Resumo em Inglês:

In this study, we replaced 30% of the cement with steel slag to prepare binding material; additionally, small amounts of CaCO3 and CaSO4·2H2O were added. This was done to study the compound effect of CaCO3 and CaSO4·2H2O on the strength of steel slag-cement binding materials. The hydration degree of the steel slag cementitious material was analyzed by XRD, TG and SEM. The results showed that the optimum proportions of CaCO3 and CaSO4·2H2O were 3% and 2%, respectively. Compared with the steel slag-cement binders without adding CaCO3 and CaSO4·2H2O, the compressive strength increased by 59.9% at 3 days and by 17.8% at 28 days. Acting as the nucleation matrix, CaCO3 could accelerate the hydration of C3S. In addition, CaCO3 was involved in the hydration reaction, generating a new hydration product, which could stably exist in a slurry. Meanwhile, CaSO4·2H2O could increase the number of AFt. The compound effect of CaCO3 and CaSO4·2H2O enhanced the intensity of steel slag-cement binding materials and improved the whole hydration behavior.

Resumo em Inglês:

The bauxite residue (BR) is the solid waste of largest generation by the aluminum industry, with a generation estimated in 10 million ton/year in Brazil. Its high alkalinity demands elevated costs to store it safely. Due to the high content of Al2O3 and Fe2O3 in BR, the present study evaluated its application for the synthesis of iron rich sulfobelite clinkers. Because of its composition, the cement made with this clinker presents environmental (30% to 62% reduction of CO2-equivalent emission), economic and even technical advantages over Portland cements. Formulations containing: limestone, gypsum, BR and clay, were fired at 1230°C to synthesize the clinkers. Variations in BR and clay content were studied to obtain three formulations, F-15, F-18 and F-21, of different Al2O3/Fe2O3 ratio values. Cements containing more than 10.5 wt-% of BR achieved mechanical resistance comparable to Portland cements (CP-II-Z32 and CP-V-ARI) for 7 and 28 days of curing age.

Resumo em Inglês:

The results of database based on the efficiency packed model for metallic glasses. The database contains the atomic radii information as well as elastic properties of the most commonly used alloying elements, permitting composition, packing efficiency and elastic property predictions to be made for binary, ternary and quaternary bulk metallic glasses. Twenty different alloys per system (binary, ternary and quaternary) experimentally reported in the literature were compared with those estimated by the database. Comparison charts and diagrams showed good agreement between the composition predictions and those reported from the experimentally processed metallic glasses. The elastic properties predictions could be used to elaborate Blackman diagrams in order to know, in advance, the intrinsic toughness that the investigated alloys might present. The database is intended for designing bulk metallic glasses. Finally, some quaternary alloys were experimentally produced based on the prediction obtained with the database, showing a glassy phase. The microhardness values obtained experimentally of the Zr57.52Ag10.62Al10.62Co21.24, Zr57.19Al10.7Ni10.7Cu21.41 and Hf60.22Al9.95Cu9.95Ni19.89alloys, are 3.8, 4.0 and 3.6 GPa, respectively. The Young´s modulus calculated using microhardness values (E/Hv = 20) are closed to the values obtained by the "mixing rules".

Resumo em Inglês:

A homemade Josephson junction was successfully obtained using a superconductor thin film of the BSCCO system. The film was deposited on a lanthanum aluminate, produced from a commercial powder with a nominal composition Bi1.8Pb0.4Sr2CaCu2Ox, was thermally treated by a domestic microwave oven. The XRD analysis of the film indicated the coexistence of Bi-2212 and Bi-2223 phases and SEM images revealed that a typical superconductor plate-like morphology was formed. From the electrical characterization, performed using DC four probes technique, it was observed an onset superconducting transition temperature measured around 81K. At the current-voltage characteristics curve, a step of electric current at zero-voltage could be observed, an indicative that the tunneling Josephson occurred.

