Resumo em Inglês:

Nanostructured nickel substituted zinc alluminium chromites (Zn1-xNixAlCrO4, where, x= 0.0, 0.25, 0.50, 0.75, 1.0) were prepared by simple, cost effective, sol-gel autocombustion method. Temperature of phase formation was analyzed by thermogravimetric and differential thermal analysis (TGA/DTA). Crystallographic studies of all the samples show formation of single cubic spinel phase only. The lattice parameter, crystallite size and X-ray density decreases with increase in Nickel content. The surface morphology of Zn1-xNixAlCrO4 shows spherical interlinked morphology while elemental studies show desired composition. The nanosize of the synthesized material was confirmed by transmission electron microscopy (TEM) which was lies in between 19-25 nm. The DC conductivity as well as thermoelectric power studies of the samples reveals their semiconducting nature. The nanocrystalline chromite has optimal charge separation, which make them to enhance their photocatalytic efficiency. 0.100gm palladium loaded nickel alluminium chromite shows excellent mineralization in water.

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Polydimethylsiloxane (PDMS) membranes with different concentrations of multi-walled carbon nanotubes were prepared in order to evaluate their gas separation performances. Mixed matrix membranes were characterized by scanning electron microscopy, thermogravimetric analysis, Fourier transformed infrared, positron annihilation lifetime and Raman spectroscopies and X-ray diffraction. The permeabilities to CO2, CH4, N2 and O2 were determined. No phase separation was noticed. For carbon nanotubes content of 1 wt%, it was shown a decrease in membrane permeability with slight increase in ideal selectivity, compared to pure PDMS. However, the increase in the filler load up to 6.7 wt% increased the free volume average size of the membranes, improving the contribution of the diffusion to the transport and decreasing ideal selectivities of CO2/CH4, CO2/N2 and O2/N2.

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Purely siliceous MCM-41 and Al-containing MCM-41 (Al-MCM-41) mesoporous materials were synthesized by non-hydrothermal method in alkali-free ions medium at room temperature and short reaction times. Under these synthesis conditions, it was also investigated the influence of Al incorporation in the crystal structure of MCM-41. The solids were characterized by ICP-OES, AAS, N2 adsorption at 77 K, XRD, TEM, NH3-TPD, 27Al and 29Si-MAS-NMR, FT-IR and TGA. The resulting mesoporous materials showed a well-defined hexagonally ordered pore geometry maintaining a uniform and unimodal pore size distribution with high specific surface areas (1000-1400 m2g-1). The Al+3 ions were introduced successfully in the structure of the purely siliceous MCM-41 expanding the unit cell parameter and forming four-coordinated Al species, and in a less extent, forming six-coordinated Al species. In addition, the surface acidity of the MCM-41 increased with Al loading. Contrary, the presence of Al in the MCM-41 mesoporous structure resulted in a decrease of the crystallinity and specific surface area possibly due to the presence of Al species in highly distorted tetrahedral structures and Al extra-framework or amorphous alumina occluded in the pores. The MCM-41 type mesoporous materials obtained in this work show similar characteristics of those synthesized by conventional hydrothermal methods.

Resumo em Inglês:

Aiming to better understand the effects of heat treatment parameters on Ferrite-Austenite phase transformation in a 2304 duplex stainless steel different thermal cycles were applied to this steel in a quenching dilatometer. The obtained microstructures were characterized by optical microscopy, transmission electron microscopy and electron backscatter diffraction. It was noticed that the austenite formation mechanism is strongly dependent on initial ferritized state. If the initial structure is completely ferritized, the nitrogen supersaturated solid solution leads to chromium nitrides precipitation and the rate of austenite nucleation decreases. For higher cooling rates, the ferrite grain boundaries control the austenite nucleation rate. The higher the ferrite grain size, the lower the final austenite fraction. If the steel is cooled from a partial ferritized state, the ferrite-austenite phase boundaries work as austenite nucleation site and the austenite growth rate is favored due to the high interfacial energy and the austenitic structures becomes coarser.

