Silica Aerogel Production Research Articles

Optimization of magnesium silica aerogel production and evaluation as a food additive: a comparative study of water glass and bio-based sodium silicate source as a precursor

Optimization of magnesium silica aerogel production and evaluation as a food additive: a comparative study of water glass and bio-based sodium silicate source as a precursor

Plastic deformation and heat-enabled structural recovery of monolithic silica aerogels

Drying shrinkage during ambient pressure drying of silica gels is made reversible by preventing condensation reactions of surface silanol groups via surface modification. This partial recovery of the gel volume and structure is referred to as the spring-back effect (SBE) and enables the production of monolithic silica aerogels by evaporative drying. The SBE is sometimes completed by annealing at mild temperatures. Similarities between drying-related deformations and deformations induced by mechanical stimuli suggest analogous underlying mechanisms. While the causes of drying shrinkage are relatively well-known, it remains unclear how the relaxation of the structure by drying and annealing occurs across the different length scales. Here we show a complete structural recovery of silica aerogels at the macro- and nano-scale enabled by annealing. We propose that residual deformations after drying and mechanical compression are caused by the entanglement of silica clusters that can be unraveled by annealing at 230 °C. The deformation under loading is interpreted as two different re-arrangement mechanisms for dry and annealed gels, by the sliding of the silica clusters along the loading direction and by the compression of large pores beyond the fractal structure, respectively. Our results demonstrate how the shape and structure of silica aerogels can be restored and controlled by thermal activation, broadening the various applications of these materials. We also emphasize how tuning silica gels to promote a two-step SBE by annealing can pave the way toward the production of larger monolithic aerogels by APD.Graphical

Insulating materials based on silica aerogel composites: synthesis, properties and application.

The rapidly increasing growth in the world's population has created enormous environmental issues, such as the greenhouse effect, global warming, ozone layer depletion, acid rain, and excessive energy usage. The construction sector, in particular, accounts for a significant share of worldwide energy consumption, making it a major contributor to these challenges. Effective building insulation is crucial for decreasing energy demand, minimising heat loss, and lowering environmental impact. Aerogels have acquired popularity as insulation materials due to their outstanding qualities such as great thermal insulation, flame retardancy, lightweight construction, and environmental friendliness. Silica aerogels, in particular, are emerging as game changers in the construction insulation sector, accounting for a sizable proportion due to their low thermal conductivity and simplicity of manufacture. This paper gives a thorough overview of silica aerogel production processes, the key qualities necessary for aerogel-based composites, and the most recent advances in their use in building insulation. It also examines how to overcome inherent obstacles such as mechanical fragility and high manufacturing costs, providing technologies that improve mechanical strength and long-term durability. By incorporating silica aerogels into construction materials, the industry may significantly reduce energy consumption while also contributing to the creation of sustainable, energy-efficient buildings.

Non-supercritical drying synthesis of hydrophobic, low-density, and high surface area silica aerogel using a sonication technique

Replacing the solvent in silica aerogel production with air is critical in getting the desired physical properties. Even though drying by evaporation under ambient pressure is thought to be the simplest way, it shrinks and collapses the gel network. In this research, uniform sol was prepared by sonication at room temperature. The surface of the developed wet gel was modified with trimethylchlorosilane (TMCS) after solvent exchange. The prepared aerogels underwent various characterization techniques to evaluate their functional, structural, morphological, surface, and thermal properties. The textural and physical characteristics of prepared silica aerogel were examined in relation to the precursor concentration, catalysts that affect the density of silica aerogel, volumetric shrinkage, and gelation time. The silica aerogel was found thermally stable up to 800 °C while hydrophobicity retained up to 350 °C. The contact angle of prepared aerogels confirms their hydrophobic nature. Field emission scanning electron microscopy (FE-SEM) and X-Ray Diffraction (XRD) results demonstrate the porous nature of silica aerogel. The Brunauer-Emmett-Teller (BET) surface area analysis revealed that the surface area and the pore radius were 784 m2/g and 36 Å, respectively.

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.

