Applications Of Silica Aerogels Research Articles

Effects of mechanical grinding on the physicochemical properties of silica aerogels

Mechanical grinding is a facile method to get silica aerogels (SAs) with various particle sizes. However, the relationship between the grinding parameters and physicochemical properties is still unclear. In this study, we concentrated on the effects of grinding time and grinding speed on the physical and chemical properties of silica aerogels. The results reveal that the physicochemical properties of silica aerogels are more sensitive to the grinding speed rather than the grinding time. When the grinding speed is over 200 rpm, large particles of silica aerogels are crushed into smaller particles with obviously decreasing particle sizes and the silica skeletons of silica aerogels have collapsed. The reduction of particle sizes and the collapse of skeleton lead to an increase in both the tap density and thermal conductivity. Therein, the thermal conductivity is positively proportional to the density. Furthermore, the grinded silica aerogels powders still possess the contact angles over 135°, indicating the good hydrophobicity. All these demonstrate that the mechanical grinding has evident effects on the microstructure, density, thermal conductivity and particle sizes, which further impact the performance of silica aerogels during the practical applications. Given the expanding applications of SAs across various industries, the study serves as a valuable reference for optimizing the mechanical post-treatment of SAs, facilitating the achievement of desired particle sizes. Ultimately, this research holds great potential in diversifying the application fields of SAs in their powdered form.

Silica–Chitosan Composite Aerogels for Thermal Insulation and Adsorption

The dissipation of energy in the form of heat causes a huge energy loss across the globe. Thermal insulation materials which reduce heat loss can alleviate the energy crisis. Among many thermal insulation materials, silica aerogels (SAs) have attracted extensive attention due to their high surface area, low density and low thermal conductivity. However, the applications of SAs are restricted by their mechanical fragility. In this paper, a series of different ratios of silica–chitosan composite aerogels (SCAs) were prepared by mixing sodium silicate aqueous solution and chitosan solution followed by freeze drying. The surface morphology of SAs, CAs and SCAs was studied by scanning electron microscopy (SEM). The specific surface area, pore volume and pore size of the composite aerogels were studied by N2 adsorption–desorption isotherms. The thermal conductivities, chemical structures, thermal stabilities and hydrophobicities of SAs, CAs and SCAs were tested and analyzed. In addition, the adsorption properties of SCAs were measured using different organic solvents. The results reveal that when the proportion of sodium silicate aqueous solution and chitosan solution is 1:1, the obtained SCA−1/1 has the best performance, with a low thermal conductivity of 0.0369 W/m·K, a large specific surface area of 374.7 m2/g, and good thermal stability. In addition, the prepared SCAs also have good hydrophobicity and absorption properties, with adsorption capacities of 6.7–9.4 g/g, which show great application potential in the fields of insulation and adsorption.

Ultrasensitive and Self-Powered Multiparameter Pressure-Temperature-Humidity Sensor Based on Ultra-Flexible Conductive Silica Aerogel.

The application of silica aerogel has been limited because of its poor mechanical properties. In order to expand the application scope of silica aerogel, this study fabricated an ultra-flexible conductive silica aerogel as a multiparameter sensor. The sample is fabricated by introducing poly (3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) on a base of ultra-flexible silica aerogel, which was prepared by a diene synthesis reaction at atmospheric pressure. The pressure, temperature, and humidity can be converted into electrical signals. The pressure sensitivity can reach up to 54.88 kPa-1, and the detection limit is as low as 5 Pa. The temperature resolution is up to 0.1 K, and the response time of humidity is within 4 s. More importantly, the developed multiparameter sensor can be self-powered to realize multiparameter sensing of pressure, temperature, and humidity. The ultra-flexible conductive silica aerogel is a promising candidate for monitoring human activities and fire-affected areas.

