Resumo em Inglês:

The objective of this study was to evaluate Vero cells in in vitro biocompatibility tests with pure PHBV and PCL and 75/25 and 50/50 blends developed for bone tissue bioengineering in dense or porous forms. The biomaterials were characterized morphologically by scanning electron microscopy, (SEM) stereoscopic imaging (SI), and micrometer measurement. Cellular assay was made by MTT, morphological and cytochemistry analysis. The dense and porous scaffolds presented irregular surfaces. SEM allowed to observe details of the irregular surface throughout the dense samples and confirmed the absence of pores. It was found interconnected pores on porous samples. The porous samples were thicker than the dense samples. None of the polymers was considered toxic. Lower activity measured by MTT was observed for the 50/50 blends, suggesting a slower cell adhesion pattern. The cells were able to spread almost throughout the surface of the polymers, even into the pores. The dense and porous 50/50 samples were so brittle and difficult handling. Except for the 50/50 blends, the polymers were generally good substrates for the cells, were non-toxic, and exhibited the recommended morphological features. In addition, these biomaterials did not inhibit specific biological responses identified at the cytochemical level.

Resumo em Inglês:

A geopolymer with high specific surface area was synthesized from metakaolin, amorphous silica and KOH, in the absence of foaming or saponification agents. The mixture modelling technique was selected for this study among the Design of Experiments tools, using surface area and total pores volume as response variables. The Si/K = 2.46 and Si/Al = 1.37 ratios lead to the optimal experimental conditions, allowing the formation of a geopolymer having a specific surface area of 75 m2/g and total pores volume of 0.28 cm3/g. The pores had a bimodal pore size distribution (7 and 20 nm). In spite of its amorphous nature, this structure is similar to zeolites in terms of ion exchange and metal ions accommodation. Therefore, this study envisages its application as a catalyst support.

Resumo em Inglês:

As-cast and as-extruded Mg-[x]Zn-0.3Mn (x=1.5, 2.0 wt.%) alloys were prepared by means of medium-frequency induction-heating technique and extrusion process, respectively. The microstructural characteristics, thermal conductivity and mechanical properties of the samples were characterized. The research results show that the samples are composed of major α-Mg and minor second phases MgZn2. For the as-extruded samples, the grain size is refined. After extrusion, much more second phases were precipitated from α-Mg matrix and the dislocations were reduced. The degree of lattice distortion was decreased for as-extruded samples. Because of the decline of lattice distortion degree, the as-extruded samples display much higher thermal conductivity than the as-cast samples. Additionally, on account of lower lattice distortion, Mg-1.5Zn-0.3Mn alloy has a bit larger thermal conductivity than Mg-2Zn-0.3Mn alloy. Finally, the as-extruded alloys present good mechanical properties based on the fine-grained strengthening and second-phase strengthening mechanism.

Resumo em Inglês:

This work investigates the influence of the physicochemical characteristics of heavy (17.5 °API), medium (28.3 °API) and blend (50% heavy + 50% medium) crude petroleum on corrosion of AISI 1020 carbon steel at 25.0 ± 1.0°C. The corrosion resistance of steel was analyzed by electrochemical impedance spectroscopy, potentiodynamic polarization, and scanning electron microscopy. The electrochemical results and the micrographs show that the corrosion on steel surfaces after contact with the heavy oil is lesser than medium and blend petroleum, although the heavy oil presents a higher amount of total acid number, sulfur compounds and salt. On steel sample immersed in heavy oil, a localized pitting corrosion was identified, while on samples immersed in medium and blend petroleum was found evidence of pitting and alveolar corrosion.

