Silica-based Aerogel Research Articles

Novel atmospheric pressure drying method for silica-based aerogel insulation: Inspired with the adult process of damselflies

The high production cost and extremely weak mechanical properties of SiO2 aerogels have been two major challenges hindering its widespread application. Atmospheric pressure drying (APD) has always been regarded as the optimal process to reduce costs. However, traditional APD is cumbersome, still uses a large amount of expensive raw materials, and is extremely immature. In this study, a novel APD was developed, inspired by the wing changes during adult damselfly process. Inorganic silica source/water was used as the raw material, and CO2 was used instead of low surface tension solvent to stabilize the aerogel skeleton structure in situ, and ultimately aerogel material was obtained. The thermal conductivity of pure aerogels was as low as 0.0264 W/(m·K), the porosity reached 94.7 %, and the preparation cycle was only 28.5 h. The thermal stability of the skeleton structure and the chemical stability of surface were investigated and showed the hydrophobicity to withstand temperatures up to 400 °C. Aerogel composites feature low thermal conductivity of 0.0283 W/(m·K), and prominent thermal insulation properties over a wide temperature range of 50–300 °C. For traditional APD, this method shortens preparation cycle by 1–6 times. Compared with the commercial aerogel, the cost is reduced by 38.2 %, and the process is simple and environmentally friendly under the premise of ensuring excellent performance.

Structural properties and barrier performance of low-cost aerogel composites for building insulation

The high cost and weak mechanical properties of silica-based aerogel seriously affect its wide application in the field of building insulation. In this paper, low-cost SiO2 aerogel (WSA) was prepared based on water glass/water system, and the modulation of aerogel network structure was achieved under the dual effect of sodium methylsilicate (SMS) and pH. WSA exhibits extremely low density (∼88.5 kg/m3) and thermal conductivity (0.02114 W/(m·K)) as well as high hydrophobicity (150°). The cost of WSA is 53 % lower compared to atmospheric pressure drying and 21.5 % lower than commercial aerogel. On this basis, rock wool fiber felt (RWF) and ultrafine glass fiber wool felt (UGFW) were modified with WSA. The effect of fiber arrangement on the force-thermal coupling property of WSA@RWF was investigated. Meanwhile, the addition of WSA reduced the volumetric water absorption of RWF by 85.1 % and 91.4 %. Since the sandwich structure, the thermal conductivity of WSA@UGFW can be as low as 0.01168 W/(m·W), which is 44.7 % and 44.4 % lower than that of UGFW and WSA. It features a low density of 45.7 kg/m3 and a high hydrophobicity angle of 155.87°. In addition, the compressive strength of WSA@UGFW is increased by 16.5 times. Therefore, the aerogel materials prepared in this paper have great application potential as fire-proof building insulation materials.

Investigation on the thermal properties of carbon fibres with silica-based aerogel composites

In this research, thermal protection systems of space hardware have prompted the development and study of silica aerogel composites bonded with a variety of Carbon fibres. Carbon fibres were woven into a matrix of tetra ethoxy silane (Ts) and vinyl tri-methoxy silane (Vs) to create these composites. Many different composites were developed, each with its own set of characteristics and capabilities because to the wide range of fibres used. The measured bulk density values were often relatively low, with the lowest recorded value being only 180 kg m−3. The thermal conductivity was reduced to below 30 mW m−1 K−1 and the stability was maintained up to 600°C. Nanocomposites consisting of longer fibres containing meta-Carbons are superior insulators, while short-fiber composites are stiffer and have lower thermal conductivities. The aerogel composites compliance with Space conditions was evaluated using standard Space materials qualification procedures like thermal cycling and outgassing, proving their fitness for use in this context.

