Search Results (227)

Rapid solidification by melt-spinning produces aluminum alloys with extremely refined microstructures but also introduces strong structural gradients across the ribbon thickness. In this work, the microstructural evolution of a rapidly solidified Al-Cu-Li-Mg-Sc-Zr alloy was investigated during model homogenization using in situ STEM heating experiments and correlated with bulk electrical-resistivity measurements. The as-cast ribbons exhibit two distinct solidification zones: a near-contact region consisting of columnar cells containing fine Cu-rich spherical precipitates, and a central region composed of larger eutectic cells enriched in Al₂Cu and Al₇Cu₂Fe phases. Stepwise in situ STEM annealing between 200 °C and 500 °C reveals a sequence of transformations, including matrix depletion due to precipitation of strengthening phases, coarsening of primary phases, and formation of Al₃(Sc,Zr) dispersoids. Above 500 °C, rapid dissolution of Cu-rich primary phases occurs, leaving only a limited number of stable grain-boundary particles of the Al₇Cu₂Fe phase, eliminating the original two-zone structure, and resulting in a fully homogenized ribbon. Ex situ annealing confirms that the resulting microstructure is uniform across the ribbon thickness and enables consistent precipitation strengthening during artificial aging. The proposed annealing treatment is based on numerical models for homogenization of eutectic systems. The final annealing step combines homogenization and solution treatment at 530 °C for periods close to 5 min—two orders of magnitude shorter than standard holding times. Microhardness measurements from both ribbon surfaces reveal an identical peak-aged hardness of 135 HV, validating the effectiveness of the short-time homogenization strategy for rapidly solidified Al-Cu-Li-Mg-based alloys. Full article

This study investigates the synthesis and kinetic behavior of a magnetic biochar derived from avocado seed biomass for the removal of hexavalent chromium (Cr(VI)) from aqueous solutions. Magnetite (Fe₃O₄) was synthesized through different routes, including nitrogen-assisted coprecipitation, redox-controlled coprecipitation, polyol, sol–gel, and sonochemical methods, to evaluate their structural properties and iron incorporation efficiency. Based on compositional and crystallographic analyses, the coprecipitation under an inert atmosphere exhibited improved phase purity and higher Fe₃O₄ content, which was selected for in situ incorporation onto biochar produced by pyrolysis at 450 °C. The resulting magnetic material and composite were characterized using X-ray diffraction (XRD), X-ray fluorescence (XRF), Fourier-transform infrared spectroscopy (FTIR), and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM–EDS), confirming the suitability of the synthesis method and the successful deposition of magnetite onto the porous carbon matrix while preserving its structural integrity. Batch adsorption experiments were conducted at pH 2.0 to evaluate the effect of adsorbent dose and initial Cr(VI) concentration. The adsorption process reached equilibrium within 120 min and was better described by the pseudo-second-order kinetic model (R² ≥ 0.98), suggesting that chemisorption governs the rate-controlling step, with diffusion phenomena contributing but not dominating the overall mechanism. The maximum adsorption capacity predicted by the kinetic model reached 42.49 mg g⁻¹ at an initial concentration of 100 mg L⁻¹. The results demonstrate that avocado-seed-derived magnetic biochar represents a sustainable and effective material for chromium-contaminated water treatment, integrating agro-industrial waste valorization with enhanced adsorption performance and magnetic separability. Full article

This study demonstrates how synthesis conditions and bacterial cellulose (BC) functionalization influence the physicochemical properties and antibacterial performance of BC membranes containing green-synthesized silver nanoparticles (AgNPs). Mint and avocado-seed extracts enabled AgNP formation in aqueous media but differed in composition. UV–Vis screening across pH and temperature revealed inefficient synthesis at acidic pH, whereas higher temperatures produced broader localized surface plasmon resonance (LSPR) bands. Neutral conditions generated the most intense and narrow LSPR signals. Under optimized conditions (pH 7, 23 °C), AgNPs were confirmed by TEM, and their colloidal properties differed between extracts: mint-derived particles exhibited smaller hydrodynamic diameters and lower polydispersity than avocado-derived AgNPs. Two BC functionalization strategies were evaluated: immersion in pre-formed AgNP dispersions and in situ synthesis within the BC matrix. In situ membranes displayed stronger and better-defined LSPR peaks. Agitation released nanoparticles from all BC-AgNP membranes, with smaller species released from in situ systems. Antibacterial assays against E. coli showed greater bactericidal activity for in situ membranes. Avocado-derived in situ BC-AgNPs produced larger inhibition halos and prevented bacterial regrowth in liquid culture. Overall, in situ green synthesis within BC provides an effective route to robust and sustainable antibacterial BC membranes. Full article

