Search Results (195)

This study realizes the synergistic improvement in mechanical properties and ablation resistance of Si-modified phenolic aerogel composites with preserved lightweight characteristics and excellent thermal insulation. The resin matrix forms a uniform nanoporous structure, providing prominent thermal insulation performance. The composite with a fiber density of 0.62 g/cm³ has a low thermal conductivity of 0.086 W/(m·K). The material exhibits reliable tensile strength within a wide temperature range, and its tensile strength rises significantly with an increase in fiber density. The composite with a fiber density of 0.62 g/cm³ delivers a tensile strength of 129 MPa at 20 °C and 102 MPa at 300 °C, which are 79.4% and 122.2% higher than those of the composite with a fiber density of 0.36 g/cm³. In addition, methyltriethoxysilane and quartz fiber knitted felts form in situ SiO₂ and SiC ceramic cladding layers under high-temperature ablation, effectively enhancing the ablation resistance of the composites. Higher fiber density greatly reduces the linear ablation rate. With an oxygen flow of 950 L/h and acetylene flow of 700 L/h, the linear ablation rate of the composite with a fiber density of 0.62 g/cm³ is only 0.13 mm/s, 23.1% lower than the composite with a fiber density of 0.36 g/cm³. Full article

This article focuses on the research and development of innovative polymer-concrete composites for the manufacture of precision machine tool frames and critical mechanical engineering components. The relevance of this work stems from the need to replace traditional cast iron and cement concrete with materials with superior damping properties and thermal stability. The polymer matrix used in this study was ED-20 epoxy-diane resin, modified with (FAM) furan resin and cured with polyethylenepolyamine (PEPA), which together ensured minimal linear shrinkage (less than 0.5–1%) during polymerization. The focus was on the effect of multimodal filler distribution, including quartz sand, gabbro, and basalt, as well as reinforcing additives such as silicon carbide and fiberglass, on the final performance characteristics of the material. Experimental studies determined the key physical and mechanical parameters of the obtained samples. The results showed that the optimized composition (Smp_001) exhibited compressive strength up to 92.3 MPa, significantly exceeding that of standard high-strength concrete. It was established that the use of silicon carbide and glass fiber promotes the formation of a dense heterogeneous microstructure characterized by extremely low porosity (1.2–2.5%) and record-low water absorption (less than 0.05%). These characteristics guarantee high dimensional stability of the frames during prolonged contact with process fluids and cutting fluids. The scanning electron microscopy (SEM) and (EDS) energy dispersive X-ray spectroscopy methods confirmed the dense packing and high degree of interaction of the polymer matrix with the crystalline phases of the filler. This condition of the interfacial boundaries guarantees stable stress transfer throughout the entire volume of the material, which minimizes the risk of local damage during operation. The study confirmed that the developed material has vibration damping properties 6–10 times more effective than gray cast iron, a critical factor in improving machining accuracy on modern metal-cutting machines. The scientific novelty of the study lies in its substantiation of the synergistic effect of the combined use of basalt fillers and silicon carbide to achieve the precision properties of a structural material. Its practical significance is confirmed by the possibility of producing large-scale parts by casting without the need for complex finishing, opening up new prospects for modernizing the machine tool industry. Full article

This article describes a study on the synthesis and annealing processes of thin-film coatings of vanadium oxide on flat, parallel substrates made of quartz glass, sapphire, and silicon, as well as optical fibers using an organometallic precursor, triisopropoxy vanadium (V) oxide. For the first time, optical constants of nanomaterials were estimated in real time during synthesis and subsequent annealed using the lossy-mode resonance effect. The coatings produced in an inert atmosphere after deposition were amorphous, comprising a mixture of VO₂, V₂O₅, V₆O₁₃, and V₃O₅. This method allowed for accurate determination of the threshold temperature for the transformation of oxide mixtures into a monocomponent phase. Optimal conditions for synthesis and annealing were determined for the production of vanadium dioxide (VO₂) and pentoxide (V₂O₅). Morphological changes in coated surfaces were observed as a result of heat treatment. The composition and properties of these samples were studied using optical, terahertz and Raman spectroscopy, as well as temperature-dependent analysis of electrical resistance. The morphology of the coating surface was determined using a scanning electron microscope and an atomic force microscope. The reduction of VO_x to VO₂ was studied in an atmosphere of hydrogen and argon during annealing after deposition, with its effectiveness being compared. It was shown for the first time that the reduction of higher vanadium oxides is due to the presence of elemental carbon in the volume of the material formed from a metalorganic precursor during growth of vanadium oxide. Coatings obtained by annealing in hydrogen had a smaller hysteresis loop width (~5 °C) during phase transition compared to coatings obtained by argon annealing (~9 °C). Both types of coatings demonstrated a 50–60% increase in transmission at 1 THz frequency and in the IR region, accompanied by a 10³–10⁴-fold change in electrical resistance. Full article

