Resumo em Inglês:

In this work, it is reported a comparison between solid microspheres produced from glass having conventional industrial sand (IS) and glasses made with rice husk ashes (RHA) as a source of silica. The same composition was used to fabricate both glasses. The focused was the production of glass microspheres for road horizontal marking, which would attend the type classification called Premix. The microspheres were obtained by the horizontal flame method. The results showed that characteristics such as production yield, morphology, granulometry and, mainly, retroreflectivity measurements are not altered when rice husk ash is present in the glass composition, showing that this can be a sustainable alternative material for this important application.

Resumo em Inglês:

This paper aims to explore the production of porous Nb2O5 pellets by pressing and adding anaerobic biomass (sludge) in order to evaluate the microstructure porosity. The thermal treatment temperature of the pellets varied between 300 ºC and 900 ºC. Their structural, morphological, and physical properties were measured, and the adsorption potential of Mn2+ and their reuse were evaluated. All samples had a monoclinic phase. Density average values of samples pressed using sludge ranged between 2.45 and 2.52 g.cm-3, while the one obtained without sludge pressing achieved higher values of around 2.72 g.cm-3. All samples presented high porosity values after the heat treatment (above 40%), which confirms the efficiency of sludge as a means to enhance porosity. These pellets were used for Mn2+ ions adsorption in aqueous medium. The Langmuir isotherm model was the one that achieved the best goodness-of-fit. In kinetic studies, the adsorption reaction was in accordance with second-order kinetics. Adsorbents in the form of pellets are environmentally friendly on account of their significant reuse and recycling potential. However, the particulate matter might become an environmental liability and incur high treatment costs. The samples proved to be reusable, promoting the adsorption of 67% of the Mn2+ after the fifth reuse cycle.

Resumo em Inglês:

Developing biomaterials for tissue regeneration is a promising alternative for the recovery of various tissues, including bone. Atorvastatin (ATV) has a series of beneficial effects which includes bone anabolism, vasodilating, and anti-inflammatory actions. The main objective of this work was to produce and characterize polycaprolactone (PCL) matrices incorporated with ATV. Samples were prepared by the solvent casting technique. Scanning electron microscopy (SEM), X-Ray diffraction (XRD), Fourier transform infrared spectrometry (FTIR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and in vitro release studies were performed. FTIR analysis showed that no chemical bonds were formed between PCL and ATV. SEM analysis showed that the amount of ATV affects sample morphology. According to XRD and thermal analysis, the main ATV characteristics were maintained. The studies showed that PCL/ATV samples release the drug in a prolonged way since its release reaches around 50% after 15000 minutes of analysis and the model that showed the best fit for the studied matrices was the Higuchi model, with a correlation coefficient above 0.95.

Resumo em Inglês:

Hydrogels are polymeric matrices having minimal toxicity, elastomeric consistency and high permeability, making them useful for the controlled release of actives. These products have extensive applications in the cosmetic area as drug vehicles. In this work, hydrogels were prepared with concentrations of Polyvinylpyrrolidone (PVP, 7.5%wt), Polyethylene glycol (P.E.G., 3%wt) and agar (1%wt) containing pseudoboehmite, mandelic acid with essential oil of Palmarosa, Lavender, Geranium and/or Lemongrass, subjected to 25 kGy radiation. The hydrogels were characterized using sensory analysis, isothermal dehydration with air entrainment and dehydration as a function of time. The results showed that the hydrogels containing different essential oils undergo dehydration as a function of time from 2% to 4%. The hydrogel containing Lavender essential oil showed 23% isothermal dehydration with air entrainment. As for the degree of satisfaction, the hydrogel with Lemongrass essential oil was the most suitable for the consumer market. Therefore, it is concluded that these analyses are relevant for cosmetic development.

Resumo em Inglês:

The objective of this work is to study the possibility of obtaining dense parts using water atomized AISI 316L steel powder in the L-PBF process. Despite its irregular, non-spherical, particle morphology, it has a significantly lower cost. 25 samples were produced varying the laser power and the scanning speeds to determine the optimal processing conditions. Additionally, hot isostatic pressing (HIP) was performed after the L-PBF process to further increase densification. Selected samples were subjected to microstructural characterization. The best densification results obtained were for the sample produced with the laser power of 173 W and scanning speed of 600 mm/s, where densifications close to 98% were obtained. HIP post-processing promoted increased densification of samples with closed porosity, allowing samples with densification above 95% to reach values close to 100%. HIP did not promote the closure of open pores. The results indicate that the use of water atomized AISI 316L in the L-PBF process combined with post-processing by HIP can produce dense engineering components and at the same time reduce the production costs of the manufactured components, mainly because it is a lower cost raw material when compared to the commonly used feedstock obtained by gas atomization.

Resumo em Inglês:

The use of conducting polymers as coating layers for the protection of surfaces against corrosion represents an important topic for investigation, as reported in the literature. In this work, polypyrrole/Fe3O4 nanoparticles (Fe3O4_NPs/PPy) hybrid nanocomposites (HN) were incorporated as anticorrosive additives in an epoxy paint to protect SAE 1010 carbon steel from corrosion. The HN particles were obtained by chemical polymerization of pyrrole in an aqueous solution in the presence of Fe3O4_NPs and were characterized by infrared absorption spectrophotometry, dynamic light scattering (DLS), X-ray diffraction (XRD), transmission electron microscopy (TEM). The electrochemical impedance spectroscopy (EIS) was used in the analysis of the electrochemical response of the coated surface with and without HN. DLS data showed that the Fe3O4_NPs and Fe3O4_NPs/PPy obtained in solution present average diameters of (19.7 ± 9.6) nm and (63.5 ± 27.7) nm, respectively. TEM images showed Fe3O4_NPs with smaller sizes (10 nm - 30 nm), and that the HN had diameters smaller than 100 nm, consisting of Fe3O4 cores coated with polypyrrole. EIS measurements have shown that the addition of HN to the epoxy paint could improve the efficiency of the anticorrosive coating when compared to the original epoxy paint prepared without any corrosion inhibitor.

Resumo em Inglês:

We discuss the preparation of Polypyrrole and Polylactic Polyacid (PPy/PLA) based blends and the subsequent investigation of their antibacterial properties. After being molded through injection processing, the blends were characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), Impedance Spectroscopy (IS), contact angle, thermogravimetry (TGA), and dynamic mechanical analysis (DMA). FTIR analysis confirmed the presence of PPy chains and the IS results indicated that the blends prepared with a 50% mass fraction of PPy have a conductive character. While the SEM images reveal the presence of small cracks on the surface of the samples, DMA analyses show that a decrease in their mechanical strength occurs in the 50°C-60°C range, with the blend with a 50% PPy load exhibiting the greater resistance and being able to withstand temperatures of the order of 120°C. The TGA degradation profile varies according to the amount of polypyrrole present in the blends, with those containing 50% PPy being able to retain about 32% of the polypyrrole mass at 600°C. The antibacterial activity tests done with the injected blends reveal that while no inhibition halo was formed for the Escherichia coli bacterium, the growth of Staphylococcus aureus is inhibited in the 50% PPy blend.

Resumo em Inglês:

Complete understanding of the local stress triaxiality and stress concentration is essential to ensuring structural safety of several structures. A combination of mechanical tests with numerical simulations can be used to obtain this information. One way to study stress triaxiality is by modifying the standard tensile test geometry (ASTM E8) with a notch. Based on previous results from the literature, five notches were chosen: 10, 5, 3, 2, and 1 mm. These geometries were tested, and the results were numerically reproduced using the Abaqus/Explicit 2020 software. The models used were a non-linear model with the Gurson-Tvergaard-Needleman damage model to reproduce the failure. The numerical analyses allowed the assessment of the von Mises stress and stress triaxiality near the notch to compare with the standard smooth specimen. Two instants were considered as crack propagation onset; the instant of the maximum von Mises stress in the element at the center of the specimen, where the failure process begins; and the moment of maximum stress in the true stress x true strain curve. For the von Mises stress analysis, the difference between the curves was small. The stress triaxiality is a better variable to visualize the influences of the notch. When the strain is equal to a 0.07 (instant of the maximum force for the standard specimens), for the smaller notches (1 and 2 mm), there is a region where the effective plastic strain is zero. Consequently, the stress triaxiality is larger in this region than in the center. For the crack propagation onset instant, the plastic strain occurs along the whole transversal section. In this instant, the maximum value of stress triaxiality occurs in the center for all specimens. These results demonstrate that the stress triaxiality changes as the strain increases, i.e., varies with time.

Resumo em Inglês:

This study aimed to evaluate the possibility of reusing industrial scraps of Surlyn® ionomer by obtaining blends with Low-Density Polyethylene (LDPE). Blends of LDPE and Surlyn® scraps were obtained by extrusion with compositions ranging from 25 to 75 wt% of the ionomer. Their melt flow index (MFI), morphology (SEM), mechanical (tensile, flexural, impact tests) and thermal properties (DSC, TGA, HDT tests) were analyzed. The morphology of the blends presented two phases, indicating the immiscibility of phases. Surlyn® incorporation promoted a decrease in the degree of crystallinity of LDPE and a slight increase in the thermal decomposition temperature. In addition, Surlyn® decreased the decomposition rate of LDPE. However, the decrease in the degree of crystallinity did not affect the mechanical properties of the blends. Incorporating ionomer in LDPE promoted an increase in tensile and flexural strength, tensile and flexural modulus and strain at break. Impact strength decreased with increasing ionomer concentration.

Resumo em Inglês:

Structural adhesives emerge as an alternative technique for joining materials used in tertiary structures in the oil and gas industry instead of welding, for example, in order to mitigate risks caused by the use of sparks on offshore platforms. Therefore, the present work aims to evaluate the influence of different surface treatments of the adherent material (carbon fiber/epoxy composite) on the mechanical behavior of the adhesive joints through the lap shear test. Furthermore, the viscoelastic properties of the epoxy-based structural adhesive were analyzed via dynamic-mechanical analysis (DMA). The results indicates that the adhesive exhibits residual curing when cured at room temperature and a post-curing process is required to increase its glass transition temperature (Tg) and its stiffness, Lap Shear tests results shows that the adherent surface treatment that generated the best mechanical response was cleaning with solvent, despite its lower roughness compared to the fuseply treatment, which indicates a strong correlation between roughness and wettability in obtaining resistant adhesive joints.

