Resumo em Inglês:

In the present work, the Co/TiO2 nanocomposite was prepared by sol-gel method. The structural and optical properties of nanocomposite were studied using, X-ray diffraction (XRD) and diffuse reflectance UV-VIS spectrometry. The XRD spectra revealed its tetrahedral anatase structure. The grain size and optical properties of composite are also reported. Syntesied Co/TiO2photocatalyst showed excellent activity for the photodegradation of Methyl orange whether under visible and ultraviolet light irradiation.

Resumo em Inglês:

Abstract This paper reports on a study of highly filled composites of polypropylene (PP) and 75% by weight sugarcane bagasse fiber with and without alkali treatment and with and without coupling agent (SEBS-g-MA). Composites were prepared using a Rheomix600 mixer connected to a HAAKE torque rheometer. The thermal and mechanical behavior of these composites were investigated by thermogravimetry (TGA), differential Scanning Calorimetry (DSC), flexural tests, impact tests and scanning electron microscopy. Scanning electron microscopy (SEM) images taken from sugarcane bagasse fibers showed enhancements in the fiber's surface topography after the surface treatment process. The FTIR, TGA and SEM results for the fibers showed that the alkali treatment modified the fiber surface as well as the chemical composition. The impact test results showed a good potential of SEBS-g-MA as coupling agent and impact modifier in highly filled composites, increasing by more than 100% the impact strength of the composite as compared to those without the coupling agent. Scanning electron microscopy showed that addition of coupling agent improved the interfacial adhesion between the fibers and polypropylene.

Resumo em Inglês:

Abstract Plastic disposal is a worldwide issue due to its long degradation time. Environmentally degradable polymers (EDPs) have received considerable attention because of their faster degradation. However, the use of EDPs is limited by high cost and restricted properties. The incorporation of organic fillers is an alternative to reduce cost while increasing biodegradation. Poly-caprolactone (PCL) is a biodegradable polyester compatible with organic fillers. Coffee husk (CH) is a sub-product of coffee processing with potential use as organic filler. We prepared a novel PCL-CH composite film and investigated the effects of CH incorporation on the biodegradation of PCL. Biodegradation study was carried out in soil for 120 days, and evaluated by weight loss measurements. Additionally, soil microbiological and granulometric analyses were performed. Bacteria and fungi were found in the soil that was classified as sandy. The composite film degraded twice faster than PCL film probably due to the adhesion of microorganisms on the coffee husk.

Resumo em Inglês:

The present work is concerned with the photodegradation and photostabilization of poly(3-hydroxybutyrate) (PHB) biopolymer. Two commercial grades of PHB were investigated, containing of 4.0% and 6.2% of hydroxyvalerate (HV) comonomer, named PHB1 and PHB2, respectively. Injection moulded specimens were exposed to ultraviolet radiation (UV-A) in the laboratory for periods of up to 12 weeks and then characterized by tensile testing, surface appearance, size exclusion chromatography (SEC), and scanning electron microscopy (SEM). The exposure to UV radiation caused great damaged on the surface color, reduction of molecular size and mechanical properties. The effects were more pronounced on PHB2, probably due a lighter surface color and less packed macromolecular structure which facilitates the transmission of light throughout the samples. Specimens of PHB1 were also injected with the addition of a UV absorber and antioxidant, resulting in a higher UV stability of PHB, as shown by a low reduction in molar mass and better mechanical properties.

Resumo em Inglês:

Abstract Microwave assisted rapid sintering was carried out to fabricate aluminum-ZrB2 metal matrix composites containing 1 wt% cobalt and 10, 15 and 20 wt% ZrB2 as the reinforcements at temperatures of 600, 700 and 800°C. The results showed that the highest values of density and bending strength (97% of theoretical density and 240 MPa, respectively) were obtained in a composite containing 15 wt% ZrB2 and 1 wt% Co sintered at 600°C. Furthermore, the optimum values of compressive strength and hardness (350 MPa and 63 Vickers, respectively) were measured for a composite containing 20 wt% ZrB2 sintered at 600°C. At all sintering temperatures, XRD analysis revealed ZrB2 and aluminum as the only crystalline phases. Microstructure investigations demonstrated a homogeneous distribution of ZrB2 particles in the aluminum matrix.

