In the field of materials science, aerogels have emerged as "star materials" across industries due to their unique nanoporous structure and exceptional comprehensive properties. From thermal protection for aerospace vehicles to battery safety in new energy vehicles, from building energy efficiency to wearable devices in extreme environments, the applications of aerogels continue to expand. However, with a wide range of aerogel products on the market, how do you accurately choose the most suitable material for your needs? This article analyzes the core properties to prioritize when selecting aerogels from multiple angles, combining the latest research progress and real-world application cases to provide practical guidance for readers.
Thermal Performance: The Dual Test of Thermal Insulation and High-Temperature Resistance
The thermal performance of aerogels is one of their core competitive advantages, primarily reflected in two aspects: thermal conductivity and high-temperature resistance.
Thermal conductivity is a key indicator for measuring a material's heat-insulating performance. For example, in the field of new energy vehicle power batteries, aerogel thermal insulation pads typically require a thermal conductivity below 0.025 W/(m·K) to effectively block heat transfer between battery cells and prevent the "domino effect" of thermal runaway. In building energy efficiency, novel cement aerogels use nano-micro multi-scale void designs to significantly extend heat transfer paths, achieving efficient blocking of heat conduction, convection, and radiation-with thermal conductivity even lower than that of traditional aerogels.
High-temperature resistance directly determines the material's application scenarios. A metal oxide nanoribbon aerogel developed by Tongji University maintains structural integrity after heat treatment at 1300°C for 2 hours. After being (burned) by a butane torch flame for 300 seconds, its average back temperature is only 68.6°C, demonstrating excellent high-temperature stability. In contrast, traditional aerogels are prone to sintering phase changes at high temperatures, limiting their use in extreme environments.
Mechanical Performance: The Art of Balancing Brittleness and Toughness
The mechanical performance of aerogels has long been a bottleneck for commercialization. Traditional inorganic aerogels, with their nanoparticle-assembled porous structures, often exhibit brittleness and poor compressibility. For example, traditional alumina aerogels can only withstand 4% compression, while Al-MNB aerogels prepared using a polymer micro-template method can endure up to 80% compression without fracturing.
To improve mechanical properties, researchers have proposed various strategies. Professor Liu Tianxi's team at Jiangnan University developed cellulose-silica aerogel composites using a freeze-polymerization strategy. Their core-shell nanofiber matrix structure gives the material excellent mechanical elasticity, maintaining stability even after long-term air calcination at 800°C. Additionally, composite fiber reinforcement (such as pre-oxidized fibers and glass fibers) is a common method to enhance aerogel toughness, preserving light weight while improving impact resistance.
Chemical Stability: Survival Capability in Extreme Environments
Aerogels may face chemical challenges like acid-base corrosion and oxidation in practical applications. For instance, in chemical pipeline insulation, materials must withstand corrosive media long-term. A pure polymer aerogel fiber fabric developed by Suzhou Institute of Nano-Tech and Nano-Bionics remains stable at 650°C and maintains structural integrity after soaking in strong acid or alkali for over half a year.
Chemical stability is closely related to material composition. Organic aerogels (e.g., polyimide aerogels) offer higher chemical resistance, while inorganic aerogels (e.g., silica aerogels) may undergo crystalline phase changes at high temperatures. Therefore, material selection should consider specific environmental conditions (e.g., pH value, redox conditions).
Environmental Adaptability: Strategies for Humidity and Temperature Fluctuations
Environmental factors significantly impact aerogel performance. In terms of humidity, hydrophilic aerogels absorb moisture easily, leading to structural damage, while hydrophobic aerogels (e.g., silica aerogels with organic functional groups) remain stable in high-humidity environments. For example, Southeast University's cement aerogel achieves a transformation from hydrophilic to super-hydrophobic through super-hydrophobic modification, significantly enhancing protection in humid conditions.
Temperature cycling is another key test. Aerospace aerogels must withstand extreme temperature differences from -230°C to 1400°C. New polyimide aerogels optimize their skeleton structure to not only provide effective thermal insulation but also absorb vibrational sound energy, reducing noise during launches.
