Search Results (2,241)

In order to investigate the microstructure evolution and the degradation mechanism of SiC fiber in a high-temperature oxidative environment, the SiC fiber was thermally exposed at temperature up to 1600 °C in air. The morphologies of the surface and fracture surface were characterized by scanning electron microscopy. The consisting phase and crystallite size were analyzed by X-ray diffractometer. The mechanical properties of SiC fiber was characterized by a single-fiber tensile test technique. It was found that an obvious grain coarsening occurred at temperature above 1400 °C. A visible silica layer was formed at 1300 °C, and the morphology of silica layer was dependent on the exposure temperature. At 1400 °C, fiber surface formed a thick silica layer with cracks, while the silica layer exhibited a multilayered structure at 1600 °C. As for the tensile strength of fiber, it firstly decreased to about 1 GPa at 1200 °C, then the strength was maintained at 1400 °C. After thermal exposure at 1500 °C and 1600 °C, the strength decreased again. The degradation of mechanical properties was attributed to the grain coarsening and the decomposition of amorphous phase in fiber. Particularly, the decomposition of amorphous phase would damage the structure integrity of fiber. The current work would provide a valuable reference for research and application of SiC fiber. Full article

To avoid dependence on conventional raw materials, global emphasis has been placed on obtaining alternative plant celluloses and the chemical synthesis of cellulose. The use of synthetically derived cellulose as a precursor for cellulose nitrates (NCs) is currently absent in global practice, which underscores the undoubted relevance of this research. Cellulose nitrate (NC) was synthesized in a 138% actual yield by nitration of synthetic cellulose (SC)—a new type of cellulose—prepared by electropolymerization from an aqueous glucose solution in the presence of catalytic tungsten–vanadium heteropolyacid of the 1–12 series with the chemical formula H₆[PW₁₀V₂O₄₀]: a nitrogen content of 11.83%, a viscosity of 198 mPa·s, a high solubility of 91% in an alcohol–ether solvent, and an ash content of 0.05%. SEM provided a general concept of the morphological structure of SC and SC-derived NC. The initial SC consisted of flat, curly fibers with a smooth surface approximately 10–20 μm wide, with no aggregation observed. The fibers of SC-derived NC had a cylindrical shape with a diameter of up to 25 μm and a rough surface. FT-IR spectroscopy revealed that SC and SC-derived NC have the main functional groups characteristic of classical cellulose (3346, 2901, 1644, 1429, 1162, and 1112 cm⁻¹) and nitrate esters of cellulose (1650, 1278, 832, 747, and 689 cm⁻¹), respectively. For the first time, a full-profile analysis discovered that SC is made up of the monoclinic phase of cellulose Iβ with an antiparallel chain arrangement. SC with a crystallinity index (CrI) of 81–86% was shown to undergo amorphization upon nitration, with the CrI declining to 17% and the crystallite sizes decreasing from 44 × 62 × 59 × 94 Å to 29 × 62 × 26 × 38 Å. Coupled TGA/DTA revealed that SC exhibits a high-temperature endothermic peak of decomposition of 374 °C, with a weight loss of 84%. The thermostable SC-derived NC exhibits a high onset temperature of intense decomposition of 200 °C and an exothermic peak of 208 °C, with a weight loss of 88%, and is characterized by a high specific heat of decomposition of 7.74 kJ/g. This study provides new insights into the functionalization of SC with a high degree of polymerization, expanding the classical concepts of cellulose nitration. Full article

