Abstract in English:

Ni-Co ferrites, especially the ones with lower cobalt fractions, are candidate materials for applications in magnetomechanical sensors and electromagnetic wave absorbers. This work studied the microstructure, magnetostriction, flexural strength, and complex magnetic permeability of Ni0.9Co0.1Fe2O4, presenting data that weren't covered by previous literature on this composition. It was found that sieving the calcined powder before the forming operation increased the flexural strength of the ceramic. The Ni-Co ferrite had a saturation magnetostriction of 36ppm. The real part of the complex magnetic permeability varied between 2.2-2.3 in frequencies from 100MHz to 1GHz. In frequencies higher than 1GHz, µ' decreased sharply and reached 1 at 3.9GHz. It was found that the grinding media provided a small fraction of Al to the ferrite composition, which apparently affected the complex magnetic permeability of the material but the magnetostriction results were very close to Al-free Ni-Co ferrites with similar composition.

Abstract in English:

The use of composites in structural applications requires the study of specific properties to ensure that these materials are safe and an excellent option to replace some metals, for example. In the present study, vacuum assisted resin transfer molding (VARTM) was used prior to obtain carbon/epoxy non-crimp fabric composites. Dynamic mechanical analysis and creep - by using Findley and Burger's methods - tests were performed aiming to evaluate the viscoelastic properties of the composites, in three different temperatures (30, 60 and 90°C) and static stresses (2, 5 and 10 MPa). The viscoelastic properties were also discussed using Weibull parameters obtained from creep curves. In general, the deformation was temperature and stress dependent, which was corroborated by the viscoelastic parameters obtained from both models.

Abstract in English:

The use of niobium containing materials' has gained much attention of the scientific community in the late years due its various applications in diverse fields. NbC is a highly versatile material. Copper addition may alter several of its properties, such as morphology, crystal structure etc. as well as enhance its catalytic behavior. Nanostructured NbC with copper addition synthesis' presented here had the precursor [(NH4)3[NbO(C2O4)3]xH2O] as starting material, which was doped with Cu(NO3)2 at 5% and 10% (molar) ratios. Doped NbC was obtained via gas solid reaction in fixed bed reactor at lower temperature (980°C) and with shorter reaction time (2h) than traditional methods. Reaction products' were characterized by XRD, crystal sizes were estimated according to HWL method, and SEM, XRF, BET and laser particle size analysis were performed. XRD indicated the formation of NbC and Cu phases with cubic crystal structure of ~20nm. SEM showed slight morphological change upon increasing copper content, indicating a less porous structure, which is consistent with BET data (43.7m2/g for 5%Cu-NbC and 37m 2/g for the 10% Cu-NbC). Crystal size calculations showed that increasing dopant content particle sizes were also increased, probably due to the presence of the dopant, in some extent, in the crystal structure.

Abstract in English:

Na0.5Bi0.5TiO3-xBaTiO3 (0<x<6) relaxor ferroelectrics crystals were investigated by means of dielectric and acoustic emission methods. Dielectric curves exhibit the slightly visible small maxima near the depolarization temperatures, Td, and the wide maxima at the temperatures of Tm, whereas the acoustic emission exhibits the sharp bursts, corresponding to Td, Tlm, which is known to be a temperature exhibiting a strong frequency dispersion, TRE, which is known to be a temperature above which a frequency dispersion vanishes, and the Tm and the Tp manifesting a transition to the paraelectric phase. Based on the AE data it was established that all these characteristic temperatures shift down as x increases, but with different slopes. A mechanism of such the differences is discussed.

Abstract in English:

In this article, Nickel doped Cobalt oxide thin films and powders have been prepared on glass substrates using sol gel based dip coating process in order to investigate their optical, structural and electrical properties. The Ni concentration was changed from 0 to 9 wt(%).The synthesized samples were characterised by Ultraviolete visible analysis, X-ray diffraction, Fourier transform infrared spectroscopy and Complex impedance spectroscopy to depict the optical, structural, vibrational and electrical properties. Our structural results show that the obtained samples were composed of (Co3O4) polycrystalline with spinel-type preferentially oriented in the (311) plane. Our optical results show that the films have high transparency over the visible region (85% for Co3O4 and ∼ 60-75% for all doped samples). The optical band gaps were found to be (Eg1 = 1.50 eV, Eg2 = 2.20 eV) and (Eg1 = 1.42 eV, Eg2 = 2.07 eV) for the case of (pure Co3O4 and 9% Ni-doped Co3O4) respectively. The complementary phase information is provided by FT-IR spectroscopy. FT-IR spectra confirms the presence of Co2+-O and Co3+-O vibrations in the spinel lattice. The Nyquist plots suggests that the equivalent circuit of our films is an parallel circuit RpCp. It was found that the resistance Rp decreases whereas the capacity Cp increases with increasing doping levels.

