal fiber (SF) and glycerol (G). The biocomposites were obtained by casting method. The tensile strength (TS), modulus of elasticity (ME) and elongation at break (El) for the biocomposites were determined by tensile tests. Representative models were obtained to explain changes in mechanical properties of biocomposites as function of composition variables. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were employed to elucidate interactions between the starch matrix and additives A biocomposite with 7.5% sisal fiber, 10% carnauba wax and 10% glycerol showed the best properties to possible applications.
Abstract in English:Hyperbranched biopolymers is an important class of polymer that is used in different areas, mainly in biomedicine. AB2 monomers are crucial to the development of a "hyperbranched" architecture of polyglycerol, being glycidol the most commonly used, even considering its environmental hazard. Glycerol carbonate is an ecologically accepted monomer synthesized directly from glycerol, and the chosen for the studies herein. In literature, no studies described the use of glycerol and cyclic carbonates to prepare hyperbranched polymers. This work describes the obtainment of hyperbranched polymers using glycerol and TMP salt as core-initiator and glycerol carbonate and propylene carbonate as monomers. The polymers were characterized by FTIR, NMR, MALDI-TOF and TEM. NMR spectroscopy showed linear, dendritic, and terminal units of hyperbranched polymer. The degree of branching PGLYGC and PTMPGC was 0.669 and 0.667, respectively. The molecular weight of PTMCGC, PTMPPC, PGLYPC was found and compared with MALDI. The molar mass was not different from the calculated by Inverse Gated. These polymers have enormous potential as drug delivery and an environmentally correct synthetic route due to the substitution of glycidol by biocompatible monomers.
Abstract in English:This study aims to make a comprehensive analysis on the viscoelastic behavior of typical tropical hardwoods and its influences in making musical instruments. For that a Dynamic-Mechanical Analysis was done and the mechanical parameters dependence on test control parameters like temperature, frequency and test duration time were measured. For Dalbergia Nigra the final value of Module of Elasticity (MOE) was 17551.0MPa and 0.022020 for tangent delta (tg(δ)), but a great variation in those parameters was observed during the tests, for all species the MOE increases and tg(δ) decreases, even with constant temperatures, which may be caused by water loss. Besides that, a discussion was made relating the obtained data and historical knowledge about the usages of the studied woods for musical instruments manufacture, and density was shown as the main variable for that purpose.
Abstract in English:Fish bone is rich in calcium carbonate, which makes it an alternative source of low cost calcium carbonate for the synthesis of calcium phosphate bioceramic for use in bone regeneration. The calcium phosphate bioceramic was prepared by a wet precipitation method with acid and base reactions. The synthesized bioceramic was characterized in terms of X-ray diffraction (XRD), scanning electron microscopy (SEM/EDS), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTRI), average crystallite size and refinement by the Rietveld method for the quantification of crystalline phases. The results indicated the formation of a biphasic calcium phosphate bioceramic comprising 67.6 % of β-calcium pyrophosphate (β-CPP) and 32.1 % of β-tricalcium phosphate (β-TCP). This biphasic calcium phosphate bioceramic synthesized using fish bone waste presented nanostructured nature with an average crystallite size of 69.58 nm, which is very promising for biomedical applications.
Abstract in English:Duplex stainless steels (DSS) are corrosion resistant alloys largely used in chemical and petrochemical industries. Some commercial DSS contain 0.5-1.0% copper addition to improve the corrosion resistance by reducing the corrosion rate in non-oxidizing environments. Higher copper addition (≥ 2%) can also hard by precipitation, especially when fine copper precipitates (ε phase) are produced. In this work, a cast copper alloyed DSS type ASTM A890 grade 1B with 3.01%Cu was investigated. Different levels of hardness were produced by solution treatment and aging at 450, 500, 550 and 600 oC for periods of time up to 1 hour. The corrosion resistance of aged DSS was evaluated by electrochemical tests in three media: 0.6 mol/L NaCl, 0.3 mol/L H2SO4 and 0.6 mol/L NaCl + 0.3 mol/L H2SO4 solutions. The results indicate that the effect of Cu addition depends on the media studied. Polarization studies in 0.6 mol/L NaCl showed a small anodic current peak occurred at around 400 mV vs. Ag/AgCl, with a strong influence on the passive film stability. Additionally, chronoamperometric measurements at 400 mV vs. Ag/AgCl showed a high electrochemical activity for the samples in 0.6 mol/L NaCl.
Abstract in English:Ionic liquids (ILs) physical immobilization in solid materials is a key strategy for developing efficient and low cost CO2 capture processes. In this work, two porous commercial substrates with different characteristics (silica and alumina) were impregnated with ILs by physical wet method. Imidazolium based IL combined with [Br]- and [Tf2N]- anions were used in impregnation process. CO2 sorption capacity and selectivity (CO2/N2) of these materials were investigated. The best results regarding CO2/N2 selectivity and CO2 sorption were obtained with [Tf2N]- anion. In relation to solid support, commercial alumina exhibited enhanced CO2 uptake and higher selective capacity (CO2/N2) (6.1 (± 0.1)). Combination of commercial alumina as support and 20 wt% of mbmim [Tf2N] resulted in higher CO2/N2 selectivity of 9.5 ± 1.0. In addition, this material also showed fast sorption kinetics when compared to pure IL besides reuse capacity.
Abstract in English:The production of a material with rigid, multifunctional three-dimensional porous structure at a low cost is still challenging to date. In this work, a light and rigid carbon foam was prepared using rice husk as the basic element through a simple fermentation process followed by carbonization. For the fermentation process, the amount of biological yeast (7.5 g for the carbon foam CA-1P and 5 g for the carbon foam CA-2P) was used to evaluate its influence on the morphology of the foams. In order to prove that the heat treatment made in the foam alters the hydrophilic character of the rice husk foam, a chemical treatment with steam deposition was carried out. The foams were characterized by the following analyzes: apparent density, micrograph, thermogravimetry, contact angle, water sorption capacity and thermal conductivity. Visually, the CA-1P foams presented a structure with larger pores due to the greater amount of yeast used in its formulation. The heat treatment of rice potato foams proved to be as efficient as the chemical treatment for water contact angle above 90º, proving the ability of the foams to repel water/moisture. The thermal conductivity of the foams (0.029 and 0.026 W m-1 K-1 for CA-1P and CA-2P, respectively) was close to the conductivity of polyurethane foams (0.032 W m-1 K-1). Thus, the method used in the production of the carbon foams produced from the rice husk proved to be effective. In addition, the foams produced have the potential to be used for thermal insulation.