Sodium-ion batteries (SIBs) present a sustainable alternative to lithium-ion systems due to the abundance and low environmental impact of sodium. However, their integration into multifunctional structural battery systems that combine electrochemical and mechanical properties remains unexplored. This work investigates the electrochemical performance of sodium-ion chemistry within a structural battery framework using unsized carbon fiber (UCF) as both a structural substrate and active electrode material. Ultrasonic spray coating was employed to deposit Mesocarbon Microbeads (MCMB) and NaNi${}_{1/3}$Fe${}_{1/3}$Mn${}_{1/3}$O${}_2$ (NFM) on UCF to form hybrid anode and cathode half-cells, respectively, with 1 M NaPF${}_6$ in diglyme electrolyte. The MCMB on UCF hybrid anode demonstrated dual graphitic and carbon fiber storage mechanisms, achieving 50 mAh g${}^{-1}$ capacity over 500 cycles at 1C with excellent Coulombic efficiency. The NFM–UCF cathode exhibited an initial capacity of 27.5 mAh g${}^{-1}$ and maintained over 80% capacity retention for 230 cycles, continuing to cycle stably beyond 400 cycles. Post-cycling SEM imaging revealed surface cracking, particle expansion, and gas-pocket formation in both electrodes. These results demonstrate the electrochemical viability of sodium-ion chemistry in a multifunctional structural configuration and establish ultrasonic coating as a scalable, precise method for fabricating carbon fiber electrodes toward future sodium-ion structural batteries. Full article

Developing sustainable, high-performance biomass composites is crucial for replacing non-renewable structural materials. In this study, a “bamboo steel” composite was fabricated using a multilevel modification strategy involving alkali pretreatment, toughened resin impregnation, and surface functionalization. Bamboo fibers were treated to remove hemicellulose and lignin, enhancing porosity and interfacial bonding. The bamboo scaffold was subsequently impregnated with a thermo-plastic polyurethane-modified epoxy resin to create a robust, interpenetrating network. The optimized composite (treated at 80 °C) exhibited a flexural strength of 443.97 MPa and a tensile strength of 324.14 MPa, demonstrating exceptional stiffness and toughness. Furthermore, a superhydrophobic coating incorporating silica nanoparticles was applied, achieving a water contact angle exceeding 150° and excellent self-cleaning properties. This work presents a scalable strategy for producing bio-based structural materials that balance mechanical strength with environmental durability. Full article

The effects of pectin extraction, cellulose purification, and sonication on the juice extraction residue from grapefruit were investigated. Pectin extraction using pressurized carbon dioxide (pCO₂) in a sodium oxalate solution (U-OX) lowered the cellulose content and increased the hemicellulose and lignin contents, whereas pectin extraction in deionized water (U-DW) did not affect these contents. Pectin extraction and cellulose purification induced hydrolysis and removal of non-crystalline cellulose regions. The sonication of the purified cellulose samples formed fiber-like structures with widths of <100 nm on their surfaces. The cellulose purification process increased the surface charge and formed a gel-like structure with increased hardness, adhesiveness, and film structure. These processes enhance the absorption of amphiphilic dyes, although to a lesser extent than that of the untreated juice extraction residue (UJR) after sonication. Before sonication, UJR adsorbed cationic dyes, whereas after, UJR adsorbed both polar and nonpolar dyes. These results suggest that juice residue could be used as a biomaterial with diverse potential applications. Full article

Carbon fiber reinforced silicon carbide (C/SiC) composite material exhibits exceptional properties, including high strength, high stiffness, low density, outstanding high-temperature performance, and corrosion resistance. Consequently, they are widely used in aerospace, defense, and automotive engineering. However, their anisotropic, high hardness, and brittle characteristics make them a typical difficult-to-machine material. This paper focuses on achieving high-quality micro hole machining of C/SiC composite material via electrical discharge machining. It systematically investigates electrical discharge machining characteristics and innovatively develops a hollow internal flow helical electrode reaming process. Experimental results reveal four typical chip morphologies: spherical, columnar, blocky, and molten. The study uncovers a multi-mechanism cutting process: the EDM ablation of the composite involves material melting and explosive vaporization, the intact extraction and fracture of carbon fibers, and the brittle fracture and spalling of the SiC matrix. Discharge energy correlates closely with surface roughness: higher energy removes more SiC, resulting in greater roughness, while lower energy concentrates on m fibers, yielding higher vaporization rates. C fiber orientation significantly impacts removal rates: processing time is shortest at θ = 90°, longest at θ = 0°, and increases as θ decreases. Typical defects such as delamination were observed between alternating 0° and 90° fiber bundles or at hole entrances. Cracks were also detected at the SiC matrix–C fiber interface. The proposed hole-enlargement process enhances chip removal efficiency through its helical structure and internal flushing, reduces abnormal discharges, mitigates micro hole taper, and thereby improves forming quality. This study provides practical references for the EDM of C/SiC composite material. Full article