Resumo em Inglês:

Ni was added into graphite-lead free tin bronze composite layers on surface of steel sheets by primary sintering mixed powders of graphite and CuSn10 with addition of a nickel nitrate and poly(vinyl alcohol) (PVA) solution in an ammonia decomposition atmosphere. The reduced Ni particles attached on the surface of graphite and CuSn10 particles help to link them together. The conjunction of graphite and CuSn10 matrix in the composites treated by cold rolling and second sintering is well, and no cracks can be observed at the interface between graphite and CuSn10 matrix. The addition of Ni will improve the interface; increase hardness, anti-friction and anti-wear performance of the composites greatly. The Ni containing graphite-CuSn10 composites demonstrate better tribological performance than CuSn10Pb10 alloy, which makes them promising lead free bearing materials for heavy load engines.

Resumo em Inglês:

Melt and quench technique was used for the preparation of glassy samples of the composition x Bi2O3-(1-x) B2O3 where x= .05 to .040. XCOM computer program is used for the evaluation of gamma-ray shielding parameters of the prepared glass samples. Further the values of mass attenuation coefficients, effective atomic number and half value layer for the glassy samples have been calculated in the energy range from 1KeV to 100GeV. Rigidity of the glass samples have been analyzed by molar volume of the prepared glass samples.

Resumo em Inglês:

ZnWO4 particles were synthesized as a single-phase by a simple and easy solvo-hydrothermal technique using water-ethylene glycol mixture as solvent, without using surfactant. Physical properties of produced particles were analyzed by X-ray diffraction (XRD), infrared spectroscopy (FTIR), surface area (BET), particles size distribution and atomic force microscopy (AFM). This material was used as support for inulinase immobilization by physical adsorption and the influence of temperature (30 and 50 ºC) was evaluated. Material with mesoporous characteristic and with a surface area of 35.5 m2.g-1 was obtained. According to the findings, ZnWO4 present a satisfactory inulinase adsorption, and the better result was 605 U.g-1 support at 30 ºC. Therefore, ZnWO4 particles prepared by one-step solvo/hydrothermal route provide a new potential support for inulinase immobilization.

Resumo em Inglês:

In the present work, mixed manganese-copper ferrite of composition MnxCu1-xFe2O4 (within x=0.40, 0.42, 0.44, 0.46, 0.48 and 0.50) have been investigated for their electric and magnetic properties such as dc resistivity, Curie temperature, saturation magnetization. MnxCu1-xFe2O4 ferrite samples were prepared by uniaxial pressing from the oxide mixture, synthesized at 1000°C during 45 hours and finally heated to 1200°C by 5h, at room atmosphere. The X-ray diffractograms show that the samples with different compositions were formed by compact structure spinel with cubic cell. The saturated magnetization of the MnxCu1-xFe2O4 ferrites increased with x up to 0.46, which presented the smallest coercitive field. All samples showed hysteresis characteristic of soft magnetic materials. This electrical behavior is compatible with an insulator. The results were analyzed in the framework of grain/barrier model.

Resumo em Inglês:

Technetium-99m is the clinically most used radionuclide worldwide. Although many techniques can be applied to separate 99Mo and 99mTc, the most commonly used method is the column chromatography with alumina as stationary phase. However, the alumina nowadays used has limited adsorption capacity of molybdate ions which implies the need to develop or improve materials to produce high specific activity generators. In this paper, alumina was obtained by a solid state method and heat treatments at different conditions. The powders had a microstructure with porous particles of γ, δ, θ and α-Al2O3 phases as well as specific surface area between 36 and 312 m2 g-1. Most interesting results were reached by powders calcined at 900ºC for 5 hours which had high chemical stability and a molybdenum adsorption capacity of 92.45 mg Mo per g alumina.

Resumo em Inglês:

A number of applications may require cast iron. Engine cylinder blocks, flywheels, gearbox cases, machine-tool bases may be manufactured by using grey cast iron while bearing surfaces with white cast iron. Thus, understanding the solidification behaviour of eutectic cast iron becomes an essential task, with certain points to be accomplished. Transient directional solidification may provide particular advantages in order to deal with these items, such as the large variation of growth rate (V) and cooling rate (Ṫ) values, which may allow a variety of microstructures and morphologies to be studied. The aim of this work is to examine the macrostructure regions, scale of the dendritic microstructure, proportions of the formed phases and hardness of samples obtained by transient directional solidification of a eutectic cast iron (Fe-3.5wt%C-2.5wt%Si). It was shown that a CET criterion should be based on a critical V value at the solidification front of about 0.6 mm/s. The effects of the formed phases, their proportions and λ2 on hardness of the cast alloy are assessed.