Certain clayey soils are susceptible to swelling and shrinkage due to moisture variations, which can lead to ground deformation and structural damage. Although traditional stabilization methods using lime and cement are effective, they involve high energy consumption and significant CO₂ emissions. In response to sustainability concerns, this study investigates the potential of in situ geopolymer stabilization of clay soils using industrial by-products as eco-friendly binders. Experimental studies were conducted on clay specimens stabilized with geopolymer binders produced from fly ash and waste brick powder activated by alkaline solutions. The selected clay exhibited stiff to very stiff behavior and was used as a reference material to ensure reliable evaluation without the influence of severe initial degradation. Reference samples with identical water content but without alkaline activation were also prepared. The primary objective was to assess geopolymers as a sustainable alternative to conventional binders, focusing on moisture sensitivity and long-term mechanical performance. Laboratory strength tests demonstrated that geopolymer-treated specimens exhibited significantly higher strength compared to untreated samples, indicating substantial improvement in engineering properties. Furthermore, Scanning Electron Microscopy (SEM) analyses revealed that the combination of dual activators (NS+NH) and thermal curing at 85 °C transformed the weak clay matrix into a dense, fibrous geopolymer network. However, the high curing temperature was primarily used to study the reaction mechanisms; the practical applicability of the method should be evaluated based on results obtained at ambient temperature. This structure enhanced particle bonding and mechanical interlocking by filling voids within the matrix. Overall, the findings confirm that geopolymer stabilization using industrial waste materials is an effective and environmentally sustainable alternative to conventional soil stabilization techniques, contributing to reduced carbon emissions in geotechnical engineering. Full article

The large-scale generation of waste graphite not only poses environmental challenges but also provides an opportunity for resource recovery. This study proposes a sustainable strategy that utilizes the graphite cutting waste produced during the production of large graphite electrodes through chemical intercalation, microwave-assisted expansion, and in situ urea nitrogen doping techniques to prepare nitrogen-containing micro-expanded graphite (NMG) composite materials. Structural analysis reveals that the nitrogen-doped amorphous carbon layer formed on the expanded graphite (EG) matrix effectively suppresses excessive expansion while preserving its typical worm-like interlayer morphology and porous structure. XPS confirms successful nitrogen doping with predominant pyridinic-N configuration, introducing abundant defect sites and enhancing lithiophilicity. As an anode for LIBs, NMG delivers an exceptional initial discharge capacity of 1907.5 mAh g⁻¹ at 20 mA g⁻¹ and maintains 798.2 mAh g⁻¹ after 50 cycles, nearly twice that of purified waste graphite (G). Remarkably, after 1000 cycles at 1 A g⁻¹, it retains 650.4 mAh g⁻¹ with 89.9% capacity retention, indicating an electrochemical activation process. Kinetic analysis reveals that the superior performance originates from synergistic diffusion-controlled intercalation and surface-dominated pseudocapacitance, with nitrogen-doped defect sites and hierarchical pore architecture promoting rapid ion/electron transport and surface faradaic reactions. This work demonstrates a viable pathway for value-added upcycling of waste graphite while providing insights into designing high-performance anodes through integrated defect engineering and heteroatom doping. Full article