Abstract in English:

Nanostructured undoped zinc oxide (ZnO) thin films were deposited using atmospheric pressure chemical vapor deposition (APCVD) on glass substrates using zinc acetate dehydrate [C4H6O4Zn·2H2O, ZnAc] in less than 2 minutes for each sample. In order to reduce the resistivity of ZnO films, a very thin layer of Ag was deposited on top of the films via the sputtering method to reduce resistivity from 2.89 to 0.31 Ω.cm, using only a 30Å silver coating. Structural, electrical and optical properties of the resulting bilayers were also investigated. The results show a polycrystalline structure in higher temperatures compared to rather amorphous ones in lower temperatures such as 325℃. The XRD patterns of the optimum polycrystalline films were identified as a hexagonal wurtzite structure of ZnO with the (002) preferred orientation. Also, sheet resistance decreased from 17.8 MΩ/⧠ to 28.9 KΩ/⧠ for the temperatures of 325℃ to 450℃, respectively. Based on the physical properties of undoped ZnO, substrate temperature is an important factor which affects the crystallite size and modifies electrical parameters. UV-vis measurements revealed a reduction in the transparency of the layers with increasing substrate temperature. A sharp cut-off was observed in ultraviolet regions at around 380 nm.

Abstract in English:

Ternary Al-9.0wt%Si-4.0wt%Cu alloy was solidified in a vertical directional solidification system under unsteady-state heat flow conditions. The resulting dendritic morphology and microsegregation were investigated. A more detailed analysis was dedicated to the microsegregation phenomena where a multielement interaction was observed. The solidification parameters such as: solidification speed (VL) and cooling rate (T˙) were determined from the cooling curves obtained during the solidification process. The thermal variables effect on the dendritic morphology is presented. The measurements of tertiary dendrite arm spacing (λ3) and microsegregation were performed for different positions along the casting. The experimental curves for microsegregation were obtained for Si and Cu from the center of dendritic tertiary arm to the next nearest tertiary arm. The solidification speed (VL) influence is "built into" the effective partition coefficient (Kef_Cu and Kef_Si) that has been determined for the range of VL and microsegregation curves are calculated by Scheil's equation for comparison with experimental data. Good agreements of the Scheil's equation with experimental data on microsegregation curves of the Si and Cuwere obtained when effective partition coefficient (Kef_Cu and Kef_Si) is taken into consideration. The multielement interaction effect on the Si microsegregation is investigated. Experimental results show that, Cu-rich dendrites were accompanied by minute amounts of Si. The concentration profiles obtained experimentally point to a strong negative correlation between Si and VL on ternary Al-9.0wt%Si-4.0wt%Cu alloy.

Abstract in English:

Co and Zn ferrites with general formula CO1-XZnXFe2O4 (x = 0; 0,2 and 0,8) were synthesized by combustion reaction method, using urea as fuel. The structure of inverse-spinel-type ferrite were characterized through XRD using Rietveld refinement method to identify, quantify phases and determine lattice parameters. The crystallites had mean size of 37,33 nm, 43,66 nm and 51.88 nm with the increment of Zn2+, respectively. Samples were sintered in a resistive oven at 900 °C for 3 hours. Analysis by SEM indicated that the particles have irregular sizes and high concentration of open pores. The magnetic properties were measured using a vibrating sample magnetometer (VSM), through which a decrease in the magnetization variation was observed as the non-magnetic Zn2+ concentration increases. The permittivity and loss tangent were determined using vector network analyzer equipment, permittivity increases with the increase of zinc concentration and the tangent loss measurements were small for all ferrites synthesized in this work.

Abstract in English:

The Avitzur's limit analysis for the calculation of the drawing force in a wire drawing process is used to study the real behaviour of a carbon steel in an industrial case. The linear hardening assumption, used by Avitzur only for the first step, is extended to the whole process and tested against experimental data. The result shows that the predictions resulting from this extension are in good agreement with the experimental results and are, as rule, conservative.

Abstract in English:

The aim of this work is to predict the temperature field generated by welding a steel butt joint (API 5L X80). The prediction was modeled by finite element software Abaqus where the subroutine was developed in Fortran so that heat source motion may be included. The motion was based on the Goldak's double ellipsoid. In the model material nonlinearities were included such as thermophysical properties (coefficient of thermal expansion, specific heat, thermal diffusivity and thermal conductivity), which are dependent on temperature and latent heat, heat exchange by convection and radiation and mechanical boundary conditions. The thermal field predicted by the model was validated by infrared thermography. GMAW simulations with the use of an "evenmatched" solid wire (filler metal) carried out the welding process. The results obtained from the numerical model and thermography were in good agreement.

