Abstract in English:Activated (AS) and carboxymethylated (CMS0.24) cassava starch derivatives were studied as corrosion inhibitors for carbon steel XC35 in a 200 mgL-1 NaCl solution. They were characterized by back titration and Fourier Transform Infrared Spectroscopy (FTIR). Electrochemical techniques were used to evaluate the inhibitive properties of starches at room temperature and the chemical composition of the protective films was determined by X-Ray Photoelectron Spectroscopy (XPS). Electrochemical measurements revealed that AS acts as mixed inhibitor, whereas CMS0.24 mainly inhibits the anodic reaction. In both cases, the protection increased with the inhibitor concentration; nevertheless, after 24 hours of immersion, the CMS0.24 loses its properties, while AS molecules still maintains them. XPS analyses show that the inhibitive films are composed of an iron oxide/hydroxide mixture in which starch molecules are incorporated. Results were explained taking into consideration the hydrophilicity and the strength of the ionic interaction of the starches with the metal surface.
Abstract in English:Poly(butylene terephthalate) (PBT)/ acrylonitrile-butadiene-styrene (ABS) terpolymer blends were prepared in a twin screw extruder and the use of methyl methacrylate-glycidyl methacrylate-ethyl acrylate (MGE) terpolymer as compatibilization additive was evaluated. The effect of different screw profiles and mixing conditions were evaluated on the crystallization of the blends. Differential scanning calorimetry (DSC) was used to evaluate melting and crystallization behaviors of the PBT/ABS blends. The binary PBT/ABS blend has shown a double melting peak when cooled at lower cooling rates, mainly due to its melt-recrystallization during the heating up step. ABS has not affected the melting characteristics of neat PBT. The presence of MGE, as a reactive compatibilizer, in the PBT/ABS blends has reduced its heat of fusion and has partially inhibited its melt-recrystallization under heating. As result, it has prevented the occurrence of double melting peak. The epoxy functional groups of the MGE may react in situ to the carbonyls and hydroxyls end groups of the PBT molecules, thereby hindering the mobility of PBT molecules during the crystallization process due to its grafting to the compatibilizer molecules. The melt mixed blends prepared at lower feeding rate have shown a higher degree of crystallinity for the PBT/ABS blend, probably due to degradation of PBT caused by longer residence time in the extruder. The highest shear stress imposed to the blends at higher screw speed increased the degree of crystallinity of PBT, also due to its degradation.
Abstract in English:The cooling rate, density of stacking faults, austenite grain size, and temperature strongly influence the γfcc → εhcp → a'bcc martensite transformation in austenitic alloys. During cooling, austenitic Fe-Mn steels can partially transform to ε and α'martensites within a restricted chemical composition. Martensite formation will influence the mechanical behavior of the alloy. The microstructure evolution under three cooling rates of a hot-rolled austenitic steel, Fe-17.0Mn-0.06C (wt%), was analyzed by optical microscopy and scanning electron microscopy/electron backscatter diffraction. The volume fraction of martensite and austenite were measured by X-ray diffraction line profile analysis by directly comparing the as-cast alloy, alloy subjected to different cooling conditions, and this processed with hot rolling.
Abstract in English:This article investigates a fatigue approach conducted from the design phase to testing approval. It considerers modern analytical and experimental tools for structural durability assessment over each development phase for two reference components aiming an early approval methodology validation for a new design. A Finite element analysis procedure was used to set critical spots for measurements minimizing the data acquisition efforts. Based on measured data, strain life calculation was done for two reference components in order to set the release goals for a new design submitted to this approach. An innovative fatigue experimental technique is proposed using component extracted specimens and an edited input cycle loads. Considering the random data from a standard test track and signal proportionality evaluation, while assuming the Brown Miller equation for bi-axial fatigue together with Ramberg-Osgood model, equivalent damage load blocks were edited and used as input for durability assessment on specimens representing the component material. The results for the three parts materials were plotted as Weibull diagram for B10 life estimation. Fatigue life results showed good correlation with the reference parts structural performance thus validating the method as well as approving the new design for production without additional on-vehicle durability testing. The methodology and the fatigue testing proposal is therefore recommended for future applications on similar developments.