The development of selective and sustainable catalysts is essential to enable the chemical recycling of mixed plastic waste. In this work, calcium-modified biochars derived from cocoa pod husk (CPH) and palm kernel shell (PKS) were prepared for treating a mixture of poly(ethylene terephthalate) (PET) and poly(lactic acid) (PLA). The aim was to separate the mixture through the PLA methanolysis, while maintaining the PET unreacted for a potential physical recycling. Biochar was ex situ modified with calcium precursor using a value-added concentrate recovered from the hydrothermal treatment of Jatropha fruit husk. Subsequently, a pyrolysis step was further applied to convert the calcium species into CaO, which is the active phase for the methanolysis reaction. Structural, microscopic, and spectroscopic analyses revealed that the carbon matrix strongly influences the evolution and stabilization of calcium phases during pyrolysis and post-treatment. CPH-derived biochars promoted the formation of highly dispersed CaO, whereas PKS favored the growth of larger, less reactive Ca(OH)₂ domains. As a result, the CPH_Ca10 (i.e., 10% desired calcium loading based on CPH-biochar mass) catalyst exhibited superior basicity and catalytic activity, achieving near-complete PLA conversion under mild conditions (90–110 °C) depending on the system with only 2 wt.% catalyst. Importantly, under these mild conditions, PET remained chemically intact, demonstrating the process’s high selectivity and applicability to mixed bioplastic–fossil plastic streams. This study highlights a circular, low-carbon route to producing effective Ca-based catalysts from agricultural residues. It establishes a promising strategy for selective depolymerization and separation in complex plastic waste systems. Full article

Friction stir-welding (FSW) is widely recognized as a modern solid-state technology used to join dissimilar materials by solid-state mechanical mixing. Such mechanical mixing can be exploited to fabricate in situ composite structures through solid-state deformation mechanisms. The present investigation highlights the microstructural evolution and mechanical properties of an in situ composite structure fabricated by FSW of aluminum (Al) to titanium (Ti) incorporating a thin Nickel (Ni) interlayer. A 0.1 mm thick Ni foil was placed across the full butt interface between 4 mm thick Al and Ti plates before friction stir-welding. Properties of the composite were investigated in detail, and the results revealed that fragmented Ti and Ni particles of different sizes were consolidated in the weld nugget. Al, on the other hand, exhibited substantial microstructural refinement and developed an equiaxed microstructure with random grain orientation, mixed grain boundaries and low micro-strain accumulation in the weld nugget. At the processing temperature, Al reacted with both Ti and Ni to form multiple intermetallic compounds. Tensile testing indicated that the tensile properties of the weld were close to those of the base aluminum. This retention of mechanical properties in spite of recrystallization is attributed to the following mechanisms: (1) Ti and Ni undergo severe deformation, forming fine particles with varying sizes and shapes; (2) at particle interfaces, diffusion and chemical reactions produce interlayers and intermetallic compounds; (3) these particles are consolidated within dynamically recrystallized Al, imparting composite characteristics to the weld nugget; and (4) the particles containing intermetallic compounds act as dispersoids in the Al matrix. Quantitatively, the weld retained 98% (104.2 ± 3.3 MPa) UTS and 90% (17.1 ± 1.2) ductility of base aluminum, demonstrating the effectiveness of the Ni interlayer approach in controlling brittle intermetallic formation. Full article

To address the practical requirements for in situ equipment restoration, this study investigates a portable and cost-effective approach for the localized repair of SAE 10SAE 1045 components using a 1Cr13 martensitic stainless steel coating prepared via an arc-based additive manufacturing (WAAM) process. The microstructural evolution and tribological response of the layers were analyzed, with a focus on the effects of discrete thermal cycling and controlled solidification inherent to portable arc equipment. The WAAM process produced a refined martensitic matrix with a microhardness of 551.94 HV0.2, which is 2.26 times that of the substrate. Under dry sliding conditions, the 1Cr13 coating exhibited a lower friction coefficient and a reduced wear volume compared to the untreated SAE 1045, primarily through the mitigation of severe plastic deformation. This additive route provides a millimeter-scale reinforcement layer with metallurgical integrity suitable for heavy-duty service, aiming to offer a practical reference for the low-cost, on-site restoration of industrial components. Full article