Resumo em Inglês:

The process of vacuum degassing occurs during the secondary refining of special steels. Its main function is to remove undesirable gases. However, during this process, flotation phenomenon and inclusions absorption are reported. The aim of the present work was to study the slag viscosity and vacuum degassing (tank type) capacity in steel cleanliness from an industry perspective. To achieve this objective, slag and steel samples were taken before and after the vacuum stage. The results in steel cleanliness were related to a kinetic stirring parameter (βs) of the vacuum station and to the effect of slag viscosity. The removal of inclusions during the vacuum stage reached 64, 75 and 78% in the diameter ranges of 2.5-5, 5-15 and ≥ 15 µm, respectively. After the degassing process, the composition of non-metallic inclusions seemed to approach the slags' chemical compositions. The stirring process in the vacuum degassing station promotes a significant decrease in the inclusion densities for the 2.5-15 µm diameter range and also in the sulfur content in liquid steel. Regarding the effective viscosities of slags, it was concluded that lower values (0.20 Pa.s) increased slag capacity in inclusion removal, whereas higher values (> 0.40 Pa.s) were detrimental to steel cleanliness.

Resumo em Inglês:

The corrosion inhibition of nanoparticulates zinc ferrite (NZF) pigment was studied. The steel samples were immersed in the NZF pigment extract in 3.5 wt. % NaCl. Electrochemical tests such as electrochemical impedance spectroscopy (EIS) and polarization as well as surface analysis were employed to evaluate the effect of NZF on the steel corrosion. The concentration of Zn and Fe in the pigment extracts before and after immersion of mild steel samples was evaluated by inductively coupled plasma-optical emission spectrometry (ICP-OES). EIS results in total agreement with results of polarization test demonstrated superiority of NZF as an anticorrosion pigment. In the case of samples exposed to NZF extract, the higher resistance and lower double layer capacitance extracted from impedance spectra as well as lower current density from polarization results might be attributed to precipitation of an inhibitive layer on the surface. This was also supported by SEM/EDS and ICP-OES results.

Resumo em Inglês:

Poly(3-hydroxybutyrate) (PHB) was compounded with three different Bentonite clays: natural, purified by ultrasound/sonicated and organically modified with hexadecyltrimethylammonium bromide. PHB/Bentonite masterbatches with 30% clay were prepared in a laboratory internal mixer and letdown with pure matrix to 1% and 3% w/w clay. Test samples were injection molded and characterized by x-ray diffraction (XRD), differential scanning calorimetry (DSC), infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). Increase in Bentonite hydrophobic character was evinced by FTIR for organoclays. XRD of composites showed increase in clay interlayer distance and peak broadening, suggesting formation of intercalated nanocomposites. DSC showed increase in crystallinity and crystallization rate for compounds, especially for PHB/organoclay formulations. Thermal aging was conducted by exposing specimens at 115ºC for up to 120 hours, and mechanical properties were measured according to ASTM standards. Elastic modulus increased and impact strength decreased with time and clay content; clay purification had little effect on the tensile properties. Tensile strength of thermal aged samples showed little variation, except for the organoclay nanocomposites, for which it significantly decreased with exposure time. SEM images displayed a whitened honeycomb structure and detachment of PHB/Bentonite layers which may be connected to cold crystallization and degradation processes taking place during thermal aging.

Resumo em Inglês:

Samples with 40% vol. of pores and a pore size distribution between 100 and 500 µm were produced by powder metallurgy from Ti6Al4V alloy powders. Sintering was performed at 1300 °C during one hour in an inert Argon atmosphere in a vertical dilatometer. The compressive strength and the porosity of these samples was investigated before and after compression tests through X-ray microtomography. The values of the elastic modulus (8GPa) and yield strength (80MPa) are within the range of those used in bone implants. Porosity leads to greater deformation whereas fracture of compacts occurs perpendicularly to the applied load. It was determined that the origin of the failure is generated by rupture of interparticle necks and, large pores enhance the propagation of cracks.