Abstract in English:A new kind of crosslinkable potato starch-based graft copolymer emulsion (PoSt-g-BMD) has been prepared using butyl acrylate (BA) and methyl methacrylate (MMA) as main monomers, and diacetone acrylamide (DAAM) as functional monomer. The keto-carbonyl group of DAAM in PoSt-g-BMD copolymer could react with adipic dihydrazide (ADH) at ambient temperature to form cross-linked copolymer. The PoSt-g-BMD had been characterized by the FT-IR spectra and thermogravimetric analysis (TGA). It was applied to prepare the humidity-controlling coatings (PoSt-g-BMD-C). The water absorption of PoSt-g-BMD-C was 105%. The humidity controlling properties were also measured, and the PoSt-g-BMD-C exhibited humidity sensitivity and humidity retention because fillers of porous structure combined with PoSt-g-BMD copolymer emulsion based on scanning electron microscopy images (SEM). It could be widely applied in indoor coating for controlling humidity.
Abstract in English:316L stainless steel and Hydroxyapatite (5, 20 and 50 wt. (%) HA)-316L stainless steel composites were fabricated by mechanical alloying technique, pressing and sintering from 316L and HA powders. The corrosion behavior of both sintered 316L and HA-316L composites was evaluated by electrochemical techniques in simulated body fluid (Ringer's solution) and in 0.1M HCl solution which simulates occluded cell corrosion conditions. The results indicate that 316L stainless steel and HA-316L composites are passive in Ringer's solution and active in HCl solution. All materials are highly corrosion resistant in Ringer's solution with corrosion current density in the order of 10-6 A cm-2 or less. Both 316L stainless steel and 5% HA-316L composite present good corrosion resistance in HCl with corrosion current density in the order of 10-5 A cm-2. The corrosion resistance decreases with increasing HA content in both solutions.
Abstract in English:The improved technology has allowed the study of electronic structure of solids with a complex crystalline structure and containing various atoms, different in the unit cell, and thus we can calculate the energy of formation and obtaining the bulk modulus and cohesive energy, which lets us discussing the compounds stability. The importance of this work is to obtain the ground state properties of solids face the crystal lattice deformation when subjected to pressure. The nitrogen replacement by oxygen in the interstitial structure γ - Fe4N forming Fe4O was studied. Calculations indicate that the critical pressure to transform the ferromagnetic into non-magnetic phase is greater in the γ - Fe4N 528,8851 Kbar showing a greater magnetic character. Regarding the resistance to uniform compression (bulk modulus), our calculations show that γ - Fe4N is higher, because a bulk modulus of 281.4045 GPa for non-magnetic phase and 173.7893 GPa for Fe4O 251.3927 GPa for non-magnetic and 170.1810 GPa for ferromagnetic, showing that the non-magnetic phase have higher bulk modulus for both compounds.
Abstract in English:This work examined the influence of different chemical blowing agents (CBA), one endothermic and one exothermic, at the same concentration (2% by mass), on poly(acid lactic), PLA foams. The CBA was incorporated into the PLA in a single-screw extruder, and the foams were expanded by heating in an electric oven under free pressure conditions. Foam degradation in a simulated soil was performed according to the ASTM G160-03 standard. Changes in the physical-chemical, morphological and mechanical properties were used to evaluate the degradation. The results indicated that the different chemical blowing agents led to different mechanical and morphological properties for the foams, which resulted from the nature and decomposition rate of the blowing agents. Cells in the foams accelerated the degradation since they facilitated the infiltration of water toward the interior of the polymer and triggered the degradation process by hydrolysis.
Abstract in English:This study focussed on the work hardening behaviour and microstructure of austenitic manganese steel relative to premature failure of crusher jaws. Samples of sound and failed crusher jaws were taken, the change with depth from the working surface to the sample core was measured and their microstructures observed. The study revealed a sharp hardness gradient in the failed crusher jaws, and presence of large carbides at both the austenite grain boundaries and in the austenite matrix. The failure of crusher jaws was attributed to brittle fracture as a result of precipitates of carbides from the inability of precipitated carbides to absorb shock during impact working. Finally, we conclude that the failure occurred as a result of inadequate quenching operations during the manufacturing process that resulted in the formation of carbide precipitates which embrittle the austenitic manganese steel, reduce its ability to withstand shock and create a non uniform plastic flow as it is work hardening.