Fire Resistance and Flame Retardancy: Hard for Safety Performance
In construction, transportation, and other fields, fire resistance is a basic requirement for aerogel materials. According to national standards, aerogel blankets must achieve fire rating A1 (non-combustible material), maintaining integrity in flames without producing molten drips. For example, the aerogel flame-retardant thermal insulation mortar developed by China Construction Eighth Engineering Division has low thermal conductivity and stays structurally stable under high-temperature flames, delaying fire spread.
Additionally, the combustion products of aerogels are important to consider. Tests show that high-quality aerogels mainly produce water vapor and carbon dioxide when burned, posing minimal harm to the environment and humans-meeting green safety standards.
Hydrophilic/Hydrophobic Properties: Critical Choices for Moist Environments
Hydrophilic and hydrophobic properties directly affect aerogel applicability in wet environments. Hydrophilic aerogels (e.g., pure inorganic silica aerogels) are lower in cost but prone to moisture absorption and fragility, suitable for dry conditions. Hydrophobic aerogels (e.g., organically modified aerogels), with hydrophobic groups introduced via surface modification, resist moisture and corrosion, ideal for high-humidity or underwater scenarios.
For example, hydrophobic aerogels prevent condensed water penetration in LNG cryogenic pipeline insulation, ensuring long-term stable thermal insulation. In adsorption applications (e.g., wastewater treatment), hydrophilic aerogels are preferred for their high specific surface area and adsorption capacity.
Density and Porosity: The Trade-off Between Lightweight and Functionality
Aerogels' low density (e.g., silica aerogel density as low as 0.2 g/cm³) and high porosity (80%-99.8%) are significant advantages, but trade-offs are needed for different applications. Aerospace demands extreme lightweighting, while construction may prioritize porosity for thermal insulation.
Porosity negatively correlates with thermal conductivity, but excessively high porosity may degrade mechanical properties. Material design (e.g., introducing nanofiber reinforcement) balances lightweighting and functionality. Tongji University's team, for instance, adjusted the nanoribbon structure of metal oxide aerogels to enhance compressive strength while maintaining high porosity.
Environmental Friendliness and Sustainability: Inevitable Requirements for Green Development
With growing environmental awareness, the sustainability of aerogel production processes and materials themselves has gained attention. Southeast University's cement aerogel uses a freeze-drying process, avoiding the high energy consumption of traditional supercritical drying, with recyclable raw materials that align with green manufacturing principles.
Service life is also an environmental consideration. High-quality aerogels degrade slowly over time, reducing replacement frequency and waste. For example, hydrophobic aerogels for buildings can serve stably outdoors for decades.
Cost-Effectiveness: Technological Considerations Behind Price-Performance Ratio
Aerogel costs depend on production processes, raw materials, and scale. Traditional supercritical drying is expensive, but new technologies like ambient pressure drying and freeze-drying have reduced costs significantly. Southeast University's cement aerogel, for example, costs just 1/20th of traditional aerogels, promoting its use in construction.
Selection requires balancing performance and cost. Cost-sensitive markets like building insulation favor low-cost aerogels, while high-end fields like aerospace prioritize performance over cost.
Optical Properties: Innovative Breakthroughs in Emerging Fields
In recent years, aerogels' optical properties have become a research hotspot. Silica aerogels, for instance, have a ratio of extinction coefficients for infrared to visible light exceeding 100 and a refractive index close to 1, making them suitable as transparent thermal insulation materials for smart windows and solar collectors. The "super-black" material developed by Suzhou Nano-Tech achieves a light absorption rate of 99.72% by suspending light-absorbing nanoparticles in ultra-low reflectivity aerogels, with broad applications in photocatalysis and pyroelectricity.
In building energy efficiency, transparent thermal-insulating aerogel glass allows visible light transmission while blocking infrared radiation, reducing building energy consumption. A new aerogel composite glass, for example, reduces heat transfer by about 50% compared to conventional hollow components while meeting daylighting needs.
Conclusion
When selecting aerogel materials, core indicators such as thermal performance, mechanical properties, chemical stability, environmental adaptability, fire resistance, hydrophilic/hydrophobic properties, density and porosity, environmental friendliness, cost-effectiveness, and optical properties must be evaluated based on specific applications. For example, new energy vehicle batteries prioritize thermal conductivity and flame retardancy; aerospace focuses on high-temperature resistance and impact resistance; and building energy efficiency balances thermal insulation and cost.