Resumo em Inglês:

Powder metallurgy is a growing sector in industrial production, as it offers outstanding energy, cost and material savings in comparison with established processing routes such as casting. Hot work toll steels are usually produced by ingot metallurgy, but also by powder metallurgy, namely hot isostatic pressing and powder forging routes. In this paper we investigate the possibility of production of a hot work tool steel (AISI H13) by conventional (die compaction and pressureless sintering) and metal injection molding routes, aiming to reduce cost and production time. The sintering behavior was studied from 1250 °C until 1430 °C and the resulting parts were compared in terms of microstructure, hardness and tensile strength. The results showed that both shaping routes together with pressureless sintering are suitable to produce this alloy. By combining the best shaping approach and a tailored sintering cycle, it was possible to produce samples with 400 HV10 as well as tensile strength of 1 GPa, which are comparable to the ones obtained by powder forging.

Resumo em Inglês:

Approximately thousand years ago it was reported the use of mandibles of ants for suture. In this sense, bioinspired components, as absorbable surgical clamps, can be designed. This study is aimed to characterize the mandible of the ant Atta laevigata in order to help the selection of candidate biomaterials for application as surgical clamps. Three pairs of mandibles were used and ten nanoindenations were performed in each pair. The average hardness for the samples in the internal and external regions were 0.36 ± 0.06 GPa and 0.19 ± 0.04 GPa, respectively and the average elastic modulus for the internal and external regions were 6.16 ± 0.23 GPa and 2.74 ± 0.44 GPa, respectively. The morphology of the mandible was observed in detail by scanning electron microscopy, as well as Energy-dispersive X-ray spectroscopy. The average roughnesses on the internal and external regions, measured by atomic force microscopy, were 6.73 ± 0.90 nm and 11.87 ± 1.42 nm, respectively. From these results, it was possible to identify biomaterials that mimic the mandible behaviour for surgical clamp.

Resumo em Inglês:

In this work we evaluate the use of silane agent 3-aminopropyltrimethoxysilane and biopolymer chitosan to functionalize ferrites Ni0.5Zn0.5Fe2O4 using the solvent evaporation method aiming at obtaining hybrid material Ni0.5Zn0.5Fe2O4@SiO2/chitosan for use as a biosensor. The nanoparticles before and after the functionalization showed the major phase Ni0.5Zn0.5Fe2O4. The FTIR spectra showed absorption bands characteristic of CO, axial deformation of CN and SiO band from the silane agent which proved functionalization. The functionalization of ferrite Ni0.5Zn0.5Fe2O4 with chitosan caused a 36.36% reduction in saturation magnetization as compared with ferrite synthesized, however it maintained the ferrimagnetic characteristic indicating to be a promising material for the use in biotechnological applications as for example in magnetic biosensors.

Resumo em Inglês:

We studied physical properties of main-chain liquid crystalline elastomers (MCLCEs) to observe the influence of variations of cross-linker concentrations on properties such as spontaneous deformation, elastic free energy, and order parameter. Cross-linker concentrations of four MCLCE samples were 8%, 12%, 14%, and 16%. Samples with higher cross-linker concentrations underwent spontaneous deformation to a greater extent than those with lower concentrations, indicated by a smaller aspect ratio of length from the end to the beginning of heating. We also reformulated the elastic free energy expression to observe the dependence of the physical quantity on temperature variation. It showed that the maximum relative elastic free energy of the MCLCEs occurred at different temperatures, dependent on cross-linking density, where higher density caused the maximum relative free energy to decrease. The cross-linker concentration also significantly influenced the order parameter of the samples, where the higher the cross-linker concentration, the higher the maximum order parameter.

Resumo em Inglês:

This work presents a consolidated view of the autocatalysis, thermal and entropic effects in martensitic transformation of polycrystalline Fe-31wt%Ni-0.02wt%C, which has been a standard material for the investigation of fundamental aspects of the martensite transformation. The present work is based on the description of classical microstructure descriptors of the transformation and on generally accepted concepts regarding the martensitic transformation in iron base alloys. Present work agrees with the view that the autocatalysis is a means by which the martensite transformation promotes further nucleation and growth. Autocatalysis induces the nucleation and growth of secondary plates in addition to the relatively small number of primary nucleation sites and their corresponding primary plates. We demonstrate that autocatalysis can be factored out into intragrain and intergrain components. The analysis of these factors establishes that intragrain autocatalysis is athermal but intergrain autocatalysis possess an Arrhenius temperature dependence. The reasons for such a behavior are discussed in detail.

