With the growth of the 3D printing industry, there are concerns regarding the PLA residues from the manufacturer and the temporary use of the material. To address these concerns, this work presented a sustainable approach to recycling polylactic acid (PLA) residues from 3D printing by incorporating graphene as a reinforcement material. Aiming to simulate a mixed material scenario, the residue is generated by processing on a Creality Ender 3 printer, heated to 200 °C at a speed of 25 mm/s. Then, PLA residues were ground and mixed using a co-rotating twin-screw extruder at 190 ºC with 0.18% by weight of graphene. In general, graphene was incorporated, resulting in a homogeneous distribution that does not contribute to increasing the tensile strength compared to recycled PLA; however, it is higher than that of the original PLA filament. Regarding the thermal properties, the reprocessed material retains its original thermal stability, with a slight decrease in the degradation temperature. The recycled PLA exhibited a crystallinity of 20.3%, which was higher than that of the original PLA filaments and recycled PLA with graphene (3.4%). In conclusion, PLA residues from 3D printing can be recycled to obtain PLA nanocomposites without compromising the mechanical and thermal properties.

One of the solutions to flooding problems, especially in large cities, is the use of permeable pavements that can be produced using mineral waste, reducing costs and environmental impacts, and generating a circular economy. In this study, wastes from the exploitation and processing of kaolin, scheelite, and granite were used to produce ceramic permeable pavements. After characterization, the mineral wastes were mixed with a commercial red clay with samples uniaxially pressed (20 MPa) and sintered at 1050, 1100 and 1150 °C, with a heating rate of 5 °C/min. The formulations of kaolin processing residues sintered at 1050 °C and scheelite processing residues sintered at 1100 °C stand out with the highest porosity (close to 40%), high permeability (up to 7.42×10−4 m/s) and flexural strength ranging from 2.45 to 4MPa. These results emphasize the role of formulation parameters, highlighting the potential of ceramic permeable pavements as a high-performance, cost-effective, and sustainable solution.

The transition from upper-to-lower bainite in carbon steels is a complex process yet not fully explored. This study examines such transition in a 0.7C, 0.74Mn, 0.61Si, 0.2Cr (wt%) low-alloy steel using a comprehensive approach that integrates dilatometry, scanning electron microscopy (SEM), ex-situ HEXRD, and microhardness testing. Microhardness and dislocation density were found strongly coupled, both increasing with decreasing austempering temperature and presenting changing trends at approximately 350°C and 300°C. Likewise, an Arrhenius plot derived from the curves of transformed fraction as a function of austempering temperature presented the same behaviour. These turning points are considered, respectively, the onset and the end of the transitional interval between upper and lower bainite. Furthermore, SEM analyses confirmed a progressive change in morphology, from coarse upper bainite at high temperatures (400°C), to a mixture of upper and lower bainite in the transitional range, and finally to exclusively fine lower bainite at low temperatures (275°C). The results support that the upper-to-lower bainite transition is not a discrete step but a continuum and offer insights into the interplay between bainite morphology, overall transformation kinetics, and microhardness, which are critical for optimizing heat treatments routes.

Over the last decades, high-entropy refractory alloys with shape memory (SM) effect have been increasingly studied. However, identifying the optimal composition among the vast array of potential systems remains a significant challenge for the scientific community. In this work, Ni-Ti alloys are studied via molecular dynamics simulations to determine the range of martensitic phase transformations, with the goal of developing in the future medium- (MEA) and high-entropy alloys (HEA) that exhibit SM behavior. Virtual samples with compositions of Ni(100-x)Tix (45 < x < 55) were created using the LAMMPS software, in a system consisting of 2000 atoms that interacted under the modified embedded atom method (MEAM) interatomic potential. In addition, simulations were also performed on systems with sizes of 4000 and 8000 atoms to assess the effect of system size on the phase transformation behavior. The structural evolution and phase transformations were analyzed by applying heating and cooling rates of 1 K/ps, controlled by the isothermal-isobaric (NPT) ensemble. The compositional range, in atom percent, for martensitic transformations was found to be 47.5 to 52.5% nickel. Martensitic transformations are complex, showing either direct or two-step transformations. At lower temperatures, the phases R and B19’ can be formed as a function of Ni content. In several cases, at intermediate temperatures, the Ni4Ti3 compound forms and influences the phase transformation process. Also, the larger the system size, the lower the phases transformation temperatures.

First-principles calculations based on the density functional theory (DFT) represent a sophisticated technique to investigate the mechanical strength of materials in general, although underexplored in polymeric structures such as high-performance thermoplastic polymers. In this study, DFT calculations were systematically conducted to evaluate the effects of strain on the structure of polyether ether ketone, determining the maximum elasticity modulus in a perfect alignment condition of the polymer chain. The atom positions and arrangement of the polymer chains were set based on total energy and force minimizations. The four lowest energy structures were stretched up to 10 Å per monomer, and the results have shown a mean elasticity modulus of 5.93±0.74 GPa, which we attribute to the upper limit for aligned and stretched polymeric chains.