115 Fibre-Aerogel-Mats for façade Insulation: How to Guide SSbD Development by Screenings?

Abstract The HARMLESS project focusses upon assessment approaches to support Safe-and-Sustainable-by-Design (SSbD) development of advanced materials (AdMa). Case studies comprise several industry sectors. Specifically for the construction sector we study façade insulation by fibre-aerogel-mats. Beyond the relatively simpler mono-component organic aerogels presented earlier (Keller et al. 2021), here we deal with multi-component materials: Glass fibers provide structural integrity for the silica-based aerogel that provides the thermal insulation performance, though is coated by organosilane as a hydrophobizing agent to prevent moisture uptake. Optionally, an additional inorganic coating can be applied to enhance mechanical stability. Here we explored this wide SSbD design space by four industrially relevant SSbD-versions of fibre-aerogel-mats; these were ranked and compared against each other as well as conventional insulation material (i.e. stone wool). We assessed the release by performing several typical occupational operations under clean-air conditions within a laboratory setting. Up to 106/ccm particles are released, with respirable aerodynamic diameters. We collected the dust and assessed the structure and behavior with respect to its biological reactivity and biodissolution, focusing on the screening and ranking of inhalation hazards. The data on exposure and hazard was complemented by data on functionality in the intended use, where all SSbD versions performed significantly better than the conventional alternative. The new data refines the risk screening and categorisation schemes for advanced materials, including Early4AdMa (RIVM 2022), AdmGRID (Kennedy et al. 2019), InnoMat.Life (Wohlleben et al. 2022) and an environmental risk screening (Arvidsson et al. 2022).

Silica aerogel infused hierarchical glass fiber polymer composites

Hierarchical systems can address the matrix-dominated failures of structural fiber polymer composites. Here, a new synergistic hierarchical structure combines conventional structural glass fibers with a bi-continuous silica-based aerogel matrix; both pure-silica and organically-modified silicate aerogels are demonstrated. When infused with an epoxy matrix, this type of hierarchical architecture showed a marked improvement in mechanical properties: without any loss in modulus, both the compressive strength and the interlaminar shear strength increased by up to 27%, relative to the equivalent glass-fiber reinforced epoxy composite baseline. The bi-continuous network modification strategy uses industrially-relevant infusion techniques, at or near room temperature, and retains a similar final composite density (within 2%). The strategy presented here provides a versatile and readily applicable means to improve state-of-the art continuous fiber reinforced composite systems in compression and offers an opportunity to develop a new generation of composite materials.

Silica Aerogel-Rubber Composite: A Sustainable Alternative for Buildings' Thermal Insulation.

Silica aerogel composites with recycled tire rubber have been synthesized and evaluated for their potential use for thermal protection in buildings. The present work describes for the first time the preparation of silica-based aerogel composites containing recycled rubber tires reinforced with polyvinyl butyral (PVB) by hot pressing. The developed composite was extensively characterized regarding its physical, morphological, thermal and mechanical features, and the results showed their properties were relevant, leading to composites with different properties/performances. The obtained bulk density values were satisfactory, down to 474 kg·m−3, and very good thermal properties were achieved, namely, thermal conductivity as low as 55 mW·m−1·K−1 for composites with silica aerogel, recycled tire rubber and PVB. The most promising composites were those based on low bulk density and thermal conductivity values, and they were thermally stable, indicating their suitability for thermal insulation applications.

Silica-Based Aerogel Composites Reinforced with Reticulated Polyurethane Foams: Thermal and Mechanical Properties.

In this work, silica aerogel composites reinforced with reticulated polyurethane (PU) foams have been manufactured having densities in the range from 117 to 266 kg/m3 and porosities between 85.7 and 92.3%. Two different drying processes were employed (ambient pressure drying and supercritical drying) and a surface modification step was applied to some of the silica formulations. These composites, together with the reference PU foam and the monolithic silica aerogels, were fully characterized in terms of their textural properties, mechanical properties and thermal conductivities. The surface modification with hexamethyldisilazane (HMDZ) proved to improve the cohesion between the reticulated foam and the silica aerogels, giving rise to a continuous network of aerogel reinforced by a polyurethane porous structure. The samples dried under supercritical conditions showed the best interaction between matrixes as well as mechanical and insulating properties. These samples present better mechanical properties than the monolithic aerogels having a higher elastic modulus (from 130 to 450 kPa), a really exceptional flexibility and resilience, and the capacity of being deformed without breaking. Moreover, these silica aerogel-polyurethane foam (Sil-PU) composites showed an excellent insulating capacity, reaching thermal conductivities as low as 14 mW/(m·K).

The Effect of Heat Treatment of β-Tricalcium Phosphate-Containing Silica-Based Bioactive Aerogels on the Cellular Metabolism and Proliferation of MG63 Cells.

