SiO2 Aerogel Research Articles

Preparation of SiO2 aerogel by water glass: effect of different sodium removal methods on aerogel properties

Preparation of SiO2 aerogel by water glass: effect of different sodium removal methods on aerogel properties

Heat-confinement, water-resistance, and moisture-release electrospun membrane based on aerogel filler incorporation

The maintenance of a comparatively stable human body temperature through heating is essential for numerous physiological activities. However, the majority of the existing heating strategies are inefficient and wasteful in terms of energy usage, while also falling short in sufficiently protecting the human body against environmental hazards. Fabrics possessed the abilities to retain heat, repel water, and permit moisture to travel through are in high demand, which are essential for energy conservation and protective purposes. Herein, we introduce a highly efficient approach for producing electrospun membranes that exhibit excellent properties of heat confinement, water repellency, and moisture release properties, achieved by incorporating SiO2 aerogel fillers into interconnected nanofibers. As a result, the obtained aerogel filler incorporation membrane (AFIM) composed of PVDF@SiO2 exhibited a reduced thermal conductivity and reinforced moisture-release capability, leading to a 2 °C increase in temperature differential over its cotton counterpart and a water vapor transmission rate (WVTR) of 26.83 kg•m−2day−1. This work offers insights into the advancement of the thermoregulatory textiles to conserve energy and prevent waterlogging in future challenging conditions.

PI-SiO2 aerogel as a versatile high transparent material for photothermal cooperative management

Effectively insulating against excessive heat generated by sunlight while also avoiding harmful ultraviolet (UV) and maintaining suitable levels of visible light transparency is vital for minimizing energy consumption and optimizing sunlight utilization. To address the challenge of photothermal collaborative management, the PI consisted of high fluorinated dianhydride and aliphatic diamine was used to effectively improve the performance of SiO2 aerogels. The resulting PI-SiO2 aerogels retain the characteristics of SiO2 aerogels, such as low density, high transparency between 82∼89 %, and excellent thermal insulation properties with an ultralow thermal conductivity range from 0.023 W/(m.K) to 0.028 W/(m.K). Meanwhile, the coarsened skeleton of aerogels can withstand the extreme temperature difference between −196 ℃ and 200 ℃ without brittle fracture and yellowing. In addition, PI-SiO2 aerogels exhibit the capability to absorb a significant proportion of UV light within the 200–400 nm, offering distinct advantages in transparent thermal insulation materials. The multifunctional PI-SiO2 aerogels can be used as candidate materials in the fields of architecture, automobile, electronics, solar energy and aerospace.

Amine-modified SiO2 aerogel for efficient adsorption of low-pressure CO2: Response surface methodology optimization and adsorption mechanism

Amine-modified SiO2 aerogel (AMSA) has shown tremendous potential in CO2 capture due to its unique three-dimensional network structure and excellent stability. However, it still faces many challenges in the preparation optimization, adsorption enhancement at low CO2 partial pressure, and mechanism elucidation. Hence, in this paper, the response surface methodology is employed for the first time and the optimal preparation conditions for AMSA are determined. A regression model is successfully established to accurately predict the CO2 adsorption capacity of AMSA under different synthesis conditions (with a relative error of only 0.98 %). Additionally, the AMSA prepared at optimal conditions exhibits high CO2 adsorption capacity of 2.11 mmol/g and excellent stability (only decreased by 1.44 % after 8 cycles) at 10 % CO2 partial pressure, indicating enormous application potential. Notably, the CO2 adsorption mechanism by AMSA at different temperatures and partial pressures are revealed in detail through fitting with the Freundlich isotherm and the double-exponential model, as well as thermodynamic parameter calculations. Firstly, the CO2 adsorption behavior belongs to the multi-layer adsorption behavior with uneven energy of active sites. Secondly, the CO2 adsorption capacity and rate are jointly controlled by molecular motion and chemical reaction equilibrium, diffusion and chemical reaction steps, respectively. Finally, the adsorption process is exothermic and spontaneous, and the level of disorder decreases at the gas-solid interface. This study not only achieves efficient adsorption of low-pressure CO2, but also deepens the understanding of gas-solid interface adsorption mechanisms, providing scientific basis and technological support for the development of novel efficient AMSA adsorbent materials.