Resumo em Inglês:

In this study, MAO treatment was used to enrich, with bioactive Ca, Mg and P atoms, as-casted and heat-treated Ti-15Zr-xMo (x = 0, 5, 10 and 15 wt%) alloys, for potential use as advanced metallic biomaterials. The chemical composition of the surface was evaluated by EDS and XPS measurements. The morphology and microstructure was analyzed by OM and SEM images. Crystalline structure and phase composition were characterized by XRD measurements. The results indicated that the oxide layers were porous, with microstructural features of the bulk (grain size and secondary phases) slightly affecting the surface characteristics (pore size, chemical and phase composition). The crystalline structure of the oxide layers were composed by a mixture of anatase and rutile phases (TiO2), with a minority of tetragonal zirconia (ZrO2) and traces of CaCO3 and P2O3 compounds. Chemical analysis indicated that the oxide layers were composed mainly by Ti and Zr oxides, with successful incorporation of the bioactive elements. The obtained results evidenced that the surface characteristics of MAO-treated Ti surfaces can be properly adjusted by the addition of alloying elements and implementation of specific heat treatments on the substrate. This finding can be quite useful for the development of novel biomedical implants.

Resumo em Inglês:

Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is the most successful transparent conductive polymer widely used in functional organic devices. However, its potential in fabrication of highly conductive electrodes still has not been fully explored. This paper is an attempt to fill the existing gap of knowledge on possible post-treatments of dimethyl sulfoxide (DMSO)-doped PEDOT:PSS thin films. In the present study, surface morphology, optical and electrical properties of untreated and sulfuric acid treated DMSO-doped PEDOT:PSS multilayers on the glass coverslip substrates are examined. It is demonstrated that short-time sulfuric acid treatment enhances electrical and optical properties, and smoothens surface of the transparent conductive films. Enhancement of electrical conductivity by more than 30 % can be associated with increase in doping level, removal of excess PSS and accompanied shape alterations of the conjugated PEDOT chains. Acid treatment also results in smoother transmittance spectra and a slight improvement of optical transparency. Hence, sulfuric acid post-treatment can be considered as a simple and inexpensive technique for the complementary doping of DMSO-doped PEDOT:PSS films with the aim to develop the more effective transparent electrodes.

Resumo em Inglês:

High Temperature Nitrogen Plasma Based Ion Implantation (HT-NPBII) has been used to treat the surface of niobium superconducting reentrant cavities, which are part of parametric transducers in a resonant-mass gravitational wave detector. The aim is to enhance the corresponding electrical quality factors (Q-factors) which are closely related with the increase of the sensitivity of the system. In this experiment, the cavities are immersed in plasma and bombarded by energetic nitrogen ions, which are implanted into the surfaces of these heated substrates. The heating temperature of the cavities is controlled during the treatment and its level directly affects the N implantation depth profile due to the diffusion process. Additional tailoring of the nitrogen doping can be performed by the adjustment of the intensity and the duty cycle of the high negative voltage pulses used for ion implantation. For implantations performed at 5 kV /20 µs /300 Hz/ 700 °C, nitrogen atoms occupy interstitial spaces in the crystal lattice of niobium. The treatment of niobium superconducting cavities under these parameters caused the enhancement of two orders of magnitude of respective Q-factors. A set of characterization techniques was performed herein in order to help with the understanding of the underlying mechanism behind this phenomenon.

Resumo em Inglês:

Gamma tomography was used in this work to evaluate the recurrent defects in welding processes in naval steel sheets. It was used a first-generation equipment consisting of a source of Cesium-137, with activity of the order of 200 mCi, coupled to a Thallium-doped Sodium Iodide detector, NaI (Tl). For the study, specimens were produced in ASTM A131-AH36 steel sheets with 13.7 mm thickness; all welded by Metal Active Gas process. One reference sample was fabricated, with no macroscopically measurable defects and another welded under wind conditions producing a weld bead with different types of discontinuities. The microstructural characterization of welded joints made possible a qualitative evaluation between defective joints, in relation to the joint without defects. With the data of the tomography, 3D graphics were drawn that enabled the statistical survey and analysis of clusters of the results that allowed the localization and the dimensioning of the discontinuities that appeared as counting peaks in these graphics. It was revealed that the defective welding showed porosity of up to 39.28% of its volume, and the acceptable size crack must be less than 1 mm based on ASME-B31.3, showing the viability of the tomography for this type of nondestructive analysis.