Resumo em Inglês:

In bone tissue engineering, cell-scaffold constructs are used to stimulate complete, functional tissue replacement that does not occur naturally in critical-size defects. In this report, we describe the application potential of poly (L-co-D,L lactic acid)-PLDLA 70/30, synthesized in house as constructs loaded with osteoblast-like cells on bone tissue engineering. In vitro biological results show that the porogen leached PLDLA scaffolds are cytocompatible with osteoblast cells, able to stimulate significant cells growth during the first 14 days of culture, during which the morphology and cell behavior of osteoblasts cultured on the scaffolds were monitored by scanning electron microscopy (SEM). In vivo, PLDLA constructs were implanted in 5 mm bilateral critical-size defects created in rat-calvariae and then evaluated histologically 8 and 12 weeks after implantation. The histological results showed that PLDLA constructs supported the growth of new tissue, with a degradation rate close to that of native bone formation and decrease of inflammatory response over time of implantation. These data provide evidences that the synthesized PLDLA polymer has application potential as construct for bone tissue engineering.

Resumo em Inglês:

In order to develop new-typed multifunctional composite nanofibers, PANI/Fe3O4/PVP flexible bifunctional composite nanofibers with simultaneous electrical conduction and magnetism have been successfully fabricated via a facile electrospinning technology. Polyvinyl pyrrolidone (PVP) is used as a matrix to construct composite nanofibers containing different amounts of polyaniline (PANI) and Fe3O4 nanoparticles (NPs). The bifunctional composite nanofibers simultaneously possess excellent electrical conductivity and magnetic properties. The electrical conductivity reaches up to the order of 10-3 S · cm-1. The electrical conductivity and saturation magnetization of the composite nanofibers can be respectively tuned by adding various amounts of PANI and Fe3O4 NPs. The obtained electricity-magnetism bifunctional composite nanofibers are expected to possess many potential applications in areas such as electromagnetic interference shielding, special coating, microwave absorption, molecular electronics and future nanomechanics. More importantly, the design concept and construct technique are of universal significance to fabricate other bifunctional one-dimensional nanostructures.

Resumo em Inglês:

Recently, Rahmati et al., 1 have published a paper in Materials Research 2014; 17(2): 303-310. They have investigated the structural, elastic, electronic and optical properties of Cu3N in its phase cubic anti-ReO3 structure. But it is to be noted, that the numerical values of the density, the longitudinal (vl), transverse (vt) and average (vm) elastic wave velocities, and the Debye temperature obtained by Rahmati et al., 1 seem to be inaccurate. These errors are certainly due to the inaccuracy application of the formula used to calculate the density. In the present comment, we recalculated, and we gave the right numerical values of the density, the longitudinal (vl), transverse (vt) and average sound velocity (vm) and of the Debye temperature of Cu3N material, based on the lattice parameter and the elastic constants obtained in their work.

Resumo em Inglês:

The microstructure and defects of CuO nanoparticles under isochronal annealing were investigated by positron annihilation spectroscopy (PAS), X-ray diffraction (XRD) and scanning electron microscope (SEM). XRD and SEM results indicated that the average grain sizes of CuO nanoparticles grew slowly below 800 °C, and then increased rapidly with the annealing temperature from 800 to 1000 °C. Positron lifetime analysis exhibited that positrons were mainly annihilated in mono-vacancies (VCu , VO) and vacancy clusters when annealing from 200 to 800 °C. Furthermore,W-S plot of Doppler broadening spectra at different annealing temperatures found that the (W,S) points distributed on two different defect species, which suggested that VCu−−VO+ complexes were produced when the grains grew to bigger size after annealing above 800 °C, and positrons might annihilate at these complexes.

Resumo em Inglês:

The rolled AZ31 Mg alloy sheets were processed by multi-pass bending (MPB) process at room temperature and followed by annealing treatment. Mechanical properties of the as-received and MPB sheets in annealed conditions were examined based on the concurrent microstructure and texture evolution. The results show that the room temperature ductility of the Mg sheets was improved by multi-pass bending process. Moreover, the (0002) basal texture was drastically weakened. Enhanced the ambient mechanical properties, such as lower yield strength and larger uniform elongation, were fabricated by MPB path due to the weak basal texture. The microstructure and mechanical responses were characterized and discussed.

Resumo em Inglês:

An uranyl complex [UO2(TFA)2(DMSO)3] (TFA=deprotonated trifluoroacetic acid; DMSO=dimethyl sulfoxide) has been successfully synthesized by reacting UO2(CH3COO)2·H2O with one equivalent of (CF3CO)2O and DMSO. The complex has been characterized by single-crystal X-ray diffraction, X-ray powder diffraction, elemental analysis, FT-IR spectroscopy, thermal analysis and absorption and emission spectroscopies. The spectroscopic properties of the material make it suitable for its application in the sensing and monitoring of uranyl in the PUREX process.