Abstract in English:The recent rise of nanotechnology and nanomaterial research is marked by the huge amount of publications indexed in electronic databases, which can be evaluated using bibliometric indicators in order to help researchers find hidden trends, gain novel insights and support new scientific developments. Although in-depth analyses require specialized software and advanced methodologies, some initial indicators can be developed using the analytical tools available in databases and provide useful information about a specific subject or research field. This paper aims to explore the Web of Science's analytical tool for analyzing the scientific output regarding carbon-based nanomaterials. The results provide several key findings, including research trends and publications in carbon nanotubes, fullerene and graphene, as well as revealing the main global players and journals from 2001 to 2010. Despite the usefulness of the analytical tool, a number of limitations hindered the development of important indicators, such as those involving citation and collaboration.
Abstract in English:In the present work the effect of substituting Mo with Nb on the glass forming ability and corrosion resistance of Fe-Co-Cr-M-Si-B-Y (M=Mo, Nb) ribbons with high corrosion resistance is investigated. The X-ray powder diffraction pattern indicates that the alloy containing both Nb and Mo presented greater glass forming ability than the alloy containing either of these elements separately. The results obtained indicate that Mo is more effective in enhancing corrosion resistance than the Nb in 4.0 M HCl solution. The alloy containing both Nb and Mo presented greater overall corrosion resistance than the alloy containing only one of these elements.
Abstract in English:Nanostructured polymer composites have opened up new perspectives for multifunctional materials. In particular, carbon nanotubes (CNTs) present potential applications in order to improve mechanical and electrical performance in composites with aerospace application. The combination of epoxy resin with multiwalled carbon nanotubes results in a new functional material with enhanced electromagnetic properties. The objective of this work was the processing of radar absorbing materials based on formulations containing different quantities of carbon nanotubes in an epoxy resin matrix. To reach this objective the adequate concentration of CNTs in the resin matrix was determined. The processed structures were characterized by scanning electron microscopy, rheology, thermal and reflectivity in the frequency range of 8.2 to 12.4 GHz analyses. The microwave attenuation was up to 99.7%, using only 0.5% (w/w) of CNT, showing that these materials present advantages in performance associated with low additive concentrations.
Abstract in English:The true stress-strain data from isothermal hot compression tests, in the temperature range of 300-500 ºC and strain rate of 0.001-0.1s-1, were employed to study the flow behavior of AZ31 and to develop constitutive equation based on an Arrhenius-type equation. The flow stress increases with the decrease of deformation temperature and the increase of strain rate, which can be represented by Zener-Hollomon parameter in an exponential equation. The influence of strain was incorporated in the developed constitutive equation by considering the effect of strain on material constants. The results show that the proposed constitutive equations give a precise estimate for high temperature flow stress AZ31 alloy, which means it can be used for numerical simulation of hot deformation process and for choosing proper deformation parameter in engineering practice accurately.
Abstract in English:Chromate coatings used as corrosion protection technologies for aluminum alloys are environmentally harmful and extremely toxic. This paper presents an investigation on the deposition of environmentally friendly cerium oxide-based anticorrosive coatings on aluminum alloy 2024 substrates by the sol - gel method. The influence of the calcination temperature on both the microstructural characteristics and the electrochemical corrosion performance was tested using scanning electron microscopy, X-ray diffraction, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS), before and after, periods of immersion in saline corrosive solutions. The ceramic coatings synthesized at 200, 300 and 400 °C showed very resistive behaviors leading to both an efficient passivation of the alloy surfaces and good corrosion protection. This passivation was maintained for 30 days of immersion in saline solutions, as well as, when aggressive electrochemical polarization experiments (until 2.0 V versus saturated calomel electrode) were used. Very high resistances for the charge transfer (0.14-0.28 GΩ) and very low current density values (5 × 10- 14 -5 × 10- 11 A cm- 2) were estimated by EIS and potentiodynamic polarization, respectively, for coatings prepared at 200-400 °C. Thus, the coatings prepared in this study by the sol - gel method appear as an efficient treatment for the corrosion protection of aluminum alloys.