Microstructural properties and heat transfer characteristics of in-situ modified silica aerogels prepared with different organosilanes

• In-situ modified silica aerogels were synthesized in ambient pressure by a facile sol-gel method. • Various organosilanes MTMS, MTES, VTMS, MEMO and GLYMO were utilized as silica precursors. • Heat transfer mechanisms were investigated both theoretically and experimentally. • SA-MTMS had the lowest density (92 kg⁄m 3 ) and high thermal stability (up to 700 °C). • All samples exhibited similar insulation performances (λ in between 42 and 47 mW/mK). • The density was the most decisive parameter for different heat transfer modes in aerogels. • Coupling thermal conductivity term is the key contributor to the total thermal conductivity. Conducting an in-situ modification during the sol-gel reactions, without any post gelation-modification, offers a cost-effective and time-saving strategy in the production of silica aerogels. Therefore, in this study, in-situ modified silica aerogels were synthesized as potential thermal insulation materials via a two-step sol-gel process under ambient pressure. Different organosilanes having methyl (SA-MTMS), ethyl (SA-MTES), vinyl (SA-VTMS), epoxide (SA-GLYMO), and methacrylate functional (SA-MEMO) groups were used as silica sources. According to the selected precursor, the change in the heat transfer properties were investigated both by thermal conductivity measurements and by theoretical models. SA-MTMS possessed the lowest density (92 kg / m 3 ) and high thermal stability (up to 700 °C). Despite the existence of bulk organic groups in its structure, the SA-GLYMO had the highest specific surface area (531 m 2 / g ) . Regardless of their morphology, all samples have exhibited similar insulation performances (λ=42–47 mW/mK). However, the prominent heat transfer mechanisms were directly affected by the bulk density and the underlying microstructure. For low-density samples, gas-contributed thermal conductivities were the key contributor to the total thermal conductivity whereas solid thermal conduction was the dominant mechanism in high-density samples. The coupling thermal conductivity term was also crucial as the total conductivity would have been significantly underestimated without it.

Synthesis and Characterization of Industrial Casting Sand Based Silica Aerogel

Abstract: In this study, a commercial foundry sand (Seydisehir Eti Aluminium Co. Inc.) was provided as the starting material. Using this supplied casting sand, silica aerogel production was carried out by sol-gel method. Starting materials chemical components were determined by doing XRD and XRF analyses to starting industrial casting sand respectively. After analysing studies, sodium silicate solution was produced from commercial casting sand. During silica aerogel synthesize, 5 different pH degree was investigated including 2-4-6-8 and 9. Silica aerogel modification (Super hydrophobic) was made by choosing the optimum pH value. Afer then, on the synthesized experiment sample, FT-IR, BET, SEM and contact angle characterization studies were realised respectively. As a result of preliminary experiments done with different pH experiments, sample with the lowest density was determined as pH 8 value. Keywords: Casting sand, Sol-gel, Silica aerogel

Hydrophobic silica aerogels synthesized in ambient conditions by preserving the pore structure via two-step silylation

Surface modification, which is simply about the end-capping of the reactive silanol groups located in silica wet gel to satisfy hydrophobic behavior, has great importance in the production of silica aerogels in ambient conditions. In this study, silica aerogels were synthesized with a sol-gel method via ambient pressure drying. A two-step surface modification was performed on wet gels by using various silanes with different contents (6%, 10% or 20% by vol in n-hexane) to control the extent of irreversible shrinkage during drying. Mono-functional (TMCS) and three-functional silanes (MTMS, MTES and MEMO) were selected for this purpose. The impact of the type and amount of the silylating agents on the microstructure, pore characteristics and hygroscopic nature of resulting aerogels were identified by conducting FTIR, SEM and BET analyses and contact angle measurements. According to characterization results, MTES exhibits a competitive performance compared to classically used TMCS, as the silica aerogels modified with 10% of MTES was obtained in a well-developed with mesoporous structure with very high specific surface area (SBET = 964m2/g) and high hydrophobicity (Θ = 137°). On the other hand, organically functionalized silane MEMO and MTMS, also display noteworthy results (monolithical structure with highly developed porous network and high degree of hydrophobicity) at the low contents (at 6% and 10%). These outcomes are crucial as they may encourage the future attempts on introducing three-functional silanes during surface modification, as these silanes yield high silylation performance and causes the synthesis of well-qualified silica aerogel in ambient conditions.