Abstract in English:This work aims to numerically study the moisture absorption in polymer composites reinforced with vegetal fiber, using the diffusive model of Langmuir, which considers the existence of water molecules inside the material free to diffuse and adsorb at the capillaries walls, in the solid. A three-dimensional and transient mathematical modelling to describe the water absorption process by the composite and its numerical solution via finite volume method are presented and discussed. Results of the free solute concentration, entrapped solute concentration, local moisture content and average moisture content obtained at different instants of the process are presented and analyzed. It was verified that the concentration gradients of the molecules (free and entrapped) are higher at the material surface. In addition, as the concentration of free water increases, there is also an increase in entrapped water concentration within the material at any time of the process.
Abstract in English:Polymeric syntactic foams are composites made from the mixture of Hollow Glass Microspheres (HGM) and polymer matrices. One of their main characteristics is their low density and the production of these composites using a matrix derived from renewable sources potentiates their development without neglecting sustainability. In this paper , the properties of High Density Polyethylene (HDPE)/HGM syntactic foams containing 1% and 5% w/w HGM and 5% w/w of a compatibilizer are assessed. The composites were prepared by two processing routes: single screw extruder and twin screw extruder. The morphology and mechanical properties (tensile and impact) of the syntactic foams thus manufactured were ascertained. Morphological analysis indicated that matrix/filler adhesion was poor for all samples and that the best HGM dispersions were obtained in twin screw extruded samples. Mechanical properties were affected by the processing route adopted and by the content of hollow glass microspheres added. Elastic modulus, tensile strength and strain were reduced by 20, 10 and 23%, respectively, in systems processed in a twin screw extruder. Impact strength was the exception, with an increase of more than 300%. Higher contents of hollow glass microspheres led to reductions in mechanical strength of the syntactic foams, varying from 5% for the elastic modulus to 50% for strain.
Abstract in English:The objective of this work was to investigate the effects of anodization parameters on the anatase phase formation of titanium oxide films, which have been grown on both electropolished and non-electropolished titanium surfaces by direct current anodization in 0.25 and 2.5 mol L-1 H3PO4 solutions, respectively, at three anodization times (3, 6 and 12 hours). SEM, Raman spectroscopy and X-ray diffraction techniques revealed the characteristics of anodic films. Films were characterized according to presence of crystalline nuclei of anatase phase on an amorphous matrix. It was found that differences in size, shape and distribution of crystalline grains on anodized surfaces are affected by the type of polishing given to substrates. The particles on electropolished surfaces were grown in well-defined layers following cone-shaped grains. On the other hand, the crystallization phenomenon on non-electropolished substrates has led to the appearance of smaller particle sizes and a larger number of particles distributed along the surface as well.
Abstract in English:This work aimed to synthesize bacterial cellulose (BC) membranes functionalized with Ce(NO3)3 and silver nanoparticles (AgNPs) heat-treated in oven and autoclave. The AgNPs were characterized by TEM and the membranes were characterized by their rehydration capacity, Thermogravimetric Analysis (TGA), Scanning Electron Microscopy with Dispersive Energy Spectroscopy (SEM/EDS), Wide-angle X-ray Diffractometry (XRD), Atomic Absorption Spectroscopy (AAS), antimicrobial activity and cytotoxicity. The BC membranes were white to light yellow or brown indicating functionalization with AgNps with 20 nm. XRD detected a decrease in the degree of crystallinity in functionalized membranes. The autoclaved samples exhibited the largest porosity and good rehydration capacity. AAS showed Ag presence in all samples. The best antibacterial activity was achieved for the membrane’s oven treated with 40 ppm of AgNPs. Among the functionalized membranes, the most recommended to be used as burn dressing is the Ag40A and Ag20CN1.1A since they showed good porosity, good antimicrobial activity, and better suitable cell viability.
Abstract in English:This paper presents a thermal and microstructural characterization of Cu87-xAl13Nbx (wt%) high temperature shape memory alloys (HTSMA), with Nb contents ranging from 1 to 3%. The alloys were obtained by arc melting under argon atmosphere. Thermal characterization was performed by differential scanning calorimetry (DSC), revealing that the phase martensitic transformation of all the studied alloys occurs in the range of 200 ºC to 450 ºC. Thermal cycling in this temperature range caused the martensitic transformation to disappear after approximately 6 cycles. However, a new heat treatment at 850 ºC followed by water quenching causes the martensitic transformation to be recovered. Microstructural characterization was performed using optical microscopy (OM) and scanning electron microscopy (SEM), revealing the presence of Nb precipitates in a Cu-Al martensitic matrix, mainly in the Nb-rich compositions. These different microstructures with Nb particles cause a hardness variation that initially decreases between 0.5 %Nb (275HV) and 1.0 %Nb (225HV), then increasing continuously up to 3.0% Nb (380HV).
Abstract in English:The textile industry needs a high volume of water to carry out its processes, which among them; textile chemical finishing is the main responsible for high water expenditure. However, nowadays there is a worldwide concern regarding the scarcity of fresh water. This research aims to study the use of seawater in the cotton bleaching process and compare the results obtained with the bleaching process made with distilled water. The characterization of the substrates was performed through the following analyses: reflectance spectrophotometry, white degree (ºBerger), wettability, tensile strength, elongation, scanning electron microscopy and dispersive energy spectroscopy. The bleaching with seawater presented good whiteness index, high tensile strength values and excellent hydrophilicity, which suggest that it may be possible to perform this process in cotton fabric using seawater.
Abstract in English:The mineralogical characterization studies search for the best processing route, with the lowest environmental impact, aiming to improve the use of mineral resources. The electronic quantitative mineralogy (EQM) provides quickly and accurately great information about the characteristics of these materials. This work aims to characterize iron ore tailings by EQM as the main tool. It has selected seven samples of itabirite ores flotation tailings from the main mining regions of the Quadrilatero Ferrifero, Brazil. All samples were mostly composed by quartz and iron minerals, with a low presence of mixture particles of these minerals - less than 20% of the sample mass. Due to the difference between the size of particles of quartz and iron minerals, it has observed an opportunity to reprocess the fractions -37µm + 5µm of the studied tailings, with a potential recovery of 12% of the total sample mass generated for AM4, AM6 and AM7 and more than 5% for samples AM1, AM2, AM3 and AM5.