Resumo em Inglês:

This paper aims at analyzing the effects of the roller pre-straightening of wire-rods on residual stress distributions in SAE 1045 steel bars. The combined drawing process is used in industrial production of bars in order to obtain a good surface quality and improved mechanical properties complying with specifications of the final products. In this process, prior to the drawing step, a roller straightening of the steel wire-rod is essential, because it provides the minimum straightness necessary for drawing. Metallographic analysis and hardness test were done for selected samples after different processing steps. Also, residual stress analysis of pre-straightened wire-rods by X-ray diffraction and neutron diffraction were carried out. The hardness tests show higher values near the surface and lower in the center of the wire-rod. Besides, the residual stresses results show a big inhomogeneity from one peripheral position to another and also in the evaluated cross section.

Resumo em Inglês:

AgI thin films were grown on amorphous commercial glass substrates with chemical bath deposition (CBD) at different pH values (2, 3, 4, 5, 6), 6 hours deposition time and 60 °C. The structure of the nanocrystals was characterized by X-ray diffraction (XRD). The ratio of Ag+ and I- ions changed the crystalline structures. The presence of the Ag+ ions produces the γ-phase of AgI and excess of iodine concentration produces β-phase of AgI. The pH: 4 was like a transition pH for these phases. The number of crystallites per unit area has maximum value at pH: 5, as the structure is re-crystallization to hexagonal phase. Also, the thicknesses of produced thin films were decreased with increased pH values. Therefore, transmission, reflection, extinction coefficients and refractive index of the materials were affected by thicknesses, and calculated to be 32, 35, 3, 11, 9 (%) - 27, 25, 61, 45, 49 (%) - 0.036, 0.032, 0.067, 0.107, 0.075 and 3.21, 3.02, 5.16, 8.35, 5.70 in 550 nm at pH: 2-3-4-5-6 values, respectively. The exciton peaks of AgI were observed at between 320 and 420 nm. Surface properties were investigated by using scanning electron microscopy (SEM).

Resumo em Inglês:

In the present paper a continuous Finite Element Analysis (FEA) simulation method of the ball indentation hardness test is introduced in order to describe the deformation behavior of nanosilica composites and with this to extract precisely the material's stress-strain behavior. The developed procedure demonstrate in particular the adequacy of this method to determine the nanocomposites' elastic modulus which is compared with Halpin-Tsai and Lewis-Nielsen models as well as with experimental measurements taken from uniaxial tensile tests. The fracture area of all the tensile specimens was examined using a scanning electron microscope (SEM). It is shown that the correlation between the experimental results, the semi-empirical models and the FEA computational models concerning the elastic modulus values was satisfactory with very small deviations.

Resumo em Inglês:

Shape memory alloys (SMA) are attracting considerable attention owing to possible applications from biomedical to aerospace. In particular, CuAlNi alloys present significant advantages associated with low cost, easy processing and superior thermo-electric conductivity over other SMAs such as the NiTi alloys. Characterization of some properties and structural changes caused by martensitic transformation are still open to investigation. The present work evaluated these characteristics in an as-cast plasma processed shape memory Cu-14wt.%Al4wt.%Ni, which was compression tested until fracture. Experimental results showed that an as-cast ingot presents not only chemical and phase homogeneity, but also microstructures composed of grains with martensitic morphology. Martensites β'1 and γ'1, as well as intermediary martensitic R and high temperature β1 were identified by X-ray diffraction tests. It was found that the compressive deformation does not interfere in the phase composition and martensite morphology. However, compression changes the volumetric fractions and crystallographic orientation of the martensites. The mechanical behavior is characterized by an apparent elastic response until the fracture. The fractured surface exhibits brittle aspect like "river patterns" and evidence of intergranular rupture.

Resumo em Inglês:

Stabilization of ferritic stainless steel ASTM 409, for use in automobile exhaust systems, is increasingly in demand, due to higher exhaust gas temperatures. Ti is one of the most commonly used elements. However, high concentrations cause problems during steel casting; however, stabilization with Ti and Nb represents a good alternative. The present study aims to investigate the effect of adding Nb on the microstructure, texture, and forming properties of Ti-stabilized ferritic steels. The results demonstrated that Nb-addition leads to a more deformed microstructure after hot rolling with the strongest {110}〈001〉 Goss component. In the deformed state, the steels displayed the α-fiber, but 11CrTi+Nb steel showed a more intense γ-fiber. After annealing, Nb-addition led to an increase in the γ-fiber and in average normal coefficient of anisotropy (R). Thus, it was demonstrated that the dual stabilization (Ti+Nb) of the ferritic steel was responsible for improving the recrystallization texture and forming proprieties.