Resumo em Inglês:

The coatings of FeAlCuCrCoMn high entropy alloy were deposited by direct current magnetron sputtering. The microstructure and the mechanical and corrosion properties of the coatings are investigated. A perfect dense and smooth coating could be obtained. The coatings exhibit single FCC solid solution as increasing deposited time. The thickness of the coatings increases with the increasing deposited time, the biggest thicknesses is 1.788 µm. The hardness and Young's modulus of the coatings are 17.5 and 186 GPa, respectively. All coatings exhibit better corrosion resistance than the 201 stainless steel in acidic alkali and salt corrosion mediums.

Resumo em Inglês:

Many polymers have been used as biomaterials due to their physicochemical characteristics and structural versatility. However, usage on the human body requires sterilization in order to prevent microbial contamination and diminish the risk of rejection or inflammation. This study presents the use of thermogravimetric analysis (TGA) as an alternative to monitor the presence of residual ethylene oxide from polymers sterilization processes. This is a simple technique and does not require sample preparation stages which can imply in some ethylene oxide loss. Ethylene oxide has been used to sterilize polymeric biomaterials, but with restrictions in the amount used due to the difficulty in removing the toxic waste after the sterilization procedure. Samples of commercial (PEEKc) and medical (PEEKm) grade poly(ether ether ketone) (PEEK) were manufactured in the form of cylindrical tubes, hygienized and sterilized with ethylene oxide. PEEKs showed no chemical changes, but exhibited thermal changes by TGA, which evidenced weight loss between 100 and 500ºC that was attributed to the removal of residual ethylene oxide, so this technique, at a 10ºC‧min-1 heating rate, can be used to monitor the sterilization processes.

Resumo em Inglês:

Yttria stabilized zirconia (YSZ) nanoparticles were synthesized by the co-precipitation method. The crystallinity, morphological and optical properties of the YSZ nanoparticles were studied by using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), FT-Raman, photoluminescence (PL) spectrum analyses. The grain size and crystal structure of the YSZ was confirmed by XRD. SEM and TEM analyses showed that the synthesized samples were composed of the size of nanometers. The optical property of the synthesized nanoparticles was studied from the photoluminescence spectrum. The dielectric properties such as the dielectric constant, the dielectric loss and AC conductivity of the YSZ nanoparticles were studied in the different frequencies and temperature.

Resumo em Inglês:

The use of lightweight materials in the production of cryogenic tanks, spacecraft body etc. are becoming the need to develop dissimilar metal FSW joints. Friction stir welding (FSW) is a novel and inspired light metal joining process since it is not involved with the melting of the parent metal. In this work, two Aluminium 7020 plates were welded with Zn as an interlayer, using friction stir welding method. Different joints were made by varying the thickness of interlayer (Zn) and thereafter the characterization is done against mechanical properties and microstructure of weld nugget. The test result shows that the specimen joint with 10μ Zn interlayer has higher mechanical properties than samples made with 5μ, 10μ, 20μ, 40μ and 100μ Zn interlayer. To analyze the cause, further optical studies (Image analyzer and SEM analysis) were carried out and found the interlayer dispersion plays a vital role in weld strength. As a conclusion addition of Zinc interlayer with preferable thickness (10μ) in Al7020 FSW joints improve tensile strength and hardness than the FSW joints made with higher and lower interlayer thickness.

Resumo em Inglês:

Inorganic compounds doped with rare earths (Ce3+, Pr3+, Nd3+, Sm3+, Eu 3+, Gd 3+, Tb 3+, Tm3+) have been used in various applications including light-emitting devices such as fluorescent lamps, cathode ray tubes, lasers and inorganic pigments. In this study, Pr3+ is doped in spinel Li2ZnTi3O8 system and synthesized by the polymeric precursor method, which is based on the process developed by the Pechini, and characterized by X-ray diffraction, UV-visible and CIE-L colorimetric measures * a * b *., in order to study the effect of doping and thermal treatment on its colorimetric properties. With three different samples of Pr3+ doping (0.01; 0.05 and 0.1 mol%) were prepared and calcined at 500°C, 600°C, 700°C, 800°C and 900°C for 4 h. The analysis of X-ray diffraction confirmed the formation of pure phases with spinel structure and average crystallite size of less than 46 nm. It was found that the colorimetric properties ranging from green to red, in accordance with the increase in the concentration of Pr3+ and thermal processing temperature.