Resumo em Inglês:

Stainless steel (SS) is successfully used in food industries due to the characteristics of its surface, which is essential for the maintenance of the properties of food. Tanks and stainless steel pipes, which come into direct contact with food and drink, undergo a process of cleaning and disinfecting called CIP (Clean-in-Place). This method consists of automatic recirculation of a detergent solution for a controlled time followed by a rinsing with water, and finally a cleaning and sanitizing solution immersion. This work consists of investigating the corrosion resistance of stainless steels used in the food industry using sanitizing solutions employed in the CIP procedure, and using electrochemical techniques such as potentiodynamic anodic polarization and electrochemical impedance spectroscopy.

Resumo em Inglês:

This study proposes a methodological guide to explore and select materials for executive aircraft interiors, contributing toward a perspective of materials requirements, indicators and strategies to design more environmentally sustainable products. This was motivated by the signs from the aviation industry to reduce its environmental impact and the permanent need to push for cost efficiency. The guide includes a schedule framework of materials requirements for sustainable design, and also aeronautical materials and marketing requirements. It was prepared by mapping sustainability demands for materials selection during product development, supported by a case study. Patented eco-friendly materials solutions for the case study involving the aircraft furniture structural panels were described and analyzed, considering the materials requirements of the aeronautical project. Composites of bio-polymers reinforced with natural fibers, preferably with solid cores, seem to be the most promising solutions to substitute the current panels.

Resumo em Inglês:

A diffusion/transformation coupled model has been developed which combines finite difference (FD) model with a phenomenological model. The composition of the different iron-nitrogen(Fe-N) hardening phase can be regard as a function of nitriding time and nitrogen concentration. The diffusion model and transformation model are linked by the limiting nitrogen solubilities and the effective diffusion coefficients. The effect of alloy elements (Cr, Mo, Mn, V, Ni etc.) is considered by introducing an alloy coefficient for limiting nitrogen solubilities and diffusion coefficient. The diffusion/transformation model can predict nitrogen concentration, phase composition and hardness distribution. The model is employed to simulate the nitriding process of SCr420H low-alloy steels. The simulated nitrogen concentration and hardness profiles are consistent with the measured ones. In addition, the predicted depth distributions of iron-nitrogen phase agree well with the available experimental results. Therefore, the comparison shows the reliability of the coupled model. It can be applied to improve the nitriding process parameters.

Resumo em Inglês:

Milling of hardened steel components provides considerable benefits in terms of reduced manufacturing cost and time compared to traditional machining. Temperature variation in milling is an important factor affecting the wear of cutting tools. The poor selection of milling parameters may cause excessive tool wear and increased work surface roughness. Hence, there is a need to study the machinability aspects during milling of hardened steel components. In the present work, influence of cutting speed, feed rate and radial depth of cut on milling temperature, surface roughness and cutting force during milling of AISI D2 steel has been investigated using response surface methodology (RSM) based models. From the parametric analysis, it is revealed that temperature increases linearly, whereas surface roughness increases non-linearly with cutting speed. However, for higher values of feed rate, an increased cutting speed considerably reduces the cutting force for specified depth of cut range. The present work also reveals that the selection of best cutting conditions is useful at the CAPP stage in the milling process particularly with tight tolerances.

Resumo em Inglês:

The Sn–10.2 Sb (mass fraction) peritectic alloy was prepared using a vacuum melting furnace and a hot filling furnace. The samples were directionally solidified upwards at steady state conditions with a constant temperature gradient (G=4.5±0.2 K. mm-1) under different growth velocities (V=13.3–266.7 µm. s-1) in a Bridgman-type directional solidification apparatus. The effects of the growth velocity (V) on the dendritic spacings were investigated. Primary dendrite arm spacing (PDAS) of α phase in directionally solidified Sn–10.2 Sb peritectic alloy was measured on the longitudinal and transverse sections of 4 mm diameter cylindrical samples. Secondary dendrite arm spacing (SDAS) was measured on the longitudinal section. The experimental results show that the measured PDAS (λ1L, λ1T) and SDAS (λ2) decrease with increasing growth velocity. The dependence of PDAS, SDAS, microhardness (HV) and compressive strength (σc) on the growth velocity were determined by using a linear regression analysis. The experimental results were compared with the previous experimental results and the results of the experimental models.