Abstract in English:

Supermartensitic stainles steels (SMSS's) are a new generation of martensitic steels that have been increasingly used in oil and gas applications due to their adequate corrosion resistance and mechanical properties. In the present study, SMSS specimens (UNS S41425) were solution heat treated and air cooled followed by plasma nitriding and nitrocarburising at 400, 450 and 500°C for 5h. The produced layers were characterized by optical microscopy, microhardness testing, X-ray diffraction and corrosion testing in NaCl 3.5% solution. Surface alloying with nitrogen or both nitrogen and carbon results in increased surface hardness and homogeneous layers in which layer thickness increases with temperature. However, plasma nitriding yields a slightly thicker case than nitrocarburising. X-ray diffraction indicates very broad and overlapped peaks for the treatments conducted at 400°C. Increasing treatment temperature appears to result in the formation of chromium nitrides and iron nitrides and carbides, depending on the treatment. It was also found that treatment temperature drastically affects the corrosion response of the steel. The untreated steel presented a pitting potential close to 250mV. Plasma nitriding at 400°C was the only condition in which significant improvement of corrosion is observed. For plasma nitriding and nitrocarburising at 450 and 500°C, some pitting was detected.

Abstract in English:

The in situ reaction between alumina and silica to obtain mullite (Al6Si4O13) can be significantly affected by using synthetic amorphous silica (SAS) sources instead of crystalline ones (quartz and cristobalite). For instance, SASs promote early mullite formation (below 1300°C) and greater densification during sintering. This paper reports the "in situ" formation of mullite-alumina structures from fine calcined alumina (α-Al2O3) and four grades of SAS of different particles' morphology, specific surface area and internal porosity. After sintering assisted by dilatometry (up to 1500°C), the samples' total porosity, density and flexural strength were measured. The relative density and strength levels of some of these structures were greater than or comparable to other studies in which similar compositions were sintered at higher temperatures (1600-1700°C). Their microstructure assessment indicated that the specific surface area and internal porosity of SAS particles showed a major influence in the development of these physical properties.

Abstract in English:

Eutrophication is an undesirable environmental process that occurs in water bodies affected by high concentrations of phosphate. Different economic sectors are responsible for discharge effluents with extremely high phosphate content. Therefore, is important to develop technologies capable of remove phosphate from these effluents, before that reach other and larger water bodies. This work proposes the use of layered double hydroxide (LDH) as an adsorbent matrix for phosphate removal from aqueous solution. Different isomorphic structure of LDH ([Mg-Al]-LDH and [Zn-Al]-LDH) were employed to incorporate loadings of phosphate by ion exchange. The obtained materials were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), fourier transform infrared spectroscopy (FTIR), and thermal analysis (TG/DTG). The crystalline structure of [Mg-Al]-LDH was preserved after phosphate adsorption, however the performance was low in comparison to [Zn-Al]-LDH, for which a high phosphate removal efficiency of 116.07 mg P. g-1 of LDH was achieved. The [Zn-Al]-LDH material showed good potential for use as matrix for the adsorption of phosphate in effluents.

Abstract in English:

Present research work analyses the effect of heating modes on the densification, microstructure and mechanical properties of aluminum alloys [65Al-20Cu-15Mn] fabricated through powder metallurgy route. Sintering of compacts using conventional, microwave and spark plasma sintering methods has been carried out at 525°C. From the results, it has been observed that the spark plasma sintering method produced the samples with better mechanical properties than the other two methods, followed by microwave and conventionally sintered counterparts. Microstructural analysis using optical microscopy revealed that spark plasma sintered sample has finest microstructure due to faster rate of heating than microwave and conventional methods.

Abstract in English:

A novel adsorbent based nanostructured bismuth oxyiodide (BiOI) microspheres combining the highly effective adsorption and green photocatalytic regeneration were fabricated by a facile and rapid low-temperature chemical bath method. The resultant products were characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), Nitrogen adsorption-desorption measurements, and UV-Vis diffuse reflectance spectroscopy (DRS). The BiOI microspheres displayed remarkable performance towards removal of Rhodamine B (RhB) and Cr (VI) from aqueous solution, showing a maximum adsorption capacity reached up to 40.78 mg g-1 and 38.01 mg g-1, respectively. The kinetics and equilibrium of adsorption process were found to follow the pseudo-second-order kinetic and Langmuir isotherm models. Notably, the BiOI microspheres have excellent photocatalytic regeneration capability due to their intrinsically prominent photoresponse in visible light region. By meaning of providing a new insight into the design of new generation adsorbent that could combine adsorption and solar-driven photocatalysis, the synthesized BiOI microspheres are very promising for the large-scale industrial application for water treatment.