Resumo em Inglês:

The biodiversity of plant resources is a renewable source that can use as a sustainable component in various applications. The use of vegetable waste as a filler element in polymeric composites is part of the solid waste management policy and the sustainable development of agribusiness. In this work, the natural rubber composites were prepared with acai seed in proportions of 0, 10, 20, 30, 40, and 50 phr (per hundred rubber). The composites were homogenized in an open cylinder mixer and characterized by rheometric, morphological, mechanical, and thermal tests. The addition of the organic fillers significantly reduced the vulcanization process time. Thermogravimetric analysis and infrared spectroscopy showed that the composites were thermally stable and showed no structure changes after the vulcanization process, respectively. The Lorenz-Parks method's evaluation of matrix/filler interactions showed a strong interaction between NR/Acai. The new biocomposite can replace non-ecological composites economically and sustainably.

Resumo em Inglês:

Composites based on green high-density polyethylene (G-HDPE) and hydroxyapatite (HA) compatibilized with maleic anhydride grafted high-density polyethylene (HDPE-g-MAH) were developed in this work. The main objective was to evaluate the effects of HA and HDPE-g-MAH contents on the mechanical and thermal properties and hydrolytic degradation of composites through design of experiments and statistical analysis, as well as to evaluate the hemolytic stability. Hydroxyapatite acts as a reinforcing agent for the G-HDPE matrix while the HDPE-g-MAH acts as a compatibilizing agent, improving the dispersion of the HA particles in the polymer matrix and thus increasing the mechanical properties. The crystallization temperature and the degree of crystallinity of the polymer matrix were increased with the addition of HA, suggesting the filler acts as a heterogeneous nucleating agent. Hemolysis tests performed on a composite sample with best mechanical performance did not indicate significant hydrolytic degradation, which suggests this composite is a promising material to be used in bone tissue engineering, for application in implants and bone grafts.

Resumo em Inglês:

Ionic polymer-metal composites (IPMC) are typical electromechanical transducing materials suitable for use as soft actuators, bioinspired artificial muscles and sensors. However, IPMC produced with platinum films has the great disadvantage of the large number of cracks and wrinkles, which reduce the performance of the electrode. Polyaniline (PANI) is a promising conductive polymer that can address this issue, especially when it is electropolymerized on the platinum surface. An IPMC/PANI actuator was developed by potentiostatic electropolymerization of PANI at 0.9 V in 0.1 M and 0.3 M aniline solution. The characterization revealed that PANI is preferentially electropolymerized in the platinum film cracks and improve the electronic conduction mechanisms, which is not reported so far. The maximum tip displacement of the IPMC/PANI under 5 V was 8.3 mm, while for the IPMC was equal 5.2 mm. These results provide a simple and effective method to repair IPMCs and enhance their electromechanical performances.

Resumo em Inglês:

Local drug delivery systems used in dental implants need to have uniform pore size distribution, adequate wettability, chemical composition, and biocompatibility. In the present work, titanium was treated by pulsed plasma electrolytic oxidation (PPEO), using 0.025 M sodium dihydrogen phosphate and 0.25 M calcium acetate as electrolytes, aiming at use in drug delivery systems. Pulse with Ton/Toff (width pulse/repetition time) of 50 μs/100 μs or 100 μs/50 μs, duty cycle 0,33, and 0.67, respectively, were used. After treatment, Ca/P ratio, wettability, crystalline phase, pore size and distribution were determined. The average pore size ranged from 1.5 μm to 2.3 μm according to the increase of energy supplied to the system. Pore distributions with lower dispersion were verified for the Ton/Toff condition of 50 μs /100 μs, using a current density of 30 mA/dm2. On the other hand, the 100 μs/50 μs conditions produce larger pores, but with greater dispersion. In general, conditions with lower currents (30 mA/dm2 and 38 mA/dm2) and Ton/Toff ratio = 50/100 were the most appropriate for use in drug delivery systems, due to their size and distribution of uniform pores, greater hydrophilicity, and Ca/P ratio close to desirable (1.67) was obtained.

Resumo em Inglês:

Cross-linked polyethylene (XLPE) is primarily used as a coating and insulator for electrical wires and cables. The cross-links render recycling through remelting unfeasible, and XLPE waste is usually incinerated or sent to landfills. Previous investigations showed that XLPE increased the impact strength of commodity thermoplastics. Hence, incorporating XLPE in polyamide 12, an engineering thermoplastic, was studied using maleic anhydride grafted polyethylene (PE-g-MA). Formulations were prepared using a co-rotating twin-screw extruder containing 20 wt% XLPE with 0, 2, 4, and 8 wt% compatibilizer. Test specimens were injection-molded. DSC results showed that adding XLPE and compatibilizer reduced PA12 crystallinity but affected little melt and crystallization temperatures. Morphological analyses revealed poor adhesion between polyamide 12 and XLPE, which improved when adding PE-g-MA. The lack of adhesion when XLPE is added strongly reduces the mechanical properties, except for impact strength, which increased by ca.120% compared to the formulation without XLPE; while using 4 wt% compatibilizer this increase was ca. 140%. When adding PE-g-MA as a compatibilizer, some recovery was achieved in tensile strength and strain at break, and impact strength increased furthermore. Flexure and HDT tests showed a decrease in stiffness after adding XLPE. Stiffness was further reduced in compositions containing compatibilizer.

Resumo em Inglês:

Gas-Shielded Tungsten Arc Welding (GTAW) was modified to a Flux-Cored-Double-Wire GTAW (FCDW-GTAW); in this technique, wires of different compositions are used simultaneously to obtain different microstructures. In the modified GTAW, automatic flux-cored double-wire was used with a combination of four different wires deposited in AISI1020 steel, allowing different microstructures. Pin-on-disk wear tests described by ASTM G99 was used to evaluate the wear coefficients of four hardfacing materials combining Fe–Cr–C, Fe-Cr-C-Nb, Fe-Cr-C-Mo-Nb, and Fe-Cr-C-Mo-Ti alloys. The combination of these wires resulted in a hypoeutectic microstructure with niobium and titanium carbides, with an average hardness of 650 HV0.3, and hypereutectic microstructures formed by different niobium contents, with a microhardness range from 820 to 1020 HV0.3. The wear tests were performed without lubrication at room temperature, using a 6.0 mm diameter polished alumina sphere as a counter-body. The total distance covered was 1000 m with a speed of 0.1 m/s, a track radius of 6.0 cm, and an applied load of 10 N. Hardness, microstructure, wear coefficient, and wear mechanisms were compared. The results showed that wear resistance could be differentiated by the predominant wear mechanism: polishing for the hypoeutectic hardfacing and cracking for the hypereutectic ones.

Resumo em Inglês:

The copper alloy UNS-C27200 is a binary brass, composed of 38wt%Zn, beeing one of the most used in the industry. The union of Cu-Zn alloys by conventional welding by fusion in thin plates presents several challenges. The Friction Stir Welding (FSW) process performs the union of two, or more materials, through a rotating tool that travels throughout the welding region. One the great advantages of FSW is working below the melting point of the material, which reduces the change in the microstructure and properties of the material, when compared to conventional welding processes. Due to the lack of research on FSW process in lap brass joints with thin thicknesses, the present work aims to expand these studies in order to contribute to future research. Eight conditions were evaluated, varying rotation and welding speed. In the best results by visual inspection, analyzes of microstructure, temperature, microhardness and mechanical strength were performed. The better welding results were obtained with ω=1050 rpm and ν=20 mm/min. There was reduction of approximately 50% between Stir Zone and Base metal. The mechanical strength was affected by the pin hole resulting from the process. The microstructure revealed a homogeneous mixture in the stir zone and no defects were detected.

Resumo em Inglês:

To increase oil sorption, polyurethane foams were modified with MoS2, ZnO grafting and/or hexadecanoic acid coating. The foams were characterized by Scanning Electron Microscopy + Energy Dispersive X-ray Spectroscopy and Contact Angle techniques. Three sorption tests were performed. In tests with 100% water, the ZnO-PC modification showed a reduction of 35.7% in the seawater sorption when compared to Un-PC. In tests with 100% oil, there was a 29-fold increase in sorption (more than 2803%) of S46 lubricant oil when Un-PC performance was compared with ZnO-PC. In tests on the multicomponent systems, the lowest seawater sorption was 0.01 ± 0.00 g.g-1 (HA-PC), 0.08 ± 0.01 g.g-1 (Un-PC), and 1.39 ± 0.02 g.g-1 (Un-PC) for 20W40 engine oil, S46 lubricating oil, and diesel, respectively. The highest oil sorption in the systems was 41.34 ± 1.02 g.g-1 (HA-PC), 32.81 ± 0.31 g.g-1 (MoS2-PC), and 14.78 ± 0.27 g.g-1 (ZnO-PC) for diesel, S46 lubricating oil, and 20W40 engine oil, respectively. The reuse tests indicated that even after 10 cycles, the ZnO-PC foam kept its sorption capacity unchanged. Post-consumer foams proved to be effective in the sorption of different oils spilled into seawater, especially those grafted with ZnO rods or impregnated with MoS2.

Resumo em Inglês:

In Brazil, native forests and replanted forests are poorly managed, and there is concern about reusing plastic residues as well. These two factors play a significant role in the impacts on the environment in the past decades. In this study, the influence of polystyrene (PS) waste partially replacing polyurethane (PUR) as a binder for wood particles (Pinus taeda L. and Eucalyptus saligna) was examined on the physicomechanical and thermal properties of homogeneous particleboards. For the production of particleboard composite, the moisture content of wood particles was set at 2%. A variety of physicomechanical characteristics were evaluated, including density, moisture content, swelling in thickness after 24 hours of immersion in water, rupture modulus (MOR) and elasticity modulus (MOE). Increasing PS relative to PUR decreased MOR and MOE properties in particleboard composite specimens. Thermal analysis shows that replacing PUR with PS in particleboard composite specimens has not adversely affected the thermal stability, and even less its thermal profile of specimens. ABNT NBR standards were exceeded by particleboard composite-based panels, but ANSI standards were met, indicating their potential application. As a result of this study, PS waste could be used as a binder for particleboards and composite materials manufactured from pinus and eucalyptus wood chips in place of PUR.