The conservation of tuff- and coral rock-built architectural heritage structures (AHS) is challenging because access to original tuff and coral rock has become difficult and severely limited due to urbanization, land reclamation, the depletion of stone quarries, anti-mining and anti-quarrying legislation. An emerging approach to address this issue is to create compatible “replacement” rocks via geopolymerization, a process that is more sustainable and greener than the use of conventional cement and concrete. To explore the potential of geopolymers for AHS conservation strategies, the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines were implemented; 103 eligible articles were identified and classified into geopolymers for AHS (34 articles), tuff-built AHS (60 articles), and coral rock-built AHS (9 articles). Tuff substrates in AHSs appear in a variety of colors (yellowish-brown, grayish-cream, reddish-brown, pale greenish-gray and pink hues), densities (1.0–2.5 g/m³), and compressive strengths (3–100 MPa). Meanwhile, coral rock substrates in AHSs appear in whitish-cream color and are coarse-pored (1–5 MPa), fine-grained (8–15 MPa), and calcarenite (50–60 MPa). In terms of geopolymer formulation, metakaolin was reported as the most popular main precursor or admixture, while NaOH and Na₂SiO₃ were used simultaneously as alkaline activators. Aggregates used in geopolymer formulations depended on local availability, including quartz sand, river sand, crushed stones, carbonate stones, volcanic rock, volcanic sand, tuff, brick, ceramic tiles, and waste materials. Aesthetics, chemical composition, physical attributes, and mechanical properties have been identified as key criteria to ensure geopolymer compatibility for AHS conservation application. To date, geopolymers have been applied for AHS conservation as repair mortars, consolidants (i.e., grout and adhesives), and masonry strengthening (i.e., fiber-reinforced mortar). Finally, geopolymers formulated for AHS conservation have similar durability as the original substrate based on accelerated aging tests (i.e., salt mist, wet-dry, and freeze–thaw) and long-term outdoor exposure experiments. Full article

Composite materials are critical components in advanced equipment such as aerospace, however, delamination defects that readily arise during manufacturing and in service present serious risks to equipment safety. Terahertz non-destructive testing is highly effective for analyzing the internal structure of composite materials, making it an effective approach for precise identification of delamination defects. Current terahertz detection approaches mainly depend on single domain features, making it difficult to capture complementary information from both the time and frequency domains. To address this, a Time-Frequency Feature-fusion Network (TFFN) is proposed. In this network, a three-branch architecture is employed: local transient patterns and pulse-related structural features are extracted by the local time-frequency branch; damage-sensitive frequency bands are focused on by the frequency-domain branch through a channel-space-frequency band attention mechanism; and deep integration of time-frequency features is achieved by the time-frequency fusion branch using Manifold Mixup. Finally, the features extracted from the three branches are adaptively fused via a cross-branch attention mechanism, and defect identification is accomplished by the classifier. Experimental results show that this method achieves accuracies of 98.40% on the glass fiber reinforced polymer (GFRP) dataset and 98.63% on the quartz fiber reinforced polymer (QFRP) dataset, surpassing the best existing method by 2% and 1.25%, respectively. A substantial improvement in both defect identification accuracy and the model’s generalization ability for layered structures is thereby achieved. Full article

