Resumo em Inglês:

This work aims to deposit silica (SiO2) on polyamide 6,6 fabrics by hybrid corona-dielectric barrier discharge plasma at atmospheric pressure. The reactor used, developed at the Laboratory of Plasma and Processes of the Aeronautics Institute of Technology (LPP/ITA), allows the treatment of fabric surfaces by activation and plasma deposition processes, aiming, in this order, the alteration of wettability and the deposition of silica on its surface, using a silicic acid solution (Si(OH)4) as a silica precursor. The morphology of the deposited films was evaluated by scanning electron microscopy (SEM). To identify the chemical modifications generated by the plasma treatment, the untreated and treated samples were analyzed by Fourier transform infrared spectroscopy with attenuated reflectance (FTIR-ATR) and Energy Dispersive Spectroscopy (EDS). The thermal behavior of the treated and untreated samples was evaluated by Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Additionally, X-ray diffraction (XRD) was also used to identify crystalline phases in the film. The results showed that plasma processing proved to be an effective technique for modifying the surface characteristics of polyamide 6,6.

Resumo em Inglês:

This study presents a detailed analysis of the feasibility of Ti-15Mo alloy for coronary stents by independently applying the TOPSIS and RADAR multi-parameter selection methods independently and comparing the results obtained. The research focused on evaluating β-metastable titanium alloys for use in coronary stents, employing the TOPSIS and RADAR methods for a comprehensive and independent analysis. The independent application of these methods enabled for a robust and detailed comparison between different candidate materials, considering crucial criteria such as mechanical strength, biocompatibility, and cost-effectiveness. The results showed that the Ti-15Mo alloy excelled in terms of safety and mechanical performance in both methodologies, offering a combination of mechanical properties and biological compatibility suitable for this application. Compared to 316L stainless steel and Co-Cr L605, Ti-15Mo consistently outperformed across multiple criteria. This study positions Ti-15Mo as a promising candidate for coronary stents and emphasizes the effectiveness of combining TOPSIS and RADAR methodologies for comprehensive material selection in biomedical applications. The research underscores the importance of detailed and methodological evaluation to optimize the performance and safety of advanced biomedical devices.

Resumo em Inglês:

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

Resumo em Inglês:

We followed the microstructural evolution of UNS S32205 duplex stainless steel during cold rolling up to 79% reduction in thickness and at early stages of isothermal annealing at 1080ºC. Qualitative analysis of peak broadening and kernel average misorientation (KAM) parameter obtained by X-ray diffraction (XRD) and electron backscatter diffraction (EBSD), respectively, indicated a higher work hardening of austenite. Strain-induced martensite was not detected within this strain range by using X-ray diffraction and DC-magnetisation measurements. Two particular rolling thickness reductions were chosen for recrystallisation studies; i.e., 43% and 64%. After annealing for 1 min, primary recrystallisation occurred in ferrite (42% of recrystallised grains for 43% cold rolling), whereas austenite only recovered. For a reduction of 64%, the recrystallised fraction of ferrite did not change significantly, while austenite reached a recrystallised fraction of 43%. Full recrystallisation is noticed after annealing for 3 min for both conditions resulting in a bamboo-like grain structure.

Resumo em Inglês:

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

Resumo em Inglês:

Zirconia-toughened alumina (ZTA) is a promising material for dentistry; however, its current formulation exhibits a mauve coloration. This study aimed to synthesize a white ZTA ceramic by doping it with 0.7 wt% magnesium oxide (MgO). Specimens (1.2 mm in thickness x 12 mm in diameter) were divided into 3 groups (n = 15): ZTA doped with chromium oxide (ZTA-Cr2O3), ZTA doped with MgO (ZTA-MgO) and ICE-Zirkon (control group). The materials were analyzed using X-ray diffraction, energy-dispersive X-ray fluorescence spectrometer, scanning electron microscopy, and spectrophotometer. Biaxial flexural strength was conducted, and the Weibull modulus (m) and probability of failure were calculated. ZTA-MgO group had a white color, showing the pattern for alumina and zirconia grains in ZTA with a typical composition of the materials. It demonstrated superior BFS (915 ±41 MPa) and higher reliability than the ZTA-Cr2O3. ZTA-MgO proved to be able to produce white ZTA for future use in dentistry.

Resumo em Inglês:

Hybrid metal matrix composites (MMCs) have a higher potential for widespread use in structural engineering and functional device applications because they show better overall mechanical and functional response than their conventional equivalents. Silicon Carbide (SiC) and Yttrium Oxide (Y2O3) reinforced Copper hybrid composites were produced by powder metallurgy (PM) process sequence. Both the reinforcements were included in the wt. % of 2.5, 5.0 and 7.5. The homogeneous presence of SiC and Y2O3 particles in copper MMC’s was confirmed by morphology and characterization studies. The blended milled powders were produced in the form of cylindrical billets using a punch and die arrangement, by cold compaction method at 400 MPa pressure, in a hydraulic press. Sintering was carried out at 900°C for 5 hours in a Box furnace. The inclusion of SiC and Y2O3 in the copper matrix composites improved the density, hardness, compressive strength (CS), wear resistance and decreased the corrosion rate (CR).Pin on disc (POD) experiments was conducted to study the wear behavior of the composite samples. The minimum wear rate (WR) 3.31049 x 10-4 mm3/m was obtained for the composite contain 7.5 wt. % of SiC and 7.5 wt. % of Y2O3.

Resumo em Inglês:

The present study investigates friction stir welded AA6065-10% Al2O3MMC by incorporating varying percentages of heat treated biosilica. The biosilica is first extracted from waste cassava peel, and it is heated under 1500°C, to get properly arranged crystalline structured biosilica particle. During friction stir welding process, the biosilica particle is dispersed around the welded zone, which in turn impacts load carrying capacity of the material. The study revealed that 3 vol.% of biosilica infused FSW composite ‘C’ shows maximum tensile strength of 276 MPa, yield strength of 238 MPa, impact energy of 20.8 J, elongation of 5.2%, fatigue strength of 176 MPa. Further, the 5 vol.% of biosilica infused FSW composite ‘D’ shows hardness strength of 121 Hv. Additionally, it has been discovered under microstructural analysis that the inclusion of fine-grained heat-treated biosilica exhibits the greatest dispersion of biosilica within the nugget zone, heat affected zone, and thermo mechanically affected zone, which affects the composite's overall strength characteristics. Thus, because of their less dense, better thermo mechanical properties, it could be influenced in areas where joint application, load bearing are needed such as aerospace, heavy industrial, infrastructural, transport and military sector.