Resumo em Inglês:

The elastic wave attenuation in artificial composites, known as phononic crystals (PnCs), is an important topic in the context of wave manipulation. However, there is a lack of knowledge in the obtainment of the wave attenuation of PnCs when the viscoelastic effect of different polymers is considered. In this study, the complex band structure of longitudinal waves in 1-D viscoelastic PnC (VPnC) rods composed by steel inclusions (elastic material) in a polymeric matrix (viscoelastic material) is investigated. The viscoelastic effect is modelled by the standard linear solid model (SLSM), which can be used to closely model the behavior of polymers for practical applications. It is also studied the influence of different polymers (i.e., epoxy, nylon, silicon rubber, natural rubber, and low density polyethylene (LDPE)) on the complex band structure of 1-D VPnC rods. The improved plane wave expansion (IPWE) and extended plane wave expansion (EPWE) are used to compute the band structure. It is observed that the viscoelastic effect influences significantly both the propagating and evanescent waves. The viscoelasticity increases the unit cell wave attenuation for most range of frequency considering all polymeric matrices. The highest unit cell wave attenuation is for the polymeric matrix of natural rubber.

Resumo em Inglês:

This paper aims to analyze the structure of the Ti-25Ta-xZr system alloys (x = 0, 10, 20, 30, and 40% wt.) after melting and hot-rolling by Rietveld's technique. The results confirm that zirconium acts as a β phase stabilizer (in which the Ti-25Ta-40Zr alloy is fully β in the as-cast condition), increases the lattice parameters of the phases, decreases the c/a ratio of the α phase, consequently, decreases the elastic modulus values (86 to 72GPa) and decreases the atomic packing factor (APF) of the alloys (60% reduction compared to alloys with and without zirconium in the as-cast condition and 50% reduction in the hot-rolled condition). Concerning hot-rolling, this mechanical process induces the α phase formation and increases the atomic packing factor of the alloys (APF). By the William-Hall technique, it was possible to calculate the average crystalline size and the micro-strain of the structures.

Resumo em Inglês:

The solidification process of Ti52-xNi38Cu10Nbx alloys was evaluated using the CALPHAD method and microstructural analyses of as-cast alloys with Nb additions of x = 4, 6, 8 and 10 at%. Both in Scheil calculator and structural analyses, the observed phases were TiNi, β-Nb/Ti, and Ti2Ni. TiNi is the matrix phase, and it presented similar amounts of Ti and Ni with varying Nb contents. Enrichments of Ti content and depletion of Ni are expected in the liquid with the solidification of this phase. Formation of Ti2Ni and β-Ti is related to the excess of Ti. Increasing Nb content hinders the formation of Ti2Ni, favoring β-Ti. In turn, Ni depletion and Nb accumulation led to the TiNi/β-Nb eutectic. In the intermetallic phases, coherent ratios were obtained when Cu was considered a substitute for Ni, and Nb, for Ti.

Resumo em Inglês:

The effects of small amounts (up to 5 wt.%) of scandia- and ceria-stabilized zirconia on the electrical conductivity, and the elastic modulus and hardness of yttria-stabilized zirconia were investigated by impedance spectroscopy and nanoindentation tests, respectively. The main purpose of this work was to obtain solid electrolyte compounds with improved properties compared to those of the base materials. Solid electrolytes compounds were prepared by solid-state reaction synthesis with sintering at 1450 ºC for 4 h. All prepared compounds exhibit a cubic fluorite-type structure. The microstructure of the compounds consists of polygonal grains with low (< 2%) porosity. The mean grain size estimated by the intercept method was 5 ± 1 μm. The electrical conductivity of the compound ceramics is lower than that of the base material. Addition of scandia-stabilized zirconia is found to exert a beneficial effect on the matrix by increasing the elastic modulus, achieving 221 MPa for 5 wt.% of the additive.

Resumo em Inglês:

Two cast superduplex stainless steels were aged at 850°C for different times. The effect of aging on the electrochemical behaviour and hardness of both steels has been investigated. A comparative study between the two steels was carried out considering the difference in chemical composition between the alloys, that is, the presence of copper and tungsten in the 6A steel. Corrosion resistance was evaluated by potentiodynamic polarization test, electrochemical impedance spectroscopy and Mott Schottky analysis. The results showed the beneficial effect of 0.99%pCu and 0.70%pW addition to the cast SDSS retarding the embrittlement of the 6A steel aged at 850°C for 10 hours. The characteristic mechanism of localized corrosion in the aged samples for both materials was the selective dissolution of the ferrite phase.

Resumo em Inglês:

The problem of improper disposal of polymeric waste is increasingly in present. Thus, the use of biodegradable polymers is a good alternative, especially for packaging. Compostable and biodegradable polymers such as PHBV can be completely degraded, making them ideal. But the short processability window and fluid instability is an important drawback to the wider application of this polymer in pure form. Production of composite materials has been indicated as a possibility for using this polymer. One source of filler is cellulose, because besides being widely available from agroindustrial waste. In this context, the present work reports the formulation of rigid packaging with PHBV and cellulose waste. An analytical mill was used to promote the dispersion of cellulose fibers. In general, the cellulose fibers increased the Vicat softening point of the polymeric matrix. There were more crystalline structures, according to DSC, and a decrease in impact strength, probably due to increased crystallinity and agglomerate formation. The microscopic analysis indicated greater surface roughness of the composite due to the increase of fibers, resulting in increased contact angle.

Resumo em Inglês:

This paper evaluates the use of the airbrush adapted solution blow spinning process as a secondary recycling method to produce recycled polycarbonate nanofibers. The results show a gradual improvement in fiber morphology and reduction in fiber diameter with increasing concentration, obtaining fibers at 18% w/v, indicating that the process is effective in producing high-quality nanofibers. The ideal morphology for the samples was obtained under 21%w/v and 60 Psi of air pressure with an 80nm average diameter. The thermal analysis demonstrates that the fibers possess similar thermal behavior to pure polycarbonate while the oxidation index didn’t show significant degradation on the fibers, suggesting that they can be used as standalone nanofibers for advanced applications. The produced nanofibers have diameters below 100 nm, making them suitable for use in face mask filters, among other applications. The study provides a new approach for the recycling of polycarbonate materials, offering a sustainable solution for their reuse.

Resumo em Inglês:

Ladle Furnace Slag (LFS) is a solid waste from steel production that can be used in civil construction due to its high content of calcium oxides (> 50% CaO), contributing to the sustainability of both industries. Seeking to study its function as a supplementary cementitious material, the objective of this work was to determine the properties of coating mortars with the replacement of Portland Cement (PC) by 30% LFS combined with the pozzolanic effect of Rice Husk Ash (RHA). Prismatic specimens were produced in a 1:6 mixture proportion (PC:sand) and subjected to mechanical tests and determination of the dynamic modulus of elasticity. The results indicated that the replacement provided a reduction in mechanical strength, however the presence of LFS+RHA was beneficial to improve water retention. These changes were caused by the bigger surface area of RHA grains and the higher CaO content, in relation to the reference mixture.

Resumo em Inglês:

Hybrid casting is a new fabrication concept that can reduce costs and production time of large tools, such as stamping tools for the automotive industry. In this work, we analyzed a hybrid material composed of a high chromium cast iron (HCCI) and a low carbon steel (WCB). SEM analyses indicate that the interface is free of non-metallic inclusions and porosities. The metallurgical bonding between alloys is confirmed by the diffusion of chromium and carbon from HCCI to WCB. Vickers microhardness, EDS and XRD confirmed the presence of M7C3 carbides in the HCCI and at the interface. One set of the samples was submitted to regular quenching in calm air and tempering, while another set was additionally submitted to subzero quenching before tempering. In both cases, a slight reduction of the HCCI hardness and an increase of the interface hardness were observed. The subzero treatment was effective to reduce the amount of retained austenite at the HCCI and limiting its hardness reduction. WCB microstructure and hardness showed no significative change, making it an ideal material to use with HCCI in hybrid casts. The results showed that is possible to produce bimetallic reliable components for industrial applications by means of hybrid casting.

Resumo em Inglês:

The good properties and high productivity obtained through injection molding have enabled the use of composites reinforced with short carbon fibers for the production of automobile components. Their low strength and stiffness, however, have limited the use of these materials in some applications. The incorporation of inorganic nanoparticles such as alumina (Al2O3) is a proposed solution to this problem. There is evidence that nanoparticles promote better interfacial interaction between the polymer and short carbon fibers, improving the mechanical performance of composites. The aim of this work was to develop polypropylene (PP) composites reinforced with alumina nanoparticles and short carbon fibers for the automotive industry. The composites were processed in a twin-screw extruder. The response surface methodology was used to define the content of nanoparticles in the composites and to evaluate the effect of the incorporation of the alumina and polypropylene-grafted maleic anhydride (PP-g-MA) on the properties obtained. The hybrid composite that showed the best tensile properties was used as a matrix for reinforcement with different levels of short carbon fiber. The tensile properties were determined by the standard techniques. The results showed that the materials obtained can be used in applications that require low density along with high productivity, rigidity and resistance.

Resumo em Inglês:

The Ti-19Nb-2.5Fe-6Sn alloy subjected to proper heat treatments is a promising material to be applied in orthopedic implants. This type of Ti alloy presents relatively low cost, good biocompatibility, and reasonable mechanical strength combined with low elastic modulus. In such an alloy, Fe improves mechanical strength while ω phase precipitation can be controlled by Sn addition. In this work, samples of the Ti-19Nb-2.5Fe-6Sn (wt.%) alloy were prepared by arc melting, hot swaging, and solution heat treatment. Results from the literature combined with thermodynamic simulations, differential scanning calorimetry (DSC), and heating/cooling experiments coupled with microstructural analyses were applied to determine the β transus temperature of this alloy. Following, the samples were solution heat treated in the β field and continuously cooled to room temperature at different rates. The effects of cooling rates on intergranular and intragranular α phase precipitation were evaluated. It was found that low cooling rates lead to intergranular precipitation while moderate cooling rates provide more expressive intragranular precipitation.

