Resumo em Inglês:

Abstract Polymeric membrane separation technologies have gained widespread prominence in many applications, including water and wastewater treatment to remove contaminants of emerging concern (CEC). These technologies can be recognized as sustainable separation techniques due to their scalable potential and low energy consumption. However, the membranes are usually prepared with organic solvents such as N-methyl-2-pyrrolidone (NMP) and dimethylacetamide (DMAc), which are toxic and harmful to the environment and human health. Furthermore, these solvents are being banned in some countries and included on lists of substances of high concern. Therefore, finding environmentally sustainable solvents (green solvents) to produce “green membranes” has been a matter of great interest. The objective of the present study is the development of porous membranes, prepared with green solvents, Cyrene (Cyr) and γ-Valerolactone (GVL). The membranes were prepared by the phase inversion technique using Polysulfone (PSF), Polyvinylpyrrolidone (PVP) and Cyr or GVL or a mixture of both solvents. In this work, it was possible to produce membranes with both green solvents, as well as using a mixture of them. The membranes were characterized and tested for removing a CEC (Rosuvastatin) from water. Rosuvastatin rejection of 80% was achieved for membranes produced with a mixture of green solvents Cyr and GVL. These results are promising, as they make the membrane production process more sustainable as recommended by the 2030 Agenda through the 17 SDGs.

Resumo em Inglês:

Abstract New processing routes and alternatives have been studied in the manufacture of automotive parts aiming for lower energy consumption and less environmental impact. In this context, continuous cooling bainitic steels have emerged to address this demand by eliminating the quenching and tempering treatments. In substitution to heat treatments to improve wear resistance on the surface, plasma nitriding is a candidate. However, the effects on the core of bainitic microstructures over long time processes at subcritical temperatures are limited and should be further investigated. Especially in case of unexpected effects on the core of steels depending on time and temperature, compromising performance in service. The aim of the present study was to evaluate the effects of two plasma nitriding conditions at 500 ºC on the core of DIN 18MnCrSiMo6-4 continuous cooling bainitic steel, for 20 h and 30 h of treatment. For this purpose, characterization techniques, such as optical microscopy and SEM were applied to evaluate microstructural changes on the core followed by the Vickers hardness test to estimate possible softening effects. The research found a decrease of austenite fraction in the nitride conditions in comparison to the initial microstructure of the bainitic steel, a reduction of dislocation density of ferrite measured by Williamson–Smallman relation and the hardness dropped about 10% after 20 h and 20% after 30 h of treatment. The conclusion pointed out alteration on the core for the plasma nitriding treatments for long time cycles at a temperature of 500 °C, similarly to effects observed in tempering treatments.

Resumo em Inglês:

Abstract Ductile iron is typically used in as-cast conditions. However, a typical heat treatment applied to ductile iron is austempering, which allows for increased tensile strength with good levels of elongation and toughness. The traditional means of austempering involves molten salt baths, but these baths have environmental and operational restrictions. Laboratory-level studies have found the feasibility of using heated air for cooling and holding during austempering. Due to the lower cooling severity of heated air, it is necessary to increase the austemperability of ductile iron. Elements that contribute to austemperability are manganese, copper, molybdenum, and nickel. This study used numerical, thermodynamics, and kinetics simulation to develop a suitable ductile iron alloy for obtaining ADI in a standard ASTM test specimen using heated air for cooling. According to the numerical simulation results, the average cooling rate between 900°C and 500°C in the critical region for air velocities of 5 m/s and 10 m/s at a temperature of 280°C ranged from 75°C/min to 82°C/min. Through thermodynamic and kinetic simulation, nickel has the most significant capacity to alter the austemperability of ductile iron. Based on these results, six ductile iron alloys with nickel contents ranging from 0.2 to 2% were developed. The experimental cooling rate is approximately 70°C/min, with the 3.41C, 2.72Si, 1.01Cu, 0.31Mn, 0.18Mo, and 1.13Ni alloy suitable for obtaining ADI.

Resumo em Inglês:

Abstract Resistance spot welding (RSW) processes are applied across a diverse range of manufacturing processes in industry with the objective of permanently joining two metal parts. RSW occurs due to heat generated on focal points by the resistance that an electric current flow (AC or DC) encounters when passing through metallics pieces pressed against each other by electrodes. This study is based on a design of experiments (DOE), focused on the manufacture of aluminum electrolytic capacitors, and seeks to characterize the influence of RSW parameters (electrical current density, weld time and electrodes pressure) on the tensile strength of the weld joint formed between aluminum alloy AW3003 and a low carbon steel sheet coated with copper and tin by electrodeposition. The DOE consists of a sweep on the electrical current between 12kA and 20kA, weld times 8ms and 12ms and pressures 0.3Mpa and 0.4Mpa. The welding interface of the specimens was also analyzed by SEM and EDS, revealing different types of morphologies. The results obtained highlighted the electrical current as the main influence factor on the tensile strength, also enabling the identification of different types of morphology on welding interface. The observed tensile strength results for the studied parameters ranged from 376N to 1095N (average), and an optimized combination of parameters based on a statistical analysis in Minitab software is suggested at 18kA, 12ms and 0.3Mpa.