β-Tricalcium phosphate was combined with silica aerogel in composites prepared using the sol–gel technique and supercritical drying. The materials were used in this study to check their biological activity and bone regeneration potential with MG63 cell experiments. The composites were sintered in 100 °C steps in the range of 500–1000 °C. Their mechanical properties, porosities, and solubility were determined as a function of sintering temperature. Dissolution studies revealed that the released Ca-/P molar ratios appeared to be in the optimal range to support bone tissue induction. Cell viability, ALP activity, and type I collagen gene expression results all suggested that the sintering of the compound at approximately 700–800 °C as a scaffold could be more powerful in vivo to facilitate bone formation within a bone defect, compared to that documented previously by our research team. We did not observe any detrimental effect on cell viability. Both the alkaline phosphatase enzyme activity and the type I collagen gene expression were significantly higher compared with the control and the other aerogels heat-treated at different temperatures. The mesoporous silica-based aerogel composites containing β-tricalcium phosphate particles treated at temperatures lower than 1000 °C produced a positive effect on the osteoblastic activity of MG63 cells. An in vivo 6 month-long follow-up study of the mechanically strongest 1000 °C sample in rat calvaria experiments provided proof of a complete remodeling of the bone.

The Application of Silica-Based Aerogel Board on the Fire Resistance and Thermal Insulation Performance Enhancement of Existing External Wall System Retrofit

Due to the need of good thermal performance, external wall insulation (EWI) is usually made of materials that are not fire resistant and sometimes flammable. That restricts its application to a particular circumstance such as limited building height. Hence, a material with good thermal insulation and fire resistance performance would allow EWI to be more widely applied. This paper introduces a novel material: a silica-based aerogel porous board, which differs itself from mainstream products available in the market because of its outstanding properties, such as low density, high surface area, low thermal conductivity and superhydrophobicity. Herein, its thermal insulation and fire-resistant performance were tested and compared with commercial products. The cone calorimeter analysis results indicated that the aerogel porous board could improve the fire resistance performance. Moreover, the evaluation of thermal insulation performance suggested that the application of an aerogel porous board on the external stone wall of existing buildings can decrease the U-value by 60%. Through the detailed insight into the case-study, it is quite clear that the carbon impact of building stock could be greatly reduced by means of a coherent set of building envelope retrofitting actions based on this innovative heat insulation material, without compromising the fire safety.

Silica-based aerogel composites reinforced with different aramid fibres for thermal insulation in Space environments

Silica aerogel composites reinforced with different aramid fibres have been synthesized and compared considering their potential use in thermal protection systems of Space devices. These composites were prepared from tetraethoxysilane and vinyltrimethoxysilane and the network was strengthened with aramid fibres. The results showed that the physical and chemical properties of the fibres were relevant, leading to composites with different properties/performance. In general, the obtained values for bulk density were low, down to 150 kg m−3. Very good thermal properties were achieved, reaching thermal conductivities bellow 30 mW m−1 K−1, and thermal stability up to 550 °C in all cases. Short length fibres produce stiffer composites with lower thermal conductivities, while among longer fibres, meta-aramid-containing fibres lead to nanocomposites with best insulation performance. Standard tests for Space materials qualification, as thermal cycling and outgassing, were conducted to assess the compliance with Space conditions, confirming the suitability of these aerogel composites for this application.

Thermal and Mechanical Performances of the Superflexible, Hydrophobic, Silica-Based Aerogel for Thermal Insulation at Ultralow Temperature.

A superflexible hydrophobic silica-based aerogel (FHSA) was prepared via a facile sol-gel process and ambient pressure drying method. The FHSA was treated at different temperatures varying from -196 to 450 °C to evaluate its thermal and mechanical performances. The evolutions of the physical property, hydrophobicity, microstructure, pore structure, and chemical structure of the FHSA with the various treatment temperatures were investigated comprehensively. The structure of the FHSA did not show an obvious change after treatment in the liquid nitrogen. The bulk density of the FHSA increased from 0.047 to 0.077 g cm-3 when the thermal treatment temperature increased from 25 to 450 °C. The specific surface area and pore volume of the FHSA increased with the treatment temperature owing to the decomposition of the organic moieties. The Fourier transform infrared spectra showed that the methyl groups in the FHSA had excellent thermostability up to 400 °C. The water contact angles of the FHSA after treatment at -196, 25, 200, 300, 350, 400, and 450 °C were 131, 151, 162, 150, 132, 119, and 34°, respectively. The thermal conductivity of the FHSA at a low temperature of -10 °C was 0.022 W m-1 K-1. The reversible deformation rate of the FHSA was more than 80% within 100 compression cycles. After treatment in liquid nitrogen, the reversible deformation rate of the FHSA remained at 50%. The synthesis method of the FHSA is simple, the resulting FHSA showed good performance both in thermostability and flexibility, and it is promisingly applied for thermal insulation and sealing in ultralow-temperature environments.