Abstract in English:

The research of natural fiber composites is growing due to the fact that the green materials combine low weight with good mechanical properties. Curaua fiber arises as a competitive natural fiber due to its abundance, low cost and a variety of applications. In this work, different weight fractions of Curaua fiber were used in order to obtain this natural composite material. Specimens of Curaua/Epoxy composites were tested in tensile and in flexion to observe the quasi-static mechanical properties and its physical properties due to temperature variation were evaluated by Dynamic Mechanical Analyses (DMA) analyses. An increase in fiber quantity showed an increase in both the modulus and the strength, leading to a stiff and less ductile material. The results also showed an increase in the viscoelastic stiffness of the epoxy matrix by the incorporation of Curaua fibers. The interaction between Curaua fibers and epoxy matrix affects segmental mobility of the epoxy chains.

Abstract in English:

In this paper, Y3AlxFe5-xO12 powders with x = 0.0, 0.2, 0.4, 0.6, 0.8, and 1.0 were prepared via solid state reaction method. X-ray diffraction, Vibrating Sample Magnetometry, and Mössbauer Spectroscopy were used to study their structural and magnetic properties. The XRD patterns of the samples show single phase structure with decreasing lattice constant when increasing Al concentration. The saturation magnetization decreases from 28.0 to 10.1 emu/g with increasing Al3+ from 0.0 to 1.0 due to the reduction of the superexchange interactions between iron ions in the a and d sublattices. Room temperature Mössbauer spectra for the samples were collected and analyzed. The hyperfine field values for octahedral and tetrahedral sites of the samples decreased with increasing Al concentration. Moreover, Mössbauer results have shown that Al3+ ions prefer to replace Fe+3 at the octahedral sites.

Abstract in English:

The present work briefly reviews the convolution of crystallite shape functions and discusses its experimental limitations. The diffraction from a theoretical spherical shape powder is used to exemplify the limits of the convolution procedure. Mean lattice distortions were not considered since the discussed limitations are inherent to the convolution method using Fourier transforms. The diffraction pattern and the convolution were calculated using appropriate macros for the Topas program. It is shown that very small crystallites require a large 2θ convolution span and the smallest subdivision for the distribution will depend on this convolution span. To show the importance of the convolution limits and its application, the nanocrystalline CeO2 round-robin diffraction pattern was evaluated. The chord frequency distribution by XRD showed conformity with the chord distribution calculated from a grain size histogram obtained by transmission electron microscopy for this sample.

Abstract in English:

The friction surfacing process of two deposited layers on two deposition surface conditions, i.e., a smooth interface and a rough interface, was investigated. The control parameter of the deposition process was the rod feed rate with the use of a conventional milling machine. Analyzes of the surface characterization and microstructural characterization along the produced deposits were performed. The interface strength of the substrate/deposit1 (smooth) and deposit1/deposit2 (rough) was evaluated by bending tests and the micro-hardness profile along the transverse section of the substrate/deposit1 and deposit1/deposit2. The bending tests revealed the presence of smalls delaminations with no evidence of fracture at the rough deposit1/deposit2 interface (D1/D2) with less predominance in the deposition condition 3B. This suggests that the combination of the travel speed of 5.5 mm/s and an increase in the consumable rod feed rate of (≥5.5 mm/s) increases the adhesive strength of the two produced interfaces.

Abstract in English:

The polyol-based co-precipitation process was employed for synthesis of GdF3:Pr (core) and GdF3:Pr@LaF3 (core-shell) microspheres (MSs). Subsequently, an amorphous silica layer was deposited surrounding the core-shell MSs, which was verified from high-resolution transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDX) and FTIR results. The absorption spectral results revealed the high solubility with good colloidal stability in aqueous solvents. The detailed structural and morphological analysis, as well as crystallinity of the samples, was investigated through X-ray diffraction, TEM and band gap energy results. The experimentally calculated band gap energy was found to decrease after gradually coating insulating layers of LaF3 and amorphous silica over the surface, because of an effective increase in particle size. The Pr3+-doped GdF3 shows sharp 4f15d1→4f2 emission bands (260-480 nm) as well as typical 4f2→ 4f2 emission lines (460-800 nm) of Pr3+ under 4f2 →4f15d1 excitation. After surface coating, comparative photoluminescence properties of the MSs were investigated by excitation and emission spectra. The origin of the different types of emission transitions were analyzed in details.