Resumo em Inglês:

Materials based on doped ceria are considered promising elements for applications in solid oxide fuel cells (SOFCs). Cerium oxide can be classified as a mixed conductor. The type of dopant also greatly influences properties of doped ceria. Hence, studying the type of dopant to be used in the synthesis process is of great importance. Recent studies have shown that the lanthanide or alkaline earth ions are the most commonly dopants used in ceria. In order to obtain nanometric powders, which favor the catalytic effect and are more reactive than other powders, a technique of obtaining powders via solution combustion synthesis (SCS) was selected, and the type of fuel used, and its excess (content) were analyzed. The parameters that were varied in this study were related to the dopant (Ce(1-x) La(x) O(2- δ), where x = 0.1, 0.2, 0.3) and the type of fuel used (urea or sucrose) The powders were characterized by thermogravimetric analysis (TGA), X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). In the TGA, a significant increase in the remaining mass loss was observed with an increase in the dopant content when both urea and sucrose were used. The SCS method enabled the production of lanthanum oxide doped ceria phase using both fuels. The XRD of the samples obtained using urea as fuel exhibited well-defined, narrow, and intense peaks immediately after synthesis, and this characteristic was maintained after thermal treatment. On the other hand, the use of sucrose as fuel enables the production of the same cristalinity after thermal treatment at 850°C. In addition, these samples had a higher specific surface area and smaller crystallite size compared to those obtained using urea as fuel.

Resumo em Inglês:

Aluminum Metal matrix composites (AMMCs) have gained significant attention in the automotive and aerospace industries due to their outstanding mechanical properties, combined with their lightweight and fuel-efficient characteristics. AMMCs have also garnered significant attention from researchers due to their potential to minimize the wear of counter face materials. This study investigates the dry sliding wear behavior of aluminum-based hybrid MMCs using an experimental approach. Friction Stir Welding (FSW) has emerged as a promising solid-state technique for welding AMMCs. The FSW experiments were designed using a Central Composite Rotatable Design (CCRD) with four factors and five levels. Empirical models were developed to predict the influence of FSW process parameters including tool rotational speed (TRS), Welding Speed (WS), Axial Load (AL), and the percentage of Boron Carbide (B4C) reinforcement on key properties such as wear rate and wear resistance of the AMMCs. The developed regression model was developed to minimize the wear rate using response surface methodology (RSM) method and predicted wear rate is found to be 154.21 x 10-5 mm3/m. The maximum percentage errors for predicting optimal Wear Rate, and Wear Resistance (WR) were + 5.39%, and + 2.65%, respectively. The wear resistance of the AMMCs was also improved by following Friction Stir Welding (FSW).

Resumo em Inglês:

This study aims the applicability and efficacy of a new DC water plasma method at low temperature, for the sterilization of titanium contaminated samples and its effects on the surface oxide layer and morphological structure. The plasma treatment was carried out at a temperature of 60°C, for a predefined time of 10 minutes. Water vapor was generated from distilled water and polarized at -700 V during plasma-on period. Elemental analysis revealed that Ti surfaces showed a complete absence of organic and inorganic molecules (0% at detected /0.1% sensitivity) and complete bacteria elimination. Additionally, the oxygen content remained around 8% indicating a positive outcome for bioactivity titanium surface due to oxide presence. Initial results support that the water plasma system enables effective elimination of surface microorganisms while enhancing the natural oxide layer make up of titanium using a low temperature and water-based sterilization system that can be envisioned for clinical use.

Resumo em Inglês:

Calcium addition to steels normally aims at modifying inclusions to improve castability and cleanliness. This study investigated the inclusion modification efficiency in liquid steel for three conditions varying injection timing: all Ca after RH degasser, all Ca before RH degasser and split addition. Six industrial heats were produced at Usiminas Steelworks, two for each condition. The heats were sampled for automated SEM/EDS inclusion analysis and total oxygen and the results compared to computational thermodynamics simulations. Inclusion modification was most efficient for the split addition condition. This condition was the closest to the calculated castability window, resulting in low inclusion density, a higher percentage of liquid inclusions during casting and lower CaS formation. Furthermore, computational thermodynamic simulations and inclusion analysis presented good agreement. These findings not only enhance the understanding of calcium treatment in steel production but also provide practical insights for optimizing the calcium addition process.

Resumo em Inglês:

In this paper, four negative re-entrant hexagonal honeycomb (NRHH) porous scaffolds with different extension angles θ (15°, 30°, 45° and 60°) cell structures were designed and their preparation was accomplished by selective laser melting (SLM) in 3D printing technology so that Negative Poisson Ratio metamaterials could be applied to bone implants to treat bone defects. The effects of structural design on residual stress, surface roughness, and compressive properties of NRHH porous scaffolds were evaluated by finite element analysis and experimental analysis. The results showed that the 15°-NRHH porous scaffold exhibited optimal performance. When the θ angle increased, the scaffold introduced increased residual stresses, increased surface roughness, generated increased deformation, stress, and strain, and decreased compressive performance.

Resumo em Inglês:

Volatile corrosion inhibitors (VCIs) are used to protect metal objects temporarily, such as during storage and transport. Although widely used, in the last two decades traditional synthetic VCIs have been gradually replaced due to their high toxicity. A viable solution is the use of natural inhibitors. The objective of this study was to evaluate the efficiency of limonene-based natural VCI to protect AISI 1020 carbon steel against corrosion. The vaporization capacity of VCI was evaluated by the standardized sublimation test; the ability to form a protective barrier was analyzed by testing kraft paper as anticorrosive packaging; and the inhibition mechanisms against carbon steel corrosion were investigated by electrochemical methods of open circuit potential (OCP) measurement, potentiodynamic polarization (PP) and electrochemical impedance spectroscopy (EIS). According to the sublimation test, limonene-based VCI provided effective protection to the carbon steel at a concentration of 1.5 g/L. The kraft paper test confirmed the efficiency of the temporary use (4 days) of the natural VCI in packaging, without residue deposition. Furthermore, through electrochemical measurements, we found that limonene-based VCI provided an inhibition efficiency of 99% to AISI 1020 carbon steel in a 3.5% NaCl aqueous solution, thus identifying a potential alternative to toxic synthetic VCIs.