Improving electronic and ionic transport and the structural stability of electrode materials is essential for the development of advanced lithium-ion batteries. Despite its great potential as a high-power anode, Ti₂Nb₁₀O₂₉ (TNO) still underperforms due to its unsatisfactory electronic and ionic conductivity. Here, a TNO/carbon microtube (TNO@CMT) composite is constructed via an ethanol-assisted solvothermal process and controlled annealing. The hollow carbon framework derived from kapok fibers provides a lightweight conductive skeleton and abundant nucleation sites for uniform TNO growth. By tuning precursor concentration, the interfacial structure and loading are precisely regulated, optimizing electron/ion transport. The optimized TNO@CMT-2 exhibits uniformly dispersed TNO nanoparticles anchored on both inner and outer CMT surfaces, enabling rapid electron transfer, short Li⁺ diffusion paths, and high structural stability. Consequently, it delivers a reversible capacity of 314.9 mAh g⁻¹ at 0.5 C, retains 75.8% capacity after 1000 cycles at 10 C, and maintains 147.96 mAh g⁻¹ at 40 C. Furthermore, the Li⁺ diffusion coefficient of TNO/CMT-2 is 5.4 × 10⁻¹¹ cm² s⁻¹, which is nearly four times higher than that of pure TNO. This work presents a promising approach to designing multi-cation oxide/carbon heterostructures that synergistically enhance charge and ion transport, offering valuable insights for next-generation high-rate lithium-ion batteries. Full article

Supramolecular proteins have emerged as promising templates for guiding metal ion mineralization into well-defined nanomaterials because of their structural versatility and chemical diversity. However, the precise control of metal ion nucleation on the different reactive sites of protein templates remains challenging. In this study, a genetically engineered hollow tobacco mosaic virus protein fiber (TMVF) with excellent structural stability was employed to achieve selective mineralization of noble metal nanostructures either on its external surface or within its internal channel. Moreover, the Pt/Pd bimetallic nanowire (NW) was also successfully prepared by co-depositing Pt and Pd on the TMVF. The bimetallic NWs demonstrated a peroxidase-like activity, which enabled their application for cholesterol detection by cooperating with cholesterol oxidase. Full article

The existing scientific literature indicates that flowable short fiber-reinforced composites (SFRCs) can be used for direct restoration due to their favorable mechanical properties. However, there is a lack of data on the mechanical properties of SFRCs designed specifically for indirect CAD/CAM restorations. This study aims to fabricate a novel experimental SFRC CAD/CAM block and evaluate its fracture toughness and polishability as an indirect restoration in comparison with different conventional resin-based CAD/CAM blocks with different compositions. Fourier-transform infrared spectroscopy (FTIR) was employed to analyze the chemical structure of the Experimental SFRC group, while the microstructure of specimens from each group was examined using scanning electron microscopy (SEM). Then, this study divided the specimens into three groups—Group 1 (Grandio blocks), Group 2 (Cerasmart 270), and Group 3 (Experimental SFRC)—with 30 specimens in each group. Each group was then subdivided into sub-groups for the fracture toughness test, which evaluated resistance to crack propagation, and the surface roughness test, which assessed surface topography. FTIR analysis showed that the experimental SFRC exhibited distinct spectral changes after polymerization, confirming successful chemical reactions and network formation. SEM analysis showed that the Experimental SFRC block had a polymeric matrix with randomly oriented, well-dispersed short fibers. Grandio blocs exhibited a dense nanohybrid structure with irregular fillers, while Cerasmart 270 displayed a more uniform microstructure with evenly dispersed nano-sized spherical fillers. The Experimental SFRC showed the highest fracture toughness (2.758 MPa·√m), surpassing the other groups (p < 0.05) and highlighting its superior resistance to crack propagation. Regarding surface roughness Ra, the novel Experimental SFRC group (0.182) presented a significant difference compared to other groups (p < 0.05) but within clinical acceptance, and they can be well polished for clinical use after milling. The Cerasmart 270 block showed the lowest surface roughness Ra (0.135) among the groups, which is attributed to its filler size, geometry, and composition, resulting in a smoother surface. The higher fracture toughness of the Experimental SFRC among the groups suggests superior resistance to crack propagation, attributed to the incorporation of short fibers that enhance energy absorption and reduce brittleness, thereby supporting its suitability for high-stress-bearing clinical applications. Full article