Thermal radiation shielded, high strength, fire resistant fiber/nanorod/aerogel composites fabricated by in-situ growth of TiO2 nanorods for thermal insulation

• Vertically aligned TiO 2 nanorods were synthesized directly on the surface of microfibers by in-situ growth. • A novel ‘fiber/nanorod/aerogel’ composite was constructed for thermal insulators. • The composite with low thermal conductivity exhibited significantly enhanced infrared radiation shielding. • In-situ growth of TiO 2 nanorods reduced the gaseous conductivity by increasing the interfacial adhesion force. Fiber/aerogel composites attract considerable interest as thermal insulation materials due to their low thermal conductivity. However, in practice they deliver unsatisfactory performance due to their high infrared radiation transmittance and poor interfacial adhesion. Herein, we report a simple strategy for constructing vertically aligned 1D rutile TiO 2 nanorod arrays (TiO 2 -NRAs) directly on the surface of quartz fibers (QFs) by in-situ growth. A novel ‘fiber/nanorod/aerogel’ composite was synthesized by filling the pores of QF/TiO 2 -NRAs with SiO 2 -Al 2 O 3 aerogels (ASAs) through vacuum impregnation. The QF/TiO 2 -NRAs/ASA composite exhibited excellent thermal insulation (0.071 W·m −1 ·K −1 at 1100 °C), infrared radiation shielding performance (an extinction coefficient greater than 150 cm −1 and an infrared reflectivity greater than 95%), fire resistance (more than 1200 °C), and compressive strength (0.37 MPa, 10% strain). In-situ growth of TiO 2 -NRAs can reduce the gaseous thermal conductivity by increasing the interfacial adhesion force between fibers and aerogels, and reduce the radiation heat transfer by shielding infrared radiation. This strategy is applicable to multi-type fibers reinforced silica-based aerogel materials used for insulation and protection in extreme environments.

Utilization of aerogel in building construction –A Review

Aerogel are synthetic light weight material obtained in a gel form with gas without any shrinkage. The first form of aerogel is produced by using Silica gels. There are several other types of aerogels such as carbon-Based aerogel, clay-Based aerogel and silica-Based aerogel. Aerogel are mostly in solid form with extremely low conductivity and possess very low density and high porosity ( < 100nm). Aerogel are water repellent material. In recent years, Aerogel have attracted towards various sectors, including building construction based on their promising properties and surprising applications in wide range of technical spaces. Aerogel based materials are prepared for its high-performance thermal insulation applications in building sectors. Despite, it also used in manufacture of chemical products, Electronics, thermal and acoustic insulations, energy absorbers, space suits and in building systems. This paper reviews the properties, formation and applications of aerogel in various sectors and its abundant utilization in building construction.

Kinetics of MTMS-based aerogel formation by the sol-gel method - experimental results and theoretical description

The kinetics of silica-based aerogel formation was investigated and described analytically. Experimental gelation kinetics was designated by (i) filtration and determination of the resulting product mass, (ii) absorbance measurements during gelation. The dependence of aerogel mass on gelation time, in general, has a form similar to a sigmoid function. However, for small initial precursor concentration, a deviation from this function is observed. The proposed theoretical description explain these tendencies. It assumes that the aerogel condensation has a form of reaction between free precursor molecules and already formed aerogel particle. However, at the very beginning, before the clusters start to appear, the bonding between free molecules plays a dominant role what is especially visible for low precursor concentration. It was shown that such a description explains the shape of the dependence of aerogel mass on reaction time. Moreover, the research enabled the estimation of the kinetic constant and the activation energy.

Advanced Opacified Fiber-Reinforced Silica-Based Aerogel Composites for Superinsulation of Exhaust Tubing Systems in Semi-Stationary Motors.