Resumo em Inglês:

This study investigated the kinetics and thermodynamics of starch acetylation and examined the influence of the degree of substitution (DS) on the properties of acetylated starches. Starch acetylation kinetics followed a pseudo-first-order model, reaching a degree of substitution of 2.62 after 50 minutes. Negative enthalpy and entropy values revealed a non-spontaneous reaction requiring catalysis. Fourier Transform Infrared Spectroscopy confirmed acetylation through the appearance of a carbonyl band and the reduction of the glycosidic bond peak. Increasing degree of substitution caused granule breakage, agglutination, and reduced crystallinity, as evidenced by Scanning Electron Microscopy and X-Ray Diffraction. Dynamic Mechanical Analysis demonstrated that these structural changes reduced the glass transition in high degrees of substitution (DS 2.62) and enhanced thermal stability and viscoelastic properties due to the loss of crystallinity. Understanding these processes facilitates the industrial optimization of starch acetylation, resulting in modified starches with improved properties for diverse applications.

Resumo em Inglês:

This study investigates the impact of porosity on the mechanical properties of aluminum matrix composites reinforced with ceramic particles, focusing on the optimization of volume fraction and porosity to enhance tensile strength. Using Finite Element Analysis (FEA) and Analysis of Variance (ANOVA), the effects of varying volume fractions (5%, 10%, 15%, 20%, and 25%) and porosity levels (1%, 2%, 3%, 4%, and 5%) on Von Mises stresses were systematically analyzed. The results demonstrated that as porosity increased, Von Mises stress also increased, while higher volume fractions contributed to better stress distribution and enhanced mechanical properties. Optimization analysis identified the optimal parameters as a volume fraction of 25%, porosity level of 1.01%, particle size of 30.083 µm, and pore diameter of 9.020 µm, achieving a desirability score of 0.895 and a Von Mises stress of 9.06E-08 N/µm2. The ANOVA results confirmed the statistical significance of these parameters, with a P-value threshold of <0.05. These insights are crucial for understanding how to optimize porosity and reinforcement in composite materials, providing valuable guidance for applications in the aerospace and automotive industries, where lightweight and high-strength materials are vital.

Resumo em Inglês:

Given the vast universe of high-entropy alloys (HEAs), solid solution formation (SSF) prediction is increasingly relevant. The processing route leads to uncertainty in the mass of each alloy component, affecting SSF. Furthermore, investigations led to atomic radius modification under interaction with neighboring atoms, also influencing SSF. Therefore, this paper presents an uncertainty quantification framework implemented over the thermophysical parameters calculation (TPC) approach to verify the behavior of the SSF parameters as the mass of the alloy components vary and the atomic radii are modified. The AlCrFeMoNbTaTiVW alloy was subjected to this framework, being the tungsten mass the most influential, and tantalum the less influential overall. Moreover, the atomic radii modification does not work properly under TPC theory, implying in non-SSF prediction even when a solid solution is formed. Thenceforth, equimolar HEAs are now near-equimolar, and the SSF parameters may indicate that some samples of the same alloy batch may result in SSF, others not.

Resumo em Inglês:

Heat dissipation materials with high thermal conductivity (TC) can meet the high demand for improving heat dissipation in high-power IGBT modules. The current study focused on soldering Al-graphite composites (Al-Gr) with a copper (Cu) base plate using an active type Sn-Ag-Ti (SAT) solder. Ultrasonic active soldering (UAS) was performed in air at 250 °C for 30 sec. The relative spreadability rates of the direct UAS process versus conventional soldering were + 276.6% for SAT/Cu and +186.1% for SAT/Al-Gr. After direct UAS, a Cu6Sn5 layer formed at the active solder/Cu interface and Al dissolved into the active solder zone, thus forming a ternary coarse Al-Ag-Sn solid solution in the active solder region. In addition, submicron particles (e.g., Al-Ag-Sn and Ag3Sn) adsorbed on the surface of active solder/Gr interface. The calculated Gibbs free energy results indicated that both solute Ti and Ti-Sn compounds could react with C to form TiC compounds, and TiC reacted with Ti-Sn compounds to form the Ti2SnC phase, which was accelerated with the direct UAS process. The shear strengths were measured to be 31.0 ± 4.1MPa for Cu/SAT/Cu joints, 14.3 ± 3.2 MPa for Al-Gr/SAT/Cu joints, and 12.8 ± 3.8 MPa for Al-Gr/SAT/Al-Gr joints, respectively.

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The mineralization process to reach Tungsten (W) involves several steps to reduce the impurities (residues), which makes the process more expensive. However, it is possible to explore the pure scheelite (CaWO4) and residue doped-CaWO4 on flexible sheets using the Tape Casting technique. In particular, the high frequency dielectric properties of flexible multilayers have an increased appeal in the electronics industry. In this study, we present a systematic investigation of structural, morphological, electrical and high-frequency dielectric properties of flexible ceramics sheet multilayers composed of pure CaWO4 and residue-doped CaWO4. Our findings demonstrate that the dielectric constant has a small dependence on the residue amount, but a remarkable modification in the dielectric constant as the number of layers increases. Here we achieved a 34% increase in the dielectric constant for pure CaWO4 flexible ceramic sheets when the number of layers increased from 1 to 3.

Resumo em Inglês:

Although biocomposite foams have been used as wound dressings, achieving accelerated healing with reduced complications requires precise control of exudate absorption and evaporation. This study evaluated the fluid handling capacity, water vapor transmission, and cytotoxicity of novel chitosan/bioactive glass composite foams. Prepared following a simple process, these foams have up to 60% porosity and interconnected pore networks. Cytotoxicity assays confirmed their non-toxicity to L-929 fibroblast cells. The foams demonstrated a liquid absorption capacity of up to 160%, with improved performance at higher levels of bioactive glass. Fluid handling tests showed effective moisture absorption and transfer, making these dressings suitable for the treatment of wounds such as burns and pressure ulcers. The water vapor transmission test confirmed the ability of the foams to promote high exudate removal rates, suggesting that chitosan/bioactive glass composites are promising for wound dressing applications.

Resumo em Inglês:

Traditional biomaterials like CoCrMo, Ti, and stainless-steel face challenges due to their instability in biological settings. As an alternative, exploring multicomponent alloys is viewed as a viable path for bettering both mechanical performance and biocompatibility. Our research explores the potentiality of the MoNbNiTiZr based alloy for biomedical applications. The microstructural characterization was realized using X-Ray Diffractometry (XRD) and Scanning Electron Microscopy (SEM/EDS). We also conducted Vickers microhardness tests and assessed it’s in vitro biocompatibility and antibacterial action against S. aureus and S. aureus HU25 strains relative to cp-Ti. Our observations denote that this alloy showcases a triphasic structure, consisting of dendritic and interdendritic zones with BCC, HCP, and Laves formations. A microhardness of is approximately 576.5 HV align with values for comparable multicomponent alloys in the biomedical field. Pertaining to its antibacterial efficiency and in vitro compatibility, this alloy manifests commendable antibacterial performance and relevant compatibility in comparison with cp-Ti.