Resumo em Inglês:

ZrO2(Y2O3)-based ceramics are widely used as biomaterials due to high fracture toughness, resulting from the tetragonal-monoclinic phase transformation in which the ceramic is submitted during crack propagation. In this context, studies involving the possibility of optimization of the tetragonal phase are important for the properties improvement of this ceramic. This study investigated the recovery of tetragonal phase from a previously transformed ZrO2(3 mol% Y2O3) ceramic. Zirconia samples were sintered at 1450 °C, at 1530 °C - 2 h and at 1600 °C - 4 h, in order to obtain materials with distinct microstructural features. The sintered samples were characterized by relative density, X-ray diffraction and scanning electron microscopy. Samples sintered at 1450 °C, 1530 °C - 2 h and 1600 °C - 4 h, presented relative densities of 94.2, 99.6 and 99.7% with grains size averages of 0.28, 0.49 and 1.31 µm, respectively. All samples were submitted to milling to induce the tetragonal→monoclinic phase transformation presenting 5, 50 and 65 vol% of monoclinic phase. Subsequently, heat treatments between 400 °C and 1200 °C were conducted to retransform monoclinic in tetragonal phase. It has been found that the smaller the grain size after sintering, the lower the necessary annealing temperatures for fully recovering of tetragonal phase. Annealing temperatures of 950, 1100 and 1200 °C were sufficient to recover almost fully the tetragonal phase.

Resumo em Inglês:

Six new rare-earth orthoborates NaBaR(BO3)2, with R = Tb, Dy, Ho, Er, Tm, Lu were synthesized using a multiple-step solid-state reaction. These new orthoborates continue the previously described isostructural lines of three-cation orthoborates NaBaR(BO3)2, by R = Sc, Y, Yb. The structure of synthesized solid compounds is isotypic with the mineral eitelite, Na2Mg(CO3)2, crystallizing in the trigonal system with space group R3. All prepared borates are isostructural, as evidenced by the presence of the same vibration modes in Raman spectra and of the same diffraction peaks in X-ray patterns. The photoluminescence of NaBaTb(BO3)2 have been investigated in a detail.

Resumo em Inglês:

One of the main components for being successful in tissue engineering is developing a scaffold with an appropriate architecture for allow migration, cell proliferation, and differentiation. A gelatin-chitosan scaffold by vacuum freeze-drying has been developed for tissue engineering applications. The effects of solid concentration and freezing processing on the scaffold morphology and porous size were investigated. As the chitosan content was increased the viscoelastic properties of pigskin gelatin was modified, the maximum G' values were lower than the values for pure gelatin solution, and the thermal transition points also occurred at lower temperatures, as well as a decrease of pore size tendency was observed and the scaffold visibly increased porosity, the structure scaffold was observed with an interconnected and more homogeneous pore matrix. The pore sizes become smaller and pore walls thinner, while interconnectivity increases along with declining pre-freezing temperature. The chitosan-gelatin scaffold will be a promising candidate in tissue engineering.

Resumo em Inglês:

Modelling of a crack propagating through a finite element mesh under mixed mode conditions is of prime importance in fracture mechanics. In this paper, three different crack growth criteria and the respective crack paths prediction in the cement mantle of the reconstructed acetabulum are compared. The maximum tangential stress (MTS) criterion, the minimum strain energy density (MSED) criterion and the new general fracture criterion based on the energy release rate G(θ) are investigated using advanced finite element technique. The displacement extrapolation technique (DET) is used, to obtain the SIFs at crack tip. Several examples are presented to show the robustness of the numerical techniques. The effect of the inclusions and cavities on the crack propagation in cement orthopedic are highlighted.