A silica aerogel synthesized from olivine and its application as a photocatalytic support

This study investigates the performance of a silica aerogel-based air purifying coating to functionalize building materials. The air-purifying function comes from an increased photocatalytic activity when the photocatalyst is supported on a silica network with a large specific surface area like silica aerogels. In this study, silica aerogel was first synthesized with a low energy-consumption method from olivine via ambient pressure drying and was applied as a support to load photocatalytic anatase crystals. The silica aerogel production includes sol-gel synthesis, ion-exchange, surface modification and ambient pressure drying. The produced silica aerogel obtained a high specific surface area (694 m2/g) and pore volume (2.99 cm3/g), with a uniform pore size distribution and mesoporous structure. Titania was loaded onto the prepared silica aerogel through a precipitation method. The resulting samples were characterized by measuring the conversion efficiency to oxidize nitric oxide under UV-light irradiation, nitrogen physisorption and FTIR. The silica aerogel coating with titania crystals had a photocatalytic activity of 99.6%, showing it to be a promising photocatalyst in the built environment.

Environmental impact of the subcritical production of silica aerogels

Abstract This study evaluates for the first time the environmental impacts of three different syntheses of subcritical silica aerogels. These aerogels are produced by subcritical drying, a more economical and safer process than that of the supercritical aerogels. The environmental evaluation was performed using the standardised Life Cycle Assessment (LCA) methodology, using a cradle to gate approach. The life cycles of these materials were modelled using production data collected in laboratory and a LCA software. These aerogels are produced to be used as aggregates in wall coating mortars for buildings, conferring them thermal insulating properties. It was concluded that the most critical stages in the LCA of these aerogels are the production of raw materials and the production in the laboratory, the latter mostly due to the high energy consumption. The results presented in this paper correspond to a laboratory-scale production, which makes them expectedly higher than if the aerogels were produced at an industrial scale. It was also found that aerogels obtained using subcritical drying generally lead to lower environmental impacts than supercritical aerogels.

Effect of Acidity Levels and Feed Rate on the Porosity of Aerogel Extracted from Rice Husk under Ambient Pressure.

Silica aerogels have attracted tremendous interest due to their high specific surface area and the physical, chemical, and mechanical properties as promising materials for thermal insulation, chemical sensors, and energy storage devices. However, large-scale production of silica aerogels remains a challenge due to costly alkoxide precursors and energy-intensive supercritical drying processes. This paper analyzes the effect of acidity levels and feed rate on the porosity of rice husk aerogels with high specific surface area under ambient pressure. This synthetic approach is cost-effective, eco-friendly, and facilitates recycling. Rice husk ash, which consists of 92% amorphous pure silica, was produced by combustion. A process of solvent exchange and surface modification under ambient pressure at different pH levels was conducted for synthesis of the aerogel. The specific surface area of rice husk aerogel was confirmed as ranging from 385 to 861 m2/g under pH 1 to pH 9 and acid feed rate of 0.5 to 5.0 mL/min. The optimized aerogel had a specific surface area of 861 m2/g, a pore volume of 3.33 cm3/g, and an average pore diameter of 12 nm when synthesized at pH 1 and an acid feed rate of 2.5 mL/min. The aerogel was found to be highly hydrophobic, with a water contact angle of 156° up to about 340 °C.