Resumo em Inglês:

Cadmium oxide powder doped with Tb ions was synthesised by thermal decomposition of cadmium Hydroxychloride Cd(OH)Cl. The molar content of Tb is 2.6%. The purpose of the present study is to tailoring room-temperature ferromagnetic (RT-FM) properties to CdO in order to use it in the field of dilute magnetic semiconductors (DMS). The samples characterised by X-ray fluorescence (XRF) and X-ray diffraction (XRD). The optical band gap of the prepared powders was determined by diffuse reflection spectroscopy (DRS). Terbium ions doped in CdO are employed as source of FM properties. The electronic medium of Spin-Spin interaction in host CdO is studied by annealing in hydrogen atmosphere. Magnetic measurements reveal that Tb-doped CdO powder behaves as paramagnet defeating the intrinsic diamagnetic behaviour of CdO. However, after annealing in hydrogen atmosphere, RT-FM properties were created. Thus, it was proved that magnetic properties could be tailored by doping and post treatment under H2 atmosphere.

Resumo em Inglês:

The formation of aluminum titanate was investigated by isothermal treatments of samples obtained from equimolar mixtures of alumina and titania, containing small amounts of silica and magnesia. Results of differential thermal analysis and Rietveld refinements of data collected by X-ray powder diffraction (XRPD) showed that additions of silica in amounts used in this work did not influence the formation of aluminum titanate. However, the presence of magnesia favored the formation of aluminum titanate in two steps, first one by incorporating Mg2+ into Al2TiO5 lattice during its initial formation, and the second one by accelerating the Al2TiO5 formation, contributing to large quantities of this phase. MgO doped samples have also developed a more suitable microstructure for stabilizing of Al2TiO5, what make them promising for applications such as thermal barriers, internal combustion engines and support material for catalyst.

Resumo em Inglês:

Neodymium orthoferrite NdFeO3 was obtained at room temperature by mechanosynthesis with a stoichiometric ratio of Nd2O3 and Fe2O3 powders, whereas the traditional synthesis requires a temperature of approximately 1000 °C. The crystal structure was analyzed by X-ray diffraction analysis using Cu radiation and a LynxEye XE detector, whose strong fluorescence filtering enabled a high signal intensity. The analysis indicated that the obtained crystallites were nano-sized. The particle morphology was observed by scanning electron microscopy, and the magnetic saturation was tested by vibrating sample magnetometry. The synthesis of NdFeO3 was detected after a few hours of milling, indicating that the milling imparted mechanical energy to the system.

Resumo em Inglês:

In this paper, we report on the synthesis and characterization of high molecular weight copolyesters from Terephthalic acid, 1, 4 butane diol and Succinic acid /Sebacic acid through a two step process of melt polycondensation using titanium tetra butoxide as catalyst. The synthesized aromatic-aliphatic random copolyesters were characterized by means of FTIR, 1H NMR,13C NMR, Differential Scanning Calorimetry (DSC), X-ray Diffraction (XRD), Gel Permeation Chromatography (GPC) and Scanning Electron Microscope (SEM) studies. The effect of copolymer composition on the physical and thermal properties as well as degradation test was investigated. The degradation test was carried out in alkali medium. The phase behaviour of the polymers was studied by differential scanning calorimetry and optical polarising microscopy. The results revealed that the newly synthesized copolyesters exhibited degradability and thermotropic liquid crystalline behaviour with nematic texture which was revealed by optical polarising microscopy. The Novelty of this work is that the glass transition temperature and melting temperature are above the room temperature for the synthesized polymers. This shows the good thermal stability which results in early processing of liquid crystalline materials.

Resumo em Inglês:

Mn-C-codoped TiO2 catalysts were synthesized by modified sol-gel method based on the self-assembly technique using polyoxyethylenesorbitan monooleate (Tween 80) as template and carbon precursor and the effect of calcination temperature on their structural properties and photocatalytic activity were investigated. The XRD results showed undoped and Mn-C-codoped TiO2 calcined at 400 oC only include anatase phase and the rutile phase appears when the calcination temperature reached to 600 oC. UV-vis absorption spectroscopy demonstrates that the absorption spectra are strongly modified by the calcination temperature. Moreover, the Mn-C-TiO2 calcined at 400 oC showed the lowest PL intensity due to a decrease in the recombination rate of photogenerated electrons and holes under light irradiation. The photocatlytic activity of Mn-C-codoped TiO2 were evaluated by the degradation of methyl orange (MO) under the simulate daylight irradiation and all the prepared Mn-C-codoped TiO2 samples exhibited high photocatalytic activities for photocatalytic decolorization of methyl orange aqueous solution. At 400 oC, the Mn-C-codoped TiO2 samples showed the highest photocatalytic activity due to synergetic effects of good crystallize ation, appropriate phase composition and slower recombination rate of photogenerated charge carriers, which further confirms the calcination temperature could affect the properties of Mn-C-codoped TiO2 significantly.

Resumo em Inglês:

The secondary steel refining process uses filler sand as a thermal insulating barrier that separates the liquid metal from direct contact with slide-gate system of the steel ladle. The effective use of this practice must provide a high free opening rate, impacting on increased productivity and quality of steel, reducing the number of stops, thermal loss and even the steel re-oxidation. Both operational parameters and material properties have influence on the free opening rate. In the present work, two chromite-silica sands were analyzed, and some composition changes were proposed. The properties of these materials and the relevant process parameters were evaluated according to the free opening rate under normal operational conditions. The increases in carbon content and in particle size were considered the main factors relating to the filler sand. The percentage of free opening is also strongly influenced by time and temperature of the steel contact.

Resumo em Inglês:

Titanium dioxide (TiO2) thin films were prepared by Chemical Bath Deposition (CBD) method. The X-ray diffraction (XRD) analysis was used to examine the structure and to determine the crystallite size of TiO2 thin film. The surface morphology of the film was studied using Scanning Electron Microscopy (SEM).The optical properties were studied using the UV-Visible and photoluminescence (PL) spectrum. Optical constants such as band gap, refractive index, extinction coefficient and electric susceptibility were determined. The FT-IR spectrum revealed the strong presence of TiO2. The dielectric properties of TiO2 thin films were studied for different frequencies and different temperatures. The AC electrical conductivity test revealed that the conduction depended both on the frequency and the temperature. Photoconductivity study was carried out in order to ascertain the positive photoconductivity of the TiO2 thin films.

Resumo em Inglês:

Zinc doped Tin oxide (SnO2) nanoparticles were prepared by co-precipitation method. The average crystallite size of pure and Zn-doped SnO2 nanoparticles was calculated from the X-ray diffraction (XRD) pattern. The FT-IR spectrum indicated the strong presence of SnO2 nanoparticles. The morphology and the particle size were studied using the scanning electron microscope (SEM) and transmission electron microscope (TEM). The particle size of the Zn-doped SnO2nanoparticles was also analyzed, using the Dynamic Light Scattering (DLS) experiment. The optical properties were studied by the UV–Visible absorption spectrum. The dielectric properties of Zn-doped SnO2 nanoparticles were studied at different frequencies and temperatures. The ac conductivity of Zn-doped SnO2 nanoparticles was also studied.

Resumo em Inglês:

Poly(vinylidene fluoride – tryfluorethylene) [P(VDF-TrFE)] copolymers were mixed with zirconia nanoparticles. The investigation was conducted with the intention to produce nanocompounds with potential to be used as protective patient shielding in radiological procedures. Polymer based nanocomposites with 1, 2, 3, 5 and 10 wt% of ZrO2 nanoparticles were prepared using sol-gel route with zirconium butoxide as the precursor for zirconium oxide nanoclusters. UV-Vis and FTIR spectrometry and differential scanning calorimetry (DSC) were used to characterize the composite samples. We observed a more homogeneous distribution of ZrO2 nanoparticles encapsulated by methyl methacrylate (MMA) into the polymeric matrix, when compared to composites made without the use of surface modifiers from methacrylate group. Apparently, this property is related to the absence of the strong MMA absorption band at 1745 cm-1, attributed to C=O bond, in the P(VDF-TrFE)/ZrO2-MMA nanocomposites. The radiation damage due to high dose exposuring was performed for gamma doses ranging from 100 kGy to 1,000 kGy. The radiation shielding characterization conducted using x-rays with effective energy of 40 keV has demonstrated that composites with 10% of ZrO2,and only 1.0 mm thick, can attenuate 60% of the x-rays beam.