Resumo em Inglês:

This paper investigates the tensile properties and bending performances of stitched thermal protection structure in engineering, and the effect of stitching density on mechanical properties, via a model of ceramic-aerogel stitched sandwich. With the help of ANSYS, titanium alloy bottom plate was added to the bottom surface of the thermal protection structure, which was regarded as the protected body, and the two were synergistically deformed. The validity of the entire model was verified. The distribution of stress field inside the structure was determined by substructure precise analysis method and the law of the finite element solution was given. The results show that interlaminar performance of the stitched sandwich is improved by 30% on average under tensile or four-point bending conditions.

Resumo em Inglês:

This aim of this work is to present an analysis of the influence of impregnation against biological demand, realized with saline solution of CCB (Chromated Copper Borate preservative) by vacuum-pressure process, on physical-mechanical properties of tropical wood species Simarouba sp., Cedrelinga catenaeformis and Erisma uncinatum Warm. In theory, such process could increase the number of surface defects in wood pieces and reduce its strength properties. To investigate this influence, the complete species characterization was carried out in two conditions (without treatment and CCB treated wood). Tukey’s multiple comparisons test (5% significance level) was applied. In addition, scanning electron microscopy (SEM) photomicrographs were obtained with the energy dispersive spectroscopy (EDS) to investigate preservative presence at the cellular level. Results permitted to conclude that CCB impregnation process did not affect physical-mechanical properties of the studied species.

Resumo em Inglês:

Cobalt ferrite (CoFe2O4) nanoparticles (NPs), with an average diameter of about 4-10 nm, were produced by the proteic sol-gel method and successfully doped into the active layer of poly(3-hexylthiophene-2,5-diyl) (P3HT):[6,6]-phenyl-C61-butyric acid methyl ester (PCBM) organic solar cells. Pristine and CoFe2O4 NPs-doped blends of P3HT:PCBM were dispersed in a mixture of o-xylene:tetralin (1 mg/mL) based non-halogenated solvents and deposited via a semi-industrial blade coating process on flexible substrates to fabricate large area (0.55 cm2), flexible organic solar cells with inverted configuration. The main focus of this study aims to assess the influence of NPs on the efficiency, stability and lifetime of the produced devices. From the photovoltaic parameters it was observed that the optimization of the bulk-heterojunction through the incorporation of CoFe2O4 NPs resulted in increased short-circuit current density. As a result, the power conversion efficiency of doped devices increased by 10 % when compared with the undoped reference devices. Tests of lifetime and stability were performed using International Summit on OPV Stability (ISOS) protocols ISOS-D-3, ISOS-O-1 and ISOS-L-1. For the duration of the tests (1200 h), the results showed that doped cells presented performances at least comparable with those of reference cells.

Resumo em Inglês:

Refill friction stir spot welding (refill FSSW) is a solid state joining technology developed and patented by Helmholtz-Zentrum Geesthacht. Refill FSSW is a welding process suitable for spot joining lightweight materials in similar and dissimilar joint configuration. The result is a spot welded in lap configuration with minimal material loss and a flat surface with no keyhole. In the present study, refill FSSW was applied to join the similar 6061 aluminum alloy sheet with 1.25 mm thickness. The objective of this work is to investigate the influence of the hook on the microstructure and mechanical properties of the weld. The hook is a geometrical feature, formed as a result of the upward bending of the sheet interface during the sleeve plunge and retraction during welding. The weld strength had a negative correlation with the hook height, however it was concluded that the shape of hook changes according to the combination of process parameters. The highest value of the lap shear corresponded to the smallest hook height.

Resumo em Inglês:

A kind of novel anti-wear Ni-TiC composite coatings was deposited successfully on 42CrMo steel by pulsed electrodeposition method with various TiC particles concentration. The effect of TiC concentration on morphologies and properties of Ni-TiC composite coatings were investigated and the optimum concentration of TiC particle was obtained. Results demonstrate that TiC particles were distributed uniformly in the Ni-based coatings and Ni-TiC composite coatings consisted of refined nickel nanocrystalline size. When the TiC particles concentration was 32 g/L, the highest volume percentage of TiC particles with 23.9 Vol.% and maximum micro-indentation hardness of the Ni-TiC composite coatings with 475 HV were achieved. Ni-TiC composite coatings show significant improvement in wear resistance in comparison with TiC free Ni-P coating.