Elastic superhydrophobic and water glass-based silica aerogels and applications

Silica aerogels with high elasticity and superhydrophobicity have several scientific and technological applications such as in multidisciplinary subjects dealing with liquid/solid interfacial energies, long-range attractive interactions, frictionless flow of liquids through nano and microchannels, pipes, and storage of mechanical energy. In addition, the aerogels are being used as light weight super thermal, acoustic and electrical insulating materials especially in microelectronics, aeronautics, Space, in high-energy physics; as bandages for leaks in oil supply pipes, and underwater pressure sensitive devices. The present paper describes the preparation, physicochemical properties along with applications of elastic superhydrophobic silica aerogels with a water contact angle as high as 175o and Young’s modulus as low as 3 × 104 N/m2 with one of the highest reverse compressibility of around 60% known for any solid state material. The Young’s modulus is measured by uniaxial compression. The water droplets placed on surfaces coated with the superhydrophobic aerogel powder at 55° of angle of inclination showed velocities as high as 1.44 m s−1 (free fall velocity ≈ 1.5 m s−1). Water intrusion into the superhydrophobic aerogels at pressures greater than the Laplace pressure exhibited hysteresis resulting in the storage of water in the aerogels, and indicating the sizes of the pores. It has been shown that the elastic superhydrophobic aerogels are very efficient adsorbents of oil and organic compounds and hence useful for oil-spill clean-up applications, in addition to their potential use as laser induced X-ray and plasma emission sources. Moreover, the recent developments in the field of aerogels have shown a great potential for the combination of ambient pressure drying and a low-cost inorganic, and easily available precursor such as sodium silicate, which is also called as water–glass, for the production of hydrophobic silica aerogels on a large industrial scale for commercial applications. The properties of such aerogels are comparable to those obtained by the conventional supercritical drying methods. So far, only powders and translucent and transparent grains of sizes 2–4 mm, are being produced. The experimental results on the preparation and properties along with various applications of elastic superhydrophobic and sodium silicate-based silica aerogels, are presented in this paper. Several sol–gel and drying parameters affecting the quality of the aerogels, in terms of low-density ( 90% in the visible range), are also presented and discussed.

A Novel Environmental Route to Ambient Pressure Dried Thermal Insulating Silica Aerogel via Recycled Coal Gangue

Coal gangue, one of the main hazardous emissions of purifying coal from coalmine industry, is rich in silica and alumina. However, the recycling of the waste is normally restricted by less efficient techniques and low attractive output; the utilization of such waste is still staying lower than 15%. In this work, the silica aerogel materials were synthesized by using a precursor extracted from recycled silicon-rich coal gangue, followed by a single-step surface silylation and ambient pressure drying. A low density (~0.19 g/cm3) nanostructured aerogel with a 3D open porous microstructure and high surface area (~690 m2/g) was synthesized, which presents a superior thermal insulation performance (~26.5 mW·m−1·K−1of a plane packed of 4-5 mm granules which was confirmed by transient hot-wire method). This study offers a new facile route to the synthesis of insulating aerogel material by recycling solid waste coal gangue and presents a potential cost reduction of industrial production of silica aerogels.

The Peculiarities of Silica Aerogel Production Using Azeotropic Mixtures

At the first time it was carried out the theoretical researches regarding pathways to get into a supercritical region at the ambient pressure with the main aim to avoid expensive and hazardous supercritical drying process and to make a silica aerogel production in whole more economical and commercial. These investigations based on fundamental knowledge about the critical phenomena in multicomponent systems. The representation of phase states in such systems by graphical images was used for the estimation of LV (xL = xV) azeotrope influence on SLV and L˭V equilibria. In the course of empiric selection of azeotropic mixtures the negative azeotropes advantage over positive ones was determined and grounded in theory. We report on the synthesis of hydrophobic silica aerogel by ambient pressure drying (APD) procedure, which involves two-step sol–gel process with tetraethyl orthosilicate (TEOS) as a silica precursor and isopropanol as the solvent and an elaborated flow chart using both types of azeotropes as the pore fluids. Guided by receiving our theoretical investigation, we obtained transparent crack-free silica aerogel samples with specific surface in the range of 711–913 m2/g, average pore diameter of ∼95–137 nm, and density of ca. 0.39–0.081 g/cm3.