Resumo em Inglês:

This study investigates the effects of different post-weld heat treatments (PWHT) on the mechanical properties and microstructure of ASTM 335 Gr P91 martensitic steel, commonly used in boiler applications. Mechanical tests were conducted at room temperature, 300°C, and 600°C. Two PWHT conditions were applied: (i) PWHT-1, involving a 300°C isothermal treatment followed by heating to 770°C, and (ii) PWHT-2, following the same profile but without cooling to room temperature after the initial isothermal step. The resulting microstructure exhibited martensitic features, with a gradient of prior austenite grain boundaries in the heat-affected zone (HAZ) and δ-ferrite formation in the fusion zone (FZ), reducing toughness. Ultimate tensile strength decreased with increasing temperature, ranging from 675–750 MPa (RT), 525–615 MPa (300°C), and 375–440 MPa (600°C). Elongation was highest at 600°C (BM: 25–30%, FZ: 8–20%), decreasing at room temperature (BM: 20–25%, FZ: 2–12%). Toughness tests showed crack propagation across BM, HAZ, and FZ, with the lowest energy absorption in FZ (0.05–0.4 mm, 12–50 J). At 600°C, toughness decreased in BM and HAZ but increased in FZ, suggesting a change in deformation mechanisms at elevated temperatures.

Resumo em Inglês:

Compared with other metal implant materials, titanium has become the preferred material for hard tissue substitutes and restorations. However, titanium implants are bioinert and cannot effectively promote adhesion or proliferation of bone marrow mesenchymal stem cells (BMSCs) after implantation in vivo. In this study, a microporous Cu-doped titanium dioxide (Cu-TiO2) film was prepared on a titanium surface via microarc oxidation. This film not only has a good porous surface morphology, with Cu distributed on the surface of the film, but also improves the surface roughness and hydrophilicity of titanium. In vitro cell experiments revealed that the Cu-TiO2 film has good biocompatibility and bioactivity and enables adhesion and growth of BMSCs. In addition, the Cu-TiO2 film can promote the expression of integrin β1 in BMSCs. This study enhances our understanding of the interactions between titanium implants and cells and provides a theoretical basis for the clinical application of Cu-TiO2 films.

Resumo em Inglês:

This study investigates the torsional fatigue behavior of Ti-15Mo alloy through comprehensive analyses of its mechanical properties, microstructure, fatigue stress-life curves, and fracture surfaces, providing valuable insights into its fatigue characteristics. The hot-forged and air-cooled Ti15Mo alloy exhibited a microstructure predominantly consisting of equiaxial β phase grains, deformation twins, and ω athermal phase. Mechanical testing revealed a microhardness of 347.4 HV, yield and ultimate tensile strengths of 873 MPa, elongation of 20.7%, Young's modulus of 83.7 GPa, ultimate shear strength of 673 MPa, shear modulus of 30.5 GPa, and a fatigue strength limit of 190.2 MPa, as estimated by Basquin's model at 5 x 106 cycles. Fracture analysis indicated that crack nucleation predominantly occurred on the surface under pure torsion loading. In high-cycle fatigue (HCF) tests, cracks propagated at approximately 45° (Mode I), while in low-cycle fatigue (LCF) tests, propagation occurred at around 90° (Mode III). Fracture profiles also revealed significant number of deformation twins and instances of intragranular fracture near the fracture surface.

Resumo em Inglês:

SnO2-based TCO films can decrease the cost of solar cells, but its corresponding ceramic targets are difficult to sintering densification. Therefore, Ta2O5 and ZnO are used to enhance the density and conductivity of targets. The targets have rutile phase structure, dense microstructure and fine grains. The 0.85 wt% ZnO and 3 wt% Ta2O5 doped target sintered at 1500 °C achieve high relative density (>99%) and low resistance (< 50 Ω). The as-designed targets contribute to depositing SnO2-based TCO films by magnetron sputtering.

Resumo em Inglês:

The present study aimed to analyze the effects of the anodization process and addition of silver nanoparticles by sealing process on corrosion resistance and biofilm formation in titanium. For this purpose, CP grade 2 titanium samples were pickled and anodized in Psidium Guajava-based electrolyte, in galvanostatic mode with the application of 0.1 mA/cm2 for 300 s. For the incorporation of silver nanoparticles, the sealing process was used. The sealing of the anodized samples was performed in sodium carbonate solution without and with the addition of 0.25, 0.5, 1 and 2 mM AgNO3, for 30 minutes at a temperature of 75 ºC. The samples were characterized regarding their morphology by Scanning Electron Microscopy (SEM), Energy-Dispersive X-ray Spectroscopy (EDS) and atomic force microscopy (AFM), corrosion resistance by potentiodynamic polarization, and bactericidal action by optical density microtiteration. The anodizing process resulted in the formation of an oxide layer (TiO2), with greater surface roughness and better anticorrosive performance, compared to pure titanium. The sealing process proved to be effective for incorporating silver into the anodized titanium surface, at all concentrations evaluated, inhibiting the proliferation of Escherichia coli and Staphylococcus aureus bacteria, favoring the bactericidal effect.

Resumo em Inglês:

Silica gel was synthesized from rice husk silicate, a sustainable feedstock, and functionalized with Ag, Cu, and ZnO nanoparticles to evaluate the liquid absorption capacity of these nanocomposites and their potential use in active packaging. From a two-level full factorial experiment, where pH, silicate modulus and SiO2 concentration were tested, silicas with varied surface areas (250-750 m2/g) and pore volume (0.4-1.0 cm3/g) were obtained. The silica with the highest porosity (1.0 cm3/g) was synthesized from a solution containing silicate with a modulus of 2.0 and a SiO2 concentration of 20 g/L, by acidification to pH 6. The product obtained showed the highest absorption of water and simulated body fluid (190%) and was chosen as the matrix for functionalization with nanoparticles produced from chemical reduction (Cu, Ag) and precipitation (ZnO) methods. The incorporation of ZnO nanoparticles into the silica matrix had an additional contribution to liquid absorption, at a rate of 0.04%/ppm.