Resumo em Inglês:

The electric upsetting process is an excellent electrically assisted preforming technique with electrical-thermal-mechanical multi-field coupling characteristic. The secondary upsetting defect in electric upsetting with inappropriate parameters combinations could result in folds in subsequent forging process. In order to analyze the formation process of the secondary upsetting defect, the finite element model of electric upsetting was constructed based on the multi-field coupling solver platform, MSC.Marc. It is concluded through the numerical simulation with inappropriate parameters combination that the main factor causing the secondary upsetting defect is the large temperature decrease of the deformed portion after the formation of drum-shape in the preliminary stage of electric upsetting. Subsequently, the secondary upsetting defect has been successfully avoided via a three-stage current mode. Finally, a novel optimization method based on close-cycle control of current in numerical simulation was established by developing a current subroutine in MSC.Marc, which was proved to be effective for the elimination of the secondary upsetting defect.

Resumo em Inglês:

The present paper's objective was to synthesize and characterize both the oxalic niobium precursor (NH4)3NbO(C2O4)3.H2O, and the product of its doping with Cu and calcining, CuNb2O6. In order to obtain the niobium precursor, commercially available niobium oxide (Nb2O5) was subject to fusion with potassium bisulfate (KHSO4). Once leached with water, the powder was complexed with oxalic acid and ammonium oxalate. The as produced material was manually mixed with copper nitrate Cu(NO3)2.2H2O (25% Cu molar) and calcined at 1000°C in a muffle furnace. CuNb2O6 was then obtained. The precursor was characterized by XRD, SEM, FT-IR, XRF, TG/DTG. The calcination product was characterized by XRD, XRF and SEM. Results show that single phase CuNb2O6 could be obtained by this method without Nb2O5 contamination.

Resumo em Inglês:

The present paper studies the effects of the additions between 3.00 and 7.00 wt% of additive Granic 422 instead of polypropylene on polymeric tapes properties as color difference, structure and tensile parameters. Micro-structural analysis revealed additional agglomerations of calcium carbonate particles on the surfaces of the tapes after application of new portions of the variable additive. Composition-property relations showing the changes in properties of tapes were suggested. For increase in color difference of the tapes from zero to 0.18, a logarithmic relation was used. For other indices, the linear relations were proposed. On the basis of the relations, the positive changes of 2.0-2.7% in macro-structural parameters (width, thickness, linear density) and negative changes of 2.1-8.8% in tensile characteristics were obtained.

Resumo em Inglês:

The Sr2HoNbO6 complex perovskite has been synthesized by solid-state reaction. X-ray diffraction pattern reveals that Sr2HoNbO6 material crystallizes in a cubic structure, Fm3̅m space group, lattice constant a=8.018 Å, which has a lattice mismatch ~3% with YBa2Cu3O7-δ. The chemical stability of Sr2HoNbO6 with YBa2Cu3O7-δ superconducting has been studied by x-ray diffraction and measurements of magnetization as a function of temperature on Sr2HoNbO6-YBa2Cu3O7-δ composites. X-ray diffraction patterns of the composite shown that all the X-ray diffraction peaks could be indexed for either Sr2HoNbO6 or YBa2Cu3O7-δ with no extra peak detectable. This result implies that these compounds remain as two different separate phases in the composite with no chemical interaction. Magnetic response shows that superconducting transition temperature of pure YBa2Cu3O7-δ and Sr2HoNbO6-YBa2Cu3O7-δ composites is 93,5 K. These favorable characteristics of Sr2HoNbO6 show that it can be used as a potential substrate material for growth of YBa2Cu3O7-δ superconducting films.

Resumo em Inglês:

In this work, an active screen plasma discharge system based technology was incorporated in a PECVD reactor for DLC films growth, making it a new development in DLC films deposition. In this case, the active screen system is used to seek better electrons confinement, which might result in high ions density due to the collisions number increase, leading to a possible increase in ionization. DLC films were grown on steel substrates, using two variations of this system. In order to enhance adhesion between coating and substrate, a silicon interlayer was deposited, using different bias voltages. Morphological and structural characterization was performed by scanning electron microscopy, optical profilometry and Raman scattering spectroscopy. Tribological tests were performed by nanohardness, scratch and wear tests. Results showed that the plasma confinement promoted good films adhesion, which may be related to a high sub-implantation. This might be a consequence of the pressure decrease, as well as, to the ions energy distribution narrowing.