In this article, the authors present the impact of laser treatment on the structure of magnetic composite microfibers. Changes occurring on the surface can have a significant impact on the conductive properties of functional materials produced on a micro- and nanoscale. The fibers presented are functional materials that gain technical applications when combined with other materials. In this case, we refer to the concept of textronics, i.e., the combination of textiles with electronics to create various types of flexible sensors. The authors performed microscopic analysis to observe the changes occurring in the materials. For this purpose, scanning electron microscope and atomic force microscope were used. Full article

In the context of increasing resource scarcity and environmental concerns, the development of green composite materials is essential for promoting sustainability in the automotive industry. However, poor interfacial compatibility between plant fibers and polypropylene (PP), as well as the performance deterioration under complex environmental aging conditions, severely limits their engineering applications. In this study, a synergistic interfacial modification strategy combining alkali treatment of hemp fibers (HFs) with polypropylene grafted maleic anhydride (PP-g-MAH) was employed to enhance fiber–matrix interaction. Hemp fiber-reinforced polypropylene composites (HFRPs) with varying fiber contents (7.5–30 wt%) were fabricated via injection molding. Accelerated aging tests were conducted on the compatibilized HFRPs for up to 2400 h under ultraviolet–thermal–moisture coupled conditions, in accordance with the SAE J2527 standard. The evolution of surface color, mechanical properties, chemical structure, and microstructure was systematically characterized. After aging, surface whitening of the composites was observed. Tensile strength and impact strength decreased by 9.57–22.12% and 38.68–46.03%, respectively, while flexural strength remained relatively stable due to the supporting effect of the fiber skeleton. The aging of compatibilized HFRPs follows an outside-in progressive degradation mechanism, characterized by a stepwise cascade of surface oxidation, crack propagation, moisture ingress, interfacial degradation, and mechanical performance deterioration. These findings offer valuable insights into the long-term durability of natural fiber-reinforced thermoplastic composites and provide theoretical and practical guidance for their structural design and application in demanding service environments. Full article

With the continuous development of cities and the increasing utilization of underground space, ambient noise seismic imaging has become an essential approach for exploring and monitoring the urban subsurface. The integration of Distributed Acoustic Sensing (DAS) with ambient noise imaging offers a more convenient and effective solution for investigating shallow subsurface structures in urban environments. To overcome the limitations of conventional ambient noise seismic nodes, which are costly and incapable of achieving high-density data acquisition, this work makes use of existing urban telecommunication fibers to record ambient noise and perform sliding-window cross-correlation on it. Then the Phase-Weighted Stack (PWS) technique is applied to enhance the quality and stability of the cross-correlation signals, and fundamental-mode Rayleigh wave dispersion curves are extracted from the cross-correlation functions through the High-Resolution Linear Radon Transform (HRLRT). In the inversion stage, an adaptive regularization strategy based on automatic L-curve corner detection is introduced, which, in combination with the Preconditioned Steepest Descent (PSD) method, enables efficient and automated dispersion inversion, resulting in a well-resolved near-surface S-wave velocity structure. The results indicate that the proposed workflow can extract useful surface-wave dispersion information under typical urban noise conditions, achieving a feasible level of subsurface velocity imaging and providing a practical technical means for urban underground space exploration and utilization. Full article