Abstract in English:Stainless steel and nickel alloy have high corrosion resistance in high-temperature environments due to the high Cr content present in their chemical composition, being widely used in components of nuclear reactors, petrochemical industries, etc. Through proper processes and procedures, it becomes possible to join these alloys. However, this union can generate detrimental factors in its performance, among them, the residual stresses. In this work, the residual stresses generated by the autogenous GTAW process, due to different interpass temperatures on the weld bead geometry, were analyzed by the Hole-Drilling technique in dissimilar welding joints of stainless steel AISI 316L and Inconel 718 alloy. In addition, the Vickers microhardness measurements were carried out to evaluate the hardness profile in the cross section of the weld bead covering base metal (BM), heat affect zone (HAZ) and weld metal (WM). We found that in the interface region between BM and HAZ of each dissimilar joint metal, residual stresses increased above 300 MPa, while hardness increased above 160 HV.
Abstract in English:The aim of this work was to evaluate mass loss in each stage of the recycling process for metal recovery from PCBs of controllers and temperature indicators of cold chambers. The stages of process consists of grinding, particle size classification, magnetic and electrostatic separation. It was analyzed 13 kg of PCBs. These PCBs were crushed and ground. The ground material were subjected to magnetic and electrostatic separator. The losses in the comminution stages were 12.69 % and are lower than those found in other related works that used mixtures of different types of PCBs, whereas in this work only one model plates were analyzed. 27.2 % absolute mass loss we reached out after particle size separation with Tyler Series with 1 mm sieve presents the higher mass losses in the whole process and this fraction was not processed as it results in PCBs powder dust that interferes negatively in the electrostatic separation. Comparing the losses in the stages of shredding of PCBs employed in temperature controllers with other studies involving PCBs from the automotive industry and from computers and cell phones, is remarkable that this type of board presents significantly greater potential to be processed for recovery of its materials.
Abstract in English:AISI D6 hardened steel is a difficult to cut material that it is employed in mould and die manufacturing where long ball-end mills are frequently required to machine deep cavities. This condition can lead to excessive vibration between tool and workpiece resulting in a poor surface finishing and reduced tool life. This work analyses the dynamic stability of ball-end milling of AISI D6 hardened steel for different tool path orientations at inclined workpiece angles of 15º and 75º. The evaluation of stability is based on the surface texture and spectrum analysis of the vibration signals. The results showed that for workpiece inclination angle of 15º chatter occurred in vertical upward down-milling and vertical downward up-milling. Best surface texture with tool marks consistent with pick feed and feed directions were generated by applying horizontal downward tool paths that produced the least vibration. Only forced vibrations occurred for the workpiece inclination angle of 75º. The highest peaks of the spectra corresponded to the harmonics of the tooth passing frequency closer to the natural frequency of the system. High magnitudes in the spectrum were found for vertical upward down-milling that generated a less uniform surface texture.
Abstract in English:Corrosive processes in acidic medium reduce the performance and durability of metallic materials, causing problems to several industries. Corrosion inhibitors are commonly used to decrease these effects. As these inhibitors must be ecologically friendly currently, this work evaluated the anticorrosive effect of natural extracts of coffee husks (Coffea arabica L.) in the protection of carbon steel in 1 mol L-1 HCl solution. Extractions were performed using water as the extraction solvent. The polyphenols content increased with the extraction temperature, and the extracts were produced using 100 ºC. Extract concentrations of 10, 20 and 30 % v/v were analyzed as inhibitors for carbon steel in acid medium, using weight loss and electrochemical tests, as well as scanning electron microscopy. There was an increase in the inhibition efficiency as the extract concentration increased, reaching values around 97 % using 30 %v/v of extract for the weight loss tests.
Abstract in English:The clay samples endure the incorporation of industrial and urban wastes, which do not cause large variations in their properties if added in controlled quantities. Wastes can be classified as fuel, fluxing and property affecting wastes. The fuel wastes usually have a high amount of organic matter, that when heated cause exothermic reactions, releasing heat to the process. The fluxing wastes cause a reduction in the ceramic melting points. The main aim of this work was to study the behavior of ceramics incorporated with fuel wastes (Eichhornia crassipes dry biomass) and fluxing wastes (granite) as well as blends of both wastes. Different compositions were prepared with incorporation of different percentages of these wastes in the clay samples, conformed by uniaxial pressing and fired at 550, 650, 750, 850, 950 e 1050ºC. The technological properties tested were: dry apparent density, linear shrinkage, water absorption and flexural rupture strength. Results indicate that the high calorific value of the biomass waste represents a great possibility of saving energy for the firing process. Incorporations can be indicated as a possibility of correct destination for the investigated wastes.
Abstract in English:The liquefied natural gas volumes that currently need to be stored and/or transported require engineering to consistently develop materials that combine high mechanical strength and low manufacturing costs. The present work brings the study of four models of high manganese steels (non-commercials), to demonstrate the feasibility of being used in the petrochemical industry. The tests contemplate the characterization (composition, phase diagram, metallography, EBSD, microhardness), corrosion resistance in NaCl solution (Open Circuit Potential, Linear Polarization) and characterization of corrosion products (EDS, SEM, Raman Spectroscopy). The obtained results showed a relationship between the increases of the manganese content with: formation of twins that help their hardening, as well as the decrease of their corrosion resistance; the steel with less amount of this element had a more noble behavior. Quantities of chromium, silicon and aluminum in these steels could not contain the high dissolution of manganese, which caused low stability of the formed oxides that allows the electrolyte ions to reach the metal surface, accelerating the dissolution process.
Abstract in English:TiO2 nanorods present good performance as catalysts in the sorption behavior of magnesium hydride. In the present study, the morphology of TiO2 nanorods produced from titanate nanotubes heat-treated at 550 °C (NR550), 650 °C (NR650) and 750 °C (NR750) was characterized and their catalytic role on the sorption kinetics of MgH2 was evaluated. For this, ball-milled MgH2-TiO2 nanocomposites with 5 wt% of additives were prepared and the materials were characterized by X-ray diffraction (XRD), BET surface area and Transmission Electron Microscopy (TEM). The hydrogen sorption kinetics of the composites were evaluated in a Sievert’s apparatus at 350 °C. The results indicated that NR550 and NR650 consisted of a mixture of nanorods and nanoparticles and NR750 of coarser nanoparticles of TiO2-anatase with a small amount of rutile. Composites with NR750 and NR550 presented the best sorption kinetics, suggesting the positive effect of the presence of rutile and of anatase nanorods, respectively, on the sorption properties of the material.