Resumo em Inglês:

In this paper, it was targeted to the enhance thermal stability and wettability behavior of thermoplastic polyurethane (TPU) by adding barium metaborate. TPU-Barium metaborate composites were prepared by adding various proportions of barium metaborate to TPU. The chemical structures of the composites were characterised by fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) analysis. All prepared composites have extremely high Tg and thermal stability as determined from DSC and TGA analysis. All composite materials have the Tg ranging from 15 to 35 °C. The surface morphologies of the composites were investigated by a scanning electron microscopy. Mechanical properties of the samples were characterized with stress-strain test. Hydrophobicity of the samples was determined by the contact angle measurements. The obtained results proved that thermal, hydrophobic and mechanical properties were improved.

Resumo em Inglês:

The effect of montmorillonite (MMT) loading (0, 2.5, and 5 wt%) and almond shell flour (ASF) content (30, 35, and 40 wt%) on the decay resistance, hardness, water resistance of injection molded polypropylene (PP) composites was investigated. The amount of maleic anhydride grafted polypropylene was kept constant at 2% for all formulations. White-rot (Trametes versicolor) fungal treatment was applied to the produced composites for 14 weeks according to BS 838:1961 with the Petri dishes method. The weight loss of the composites decreased with increasing MMT content. The highest hardness (66 Shore D) was noted in the undecayed control composites (40ASF60PP0MMT) while the lowest hardness (61.3 Shore D) was recorded in the decayed control composites (30ASF70PP0MMT). The water absorption of the undecayed and decayed composites decreased with increasing amount montmorillonite at 30-40 wt% content of the ASF loading level. The water absorption of the decayed composites was higher than that of the undecayed composites but their thickness swelling was lower. Based on the findings obtained from the present study, a 35/5/65/2 formulation of the ASF/MMT/PP/MAPP can be used in outdoor applications requiring a high dimensional stability.

Resumo em Inglês:

A novel process was developed for the synthesis of a mixed phase (constituted of 66% anatase phase) of TiO2 nanoparticles at lower calcination temperature (400 oC) by the sol gel technique using a cost effective and easily available propanol solvent. Stereochemistry of propanol played a crucial role towards crystallographic phase of resultant TiO2nanoparticles where n-propanol gave mixed phase while i-propanol gave pure anatase. A plausible mechanism has been proposed. An effect of crystallographic phase on their photocatalytic activity was studied using degradation of bromophenol blue dye. The rate constants of the dye degradation reaction for anatase phase and mixed phase were found to be 6.86 x 10-3 /s and 1.56 x 10-2 /s respectively. A mixed phase of TiO2 showed faster (120 min for 84%) photodegradation compared to the anatase phase (270 min. for 84%) due to an effect of crystalline and electronic parameters. The cyclic voltammetry results depicted the reducing nature of i- TiO2than n-TiO2, which creates unfavorable situation for the electron transfer from TiO2 to dye.

Resumo em Inglês:

The degradation of AISI 304L stainless steel under static corrosion, liquid impingement and corrosion-erosion was studied using polarization curves. Static corrosion and liquid impingement tests were performed in 3.5% NaCl solution. Corrosion-erosion tests were performed in the same solution, containing 10 wt-% of three different SiO2 particle sizes. Synergism between erosion and corrosion was correlated to shifts in the polarization curves. The passive current densities increased and the pitting potential decreased for liquid impingement and with addition of SiO2 particles to the electrolyte. Increasing the particle size led to a greater increase in the current densities, although the pitting potential did not significantly changed. The effects of erosion on corrosion are discussed in terms of the passive film breakdown and reformation.

Resumo em Inglês:

In this paper, we report the synthesis of polystyrene end- capped with three- short- arm PDMS (PS-(PDMS)3) using poly(styrene – co–vinyltriethoxysilane) copolymers as precursors. These materials were obtained in a two-step process; first, two random copolymers of poly(St –co – VTES) having different molecular weight, and vinyltriethoxysilane content were prepared via free radical polymerization. The materials thus obtained, were treated with an excess of dimethyldimethoxysilane to produce PS-(PDMS)3 by co-condensation of alkoxysilane groups. The formation of the copolymers was confirmed by proton nuclear magnetic resonance, infrared spectroscopy, and gel permeation chromatography. Surface properties of films formed by casting the copolymers on a glass sheet were studied by Atomic force microscopy (AFM), and water contact angle measurements. We found that PS-(PDMS)3 copolymers exhibit a hydrophobic behavior, showing water contact angles close to values early reported for block copolymers composed by PS and PDMS segments, and comparable with the corresponding value of PDMS.