Resumo em Inglês:

This study investigated the mechanical and anti-corrosive properties of two graphene derivatives multi-layer coatings applied to a superelastic NiTi alloy. Several aspects of the coating process and electrochemical characterization remain unclear, including the impact of a multilayer during dip-coating on the final morphology and corrosion resistance of the system. Additionally, the relationship between long-term immersion tests, mechanical cycling and the anti-corrosion performance of these coatings requires further investigation. The coatings were formulated with GO and rGO dispersed in SEBS to be deposited as flexible nanometer films on NiTi wires using the dip-coating technique. The coating characterization was conducted through scanning electron microscopy, atomic force microscopy, X-ray diffraction and energy dispersive scattering. The mechanical performance under superelastic loading-unloading cycles was evaluated using uniaxial tensile tests. Potentiodynamic polarization and electrochemical impedance spectroscopy analyses were employed to assess corrosion. The potentiodynamic polarization results demonstrated an enhancement in corrosion resistance for the coated samples, particularly in specimens coated with rGO. Additionally, electrochemical impedance spectroscopy analysis revealed superior performance of the coating containing GO after 21 days of immersion in a simulated body fluid. These findings represent an advancement in the investigation of the NiTi surface modification by graphene derivatives.

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The Fe-8.2wt.%Cr-0.6wt.%C-Xwt.%Nb surfacing alloys were successfully applied to the substrate of 60CrMnMo steel through the submerged arc surfacing process utilizing a flux-cored welding wire. This study systematically explores the influence of niobium content on the microstructure and properties of these alloys, and delves into the underlying mechanisms. The results show that the microstructure of the surfacing alloy is mainly composed of γ-Fe, α'-Fe, NbC, and Fe-Cr phases. As the niobium content in the surfacing alloy was increased from 0.06% to 4%, the morphology of NbC transitioned from dispersed particles within the matrix to short rod-like structures concentrated at grain boundaries, accompanied by a refinement of the martensite structure. The hardness of the surfacing alloy exhibited an increase of 28%, while its wear rate was halved, resulting in a twofold enhancement in wear resistance. Under identical wear conditions, the wear rate of the experimental 60CrMnMo steel plate was found to be 125 times greater than that of the 4 wt.% Nb surfacing alloy, indicating a significant improvement in wear resistance for this latter alloy. This improvement can be attributed to the rich presence of rod-like NbC in the 4 wt.% Nb surfacing alloy, which is deeply embedded in the martensite matrix and effectively enhances the material, thereby jointly improving overall wear resistance.

Resumo em Inglês:

This study developed a bone cement based on hydroxyapatite (HAp) and magnetically activated with cobalt ferrite (CoFe2O4) and magnetite (Fe3O4) nanoparticles for potential use in orthopedic surgeries like vertebroplasty. Magnetic nanoparticles (MNPs@SiO2) were mixed with HAp in varying ratios (30:70, 50:50, 70:30) and incorporated into a hydrogel matrix of carboxymethylcellulose, glycerin, and distilled water, forming fluid-viscous magnetic cements. These were analyzed through XRD, SEM, swelling degree, pH, setting time, mechanical strength, magnetic properties, and cell viability. XRD confirmed the crystalline phases of each component, while SEM revealed hybrid morphologies with micropores. Cements with higher HAp content exhibited greater swelling in simulated body fluid (SBF) and faster reaction kinetics, with swelling values between 58% and 91%. After 7 days in SBF, the pH stabilized between 7.0 and 7.3, ensuring biocompatibility. Setting times ranged from 12 to 25 minutes, making them suitable for clinical use. Compressive strengths of 28.91 MPa and 30.06 MPa were achieved after 14 days, indicating structural stability. Ferrimagnetic behavior was observed, with magnetizations reaching 27.30 emu/g for magnetite and 31.08 emu/g for cobalt ferrite. All formulations exhibited non-cytotoxic behavior, confirming their safety for biomedical applications.

Resumo em Inglês:

In this study, Al2O3-based ceramics were obtained by 3D extrusion printing using an ink containing carboxymethylcellulose (CMC) and polyethyleneimine (PEI) as additives. The-ceramic pieces were printed using syringes with nozzles of either 0.25 mm or 0.41 mm diameter at a printing speed of 10 mm/s. After drying, the samples were sintered at 1600 °C for 2 hours and characterized for relative density, microstructure, and crystalline phases. The mechanical properties, including Vickers hardness and fracture toughness, were also evaluated. After sintering, groups of samples were re-sintered at 1610 °C with an isothermal plateau of 0 h, 2 h, or 6 h and then characterized. A group of Al2O3 samples, the control group, was processed conventionally (uniaxial pressing→sintering at 1600 °C for 2 hours) for comparative analysis. The results indicate that, under all manufacturing conditions, α-Al2O3 was the only crystalline phase observed. Additionally, the results showed improvements in the mechanical properties of the samples printed by Robocasting after the re-sintering process, regardless of the extrusion nozzle diameter. The relative density increased from 95.3 ±0.4% to 97.4 ±0.3%, Vickers hardness improved from 1322 ±62 HV to 1526 ±45 HV, and fracture toughness increased from 2.3 ±0.4 MPa.m1/2 to 3.2 ±0.6 MPa.m1/2.

Resumo em Inglês:

In this study, we explored the effects of etching on the surface properties and tribological performance of silicone rubber for hydrogen compressor applications. Ceramic particle-coated silicone rubber specimens were etched using a solution of nitric acid and ammonium fluoride for different durations. XRD and Raman analyses confirmed that the etching process did not alter the crystalline structure and molecular bonding of the PDMS matrix. EDS analysis revealed changes in surface composition after etching. The findings demonstrated that extended etching times resulted in the formation of complex surface structures, profoundly modifying the topography and wettability of silicone rubber. These surface alterations influenced the interfacial adhesion with ceramic coatings. However, prolonged etching reduced the optical transparency. Compared to bare PDMS, the ceramic-coated specimens showed enhanced wear resistance. Tribological investigations revealed an initial increase in the friction coefficient with increasing etching duration, followed by a slight decrease for the 30-minute etched specimen. Wear analysis indicated that longer etching times resulted in more severe wear tracks, implying increased surface damage and material loss.

