Search Results (346)

Phenolic aerogels, owing to their low density, high char yield, large specific surface area, and well-defined three-dimensional topological networks, hold considerable promise for applications in extreme thermal protection and multifunctional material systems. The sol–gel process, a cornerstone methodology for constructing the three-dimensional nanoporous architecture of these materials, critically governs the resulting microstructural topology and macroscopic performance through its reaction kinetics, phase-separation behavior, and drying dynamics. This review systematically surveys recent advances in the sol–gel synthesis of phenolic aerogels, focusing on the polycondensation mechanisms operative under acidic and basic catalytic conditions, nucleation-and-growth kinetics, and strategies for tailoring multiscale pore structures. It further provides a comparative analysis of interfacial regulation mechanisms for capillary-stress elimination across supercritical drying, freeze-drying, and ambient-pressure drying routes. We also dissect the structure–property relationships underpinning Knudsen-effect-mediated gaseous thermal insulation, multi-scale hybrid network toughening, and inorganic phase-transition-induced in situ ceramization for thermal protection, demonstrating the synergistic optimization of thermal insulation, structural load-bearing, and ablation resistance. Finally, we summarise current applications in extreme thermal protection, environmental adsorption, electromagnetic interference shielding, and electrochemical energy storage and highlight future directions towards green, scalable manufacturing and intelligent materials design. Full article

To improve the resource utilization of decoration waste and enhance the thermal insulation performance of building mortar, this study designed and prepared decoration waste aerogel mortar (DWAM) using decoration waste recycled fine aggregate (DWRA) combined with silica aerogel. The effects of paste-to-aggregate ratio (30/70, 35/65, and 40/60), aerogel content (60–100 vol.%), and air-entraining agent (AEA) dosage (0.1–0.5 wt%) on workability, dry density, mechanical strength, and thermal conductivity were systematically investigated. Microstructural evolution and pore characteristics were analyzed using scanning electron microscopy (SEM) and X-ray computed tomography (X-CT). Results showed that increasing the paste-to-aggregate ratio improved workability and mechanical strength, while aerogel and AEA incorporation significantly reduced thermal conductivity at the expense of strength. An optimum mix with a paste-to-aggregate ratio of 40/60, aerogel content of 80 vol.%, and AEA dosage of 0.4 wt% achieved a dry density of 623.8 kg/m³, compressive strength of 1.27 MPa, flexural strength of 0.61 MPa, and thermal conductivity of 0.0784 W/(m·K). X-CT revealed that closed micropores enhanced thermal insulation by disrupting heat transfer. The developed DWAM offers balanced workability, mechanical properties, and thermal insulation, demonstrating strong potential as a sustainable material for building applications. Full article

This study investigates the thermal performance of additive-free bacterial cellulose (BC) aerogels and cryogels produced by Acetobacter xylinus under controlled static cultivation conditions. The influence of supercritical CO₂ (ScCO₂) drying and freeze-drying on the multiscale structure and functional properties of BC materials was evaluated. Since BC is biosynthesized by a living microbial system, minor biological variations in fibril organization and network formation may occur even under standardized cultivation conditions. To minimize variability, all samples were produced, purified, and processed using identical procedures prior to drying. The materials were characterized using SEM, DSC, and Alambeta thermal analysis, while environmental temperature and relative humidity were monitored during testing. The two drying routes produced differences in fibrillar organization, accessible pore characteristics, and thermal transport. ScCO₂-dried aerogels showed a more homogeneous nanofibrillar morphology, whereas the lyophilized cryogels exhibited thermal conductivity values of 0.032–0.041 W·m⁻¹·K⁻¹, comparable to those of the ScCO₂-dried specimens (0.040–0.042 W·m⁻¹·K⁻¹). Overall, the results demonstrate that controlled lyophilization can produce additive-free porous BC with thermal performance comparable to ScCO₂ drying under the investigated conditions. The lightweight, highly porous, fibrous character of these materials further supports their relevance for functional textile systems, including bio-based nonwoven or layered thermal-insulation structures, while lyophilization offers a comparatively simple processing route. Full article