Abstract in English:CoCrMoSi alloys microstructure is affected by processing and their properties have been associated with the high volume fraction of Laves phase. However, not much has been reported on the effect of structure refinement and morphology on the properties of these alloys. This paper evaluates a CoCrMoSi alloy processed by centrifugal casting and Plasma Transferred Arc (PTA) hardfacing, aiming to understand the correlation between microstructure and properties at room temperature in the as-processed condition and following exposure at 600 °C. Characterization was carried out using scanning electron microscopy, X-ray diffraction, hardness and wear tests. The cooling rates associated with each of the processing techniques used account for the developed microstructures and associated hardness, a 626 HV0,5 cast alloy and 649 HV0,5 deposited alloy, the former exhibiting a coarser microstructure. Wear behavior was determined by the dispersion of solid solution areas in the microstructure and as a consequence temperature exposure aggravated the poorer wear resistance of the cast alloy. The finer phase dispersion formed in coatings overlapped the deleterious effects of dilution and account for the stable wear behavior after temperature exposure.
Abstract in English:This paper presents results describing the physical, mechanical, and thermal properties (melt flow index - MFI and oxidative induction time - OIT) of high density polyethylene and poly (vinyl chloride) after weathering exposure (6, 12, 18, and 30 months). The materials exposed were geomembranes of two thicknesses: 1.0 and 2.0 mm (PVC) and 0.8 and 2.5 mm (HDPE). The climate parameters (average) obtained were 25 ºC (temperature), 93 mm (precipitation), 66% (relative humidity), and 19 MJ/m².day (intensity of global radiation). Some results showed, for instance, that the behavior of the geomembranes changed after the exposures. A few minor variations in physical properties occurred. The density and thickness, for instance, varied 0.5-1.0% (average) for both the PVC and HDPE geomembranes. The mechanical properties changed as a function of the period of exposure. In general, some decreases were verified by the deformation of PVC. The samples became more rigid. In contrast, HDPE geomembranes became more ductile. Despite the variations in elasticity, some increases in deformability were verified. An MFI test showed some degradation in HDPE geomembranes. OIT tests revealed small values for both intact and exposed samples.
Abstract in English:This work evaluates the phase transformations during aging of an UNS S31803 DSS at 650ºC and its influence on the DOS. The material was solution treated at 1175ºC and then aged at 650ºC for times up to 360 h. SEM-BSC images indicate the formation of Cr2N, σ and χ phases in the samples aged at 650ºC. The analysis of DL-EPR curves, obtained in a 1 M H2SO4 + 0.25 M NaCl + 0.01 M KSCN solution, shows an increase in DOS values for samples aged at 650ºC. Probably, this increase observed in DOS values is mainly related to the presence of Cr- and/or Mo-depleted α, as a result of σ phase, χ phase and/or Cr2N formation at 650ºC. Moreover, a possible healing up of Cr- and/ or Mo-depleted areas is observed between 1 h and 4 h of aging at 650ºC.
Abstract in English:The present study reports the results of thick films (20-130 µm) produced through electrophoretic deposition of BaTi0.85Zr0.15O3 (BTZ) nanometric powders synthesized by the Pechini's method. The BTZ powderscalcined at 600°C/2h presented a single crystalline phase with an average particle size of ~20nm. To thick films deposition, a stable suspension of acetylacetone (Acac) and ethanol (EtOH)was prepared and the powder was deposited on platinum substrates. The viscosity of BTZ powders suspensions as a function of operational pH (OpH)was measured and the reactions between nanoparticles and the media were discussed. A milling process was used to deagglomerate the powders and it had a great influence in the suspension stability and deposition of thick films. Dense and crack-free thick films were obtained after sintering at 1220 °C/1h. The dielectric properties results, comparable with those of bulk BTZ ceramics, suggested potential applications of the EPD process for the deposition of ferroelectric/piezoelectric thick films.
Abstract in English:Many studies propose thermomechanical routes to improve HSLA (high strength low alloy) steels by microstructural modification but ignore the study of occurrence of CSL boundaries. The occurrence of these special boundaries is influenced by thermomechanical treatment in which the modification of misorientation profile is related with the increase of Σ3 and Σ11 boundaries and inhibition of Σ5 Σ7 and Σ9 ones. The formation of Σ3 boundaries, beneficial to improve strength, is highly stimulated by this treatment in which deformation plays an important role in the development of CSL boundaries.