Resumo em Inglês:

Semiconductors films have many applications, energy conversion is one of the main ones. Oxides are often the material used to fabricate these films. Electrophoresis technique can deposit oxides semiconductors at different voltages and time. Films of zinc oxide (ZnO) were electrodeposited on conductive glass, adding weight percentage of tin chloride to improve its photo catalytic properties. The films and cells were characterized by X-ray, UV-Vis and EIS. The characterization showed that higher voltage decreased the band gap value from 3.3 to 3.26 eV, below the average for pure zinc oxide, around 3.30. The films acted as photoanodes in solar cells, with maximum current density of 2.88 mA/cm2 and open circuit of 0.68 V. The synthesis method was efficient and can be used for further reseach into semiconductors’ films and be applied for membranes, photoanodes and other applications.

Resumo em Inglês:

Zirconia woodpile scaffolds (3Y-TZP/PL, n = 20), designed with null inter-filament spacing, were manufactured using the Direct Ink Writing (DIW), an extrusion 3D printing technique. A ceramic ink containing 40%v/v 3Y-TZP powder, 59%v/v PEG (Polyethylene glycol)/Laponite ink, and 1%v/v DBP (Dibutylphthalate) was used. For 3D printing, we used Ø 0.63 mm nozzles, a printing speed of 10 mm/s, a cross-layer deposition strategy, and no air gaps between filaments. The scaffolds were sintered at 1550 °C for 2 h. The mechanical characterization involved measurements of X-ray diffraction, scanning electron microscopy, Vickers microhardness, Vickers nanohardness, and modulus of elasticity and compressive strength. The sintered samples showed predominantly the ZrO2-tetragonal phase and a microstructure characterized by a bimodal distribution of grain sizes. The samples had a relative density of 90.1 ±1.5%, a Vickers microhardness of 1172 ±45 HV, a Vickers nanohardness of 1608 ±78 HV, a modulus of elasticity of 203 ±16 GPa, and a compressive strength of 192 ±54 MPa. The results showed that DIW processing followed by proper sintering is a promising method for making zirconia scaffolds for biomedical applications.

Resumo em Inglês:

This research examines the effect of thermal power plant desulfurization by-products on pipeline carbon steel alloy corrosion dynamics in soil aqueous solutions to improve soil properties and decrease carbon steel pipeline corrosion rates. Electrochemical tests such as chronopotentiometry, potentiostatic polarization, and electrochemical impedance spectroscopy (EIS) assessed corrosion behavior. Adding desulfurization by-products to soil solutions (DBS) created a transpassive layer during potentiostatic polarization, with a passive current density of about 10μA.cm-2. EIS measurements showed a substantial increase in polarization resistance, with the DBS exhibiting nearly 700 times higher resistance than the standard soil solution (SSS) at 0V (OCP). Raman spectroscopy identified lepidocrocite (γ−FeOOH) in the DBS-treated coupons, while maghemite and akaganeite were found in chloride-enriched conditions.AFM analysis indicated heightened surface roughness with DBS addition, especially with NaCl. XRF and FTIR spectroscopy of the waste products identified them as primarily composed of silica, aluminosilicates, and oxides of calcium, magnesium, and aluminum. The results elucidate DBS's impact on soil corrosion and suggest methods to mitigate corrosion in industrial and environmental contexts. This study enhances the understanding of buried pipeline corrosion mechanisms and presents a new use of thermal power plant waste for corrosion protection.

Resumo em Inglês:

Polyhydroxybutyrate (PHB) is a crystalline and linear biopolymer that is biodegradable and biocompatible. However, due to its high crystallinity, PHB is rigid and brittle, limiting its applications. The brittleness of PHB can be reduced by incorporating reinforcing fillers. In this context, this study aimed to produce biodegradable composites based on a PHB matrix and mica, as a filler. Scanning electron microscopy (SEM) revealed the lamellar structure of mica within the PHB matrix. Fourier-transform infrared spectroscopy (FTIR) confirmed characteristic mica vibrations, while X-ray diffraction (XRD) identified crystalline phases from both PHB and the filler. Differential scanning calorimetry (DSC) demonstrated mica’s effect on crystallinity. Thermogravimetric analysis (TGA/DTG) showed increased thermal stability, with Tonset rising from 144 °C (pure PHB) to 212 °C (PHB/mica 12%) and Tmax from 207 °C to 260 °C. Tensile testing indicated reduced stiffness, from 413 MPa (pure PHB) to 333 MPa (PHB/mica 12%). These findings highlight mica’s role in modifying PHB’s structural, thermal, and mechanical properties, addressing gaps in the literature regarding this composite system.

Resumo em Inglês:

In this research study, Aluminium-based alloy (AA6092) reinforced with 3 wt.% Boron Carbide (B4C) and 5 wt.% Zirconium dioxide (ZrO2) particulates was fabricated into Aluminium Metal Matrix Hybrid Composites (AMMHCs) via stir casting. These AMMHCs were subsequently friction-stir welded under various conditions to optimize the ultimate tensile strength (UTS) and weld nugget hardness (WNH) of the welded joints. This innovative AMMHC material is replacing the AA6061, and AA6082 composites for the applications like bulkhead partitions in ship hulls since this AMMHC has superior properties such as reduced weight, enhanced specific strength, and lower thermal expansion coefficient. To optimize the performance of friction stir welded butt joints in AA6092/3% B4C/5% ZrO2 composites, key Friction Stir Welding (FSW) process parameters including Tool Rotational Speed (TRS), Welding Speed (WS), Axial Load (AL) and Tool Tilt Angle (TTA) were examined. In this research work, empirical relationships were established between the most influential parameters (TRS, WS, and AL) and the resulting responses (UTS and WNH). A desirability function approach was employed to predict optimal values for UTS and WNH, leading to recommended process parameters of 1279.18 rpm for TRS, 53.54 mm/min for WS, and 4.9 kN for AL and TTA for 1.5°. The calculated UTS, and WNH values of 513.09 MPa and 194.92 HRB, respectively, were subsequently validated through experimental verification.

Resumo em Inglês:

Metallic cobalt is valued for its thermal and corrosion resistance. In 2018, cobalt prices surged to 95,250 USD/t, fueled by the growing electric vehicle market. However, metallurgical challenges persist, including cost reduction and impurity control. Manganese, a frequent impurity in cobalt electrowinning from laterite and copper ores, can reach up to 560.6 mg·L−1 in leach solutions. Though solvent extraction removes ~90% of manganese, residual amounts impact current efficiency (CE), specific energy consumption (SEC), and deposit quality. Electrowinning tests at 200 A·m−2, 60°C, and pH 4 showed that 0.12 g·L−1 Mn2+ increased CE to 92.2% but raised SEC to 1.96 kWh·kg−1. Mn2+ altered deposit morphology, reducing microhardness and increasing brittleness. Thermogravimetric analysis revealed ~1.35% mass loss in deposits with Mn2+, while higher concentrations enhanced residual strain and enlarged crystallite sizes. Deposits exhibited primarily hexagonal close-packed (HCP) structures with occasional face-centered cubic (FCC) phases.