Resumo em Inglês:

The microstructure and microhardness of isothermally aged Al-0.22Zr and Al-0.32Zr alloys were investigated. Peak microhardness occurred after aging at 650K for 100 h for both alloys and decreased slightly after aging at 400 h. Nanometer-scale spherical L12-structured Al3Zr precipitates were observed using Transmission Electron Microscopy, these presented r < 7 nm at the center of dendrite branches. In the Al-0.32Zr alloy, particles increased in radius after aging at 650 K from 100 to 400 h while in the Al-0.22Zr alloy, precipitate radii remained constant in the same range. This is possibly due to solute migration to the periphery of dendritic branches, where larger particles nucleated. After aging at 700 K for 100h, there are growth instabilities at the interface of the particles. A theoretical model, used to predict particle growth by diffusion, presented good agreement with the experimental findings.

Resumo em Inglês:

Titanium (Ti) and its alloys are widely used for medical and dental fields due to their excellent biocompatibility, high corrosion resistance, high specific strength and excellent mechanical properties. Different methods have been developed to improve the surface properties of titanium-based implant materials, and consequently the bone-bonding ability. The Ti-7.5Mo alloy was activated by an alkaline treatment with 5M NaOH, heat treatment and subsequent immersion in SBFx5 to investigate the in vitro response of osteoblastic-like cells MG-G3 on altered biomimetic surfaces. Sample surfaces were characterized by scanning electron microscopy. Cytotoxicity was assessed by the MTT assay, total protein content, alkaline phosphatase activity (ALP) and mineralized bone-like nodule formation. It was shown the que alkali treatment led to the formation of sodium titanate and immersion in SBFx5 formed a film of calcium phosphate. The alkaline treatment and heat treatment of 7.5 Ti-Mo alloys followed by soaking them in SBFx5 for 24 hours is a suitable technique once the final samples were biocompatible, allowed the attachment of the osteoblastic-like cells (MG-G3), and increased the mineralized like-bone nodules formation by these cells.

Resumo em Inglês:

CA6NM steel is widely used in the manufacture of hydraulic turbines metallic parts, due to its resistance to corrosion and cavitation damage, combined with good weldability and fatigue properties. However, welding of this type of steel is complex and to ensure a minimum residual stress after welding it is necessary perform a post welding heat treatment (PWHT) of the part. This study aims to analyze the effect of a PWHT on the microstructure and mechanical properties of CA6NM steel weld joint produced by the FCAW process and compare it with the characteristics of an as-welded joint. A martensitic microstructure has been present in both materials. However, the PWHT material has shown finely dispersed retained austenite, in an amount near 10 vol.%. Vickers microhardness values of all regions of PWHT welded joint present lower hardness values compared to those of the as-welded joint. Despite nearly identical toughness values of the weld metal from AW and PWHT samples, results of fracture analysis have shown distinct features in appearance of the fractures.

Resumo em Inglês:

The effect of maleic anhydride (MA) content on morphological, thermal, thermomechanical and mechanical properties of PA6/AES/MMA-MA (66.5/28.5/5 wt%) system was investigated. In general, the simple incorporation of MMA-MA to PA6/AES system is responsible for enhancements in mechanical performance. PA6/AES/MMA-MA3% and PA6/AES/MMA5% exhibited similar morphology and final properties, indicating no MA content effect on the studied system. On the other hand, PA6/AES/MMA-MA10% exhibited a quite different morphology and lower mechanical performance compared to the other compatibilized blends. Such unexpected behavior was not attributed to the effective maleic anhydride content in this composition, but to the reduced molar mass resulted from the excess of non-reacted MA monomer during the synthesis procedure.

