Science and Technology of Materials最新文献

The proposed work aims to functionalize leathers for footwear industry with antimicrobial properties based on Ag–TiO₂ nanoparticles. The synthesis of nanoparticles was carried out by the hydrothermal method with significant advantages in terms of time, energy savings and low cost. Anatase TiO₂ nanoparticles with dimensions below 10 nm were obtained as observed by X-ray diffraction and transmission electron microscopy. Fourier transform infrared spectroscopy showed that the based structure of leather was not modified by the addition of the nanoparticles. The antimicrobial activity was evaluated and it was observed that Ag containing leathers gained antimicrobial activity. In addition, the nanoparticles were found to be non-cytotoxic. This achievement, by itself, should be quite appealing to the footwear industry as it could consist in a solid value-preposition given the commonness of fungal infections promoted by humidity, poor breathability and temperature that promote the expansion of the microflora of the skin.

The fast pyrolysis bio-oil is a promising product to be used as fuel. It is produced by means of wood particles subjected to high heat rates for very little time. However, the resulting oil has a very high oxygen content, which to be used as fuel requires upgrading processes, which makes its costs higher than mineral oil. The aim of this paper is to study the fast pyrolysis bio-oil as a precursor of carbon fibers. A heat treatment in the bio-oil was used until the optimum softening point temperature was reached for the subsequent melt spinning process. Additives such as kraft lignin and furfuryl alcohol improved the spinning process and caused the fibers to resist the carbonization step. Characterization by Fourier-transformed infrared, ¹³C VACP-MAS NRM and Raman revealed that the heat-treated bio-oil presented a great amount of oxygenated groups and that mainly the aromatization of the samples was verified after the carbonization process. SEM images showed that the fibers diameters were too high.

The knowledge of the characteristics and behavior of the composite material is of great importance, bearing in mind of its wide application besides serving as a parameter for identification of possible problems caused by material degradation, avoiding that greater damages could irreversibly damage the composite. In this way, the present work makes an analysis of the mechanisms of failure of the polymeric composite PMMA (polymethylmethacrylate) reinforced with fiberglass. And, using experimental data obtained in the laboratory and simulating the behavior of the material in the software Abaqus through the implementation of the tool XFEM (Xtended Finite Elements Mode) in Loading Mode I, which analyzes fissures generated by fields of discontinuities without the need to constantly update the mesh, allowing to observe the critical stresses acting on the fiber/matrix interface.

In this paper, two kind of polyethylene terephthalate fibers and two woven textiles, taken from endovascular Stent-Grafts were analyzed by tensile tests. A non-contact video extensometer was used, which allowed precise strain measurements on material test samples. The technique used, allied with yarns image analysis, allowed to determine the yarn and textile stresses and to study their elastic/plastic deformation with much more accurate properties measurements. It was observed that the textiles present an anisotropic behavior although the textiles present similar weaving in the two woven directions. The yarns specimens were also analyzed by differential scanning calorimetry in order to study their crystallinity ratio, when subject to different stress levels. The properties measured are important for future performance analyses by finite element modeling and for defining improvements in devices design.

Advances in computational tools for welding process simulation have been noteworthy, allowing to assess complex phenomena, as is the case of welding distortion and residual stress. The most advanced tools take into account the thermo-metallurgical and thermo-mechanical changes that take place during the welding processes. Considering these changes and the materials properties at the different temperature values, it is possible to obtain reliable models of the welding processes. In this communication, T-joint welded configurations are investigated, considering arc welding and laser beam welding processes. For this purpose, the commercial software ESI SYSWELD was adopted, since it is one of the most advanced tools for this purpose. These models are based on finite elements; therefore, a mesh sensitivity analysis was performed in order to evaluate the minimum element size required for accurate results. In arc welded double side T-joint, different procedures were explored in order to understand the influence in the residual stress; the second pass does not increase the maximum residual stress, however it increases the area with tensile residual stress. Results for a T-joint between a steel tube and a steel plate using laser beam welding (LBW) and arc welding were obtained. The laser beam welds presented a significant reduction of the heated affected zone and, consequently, the tensile residual stresses are confined to a smaller area.