Resumo em Inglês:

Homogeneous and stable ceramic suspensions with high solids loading and low viscosity pose a significant challenge in vat photopolymerization additive manufacturing, once solid particles tend to increase viscosity. Instead, organic materials can contribute to decrease viscosity and post-sintering shrinkage. A base suspension was formulated using PEGDA along with dispersant DISPERBYK-111 (3 wt.% of the monomer powder), zirconia powder (40 vol.%), n-methyl-2-pyrrolidone (10% vol.), and a photoinitiator (2 wt.% of the monomer). The introduction of 10 vol.% solvent resulted in a 22.6% reduction in the suspension viscosity. The average post-sintering shrinkage measured 26.11% across all three dimensions. Sintered components exhibited an average density of 5.95 g/cm3 and an average flexural strength of 256 ± 49 MPa. Additionally, the parts demonstrated anisotropic tribological behavior, low porosity and low surface roughness for polished (Ra 0.032) and untreated (Ra 0.33) surfaces. It was concluded that incorporating minimal amount of solvent into ceramic suspensions does not adversely affect their rheological and mechanical properties, while ensuring satisfactory surface quality of the sintered components.

Resumo em Inglês:

AA6060 aluminum is an alloy widely used in the electrical and marine industries. However, its corrosion resistance can be compromised in certain aggressive environments. This study examines the combined effect of magnetic field and imposed potential on the corrosion of AA6060 aluminum wire in seawater. Electrochemical tests and surface analyses were carried out in free immersion, in the presence of a magnetic field, under an imposed potential, and in the simultaneous presence of a magnetic field and an imposed potential. The corrosion kinetics and the mechanisms involved were analyzed by mass loss measurements and microscopic observations.

Resumo em Inglês:

This study investigates the microstructural and crystallographic changes in a novel Nb-enhanced, Ti-reduced maraging steel. The hot-rolled steel was solution annealed at two different temperatures followed by aging. The Electron Backscatter Diffraction (EBSD) analysis of hot-rolled sample revealed a predominant {112}//RP texture, reoriented to {110}//RP during aging to minimize internal energy and stress. Solution annealing at 820oC followed by aging favored a {111} orientation, resulting in minimal crystallographic defects and grain distortion. In contrast, higher solution annealing temperatures promoted the formation of {001} cleavage planes, increasing brittleness and crystal defects, thereby impacting the material's suitability for high-performance applications.

Resumo em Inglês:

Based on the sol-gel titration technology, a novel process method to prepare the ZrO2 beads with the advantages of 130 nm grains and no pores is proposed. These advantages can greatly improve the bead density and hardness, decline the sintering temperature. Furthermore, the proposed method can prepare different types of the beads whose diameters range from 0.1 mm to 0.8 mm, and with uniform size and well spherical type. The density of the bead tested results mainly concentrate on 6.04 g/cm3, and the hardness on 1280 HV. The SEM investigation results illustrate that the bead grains are evenly distributed. The surface and cross section of the bead grains are consistent, no pores exist among the grains of finely polished section. The XRD tested results demonstrate that no monoclinic phase exists in the bead. The bead sintering temperature is only 1250 °C.

Resumo em Inglês:

The role of the CTAB concentration (0.0 M, NS; 5x10-4 M, ½CMC; 2x10-3 M, 2CMC) and the residence time on the composition, morphology and magnetic properties for the nickel nanoferrite formation by hydrolytic stripping (33% v/v naphthenic/kerosene) at 200°C were studied. X-ray, SEM/EDS, FTIR, VSM, and ICP/OES were used to characterise solids and solutions. Regardless of the experimental conditions, all samples present nickel spinel ferrite as the only phase, with similar Fe/Ni molar ratio. However, those precipitates in the presence of CTAB show more homogeneous morphology than in its absence. CTAB at high concentration (2CMC) increases the discharge rate, reaching 100% at 40 min; 14.79 nm average size nanoparticles were obtained, with better magnetic properties (Ms=53.02 emu/g and Hc=35.59 Oe) than those achieved at low concentration (½CMC) and in the absence of CTAB.

Resumo em Inglês:

The optical properties of polyvinyl alcohol (PVA) doped with copper chloride II (CuCl2) were studied. The copper chloride was added to polyvinyl alcohol with different concentrations (0, 1, 3, 5, 7, and 12 wt.%). The PVA:CuCl2 films were prepared using the casting techniques. The absorption and transmission spectra have been recorded in the wavelength range (300-800) nm by using UV-VIS spectrophotometer. The fundamental optical parameters such as optical band gap energy, refractive index, extinction coefficient, and dielectric constants have been investigated. Results show that by adding copper chloride to PVA, the optical parameters (refractive index, extinction coefficient, real and imaginary dielectric constant) are increasing with the increase of concentrations of CuCl2 While the optical band gap energy decreases. The single oscillation energy E0 and the dispersion energy Ed were determined by using the Wemple-DiDomenico model. The results show that E0 and Ed values increase with increasing the dopant CuCl2 concentration.

Resumo em Inglês:

Amongst numerous traditional coatings to protect internal surfaces, Diamond-Like Carbon (DLC) films attract significant interest from many industries, due to the ability of these coatings to overcome the toxic and/or environmentally unfriendly aspects of some common deposition techniques, especially electroplating. In addition, DLC coatings can be used to reduce corrosion, wear and importantly, abrasion on the inside of components, providing improved efficiency and prolonged lifetime. This work evaluates the performance of hydrogenated and silicon DLC coatings deposited by Plasma-Enhanced Chemical Vapour Deposition (PECVD) on carbon steel in terms of their erosion and electrochemical corrosion resistance. Erosion studies were conducted in a saline solution under different velocities and sand concentrations - modelling the direct impingement of high velocity, sand-laden fluid encountered in multiphase equipment flow. These experiments showed that for all impingement velocities, the Si-DLC exhibited lower mass loss. This coating enhanced integrity against erosion-corrosion acting together under saline environments with sand. The enhanced resistance was attributed to improved ductility of the surface layer, as well as the generation of an effective corrosion barrier which reduced pitting corrosion and suppressed significantly the anodic reaction.