Resumo em Inglês:

The present paper sets out to investigate the role of voltage pulse length on the properties of Nb:TiO2 films deposited by High Power Impulse Magnetron Sputtering (HiPIMS). Several characteristics of the films were investigated, namely, resistivity, transmittance, crystallinity and band gap values of Nb:TiO2 films. Reactive depositions were carried out in Ar/O2 plasma with 40 µs, 50 µs, 60 µs, and 70 µs pulses. Increasing the pulse length changes the deposition from compound to metal mode. As it gets closer to metal mode, the deposition rate increases by up to one order of magnitude, while the resistivity of the resulting Nb:TiO2 film becomes as low as 10-4 Ω.cm, without any significant loss in optical transmittance, which remains close to 90% for a wavelength around 450 nm, but reduction in 25% of heat transmission (above 800 nm) were observed. Results indicate the anatase phase for all deposition conditions, and Ti3+ states increase with the pulse length, which can be explained by the generation of a second band gap. Both the niobium doping and the Ti3+ states can contribute to increase the conductivity of the Nb:TiO2 films in the as-deposited condition.

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The purpose of this work was to evaluate the microstructural alterations associated to the aging thermal treatments performed at 450, 475, 800 and 850°C, for 1, 3 and 12h, besides evaluating the influence of the precipitation of the alpha line phase on corrosion resistance. The samples were characterized by scanning electron microscopy, energy dispersion spectrometry, X-ray diffraction, feritscope, hardness, microhardness, in addition cyclic potentiodynamic polarization and double loop electrochemical potentiokinetic reactivation. In the agings performed at 450°C for 1h and 475°C for 12h, there was precipitation of the alpha line phase inside the ferrite and there was no significant effect on the resistance to pitting corrosion and the phenomenon of sensitization was not promoted. In the aging at 800 and 850°C for 1, 3 and 12h, the sigma phase was formed from the consumption of ferrite, and in the aging at 850°C there was the precipitation of the chi phase, promoting the increase in steel hardness. In agings for 12 h at 800 and 850°C, there was resistance to pitting corrosion decrease and the phenomenon of sensitization was moderated promoted at 800°C, with just the sigma phase precipitation and promoted at 850°C with sigma and chi phases precipitation.

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Hydrogels based on polyacrylamide, carboxymethylcellulose and silica are composites with good absorption and release properties over time, and this behavior allow their application in several areas. Thus, the aim of study was to analyze the absorption kinetic, spectroscopic, morphological, and structural properties of hydrogels prepared using different silica concentrations (0, 0.5, and 2.5%). The results showed that the swelling degree reduces with increasing silica, i.e., there was increase in crosslinking density, which was confirmed by SEM images. The reductions in the swelling degrees at equilibrium were 26.19% (0.50% silica) and 22.02% (2.5% silica) when compared to PAAm+CMC hydrogel. FTIR spectra showed characteristic spectroscopic bands of silica between 1384 and 1120 cm-1 indicating that its incorporation into the hydrogel matrix has occurred, which was also observed in the XRD diffractograms. Thus, the study of biodegradable hybrid hydrogels is relevant because they can potentially be applied in areas such as agriculture, tissue engineering and even civil construction.

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This work deals with different stress shot peening conditions’ effects on the compressive residual stress intensity and distribution. The tests were conducted on 15 mm x 70 mm x 1500 mm bars made of quenched and tempered EN 47 spring steel (DIN 51CrV4). Tensile tests and microstructure analysis were applied to guarantee the specification regarding resistance and microstructure. The stress shot peening process was conducted in an unloaded sample and two points bending loading with support distances of 150 and 1000 mm. The maximum flexural tension stresses were 750 and 1500 MPa for the two support distances. The residual stresses were measured by X-ray diffraction in five positions: measurements of samples with deflections were made without deflection, and a total of 95 residual stress measurements were performed before blasting. The compressive residual stresses increased as the calculated loading increased for all test conditions. Otherwise, for the 1000 mm support distance for the higher loading condition, the pre-tension calculated by the ANSYS™ showed higher flexural tension stress in the support position, while the residual stresses were constant between the supports.

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The Critical Distances Theory has been used in engineering field as a less expensive method to predict failures. Thus, this research aims to evaluate its methods in other materials, like the aluminum alloy 7075 T6, and notches. Two different notches were machined: a sharp and a blunted, with radius of 0,025 mm and 0,045 mm, respectively. The first in specimens of tests tension and the last in bend tests specimens. The DCT methods analyzed exhibited low percent differences and predictions mutually consistent. However, the Line Method stood out when presented 3% to percent difference. The analysis to stress field around of sharp notch tip, LM achieved a value of 12 MPa√m para KIc. Although, when these same results were applied in the Traditional Fracture Mechanics equations, a fracture toughness of 34 MPa√m was found. This last result is one of the best predictions achieved until the present moment in this research group. Mainly when compared with other works which determined the same property using the same thermal treatment conditions to this alloy.

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The production of conductive and organic devices from a 3D printer represents a promising strategy for several areas. In particular, the synthesis of polypyrrole-coated acrylonitrile butadiene styrene (ABS) composites can be considered an important step to produce conductive supports for 3D printing. Herein, it is reported the production of ABS samples through the additive manufacturing process (3D printing) accordingly to the Fused Deposition Modeling (FDM) method. The hydrophilic behavior was controlled by the surface treatment using air plasma for the following step of coating with polypyrrole (PPy) via an in situ polymerization, using two different oxidants: ferric chloride (FeCl3.6H2O) and ammonium persulfate (APS). The chemical, optical, surface, and electrical properties of these materials were characterized through Fourier Transform infrared spectroscopy (FTIR), contact angle measurements, cyclic voltammetry, Scanning Electron Microscopy (SEM), 4-probe electrical measurement, and mechanical tensile testing. The ABS/PPy (FeCl3) composite exhibited a low electrical contact resistance and better performance for applications that require electrodes with a good conductance level.

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In this work, thin films based on the Ti-Zr system were studied, deposited on a silicon substrate by the magnetron sputtering technique using simultaneously a combination of High-Power Impulse Magnetron Sputtering (HiPIMS) and Direct Current Magnetron Sputtering (DCMS) sources. The objective of this work is analyzing the effect of varying HiPIMS frequency (300 Hz, 400 Hz, 500 Hz, and 600 Hz) on the characteristics and properties of the thin films. The thickness increased between 300 Hz and 500 Hz, where the thickness measured 563 nm and 732 nm, respectively; then it decreased to 709 nm at 600 Hz. Hardness and elastic moduli also tended to decrease with increasing frequency, and the results for the first property were between 7 GPa and 10.3 Gpa, while the elastic moduli were from 114 Gpa to 157 Gpa, in which lower values were reached at higher frequencies. In the wettability test, lower contact angles were observed for samples with lower frequencies due to their high surface energy, providing better hydrophilic properties.

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The allotropic transformation, characteristic of cobalt-based alloys, occurs at around 970 ºC in Co-28Cr-6Mo alloys. When subjected to fast cooling, such alloys can maintain the high temperature cubic centered phase at room temperature, resulting in a CFC metastable matrix. This metastable condition leads to a nucleation of the hexagonal phase (the stable one), which is induced by deformation or isothermally. In general, Co-based alloys are submitted to solution heat treatment plus aging to control both the precipitation of carbides and the nucleation of the hexagonal phase. When the study of this type of alloy is conducted in the metastable condition, it is extremely important do not induce the hexagonal phase during sample preparation. Traditionally, the metallographic route preparation is carried out using electropolishing to avoid the deformation-induced phase transformation. The need for specialized equipment and hazardous electrolytes to perform electropolishing limits its use. Therefore, the aim of the present work is to propose the use of an adaptation to traditional metallographic techniques in order to prepare Co-28Cr-6Mo alloy samples. To this end, the samples prepared by three different routes were analyzed by X-Ray diffraction, including Rietveld refinement, as well as EBSD in order to identify and quantify the phases present in the structure. A control cold rolled sample was also analyzed. The results showed a significant reduction in the HCP phase fraction, strain-induced during grinding, after the application of the alternative preparation method proposed. Further studies might be useful to validate the present methodology.

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The formation of a stable and adherent oxide layer on the Ti-6Al-4V alloy can improve the mechanical and corrosion resistance of this material. This work studied the creep behavior of Ti-6Al-4V alloy after two different thermal oxidation conditions: at 650 °C for 12 h and at 800 °C for 2 h. In the XRD analysis of the oxidized samples, it was possible to observe the formation of rutile (TiO2) and a displacement of the peaks of α and β phases caused by the dissolution of oxygen. In the creep test at 550 °C, the material oxidized at 800 °C for 2 h showed a greater creep life at 125 MPa, the crack took longer to brake probably due to the greater thickness of the layer. At 550°C and 187.5 MPa the material oxidized at 650 °C for 12h has a better creep life, probably due to the layer more adhered.

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Spent Foundry Sand is one of the largest industrial solid wastes generated by foundries in the production of iron and steel components. Currently, millions of tons of molten sands are discarded worldwide. Therefore, this work aims to reuse the Spent Foundry Sand for the production of glass-ceramic materials, since this reuse minimizes the environmental impacts related to its discarding. The Spent Foundry Sand, composed of >60% SiO2, was mixed with limestone and melted at 1500 °C to produce the glass (melting and rapid cooling method). The materials were characterized by X-Ray Fluorescence, X-Ray Diffraction and thermal analysis. The X-Ray Diffraction results of the glass tablets treated at 875, 941 and 1050 °C show that the formed phases are Wollastonite-1A, β-Wollastonite and Akermanite. In summary, it is possible to produce glass-ceramic from Spent Foundry Sand with Wollastonite phase.

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The present work aims to contribute to the study and development of methodologies for shrinkage tests of self-compacting concrete (SCC) using the addition of polypropylene (PP) microfibers as a variable to validate the correlations between the shrinkage tests. The objective of this work was to evaluate, through correlations between the area and the age at which the cracks appeared, the role of PP fibers as a control for this pathology. Reference SCC traces with additions of 6 mm and 12 mm microfibers were created for this purpose. For the shrinkage tests, the criteria of the ASTM C1579:2013 (plates) and ASTM C1581:2016 (rings) standards were used. The microfibers showed a significant reduction in cracks in the SCC, its reduction rate ranging from 40% to 70%, also presenting a delay in its appearance, which varied from 9 to 20 days for the appearance of the first crack.