Within this study, monolithic three-dimensional silica aerogel (SA) composite parts with super insulating properties are presented. A generic part based on fiber-reinforced (FR) silica aerogel for thermal insulation of the exhaust tubing system—to keep the exhaust gases as hot as possible to improve the efficiency of the catalyst system—was produced via a sol-gel-based molding process in combination with a supercritical drying using scCO2. A thermal conductivity of 16 mW m−1 K−1 was measured via a heat flow meter technique. In this manuscript, we present a full cycle of the material compound design, starting with fundamental material evaluation including aerogel optimization, opacifier influence, and casting process. The obtained generic part in shape of a half-shell for pipe insulation is characterized under real conditions.

Optimization of Polyamide Pulp-Reinforced Silica Aerogel Composites for Thermal Protection Systems.

The present work describes for the first time the preparation of silica-based aerogel composites containing tetraethoxysilane (TEOS) and vinyltrimethoxysilane (VTMS) reinforced with Kevlar® pulp. The developed system was extensively investigated, regarding its physical, morphological, thermal and mechanical features. The obtained bulk density values were satisfactory, down to 208 kg·m−3, and very good thermal properties were achieved—namely a thermal conductivity as low as 26 mW·m−1·K−1 (Hot Disk®) and thermal stability up to 550 °C. The introduction of VTMS offers a better dispersion of the polyamide fibers, as well as a higher hydrophobicity and thermal stability of the composites. The aerogels were also able to withstand five compression-decompression cycles without significant change of their size or microstructure. A design of experiment (DOE) was performed to assess the influence of different synthesis parameters, including silica co-precursors ratio, pulp amount and the solvent/Si molar ratio on the nanocomposite properties. The data obtained from the DOE allowed us to understand the significance of each parameter, offering reliable guidelines for the adjustment of the experimental procedure in order to achieve the optimum properties of the studied aerogel composites.

Study on the Hydrophobicity and Mechanical Properties of Silica-Based Aerogel by Introducing Organic Benzene

Study on the Hydrophobicity and Mechanical Properties of Silica-Based Aerogel by Introducing Organic Benzene

Patterned Cellulose Nanocrystal Aerogel Films with Tunable Dimensions and Morphologies as Ultra-Porous Scaffolds for Cell Culture

Aerogel films are interesting as coatings due to their unique properties including high surface area, sorption capacity and insulating properties. To date, silica-based aerogel films have been most...

Silica aerogel membranes fabricated using removable nitrocellulose scaffolds

Abstract Two different methods were developed to generate silica-based aerogel membranes using nitrocellulose scaffolds. The first method involved incorporating fibers of nitrocellulose (NC) into the sol prior to gelation. NC fibers were either removed using a solvent during aging or calcining after aerogel formation to produce reticulated micron-sized channels in the aerogels. In the second method, an NC lacquer was mixed with the sol, and the mixture separated into a NC-rich phase and a sol-rich phase. The NC phase was subsequently removed from the aerogel using a solvent, creating aerogels with interconnected porosity. Aerogels were prepared from tetraethyloxysilane (TEOS) as a precursor and methyltriethoxysilane (MTES) as a co-precursor. Replacing TEOS with 25 vol% MTES increased the mechanical stability, allowing for greater ease of handling. Additionally, the more open network of the MTES gels led to higher helium gas permeability than that for the pure TEOS gels.

Thermal conductivity measurement of thermal insulating mortars with EPS and silica aerogel by steady-state and transient methods

In order to fulfil the increasing demands of indoor comfort and energy efficiency requirements of buildings, innovative materials with good thermal properties have been developed, such as thermal insulating mortars with incorporation of lightweight aggregates and nanomaterials.In the present work, the thermal conductivity of thermal insulating mortars, with EPS and silica-based aerogel, were evaluated for hardened state (28 days of curing), dry state and different moisture content values. Moreover, several methods were performed: two steady-state and two transient methods. For comparison purposes, all of the obtained thermal conductivity values were converted to 23 °C.It is concluded that the results are highly dependent on the temperature and the moisture content of the samples, and the measuring method. This study also shows that the thermal conductivity presents values with variations up to 21% and 14%, with different methods for the mortar’s formulations with and without silica aerogel. It is also concluded that the thermal conductivity evaluation methods have differences regarding the sample’s size, testing time, operation and apparatus’ accuracy and reproducibility. This must be considered, particularly when developing innovative materials, where the material availability or the measurement range of the method can limit the thermal conductivity measurement.