The Monel 400 alloy, composed primarily of nickel and copper, offers excellent corrosion resistance but exhibits relatively low wear resistance, limiting its durability in demanding applications such as maritime industries, pumps, and valves. To address this, boriding thermochemical treatment was applied to enhance the surface hardness and wear resistance of the alloy. The process used a boriding powder containing 90% B4C and 10% KBF4 at 900 °C for 4 hours, avoiding silicon activators to prevent the formation of less hard nickel silicides. The resulting boride layer, predominantly Ni2B, Ni3B, and Ni4B3, was characterized using X-ray diffraction (XRD) and evaluated for adhesion via Rockwell C indentation (VDI 3198 standard). Wear performance was assessed through pin-on-disk tests on treated and untreated samples, analyzing wear rates, removed volume, and surface roughness using profilometry, confocal microscopy, and SEM. The borided layer achieved a hardness of up to 1600 HV0,01, demonstrating significantly improved wear resistance while maintaining strong adhesion to the substrate. This study highlights the potential of boriding as an effective treatment to extend the service life of Monel 400 in abrasive environments.

This study evaluates the feasibility of modifying thermoplastic starch using citric acid through extrusion processing. The samples were characterized by FTIR, TGA, XRD, and tensile testing. In the FTIR analysis, carbonyl group formation was observed, indicating esterification between the starch hydroxyl groups and the carboxyl groups of the acid. TGA provided data on the thermal events in the materials. In the tensile test, Young's modulus increased while elongation at break decreased, making the modified starches more rigid and less ductile. XRD analysis revealed structural changes due to the increased acid concentration and the presence of plasticizer. Esterification was effective at citric acid concentrations of 1.0 to 2.5–3.0 wt%, but difficulties in processing and controlling process parameters were noted, as highlighted in previous studies. These results demonstrate the viability of starch modification, although challenges remain in controlling production and achieving the desired characteristics.

This study investigates the microstructure and corrosion behavior of WC-NiSi cemented carbide produced by conventional powder metallurgy, with comparative analysis against traditional WC-Co cemented carbide. Microstructural characterization was carried out using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD) before and after corrosion testing. Electrochemical performance was evaluated in a 3.5 wt.% NaCl solution through open-circuit potential (OCP) measurements, linear potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS). The WC-NiSi cemented carbide exhibited a microstructure similar to WC-Co, although with a slightly higher porosity and increased presence of binder islands. Electrochemical assessments revealed that the cemented carbide with NiSi binder demonstrated more noble corrosion potentials, reduced current density, and higher overall impedance compared to its Co binder counterpart, indicating enhanced corrosion resistance.

Corrosion of reinforcing bars in reinforced concrete significantly compromises the durability of structures. In aggressive environments, measures such as galvanization are common, but surface treatments with zinc chromate (Cr6+), a carcinogenic compound, demand safer alternatives. Organic acids, especially oxalic acid, have shown promise in acidic environments, but their efficacy under alkaline conditions is uncertain. This study evaluates the zinc oxalate conversion coating on galvanized steel exposed to corrosive environments with varied pH. Galvanized sheets were treated with oxalic acid [0.1 m] and exposed to alkaline solutions (pH 13) and slightly acidic nacl solutions (ph 6.5). Corrosion resistance tests and analyses of phase formation (XRD) and morphology (SEM) were conducted. Results showed that the zinc oxalate film acts as a physical barrier in acidic conditions but dissolves in alkaline environments, demonstrating ineffectiveness. In NaCl solution, treatment with oxalic acid promotes the formation of a zinc oxalate layer, which accelerates the formation of corrosion products and improves resistance to corrosive attack. In contrast, treatment with an alkaline solution results in a less effective passivation layer, offering limited protective effects and leading to a higher corrosion rate over time.

This study characterized wastes from scheelite and columbite-tantalite mining, as well as kaolin processing, to produce microfiltration membranes for wastewater treatment using a fast-sintered process. After characterization, the wastes were mixed with clays, pressed, and sintered at low temperatures of 1050 and 1100 °C. The resulting membranes exhibited pore size distributions ranging from 3 μm to 180 μm and flexural strengths exceeding 14 MPa. In a crossflow filtration system, permeate fluxes ranged from 177 L/h.m2 to 228 L/h.m2 at 2 bar, with permeabilities from 99 to 130 L/h.m2 bar depending on the waste content. Membranes with smaller pore sizes effectively removed 90% to 96% of turbidity from a water/clay suspension containing micrometric clay particles. This approach demonstrates that rapid sintering of ceramic membranes from mining waste can effectively reduce environmental impacts and energy costs, providing a sustainable solution for wastewater treatment.