Abstract in English:The ToF-SIMS technique was applied to analyze thin ZrO2 coatings deposited on the surface of a Ni-Ti alloy. Due to its nanostructured nature, these films are difficult to characterize by conventional techniques. ZrO2 coatings were deposited on near equiatomic Ni-Ti wires by pulse electrodeposition. Part of the samples was electrolytically polished before the coating process. The coated samples were then analyzed by ToF-SIMS to evaluate the influence of the deposition time and previous surface electropolishing on the structure of the deposited coating. The results indicate that thicker coatings were produced on the electropolished samples, in comparison with the as-received ones. The best uniformity in thickness was achieved when Ni-Ti samples were previously electropolished followed by ZrO2 electrodeposition for 1200 seconds. Moreover, it was possible to observe by this technique that the inclusions in the Ni-Ti matrix were not entirely covered by the coating.
Abstract in English:The objective of this study is to evaluate the surface physicochemical properties of Ti6Al4V alloy after etching with a piranha’s solution at temperatures of 25 °C, 40 °C, and 60 °C for 30 min. Scanning electron microscopy with energy-dispersive X-ray spectroscopy, optical profilometry, X-ray diffraction, and wettability analyses were used to characterize the surface of the samples. In addition, corrosion tests were performed using potentiodynamic polarization and electrochemical impedance spectroscopy. The proposed surface treatment did not alter the wettability and surface chemistry (crystallinity), but the texture, surface roughness, superficial area, and corrosion resistance of the alloy could be changed by varying the etching temperature. Considering that these properties are indirect indicators of the alloy’s potential success in the osseointegration of a dental implant, the surface treatment of the Ti6Al4V alloy using a piranha solution while controlling the etching temperature has attractive biomedical applications.
Abstract in English:The development of both versatile and inexpensive sorbents for CO2/CH4 separation has become one of the greatest challenges to the environment and natural gas processing. This study reports the preparation and characterization of polyurethane (PU)/ cellulose based poly(ionic liquid)(CPIL) composites for CO2/CH4 separation. PU matrix was reinforced with CPIL in the range of 10-30 wt%. Several characterization techniques (TGA, DSC, DMTA and FESEM ) were used to study the physical properties of composites when the PU matrix is reinforced with cellulose based poly (ionic liquids) (CPIL) up to 30%. CO2 sorption, reusability and CO2/CH4 selectivity were assessed by pressure-decay technique. Results showed that CPIL addition in PU matrix promoted the increase in both thermal stability and mechanical properties when compared to PU. The best result for CO2 sorption (35.0 mgCO2/g) was obtained for PU/CPIL-TBP 10% which presented a higher sorption value when compared to PU (24.1 mgCO2/g) and PU/CELLULOSE 10% (26.8 mgCO2/g). PU/CPIL-TBP 20% demonstrated higher CO2/CH4 selectivity. PU/CPIL composites appear as promissory materials for CO2 capture. These compounds combine the benefits of ionic liquids (ILs) (high ionic conductivity, chemical and thermal stability) and cellulose (thermal stability) with PU properties (mechanical stability, processing and tunable macromolecular design).
Abstract in English:The materials selection can affect the design component radically, with effect on the manufacturing systems efficiency, environmental impact issues, and customer satisfaction. There are different methods employed for materials selection; however, two steps are usual for most of these methods: screening and ranking. The ranking step identifies among materials candidates those that can perform the function the best as possible. Multi-criteria methods have been widely employed to materials selection, especially in the ranking step. Most of these methods take advantage of fuzzy numbers and linguistic variables to process qualitative information and information with uncertainties. One of the approaches that have been developed to solve issues related to make decisions in multi-criteria methods using linguistic information is the 2-tuple linguistic computational model. The main advantage of this approach is taking the “loss of information” away, which provides a higher precision on results. This paper aims to present a multi-criteria method for materials selection ranking step based on 2-tuple linguistic variables. The steps and several equations needed to apply the proposed method are described. Two case studies are presented and compare results with other methods to demonstrate the proposed method potential.
Abstract in English:The goal of this study is to test photoelastic resins for manufacturing models with teeth and/or implants under chewing load. Four commercial brands have been chosen: Araldite (Ciba Chemicals), Flexible GIV-Rigid GIV (Polipox) and PL2 (Measurements Group). Nine discs were manufactured, four of them from each of the photoelastic resin brands and five from different proportions of mixture between Flexible GIV and Rigid GIV. All the models were subjected to the diametral compression test, and observed in a circular polariscope. The first order fringe has always been adopted as a benchmark to calculate the photoelastic constant. To the load of interest (150 Newtons), Flexible GIV resin showed areas that followed the elastic regime. Residual stresses for the resin PL2 and persistence of bubbles within the model were observed. Rigid GIV Resin generated the first fringe order only at 280 Newtons load. Araldite resin behaved within the elastic regime and there were no areas with excessive concentration of fringes. The models generated from the manual mixing generated non-homogeneous photoelastic images. The Araldite resin showed to be the most suitable material for manufacturing birefringent models with teeth and/or implants under chewing load.
Abstract in English:Titanium is used in orthopedic and orthodontic implants because it has good corrosion resistance and excellent biocompatibility. Thus, studies seek to obtain a coating to improve the adhesion between the bone and the implant, by modifying the metal’s surface. The objective of this work was to biomimetically coat C.P. Ti with hydroxyapatite doped with silver nitrate, a component with antimicrobial properties, coating the metallic-ceramic composite with a polycaprolactone polymer film, which is known by generate improved implant-tissue interaction, and reducing postoperative complications from bacterial infections. The characterization of the material demonstrated the existence of the coating overall surface of the metallic substrate. The results obtained from the bacterial culture tests with Staphylococcus aureus showed that nitrate was effective in reducing the amount of live bacteria present in the supernatant, as well as those adhered to the surface of the material. In addition, the polymeric coating did not prevent the release of the bactericidal agent, not interfering in the effect there.
Abstract in English:Equal channel angular pressing (ECAP) is one of the severe plastic deformation processes that can also be used for metallic powder consolidation. Consolidation of blended elemental powders of iron, chromium, nickel, and manganese (Fe-25Cr-20Ni-2Mn wt. %) was performed at room temperature in a Φ = 120° die by 1 and 2 passes. SEM micrographs indicated that single pass ECAP consolidated sample presented close to full densification. Additional pass of ECAP led to hardness increase and to an apparent better mixing between the different particles. SEM/EDX analysis made before and after heat treatment of the samples showed that effective diffusion only took place after heat treatment and especially in the sample subjected to 2 ECAP passes. Results indicate that alloying by ECAP consolidation and posterior heat treatment is feasible, especially for systems that cannot be processed by conventional means, as well as mechanical alloying.