Phosphogypsum (PG) and phosphorus tailings (PT) are bulk solid wastes generated by the phosphorus chemical industry whose stockpiling poses significant environmental risks and represents a waste of resources. To achieve the goals of “treating waste with waste” and large-scale disposal, this study proposes a technical pathway involving the co-pyrolysis of phosphogypsum and phosphorus tailings to produce artificial soil-like materials. The effects of raw material ratio, pyrolysis temperature and duration, and biomass addition on the speciation transformation, leaching toxicity, and matrix characteristics of phosphorus (P) and fluorine (F) in the products were systematically investigated. Characterization techniques, including X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM), were employed to elucidate the synergistic immobilization mechanism. The results indicate that under optimized conditions (PG:PT mass ratio of 6:4, pyrolysis temperature of 800 °C, duration of 2–3 h, and biomass addition of 20%–30%), the active forms of harmful elements in the product were significantly reduced. The proportion of water-soluble fluorine decreased from ~39% in raw phosphogypsum to less than 3%, with apatite phosphorus becoming the dominant form of phosphorus. Mechanistic studies reveal that the immobilization process follows a “multi-pathway synergy” mechanism: thermal activation promotes the in situ formation of thermodynamically stable fluorapatite through the reaction of Ca²⁺, PO₄³⁻, and F⁻ (chemical fixation); iron/aluminum oxides in phosphorus tailings and the biochar derived from added biomass provide adsorption sites for surface complexation (physicochemical fixation); and the melting of silicon–aluminum components forms an amorphous silicate network that physically encapsulates pollutant microcrystals. This study provides crucial theoretical foundations and process parameters for the synergistic disposal and soil-like resource utilization of phosphogypsum and phosphorus tailings, demonstrating significant environmental and economic benefits. Full article

This work reports the elaboration and testing of polydimethylsiloxane/titanium dioxide (PDMS/TiO₂) polymer nanocomposites, focusing on producing and combining TiO₂ nanoparticles with a polymer matrix through an ex situ route. By mixing the inherent flexibility of PDMS with the unique properties of nanoparticles, the nanocomposites aim to enhance mechanical stability, optical response, and photocatalytic activity. X-ray diffraction (XRD) confirmed the successful incorporation of TiO₂ into the PDMS matrix. UV–visible spectroscopy monitored photocatalytic performance using metronidazole as a model pollutant under 365 nm irradiation. Kinetic analysis revealed degradation and showed that the reaction rate constant (k) increased with TiO₂ loading, reaching a maximum of 0.0019 min⁻¹ for the 6 wt.% composite. These findings indicate that while the reaction kinetics are slower than those of free powders, the PDMS/TiO₂ nanocomposites provide a viable, recoverable, and flexible solution for environmental remediation applications. Future efforts will target improved durability, broadened visible light absorption, and process optimization for scalable fabrication. Full article

Thermal microbial mats are laminated organo-mineral biofilms composed of extracellular polymeric substances (EPSs) and microbially mediated silica and carbonate phases. Although extensively studied from ecological and geobiological perspectives, their potential as precursors for applied, bio-derived composite materials remains largely unexplored. In this study, geothermal microbial mats from the Comanjilla hot springs (Mexico) are investigated from a materials-oriented perspective through controlled processing, inorganic tanning, and polymeric surface conditioning. The mats were treated with potassium alum and reinforced using a polyvinyl alcohol–alginate–glycerin formulation to improve cohesion, handling behavior, and structural stability. Mineralogical, physicochemical, and microstructural analyses reveal a hierarchical laminated architecture in which EPS functions as a continuous organic matrix, while in situ silica and carbonate phases provide intrinsic mineral reinforcement. Carbonate-rich mats yield softer and more flexible composite materials, exhibiting tensile strength values of 2.17 ± 0.18 MPa and elongation at break of 15–20%, whereas silica-rich mats produce stiffer and more abrasion-resistant systems. Thermal analysis shows a main organic decomposition event near 275 °C and a stable inorganic residue of approximately 45–50 wt%, confirming the hybrid organo-mineral nature of the processed materials. Prototype-scale fabrication demonstrates structural cohesion, controlled porosity, elastic recovery, and breathability, supporting potential low-load and non-structural applications. Overall, the results identify geothermal microbial mats as a renewable and naturally pre-assembled platform for bio-derived organo-mineral composite materials and provide a foundation for future studies focused on controlled processing and structure–property optimization. Full article