Resumo em Inglês:

Crystalline cellulose nanofibers are obtained from the bark of Cereus Forbesii, a cactus native to the arid areas of South America. The obtaining of cellulose nanofibers was carried out in several steps: pretreatment of the raw material, elimination of hemicellulose and lignin to obtain cellulose, and an acid hydrolysis of cellulose to obtain crystalline cellulose nanofibers. The cellulose nanofibers obtained have a crystallinity index of 82% and a nanofiber diameter of 18 nm. An average crystallite size of 6 nm was calculated for the crystalline domains that form cellulose nanofibers. The high crystallinity of the obtained cellulose nanofibers makes the sample very homogeneous and decomposes in a relatively narrow temperature range (between 290°C and 375°C). The complete degradation of crystalline cellulose polymer chains takes place between 375°C and 600°C. The morphological and structural studies are carried out by scanning electron microscopy of field emission, infrared spectrometry with Fourier transform, and powder X-ray diffraction. The thermal stability of the samples is determined by thermogravimetric analysis.

Resumo em Inglês:

Rare earth garnets (REE3Fe5O12) have magnetic-electric and optical properties that can be used in transmitters, microwave and data storage devices. These properties depend mainly on partial or total substitution of the cationic sites, as well as by the synthesis method used. Therefore, in this work was studied the influence of the substituting cation on the structural and morphological properties of new garnets with formula Sm3−xREExFe5O12 with x = 0.0 - 1.0; obtained by the solid-state reaction method. Characterization of samples was carried out by XRD, Rieltveld refinement, SEM and Raman spectroscopy. The results showed that the substitution favors system stability and formation of garnets single phase with cubic structure and space group of Ia3d (230) at temperatures lower than reported by other authors. The substitution generated a decrease of the lattice parameters, the crystal size and favored particle formation of the order of micrometers (from 1.3 to 3.6 µm).

Resumo em Inglês:

In this research work, a finite element model is developed to predict the temperature field and residual stress during plasma arc welding of thin Ti-6Al-4V sheets. Dhinakaran’s heat source model which is based on Parabolic Gaussian distribution is used to predict the temperature field and Anand’s model is used to predict the residual stress. Numerical simulation is performed using ANSYS®. Heat transfer analysis is carried out primarily and the temperature field is given as the input for structural analysis. The concept of APDL programming is used to implement the governing equations. Experimental work has also been conducted to validate the predicted data. Hole Drilling Method (HDM), a semi destructive method and XRD analysis is used to measure the residual stress on the welded specimen. A good agreement is found between the predicted values and measured values.

Resumo em Inglês:

New nanostructured Fe-(Nb,Cr)-(C,B) multicomponent alloys have been developed for hardfacing application. They have better wear resistance than traditional Fe-Cr-C alloys. The nano-alpha-Fe, eutectic and hard carboborides phases of the weld metal usually show variations with the welding procedure. 6 test samples with different heat input were welded. It was observed that the percentage of eutectic phase and the distance between carboborides increased for the high heat input. Microhardness of eutectic phases showed a linear relationship with the spacing. Samples with high percentage of alpha-Fe phases showed a severe plastic deformation. Wear resistance was optimal for thinner eutectics phases. The presence of needles carboborides improved wear resistance.

Resumo em Inglês:

In this study, porous microspheres of TiO2 (µTiO2) were synthesized, characterized and incorporated into an acrylic paint formulation to obtain a photocatalytically active paint. In a novel approach, the antifungal properties of the µTiO2 paint were evaluated using Monascus ruber as the representative microorganism and compared to those of a photocatalyst-free paint. The photocatalytic activity of paint films was determined by methylene blue (MB) degradation under real conditions of application. High photocatalytic and antifungal activity was observed, with the microorganism culture showing the formation of growth inhibition halos, typical of materials that produce biocides that diffuse into the culture medium.