To address the dependence on organic solvents, costly silicon precursors, and complex processing in conventional silica aerogel preparation, this study developed a green and low-cost aqueous route using water glass as the silicon source. The sol–gel process was optimized through an orthogonal experimental design by regulating precursor concentration, pH, temperature, and catalyst dosage, enabling the formation of a stable three-dimensional silica network. Under the optimized conditions, the unmodified silica aerogel exhibited low density, high porosity, and a typical mesoporous structure, with a specific surface area of 707.87 m²/g, an average pore size of 5.75 nm, and a thermal conductivity of 0.0408 W/(m·K). After HMDS vapor-phase modification, hydrophobic methyl groups were introduced onto the aerogel surface, increasing the water contact angle to 132.3°. Among the modified samples, S3 showed the lowest thermal conductivity of 0.0360 W/(m·K), indicating good thermal insulation performance. This work provides a feasible strategy for preparing hydrophobic silica aerogels through a cost-effective aqueous process, showing potential for greener and large-scale production of silica aerogel materials. Full article

This study evaluates high-silica fiber/silica aerogel composites (HSFACs) for the passive fire protection of bridge cables. The primary objective is to reveal the high-temperature degradation mechanism of HSFAC and quantitatively determine a reliable thickness scheme for long-term hydrocarbon-fire protection of bridge cables. HSFAC specimens were heat-treated and characterized by thermal conductivity, tensile testing, SEM/TEM, FTIR, and TG analysis. A self-built furnace was used to assess an HSFAC-based cable protection system under hydrocarbon-fire exposure. Increasing heat-treatment temperature enlarged the pore and particle sizes of HSFAC and reduced its thermal-insulation performance. During 120 min of fire exposure, the cable protected by a single 5 mm HSFAC layer reached 300 °C within 45 min, whereas the cable protected by a double-layer 5 + 5 mm HSFAC system remained below 300 °C throughout the test. Finite element simulations validated against the experimental results confirmed that increasing HSFAC thickness improved thermal protection. After 90 min, the predicted cable-surface temperatures were 556 °C and 314 °C for HSFAC thicknesses of 5 mm and 10 mm, respectively. By integrating high-temperature material characterization, HC-fire testing, and thickness-dependent numerical analysis, this study links material degradation to system-level fire performance and provides a quantitative basis for HSFAC thickness design. Full article

Localized densification of nanoporous silica under combined mechanical compression and elevated temperature involves coupled pore collapse, skeletal rearrangement, and thermally activated sintering. Clarifying how local pre-compression regulates these processes is important for understanding the surface and near-surface densification of nanoporous silica and related porous materials. In this study, the microscopic sintering behavior of a silica-inspired aerogel-like nanoporous model under the coupling of non-uniform local stress and high-temperature fields (indentation depths of 50–150 Å and temperatures of 298–1800 K) was systematically investigated using molecular dynamics simulations combined with a three-dimensional (3D) topological recognition algorithm (probe sphere method and DBSCAN clustering). The results indicate that the sintering densification of the silica-inspired aerogel model exhibits significant pore-size dependence and a “depth-temperature inverse relationship”: the local pre-compression induced by the 150 Å indentation facilitates thermally activated atomic rearrangement and shifts the onset of densification to a lower temperature, leading to an early bimodal splitting of the pore size distribution at 1300 K, accompanied by a significant jump in the elastic modulus from 3.0 to 10.07 GPa. In contrast, the 50 Å shallow region requires heating to 1800 K to achieve an equivalent densification effect. Furthermore, topological analysis quantitatively reveals the phase transition process of the pore network from connected to isolated: taking 1300 K as an example, the number of connected pore clusters decreases from the initial 86 to 70 (at 1000 ps), marking the fracture of the connected network; subsequently, the number of isolated pores surges to 4861, and the residual connected framework is severely fragmented into 136 micro-clusters. Based on the above microstructural and topological evolution data, a four-stage thermo-mechanical synergistic evolution process of the silica-inspired aerogel model is summarized. These findings provide quantitative fundamental data that conceptually supports the design of functional gradient structures with alternating “dense-thermally-conductive” and “porous-thermally-insulating” layers within a single continuous aerogel matrix; such structures may be realized in the future through strategies such as arrayed nanoindentation combined with high-temperature sintering. Full article