Abstract in English:The development of β-metastable titanium alloys that combine low Young’s modulus, good mechanical properties, corrosion resistance and biocompatibility has attracted industry interest. This type of alloy is an alternative to commercial alloys such as Ti-6Al-4V, avoiding the cytotoxic effect that occurs with Al and V in the human body in the manufactured orthopedic prostheses. In this scenario, the present work aims to characterize the effect of Nb concentration in the properties of Ti alloys based on the Ti-12Mo-xNb stoichiometry (x = 0, 3, 8, 13, 17 and 20). All alloys were produced by arc melting with non-consumable tungsten electrode in an argon atmosphere and the ingots were characterized by x-ray diffraction (XRD), optical microscopy (OM), Vickers microhardness and Young’s modulus was measured by impulse excitation and density was measured using the Archimedes’ principle. The Ti-12Mo alloy and the Ti-12Mo-20Nb alloy showed the lowest Young’s modulus. The best hardness/modulus was found for the Ti-12Mo-3Nb alloy. All the alloys studied in this work showed hardness/modulus ratio above the traditional Ti-6Al- 4V alloy (2.85), presented great potential for the biomedical application.
Abstract in English:This work aimed to analyze the damage behavior of cold rolled TRIP780 steel sheet submitted to interrupted uniaxial tensile tests performed along the rolling direction. The formation of voids is investigated as a function of the straining level using digital image analysis of scanning electron micrographs to obtain the measures of void density, void area fraction, void aspect ratio and mean void size. The volume fractions of both ferrite/martensite and retained austenite constituents were obtained from X-ray diffraction measurements. An abruptly decrease of retained austenite was observed at early stages of deformation followed by a slow saturation. The resulting strain-induced martensite is responsible for improving the formability of the TRIP780 as observed by instantaneous strain-hardening exponent. In the lower strain range, growth and coalescence of existing microvoids prevailed at both in-plane directions whereas nucleation of microvoids was also observed along the loading direction. Conversely, nucleation prevailed at the transverse direction in the intermediate strain range whereas growth and coalescence were predominant aligned to the loading direction. At larger strain levels, growth and coalescence of microvoids prevailed at both directions. The microvoids were initially found around inclusions and at the interface of ferrite-martensite phases and lastly also at the ferrite matrix.
Abstract in English:Eucalyptus bark is a waste generated in large volume and has been used as a source of energy. This study tries to use the Eucalyptus sp. bark as a source of raw material for the charcoal production and to study the influence of pyrolysis temperatures on charcoal properties. Charcoal was produced at different temperatures: 300, 400 and 500 °C, and their properties were determined by proximate analysis, higher heating value and thermogravimetric analysis. It was observed that higher pyrolysis temperature resulted in increase of the fixed carbon content and higher heating value. In the thermogravimetry and derivative thermogravimetry curves it was possible to determine the differences in the thermal stability of charcoal produced. It can be concluded that the eucalyptus bark charcoal is an alternative for the energy reutilization of this waste and also can be used as charcoal for heating.
Abstract in English:The aim of the present work was to investigate the effect of the treatment time on the surface chemistry and corrosion behavior of cerium-based chemical conversion coatings on the AZ91D magnesium alloy. The conversion coating was prepared by the immersion technique from a bath consisting of 0.05 mol.L-1 Ce(NO3)3.6H2O and 0.254 mol.L-1 H2O2 (30 wt.%) for times ranging from 20 s to 120 s. The surface chemistry was examined by X-ray photoelectron spectroscopy (XPS). The corrosion behavior was assessed by electrochemical impedance spectroscopy and potentiodynamic polarization. XPS analysis detected the presence of cerium oxides (Ce2O3 and CeO2) and cerium/magnesium hydroxides. The best corrosion behavior was observed for the treatment conducted for 60 s. The results are discussed with respect to coating morphology and composition.
Abstract in English:7XXX aluminum alloys show high mechanical resistance and low weight, both required properties for aircraft industry. Anodizing is an electrolytical process typically used to improve the corrosion resistance of aluminum alloys, through which a thicker and porous oxide is formed. Boiling water is used as a common sealing method to the anodic layer; however, it implies energy expenditure. In this work, a two-step coating system was performed: anodizing in tartaric-sulphuric acid and a post-treatment with a Zr-based conversion coating, obtained at room temperature by immersion in hexafluorozirconic acid (H2ZrF6). To establish the best condition for coating formation on the aluminum oxide layer, different concentration and pH values of the H2ZrF6 solution were studied. Morphological and chemical analyses were performed respectively by SEM and EDS. The corrosion resistance evaluation was carried out by EIS in 0.5 M NaCl. Heterogeneity was observed in the obtained coatings. However, the samples treated with H2ZrF6 had a higher corrosion resistance than unsealed samples. The best concentration and pH range observed for the H2ZrF6 solution were 1 % and 3 to 3.5, respectively. Under these conditions, a greater corrosion resistance was evidenced in comparison to that obtained with boiling water sealing.
Abstract in English:The mechanical behavior of the API 5L X80 steel exposed to the produced water by the petroleum industry, besides being dependent on the intrinsic properties of the steel, is influenced by the corrosivity characteristics of the electrolyte that may be associated with the presence of microorganisms. The objective of this work was to investigate the plastic deformation of API 5L X80 steel exposed to produced water. The tests were conducted in static systems (abiotic and biotic) containing produced water after 360 days. The process of corrosion of the coupons were evaluated by topographic 3D analysis and roughness, and the mechanical behavior by tensile test and fracture analysis by scanning electron microscopy. Surface topography and roughness were modified by the interaction of the consortium of microorganisms with the substrate associated with the corrosion process. The results indicate that microorganisms induced the formation of pits which caused the coupons to lose plasticity.
Abstract in English:Biodegradable Poly (ɛ-caprolactone) (PCL) was compounded with Brasgel PA (MMT) and Cloisite Na (CLNa), and compatibilized with maleic anhydride grafted poly(ɛ-caprolactone) (PCL-g-MA). No evidence of degradation was verified during processing, as well as particle aggregates were absent as displayed through scanning electron microscopy (SEM) images. Compatibilized compounds upon clay addition achieved higher thermal stability as visualized by thermogravimetry (TG). Montmorillonite clays acted as nucleant agent during PCL melt crystallization as evidenced by differential scanning calorimetry (DSC). Mechanical behavior of PCL was preserved, and all compounds presented Elongation higher than 350% meanwhile the heat distortion temperature (HDT) was increased by 20% in PCL compounds, which may have wider range of application and better performance.