Metal matrix composites (MMCs) are one of the significant engineering materials for many industrial applications. The growing interest in MMCs stems from their strong mechanical properties, including their higher specific mechanical strength and excellent corrosion and wear resistance. From an industrial viewpoint, the ability of MMCs to undergo secondary processing is significant. This review aims to clarify the effects of cryorolling on the microstructure, mechanical properties and wear behavior of different aluminum-based MMCs. In particular, aluminum matrix composites (AMCs) produced through the stir-casting approach experience an additional cryorolling procedure to enhance their tensile mechanical strength and wear resistance. This hybrid manufacturing approach has shown promise in creating effective structural components. This review covers the production of ex situ aluminum-based composites formed by stir casting and then cryorolling. It also highlights how the particle size, volume fraction, and the cryorolling procedure affect the microstructure, wear, and mechanical properties. This approach could broaden the uses of hybrid manufacturing by demonstrating its practical advantages and efficiency. Furthermore, this review highlights the importance of implementing machine learning (ML) models and life cycle assessment (LCA) in evaluating MMCs produced through stir casting. Full article

This study examines in situ induction-heating thermal field assistance during laser cladding of Stellite 6 on 17-4PH stainless steel. Single-layer, multi-track coatings (~2.3 mm) were produced at induction powers of 0, 300, 600, and 900 W while keeping laser parameters constant. Surface morphology, phase constituents, and microstructures were characterized by LSCM, OM, XRD, SEM, EDS, and EBSD, and nanoscale features were probed by TEM for the 600 W condition; microhardness and coating-only tensile properties were evaluated. Thermal assistance improved surface finish (minimum Sa = 16.67 μm at 600 W) and suppressed hot cracking. XRD/EBSD revealed a γ-Co matrix with interdendritic carbides and an increased ε-Co fraction under thermal assistance; TEM further showed stacking-fault lamellae and a distinct FCC/HCP interface, supporting a fault-assisted, diffusionless γ → ε transformation. Increasing induction power coarsened the microstructure (larger D_E and SDAS), decreasing hardness from 537.1 to 461.5 HV_0.1 and lowering yield/ultimate strengths from 1046 MPa and 1512 MPa to 849 MPa and 1423 MPa, while elongation increased from 4.37% to 6.27%. Considering crack-free valve hardfacing with acceptable strength loss and improved ductility, 600 W provides the best overall performance. Full article

Eco-friendly chitosan nanogels (CSNG) with an average diameter of 48.5 nm were synthesized via alkali/urea dissolution and employed as templates for in situ silver nanoparticle fabrication. Silver nanoparticle size was controlled by adjusting CSNG to AgNO₃ mass ratios, with the optimal ratio of 18:1 producing ultrasmall particles of 3.72 nm, uniformly dispersed in the matrix. The nanocomposites demonstrated superior antibacterial activity, with inhibition zones of 14.3 mm against E. coli and 12.1 mm against S. aureus, significantly exceeding pure CSNGs at 7.4 mm and 6.9 mm, respectively. Rheological analysis revealed shear-thinning behavior, with viscosity decreasing from 450 Pa·s to 0.1 Pa·s, confirming excellent injectability. Cytotoxicity evaluation showed cell viability exceeding 82.3% at 100 μg/mL, which was substantially superior to conventional silver formulations. Thermogravimetric analysis and FTIR spectroscopy verified enhanced thermal stability and coordination interactions between chitosan and silver species. This green synthesis approach yields injectable, size-tunable nanocomposites with combined antibacterial efficacy and biocompatibility for biomedical applications. Full article

The catalyst in methanol oxidation plays a pivotal role in direct fuel cell reaction. The aim of this work is to study the influence of polypyrrole polymer (PPy) added in the carbon Vulcan support for the methanol oxidation reaction. The catalytic active phase synthesized was nickel-based materials, which have been demonstrated to exhibit remarkable chemical stability in alkaline solutions. The metallic-active phase was supported at the PPy-carbon Vulcan matrix. PPy is a conductor polymer and the research of electric conduction in synergy with a carbon Vulcan and a Ni catalyst is scarcely reported. The morphology characterization of composite catalytic material was carried out by XRD, XPS, and TEM techniques. In turn, the catalytic activity of the composite is characterized by means of cyclic voltammetry (CV). Electrochemical impedance spectroscopy (EIS) showed the influence of PPy on the charge transfer resistance (Rch. t.). The results indicate that a decrease in the Rch. t. was associated with an increase in methanol oxidation; therefore, higher amounts of charge transfer is produced. Furthermore, the DEMS technique corroborates the EIS results, confirming elevated conversion toward oxidation products. In turn, the selectivity of the composite-catalytic support on the methanol oxidation was elucidated using in situ Raman spectroscopy. Full article