Cellulose-based aerogels are promising sustainable thermal-insulation materials, but their practical application is often limited by insufficient mechanical robustness and intrinsic flammability. Herein, a multiscale network-engineering strategy is proposed to fabricate a cellulose-based composite aerogel integrating structural stability, thermal insulation, and fire safety. By synergistically introducing in situ generated aluminum trihydroxide (ATH) and microencapsulated APP@ATH–MEL into the cellulose scaffold, the flame-retardant components function not only as active fire-safety agents but also as structural regulators that promote the formation of a highly interconnected hierarchical framework. This regulated architecture enhances interfacial interactions, improves load-transfer efficiency, suppresses structural collapse during freeze-drying, and introduces tortuous pathways and abundant interfaces for heat-transfer regulation. As a result, the optimized composite aerogel exhibits a low thermal conductivity of 35 mW·m⁻¹·K⁻¹ together with improved compression resistance. Thermal analysis reveals a reduced mass-loss rate and increased char yield, while cone calorimetry confirms suppressed heat release, reduced gaseous emissions, and improved residue stability. The enhanced fire safety is attributed to a synergistic multi-phase mechanism involving endothermic shielding, gas-phase dilution, condensed-phase char formation, and inorganic-residue reinforcement, which collectively inhibit heat and mass transfer during combustion. This work provides an effective strategy for the design of lightweight, mechanically robust, and fire-safe cellulose-based composite aerogels for advanced thermal-insulation applications. Full article

Polymer/Silica aerogel (SA) composites improve mechanical properties strategically, but the mixing process disrupts the aerogel’s structure, reducing its efficiency due to polymer chains filling the pores. Pre-vulcanized natural rubber latex (PVNRL) with a higher crosslink density can strain the moving chains, thereby preserving the SA-porous structure in the bulk composite for thermal insulation materials. This study aimed to investigate the effects of PVNRL pre-vulcanization time and SA-immersion time in PVNRL. For PVNRL/SA composite preparation, various PVNRL, from 0 days to 8 days of pre-vulcanization time, were mixed with a fixed SA content of 20 parts per hundred of rubber (phr) using a latex compounding method. Subsequently, the PVNRL/SA slurries were cast on glass plates with 0, 3, and 6 days to obtain the PVNRL/SA composite. Considering the effect of pre-vulcanization time, the crosslink density of the composite increased and revealed a peak at PVNRL/SA with 8-day PVNRL by 7.277 ± 0.881 μmol ${\mathrm{g}}^{-1}$, corresponding to the closest percentage of pore area in the SA’s structure to the pristine SA, and eventually a 42.41% lower thermal conductivity than the PVNRL/SA with 0-day PVNRL exhibited. In addition, the thermal conductivity increased more slowly over immersion time with the presence of 8-day PVNRL. The proposed correlation states that increasing the pre-vulcanization improves the thermal insulation performance of PVNRL/SA composites, emphasizing the reduction of filled SA’s pore with unvulcanized NR chains. Furthermore, the PVNRL/SA composite with 8-day PVNRL maintains thermal stability at 387.3 °C, and can be flexed at room temperature. These fascinating discoveries may be advantageous for further applications related to thin-film and flexible thermal insulation materials. Full article

Hydrophobic silica aerogels are widely used as thermal-insulation materials, but the thermal decomposition of their organic surface groups may affect their stability and safety during high-temperature service. In this study, ambient-pressure-dried silica aerogels modified with trimethylsilyl, dimethylsilyl, and methylsilyl groups were prepared and denoted as TSA, DSA, and MSA, respectively, to clarify how the degree of methyl substitution in the surface modifier controls the pyrolysis behavior of hydrophobic silica aerogels. Thermogravimetric analysis at different heating rates was combined with TG-FTIR, a model-free kinetic analysis, a model-fitting analysis and thermodynamic calculation. With decreasing methyl substitution from TSA to MSA, the aerogel framework became denser, the specific surface area decreased, and the contribution of solid-phase heat transfer increased slightly. The main pyrolysis process occurred at 250–800 °C and involved multiple overlapping reactions. The average activation energies of TSA, DSA, and MSA were 241.4, 246.6, and 285.5 kJ/mol according to the Kissinger–Akahira–Sunose (KAS) method and 243.0, 248.2, and 289.0 kJ/mol according to the Flynn–Wall–Ozawa (FWO) method, respectively. The higher activation energy of MSA indicates that the more condensed silica-rich framework and lower organic methyl content improves its resistance to the main degradation process. The model-fitting analysis further suggested an A1/2 mechanism for TSA and A2/5 mechanisms for DSA and MSA. TG-FTIR further confirmed the evolution of CO₂, H₂O, CH₄, and C₂H₄ and revealed distinct gas-release behaviors among the three samples. These results demonstrate that the surface methyl-substitution structure governs the balance between hydrophobic modification, pore-structure preservation, pyrolysis resistance, and volatile-product release, providing a basis for selecting surface modifiers for thermally stable silica-aerogel insulation materials under oxygen-limited high-temperature conditions. Full article