Abstract in English:

Superhydrophobic and superoleophilic oxidized copper foam (OCF) was prepared by oxidation of copper foam using (NH4)2S2O8 to generate rough surface then followed by modification with low surface energy substance polydimethylsiloxane (PDMS) and stearic acid (SA). Based on sperwetting, form-stable phase change materials (PCMs) composites were obtained by facile absorbing of organic PCMs into PDMS-OCF network. In this way, the organic PCMs can be spontaneously adsorbed and remain stable without leakage even at high temperature over their melting points, and the thermal storage capacity of the as-synthesized PCMs composites were analyzed using a differential scanning calorimeter (DSC). The latent heats of the PDMS-OCF/PCMs composites were measured to be 36.87 J g-1 and 36.81 J g-1 for PDMS-OCF/paraffin and PDMS-OCF/SA, respectively, which is greater than that of untreated copper form (CF)/paraffin composite (8.50 J g-1). The PDMS-OCF/PCMs composite shows better thermal stability and the loaded organic PCM has been reduced by 0.64% after 100 times of melting-cooling recycling for PDMS-OCF/paraffin. The thermal conductivity of PDMS-OCF/paraffin composite is about 9 times that of pure paraffin. Such excellent thermal conductivity as well as good thermal stability of the PDMS-OCF/PCMs makes it promising candidate for thermal energy storage.

Abstract in English:

Droplet flight and solidification behaviors during twin-wire arc sprayed (TWAS) composite coatings were systematically investigated. Both theoretical model and numerical method were established for calculating the droplet deformation, breakup and solidification process in air flow based on the volume of fluid (VOF) dual-phase flow model jointed with the standard k-ε model. The experimental simulation results indicate that TWAS droplet is broken through explosion or two steps breaking process. The calculation of TWAS gas flight dynamics demonstrates that the TWAS particles are accelerated at first and then slowed down. Microstructure of the TWAS prepared Ni-5wt.%Al and Ni-20wt.%Al composite coating was accordingly characterized by XRD, SEM and TEM, so the phase compositions of the Ni-Al composite coatings were obtained. TEM analysis also showed that an amorphous phase was formed according to the characteristic of diffraction ring in Ni matrix solid solution at an original state.

Abstract in English:

Hard coatings are a suitable solution for increasing the lifetime of tools and components employed in different industrial applications. Coatings of transition metal nitrides have great use for tribological applications due to due to their unique mechanical properties. Although widely employed, current deposition methods such as cathodic arc evaporation produce coatings with many defects, which in turn reduce the resistance to wear, especially under severe conditions. High Power Impulse Magnetron Sputtering is a novel physical vapor deposition technique that produces homogeneous coatings. In this study, CrN and CrAlN monolayer coatings were deposited on AISI 304 stainless steel substrates using HiPIMS. X-Ray Diffraction, Scanning Electron Microscopy, Atomic Force Microscopy were used to evaluate the microstructure, phase composition, morphology and chemical composition of the coating. Results showed that HiPIMS is a promising technique to deposit CrN and CrAlN homogeneous coatings with high hardness and good adhesion to the substrate.

Abstract in English:

In this study, an effort has been made to choose an appropriate tool pin profile and rotational speed for a tool using a submerged friction stir processed hot rolled AZ31B magnesium alloy. A defect free process region was obtained using a novel tool shoulder, which consisted of a scroll. Three tool pin profiles, namely, simple cylindrical, stepped cylindrical and stepped square pin have been used. Tensile properties and fracture behavior revealed defect free friction stir processed specimens. The microstructural studies reveal the possibility of producing a defect free processed region using the stepped square pin tool geometry. The presence of fine recrystallized grains (1.99 µm) and the absence of defects in the processed region lead to higher hardness and superior tensile properties.

Abstract in English:

Optical characterizations of preferred orientation (002) ZnO thin films, prepared by RF magnetron sputtering under pure argon plasma, with different thicknesses have been investigated, where grain size and resistivity increase with thickness. Energy band gap and refractive indices have been calculated. A correlation between band gap values and crystalline quality, which is improved with thickness, has been discussed. The calculated refractive indices of the thicker deposited films have increased as the thickness increases. Full width Half Maxima (FWHM) of band gap Photoluminescence (PL) emission decreases with thickness increasement due to quality improvement as it has been monitored by X-Ray Diffraction (XRD). A comparison between PL spectra of 1200 nm film and ZnO single crystal at low temperature is found to be similar.