Abstract in English:Wood-based panels have been widely used around the world in various segments of timber industry. Thus, alternative raw-materials have been systematically researched in order to reduce of wood demand in particleboard production. The aim of this work was to produce and evaluate particleboards of Eucalyptus grandis and oat hulls (Avena sativa), bonded under pressure with castor oil based polyurethane resin, in the proportion of 10% relative to the dry mass of the particles. The percentages of particles used per material were: Eucalyptus grandis 100, 85, 70 e 0% and oat hulls 0, 15, 30 e 100%, respectively. Physical-mechanical performance of the panels produced was evaluated based on standards ABNT NBR 14810:2006 and BS EN 312:2003. By analysis of variance (ANOVA), the fraction of particles of Eucalyptus grandis was significant only in the modulus of rupture (MOR) in static bending. Panels produced with 100% oat hulls presented highest value of MOR.
Abstract in English:Calcium phosphate cements (CPCs) have potential to be used on repairing damaged bones due to their moldability, bioactivity and bioresorbability. These materials combine calcium orthophosphate powders with a liquid leading to a paste that hardens spontaneously at low temperatures. Hence, CPCs could be applied as scaffolds to support cell/tissue growth. This paper studies CPC scaffolds processing by foaming cement's liquid phase in which was added gelatin and chitosan. The former acted to increase the foam stability while the ladder acted as a foaming agent. Moreover, these polymers would enhance scaffold's biological properties by controlling material's total porosity and in vivo resorption. The method proposed led to scaffolds with 58.71% porosity with sizes ranging from 160 to 760 µm and compressive strength of 0.70MPa. After foaming, pores' size, distribution and interconnectivity changed significantly leading to a material that could be applied on bone regeneration since it would allow nutrient's transport, cell attachment and an increase in material degradation rate.
Abstract in English:Polyacrylics have been widely used in coatings. However, their application is limited by low corrosion resistance. One way to enhance their properties is the addition of fillers with adequate properties. In this study, composite materials of PMMA and hBN were developed and deposited on steel by dip-coating. The influence of the amount of hBN in the PMMA coating regarding corrosion resistance was investigated. The surface and cross-section of the coatings were characterized by SEM, the porosity was investigated by systematic manual point count and the adhesion was classified according to the tape test standard. The produced coatings were submersed in NaCl and HCl solutions to analyze corrosion resistance. The results showed that the PMMA/hBN composite coatings improved the corrosion resistance in comparison with pure PMMA. Additionally, the coatings are crack free and well bonded to the metallic substrate.
Abstract in English:In this paper we address some aspects of the kinetics of hydrogen absorption and desorption of Mg2FeH6 nanocomposite powder. The Mg2FeH6 material was prepared from a 2Mg-Fe composition by reactive milling under H2 pressure at room temperature. After mechano-chemical processing, the material was mainly constituted of Mg2FeH6 having a hydrogen gravimetric capacity corresponding to 94% of the theoretical capacity. The kinetics of hydrogen absorption at constant temperature and the transformation of phases during this process were studied. The kinetics of hydrogen absorption presented a two-step behaviour. First, β-MgH2 was formed with faster kinetics than Mg2FeH6 under constant temperature and H2 pressure. Then, β-MgH2 reacted with α-Fe forming Mg2FeH6 in a much slower reaction. Unexpectedly, reaction of hydrogen desorption showed an one-step kinetics, even if Mg2FeH6 and β-MgH2 phases were previously present in the powder.
Abstract in English:The effect of changes in grain size on corrosion resistance of the pure tough pitch copper stripwas investigated in acidic and alkaline NaCl solutions. Accumulative roll bonding as sever plastic process was applied up to 8 cycles to produce the ultrafine graincopper. Polarization and electrochemical impedance tests were used for corrosion resistance investigations. Corrosion morphologies were analyzed by FE-SEM. Results showed that the corrosion resistance decreased up to cycle 2 and increased after rolled for the fourth time due to UFG grain formation after cycle 4. The corrosion degradation in cycle 8 was uniformand it was more intergranular for the sample of cycle 2 and the unrolled counterpart.
Abstract in English:The objective of this study was to evaluate the density, density profile, water swelling and absorption, modulus of elasticity and rupture from static bending, and tensile strength of experimental medium-density fiberboards manufactured using Dendrocalamus giganteus (Munro bamboo). The fiber production was carried out through the chemo-thermo-mechanical pulping process with four different conditions. The panels were made with 10% urea formaldehyde resin based on dry weight of the fibers, 2.5% of a catalyzer (ammonium sulfate) and 2% paraffin. The results indicate that treatments with the highest alkali (NaOH) percentage, time and splinter heating temperature improved the physical properties of the panels. The root-fiber interface was evaluated through scanning electron microscopy in fracture zones, which revealed fibers with thick, inflexible walls. The panels' mechanical properties were affected due to the fiber wall characteristics and interaction with resin. Giant bamboo fiber has potential for MDF production, but other studies should be carried out.
