Ciência & Tecnologia dos Materiais最新文献

This research presents two type of cactus (Opuntia ficus-indica) (natural cactus (NC) and dried cactus (DC)) as a biological adsorbent, evaluated for the effectiveness of hexavalent chromium Cr(VI) removal from artificially contaminated aqueous solutions. The characterization of the biosorbents were made using different techniques such as X-ray Fluorescence (XRF), Fourier transform infrared (FTIR) and Scanning Electron Microscope (SEM) to better understand the adsorption mechanism-property relationship. Adsorption kinetics showed that the adsorption behavior followed the pseudo-second-order kinetic model. The adsorption isotherms fitted by the Langmuir model showed that the highest Cr(VI) adsorption capacities using natural cactus and dried cactus are 21.19 and 2.63 mg/g respectively. Additionally, various physiochemical parameters such as contact time, adsorbent dosage, pH and temperature were investigated in a batch-adsorption technique. The results illustrated that the cactus have significant potential as economic, safe and effective adsorbent materials for the Cr(VI) adsorption from the aqueous solution.

The aim of this work was the development (design, construction and tests) of a Three-phase Synchronous Machine with permanent magnets and four poles to be used in small wind turbines, where the rotor and stator cores, usually constructed from laminated steel sheets, were replaced for massive blocks obtained from the Powder Metallurgy (PM) process. The other parts of the machine, such as housing, shaft, bearings and covers, were obtained from conventional three-phase induction motor of 10 HP. Initially, it was studied sintered alloys from pure iron, Fe-Si, Fe-P and Fe-Ni; eventually these alloys were analyzed in terms of magnetic and mechanical properties as well as electrical resistivity. From this study, it was chosen the use of sintered pure iron for the construction of the rotor and Fe1%P for the construction of the stator. The permanent magnets used were Nd-Fe-B, and the windings calculation was based on the coiling of the three-phase induction motor. According to the tests performed, it was observed the generation of a three-phase sinusoidal wave voltage of 242 VRMS, and the yield of 40.8%.

Recent interest by automotive manufacturing company is to develop a component, capable of enhancing safety features associated with lightweight materials such as using aluminum and composites. The use of aluminum metal matrix composites (MMC) and composite materials improve the performance of an automotive crash box due to their lightweight. Automotive crash box is a component, equipped at the front end of a car, and is one of the most important devices for crash energy absorption. The review is mainly divided by two topics, i.e. design of geometry profiles and the crash box material advancements, both geometry and material properties would influence the efficiency of kinetic energy absorption during collision. This review benefits both academics and corporate sector as it outlines major lines of research in the crash box design. It discusses the results from 3D simulations up to laboratory experiments of crash box specimen and the effect of material selection to the characteristic of crash box device. The information from this paper should stimulate more research and more crash box design solutions to reduce fatal damage during collision in automotive industry.

Taking the joint advantages of the thermal insulation capacity of polyurethane foams (PU) and the thermal energy storage capacity of phase change materials (PCMs), it is possible to produce PU composite foams that can be incorporated as a functional layer into buildings components, designed as latent heat thermal energy storage systems (LHTES), that improve the thermal comfort and the energy consumption of buildings. In this work, PU composite foams containing microencapsulated PCMs (mPCMs) were produced by polyol synthesis. The major aim of the present study was to improve the thermal characteristics of PU foams, by incorporating PCMs, taking advantage of their thermal energy storage capacity. The thermal and energy storage properties were evaluated for three different PU composite foams (hard foam without and with melamine and expandable graphite) with the addition of different percentage of mPCMs. The comparative characterization of the energy storage properties of the PU composite foam formulations is measured using a dynamic scan calorimeter and the thermal conductivity using the transient plane heat source method. The addition of flame retardants to the PU foam slightly influenced the latent heat storage capacity of the PU foam with mPCMs and the addition of mPCMs increases the final thermal conductivity.

The present paper reports the precipitation process of Al₃Sc structures in an aluminum scandium alloy, which has been simulated with a synchronous parallel kinetic Monte Carlo (spkMC) algorithm. The spkMC implementation is based on the vacancy diffusion mechanism. To filter the raw data generated by the spkMC simulations, the density-based clustering with noise (DBSCAN) method has been employed. spkMC and DBSCAN algorithms were implemented in the C language and using MPI library. The simulations were conducted in the SeARCH cluster located at the University of Minho. The Al₃Sc precipitation was successfully simulated at the atomistic scale with spkMC. DBSCAN proved to be a valuable aid to identify the precipitates by performing a cluster analysis of the simulation results. The achieved simulations results are in good agreement with those reported in the literature under sequential kinetic Monte Carlo simulations (kMC). The parallel implementation of kMC has provided a 4x speedup over the sequential version.

Duplex stainless steel presents an attractive combination of mechanical properties and resistance to corrosion. These properties rely on a two-phase mixture compound to produce a microstructure that is approximately equal for the ferritic and austenitic phases. The samples used in this study were cold rolled to degrees of deformation of 20%, 40%, 60% and 80% according to their thickness. The vibrating sample magnetometer (VSM), X-ray diffraction (XRD), and optical microscopy were used to characterize the rolled samples. It was observed that the cold rolled samples of 40%, 60% and 80% showed an increase in saturation magnetization compared to the samples of as received and cold rolled of 20%, and this probably occurred because of the formation of strain-induced martensite. It can be seen that the amount of the ferromagnetic phase calculated by ferritoscope tends to decrease with an increasing degree of deformation. The deformation caused by cold rolling resulted in a significant change in diffraction peaks and the mechanical and magnetic properties.

In this survey the untraditional practical applications of cork is presented. High-quality goods with improved performances have been developed by those who came up with creative ideas and develop them. From several types of industries to private entrepreneurs, cork has been calling the attention of many creative minds over the last decade. From surfboards or designer clothes to an outstanding work of art made from cork has proved that this natural material becomes a noble feedstock not only for those who appreciate a good beverage and high-performance materials but also for those who look for sustainable products from natural sources. A general overview of cork composition, origin, and industry is also briefly disclosed.