Resumo em Inglês:

Ferrosilicon powder surface coated with a dense epoxy resin membrane was prepared via coating precipitation methods using silane coupling agents as the modifier and epoxy resin as the coating agent. FTIR, FESEM, MPMS-XL, and TG-DSC were used to analyze the morphology, surface composition, magnetic property and thermostability of ferrosilicon powder before and after the modification and coating. The experimental results indicate that epoxy resin membranes of a certain thickness were successfully coated onto the surface of ferrosilicon powder; coatings of epoxy resin contributed to the decreased the rate of weight loss via the reduced wear of the coatings and provided resistance to corrosion; the apparent viscosity of medium suspension with coated ferrosilicon was smaller than that of magnetite. Meanwhile, analysis reveals that room-temperature magnetic hysteresis loops of ferrosilicon powder remain basically unchanged before and after coating.

Resumo em Inglês:

In this work we study hydroxylated carbon nanotube (CNT) assembly on polyamide (PA) and polypropylene (PP) polymers activated by UV radiation from a theoretical and experimental perspective. Molecular computer simulation was done to understand the stable conformations and bulk properties (molecular dynamics) of the polymers before and after exposure to UV radiation at the molecular level. Our experiments suggest that PA presents more -OH active groups, producing a more hydrophilic surface, whereas PP exhibits less potential UV activation. These results suggest that it is possible a facile covalent functionalization method to tune organic polymer surface properties through SWCNT anchoring for nanotechnological applications requiring defined surface roughness and chemical functionality on inexpensive polymers.

Resumo em Inglês:

The process of photooxidative destruction of high density polyethylene films containing different organic complexes of polyvalent metals as pro-oxidant additives after UV- irradiation was studied. During exposure to UV- irradiation, the more significant changes in the mechanical and thermal properties were detected for the foils containing pro-oxidant additives compared to initial high density polyethylene. This indicated for the higher degree of oxidation in these samples and confirmed the effectiveness of thеsе additives in promoting the oxidation of high density polyethylene during UV-irradiation. It was found that the decrease of the strength of the initial high density polyethylene foils was more pronounced for the samples with pro-oxidants cobalt (III) acetylacetonate and manganese (II) acetylacetonate. The use of 2 mmol/kg iron (III) acetylacetonate and 4 mmol/kg cobalt (III) acetylacetonate as pro-oxidants gave the highest decrease of elongation at break of the polyethylene foils.

Resumo em Inglês:

Abstract One of the most important characteristics of calcium phosphate cements is their resorbability when implanted in the body. However, the in vivo resorption rate is slow due to the lack of intrinsic open porosity. In this study, macroporous structures were obtained by mixing alpha-tricalcium phosphate (α-TCP) cement with a foamed liquid phase containing different concentrations of sodium hydrogen phosphate and non-ionic (Lutensol) or anionic (Sodium Lauryl Sulfate) surfactant. The cement paste was prepared by hand mixing in a system of two syringes connected by a polyvinyl chloride (PVC) valve, an environmentally friendly method. Solutions with Lutensol (L110) showed greater foamability than solutions with Sodium Lauryl Sulfate (SLS). Scanning Electron Microscopy characterization helped verify that the prepared samples showed a macroporous interconnected structure, and X-ray diffraction analysis evidenced the transformation of α-TCP into calcium deficient hydroxyapatite (CDHA). This study suggests that the calcium phosphate cement samples foamed with Lutensol may be further evaluated as suitable materials for bone filling.

Resumo em Inglês:

Abstract The objective of this study was to evaluate the physical and mechanical properties of commercial panels produced with sugarcane bagasse to investigate the possibility of us for the production of furniture. We evaluated industrial MDP (Medium density particleboard) panels made of Eucalyptus and Pinus by two Brazilian companies and an industrial MDP panel made from sugarcane bagasse, produced in China. We tested the physical characteristics of water absorption and thickness swelling of the panels after 2 and 24 h of immersion in water. To estimate the moisture content and density, we followed the procedure detailed in NBR 14810-3¹. The mechanical properties were characterized by performing bending (moduli of elasticity and rupture), compression (moduli of elasticity rupture), internal bonding, screw pullout and Janka hardness tests. We found that panels made from sugarcane bagasse showed comparable with or superior physical and mechanical properties to those made from Eucalyptus and Pinus.