Resumo em Inglês:

Modeling electrical conductivity of polymer composites with conductive fillers has great applicability to predict conductive materials behavior. In this study, the electrical behavior of simple and hybrid systems prepared from Carbon Black (CB) and Carbon Nanotubes (CNT) was studied. There have been few advances reported in the literature regarding the modeling of hybrid systems, which motivated the development of this study. More specifically, a program was developed with the intention to describe the electric percolation threshold and the effect of synergism between the conductive fillers. Simulation was performed using the Monte Carlo method and Fortran programming language, considering concentration and geometry of conductive fillers to the system in two dimensions. Finally, simulation results were compared with the experimental results and this method proved to be effective in predicting the systems percolation threshold, being an important contribution to predict material behavior, which allows reducing the number of samples to be prepared in an experimental study.

Resumo em Inglês:

A comparison of the influence of microstructure and texture on mechanical behavior between the niobium-stabilized ferritic stainless steel type ASTM 430, 430Nb, and the niobium-titanium-stabilized ferritic stainless steel type ASTM 439 was performed. The two steels were supplied as cold rolled thin sheets and the annealing was interrupted in different temperatures aiming the characterization of the microstructure and texture in different stages of recrystallization using optical microscopy, Vickers microhardness and Electron Backscatter Diffraction. The annealed samples were tensile tested to determine the mechanical properties and undergone to Swift test to evaluate the drawability. The steel 430Nb showed smaller grain size and greater yield stress. The steel ASTM 439 presented higher normal anisotropy coefficient, R, and higher Limit Drawing Ratio due to greater proportion of γ fiber. These results are presented and discussed in terms of precipitates and crystallographic texture developed in the recrystallization of both steels.

Resumo em Inglês:

Silicon carbide nanotube (SiCNTs) has been proven as a suitable material for wide applications in high power, elevated temperature and harsh environment. For the first time, we reported in this article an effective synthesis of SiCNTs by microwave heating of SiO2 and MWCNTs in molar ratio of 1:1, 1:3, 1:5 and 1:7. Blend of SiO2 and MWCNTs in the molar ratio of 1:3 was proven to be the most suitable for the high yield synthesis of β-SiCNTs as confirmed by X-ray diffraction pattern. Only SiCNTs were observed from the blend of MWCNTs and SiO2 in the molar ratio of 1:3 from field emission scanning electron microscopy imaging. High magnification transmission electron microscopy showed that tubular structure of MWCNT was preserved with the inter-planar spacing of 0.25 nm. Absorption bands of Si-C bond were detected at 803 cm-1 in Fourier transform infrared spectrum. Thermal gravimetric analysis revealed that SiCNTs from ratio of 1:3 showed the lowest weight loss. Thus, our synthetic process indicates high yield conversion of SiO2 and MWCNTs to SiCNTs was achieved for blend of SiO2 and MWCNTs in molar ratio of 1:3.

Resumo em Inglês:

The aim of the present work was to study the passive film stability and pitting corrosion behavior of the AISI 409 stainless steel. The electrochemical tests were carried out in 0.1 M NaCl solution at room temperature. The general electrochemical behavior was assessed using electrochemical impedance spectroscopy (EIS) measurements whereas the semiconducting properties of the passive film were evaluated by the Mott-Schottky approach. Pitting corrosion was investigated using potentiodynamic and potentiostatic polarization tests. Surface morphology was examined using confocal laser scanning microscopy and scanning electron microscopy (SEM). Energy dispersive X-ray spectroscopy (EDS) analyses were carried out to identify the composition of precipitates that could act as preferential sites for the onset of pitting corrosion. The results showed that the passive film presents n-type semiconductive behavior. Grain boundaries played an important role as pitting initiation sites for the AISI 409 stainless steel.

Resumo em Inglês:

Inconel 718 is widely used in the aviation, space, automotive and biomedical industries because of its outstanding properties. Near-surface residual stresses that are induced by ball end milling in Inconel 718 can be crucial for the performance and service time of the machined parts. In this paper, the influences of cutting conditions, including the use of cutting parameters, cutting fluid and spindle angles, on the residual stresses in the ball end milling process of Inconel 718 alloy were investigated experimentally. X-ray diffraction measurements reveal that residual stress distributions are highly influenced by cutting parameters, especially the depth of cut and cutting speed. The milling operation with cooling induces more compressive stresses trend and the magnitude of the residual stresses increases in the tensile direction with the increase of spindle angles. These cutting induced effects were further discussed with respect to thermal- mechanical coupling theory and some observations made by optical microscopy. From this investigation, it is suggested that the machining process parameters are not the smaller the better for the control of residual stresses in the ball end milling process of Inconel 718.