Resumo em Inglês:

Abstract This study aims to enhance the mechanical properties of the hypoeutectic Zn-Al-Cu alloys, known for their low melting point and good machinability but limited by low tensile strength and brittle fracture behavior. The present research investigates the effect of TiB2 additions in concentrations of 0.2, 0.5, 0.8, and 1.1 wt.% on a Zn-Al4-Cu1 alloy to improve these properties. The alloys were produced by gravity casting into a cast iron mold, and their mechanical properties were analyzed. Additionally, the effects of the cooling rate on the microstructure and secondary dendritic spacing (λ2) were analyzed using a stepped mold with different cooling modules. The additions of TiB2 modified the morphology of the primary η-Zn phase and the eutectic constituents (α+η). The optimal mechanical properties were obtained in the Zn-Al4-Cu1 alloy with 0.8% TiB2. Furthermore, increased cooling rates reduced the λ2 in the primary η-Zn phase from 21.4 μm to 11.3 μm. These findings show a manner to enhance the overall properties of Hypoeutectic Zn-Al alloys.

Resumo em Inglês:

Abstract The addition of nanoparticles to coatings is a widely employed strategy to enhance resin properties without compromising performance. Copper oxides are commonly used as additives in formulations, replacing organometallics, which are prohibited due to their biocidal and antifouling activities. This study focuses on synthesizing copper (II) oxide nanoparticles through co-precipitation for application in antimicrobial coatings. The synthesis process involved co-precipitation using copper sulphate (CuSO4.5H2O) as a precursor and NaOH as an alkaline agent. Characterization of the obtained nanoparticles was performed using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA). These analyses confirmed the formation of CuO nanorods with an average size of approximately 73 nm in length and 16 nm in width. Antimicrobial testing was conducted against Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, and Bacillus cereus. The results revealed noteworthy antimicrobial activity, particularly against Staphylococcus aureus and Bacillus cereus. Consequently, the findings suggest that copper (II) oxide nanoparticles have the potential to serve as additives, enhancing the biocidal properties of resins as coatings and other applications.

Resumo em Inglês:

Abstract In the northern region of Brazil, enormous amethyst quartz waste is generated in mining, currently with no final destination, being stored without commercial value. However, it can be used to produce artificial aggregates, aiming to provide a solution to the storage problem of this material. To reduce the waste, crushing and grinding were used, investigating the factors influencing comminution, such as mineralogical properties and size settings, filling, speed and grinding time. Fragmentation was carried out on a laboratory-scale using a jaw crusher and ball mill. The factors in crushing depend on the gap and set, constants, while in grinding, with constant critical speed, the filling factor, the balls:sample ratio and grinding times were considered variables. The fineness modulus for fine aggregates was used. Based on the particle size distribution of crushing and grinding products, the production of coarse particles in crushing is the highest (75%), being considered as coarse aggregates, while the production of fine particles in grinding is lower (25%) and is considered as fine aggregates. The banded quartzite influences the comminution, more favorable to produce a coarse aggregate. The distribution of particle size shows that within the coarse aggregates, 40% corresponds to G1 gravel. Crushing is determined by the size settings and grinding by the grinding time. For longer grinding times, there is a greater reduction in grain sizes, and for shorter times, the reduction is smaller. The waste could be fed into comminution to produce coarse and fine aggregates for civil construction, achieving a long-term sustainable supply of aggregates in the required quantities.

Resumo em Inglês:

Abstract Recycling LFP-type lithium-ion batteries is essential for recovering valuable metals such as lithium. The efficient extraction of this material contributes not only to the conservation of limited natural resources, but also to reducing dependence on mining. In addition, proper recycling minimizes the risks of releasing toxic substances into the environment, promoting more sustainable practices in the automotive industry. Exploring advanced recycling technologies is crucial to optimizing the process and increasing efficiency in material recovery. Methods such as pyrometallurgy and hydrometallurgy have the potential to obtain high yields in the recovery of precious metals, contributing to the economic viability of recycling automotive batteries. In this study, the effect of a hydrometallurgical process on the recovery of lithium salts from spent LiFePO4 batteries was studied, using an aqueous solution of nitric acid as the medium. Around 99.23% of Fe and 84.18% of Li were recovered as FeOH and Li3PO4. According to the proposed mechanism, the LiFePO4 cathode powder was more easily destroyed and transformed into disordered states at concentrations with a 10% stoichiometric excess, leading to a significant increase in leaching and efficiency in lithium concentration.

Resumo em Inglês:

Abstract The extraction of sand from riverbeds through dredging is a common practice in construction and has given rise to significant environmental repercussions. Sand removal contributes to heightened turbidity and alterations in watercourses, reshaping the original channels due to equipment utilization, and disrupting their flow. In response to these challenges, crushed stone dust emerges as a sustainable alternative material for partially or entirely replacing natural sand in concrete production. This study aimed to evaluate the mechanical properties and workability of concrete with a characteristic compressive strength of 25 MPa, employing total replacement (100% crushed stone dust) and partial replacement (50% crushed stone dust and 50% sand). The materials utilized encompassed crushed stone, natural sand, Portland cement CP II F - 32, crushed stone dust, and a superplasticizer additive. The results indicated no significant difference in compressive strength (P < 0.05), with values of 36.85 MPa and 30.31 MPa for total and partial replacement, respectively, comparable to the reference concrete (33.47 MPa). In terms of tensile strength by split tensile testing, concrete with total and partial replacement achieved 3.09 MPa and 3.23 MPa, respectively, while the reference mix recorded 3.31 MPa. Total replacement posed challenges to the workability of fresh concrete, necessitating a higher dosage of superplasticizer. In conclusion, crushed stone dust demonstrates its capacity to substitute natural sand, either entirely or partially, while upholding mechanical properties comparable to traditional concrete. However, careful consideration of the impact on concrete workability is essential when opting for total replacement of the fine aggregate.