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This work compares the anticorrosive properties of DC electrodeposited CuCoNi, CuCo, and CuNi alloy coatings in a NaCl 0.5 mol L-1 solution. The results showed that j and the bath composition influenced the chemical, morphological, and electrochemical characteristics of the alloy coatings. Among all the studied coatings, the CuCo, CuNi, and CuCoNi ones produced at j = 10 A m-2, j = 60 A m-2, and j = 25 A m-2, respectively, showed the best anticorrosive performances in the saline medium, exhibiting charge transfer resistances (Rtc) higher than 2000 Ω cm2 and an electrical double layer capacitances (Cdl) lower than 8 X10-4 F cm-2. These results agree with the compact morphologies and smaller grain sizes presented by these coatings. Therefore, the anticorrosive properties of the coatings cannot be related only to the less noble metal(s) contents in the alloy but also to their morphologies.

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Ti alloys are widely used in severe corrosion environments where corrosion resistance is required, as biomedical industry. Additive manufacturing produces customized and complexes products. Laser texturing is a process of structuring surfaces using laser pulses, that allows the creation of periodic patterns on the surfaces of materials, to modify them, functionally and/or aesthetically, in a precise and direct way, allowing parameterization, versatility and repeatability. Consequently, bringing together metallic additive manufacturing with laser texturing process could be an alternative to obtain parts with functional hydrophilic surfaces, which improves osteointegration and reduces bacteria adhesion. Thus, the aim of this work is to characterize and evaluate the influence of LASER parameters in as-built additive manufactured potential biomedical components. Ti6Al4V specimens were produced by L-PBF, using Ytterbium LASER with maximum power of 500 W, varying the laser power from 61 W to 244 W. The samples were characterized by SEM, Microhardness, and wettability. After that, some specimens were Laser textured using an Ytterbium optical fiber laser, and then evaluated by SEM, wettability, and 3D roughness. It was possible to observe that the surface of all studied samples was flattened after Laser texturing in comparison with as-built condition, due to the melting of the powder particles.

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Superplastic deformation has a significant industrial application value due to the large elongation, which allows manufacturing parts with complex geometries but happens at elevated temperatures and low strain rates. Therefore, it requires alloys with fine grain size but whose grains tend to grow at processing temperatures. Second-phase particles can promote grain boundary pinning to keep a fine grain size structure during superplastic forming. In 5083 aluminum alloy, Al6Mn particles make grain boundary pinning. There are two types of 5083 aluminum alloy: conventional with manganese range from 0.4 to 1.0 wt.% and superplastic with manganese between 0.64 and 0.86. It was observed in bibliographic research that the 5083 superplastic has a higher chemical concentration of manganese than the conventional one. However, no references were found covering manganese concentration in grain size stability. This work shows grain size evolution at a constant temperature of 5083 alloys with different manganese concentrations. This work indicates that the manganese substantially impacts grain boundary pinning when the chemical composition is between 0 and 0.6 wt.%. No significant effects were observed for Mn concentrations higher than 0.6%".

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This research was aimed to obtain biodegradable polymeric films with antifungal action against Aspergillus niger, through the addition of copper oxide nanoparticles (CuO-NPs) in the commercial polymer (Ecoflex®) and to evaluate its mechanical, morphological, biodegradation, and copper release properties. The microbiological results showed that the films with 4 wt% CuO-NPs inhibited 97.57% the growth of the fungus growth of 1×105 spores·mL-1 compared to the control. The morphological characterization revealed that the CuO-NPs presented irregular form with particles size of 50 to 400 nm and the XRD showed characteristic peaks of copper oxide. The addition of CuO-NPs to Ecoflex® provided increased maximum and rupture tension, strain, and elasticity modulus the obtained films with 1 wt% CuO-NPs and did not alter the biodegradability of the films. It can be said that, through the addition of CuO-NPs to Ecoflex®, it was possible to add antifungal activity for Aspergillus niger without compromising its biodegradability, meeting the safety standards established by legislation regarding the release of copper.

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Maraging steel is a special class of high-strength steels that are hardened by the precipitation of intermetallic compounds at temperatures close to 480 °C, without carbon transformation. Since its development, it has been used for strategic applications (nuclear energy, defense, and aerospace areas) and the mastery of its process and application has been constantly improved. This study aimed to characterize the weld regions of a maraging 300 steel used to manufacture a rocket motor case. Welded samples of maraging 300 steel were subjected to metallurgical and mechanical characterization. Microstructural analysis showed three different zones in the hardness range of 291 to 465 HV and reduced toughness. X-ray diffraction showed metallic phases in each region, evidencing the increase of the austenite phase. Based on the results obtained, maraging steel has great potential for aerospace applications, with excellent strength even when subjected to welding.

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Additive Manufacturing technology has continually advanced, allowing microstructure and property optimization. In recent years, several studies have been carried out with the aim of understanding mechanisms of formation and evolution of the microstructure and, consequently, their influence on mechanical properties. However, correlations between microstructure and corrosion properties are not completely understood, making more systematic investigations necessary. In this work, samples of the Ti-6Al-4V alloy were produced by combining different laser powers and scanning speeds in order to generate different energy density values (VED) with subsequent microstructures and properties. The samples were characterized by optical and scanning electron microscopy, hardness and relative density. Complementarily, corrosion tests were carried out. For the entire set of parameters used, the processed samples showed the formation of acicular martensite α´, followed by different levels of porosity depending on the applied energy density. VED proved to be an important control parameter, and the best combinations of hardness and corrosion resistance were obtained for the parameter ratio that generated energy densities greater than 100 J/mm3.

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U-7.5Nb-2.5Zr cladded in Zircaloy-4 is one of the most studied fuel prototypes. The Nb and Zr are added to the U to stabilize the body-centered cubic (BCC) gamma phase and grant mechanical and swelling resistance. The U-7.5Nb-2.5Zr undergoes the gamma to α′′ phase transformation, generating compressive stresses due to the volume reduction. The α′′ phase also can transform to a combination of α + γ2 phase (equilibrium phases), which are known to be hard and brittle. This work had the objective to test the effect of ageing the gamma to α′′ phase in thermal cycling of a U-7.5Nb-2.5Zr cladded in Zircaloy-4 part. A co-laminated specimen was aged and thermally cycled in a dilatometry experiment. The samples were characterized through X-ray diffraction and metallography. The results show that the gamma to α′′ phase transformations occur at the begin- ning of the initial ageing, followed by stress relief. During the cycling, the sample demonstrated non-equal thermal strains and presented fractures along with the U matrix.

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This work aims to evaluate the recycling of firewood ash waste as a procedure to provide sustainable raw material for ceramic floor tiles with low water absorption. For this purpose, firewood ash waste coming from a red ceramic company in Campos dos Goytacazes-RJ (Brazil) was selected as an alternative raw material into a ceramic floor tile body, replacing natural quartz material by up to 10 wt.%. Floor tile pieces containing up to 10 wt.% of firewood ash waste were prepared by the dry process, pressed, and fired between 1190 ºC and 1250 ºC using a fast-firing cycle. The floor tile pieces were tested to determine their properties (linear shrinkage, water absorption, apparent porosity, apparent density, and flexural strength). The results showed that the partial replacement of quartz with firewood ash waste, in the range up to 10 wt.%, allows the production of ceramic floor tiles with low water absorption (WA) (BIa group - WA < 0.5% and BIb group - 0.5 < WA ≤ 3%; ABNT NBR ISO 13006:2020 Standard) in different amounts of firewood ash waste at lower firing temperatures.

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Ni-based superalloys are widely used in critical components of aircraft engines and turbines and also in the petrochemical industry, for applications in highly corrosive environments. These alloys have as main characteristics their superior mechanical, corrosion and oxidation resistance at high temperatures, as well as creep resistance. The chemical composition associated with carrying out heat treatments directly influences the phases formed (such as the ordered cubic phase γ’-Ni3(Al,Ti) in the fcc γ-Ni matrix), and depending on the alloying elements and fraction, there is the possibility of an increase in mechanical strength. There is a certain gap in the literature regarding the study of ternary superalloys based on Ni-Nb, and the influence of the third alloying element on the microstructure and microhardness. In this context, the objective of the study is to characterize pseudo-eutectic alloys of the Ni-15Nb-xM and Ni-20Nb-xM systems (xM = 2Al, 4Ti, 15Fe and 15Cr, wt.%) and investigate the influence of alloy elements and solution heat treating on their microstructure and properties through X-Ray Diffraction, Optical Microscopy, Scanning Electron Microscopy and Vickers Microhardness. Microhardness and microstructures were significantly influenced by the addition of alloying elements. The addition of Cr had a significant effect on the hardness of the cast samples. All alloys showed microhardness and microstructural changes after solution heat treatment.

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Self-compacting lightweight concrete (SCLC) has become one of the most promising materials in civil construction. This work applies expanded clay as a light aggregate in the production of SCLC, seeking to evaluate the influence of the use of this material on the properties in the fresh state, mainly regarding workability, viscosity, passage capacity and resistance to segregation. In addition, density, compressive strength, thermal and microstructural properties were investigated. The results showed that expanded clay improved the workability of concrete when compared to self-compacting concrete (SCC) with conventional aggregates. As for the mechanical characteristics, resulting from the compressive strength, the SCLC, due to its reduced density, presented values lower than those found for the conventional CAA, produced with denser aggregates. It was observed that the use of lightweight aggregates promotes a reduction in thermal conductivity, a performance that guarantees better thermal insulation. As for the microstructural analysis, it was found that, with the use of expanded clay, there was a decrease in pores in the cement paste matrix and in the thickness of the interfacial transition zone (ITZ). It was evident, therefore, that the use of expanded clay maintained the mechanical characteristics and also ensured better thermal insulation than conventional concrete.