Resumo em Inglês:

The effect of ferrite phase on the precipitation of σ phase in a Z3CN20.09M cast austenitic stainless steel (CASS) used for primary coolant pipes of pressurized water reactor (PWR) nuclear power plants was investigated by using isothermal heat-treatment, optical microscopy (OM), transmission electron microscopy (TEM) and electron probe microanalysis (EPMA) techniques. The influence of different morphologies and volume fractions of ferrite in the σ phase formation mechanism was discussed. The amount of σ phase precipitated in all specimens with different microstructures increased with increasing of aging time, however, the precipitation rate is significant different. The formation of σ phase in specimens with the coarsest ferrite and the dispersively smallest ferrite is slowest. The lowest level Cr content in ferrite and fewest α/γ interfaces in specimen are the main reasons for the slowest σ precipitation due to they are unfavorable for the kinetics and thermodynamics of phase transformation respectively. By contraries, the fastest formation of σ phase takes place in specimens with narrow and long ferrite due to the most α/γ interfaces and higher Cr content in ferrite which are beneficial for preferential nucleation and formation thermodynamics of σ phase.

Resumo em Inglês:

The present study is to investigate the influence of weight percentage of silicon carbide (SiC) (5,10 %, 15%) and particle size (10,20,40µm) of SiC and constant 2% of Molybdenum disulphide(MoS2)is reinforced with aluminium matrix. Wear performance of the composite was carried out through pin-on-disc method to calculate friction coefficient and wear resistance of the composites. The experiments were conducted by varying the sliding speed of (1.5,2.5 &3.5 m/s), loads (30,50&70N) with sliding distance ranges from (500, 1000& 1500m) under dry sliding conditions. Taguchi plan of experiments and ANOVA method was carried out to find the outcome of reinforcement ceramic particles, sliding distance, sliding speed, and applied load over the friction coefficient and wear rate. The result reveals that applied load and sliding distance are the most influencing factors for friction coefficient. Load and percentage of SiC indicates the most affecting factor for wear rate. Worn out surface of the composites were studied by optical microscopic image and Gwyddion software. To conclude, it was interfered that 15% weight percentage of SiC at 10µm offers better wear resistance and friction coefficient in AHMMCs.

Resumo em Inglês:

Ammonobasic reactive sublimation (ARS) is proposed as a novel method to synthesize GaN and related oxides. Results indicate that GaN growth occurs by a nitriding process of Ga and related oxides, establishing a direct dependence on NH4OH amount added as a primary chemical reactive. The samples were grown on p-type Si (111) substrates inside a tube furnace, employing GaN powder and NH4OH. The characterizations of the samples were carried out by XRD, SEM, EDS and PL techniques, revealing the influence of NH4OH on the improvement of GaN synthesis and the enhancement of its optical and structural properties.

Resumo em Inglês:

Sol-gel modified Pechini's method was used to prepare WO3 nanopowders using dicarboxylic acid and polyethylene glycol as the chelating agent and polymeric source, respectively. WO3 powders were first prepared by calcination of resin precursor at 550ºC under various initial concentrations of metal ion (12.5-50 mmol), acid (125-500 mmol), a complexing agent (32-262 mmol), and polyethylene glycol (1-16.5 mmol) in the air atmosphere. The products were characterized using X-ray powder diffraction, field emission scanning electron microscopy, and energy dispersive spectroscopy. The results revealed that the WO3 nanopowders prepared with different amounts of chelating agent and polyethylene glycol, crystallized in monoclinic phase. The nanopowders were impurity-free due to the presence of the complexing agent and polyethylene glycol as carbon sources. Morphological evolution indicated that the nanopowders evolved from rod-like to regular and spherical shapes, depending on complexing agent and polyethylene glycol amounts. Nanopowders with an average particle size of approximately 58 nm and a narrow size distribution were obtained.