Abstract in English:Aluminum beverage cans should have very specific crystallographic textures to increase productivity, reduce losses and reduce the amount of material. The present work seeks to add information on the crystallographic texture of aluminum alloy 3104 H-19 during the different manufacturing steps, which undergoes a flat sheet of metal for a cylindrical body. The work scope encompasses from the cup drawing to the final ironing operation and its objective is to add information on the texture evolution of the aluminum alloy undergoes in the intermediary steps. Crystallographic texture continues to change from the drawn cup through the ironing stages. This rotation is assumed to be a grain alignment with the plastic flow of the material.
Abstract in English:The aim of this work was to prepare hollow fiber membrane changing the composition of polyethersulfone, polyvinylpyrrolidone (PVP) and clay, through the phase inversion technique, evaluating the influence of these constituents on the viscosity and distinct morphologies. Flat membranes were produced and their contact angles were determined and showed difference when clay was added and/or PVP. For the hollow fiber membranes, the +addition of these constituents, PVP and/or clay in the solution, can change significantly the viscosity and effect the membrane formation. From the scanning electron microscopy (SEM) images, it was identified the influence on morphology with the compositional variation of each additive, with the PVP promoting shorter precipitation time, favoring the formation of pores of the “fingers” type and increasing the presence of macrovoids. The addition of clay favored the formation of spherical pores, reducing the presence of macropores.
Abstract in English:Nickel alloy 625 is widely used in submarine equipment for the oil and gas industry, which operate in an extremely adverse environment. In order to reduce the costs of these components, weld overlay cladding is employed. The surface generated by this process presents some irregularities that represent an additional difficulty to the machining process. The present work investigates the use of whiskers-reinforced ceramic tools and SiAlON in turning of alloy 625 clad on AISI 4130 steel by an automatic tungsten inert gas (TIG) cladding system. The results indicate the feasibility of the industrial application of the SiAlON inserts in rough turning of the alloy 625 clad, as well as the impossibility of using whiskers-reinforced ceramic tools (Al2O3 + SiCw) in the same conditions. The highest flank and notch wear of the SiAlON inserts were observed for the lowest cutting speed (140 m/min), which induced the formation of burrs in the workpiece at the depth of cut. Adhesion occurred more intensively at this condition. The least flank and notch wear were achieved by using cutting speed of 160 m/min and feed-rate of 0.25 mm/rev. Prolonged turning with worn tools resulted in microstructural alterations of the workpiece material and surface damages.
Abstract in English:Duplex stainless steels are largely applied in petrochemical industries due to their high corrosion resistance and mechanical performance. Their applicability also requires a great wear resistance, which can be enhanced by friction stir processing (FSP), a surface hardening technique. In this work, FSP is utilized to process surfaces of UNS S32101 and UNS S32750. The materials were analyzed by EBSD in order to determine grain size and phase fraction. Microhardness tests were used to verify and compare the shifting of hardness values from 296 ± 8 to 314 ± 11 HV0.2/15 and from 323 ± 8 to 350 ± 8 HV0.2/15 for UNS S32101 and S32750, respectively. Abrasion tests were executed to study the wear behavior of both processed and unprocessed alloys. Abrasion tests indicated that the hardening by FSP promoted decrement of abrasive wear resistance. Volumetric loss increased after FSP, from 52.1 ± 0.5 to 53 ± 2 mm3, for UNS S32101, and from 50 ± 2 to 56.3 ± 0.3 mm3 for UNS S32750. Tensile tests results were fitted to Hollomon’s equation in order to identify mechanical properties and tendencies of strain hardening. SEM images were used to classify the wear micromechanisms acting on the samples. The results suggest that FSP can promote modifications of wear mechanisms and these changes can be correlated to the alloys’ microstructure.
Abstract in English:In powder metallurgy the addition of alloying elements is a widely used alternative to increase the service life of mechanical components. However, they have an associated cost. One less exploited process is surface enrichment (or surface alloying), whose same result is obtained on the surface, but at a much lower cost. Self-lubricating composites are especially complex to be enriched, precisely because they have to avoid the deposition of alloying elements over the lubricant stocks. This paper reports the characterization and tribological properties of self-lubricating composites enriched with molybdenum or nickel. Sintered samples were produced for comparative purposes. Wear resistance, friction coefficient and wear rate were analyzed for the evaluation of tribological properties. The results showed that the enrichment process did not cover the lubricant stocks. In addition, the Mo-enriched samples presented the best tribological results, with a 250 % increase in scuffing resistance in relation the sintered sample, and lower wear rate.
Abstract in English:This study evaluates the properties of chitosan (CS) membranes modified with different percentages (0.5%, 3%, and 5% w/w) of a graphene-based material. Graphene oxide (GO) and reduced graphene oxide (RGO) were obtained by the chemical exfoliation of graphite and thermal reduction. Then, they were characterized by electrical conductivity measurements, FESEM, XRD, AFM, and Raman spectroscopy. The composites’ morphology was evaluated by FESEM. The degree of swelling over a 48 h period and mass loss behavior in phosphate-buffered saline solution for up to 70 days were also studied. The hydrophilicity of the CS and CS/graphene nanocomposites was examined by water contact angle. The graphene materials showed small stacks (6-8 sheets) with low defect density and nanoscale thickness (1.3-5.9 nm). The dispersion of the graphene material in the CS matrix significantly decreased the degree of swelling (460%) but did not modify the hydrolytic degradation process and the hydrophilicity of membranes.
Abstract in English:The influence of Nb content variation on the microstructural and thermal characteristics of NiTiNb alloys was evaluated since these aspects are relevant to the control and adequacy of its shape memory properties for application purposes. The aim of this study was to observe how the Nb content acts in the formation of Nb-rich precipitates and the eutectic structures, which can make this alloys more complex. Microstructural characterization of the alloys was performed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and microanalysis by energy-dispersive X-ray spectroscopy (EDS), besides the thermal characterization by differential scanning calorimetry (DSC), and the comparison between the Nb alloys and the NiTi binary alloy. The results demonstrated a proportional dependence between the amount of β-Nb phase in the microstructures and the amount of Nb dissolved in the NiTi matrix with the Nb content. Although it was found that the increase in the Nb content causes the decrease of the martensitic (Mi) and reverse (Ai) transformation temperatures, the magnitude of thermal hysteresis was not significantly changed.