Hydrophobization of Silica Aerogels: Insights from Quantitative Solid-State NMR Spectroscopy

Silica aerogels have exceptional physical and chemical properties related to their nanoporous structure and high specific surface area. The hydrophobization of the silica surfaces, for example by modification with trimethylsilyl groups (TMS), is of central importance for silica aerogel production by ambient drying methods, particularly on an industrial scale. This study monitored the chemical modification of silica aerogels by quantitative and two-dimensional solid-state NMR spectroscopy. A series of two-step, acid/base-catalyzed silica alcogels were hydrophobized for different times in hexamethyldisiloxane (HMDSO) and subsequently dried at ambient pressure. Two-dimensional 1H–29Si heteronuclear correlation NMR spectroscopy confirms that both ethoxy and TMS groups are chemically bonded to the silica surfaces. For the single-pulse spectra, a procedure to calibrate the absolute 1H, 13C, and 29Si NMR signal intensities with external references was developed. The quantification procedure is validated by the internal consistency between the 1H, 13C, and 29Si results and the agreement between the measured sample mass and that predicted from the NMR data. The quantitative speciation data on the aerogel samples show that the silica surface is covered by a monolayer of ethoxy, TMS, and silanol groups. Silanol groups are progressively replaced by TMS groups with increasing modification time, and the TMS content has a strong effect on the density of the final aerogel.

An Experimental Study on Production of Silica Aero-Gel Using Fly Ash from Coal-Fired Power Plants

silica aero-gels were synthesized from coal fly ash at ambient pressure. The experimental procedure for silica aero-gels production included alkali dissolution of fly ash, surface hydrophobic treatment of the wet-gel, followed by drying of the wet-gel samples at ambient pressure wasinvestigated. Optimized experimental parameters for production of silica aero-gels from fly ash were obtained through systematic studies. BET, SEM and FTIR and contact angle measurement were used in order to investigate the structure and characteristics of the silica aero-gel powders.

Silica aerogel radiator for use in the A-RICH system utilized in the Belle II experiment

This paper presents recent progress in the development and mass production of large-area hydrophobic silica aerogels for use as radiators in the aerogel-based ring-imaging Cherenkov (A-RICH) counter, which will be installed in the forward end cap of the Belle II detector. The proximity-focusing A-RICH system is especially designed to identify charged kaons and pions. The refractive index of the installed aerogel Cherenkov radiators is approximately 1.05, and we aim for a separation capability exceeding 4σ at momenta up to 4GeV/c. Large-area aerogel tiles (over 18×18×2cm3) were first fabricated in test productions by pin drying in addition to conventional methods. We proposed to fill the large end-cap region (area 3.5m2) with 124 water-jet-trimmed fan-shaped dual-layer-focusing aerogel combinations of different refractive indices (1.045 and 1.055). Guided by the test production results, we decided to manufacture aerogels by the conventional method and are currently proceeding with mass production. In an electron beam test undertaken at the DESY, we confirmed that the K/π separation capability of a prototype A-RICH counter exceeded 4σ at 4GeV/c.

Current Research and Development of Silica Aerogel Drying Method

Silica aerogel is a lightweight nanomaterial,which was originally applied to aerospace and military fields. With the optimization and improvement of silica aerogel production process, it has more applications in the field of energy saving, environmental protection, building material etc. This paper introduces some kinds of drying processes, some methods had been used in the production, while the others are under the consideration.

Hydrophobic silica aerogel production at KEK

We present herein a characterization of a standard method used at the High Energy Accelerator Research Organization (KEK) to produce hydrophobic silica aerogels and expand this method to obtain a wide range of refractive index (n=1.006–1.14). We describe in detail the entire production process and explain the methods used to measure the characteristic parameters of aerogels, namely the refractive index, transmittance, and density. We use a small-angle X-ray scattering (SAXS) technique to relate the transparency to the fine structure of aerogels.

Tanpopo Cosmic Dust Collector: Silica Aerogel Production and Bacterial DNA Contamination Analysis

Hydrophobic silica aerogels with ultra-low densities have been designed and developed as cosmic dust capture media for the Tanpopo mission which is proposed to be carried out on the International Space Station. Glass particles as a simulated cosmic dust with 30 \mu m in diameter and 2.4 g/cm^3 in density were successfully captured by the novel aerogel at a velocity of 6 km/s. Background levels of contaminated DNA in the ultra-low density aerogel were lower than the detection limit of a polymerase chain reaction assay. These results show that the manufactured aerogel has good performance as a cosmic dust collector and sufficient quality in respect of DNA contamination. The aerogel is feasible for the biological analyses of captured cosmic dust particles in the astrobiological studies.