In engineered cementitious composites (ECCs), the use of fine quartz sand is associated with high cost and is unfavorable for reducing ECC shrinkage. Moreover, the mining and processing of fine quartz sand impose negative environmental impacts. At the same time, the polyethylene (PE) or polyvinyl alcohol (PVA) fibers added to ensure ECC ductility are expensive, which limits the widespread application of ECCs. With the aim of waste utilization and cost reduction while improving efficiency, this study employs geopolymer aggregate (GPA) as an alternative to fine quartz sand and partially replaces PE fibers with steel fibers to develop an economical and environmentally friendly geopolymer aggregate ECC. Six groups of ECC specimens with different mix proportions were designed and tested under uniaxial compression, flexural loading, and uniaxial tension. Different aggregate types (fine quartz sand and geopolymer aggregate) and volume fraction ratios of PE fibers to steel fibers (0:2.0, 0.5:1.5, 1.0:1.0, 1.5:0.5, and 2.0:0) were adopted to investigate their effects on mechanical properties, microstructural characteristics, and material sustainability. The experimental results reveal the failure process and deformation characteristics of the ECCs at different loading stages. The results indicate that geopolymer aggregate, owing to its lower stiffness and fracture energy, can promote multiple cracking behavior in ECCs. Although the complete replacement of quartz sand with porous GPA initially causes a slight reduction in the compressive and flexural strengths of the matrix, the hybridization strategy—partially replacing PE fibers with steel fibers—effectively compensates for this strength loss while maintaining excellent ductility. By comparing sustainability indicators with those of conventional ECCs, the results demonstrate that hybrid fiber geopolymer aggregate ECCs can effectively reduce material costs and carbon dioxide emissions. These findings verify the sustainability of producing green ECCs using industrial solid waste as an aggregate and provide guidance for the application of environmentally friendly geopolymer aggregate ECCs. Full article

We report on sub-50 fs pulse generation from a diode-pumped mode-locked laser based on an ytterbium-doped monoclinic potassium yttrium double tungstate crystal operating in the 1 μm spectral region. Pumping by a low-power, spatially single-mode, fiber-coupled laser diode at 976 nm, a maximum continuous-wave output power of 433 mW at 1066.1 nm was obtained. Using a quartz-based intracavity Lyot filter, an exceptionally broad continuous-wavelength tuning range of 98 nm was achieved. In the mode-locked regime, the diode-pumped Yb:KY(WO₄)₂ laser delivered soliton pulses as short as 46 fs at a central wavelength of 1069.2 nm by employing a SEmiconductor Saturable Absorber Mirror. To the best of our knowledge, these results represent the broadest continuous-wave tuning range and the shortest pulse duration ever reported for lasers based on ytterbium-doped monoclinic double tungstate crystals. Full article

Volatile organic compounds (VOCs) emitted from hardwood papers are associated with cellulose fibers, paper fillers, and the manufacturing process used. Volatiles emitted from samples of office (printing and writing) papers from various brands and countries were analyzed by gas chromatography–mass spectrometry (GC-MS) and an electronic nose (e-nose) based on piezoelectric quartz crystals. Dodecanoic acid 1-methylethyl ester (isopropyl dodecanoate) and nonanal have shown to be the dominant compounds in most of the samples analyzed, regardless of the pulpwood used in paper manufacturing: Eucalyptus globulus, acacia, and birch. 3-Hydroxybutanone was detected only in Spanish papers, suggesting it as a potential marker. Additionally, the content in acetic acid enables the identification of recycled paper. Full article

A lightweight composite that simultaneously exhibits high strength and excellent thermal insulation is of great interest for thermal protection applications. In this study, dimensionally stable needled quartz fiber felt-reinforced phenolic aerogel composites were prepared using vacuum impregnation, sol–gel, and ambient pressure drying. The composites exhibit a multiscale porous structure formed by interconnected nanometer polymer skeletons and micronscale fibers. By regulating the thermoplastic phenolic resin concentration in the precursor solution, the pore structure of the material was refined; the average particle diameter reduced from 99.76 nm to 38.91 nm, and the average pore diameter decreased from 216.79 nm to 49.53 nm. At a phenolic resin concentration of 25%, the composite exhibits outstanding thermal insulation and mechanical properties: a low thermal conductivity of 0.0646 W·m⁻¹·K⁻¹ at room temperature, with a mere 19.5 °C temperature rise on the sample backside after 1800 s heating at 200 °C, and compressive strengths of 7.70 MPa in the XY-direction and 3.87 MPa in the Z-direction (at 10% strain). X-ray micro-CT characterized the internal structural evolution during loading, revealing a failure mechanism dominated by fiber buckling. Theoretical models and experimental data were used to analyze and quantify the contribution rates of gas and solid heat conduction in NQF/PR aerogel composites, with solid conduction accounting for over 80%. Combined with microstructural evolution, the mechanism for the high thermal insulation efficiency of NQF/PR aerogel composites was elucidated. This study prepared NQF/PR aerogel composites with promising application potential. By systematically evaluating their compressive behavior and quantifying the respective contributions of gas and solid conduction, this work provides a methodological framework to guide the rational design of similar aerogel composites. Full article