Building energy consumption accounts for a significant proportion of total societal energy consumption, and reducing building energy consumption is critical to the global mission of reducing emissions. Windows are regarded as the least energy-efficient component of a building’s envelope. This study examines service-area buildings fitted with high-performance glass in Chinese cities across various climates and employs the non-dominated sorting genetic algorithm II (NSGA-II) genetic algorithm for multi-objective optimization. In considering design variables such as building orientation and wall insulation, advanced passive design strategies, including electrochromic and aerogel glass, are incorporated into the optimization process to minimize construction costs and operational carbon emissions. Sensitivity analyses were conducted to evaluate the impact of each design variable on building operational carbon emissions. The optimal solution within the Pareto optimal set was further evaluated using the technique for order preference by similarity to ideal solution (TOPSIS) decision-making method, and the preferred energy-saving solution was quantitatively analyzed. The results indicate that optimization leads to a reduction of approximately 7.70–10.50% in annual operational carbon emissions for service-area buildings across different regions, compared to the base case, with a payback period ranging from 4.90 to 13.56 years. The proposed method contributes to sustainable building design by jointly quantifying carbon-emission reduction, construction cost, and payback period, thereby supporting climate-responsive and economically feasible low-carbon envelope decisions for service-area buildings. Full article

The curing quality of epoxy resin at wind turbine blade joint seams critically affects blade integrity and service reliability, yet conventional metallic heating systems often suffer from poor temperature uniformity, limited flexibility, and slow thermal response. In this study, a flexible and lightweight heating blanket based on carbon nanotube (CNT) electrothermal film was developed for blade reinforcement and in situ curing applications. The device employs a multilayer composite architecture consisting of a CNT heating layer, a nano-aerogel thermal insulation layer, a thermoplastic polyurethane electrical insulation layer, and a silicone-coated glass fiber protective layer, together with an intelligent temperature control system. The resulting blanket, with a total thickness of 3.85 mm, exhibited rapid and stable heating performance, increasing from 25 to 120 °C within 8 min. Under resin-curing conditions, it achieved an initial heating rate of 7.2 °C min⁻¹ and a temperature uniformity of ±2.6 °C, markedly outperforming a conventional Ni@Cr alloy heating blanket. Accelerated aging tests further demonstrated stable electrothermal performance under the tested condition. Those results indicate that the proposed CNT-based heating blanket provides an efficient and reliable thermal management strategy for large curved composite structures. Full article

High-performance thermal protection materials are urgently required in harsh thermal environments, such as hypersonic vehicles, the thermal runaway of energy batteries and high-temperature equipment. Conventional aerogels only exhibit passive thermal insulation and fail to resist instantaneous high-temperature attack. Herein, a cooling material of ammonium oxalate (AO) was introduced to achieve efficient, active endothermic protection. A cellular isolation effect induced by graphene nanosheets combined with anti-solvent crystallization was adopted to significantly decrease the size of AO crystals by over 93%. Based on superfine morphology and the constructed conduction network, the decomposition rate and heat absorption capacity of obtained graphene-doped AO powders (GdAPs) are improved by 41.2% and 30.4%, respectively. The mechanisms of morphology regulation and enhanced heat absorption are explored specifically in this study. Furthermore, GdAPs are embedded in phenolic resin to prepare thermal protection composite materials. Benefiting from their nearly complete thermal decomposition, GdAPs serve as a sacrificial template to generate discrete micropores in pyrolyzed resin. So, the as-prepared carbon aerogels (CAs) with a regulable microstructure exhibit an extremely low thermal conductivity of 0.056 W/(m·K), which is lower than those of reported CAs with the same density. Based on the above advantages, a synergistic endothermic-insulating thermal protection material is reported for the first time, and its heating rate is only 28.6% of that of commercial silica aerogel under identical high-temperature shock. Therefore, a new accessible strategy is demonstrated to provide high-efficiency thermal protection for resisting both abrupt and prolonged high temperature. Full article