Abstract in English:The formation of brittle microstructures around the fusion line in dissimilar welds has required a deeper microstructural analysis in this region. The study becomes more relevant when these welds are used in environments that facilitate hydrogen embrittlement. The present work aims to characterize the microstructure and hardness at the diluted zone interface in joints welded with dissimilar materials. Aiming for a better efficacy in the microstructural characterization of this zone, samples of both normal cross-section (NCS) and section with slope were used, according to the low-angle microsectioning (LAMS) technique, which allows a greater amplification of partially mixed zones (PMZs). The results indicated the diffusion of carbon from the heat-affected zone (HAZ) towards the fusion line which, in combination with other alloying elements, form highly brittle carbides. In turn, the hardness of the base metal and the HAZ was reduced after post weld heat treatment, whereas in the weld metal an opposite behavior was observed. The dissimilar interface was promising for applications in environments facilitating hydrogen embrittlement, especially regarding the characteristics of zone Φ.
Abstract in English:The prediction of microstructure morphology is fundamental for the manufacture of metallic components, since the expected levels of mechanical properties will be associated with the final aspects of the microstructure. In this work, an Al-7wt.%Si-3wt.%Mg alloy was directionally solidified in unsteady state conditions in order to investigate the influence of the addition of 3wt.%Mg to an Al-7wt.%Si alloy on the solidification evolution. The microstructure of the examined alloy is shown to be characterized by a more complex arrangement of phases, as compared to that of the Al-7wt.%Si alloy, which includes the binary (α-Al+Mg2Si) and refined ternary (α-Al+Si+Mg2Si+Fe-rich IMC) eutectic mixtures. A higher Vickers hardness profile is shown to be associated with a more refined microstructural arrangement. However, for cooling rates lower than 2K/s the microhardness is shown to increase with the increase in the microstructural spacing, which is shown to occur caused by Si macrosegregation and higher content of free Mg.
Abstract in English:Friction surfacing (FS) is a coating technique applied mainly in corrosion protection and repair of components. The study addresses the effects of deposition and rotational speeds on the rods characteristics and process efficiency for the deposition of Ti-6Al-4V on self-mating substrates by FS. The consumption rate was 1.8 mm/s, deposition speeds of 8, 16 and 24 mm/s and rotational speeds of 2000, 3000 and 4000 rpm. It was shown that the flash forms primarily at the rod, ascending around the tip and leaving the coating without flash. The higher deposition speeds led to a decrease in rod thickness and diameter. For higher rotational speeds, an increase in diameter and decrease in thickness is observed for the flash on the rod. Experiments have shown that the rotational and deposition speeds have a decisive influence on the flash formation. Its microstructure changes due to the welding process and a change in hardness can be observed.
Abstract in English:Zr-Nb-Mn alloys were developed to investigate hydrogen diffusion and its effects among different manganese additions. Thermo-Calc® and TC-Prisma simulations were used to determine the studied chemical compositions and to estimate the volume fraction and the mean radius of precipitates. Three compositions were chosen to be melted and thermomechanically processed, resulting in an α-Zr matrix with fine β-Nb precipitation. TDS results indicated that hydrogen diffusion coefficient was 10-12 m2.s-1 for all the analyzed compositions. The manganese addition increased the strength while ductility was maintained. Although optical microscopy revealed that the increase of manganese content resulted in less oriented hydrides, the reduction in ductility was similar for the three studied compositions. Results showed manganese as a promising addition element for zirconium alloys due to the increase of hydrogen solubility, the good relationship between strength and ductility and the morphology of the hydrides.
Abstract in English:This work aims to study the influence of cutting parameters (cutting speed, feed rate, cutting depth and tool cutting edge angle) regarding surface roughness and burr formation during the milling of a mixed structure comprised of titanium and carbon fiber (stack). The parameters were varied from maximum to minimum, just as the tool cutting edge angle of the insert, through a full factorial design with 32 trials. The analyses were performed by measuring the surface roughness and burr size along with metallographic analyses through optic microscopy and scanning electron microscopy. The results showed that the surface roughness was higher for carbon fiber and burr size was higher for titanium. There were a number of tests with delamination of the carbon fiber, and the best cutting parameters to minimize surface roughness and burr formation were tool cutting edge angle of 45º, a feed rate of 0.028 mm/tooth, cutting depth equal to 0.26 mm and cutting speed equal to 150 m/min.
Abstract in English:The recycling of civil construction waste gypsum has been the subject of studies due to the non-existence of economically viable technologies or applications that would allow it to be recycled. However, studies indicate that the material setting time reduces after recycling, generating more waste, but the cause of the phenomenon is not known. In-situ XRPD monitoring of plasters’ hydration in their commercial form and after laboratory recycling process is carried out to verify both reactivity and hydration process. The samples are characterized by specific surface area, microporosity, and consistency tests. Sequential and parametric Rietveld refinements are employed to determine the weight fractions of calcium sulfate-based compounds present in the materials as a function of time. The increase in the consistency of the recycled plaster is not only associated with the increase of microporosity and specific surface area but also to the instant formation of gypsum as soon as the material comes into contact with water. These data also confirm the increase in the kinetic activity values calculated from the results of temperature kinetics tests, proving that the formation of hydrated compounds is much faster for the recycled plaster, which is associated with the increase of water contact area.
Abstract in English:Carmakers must achieve the worldwide targets for lightweight materials, safety and reducing the fuel consumption. The use of press-hardened steel (PHS), in vehicle structures has been contributing with these requirements. This type of steel is widely used for the hot-stamping which consists in heating the steel blank to total austenitization temperature and then transferring it from the furnace into the die tool where the steel is formed and quenched at the same time. PHS is usually protect with metallic coatings in order to avoid both steel oxidation and decarburization. Hot-dip Al-Si coating is currently the main used in this application. However, alternative coatings, like zinc-based, are under investigation. This work aims at evaluating the corrosion resistance of the 22MnB5 grade PHS, electroplated with Zn-Ni, before and after hot stamping, using the scanning vibrating electrode technique (SVET). Results from SVET showed that samples prior to hot stamping, the corrosion mechanism was uniform over the exposed surface, and was mainly related to selective dissolution of zinc from the coating. On the other hand, hot stamped samples showed localized corrosion mechanism with decrease in current with time of immersion due to the formation of corrosion products on the exposed surface.