Resumo em Inglês:

Abstract We have successfully synthesized Pr2O5 doped borate glasses by conventional rapid melt quench method. The XRD pattern indicates the amorphous nature of Pr2O5 doped borate glass. An optical property of prepared borate glass was studied using the Photoluminescence spectrum. Determination and differentiation of the various vibrational modes were done using FTIR spectroscopy studies. Raman spectroscopy of Pr2O5 doped borate glass was also carried out. Thermal analyses of the glasses were done using the TGA/ DTA and DSC analysis. The dielectric properties such as dielectric constant, the dielectric loss and AC conductivity of the Pr2O5 doped borate glass were studied in the different frequencies and temperature.

Resumo em Inglês:

Abstract The Friction Hydro-Pillar Process (FHPP) is an innovative process that has been recently studied regarding its possible in situ repair applications. There is still no literature about usage of the FHPP on duplex stainless steel (DSS) base materials to smaller forces than 25 kN. The investigation on DSS processing is crucial due his wide variety of critical uses in pipes and storage structures applied in chemical industry plants, where usual welding processes may lead to safety concerns. The aim of this study is to qualify the processing of SAF 2205 (UNS 31803) duplex stainless steel welded joints using FHPP as feasible repair procedure. For this, the studied samples were welded applying a range of axial forces. The welded joints were characterized by, α/γ phase ratio, intermetallic quantification, austenite spacing measurement, microhardness profile and microstructural qualitative studies. The results showed the efficiency in repair of the FHPP process on the production of DSS joints according with the material recommendations from the standard DNV-RP-F112.

Resumo em Inglês:

Abstract 4-Bromoanilinium 4-methylbenzenesulfonate (4BPTS) single crystal was successfully grown from ethanol by slow evaporation method at room temperature. The structure of grown crystal was confirmed by single crystal X-ray diffraction studies. The presence of functional groups of grown crystal was confirmed by the Fourier transform infrared spectroscopy (FTIR) spectral analysis. UV-Visible absorption study was performed on the grown crystal to determine the cut-off wavelength. The thermal stability of the grown crystal was investigated from the Thermogravimetric analysis (TGA)/ Differential thermal analysis (DTA) analysis. The mechanical behaviour of grown crystal was studied by using Vicker's microhardness test. The third order non-linear optical properties of 4BPTS were investigated by Z-scan technique with He-Ne laser radiation and the corresponding non-linear refractive index and absorption coefficients were also calculated.

Resumo em Inglês:

Abstract The thermodynamic optimization of Ti-Si-X systems requires that their respective binary systems are constantly updated. The Ti-Si system has been experimentally investigated since the 1950s and these critical experimental data can be employed to calculate the Ti-Si phase diagram using thermodynamic modeling. The most recent assessment of the Ti-Si system was performed in 1998, showing the presence of stoichiometric Ti3Si as stable phase. In the light of the dispute over the stability of Ti3Si phase in the eutectoid reaction of the Ti-Si and Ti-X-Si systems, the present work assessed the Ti-rich corner of the "stable" (featuring Ti3Si phase) and "metastable" (featuring Ti5Si3 phase) Ti-Si phase diagrams. The phase boundaries, the values of the error of the least-square method of the optimization procedure and the relative standard deviation of the calculated variables of the assessed diagrams; and previous investigations were discussed in order to inspire further experimental work on the eutectoid reaction of the Ti-Si phase diagram.

Resumo em Inglês:

Abstract Membranes for fuel cell applications were prepared using two polymer blends: poly(vinyl alcohol) (PVAL) and chitosan (CS), 80/20 (w/w) and 60/40 (w/w) with and without nylon. Sulfosuccinic acid (SSA) was used both as a crosslinking and a sulfonating agent. An increasing in the SSA content raised ionic exchange capacity and consequently proton conductivity in the membranes. The addition of nylon has improved membrane mechanical properties by decreasing stiffness. Membranes presented good proton conductivity (around 10-2 S cm-1) and lower H2 and methanol permeability rather than the standard membrane Nafion® 115. Membranes which showed to be stable under fuel cell operation were tested using hydrogen and methanol fuels. Membrane PVAL:CS, 80/20 (w/w), containing SSA crosslinker, (PVAL+CS)/SSA, of 4/1 (mol/mol), has shown the best performance under fuel cell environment. However, results have shown that an improvement is required in the adhesion between the membrane and the electrodes.