Silica aerogels: from materials research to industrial applications

ABSTRACT Silica aerogels are advanced materials with outstanding properties, including high specific surface area and porosity, low thermal conductivity, density, dielectric constant, and refractive index. However, the excellent properties of silica aerogels have shown limited utility in industrial applications, primarily as thermal insulation materials, where they hold only a small (1.1–2.6%) market share. The emergence of clean energy technologies stimulated renewed interest in silica and other aerogels. Here the recent advances in the production and applications of silica aerogels are summarized, and the current challenges and future development opportunities are discussed. The conventional and emerging syntheses and characterization methods of silica aerogels are introduced, followed by a discussion on thermophysical properties and potential applications. The fabrication processes of silica aerogels are analysed at different industry development stages. Recent advances in aerogels research are considered, highlighting the obstacles and possible solutions for the successful translation and industry uptake and focusing on the emerging applications in electric vehicles and building insulation.

Effect of silica aerogel on thermal insulation and acoustic absorption of geopolymer foam composites: The role of aerogel particle size

Silica aerogel features super thermal insulating and excellent sound absorption. Although the application of silica aerogel in building materials for energy saving has been investigated recently, the role of aerogel particle size on geopolymer foam render can be crucial but is rarely studied. In this research, four kinds of silica aerogel with different particle sizes (2–40 μm, 100–700 μm, 100–1200 μm, 700–4000 μm) are applied in geopolymer foam aerogel render (GFAR) to improve the thermal insulation and acoustic absorption performance. Results show that larger silica aerogel particles are more beneficial for acoustic absorption and thermal insulation while smaller aerogel particles are less effective for insulation properties. The microstructure of GFAR is investigated in-depth with micro-CT, optical microscopy and ultrasonic pulse velocity test. The mechanism of the improved performance of GFAR with different silica aerogel is explained. The optimal geopolymer foam aerogel render (GFAR) reaches a thermal conductivity of 0.133 W/(m·K), an average value of acoustic absorption coefficient of 0.51 with a density of 715.2 kg/m3. The result of this study is essential to enlighten the use of larger silica aerogel particles in geopolymer foam render, focusing on a low dosage of silica aerogel while utilize its full benefit.

Isocyanate-crosslinked silica aerogel monolith with low thermal conductivity and much enhanced mechanical properties: Fabrication and analysis of forming mechanisms

The applications of silica aerogels are restricted due to their intrinsic fragile property. Polymerization of di-isocyanates can be templated onto the mesoporous surface of the –NH2 group modified silica clusters, resulting in the conformal crosslinked coating on surface of silica clusters. Aminopropyltriethoxysilane (APTES), as the silica co-precursor and amine group modification agent, is involved containing tetramethyl orthosilicate (TMOS) silica precursor, while hexamethylene diisocyanate (HDI) is incorporated as the polymer crosslinking agent. The effects of different amounts of APTES on the physicochemical properties of the resulting crosslinked aerogels are investigated. The results show that the optimized APTES/TMOS volume ratio can be determined at 0.5:1. The resulting optimal crosslinked silica aerogel possesses large BET specific surface area of 150.9 m2/g, low thermal conductivity of 0.037 W/(m·K), and the Young's modulus is as large as 18 MPa under strain of 4.2%, much higher than that in the previously published works. The polymerization reaction mechanism forming the polyurethane chains has also been proposed. In addition, the interactions between silica clusters and polymer chains are studied by molecular mechanics and molecular dynamics. The interactions are mainly dependent on non-bonding energy, and the electrostatic energy has decisive impact on the combination of silica clusters and polymer chains. The density field of C, H, N, O, and Si elements overlaps with each other, indicating that the polymer crosslinked silica aerogel maintains typical three-dimensional porous structure. The N element enriches in the region between silica clusters, further verifying the formation –CONH–(CH2)6–CONH- polyurethane chains, which is actually responsible for the much enhanced mechanical property.

A novel preparation of superhydrophobic silica aerogels via the combustion drying method

Silica aerogels with prominent physical, thermal, optical, and acoustic properties are considered to be highly promising materials. However, owing to the high cost and the complex production processes associated with existing drying technologies, the application of silica aerogels is limited in many fields. In this study, a novel combustion drying method (CDM) was successfully used in the synthesis of superhydrophobic silica aerogels for the first time. It was confirmed that silica aerogel prepared by CDM has a typical aerogel structure with low density, high porosity, high specific surface area, high total pore volume, superhydrophobicity and high thermal stability. Compared with supercritical fluid drying, freeze drying and ambient pressure drying, CDM possesses significant advantages in the drying efficiency and low-cost production due to its active drying mode. Finally, the mechanism of the combustion drying method is proposed based on the combustion of organic solvents. The results will be meaningful for the design and production of aerogel materials in the future.