Aerogels were produced exclusively from recycled plastic bottles of poly(ethylene terephthalate) (rPET) by optimising a dissolution–precipitation process at room temperature and applying a product design strategy to improve their sustainability. Using a design of experiments methodology, the systematic assessment of the influence of different factors, namely rPET concentration, co-solvent ratio, and non-solvent quantity, on the key properties of rPET aerogel, namely bulk density, thermal conductivity, and mechanical resistance, was performed. The understanding of the significance of each parameter and the optimisation of a desirability function offered reliable optimum results for the adjustment of the experimental procedure for the reduction in the volume of the most critical solvent, trifluoroacetic acid (TFA), by 42.5%. The observed bulk density values were excellent, down to 110 kg·m⁻³, and the thermal conductivity was in the range of conventional commercial insulators (38 mW·m⁻¹·K⁻¹), positioning this material as a real alternative to conventional thermal insulators. Also, to deeply understand the dissolution/precipitation phenomena, molecular dynamics simulations were conducted to support the experimental outcomes. Full article

It is well-known that high-performance thermal protective clothing is crucial for personnel working in high-temperature environments, such as firefighters. Thermal protective clothing design usually integrates textile materials’ type, thickness, physical and chemical properties (such as thermal conductivity), ergonomics, and environmental adaptability. In this study, the heat transfer process and the optimal thickness are mainly discussed for providing some references on the design of this clothing. The thickness design of thermal protective clothing fabrics is carried out via numerical heat transfer simulations based on experimental data obtained from manikin tests. Firstly, one heat transfer model for thermal protective clothing, including three textile materials’ layers and one air layer, is constructed according to Fourier’s law of heat conduction, Newton’s law of cooling, and the Stefan–Boltzmann law, with appropriate boundary conditions assigned. Secondly, the finite volume element method, which has the important advantage of preserving conservation properties for physical quantities, is employed to discretize the heat transfer model. Thirdly, the convective heat transfer coefficient, which characterizes heat exchange between fluid and solid surfaces, is determined approximately by the least-squares method based on the given data, while the heat transfer process is simultaneously simulated. Fourthly, the thicknesses of the second and fourth layers are critical to the performance of thermal protective clothing. Two optimization algorithms are proposed to determine the optimal thickness configuration that effectively balances thermal insulation and wearing comfort. From the above results, it is recommended to use multilayer textile composite materials incorporating aerogel insulation layers and phase-change material interlayers. Full article

Radiative heat transfer in aerogels (semi-transparent materials) acts as a participating medium, causing notable errors in conventional steady-state thermal conductivity measurements. Coupled conduction–radiation heat transfer is numerically simulated to examine the influence of variations in the heating plate-specimen interface emissivity on thermal conductivity measurements, and the simulation results are experimentally validated using test systems with differing interface emissivities. The results show that the effect of interface emissivity on effective thermal conductivity is more obvious under high temperatures and low extinction coefficients. When the average temperature is 1273 K, the emissivity decreases from 1 to 0.2, and the effective thermal conductivity with extinction coefficients of 3.5 m⁻¹ and 3500 m⁻¹ decreases by 76.1% and 24.1%, respectively. Experimental results show that when the hot surface temperature is 873 K, the cold surface temperature differences in different test systems can reach 30 K. The experimental results have the same trend as the steady-state simulation results, which verifies the accuracy of the numerical simulations. Quantitative analysis of the steady-state heating measurement results demonstrates the effect of medium radiation in semi-transparent materials on the obtained results. The findings contribute to a more accurate characterization of silica aerogel composites and provide new insights into the influence of radiative heat transfer on thermal conductivity evaluation in semi-transparent aerogel materials, which is important for the development and application of aerogel-based thermal insulation systems. Full article