Resumo em Inglês:

There are 6 different types of equations that have been formulated to measure friction through the bending under tension test, however, there is no work to show whether these calculations actually represent what is happening in a sheet metal stamping process. This paper aims to make a direct comparison between the bending under tension test and the sheet metal forming of a test piece to see if the friction coefficient reported by the test is able to predict friction in a real part. Several sources of information were used such as computer simulations, bending under tension test with different sensors and sheet metal forming tests of a cylindrical geometry to evaluate the friction. The results indicate that the equations already developed are not able to accurately predict the friction at the sheet interface and, therefore, a new equation was developed for this that is simpler to measure and presented satisfactory results.

Resumo em Inglês:

We have examined heating-induced phase decomposition and its kinetics for Zr65Ni30Pd5 amorphous alloy in an argon atmosphere. The amorphous phase decomposes through three stages in the order of amorphous → icosahedral quasicrystal (I-Q) + amorphous → approximant cubic Zr2(Ni,Pd) → tetragonal Zr2Ni + tetragonal Zr2Pd phases. The approximant crystalline (APC) Zr2(Ni,Pd) phase includes icosahedral-like local atomic arrangements and the structural similarity between the I-Q and APC phases seems to enable the multistage phase decomposition through the precipitation of the APC phase. The primary precipitation of the I-Q phase from the amorphous phase occurs through nucleation and growth mechanisms through two-dimensional (2D) growth mode at lower heating rate and 3D growth mode at a high heating rate.

Resumo em Inglês:

In this study, the structure-properties relationship between the thermal factors of BR/SBR blends [normalize factor hBR100hBR100−hBRx, and the maximum peak temperature difference of thermal decomposition of BR and SBR ΔTmax=TmaxBR−TmaxSBR] with their aging time (1 to 40 days) was demonstrated using DTG profile of uncured compounds. The correlation between these two thermal factors with aging time yielded a linear equation with an acceptable correlation coefficient (R2 ≥ 0.95). By the obtained linear model the aging time of rubber compounds based on BR / SBR was predicted. In the second step, the curing behavior and mechanical characteristics of tire tread formulation based on BR/SBR were forecasted using the aging time of compounds, without time-consuming and costly tests. In all cases, the accuracy and reproducibility of obtained data were evaluated.

Resumo em Inglês:

Heavy haul transportation (load over 30 tons/axle), as well as the axle load, has been more and more used in Brazil and worldwide. The stress generated in the wheel-rail contact with loads up to 30 tons/axle is around 760 MPa, which causes premature wear and cracks of conventional wheels (AAR (Association of American Railroads) class C). Microalloyed wheels are fundamental on heavy haul transport, whose main function is to combine high hardness, ductility, and yield strength of the material in order to prevent shelling. The main purpose of this research is to develop a new microalloyed wheel steel with niobium addition that meets all the requirements of the AAR class D material with mixed microstructure composed of pearlite and bainite. The 0.71C/0.020Nb steel developed in this study (Nb material) for railroad achieved the standards required for AAR class D in all mechanical properties, with fracture toughness higher than the usual vanadium microalloyed steel used in comparison. The Continuous Cooling Transformation (CCT) diagram showed the presence of bainite even at very low cooling rate, in the range between 0.3 - 2 °C/s. These cooling rates to form bainite are much lower than those observed in other steels with similar composition.

Resumo em Inglês:

The pitting corrosion of three duplex steels (DSS), SAF2205, SAF2507, Z3CN20.09M thermally aged at 350 - 500 ℃ for 5500 h was investigated by the means of electrochemical techniques. The pitting potential (Ep) of thermally aged Z3CN20.09M specimens decreased with increasing of ageing temperature, however, the Ep of SAF2205 and SAF2507 thermally aged specimens decreased first and reached the lowest value at 450 ℃ and then increased slightly. The electrochemical impedance spectroscopy results are coincident with the potentiodynamic polarisation testing results. The variation in the charge transfer resistance of specimens coincided with the Ep values. There is little influence of low temperature (below 350 ℃) on resistance to pitting of SAF2205 and SAF2507 DSS. But, the pitting resistance of them degrades drastically ageing at higher temperature above 450 ℃. The deterioration in pitting resistance of thermally aged DSS specimens mainly attributes to the precipitation of Cr-rich α′ phases which affected by temperature markedly. At the range of 350 -500 ℃, the temperature the higher, the precipitation of Cr-rich α′ phases the more. The formation of G phases and the healing process during the long thermal ageing at 500 ℃ is the other reasons for the change in pitting resistance.