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Microwave-assisted sintering of ceramic materials has proven to be a very favorable processing technique that can promote lower grain growth and densification with shorter dwell times. Hematite is considered a good microwave absorber due to its high loss tangent value, calculated in the range of 0.001 to 0.2 between room temperature and 750 ºC for 2.45 GHz1, thus showing good interaction with this electromagnetic radiation. However, there are few studies on grain growth kinetics of hematite during microwave sintering, as well as the relationship with grain growth parameters. Therefore, the aim of this work was to evaluate the effect of the heating rate and dwell time on grain growth kinetics, during microwave-assisted sintering (2.45 GHz) of hematite nanopowders. In an initial characterization, dilatometry tests were performed by conventional heating and microwave-assisted heating using the same heating rate (20 °C/min). From these results, the temperature ranges of the initial and intermediate stages of sintering and the onset of linear shrinkage were determined. Considering these results, the samples were sintered in a conventional oven from 750 ºC to 1200 ºC with increments of 50 ºC, varying the dwell time in 6, 12 and 36 minutes. Thus, the diffusional mechanism (N) could be calculated, a value used for the approximate calculation of microwave sintering kinetics. Additionally, sintering was performed in a microwave oven using three heating rates (20, 30 and 50 °C/min) to evaluate the effect of the heating rate on grain growth. The estimated activation energies for the grain growth process during microwave sintering were approximately 237.5 to 272.3kJ/mol, which were higher compared to conventional sintering, in the range of 206.0 to 242.0 kJ /mol. It was found that with increasing microwave heating rate, the activation energy for grain growth tends to be higher.

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The excessive production of new tires and the inappropriate disposal of waste tires have caused serious environmental and public health problems. To properly dispose of this environmental liability, these rubber residues have been used in cement composites to improve some of their properties in the hardened state. This study evaluates the incorporation of rubber and vermiculite residues in concrete in terms of mechanical and acoustic properties. Different concrete compositions were defined where rubber waste and vermiculite were used to replace the natural sand mass. To characterize the concretes, mechanical and acoustic tests, and analysis of the microstructure of the material were carried out to better understand its properties. An improvement in the acoustic properties can be seen in the composites with rubber and vermiculite. Thus, the great contribution of this research is the development of concrete compositions for acoustic barriers, technically viable, adding environmental benefits.

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The objective of this research was to produce artificial stone plates based on granite and mirror wastes and epoxy matrix, by vibration, compression, and vacuum and to characterize them. Plates were manufactured with 15%wt epoxy resin and 85% of aggregates in the proportion of 1/3 of granite waste from Ocre Itabira gray granite and 2/3 of mirror waste. The apparent density, water absorption, and apparent porosity values ​​were 2.22 g/cm3, 0.11%, and 0.25%, respectively, the flexural strength was 34.36 MPa, abrasive wear after a 1000m track was 2.28mm and the breaking height in the impact resistance test was 0.45m. In addition, the stone was resistant to several staining agents. Therefore, the technical viability of the material developed was verified, with results compatible with studies already carried out in the area, making it possible to apply it as coatings and countertops in civil construction.

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In recent years, there has been a growing interest in the search for metallic alloys with favorable mechanical and chemical characteristics that elicit a positive biological response. Among these alloys, β-Ti alloys have attracted significant attention due to their low elastic modulus and excellent biocompatibility. The addition of Nb contributes to stabilizing the β phase at room temperatures, leading to the transformation of β into β + α (β-isomorph). Additionally, despite Zr being commonly considered a neutral element, it can exhibit a β-stabilizing characteristic when combined with betagenic elements. Both Nb and Zr have been shown to effectively increase the lattice parameter of the β phase, which is advantageous for reducing the elastic modulus. The primary objective of this study was to characterize β-Ti alloys within the Ti-Nb-Zr system, specifically Ti-40Nb-20Zr, Ti-40Nb-30Zr, and Ti-40Nb-40Zr (wt.%) produced via arc furnace casting. The study aimed to investigate the influence of the proportion of β-stabilizing or betagenic elements on the microstructure and properties of the alloys, including Vickers microhardness and elastic modulus.

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Aerospace and automotive industries utilize advanced high strength steels due to their exceptional mechanical strength and ductility. Laser beam welding has shown potential in reducing the melted zone, heat affected zone, and process time for these steels. This study focused on dissimilar welding between DP 780 and 300M steel sheets, commonly used in the automotive and aerospace industries, respectively. The aim was to expand the range of possibilities and innovations by enabling the use of these steels in both applications. The study investigated the optimal process parameters, microstructure, and mechanical properties for the laser welding process. It also examined the influence of intercritical quenching and tempering on the microstructure and mechanical properties of the laser welded steels. The materials underwent dilution and different phase transformations due to the welding process and heat treatments, as revealed by microstructural characterization. The weld showed a notable increase in hardness, however without compromising toughness. The fractures during tensile testing occurred in the DP 780 steel, far from the MZ and HAZ. Heat treatments increased ultimate tensile strength, but lowered ductility. Welding affected the fatigue life, especially in the intercritically quenched joint, which showed a quasi-cleavage crack growth mechanism and a decrease in fracture toughness.

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In this work muscovite was ultrasonically treated to obtain composites with post-industrial wood plastic residues. The muscovite was ultrasonicated for 30 or 60 min and mixed with the polymeric matrix at a constant level of 15% (weight percentage). The composites were prepared in a single-screw extruder and formed into flat films for characterization. SEM images of the ultrasonicated muscovite revealed the occurrence of delamination, while the particle size distribution results suggested a decrease in size with longer sonication time. FTIR spectra also indicated the occurrence of delamination of the material. The composites exhibited a slight increase in density and a large increase in impact resistance of the samples with ultrasonicated muscovite. The XRD of the composites suggested the occurrence of alignment of the mineral in the matrix. The results indicate that ultrasonication is an effective method to improve the interaction and dispersion of muscovite with wood plastic waste to obtain composites.

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This work aimed to manufacture scaffolds from a hydrogel composed of a sodium alginate matrix with hydroxyapatite reinforcements using a 3D bioprinter, aiming at application in bone tissue regeneration. The alginate solution was prepared by dissolving sodium alginate at a concentration of 10% (w/v). Hydroxyapatite (HAp) was added to the solution at 2.5% and 5.0% (w/v) concentrations, followed by placing the samples in a container with a 1.0% (w/v) calcium chloride solution. The scaffolds were analyzed for HAp concentration and morphological characteristics, physicochemical properties, and biological response. The scaffolds show reproducibility and spectroscopic analyses confirm hydrogel formation and hydroxyapatite incorporation in the alginate matrix. The hydrophilic properties are compatible with scaffolds obtained through 3D printing made from polysaccharides, and the thermal analysis showed the expected behavior of these same materials. Preliminary findings indicated that scaffolds containing 2.5% (w/v) hydroxyapatite are inside cytotoxicity limit (66.4 ± 7.0%) towards canine E20 lineage cells. In contrast, scaffolds with 0% and 5.0% (w/v) hydroxyapatite were non-cytotoxic. Notably, the latter scaffold demonstrated enhanced cell proliferation, as anticipated, owing to the hydrophilic properties of alginate that enable easy and swift cell seeding, facilitating nutrient transport and cellular growth within the scaffold.

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The work aims to analyze the effect of partial replacement of coarse aggregate by expanded polystyrene (EPS) in the production of hollow blocks, a type of concrete block. Substitution levels, by volume, of 0% (reference), 5%, 10%, 15%, 20%, and 25% were tested. The following tests were performed: granulometric composition, specific mass, unit mass, surface analysis tests, absorption, mass determination, dimensional analysis and compressive strength. Regarding surface analysis, the hollow blocks showed satisfactory results. As for water absorption, the blocks performed similarly to the reference blocks with small variations in the results. As for its mass and dimensional variability, the insertion of EPS did not promote significant changes. All specimens with substituted EPS contents met the requirements regarding the blocks' compressive strength. From an environmental point of view, the replacement of EPS meets the requirements of the block standard, contributing to its removal from the environment.

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In these last decades, with the advance of industrialization, the enormous quantity of residue that is discarded by the industry has been generating discussions about eco-efficient solutions. This research has the objective of developing an artificial stone with residue of quartzite and fine quarry gravel (granite), utilizing the vibro-compression vacuum method. The residue was separated in three granulometric ranges with sieving: Large and medium (fine quarry gravel) and fine (quartzite). A statistical treatment was used in the acquired data, utilizing analysis of variance (ANOVA). The characterization was through a physical, mechanical, dilatometric and microstructural analysis. The obtained results classify the material as having high potential to be used for flooring in the civil construction industry, since it has low porosity <0.17% e water absorption < 0.3%, maximum flexural strength > 30 MPa, being able to be utilized in medium and low traffic environments.

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Magnesium silicate cement is produced by mixing reactive magnesium oxide with a source of reactive silicon oxide. This cement is an interesting alternative to Portland cement due to the potential for low energy consumption, reduced greenhouse gas emissions, and use of renewable resources. Aluminosilicate-based raw materials can also be utilized to produce this type of cement. Thus, this work aims to study the use of kaolinite clay to produce magnesium aluminosilicate cement. The cement was produced by calcination of magnesium carbonate (MgCO3) and kaolinite clay at a temperature of 800 °C for 45 minutes with MgCO3/kaolin mass ratios of 90/10, 80/20, and 70/30. Mortars and pastes samples were cured at 60 °C for 1, 3, and 7 days. The results showed that the maximum compressive strength (32.7 MPa) was yielded for the 70/30 mortar mix after 3 days of curing. Microstructural studies of pastes indicated the incorporation of aluminum for the formation of magnesium aluminosilicate hydrated products, in addition to the formation of brucite.

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Short time tempering has been applied to steels to improve toughness keeping the hardness at the same level. For AISI D2 tool steel, typical thermal cycles are quench and temper. The austenitizing temperature is around 1040 ºC and the subsequent double tempering at temperatures close to 500 ºC, for 2 hours each, in order to get the maximum secondary hardness. The aim of the present work is to verify the effects of short time tempering in the AISI D2. For such purpose the Hollomon-Jaffe tempering parameter was used to determine the equivalent time at 600 and 700 °C, being 500 °C for 2 hours the standard temperature and time. The thermal cycles were carried out at a dilatometer. All the specimens were austenitized at 1040 °C followed by double tempering at: 500 and 700 °C for 2 hours each; and 500 °C, 600 °C, and 700 °C for 10 s and 1 min each. The dilatometric curves were analysed. Scanning electron microscopy, X-ray diffraction and Vickers hardness were carried out to characterize the microstructure and mechanical properties. The short time tempering conducted at high temperatures led to the formation and growth of tempering carbides and to matrix recrystallization, which were responsible for greatly reducing the hardness of the material. The short time tempering up to the intermediate temperature of 600 ºC, for 1 minute or 10 seconds, produced results like the conventional tempering in microstructural and hardness terms, denoting that the Hollomon-Jaffe tempering parameter predictability close to the secondary hardness peak.