Abstract in English:

Ni/nano-Al2O3 composite coating by pulse electrodeposition method has been used for coating on cast iron liner material. The hardness has been increased from 308 HV to 1050 HV through conventional Watts bath and by applying Taguchi's optimization technique with optimum parameters of pulse frequency 120 Hz, duty cycle 40% and peak current density 0.7A/cm2. The lubricant's pH (4) and stirring speed (400 rpm) are the foremost parameters for increasing the hardness of the coating. Furthermore, the pulse current (PC) produces homogeneous distribution of Al2O3 particles in the Ni matrices. The chemical composition, surface morphology, crystal structure, adhesion, coating thickness and the corrosion resistance of the optimized liner specimen of deposited Ni/nano-Al2O3 coatings were evaluated by Optical Emission Spectrometer (OES), Scanning Electron Microscopy (SEM), X-ray diffraction (XRD), ASTM D 3359-97, Metallurgical Microscope (ASM standards) and ASTM B117-07 standards.

Abstract in English:

Since epoxy resins are used as composite matrix with excellent results, and silica is one of the fillers most often employed, this study compared the performance of rice husk ash (RHA) as filler in epoxy composites, in replacement for high-purity silica. Composites were molded containing 20%, 40%, and 60% (wt) silica or RHA. Viscosity analysis, infrared spectroscopy (IR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) as well as mechanical and water absorption tests were carried out to evaluate composites. Glass transition temperature after curing and thermal degradation temperature of all samples analyzed were approximately 140 ºC and 370 ºC, respectively. RHA and silica exhibited similar mechanical and water absorption characteristics, indicating that rice husk ash may be a suitable replacement for silica. SEM imaging showed good filler dispersion and distribution in the polymer matrix, highlighting the more effective adhesion interface between RHA particles and the matrix.

Abstract in English:

Small scale ethanol production process faces a number of challenges that negatively impact productivity and economic costs. The present work aims at finding alternative materials with lower cost and suitable resistance to replace the stainless steel commonly used in distillation columns in small scale businesses. For that we analyzed the chemical and mechanical behavior of nine different polymeric materials. An important parameter to consider in this case is the compatibility of polymer with the ethanol, which was determined according to the ASTM D543, as well as the swelling degree and ethanol diffusion in material being also studied in this work. Three-point flexural tests were performed because the material when in service is subjected to forces or loads. The results show that some of the materials under test present chemical resistance and satisfactory mechanic performance after the contact with the ethanol in temperatures compatible with the distillation process.

Abstract in English:

Study of the solar absorber with photonic crystal or micro structures as the heat absorbing surfaces operated at a high-temperature was conducted. Numerical calculations based on rigorous coupled-wave analysis were performed to determine the absorptance of the photonic crystal surface on the absorber. The effect of nano geometry of the photonic crystal in tungsten on the selectivity of the absorber was investigated first, including period (L), aperture (A) and depth (d). A design algorithm for the photonic crystal heat absorbing surface was summarized. Based on the results, a design with combined large and small square patterns was proposed to improve the absorptance, which demonstrated the ability to broaden the absorbing band by mix-period nano patterns. Integration of an anti-reflection coating (ARC) on the photonic crystal using aluminum oxide (Al2O3) was also studied. It was shown that, under a specific thickness of ARC, the absorptance can be further improved. As considering the effect of concentration coefficient on the energy absorption efficiency, it was found that a micro structure fabricated by laser ablation on stainless steel has a conversion rate over 85% in the case using a high concentrate coefficient.

Abstract in English:

The wire drawing mechanic of Ti-49.82Ni (at. %) Shape Memory Alloy (SMA) was investigated through the true stress-strain curves and drawing stresses. The tensile tested solution treated wire presented a four steps elongation at temperatures below the austenite finish temperature (AF), and a conventional one-step behavior above the martensite deformation temperature (MD). The tensile yield stress for the formation of detwinned martensite (DTM) or stress-induced martensite (SIM) increased as the testing temperature increased; however, for larger deformation, the behavior reversed. The efficiency of drawing work, which is the ratio of uniform work to total work, increased from 10% for 0.07 mm2.mm-2 area reduction at 25 °C to 50% for 0.21 mm2.mm-2 at 110 °C. Therefore, wire drawing temperature and area reduction should be combined to increase the efficiency, taking into account the desired properties with reasonable workability. Furthermore, transformation work should be considered on wire drawing shape memory alloys as phase transformation occurs in temperatures below MD.