Abstract in English:The increasing awareness of the environment protection has contributed to concerns regarding alternative procedures for recycling of plastic wastes. Since chemical processes are high cost, energy and often environment harmful, thermo-mechanical techniques of recycling rises as a good alternative. This research deals with mechanical characterization of thermo-mechanical recycling of composites based on recycled high density polyethylene (HDPE) from post-consumed motor-oil plastic containers as matrix and natural fibers (sisal) as reinforcement. The composites were made by extrusion and then melt blended in a compression mold. The sisal fibers do not contribute to increase tensile strength. As fiber content increases loss of ductility is observed.
Abstract in English:The use of a waste from mineral processing, a spodumene-bearing rock, was investigated as a flux for bone china composition, partially replacing feldspar. The effect of lithium oxide in bone china body was favorable for reducing firing temperature. The presence of Li2O reacting with other oxides and silicates formed a liquid phase of lower viscosity, which was favorable for densification through viscous flow sintering, and to a higher mechanical strength. It was obtained a large plateau for firing, without deformation on firing (pyroplastic deformation) of parts; which is not an easy task to be achieved in bone china processing. Rheological and casting properties were also investigated. Microstructures of the fired bodies were discussed. They correlated well with the final properties of the parts.
Abstract in English:Titanium and its alloys have been used in biomedical applications because of their satisfactory mechanical properties, biocompatibility and corrosion resistance. Their high corrosion resistance has been attributed to the formation of a thermodynamically stable titanium oxide layer on the surface of these materials. In the present work, the corrosion behavior of Ti-9Mo (wt %) alloy, doped with oxygen, was evaluated in a phosphate buffered saline (PBS) solution. The results showed a small decrease in the corrosion potential and a reduction in the corrosion rate with the oxygen doping, indicating a higher corrosion resistance is desirable for biomedical applications.
Abstract in English:The goal of this paper is to present the development and comparison of p-type multicrystalline silicon solar cells with screen printed metallization. Industrial processes were developed to manufacture the n+pn+and n+pp+ solar cells. The n+pn+ structure was obtained with single phosphorus diffusion. The n+pp+ solar cell was developed and the p+ region was optimized experimentally by using one single high temperature step for phosphorus and aluminum diffusion. The results showed that the average efficiency of n+pn+ solar cells with no texturing was 12.3%. The efficiency increased 1.5% (absolute) with the implementation of acidic solution texturing. The highest efficiency achieved for solar cell without (n+pn+) and with (n+pp+) back surface field (BSF) was 13.8% and 14.1%, respectively. The BSF does not result in a significant improvement in the efficiency when the diffusion is carried out in a single step thermal diffusion in industrial process with screen printed metallization.
Abstract in English:In this work, a method was developed for the application of red mud, an alkaline leaching waste, from a bauxite processing plant located in northern Brazil (Amazon region) as starting material for heavy clay products. Samples were prepared by pressing blends of red mud and clay, which were then fired at temperatures from 900 ºC to 1190 ºC. Characterization was carried out by chemical analysis, differential thermal analysis (DTA) and X-ray diffraction (XRD), and the following ceramic properties were evaluated: water absorption, linear shrinkage and flexural strength. In order to evaluate the Na+ stability in the dense ceramic, leaching tests were also carried out on the specimens after sintering process. Results indicated that samples with 50 and 70 wt% of red mud are proper for being used in the production of ceramic bodies, due to its excellent properties, mainly high mechanical resistance and low water absorption, showing thus, an option to minimizing the environmental impacts caused by the aluminum industry.