Carbon Fiber Reinforced Thermoplastic Polymer (CFRTP) composites, particularly those utilizing Polyetheretherketone (PEEK) matrices, are becoming more demanding in the automotive and aerospace industries because of their outstanding strength, resilience to impact, and capacity for recycling. The employed heating methodology to prepare these materials is important both to improve them through uniform temperature distribution and to manage the energy consumption. The current study aims to address the encountered issues by experimentally comparing the radiative–thermal performance of medium-wave (1.4–2.5 µm) Quartz Tungsten (QTM) and long-wave (3.5–5.5 µm) Ceramic (FFEH) infrared emitters using a modular laboratory-scale heating system. While QTM emitters provided rapid heating rates, they induce significant through-thickness thermal gradients and surface degradation risks due to spectral mismatch with the polymer. In contrast, long-wave Ceramic emitters demonstrate superior spectral compatibility with PEEK, expanding the safe processing window and achieving complete melting at 343 °C with high thermal uniformity and approximately 18% lower effective energy demand compared to QTM systems. Furthermore, the structural integrity of the consolidated laminates has been validated through tensile testing, yielding an average tensile strength of 873 MPa and a tensile modulus of 56.3 GPa. These findings confirm the importance of optimizing the emitter wavelength not only for energy efficiency, but also for ensuring matrix integrity and mechanical performance in high-performance composite manufacturing. Full article

With the rapid development of aerospace technology towards hypersonic vehicles, the synergistic demand for lightweighting and high-efficiency thermal insulation performance of ablation-resistant thermal insulation materials is becoming increasingly urgent. In this study, nanoporous phenolic resin was used as the matrix to prepare quartz fiber-reinforced phenolic aerogel composites (QF/PF), mullite fiber-reinforced phenolic aerogel composites (MF/PF), and carbon fiber-reinforced phenolic aerogel composites (CF/PF), and the influence mechanisms of different reinforcing fibers on the properties of the composites were systematically investigated. QF/PF exhibits optimal thermal insulation performance with a thermal conductivity of 0.1 W/(m·K) at 20–200 °C, followed by MF/PF with a thermal conductivity of 0.11 W/(m·K). Relatively weak thermal insulation performance is demonstrated in CF/PF, whose thermal conductivity reaches 0.14 W/(m·K). However, in terms of mechanical properties, CF/PF is outstanding, with a tensile strength of 54.62 MPa and a bending strength of 29.69 MPa. In addition, the most excellent ablation resistance is displayed in CF/PF, with a linear ablation rate of 0.13 mm/s and a mass ablation rate of 0.0435 g/s, which are significantly lower than QF/PF and MF/PF. This study provides an important basis for the selection of reinforcing fibers in different application scenarios. QF/PF or MF/PF is preferred for high thermal insulation requirements. CF/PF is favored for high load-bearing requirements or extreme ablative environments. Full article

To meet the requirements of next-generation spacecraft thermal protection systems for lightweight materials with high strength, effective thermal insulation, and superior ablation resistance, a novel POSS-modified phenolic aerogel/quartz fiber composite (POSS-PR/QF) was developed using a thiol–ene click reaction combined with a sol–gel process. Covalent incorporation of polyhedral oligomeric silsesquioxanes (POSS) into the phenolic matrix effectively eliminates nanoparticle aggregation and improves interfacial compatibility. As a result, the modified resin is suitable for resin transfer molding (RTM) processes. The resulting composite exhibited an aerogel-like porous structure with enhanced crosslinking density, thermal stability, and oxidation resistance. At 7.5 wt% POSS loading, the composite achieved low density (~0.7 g·cm⁻³) and outstanding mechanical properties, with tensile, flexural, compressive, and interlaminar shear strengths increased by 114%, 79%, 29%, and 104%, respectively. Its thermal conductivity (0.0619 W/(m·K)) and ablation rates were also markedly reduced. Mechanistic studies revealed that POSS undergoes in situ ceramification to form SiO₂ and SiC phases, which create a dense protective barrier. In addition, this ceramification process promotes char graphitization, thereby enhancing oxidation resistance and thermal insulation. This work provides a promising approach for designing lightweight, high-performance, and multifunctional thermal protection materials for aerospace applications. Full article