Abstract in English:

A new study about corrosion behavior of CoCrMo alloy used as implant material exposed to the physiological serum and Hank's solution in different temperatures, electrolyte compositions and immersion time were simulated, using open circuit potential (OCP), potentiodynamic polarization curves (PPC) and electrochemical impedance spectroscopy (EIS.) From the results, it can be concluded that CoCrMo biomaterial is influenced by electrolyte composition and temperature, and the passive films were more protective when formed in presence of physiological serum. Comparing the Ecorr for both solutions, it is possible to verify that the Hank's solution presented values more negative for the two studied temperatures (25 and 37 °C), indicating a greater susceptibility to the corrosion process. Regarding the results of potentiodynamic polarization, the ipass, decreased as function of time, indicating a more protective passive film at 25 °C. In regards to the physiological serum, the highest ipass values at 37 ºC evidenced the formation of a less stable passive film. The different behavior of ipass in Hank's solution may be related to the competitiveness between a possible film of D-glucose and oxides of the alloy metals. EIS studies suggest that the film formed in presence of physiological serum is nobler than that with Hank's solution.

Abstract in English:

The influences of interrupted ageing and retrogression and re-ageing heat treatments on fatigue crack growth with a single applied overload in 7050 aluminum alloy were investigated. The main aims were: to evaluate the influence of these heat treatment conditions on tensile properties, mainly fatigue crack growth rate and fracture process in the low-moderate ΔK region; to determine how both ageing treatments generate bimodal microstructure features as a contribution of the two conditions on the crack closure phenomenon; and the influence of the single applied overload to fatigue crack growth retardation. The results show that by using the RRA heat treatment condition it is possible to enhance the ductility without detrimental effects on the yield stress. T6I4-65 and RRA conditions contributed to enhancement of the crack closure phenomenon in the low-moderate ΔK region, and, accordingly, produced a lower fatigue crack growth rate in relation to the traditional T7451 condition.

Abstract in English:

This paper presented a study of friction and wear on 9Cr18Mo when rubbed against other materials (steel-304, steel-440C, steel-GCr15 or silicon nitride ceramic ball) at high temperature conditions. Friction and wear tests were carried out with universal a friction and wear testing machine. The wear morphology was analyzed by a Nanovea three-dimensional profilometer and trinocular positive Gang metallurgical microscope. The Vickers hardness of 9Cr18Mo at different temperatures was tested by means of a high temperature vacuum hardometer. Results showed that the friction and wear on the contact surface of the 9Cr18Mo sample are higher when the hardness of counter materials is higher than or similar to that of the sample. Under dry sliding conditions, the 9Cr18Mo sample surface presented various degrees of adhesion, plowing and pit, particularly if tested in the presence of a high temperature environment. During the worn stages, the counter materials on the worn surface successively produced cracks, crack growth, and wear debris under the action of load. Moreover, the frictional pair 9Cr18Mo-ceramic showed good anti-wear behavior at 400 °C that proved the anti high temperature performance of 9Cr18Mo.

Abstract in English:

Cu-based shape memory alloys (SMAs) present some advantages as higher transformation temperatures, lower costs and are easier to process than traditional Ti-based SMAs but they also show some disadvantages as low ductility and higher tendency for intergranular cracking. Several studies have sought for a way to improve the mechanical properties of these alloys and microstructural refinement has been frequently used. It can be obtained by laser remelting treatments. The aim of the present work was to investigate the influence of the laser surface remelting on the microstructure of a Cu-11.85Al-3.2Ni-3Mn (wt%) SMA. Plates were remelted using three different laser scanning speeds, i.e. 100, 300 and 500 mm/s. The remelted regions showed a T-shape morphology with a mean thickness of 52, 29 and 23 µm and an average grain size of 30, 29 and 23µm for plates remelted using scanning speed of 100, 300 and 500 mm/s, respectively. In the plates remelted with 100 and 300 mm/s some pores were found at the root of the keyhole due to the keyhole instability. We find that the instability of keyholes becomes more pronounced for lower scanning speeds. It was not observed any preferential orientation introduced by the laser treatment.

Abstract in English:

The precursor sols of Al2O3 and mixed NbxOy/Al2O3 oxides were synthesized by the sol-gel process using acetylacetone to control the reaction kinetics of the organometallic oxides in the mixture. The layers of the precursor sols of Al2O3 and NbxOy/Al2O3 were deposited on AISI steel 1020 by manual immersion (dip coating). The lyophilized sols were characterized by X-ray diffraction, thermal analysis and scanning electron microscopy with EDXS before the recoating process. The influence of the ceramic coating of corrosive processes of AISI steel 1020 were investigated by electrochemical measurements. The only identified phase was poorly crystallized boehmite with homogeneous mixture of Al, Nb, O and C ions in mixed NbxOy/Al2O3 oxides. The ceramic layers deposited appeared to have physical and chemical homogeneity and the steel samples with these deposits had lower corrosion potential. However, the precursor sol Al2O3 showed better steel corrosion protection with lower current density, and more corrosive potential.