This study explores the potential of integrating thermoplastic surfaces into fiber-reinforced plastics (FRPs) to eliminate the need for extensive surface preparation prior to bonding. Traditional bonding techniques for FRPs, especially in aerospace applications, demand meticulous surface preparation to ensure adequate adhesion. As a potential alternative to conventional methods for generating adhesion, the formation of an interpenetrating polymer network (IPN) by diffusion of the epoxy monomers into a thermoplastic surface layer is investigated. The research involved manufacturing CFRP panels with thermoplastic surfaces, polyether sulfone (PES), and polyetherimide (PEI), followed by a bonding process with and without conventional surface preparation. The performance of the joints was tested by tensile shear and Mode-I fracture toughness tests and compared to reference samples without thermoplastic surfaces. The formation and characteristics of the IPNs were analyzed using optical microscopy, laser scanning microscopy, and energy-dispersive X-ray spectroscopy. The results demonstrate that PES surfaces, even without surface treatment, can provide high mechanical performance with shear strengths ranging from 18 MPa to 23 MPa. PEI surfaces led to a shear strength from 10 MPa up to 14 MPa, correlating to a less extensive IPN formation compared to PES. However, both thermoplastics significantly improved the bonding process performance without surface preparation. Full article

Marine risers, critical structures connecting underwater production systems and surface floating platforms, stand freely in water and endure extremely complex marine environmental loads. To meet the multi-parameter observation demand for their overall state, a fiber-optic sensing-based marine riser buoy observation system was developed. Unlike traditional point-type and offline monitoring systems, it integrates marine buoys with sensing submarine cables to achieve long-term real-time online monitoring of risers’ overall state via fiber-optic sensing technology. Comprising two main modules (buoy monitoring module and fiber-optic sensing module), the buoy’s stability was verified through theoretical derivation, simulation, and stability curve plotting. Frequency domain analysis of buoy loads and motion responses, along with calculation of motion response amplitude operators (RAOs) at various incident angles, showed the system avoids wave periods in the South China Sea (no resonance), ensuring structural safety for offshore operations. A 7-day marine test of the prototype was conducted in Yazhou Bay, Hainan Province, to monitor real-time temperature and strain data of the riser in the test sea area. The sensing submarine cable accurately responded to temperature changes at different depths with high stability and precision; using the Frenet-based 3D curve reconstruction algorithm, pipeline shape was inverted from the monitored strain data, enabling real-time pipeline monitoring. During the test, the buoy and fiber-optic sensing module operated stably. This marine test confirms the buoy observation system’s reasonable design parameters and feasible scheme, applicable to temperature and deformation monitoring of marine risers. Full article

The solubility and rheological properties of high-molecular-weight xanthan gum (XG) are crucial to its functional performance and determine its applications. Ultrasound modifies these properties mainly by altering acoustic propagation in viscous systems, which depends strongly on concentration and frequency mode. In this work, the propagation behavior of three frequency modes (33 kHz mono-frequency, 20–40 kHz dual-frequency, and 20–50–68 kHz triple-frequency) of arc-shaped flat-plate ultrasound was systematically investigated in XG solutions, as well as their effects on solubility and rheological properties. Results showed that multi-frequency ultrasound generated stronger and more uniform acoustic fields, maintaining higher space peak temporal peak acoustic intensity (I_SPTP) over a wide concentration range, which was superior to the significant attenuation observed in mono-frequency mode above 10.0 g·L⁻¹. Ultrasonic treatment effectively increased solubility from 62.0 to 63.5% (untreated) to a maximum of 85.6% in the 20–40 kHz group. In terms of rheology, ultrasound reduced viscosity and altered viscoelastic behavior by disrupting the molecular network, with multi-frequency modes showing greater effects at higher concentrations. Surface tension decreased to a minimum of 58.4 mN·m⁻¹ under mono-frequency treatment. Frequency sweep and creep recovery tests indicated enhanced chain mobility and improved structural recovery after ultrasound. Microstructure analysis confirmed fiber fragmentation and the formation of a microporous structure, especially under multi-frequency modes. Overall, the key mechanism lies in the ability of multi-frequency ultrasound to maintain effective acoustic propagation in viscous media, thereby enhancing solubility and modulating rheological behavior. Full article