Resumo em Inglês:

Welding is widely used in the manufacture of steel products. Metallurgical processes during welding produce residual stresses in different zones of the welded parts. Welding residual stresses, particularly tensile stresses, can significantly impact the reliability and the integrity of the welded components. Our recent works report the effect of residual stress redistribution in a relatively short, up to two weeks, period after the welding procedure. The hypothesis that the observed stress relaxation phenomenon is associated to the microstructure evolution that occur in the material after the end of the welding procedure was proposed. To prove this hypothesis a physical simulation of the influence of the welding thermal cycles on the base metal with GLEEBLE equipment was performed. Using SEM EBSD, technique the variation of grain boundary misorientation accompanied by the residual stresses redistribution in the first days after welding thermal cycles simulation were observed.

Resumo em Inglês:

Planetary ball mills are able to perform dry and wet grinding. Most experimental analyses and computer simulations in this field are mainly about dry grinding. In order to empirically evaluate the wet grinding process, test grindings benches were manufactured, calcined alumina powder was ground, and the particle distribution analyzed. Effects of the media geometry (size and shape) on particle distribution, morphology, and phase composition of ground alumina were investigated. Smaller media leads to smaller particle size and cylindrical media provides a poor grinding performance but its product has the narrower particle size distribution. Alumina showed no phase change in the grinding tests. The experiments presented in this study can be used as an aid in the proper choice of grinding media or even to validate emerging models capable of predicting breakage in wet grinding.

Resumo em Inglês:

Microstructure, hardness and electrical properties of the selected ternary Ag-Bi-Ge alloys were investigated in this study. Isothermal sections of the Ag-Bi-Ge system at 25, 100 and 500 °C have been extrapolated using optimized thermodynamic parameters from literature and experimentally investigated. Performed experiments were optical microscopy, scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS), X-ray powder diffraction (XRD), hardness measurements by Brinell method and electrical conductivity measurements. EDS results were compared with predicted phase equilibria and good overall agreement between experimental and calculated values was obtained. XRD results were also in agreement with predicted phase equilibria. Hardness and electrical conductivity of selected alloys were measured and by using appropriated mathematical model these properties were predicted in the whole composition range.

Resumo em Inglês:

Duplex stainless steels are materials with high mechanical strength, toughness, and corrosion resistance, properties that make them rather appealing for the application on chemical and petrochemical industries. However, the exposure of such materials to high temperatures promotes the precipitation of deleterious intermetallic phases that cause significant damage to the mechanical and corrosion properties of these materials. In this study, the UNS S31803 duplex stainless steel received a thermal treatment at a temperature of 830 °C for 30, 90, and 180 minutes. After the treatment, the precipitates were characterized by backscattered electrons (BSE) and chemical composition mapping, and the properties of impact toughness were assessed by Charpy V-notch test for the different treatment conditions. The corrosion resistance properties were assessed by cyclic potentiodynamic polarization study. The thermal treatments at 830 °C resulted in a considerable reduction of impact toughness, and the corrosion resistance was also reduced in longer treatment times along with the loss of the passivation ability of the materials treated.

Resumo em Inglês:

In this research, suspension through carbon fiber reinforced polyester fiber has given importance because of its adaptability. Leaf springs were moulded the usage of 20% short carbon fiber reinforced polyester (SF), 20% length carbon fiber reinforced polyester (LF) as well as Unreinforced polyester (UP) are evaluated for the joint strength. For determining energy storage, capability and strain rate sensitiveness of moulded leaf spring static overall performance assessments had been completed. Check joints had been subjected to absolutely reversed fatigue loads, at fixed frequency fatigue; leaf spring performance changed into evaluated, with diverse loads until 2 × 107 cycles. The tensile surface failure morphology of the cracks has exhibited via the Scanning Electron Microscope (SEM). The results confirmed the suitability of carbon fiber reinforced polyester fiber for load utility over other taken into consideration materials.