Application of Silica Aerogel in Composites Protecting Against Thermal Radiation

Abstract Aerogels are characterized by excellent insulation properties and a good resistance to high and low temperatures. The objective of this study was to investigate the effects of silica aerogel on thermal properties of textile–polymer composites. Aerogel was applied in protective clothing fabric to improve its heat resistance. The composites were produced by coating a fabric made of meta-aramid (polyamide–imide) yarns with a dispersion of polychloroprene latex and synthetic resins or an acrylic–styrene dispersion with aerogel (100–700 μm particle size). The composites were subjected to thermal radiation (20 kW/m2) and their thermal properties were determined by thermogravimetry/derivative thermogravimetry (TG/DTG). Scanning electron microscopy/X-ray energy dispersive spectroscopy (SEM/EDS) was used to characterize the microstructure and study the elemental composition of materials. The thermal conductivity and resistance of composites were measured with an Alambeta apparatus. The tests indicated an increase in resistance to thermal radiation by approximately 15–25%. In TG/DTG analysis, the initial temperature for an unmodified fabric was 423.3°C. After modification, it decreased to 361.8° and 365.3°C for composites with 7 and 14% of aerogel, respectively. SEM images revealed a reduction in aerogel particle size.

Predictive Performance of Hygro-Thermal Simulation Models: A Case Study

In recent years, many researchers have focused on the energy efficiency and performance of existing buildings. In order to predict the hygrothermal performance and minimize the risk of moisture damage in retrofit cases, user-friendly moisture calculation tools have been developed. However, concerns have been raised as to how to increase the reliability of such tools. In this context, the present study uses simulation to investigate the retrofit potential of the historical building façades via application of silica aerogels on the external walls. Monitored data provided the basis for generation of a more accurate initial simulation model, as well as the evaluation of the predictive performance of the model.

Some Applications of Silica Aerogels

AbstractFor Abstract see ChemInform Abstract in Full Text.

Some applications of silica aerogels

Silica aerogels are very highly divided materials which are synthesised through the association of a chemical step, the so-called sol–gel chemistry, with a physical step which is a particular way of drying the wet gel, namely under supercritical conditions with respect to the liquid phase filling its porosity. This drying process preserves the texture of the dry material: in practice it strongly reduces the pore collapse. The resulting hyperporous solids that have bulk densities of the same magnitude as air develop new and very interesting physical and even chemical properties. Owing to their poor chemical reactivity, very large surface areas (of the order of 1,000 m2/g), unusual porous volumes (greater than 95%), morphologies (monoliths or powders), optical properties (transparent, opaque or translucent), and very low thermal conductivity, they find high added-value applications in the physics of high-energy particles (Cherenkov emitters), transparent and superinsulating double windows, life and space science as well.

Solidification of aluminium alloys in aerogel moulds

A new application of silica aerogels is presented, using them, for the first time, as a mould material for the casting of metals. Aluminium alloy melts were cast into forms machined from thick silica aerogel plates. The excellent thermal insulation properties of aerogels lead to a nearly one-dimensional cooling and solidification process. This is reflected by the microstructure of the solidified samples. Owing to the transparency of the aerogels, it is also possible to study the cooling process with the help of optical measurements and video techniques. Using an infrared camera, the velocity of the solidification process and the temperature gradient ahead of the solid-liquid interface were obtained from video signals. These can be directly correlated with the microstructure. The successful results of these casting experiments have initiated a more detailed study of the potential offered by aerogels for researching solidification processes. One example is a new type of Bridgeman furnace using aerogels as a crucible material and a special feedback loop controlling the solidification processes without movable samples or heaters like in a classical Bridgeman configuration. The concept of such a furnace is presented and first experimental results are shown.