Resumo em Inglês:

Graphene is a versatile constituent with many applications in novel materials demanding improved electrical conductivity and mechanical resistance. Another application reported in the literature is its use as a barrier agent to gases, lipids, and water vapor, due to its honeycomb basal structure. We report on a straightforward method to achieve the surface modification of different substrates by depositing a graphene dispersion. The graphene dispersion in N-methyl-2-pyrrolidone (NMP) was prepared by liquid-phase mechanical exfoliation of graphite flakes and characterized to be comprised by multilayer graphene (mG). Ordinary commercial substrates, films produced by the packaging industry, such as low-density polyethylene (LDPE), poly(ethylene terephthalate) (PET), paper, and cellophane (CEL) were treated by a mG dispersion using drip casting. Scanning electron microscopy (SEM) was carried out on these different substrates before and after mG coating. LDPE showed irregular mG covering and aggregation, compared to the uniform distribution in PET and cellophane films, that corroborates the results obtained from tape tests. UV-Vis transmittance indicated minimal interference from the graphene layer compared to the uncoated film. The results were discussed taking into account the interplay of the surface energy of the chemical substances involved. The different modified films might work as a barrier packaging films.

Resumo em Inglês:

Cellular Automata (CA) are powerful simulation tools that operate through discrete elements and associations. CA undirected neighborhood searches may produce specific grain shapes (e.g., octahedral, cuboctahedral, cubic), but not spherical ones. However, in recrystallization modeling, the spherical shape plays a crucial role. Thus, Hybrid Cellular Automata (HCA) share several properties with CA but operate in both continuous and discrete modes simultaneously. Unlike deterministic CA, HCA enable equiaxial grain growth without the need for additional correction algorithms, generating grains that remain initially spherical until they encounter boundaries. This behavior has been addressed by other simulation techniques, but HCA provide a simple and highly effective alternative. In this work, HCA are described in detail, including their foundational principles, algorithm performance, calibration, and potential results. The findings highlight the capability of HCA for straightforward and accurate recrystallization simulations with equiaxial growth.

Resumo em Inglês:

Calcium hexaluminate (CA6) is a refractory material with good thermal properties and intrinsic difficulty in densification.This study explored the use of Cariri Stone residue, a calcium carbonate-rich limestone from Ceará, Brazil, as a precursor for producing refractory ceramics containing this phase. X-ray diffraction and preliminary tests were conducted to determine the optimal conditions for its incorporation into ceramic refractories. The results showed that a mixture of Cariri Stone residue and alumina, with a molar ratio of 0.5 moles of calcium oxide to 6 moles of aluminum oxide, achieved the best formation of CA6 at 1500°C. Specimens calcined at 1400°C exhibited the highest apparent porosity, indicating potential for thermal insulation applications. These findings highlight the feasibility of reusing Cariri Stone residue as a precursor for producing refractory ceramics containing the CA6 phase, offering a sustainable and promising alternative.

Resumo em Inglês:

Microplastics from synthetic polymers significantly impact ecosystems and human health, making biodegradable polymers a promising alternative. To enhance their properties, nanofillers have been widely explored. In this study, TiO2 nanoparticles, alone and combined with B8 OMMT clay, were incorporated into a PBAT matrix to improve its functionality for food packaging applications. Results revealed that nanofillers did not significantly alter PBAT’s crystallinity (Xc ≈ 33%) or thermal stability (Tonset ≈ 375 °C), and the nanocomposites exhibited a predominantly intercalated morphology. Furthermore, low concentrations of nanofillers improved matrix uniformity. Contact angle measurements showed increased hydrophilicity in all formulations, with B8 OMMT systems exhibiting the highest hydrophilicity. The mechanical performance of the PBAT/B8/TiO2 systems was more promising in terms of stiffness, with a 44% increase in Young’s modulus for the PBAT/B8/TiO2 0.5% system. However, all PBAT/B8/TiO2 systems exhibited a more pronounced loss of ductility. Water activity (aW) analysis demonstrated that TiO2 alone reduced aW values to 0.50–0.53, which could potentially enhance biosafety, while the addition of B8 OMMT increased aW to 0.69–0.76, potentially increasing susceptibility to microbial growth. Notably, systems with TiO2 alone showed the greatest potential for food packaging applications due to their increased biosafety, thermal stability, and favorable set of properties.

Resumo em Inglês:

This study explored the use of natural diatomaceous earth (ND) and brewery waste diatomaceous earth (BWD) as precursors for the synthesis of geopolymeric binders, with a focus on optimizing the developed compositions and analyzing their physico-mechanical and microstructural properties. Geopolymers were synthesized using various precursor combinations, with adjustments to their SiO2/Al2O3 molar ratios. ND exhibited high reactivity as a precursor, yielding compositions with compressive strengths of up to 28.59 MPa after 24 hours of curing and low porosity. This performance was attributed to the formation of an amorphous gel with a high density of Si–O–Si(Al) bonds. In contrast, systems incorporating BWD demonstrated reduced performance due to their elevated SiO2/Al2O3 molar ratio and limited geopolymerization, resulting in the presence of unreacted particles within the final microstructure. Stoichiometric adjustments and mechanical activation were critical in improving the compositions performance and enhancing the reactivity of the BWD residue, enabling the production of geopolymers with compressive strengths reaching 31.34 MPa. These findings emphasize the importance of optimizing both the chemical composition and synthesis processes to advance the development of geopolymeric materials, facilitating novel precursor combinations and the sustainable reutilization of industrial waste.

Resumo em Inglês:

The effects of CaO and ZnO as sintering aids on the electrical and thermal properties of Gd-doped CeO2 ceramics were investigated. Different systems of general formulas Gd0.1Ce0.9O1.95 and A0.02Gd0.08Ce0.9O1.94 (where A = Ca and Zn) were obtained by mechanochemistry, with a maximum milling time of 20 h. XRD analysis of synthesized samples revealed pure phases with a fluorite-type structure, derived from the CeO2 cubic system. Heat treatments from 800 to 1500°C enhanced crystallinity and confirmed the formation of the solid solution. SEM studies of samples sintered at 1200 and 1350°C showed similar characteristics across all systems. Both CaO and ZnO improved the materials’ relative density (~95%) at a sintering temperature of 1200 °C. Impedance spectroscopy demonstrated that the sintering aids did not have an adverse effect on ionic conductivity at 650°C, while thermal conductivity tended to decrease as the temperature increased, aligning with density results.