Resumo em Inglês:

Droplets deformation and solidification characteristics in twin-wire arc sprayed Ni-Al were explored in depth. Both theoretical method and numerical model were established for calculating the deformation process of the droplets impacting on the substrate and their solidification behavior in airflow, which based on two models of the volume of fluid (VOF) dual-phase flow and the standard k-ε. The morphology and the microstructure of the composite coatings were analyzed by XRD, SEM and TEM. The results of the experiment indicate the droplets cooling rate ranges from 3.0×107 to 7.5×107 K/s. The main components of Ni-5wt.% Al coating were Ni solid solution, and a small number of Ni3Al4, Al2O3 and NiO. The main phases of Ni-20wt.% Al coating are Ni3Al and NiAl. EDS and TEM analysis shows that there are a few amorphous and equiaxed crystals in the Ni-Al coating. The surface roughness increases with the decrease of spraying pressure and spraying distance.

Resumo em Inglês:

In this study, the effect of temperature treatment during the preparation process of calcium carbonate (CaCO3) nanoparticles was systematically examined for a drug delivery carrier. The CaCO3 powder was prepared by the precipitation method at different annealing temperatures. The morphologies, elemental compositions and crystal structures of the synthesized CaCO3 powder were analyzed by Scanning Electron Microscope/Energy-Dispersive Spectroscopy and X-ray Diffractometry (XRD), respectively. The result shows that the particle size increased with an increase in annealing temperature. Based on the crystal structure analyzed from XRD, the sample was perfectly matched with the calcite/vaterite polymorphs phases. The crystallite size and lattice strains of the CaCO3 powder were calculated from the full width at half maximum parameter. The results show that the increase in annealing temperature leads to an increase in crystallite size and a decrease in lattice strain. The CaCO3 powder has a dielectric constant of 6.0-6.8 that reduced with the increase in applied frequency. The crystal structure, crystallite size, lattice strain, and dielectric properties of CaCO3 powder are dependent of the annealing temperature. Such properties confirm that CaCO3 powder is suitable for drug delivery carrier application.

Resumo em Inglês:

High density polyethylene and high density polyethylene-clay nanocomposites were produced using direct solvent polymerization and a Ziegler catalyst system (TiCl4 and triethylaluminum in hexane). The produced polymer has a high average molecular weight and a multimodal molecular weight distribution composed of four distributions including a very high molecular weight component. The laboratory polymer has a thermal stability in inert atmosphere similar to the commercial high density polyethylene produced by Braskem. In oxidant atmosphere the produced polymer presents three thermal oxidation events above 400ºC due to the combustion of low, medium and high molecular weight molecules. The thermal oxidation of the nanocomposites is shifted and reduced for high temperatures indicating an improvement in the thermal stability of the polymeric matrix due to the clay barrier effect for gases and volatile compounds.

Resumo em Inglês:

In this work, we reported the effects of sputtering power on the structure, optical and electrical properties of InN nanodots prepared on Al2O3 substrate by magnetron sputtering.The results showed that the as-grown InN films exhibited uniform nanodot morphology and the size of the InN nano grains increased with the sputtering power was increased. The InN nanodot exhibited highly c-axis prefered orientation with mainly InN (002) diffraction. The optical band gap of InN samples showed an decreasing trend with the increase in sputteirng power. Moreover, the electrical properties of the InN samples were discussed in detail by hall effect and the carrier concentration and mobility could be adjusted from 3.233×1019 to 1.655×1020 cm-3 and 1.151 to 10.101 cm2/v•s, respectively. These results will lay a good fundation for the applicaion of InN material in the field of gas sensers and light emitting diodes.

Resumo em Inglês:

Red-emitting Gd2O2S:Eu3+ nanophosphors were successfully prepared using a microwave irradiation method followed by hydrogenation treatment. The optimum calcination temperature (900 ºC) was determined by thermogravimetric-differential scanning calorimetry. The X-ray diffraction results showed that all the samples consisted of the pure hexagonal Gd2O2S:Eu3+ phase. The field emission scanning electron microscopy images showed that the Gd2O2S:Eu3+ nanophosphors were spherical, and their average particle diameter increased parallel with the microwave irradiation power. The photoluminescence spectra (under 325-nm excitation) of the samples exhibited red emission corresponding to the 5D0→7F2 transition of Eu3+ ions. A Gd2O2S:Eu3+ nanophosphor screen film was fabricated using the particle-binder sedimentation method. The result shows that the luminance of the Gd2O2S:Eu3+ nanophosphor screen film increased with an increase in the X-ray energy. Hence, this film would become one of the potential candidate for future imaging applications.