Abstract in English:

This work deals with the deposition of a thin layer of porous silica antireflective coating onto glass substrates. The films were deposited with different withdrawal speeds and heat-treated at 425°C for 30 minutes. The effects of heat treatment and film deposition rate on the films reflectance were evaluated. The diffuse reflectance was measured using ultraviolet-visible (UV-Vis) spectroscopy. Scanning electron microscopy (SEM) was used for microstructural evaluation of the films. The water contact angle upon the films surface was evaluated using a tensiometer and was based on the sessile drop technique. The mechanical characteristics of the films were evaluated by tape test and pencil hardness. The obtained sol-gel silica coatings were homogeneous and free of cracks. UV-Vis analysis of the glass substrate revealed a reflectance value of 3.86%, whereas the lowest reflectance value obtained for antireflective coatings was 2.72%. The contact angle measurement showed that, for all films, there was wetting of the film by water, characterizing them as hydrophilic. The adhesion of the films were 4B and the pencil hardness were 3H.

Abstract in English:

Calcium tungstate (CaWO4) crystals were prepared by microwave-assisted hydrothermal (MAH) and polymeric precursor methods (PPM). These crystals were structurally characterized by X-ray diffraction (XRD), N2 adsorption, X-ray absorption near edge spectroscopy (XANES) and extended X-ray absorption fine structure (EXAFS) measurements. The morphology and size of these crystals were observed by field emission scanning electron microscopy (FE-SEM). Their optical properties were investigated by ultraviolet visible (UV-Vis) absorption and photoluminescence (PL) measurements. Moreover, these materials were employed as catalysts towards gas phase toluene oxidation reaction. XRD indicates the purity of materials for both preparation methods and MAH process produced crystalline powders synthesized at lower temperatures and shorter processing time compared to the ones prepared by PPM. FE-SEM images showed particles with rounded morphology and particles in clusters dumbbells-like shaped. PL spectra exhibit a broad band covering the visible electromagnetic spectrum in the range of 360 to 750 nm. XANES and EXAFS results show that preparation method does not introduce high disorders into the structure, however the H2-TPR results indicated that the catalyst reducibility is affected by the preparation method of the samples.

Abstract in English:

The paper reports comparative experimental and thermodynamic calculation of a Cu-In-Ni ternary system. An isothermal section of the Cu-In-Ni system at 300 ºC was extrapolated using optimized thermodynamic parameters for the constitutive binary systems from literature. Microstructural and phase composition analysis were carried out using scanning electron microscopy coupled with energy dispersive spectrometry (SEM-EDS) and X-ray powder diffraction (XRD) technique. Brinell hardness and electrical conductivity of a selected number of alloy samples with compositions along three vertical sections (Cu-In0.5Ni0.5, In-Cu0.8Ni0.2, and x(In) = 0.4) of the studied Cu-In-Ni system were experimentally determined. Based on the obtained experimental results and by using appropriate mathematical models values of hardness and electrical conductivity for the whole ternary system were predicted. A close agreement between calculations and experimental results was obtained both in case of thermodynamic, electrical conductivity and hardness predictions.

Abstract in English:

Corrosion of buried pipelines is a matter of concern to the oil and gas industry since the time when carbon steel began to be widely used in these pipelines for the transportation of fluids. The microbial communities associated with biofilms promote modification in the surrounding environment and may accentuate the degradation of oil and gas pipelines causing leaks or even accidents. This work aimed to evaluate corrosion and biofilm formation in carbon steel API 5LX60 coupons buried in clayey soil from an industrial region in north-eastern Brazil. The average corrosion rates were determined by gravimetric test and the quantification of bacteria and fungi were using the Most Probable Number (MPN) and Colony Forming Units (CFU) techniques respectively. The results showed a great influence of clayey soil on corrosion rates and time of adherence for microorganisms on metal surfaces.

Abstract in English:

In the present study, Friction Stir Welding (FSW) of Nickel Aluminum Bronze (NAB) alloy was carried out by varying the axial load, rotation speed and welding speed rate. Micro-structural analyses of these samples revealed the different grain sizes and shapes of the various zones. Hardness and tensile strength tests were carried out for the samples welded at different conditions such as axial load, welding speed and rotational speed. Grain refinement in the weld nugget zones was achieved for all welding conditions. The refined grains in weld nugget zone (WNZ) make a main contribution to the increase of mechanical properties of FSW welded NAB alloy. The microhardness of the stir zone and Thermo-Mechanically Affected Zone (TMAZ) was found to be higher than that of the base metal. Transverse tensile strength of weld joint was higher than that of the base metal. On the other hand, a lower or similar tensile strength value compared to the base metal was seen from other variable welding parameters. This was due to the tunnel defect in the welded nugget zone. ANOVA test result was used for finding out the contribution of the process parameter.