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In juice and pulp extraction, about 10% of fruit waste is generated, which often ends up in landfills that can cause environmental damage, serve as food for insects and rodents, and cause health problems for humans. In this work, micronized guava waste was used as a filler in vulcanized compounds in natural rubber. Mechanical properties such as hardness, tensile strength, tear resistance, and abrasion resistance were evaluated, as well as thermal properties such as thermogravimetric analysis, in addition to scanning electron microscopy, X-ray fluorescence, elemental analysis, and infrared spectroscopy. According to the results of the mechanical properties tests, the addition of up to 20 phr of the filler tends to improve the tensile strength of the composites, resulting in an increase in the density of cross-links obtained through the Flory-Rehner method. The thermal behavior analyzed by TGA and FTIR spectra were not affected by the incorporation of fillers.

Resumo em Inglês:

Carboxymethyl cellulose (CMC) is considered a non-toxic, biodegradable and biocompatible polymer. CMC-based films are rated as flexible, clear, odorless, moderately tear resistant, resistant to oil and grease migration, and water soluble. Due to its hydrophilicity, CMC can serve as matrix to encapsulate hydrophobic substances, like essential oils, by emulsion dispersions. The essential oil of rue (Ruta graveolens) has antifungal, antimicrobial, insecticide and therapeutic properties already reported in the literature. For the incorporation of rue essential oil in the CMC films, the ultrasound-assisted emulsion technique was used. The films were produced by casting evaporation. The rue essential oil emulsion and CMC polymeric films with the incorporation of emulsified essential oil were evaluated according to the emulsion droplet size, chemical composition, morphology and thermogravimetric profile. The droplet size obtained for the emulsion was 229.1 nm. The films showed good transparency, regularity and chemical characteristics similar to those of the pure polymer.

Resumo em Inglês:

The Montmorillonite-Erucamide nanocomposite (MMT-EU) can be used to reduce and to control the values of coefficient of friction of low-density polyethylene films (LDPE), widely used by the food industry. In this work, the effect of the addition of 5 wt% and 10 wt% of MMT-EU on the mechanical properties of LLDPE films involving the weld region was investigated. The MMT-EU concentration range was defined considering its possible technological application as an additive to stabilize the friction coefficient of polymeric films. The result shows a significant improvement in the values of stiffness, strength and ductility of polymeric films. In addition, it did not change the coefficient of friction, but the brightness of the LLDPE films decreased and the opacity increased, due to the increase in the crystallinity degree of the LLDPE polymer promoted by MMT-EU, not being a problem for the application of these films.

Resumo em Inglês:

At present, the friendly recycling of paper industry effluent sludge has gained great prominence due to the ecological and economic benefits. The aim of this work is to evaluate the influence of the incorporation of paper industry effluent sludge into a red wall tile formulation (BIII group), replacing natural limestone material by up to 10 wt.%. For this purpose, five red wall tile formulations were developed by the dry process, pressed at 47 MPa, and fired at 1170 ºC by using a fast-firing cycle. The wall tile formulations were characterized in terms of chemical analysis, thermal analysis (DTA-TG), and dilatometric analysis. The influence of paper industry effluent sludge on the technical properties (apparent density, water absorption, and flexural strength) and sintered microstructure was investigated. The results showed that red wall tiles containing up to 10 wt.% of paper industry effluent sludge have very good usable final properties, indicating their suitability for the wall tile industrial production (BIII group - ABNT NBR ISO 13006). Such results emphasize the feasibility of ecological and economic recycling of paper industry effluent sludge for the production of red wall tiles.

Resumo em Inglês:

The NixCu(1-x)Fe2O4 (x = 0, 0.2, 0.8, 1) mixed nickel and copper ferrites were synthesized using the EDTA-Citrate complexation method and calcined at 700°C. The structure, properties and characterization of the samples were analyzed by DRX, Rietveld refinement, SEM, and DRE UV-Vis, indicating the phase formation of tetragonal (CuFe2O4 and Ni0.2Cu0.8Fe2O4) and cubic (Ni0.8Cu0.2Fe2O4 and NiFe2O4). The materials exhibited morphologies suitable for photocatalytic applications and a UV-Vis absorption range near 2 eV as expected for spinel ferrites. These materials were evaluated as photocatalysts for the degradation of Rhodamine B dye under heterogeneous photocatalysis conditions, simulating solar light irradiation, air injection, and different pH levels (2, 6, and 10). The results showed that the catalytic efficiency was higher for samples with a higher copper content and in a basic medium. Therefore, NixCu(1-x)Fe2O4 mixed ferrites have promising potential as photocatalysts.

Resumo em Inglês:

In recent years, increasing automotive safety and energy efficiency has become a major concern in the automotive industry. Advanced high-strength steel (AHSS) was chosen for its weight reduction and high mechanical strength for the body in white (BIW). Specifically, it has been used in 22MnB5 steel press hardening type steel (PHS) with patchweld technology, which enables the production of reinforced and structural parts in a single stroke during the hot forming process. This study aimed to evaluate the resistance spot welding parameters for patchweld before hot stamping, considering the minimum and maximum residual stress, while ensuring a welding nugget diameter within the approved range. Microhardness and X-ray diffraction were used to analyze the welding zones for phase identification and residual stress measurements. After five weeks of elapsed time, the spot weld showed cracks that were not seen immediately after welding and were probably due to a high residual stress state.

Resumo em Inglês:

The following work analyzed the changes in the properties of Fatigue in a 300M aeronautical steel after the application of thermochemical treatments of plasma nitriding and laser carburizing. The microstructural characterization of the formed layers and the hardness obtained after the surface treatments were conducted. Thus, a comparison was made between the two treatments to verify which one has better efficacy. It has been observed that the treatment of plasma nitriding improves significantly the fatigue properties of 300 M steel. It was also noted that laser carburizing was not efficient to improve fatigue life.

Resumo em Inglês:

Currently, there is a severe shortage of good-quality feldspar deposits. On the other hand, porcelain tile polishing residue has been widely recognized as an alternative raw material for the ceramic industry. Thus, this research evaluated the effect of the partial replacement of feldspar by the porcelain polishing residue (PPR) in formulations for sanitary stoneware. It was replaced from 2% to 20% of the total mass of feldspar by the residue. The raw materials were characterized by X-ray fluorescence, X-ray diffraction, and particle size determination. Then, they were mixed in a wet ball mill, and the rheological properties of the suspensions were analyzed. Samples of the test were produced by slip casting and sintered at 1160 °C, 1180 °C, and 1200 °C. Rheological characteristics were not affected when up to 20% of feldspar was replaced by residue. Bodies with high amounts of PPR had flexural strength and water absorption values similar to those of bodies without PPR in formulations. Furthermore, apparent porosity values lower than the reference mass were obtained with the addition of 6% of the residue in the formulation.

Resumo em Inglês:

The current materials research field demands sophisticated tests and simulations to predict creep behavior, meet design needs, and save time and resources. This demands an appropriate mathematical formalism that can represent creep data for different materials and loading conditions. In this context, mathematical models such as θ-Projection and ν Concept can be applied to predict the behavior of materials under creep conditions. The main goal of this study involves the application of such methodologies to predict a creep curve for Ti-6Al-4V. In a preliminary assessment, both equation parameters, determined by computational techniques and an experimental database, enabled the determination of the strain-time curve of Ti-6Al-4V at 465 MPa and 500 ºC. The analysis showed that both methods have acceptable accuracy to predict primary, secondary, and tertiary creep behavior for Ti-6Al-4V. However, results indicated that the ν Concept produced a creep curve with better agreement with the experimental data. The technique used for obtaining parameters is promising and should be improved for future research.

Resumo em Inglês:

The objective of this research was the sustainable development of pullulan and its structural and rheological characterization. In addition, the cultivation of the A. pullulans Y2092 strain by submerged fermentation on a laboratory scale was evaluated, valuing the use of industrial waste (residual brewery's yeast), RBY, and a low-cost renewable raw material VHP (very high polarization sugar). A 22 factorial statistical design of experiments was used to analyze the molecular weight of the pullulans produced. The maximum value of 1955 kDa was determined for the pullulan recovered after 96 h of fermentation in the mineral medium added with 70 g/L of VHP and 50 g/L of RBY. The FTIR analysis for the pullulan obtained was similar to the commercial pullulan. The rheological behavior of pullulan solutions is shown, evidencing the relationship between this property and Mw. The results from all analyses indicate that the pullulan obtained is suitable for the future production of biopolymeric films.

Resumo em Inglês:

Cellulosic materials have several applications, from rheological modifiers to structural reinforcement and packaging components. Using cellulosic materials may also contribute to environmental sustainability because it can be sourced from agricultural byproducts. In this work, self-sustained composite films were produced by the casting of TEMPO-oxidized cellulose nanofibers/graphite composite dispersions. Oscillatory rheology and tensile strength tests showed that the presence of graphite did not significantly contribute to the enhancement of neither the rheological nor mechanical properties of the dispersions and films. Morphological analysis showed that particle segregation and setting occurred during film casting, resulting in particle concentration gradient along the thickness of the film. These results could indicate the low exfoliation efficiency of the microfluidization process and, therefore, justify why the graphite did not act as a reinforcement of the cellulose matrix. However, the graphite particles contributed to a higher barrier to water vapor permeation of the cellulosic films.