Resumo em Inglês:

The shaft furnace knowed Midrex™ is used for the production of direct reduced iron with the use of reformed gas. Another process based on shaft reactors is the Tecnored process, which exhibits the great advantage of using self-reducing agglomerates. Therefore, it was proposed a combination of the shaft furnace for direct reduction with self-reducing pellet burden. In addition, with the aim of improving the furnace efficiency and reducing the need for reformed gas, the injection of natural gas and oxygen into the bustle region is proposed. Thus, it is possible exploit the advantages of direct reduction involving high amounts of hydrogen and faster reactions of the self-reducing process to decrease the CO2 emission, compared to that of blast furnace. The energy profile, productivity, and carbon emission of the traditional shaft furnace were compared with the simulated results after partial replacement of the burden with self-reducing pellets containing fines of elephant grass charcoal. The simulation results for a combination of 15% of self-reducing pellets in the burden with 2.5% oxygen and natural gas injection were the best among the scenarios simulated, with the productivity being 2.7 ton/m3 day and the decrease in the amount of reformed gas being 10%.

Resumo em Inglês:

This paper aimed to develop and characterize superhydrophobic surfaces with anticorrosive properties obtained by the chemical modification of the 5052 aluminum alloy with variation of acid etching time, formation of lamellar double hydroxides (LDH) film and immersion in stearic acid. The specimens were etched in HCl (2M) at 5, 10 and 30 min. The aluminum plates were treated with aqueous solution of zinc nitrate (0.1 M) in the presence of ammonia and then immersed in a stearic acid and ethanol solution (1% w/w) to reduce surface energy. Contact angles (CA) were determined. Surface morphology and composition were analyzed by scanning electron microscopy (SEM) and X-ray energy dispersion spectroscopy (EDS), respectively. Linear polarization tests were performed to analyze corrosion resistance. The optimal superhydrophobic performance was obtained with a contact angle of 154º for 30 min of acid etching. This condition also showed higher corrosion resistance, obtaining higher values of Ecorr and lower values of corrosion current density.

Resumo em Inglês:

The effect of electropulsing treatment (EPT) on quasi-static compression behavior and anisotropy of AZ31 Mg alloy were investigated based on quasi-static compression test. The results show that the orientation of the sample has a significant effect on the deformation mechanism of metal and this mechanism can be changed by pre-deformation and EPT. However, the strain rate sensitivity of the material is not affected by pre-deformation. Compared with the as-received plates, the anisotropy of AZ31 Mg alloy increased in ND-RD plane after pre-compression along the transverse direction, the ∆YS of specimens increased from 87 MPa to 98 MPa. After EPT, the anisotropy of AZ31 Mg alloy gradually decreased with the change of EPT temperature and EPT time, the ∆YS of the sample reached 14.2 MPa when EPT conducted at 200 ℃ for 15 min, which decreased 72.8 MPa compared with the as-received plates.

Resumo em Inglês:

Plasma nitriding has become a powerful tool to improve wear resistance of stainless steels and sustain or improve corrosion resistance with an adequate selection of process parameters. In this work, the short treatment route with temperatures above 400ºC was selected for AISI 420 stainless steel. After the nitriding process, a wide nitrided layer, with good wear and corrosion properties was simultaneously obtained with selected parameters. A 5 hours treatment at 420 ºC resulted in a 10 µm nitrided layer. XRD revealed an expanded Fe-α layer with Fe nitrides but no signal of CrN was found. Wear resistance was improved three and four times in erosion and sliding tests compared to the non-nitrided material. Corrosion resistance was tested in anodic polarization experiments in a NaCl solution. In this test, the samples treated in the short time process presented the best results.