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Polymer blends are generally categorized into two main classes: miscible blends that exist in a single homogeneous phase exhibiting synergistic properties and immiscible blends that have 2 or more different phases. There is also a third category of blends called technologically compatible blend, which exist in two or more different phases on micro scale, yet displays combination of properties. Ethylene-propylene-diene rubber (EPDM) and Hexa fluoropropylene-vinylidinefluoride dipolymer, Fluoroelastomer (FKM) blends with and without compatibilizer (MA-g-EPDM) were prepared by two-roll mill mixing. The aim of the work is to find out the best blend ratio and the amount of compatibilizer loading on thermal and mechanical properties by applying a novel mathematical programming technique called Data Envelopment Analysis (DEA). Using the different concentration of the ingredients used as inputs and the extent to which certain properties satisfied by the blends as outputs, a DEA model is developed. The blends which will be referred to as Decision Making Units (DMUs) were classified in terms of their efficiency. It is observed that the efficiency of all the compatibilized blends is higher than that of uncompatibilized blends. The maximum efficiency is obtained for 2.5 phr compatiblized blend.

Resumo em Inglês:

This work focuses on the systematic investigation of the two well-established methods of structural surface charge density determination on magnetic colloids, labeled as Single Potentiometric Method (SPM) and Potentiometric-Conductometric Method (PCM). To compare some important features of the methods we determined the structural surface charge density of magnetic colloids samples based on CoFe2O4@ɣ-Fe2O3 core-shell nanoparticles with three different mean sizes using both strategies. Concerning quickness, easiness and cost, the PCM has proved to be more advantageous than the SPM. Regarding the effectiveness, both methods were consistent in determining the saturation value of the structural charge, but the SPM was more accurate to describe the pH-dependence of the concentration of the charged surface sites. Considering the chemical safety, the methods are equivalent. Finally, both the SPM and PCM are reproducible and can be effectively applied to determine the saturation value of the surface charge density on magnetic colloids.

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The tinplate, used in the packaging sector and formed from a metal substrate, comprises a steel base which has undergone a surface treatment to produce a thin layer of FeSn2, a tin layer and an oxide tin layer. Currently, packaging using surface treatment is based on the use of chromates because these metals provide an excellent corrosion resistance. Nontoxic alternatives to pre-treatments have been developed in recent years to replace the chromate process. The aim of this work is to analyze the performance of a new hybrid organic-inorganic film obtained from sol-gel consisting of the alkoxide precursors 3-(Trimethoxysilylpropyl)methacrylate (TMSM) and tetraethoxysilane (TEOS) with the addition of cerium nitrate with the scanning vibrating electrode technique (SVET), and electrochemical and morphological characterizations. Moreover, the evolution of the corrosion of the substrate was evaluated to propose a mechanism of corrosion. The results showed a galvanic coupling between the Sn/SnO2 coat (cathode) and the defects exposed at the ferrous base (anode). The organic-inorganic hybrid film containing a cathodic corrosion inhibitor was able to retard the corrosion of the tinplate.

Resumo em Inglês:

SnO2 nanofibers were fabricated by calcination of the electrospun PVP/SnCl4 composite nanofibers. For the first time, SnS nanofibers and SnSe nanofibers were successfully synthesized by double-crucible sulfurization and selenidation methods via inheriting the morphology of SnO2 nanofibers used as precursors, respectively. X-ray diffraction (XRD) analysis shows SnS nanofibers and SnSe nanofibers are respectively pure orthorhombic phase with space group of Pbnm and Cmcm. Scanning electron microscope (SEM) observation indicates that the diameters of SnS nanofibers and SnSe nanofibers are respectively 140.54±12.80 nm and 96.52±14.17 nm under the 95 % confidence level. The photocatalytic activities of samples were studied by using rhodamine B (Rh B) as degradation agent. When SnS or SnSe nanofibers are employed as the photocatalysts, the respective degradation rates of Rh B solution under the ultraviolet light irradiation after 200 min irradiation are 92.55 % and 92.86 %. The photocatalytic mechanism and formation process of SnS and SnSe nanofibers are also provided. More importantly, this preparation technique is of universal significance to prepare other metal chalcogenides nanofibers.