The extraction of the phosphate ore produces a high amount of waste causing serious environmental problems. This waste, termed as phosphate washing waste, was filtered and dried at 105 °C for 24 h to remove the water. The dried waste was milled and then sieved in a 100 μm sieve. The resulting phosphates washing waste (PWW) particles size are below 70 μm. The phosphate washing waste was calcined at 700 °C and 900 °C. Both calcined and uncalcined waste were investigated with X-ray fluorescence (XRF), X-ray powder diffraction (DRX), Fourier transform infrared (FTIR), simultaneous differential thermal and thermogravimetric analyses (DTA-TG) and particle size analysis. This waste was activated with sodium hydroxide (NaOH) and sodium silicate in order to produce geopolymeric materials. The influence of replacing PWW by 15% of metakaolin was also study. The results show that the highest compressive strength is obtained with metakaolin. The results also showed that compressive strength decreased with the increase of NaOH concentration.

Welding processes are generally used in almost every industrial segment, but there are some applications that demand special attention to the product obtained, due to the security it must offer against possible failures.

In the present study, the influence of the heat input variation on the weld bead geometry, the austenitic grain size in the HAZ, the microhardness in the HAZ (heat affect zone), and the δ ferrite volumetric fraction using the gas metal arc welding (GMAW) performed with pulsed chain spray transfer, on AISI316L steel plates. The samples had their microstructure characterized by optical microscopy, in their different regions, performing a comparative study of these regions for the different welding conditions. From the variations in the thermal contributions it was demonstrated that the choice of the ideal heat input for a given process has an important effect on the phenomena that occur during welding. The increase of the contribution caused a variation of almost 300% in the austenitic grain size, approximately 100% in the δ ferrite volumetric fraction, and about 240% in the area of the fusion zone (FZ). The temperature distributions of the plates were recorded using a thermal camera in order to monitor the maximum temperatures in each region of the welded joint, the microstructures resulting from the process were later compared with the results of the thermal cycles obtained through numerical simulations. The results showed good agreement and also contributed to the validation of the proposed numerical method, which allowed a better understanding of the thermal history during welding and, consequently, of their effects on the microstructural transformations developed in the AISI 316L steel.

In this article, several solar energy application possibilities in forestry and industrial processes are foreseen and discussed, focused on the case of cork harvesting and processing, in world areas where solar radiation is high. Cork processing to obtain several cork-based products has several and different operational steps in which electricity, heat and thermal fluids are necessary. Different types of existing solar technologies are considered, for the specific forestry and industrial steps of cork transformation. Most of these technologies are not yet being used in the cork sector. Besides this, the use of different cork derived products in several solar energy technologies and applications is also assessed and discussed. Cork is a sector where solar energy may be used in various ways and cork material could be a component in various solar energy systems/devices, increasing its domain of applications.

Carbon nanotubes (CNT) have been extensively studied, and special attention has been given to their introduction in epoxy matrices, for further reinforcement of carbon fibre reinforced composites. However, the obtained improvements are highly dependent on the level of CNT dispersion and distribution. In this work, we report the use of block copolymers (BCPs) as a solution to provide enhanced compatibility of the CNT in an epoxy-based matrix and as means to provide them further nanostructuration. Studied BCPs were especially formulated for epoxy matrices, being one of them customised to also have strong compatibility for CNT. BCPs were added to CNT without introduction of additional solvents. Different formulations were studied and the CNT dispersion, distribution and interaction with matrix were evaluated by rheology, electron microscopy and dynamic mechanical analysis. The results suggest that the customised BCP can have a significant improvement in the dispersion of the CNT, on the adhesion between the polymeric matrix and the CNT and can provide a mean for nanostructuration.

Valorization of waste plastic as concrete aggregates has become an opportunity. Some advantages are plastic waste recycling, consumption reduction of natural aggregates and improvement of concrete properties. This paper presents a review on addition of recycled plastic waste to cement composites and influence on their properties. Forty five international papers were selected from scientific peer-reviewed journals. The critical items analyzed were: plastic characteristics, mix proportion design and concrete properties. The last item includes fresh and hardened concrete properties, durability performance and thermal conductivity. Although some properties were negatively influenced by the plastics, this paper focuses on the variables that mitigate these effects. The improvement of insulation properties with plastic is widely analyzed, but further research is recommended. As conclusion, application of plastic waste would be useful on both, technical and environmental dimensions and this paper could be used as a helpful tool for studying and designing mortars and concrete composites with recycled plastic.