Abstract in English:The aim of this study was to evaluate the effects of deproteinization with 5.25% sodium hypochlorite (NaOCl) prior to enamel conditioning with 10% polyacrylic acid (PAA) and 35% phosphoric acid (PA) on the bond strength (BS) of brackets bonded with resin-modified glass ionomer cement (RMGIC). One hundred human premolars extracted for orthodontic reasons were divided into 5 groups (n = 20 in each group): G1 (control), enamel conditioning with PA, application of adhesive and bonding of brackets with TransbondTM XT composite resin (3M/Unitek, Monrovia, CA, USA); G2, enamel conditioning with PAA and bonding with RMGIC (Fuji OrthoTM LC, GC America, Alsip, IL, USA); G3, NaOCl-treated enamel, conditioning with PAA and bonding with RMGIC; G4, enamel conditioning with PA and bonding with RMGIC; and G5, NaOCl-treated enamel, conditioning with PA and bonding with RMGIC. Once the brackets were bonded, the teeth were stored in distilled water for 24 hours at room temperature and pressure until being subjected to shear stress in a Universal Mechanical Testing Machine (EMIC® DL 500, São José dos Pinhais, PR, Brazil). The BS value was higher in G1 (17.08 ± 6.39) than in any of the experimental groups (p < 0.05). No statistically significant differences were noted between groups using RMGIC (p > 0.05), except between G3 (9.86 ± 2.90) and G5 (5.00 ± 2.49). No statistically significant differences were noted between the mean Adhesive Remnant Index values among the evaluated groups (p > 0.05). Conclusion: The use of NaOCl combined with PAA increased the BS of brackets bonded with RMGIC. The deproteinization of the group treated with PA reduced the shear bond strength of the brackets.
Abstract in English:The species and density of Eucalyptus wood poles installed in the electrical network are useful parameters which must be considered when it is necessary to establish the service life of these structures. In this work, eucalyptus poles samples were collected and analyzed by scanning electron microscopy and energy dispersive spectroscopy (SEM/EDS). SEM image analysis showed that the lumen diameter average of fiber substantially is variable between the three species studied, in line with the wood density obtained in laboratory, for poles with several years in service in the electricity network, as well as for not used poles. In addition, EDS microanalysis was utilized for identify the presence of chemical preservatives employed in the conservation these poles. The analysis method proposed proved effective for characterization for this timber.
Abstract in English:The aim of this work was to experimentally evaluate the use of calcium carbonate as a pore-generating agent in ceramic compositions. Compositions that contained 50% kaolin, 20% limestone, and different concentrations of quartz and feldspar were prepared by uniaxial pressing. Samples were heat-treated at a heating rate appropriate to induce calcium carbonate degassing, and they were then sintered at 800, 900, and 1050 ºC. Tests of X-ray fluorescence, thermogravimetric analysis, porosimetry, and air permeation were performed. The composition (wt%) that contained 50% kaolin, 20% limestone, 20% feldspar, and 10% quartz and heat treated at 1050 ºC (k1 = 1.73×10-13 m² and k2 = 1.00×10-8 m) showed the highest level of permeability among the investigated samples. Fluid dynamics simulations showed that the prepared samples would exhibit a pressure drop greater than the range desired for applications that involve the filtration of aerosols, but alternatively would be suitable as substrates for asymmetric membranes in microfiltration applications.
Abstract in English:Textural and catalytic properties of nickel, palladium or titanium oxides supported on MCM-41 materials were evaluated in this paper. The results indicated that the MCM-41 material with well defined and highly ordered hexagonal structure was obtained. After metal ions impregnation and calcinations, the structure of MCM-41 was preserved and formed metallic oxide particles, however the decreased of surface area of these structures occurred. The catalysts studied showed maximum conversion levels of dibenzothiophene in the range of 50-65%.
Abstract in English:Since Corrosion of reinforcing steel in concrete is the cause of major economic losses, Portland cement has been traditionally replaced by cements blended with pozzalanic materials, most of which have been found to reduce the corrosion of steel. This paper shows the results of an experimental research aimed to investigate the corrosion of reinforcement in mortar using electrochemical impedance spectroscopy (EIS). For this, concrete laboratory samples containing a 0.0055 m steel bar and prepared with just ordinary Portland cement (OPC) and metakaolin at a replacement level of 20% were analyzed. In order to accelerate the steel corrosion process, all the samples were kept in a 3% NaCl solution and a constant anodic electrical potential was applied. Variations in the water to cementitious material ratio (0.5 and 0.6) and metakaolin proportion were analyzed, while the cementitious material to sand ratio was kept constant at 1:2.25 in all of the specimens. The results showed a reduction in corrosion rates when metakaolin was used as a blending admixture, especially at water to cementitious material ratio of 0.5.