Resumo em Inglês:

Abstract Objectives: To evaluate the polymerization efficiency of bulk fill resin-based composites (RBCs) and how their composition, temperature and post-irradiation polymerization influence the results. Methods and Materials: Eight bulk fill RBCs were investigated. Five specimens for each material were prepared for Vickers hardness measurements. The measurements were performed in three depths from the top of the surface of the specimens (0, 2 or 4 mm) immediately and 24 h after polymerization and for the highly viscous bulk fill RBCs after preheating at 54oC. Statistical analysis was performed using one-way ANOVA and Tukey post hoc tests ata=0.05. Results: As the depth increases microhardness values reduce. The Vickers hardness measurements 24 h after photo-polymerization revealed higher values compared to those obtained immediately after photo-polymerization(p<0.05). There was an increase in microhardness of the RBC materials when preheated at 54oC in comparison with the room temperature specimens (p<0.05). Conclusions: Polymerization efficiency of bulk fill RBCs is affected by their composition and increases with temperature and post-irradiation polymerization.

Resumo em Inglês:

Using BaCO3, SrCO3 and TiO2, et al as crude materials, La2O3 as dopant, Ba0.8Sr0.2TiO3 (BST) Ceramics of perovskite structure were prepared by solid state reaction method. We investigated the effects of La2O3-doping and sintering temperature on the dielectric properties of BaSrTiO3 ceramics. The experiment results show that: The amount of La2O3 can increase the dielectric constant of the sample, with the doping amount increasing, the dielectric constant increases. The sintering temperature has also significant impact on the dielectric properties. The dielectric constant of the sample reaches its highest point at 1280 °C.

Resumo em Inglês:

Cerium oxide (CeO2) nanoparticles were prepared by the precipitation method. The average crystallite size of cerium oxide nanoparticles was calculated from the X-ray diffraction (XRD) pattern and found to be 11 nm. The FT-IR spectrum clearly indicated the strong presence of cerium oxide nanoparticles. Raman spectrum confirmed the cubic nature of the cerium oxide nanoparticles. The Scanning Electron Microscopy (SEM) analysis showed that the nanoparticles agglomerated forming spherical-shaped particles. The Transmission Electron Microscopic (TEM) analysis confirmed the prepared cerium oxide nanoparticles with the particle size being found to be 16 nm. The optical absorption spectrum showed a blue shift by the cerium oxide nanoparticles due to the quantum confinement effect. The dielectric properties of cerium oxide nanoparticles were studied for different frequencies at different temperatures. The dielectric constant and the dielectric loss of the cerium oxide nanoparticles decreased with increase in frequency. The AC electrical conductivity study revealed that the conduction depended on both the frequency and the temperature.

Resumo em Inglês:

Solid solutions alloys may have their annealing behavior affected by solute concentration. Mathematical models assume complex equations with parameters of hard and tedious assessment making empirical tests rather necessary. This work evaluated the residual iron content (from ~100 ppm to ~600 ppm) influence on annealing of a cartridge brass. Dilatometry results showed an anomaly expansion peak on the onset of recrystallization. However, at the end of the annealing process the samples underwent a contraction of 4.68-7.51x10-4, comparable with literature. The residual iron content had no influence on recrystallization behavior of the samples, although solute drag effect clearly slowed down grain growth at 600 ppm Fe concentration, especially when annealing happens up to 500ºC. The dilatometric variations between the samples and the anomaly expansion peak during recrystallization were considered as resulting from grain growth of recrystallized nanosized grains and/or from second phase transformations. New tests are proposed to elucidate the phenomena behind observations.

Resumo em Inglês:

In a recent paper, the present authors [Materials Research. 2015. 18(3): 595-601] demonstrated that the thickness of athermal martensite plates had a thermally activated component. The reason for this was probably the interaction of the athermal glissile martensite-austenite interface with dislocations located within the surrounding austenite. Based on this result, here we derive a new expression for the volume fraction against temperature for athermal martensite transformation. This new expression includes a thermal activated term. The expression obtained here gives good agreement with athermal martensite transformation in Fe-Ni-C and Fe-C alloys.