The carved lacquer horse-hoof-shaped box excavated from Yulin, Shaanxi Province, represents a typical example of lacquerware preservation in the arid environment of northern China, exhibiting multiple deterioration phenomena, including substrate deformation, lacquer film peeling, and pigment fading. To systematically analyze its structural composition and craftsmanship features, this study employed multiple analytical techniques, including ultra-depth microscopy, scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS), confocal laser micro-Raman spectroscopy (Raman), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). Based on these analyses, a targeted conservation protocol was developed. Results revealed that the carved lacquer horse-hoof-shaped box has a wooden substrate structure, with the lacquer ash layer composed of mixed materials, including calcium carbonate (CaCO₃), quartz (SiO₂), and hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂). The lacquer film layer contains Chinese lacquer and plant oils, with cinnabar applied as surface decoration. Based on these findings, a stratified reinforcement conservation strategy was proposed: under dynamic monitoring with optical fiber sensors and three-dimensional scanning, the wooden substrate was reinforced with moisture-curable polyurethane (MCPU), the lacquer ash layer was strengthened with acrylic emulsion (Primal AC33), aged areas were restored with nano calcium hydroxide (Ca(OH)₂) aqueous dispersion, and polyethylene glycol (PEG 400) poultice application was implemented to restore the flexibility of the lacquer film. This research significantly enhanced the integrity and stability of the carved lacquer horse-hoof-shaped box, providing practical evidence and technical references for the scientific conservation of lacquerware excavated from arid regions of northern China. Full article

This study investigates the synergistic effects of steel fibers and waste rubber powder on the properties of ultra-high-performance concrete (UHPC) to advance its sustainable development. A comprehensive experimental program was conducted, incorporating three types of steel fibers (8 mm straight, and 14 mm and 20 mm hook-end) at volumes up to 2.5%, and rubber powder as quartz sand replacement at levels from 5% to 30%. The flowability, compressive strength, splitting tensile strength, abrasion resistance, and chloride ion penetration resistance of the mixtures were evaluated. The results indicate that steel fiber reinforcement significantly enhances the mechanical and durability properties. Specifically, a 2.5% steel fiber content increased the compressive strength, splitting tensile strength, and abrasion resistance by 28.9%, 55.3%, and 72.4%, respectively. Conversely, the incorporation of rubber powder improved flowability (optimal at 10% replacement) and abrasion resistance (increased by 41.1% at 30% content) but at the expense of reduced mechanical strength and increased chloride ion permeability. The primary novelty of this work lies in systematically quantifying the trade-offs and synergistic interactions between a wide range of steel fiber geometries and high-volume rubber powder content, providing a practical basis for designing UHPC with balanced performance and enhanced sustainability. Full article

In this paper, a highly ductile polyvinyl alcohol fiber engineered cementitious composite (PVA-ECC) was developed by replacing quartz sand (QS) with tuff stone powder (TP) at different replacement ratios of 20%, 40%, 60%, 80%, and 100%. The resulting mechanical properties and drying shrinkage were determined for the developed ECC. Qualitative and quantitative analyses of hydration products, pore structure, and micro-morphology of ECC were conducted by X-ray diffraction, thermogravimetric analysis, Fourier transform infrared spectroscopy, pore size and porosity, and scanning electron microscopic imaging. The influencing mechanism of tuff stone powder content on ECC performance was also studied at a micro level. It was found that with the increase in the replacement ratio of tuff stone powder, the ultimate tensile strain and tensile peak stress of ECC all exhibited an increasing trend, which declined afterward. The variation in compressive and flexural strengths also showed a similar pattern. When the replacement ratio of tuff stone powder was 40%, the ultimate tensile strain, peak tensile stress, flexural strength, and compressive strength were higher than the control group by 15.1%, 4.7%, 16.3%, and 10.7%, respectively. When the content of tuff stone powder did not exceed 80%, it could fill the internal pores of the ECC matrix, which reduced harmful pores. With the increase in tuff stone powder content, calcite content increases gradually while the Ca(OH)₂ amount decreases. It can be seen that tuff stone powder can improve ECC hydration products. However, incorporating tuff stone powder does not produce new hydration products. Incorporating tuff stone powder increased the drying shrinkage of ECC, and the value of drying shrinkage increased with the increase in the replacement ratio of tuff stone powder. Full article