Resumo em Inglês:

This study evaluates the influence of milling on the reactivity of drilling cuttings (DC) utilized as supplementary cementitious material in ternary cements (TC). The drilling cuttings milling study varied the time (2, 5, 10, 15, and 20 min) and rotation speed (200 and 300 rpm), determining the specific milling energy and grindability index. The hydration of TC pastes containing DC with different particle size distributions was evaluated by isothermal calorimetry during the first 72 hours, XRD/Rietveld at 3 and 28 days, compressive strength and absorption. The incorporation of milled DC improved the TC hydration kinetics compared to reference pastes of ordinary Portland cement (REF.PC). After 28 days, the TC pastes with the D50% diameter smaller than 11 µm reached at least 70% of the resistance to the strength of the Portland cement paste. Milled DC contributes to the physical and nucleation effect of the TC pastes studied and can be used as an SCM.

Resumo em Inglês:

Concrete structures are susceptible to several factors during their life cycles, which can cause various problems. This situation can be avoided in many cases if Structural Health Monitoring (SHM) is used. However, such monitoring is often expensive due to the large number of sensors and the use of data acquisition systems (DAQ). In this context, self-sensing cement composites (SSCCs), monitoring themselves without sensors by incorporating conductive fillers in their composition, provide a better piezoresistive effect. In this research, the Arduino platform and analog to digital converters (ADC) modules were tested, and a prototype of a low-cost DAQ was developed for monitoring SSCCs. The devices were analyzed from the compression tests on the mortar specimens, and the results were compared to measurements obtained from the reference equipment (professional DAQ). The results showed a good sensitivity and an adequate correlation between both devices in some cases. It showed that the Arduino platform has the potential to be used in the experimental monitoring of SSCCs, however it needs to be combined with an ADC module.

Resumo em Inglês:

Recycled crumb rubber can be sustainable used in mortar both to mitigate nature aggregate consumption, reducing environmental pollution, as well, to improve the acoustic and thermal performance of buildings, without damaging its mechanical properties. This paper explores workability, microstructure, mechanical, thermal and acoustic properties considering increasing contents of crumb rubber (0%, 5%, 10%, 15% and 20% replacement, by volume, of fine aggregate). Mortar characterization tests were carried out in the fresh and hardened state. It has been found that replacing the aggregate with scrap tyre rubber reduced the compressive strength on average 12% and 67% and for tensile strength 35% and 53%, for the contents of 10% and 20% respectively, compared to the reference. Furthermore, it was found that the reductions in thermal conductivity reached 16% and 29% and an increase in acoustic attenuation on average 12% and 13%. Moreover, scanning electron microscopy images were analyzed, justifying the mechanical results obtained. Although the experimental results indicated that the workability and mechanical strengths decreased with the increase of rubber replacement rate, the studied mixtures met the standard specifications, and thus suitable for walls and ceilings coating applications, improve the acoustic and thermal performance of buildings and as a sustainable material.

Resumo em Inglês:

The use of steel fibers in concrete affects its rheological properties in the fresh state and increases its energy absorption capacity in the hardened state. Rubber fibers come from tires and when incorporated into concrete, they promote an improvement in its damping factor. This work aimed to evaluate the use of rubber fibers on the mechanical properties of concrete reinforced with steel fibers. The evaluated properties were: compressive strength, tensile strength, static and dynamic modulus of elasticity and damping. The mixes of the tested concretes varied the consumption of steel and rubber fibers. From the results found, it can be seen that the rubber associated with steel fibers within the concrete mixtures improves the damping rates of the material.

Resumo em Inglês:

Mortars containing phase change materials (PCMs) were tested to determine their applicability to the thermal control of buildings. One mini-wall prototype was coated with mortar without PCM, whereas the three other prototypes were coated with mortar added with 5%, 10%, and 15% PCM. All specimens were subjected to visual analysis, scanning electron microscopy coupled with energy dispersive X-ray analysis, and differential scanning calorimetry. Thermal analysis was conducted using K-type thermocouples under irradiation by 1000 W halogen lamps. Compared with the other samples, the sample containing 15% PCM required more water in the mixture to achieve a good consistency. Compared with the reference mortar containing 0% PCM, specimens containing 5%, 10%, and 15% PCM showed greater thermal delay. The results of this study reveal that the use of PCM in buildings might lead to significant energy savings.

Resumo em Inglês:

Plate structures are widely used in civil engineering, for instance, as slabs, foundations, and retaining walls. In structural acoustics, flexural wave control becomes an important parameter for the safety of engineering thin structures. Metaconcrete is a new type of concrete where conventional aggregates are replaced by resonant aggregates, made of a solid core coated with a compliant material, which presents wave attenuation properties. Hence, the aim of this paper is to evaluate the band structure of flexural waves in a metaconcrete, using the thin plate theory associated with the improved plane wave expansion (IPWE) method. The effect of aggregate geometry, core density, Young's modulus of the coating, and number of layers are analyzed. Complete bandgaps are observed for almost all inclusions. The results reveal the possibility of adjusting the desired frequency range according to the configuration of the resonators for flexural vibration management through metaconcrete thin plates.

Resumo em Inglês:

Novel civil construction materials based on waste can be an optimal alternative for waste management, reducing its improper disposal while engaging an otherwise discarded material as a raw material in other production processes. This research’s main objective was to develop and characterize two novel artificial stones based on waste glass from bottles and aggregated with epoxy resin (ASG-EP) and polyurethane resin (ASG-PU) from castor oil, respectively, as well as the comparison of the two developed materials. Plates were manufactured with 15% of epoxy or 15% polyurethane resins and 85% of waste glass from bottles. The mixture was molded with a process of 6Hz vibration, 600mmHg of vacuum, and hot compaction at 90ºC for EP and 80ºC for PU. Results evidenced that the development of ASGs based on waste glass from bottles is technically and economically viable.

Resumo em Inglês:

The incorporation of oxygen and/or nitrogen into the titanium lattice has garnered significant attention due to the broad spectrum of intermediate properties that can be achieved between TiN and TiO2. This article delves into the investigation of surface modification of titanium through plasma-assisted thermochemical treatments employing H2-N2-O2 mixtures. The flow rate of the reducing gas (H2) remained constant at 24 sccm, while the flow rates of N2 and O2 were adjusted to yield a total flow rate of 60 sccm. Analysis using GIXRD, Raman spectroscopy, and XPS demonstrated that TiN exhibits stability exclusively in an oxygen-free atmosphere, while TiO2, in contrast, necessitates an oxygen flux equal to or exceeding 18 sccm for stability. Furthermore, it was found that the presence of nitrogen in the plasma atmosphere resulted in a greater expansion of the α-titanium lattice, although the solubility of interstitials decreased. These findings highlight the potential for a controlled approach to producing solid solutions or titanium oxynitrides.

Resumo em Inglês:

Alkali-activated binders (AAB) are inorganic materials produced by a mixture between a solid precursor and an alkaline activator, wherein, the reaction results in a material with properties similar to Portland cement hydration. The advantages of AAB over Portland cement are the possibility of using alternative materials, demanding low energy and low CO2 emission. The primary objective of this study was to produce an alkali-activated binder (AAB) using calcined wood waste ash (CWWA) as a solid precursor due to its beneficial properties. CWWA was obtained by burning wood wastes in a furnace, then calcined in a laboratory oven at 600 °C to remove unburned particles. Afterward, the ash was milled and then physiochemically characterized by chemical composition, X-ray diffraction (XRD), particle size distribution, and scanning electron microscopy (SEM). The milled CWWA was employed in AAB mortars and pastes activated with sodium hydroxide (NaOH) to assess the influence of alkaline activator concentration. In this work, the Na+ concentrations varied in the 6.5-12.5 mol.kg-1 range. Mortars were assessed by compressive strength, whereas pastes were analyzed by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDS) for samples cured after 7 days at 60 °C. Results showed that the CWWA is mainly composed of SiO2 (67.9 wt%) and the presence of an amorphous phase and quartz as the main crystalline phase (XRD). The compressive strength of mortars showed that the CWWA activated with a Na+ concentration of 6.5 ml.kg-1 achieved the highest compressive strength (23.2 ± 1 MPa). Microstructural studies of pastes showed the formation of sodium carbonate (XRD) and reaction products (FTIR) in a dense microstructure (SEM/EDS). Hence, the key findings suggest that employing CWWA as a solid precursor offers a viable choice for producing a more sustainable AAB.

Resumo em Inglês:

The inadequate disposal of waste tires has caused environmental and public health problems. One of the direct harmful effects is the noise due to traffic. Waste rubber has been used in concrete to improve its acoustic performance and energy absorption. Studies carried out by the U. S. Federal Highway Administration show that barriers, regardless the material used, do not block completely but can reduce the volume of traffic noise by half. This study proposes concrete mixes containing waste tires and vermiculite to verify their acoustic properties for road barriers. The experiments include concrete with waste tires and vermiculite to replace the sand mass from 10% to 40%. An improvement in the acoustic properties was observed, reducing the total sound intensity level of the concrete acoustic barrier to 20 dB and 29 dB, for the frequencies of 500 Hz and 1000 Hz, respectively.

Resumo em Inglês:

This article studies the fatigue behavior of the Al-5wt%Si-2.5wt%Cu alloy. The effect of combining techniques of chemical grain refining (Al-5wt%Ti-1wt%B alloy) added to electromagnetic stirring, CGR+EMS, is demonstrated in this work. This combination produced a microstructure with reduced grain size (121 ± 20 µm) when compared with the raw material produced only by electromagnetic stirring, EMS, (213 ± 38µm), with grain refiner Only, CGR, (184 ± 23 µm) or Without any Grain Refining Technique (WGRT) (413 ± 96 µm). The condition produced by associating electromagnetic stirring with the Al-5wt%Ti-1wt%B grain refiner presented the smallest grain size and less porosity. Thus, conditions CGR+EMS and WGRT were chosen to continue the evaluation of the mechanical performance of the studied alloy via tensile tests, whose results for ultimate tensile stress, yield strength and elongation were, respectively, WGRT/ CGR+EMS, UTS = 160.3 ± 9.5 / 208 ± 10 MPa, YS (0.2%) = 110 ± 2 / 135 ± 3.5 MPa and ε(%) =3.2 ± 0.1 / 2.9 ± 0.1. Fatigue tests were conducted via the staircase method. The average estimate of fatigue strength for a given life (107 cycles) and the standard deviation calculated for WGRT and CGR+EMS condition were, respectively, μ^y = 60.1 MPa / 71.6 MPa and σ^y= 3.30 / 6.42.