Abstract in English:Fiberglass/thermoset matrix composite present important properties, such as specific mass and mechanical strength, aiming to replace some engineering materials. However, its mixture of different materials transforms them into an environmental problem, due to the complex recycling process. The highlight is meeting the demands of environmental pressures and for establishing recycling mechanisms, the proposal is to study physical recycling processes, focusing on the microwave-assisted pyrolysis process and also recovering fiberglass. The results were: humidity around 3 wt. %; the average loss of mass around 68 wt. %; the tensile strength is reduced by about 76 % when a composite with recycled fiberglass is laminated, as compared to the use of virgin fiberglass. This work establishing the physical recycling mechanism and route for composite materials, identifying the thermal degradation processes, for thus applying them to other materials, still considered environmental issues, technically and economically making these materials manufacturing processes viable, as well as establishing a recycling route.
Abstract in English:Researches about nanomaterials related to properties such as superhydrophobicity, self-cleaning, corrosion and scratching resistance can be directly related to the materials’ wettability. This characteristic is quantified by the contact angle made between the surface and a water droplet, in which angles above 90 degrees are considered to be hydrophobic and those above 150 degrees, superhydrophobic. The focus of this work was the development of a superhydrophobic self-cleaning surface, using silica nanoparticles with a particle diameter around 400 nm to 800 nm (produced via sol-gel, referring to the classic Stöber method) functionalized with perfluorooctyltriethoxysilane (POTS) on a polymeric substrate polymethyl methacrylate (PMMA). Four different surface treatment conditions were analyzed: untreated, treated with non-functionalized silica nanoparticles, treated only with POTS and treated with silica nanoparticles functionalized with POTS. For this last condition, a static water contact angle of (150.0 ± 0.44) degrees and a dynamic water contact angle of (7.5 ± 0.38) degrees were obtained, which is a typical value of a superhydrophobic surface. However, the surface treated with POTS alone had a contact angle of 115 degrees. The high contact angle value was due to the low surface energy obtained, which was of (1.45 ± 0.02) dyn/cm. The modified superhydrophobic surface revealed a superior self-cleaning performance by freely rolling spherical water drops on the non-wettable solid surface. The stability of the modified surface has been proven by water jet impact.
Abstract in English:The Cr-Co-Mo alloys are commonly used in dentistry for prosthetic components and dental implant supported prosthesis. These alloys present high corrosion resistance owing to a passive oxide film on the surface. However, the oral environment is an aggressive system, due to pH variation, chloride and fluoride ions presence, that can decrease the metal alloy corrosion resistance. Although Cr-Co-Mo alloys have been used for a long time, their electrochemical properties on different pH have not been studied yet. This study aimed to evaluate the electrochemical properties of Cr-Co-Mo alloy in NaCl 0.9% solution in different pH and mouthwash solution. To imitate the oral environment, electrolytes with a pH equal to 2, 3, and 6 were used. Corrosion studies were performed by open circuit potential observation, potentiodynamic polarization curve, chronoamperometry and electrochemical impedance. The results showed that the analyzed alloy has good corrosion resistance under experimental conditions, although the acidified NaCl 0.9% solution increased the corrosion current, particularly in cathodic potentials.
Abstract in English:This paper sets out to evaluate the corrosion of ASTM A131 grade A36 carbon steel exposed to a diesel oil S10 / saline water system and the biodegradation of diesel oil S10 to simulate storage, transport and fuel use systems during a period of 30 days. The corrosion process was investigated through electrochemical tests of Open Circuit Potential (OCP), Electrochemical Impedance Spectroscopy (EIS) and Linear Polarization (LP). The morphology of the corrosion products were analyzed by Scanning Electron Microscopy (SEM). The results showed that the presence of saline water in the system containing diesel oil is an aggravating factor which promotes the biodegradation of the fuel and, consequently, aggravates the corrosion process.
Abstract in English:Shape memory alloy (SMA) helical springs are special mechanical parts that require a previous evaluation of its behavior for application. Therefore, in this paper thermal and mechanical behaviour of superelastic Ni-Ti SMA helical extension springs manufactured by investment casting (IC) are evaluated. Phase transformation temperatures were measured by Electrical Resistance as a function of Temperature (ERT) and Differential Scanning Calorimetry (DSC). Tensile tests were carried out within strain and temperatures ranges. The pitch angle and stiffness of each spring were determined. Results demonstrated that Ni-Ti SMA helical springs produced by IC presented phase transformation corresponding to the superelastic effect (SE). The reversible deformations under tensile test were of the order of 70%. The mechanical behavior as function of temperature revealed a linear relationship between maximum force and spring temperature.
Abstract in English:The objective of this work was the conformation of ribbons from Sn3Zn alloy and Sn pure, using the melt-spinning fast cooling technique, in order to investigate the applicability as biomaterial. The ribbons were coated with 1% poly-caprolactone (PCL) and subsequent incorporation of silver nanoparticles (NPAg). In the uncoated ribbon was observing a surface roughness due of agglomerate caused by rapid solidification. In the ribbon coated with PCL and NPAg incorporation, it was observed that these compounds adhered to the ribbon. X-ray diffraction analysis showed no ribbons amorphization. The analysis by differential scanning calorimetry, indicated that the Sn3Zn ribbon had a lower melting temperature (198.1°C) than the Sn ribbon (228.7°C). The microhardness of Sn3Zn ribbon was 13.38 HV and Sn ribbon was 11.00 HV, both for the face without contact with the cooling wheel. In the bioactivity assays, performed in simulated body fluid medium, all samples showed apatites formation after four weeks of testing.
Abstract in English:Corrosion of pipelines can be significantly affected by the activity of microorganisms present in the environment. The objective of this work was to investigate the influence microbial in the corrosion behavior of API 5L X80 steel in produced water by open circuit potential, polarization curves and electrochemical impedance spectroscopy measurements. Physical-chemical and microbiological analyzes were performed in the produced water and the tests were conducted in biotic and abiotic systems. The films and corrosion morphology developed in the steel over time were characterized by scanning electron microscopy. The results confirm that the activity of the consortium of microorganisms in the formed biofilm accelerated the dissolution of the iron, causing pitting corrosion in the steel exposed to the biotic system. Through the adjustment of the equivalent electrochemical circuit, the impedance results allowed to interpret the interactions between electrode, film and electrolyte.