Temperature-irrelevant superhydrophobic polyimide–SiO2 aerogels with a confined shrinkage strategy for high-temperature thermal protection (>400 °C)

Polyimide (PI) aerogels often experience substantial volume shrinkage when exposed to temperatures above 200 °C. Furthermore, research regarding the hydrophobic characteristics of PI aerogels under high-temperature conditions is limited. Herein, a confined shrinkage strategy was proposed, and the PI–SiO2 aerogels were prepared with ultralow thermal shrinkage and high-temperature superhydrophobic properties. Micrometer-sized silica aerogel powders were used in this strategy as shrinkage inhibitors during the production of PI aerogels. The silica aerogel powders were then pulled together using the PI chain and braced to each other, limiting the shrinkage of the PI aerogel matrix attached to the powders. Results indicated that the prepared aerogel experienced a shrinkage of only 6.2 % after heat treatment at 400 °C for 1 h in a muffle furnace. The surface area of the sample decreased from 669 m2/g to 649 m2/g after heat treatment, revealing a reduction of only 2.7 %. Previous studies have never reported this remarkable thermal stability. Furthermore, the aerogel exhibited superhydrophobic properties with a water contact angle of 157.4° and a water rolling angle of approximately 0° at 300 °C due to its high surface roughness.

SiO2 aerogel modified aggregates: Preparation, heat resistance and improvement mechanism

Modification of natural aggregates using SiO2 aerogel solution can not only radically reduce the rutting disease of asphalt pavement, but also avoid the problems of poor heat-resistant performance, mechanical strength and durability of ordinary heat-resistant aggregates. The effects of SiO2 aerogel solution type, modification method and SiO2 aerogel solution dosage on the thermal resistance and adhesion properties of SiO2 aerogel-modified aggregates (SM-Agg) were explored by orthogonal tests. Based on scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and infrared thermography, the surface micromorphology, elemental composition and dynamic thermal resistance properties of natural aggregate and SM-Agg were analyzed, respectively. The results showed that Both SiO2 aerogel solution type and dosage significantly affect the evaluation indexes and the modification of natural aggregates by soaking method using ZN-S type SiO2 aerogel solution with 15 % of the aggregate mass could obtain SM-Agg with good heat resistance and adhesion properties. The surface of SM-Agg was covered with a “gel layer” containing uniform and densely distributed SiO2 aerogel particles. The temperature of the top surface of the 18.3-mm-thick SM-Agg specimen gradually changed from 2.2°C higher than that of the natural aggregate to about 1.8°C lower than that of the natural aggregate within 60 min of heating at 55°C. The “gel layer” containing SiO2 aerogel particles forms one or more layers of three-dimensional heat-blocking mesh on the aggregate surface, which dramatically reduces the heat transfer area, prolongs the heat transfer path within the specimen, and increases the heat-reflecting capacity of the aggregate surface.

Radiative cooling materials prepared by SiO2 aerogel microspheres@PVDF-HFP nanofilm for building cooling and thermal insulation

Radiative cooling is promising in meeting the current global demand for green sustainable development. However, the effective cooling of the existing radiant cooler will be limited due to the serious solar energy absorption and poor thermal insulation performance on the cold side. To addresss these issues, we propose herein a novel composite material of silicon dioxide (SiO2) aerogel microspheres combined with polyvinylidene fluoride-cohexafluoropropylene (PVDF-HFP) nanofiber membrane, in which SiO2 aerogel microspheres are firstly synthesized by sol-gel method and then incorporated into PVDF-HFP nanofiber membrane to give radiative cooling performance. As we expected, the molecular vibration characteristics of PVDF-HFP nanofiber membrane and the phonon polarization resonance of Si-O-Si bond in the transparent window can enhance the infrared emissivity of the membrane surface. In addition, the high porosity and the mesoporous structure formed by the interconnection of nano-network skeletons of SiO2 aerogel microspheres determine its excellent thermal insulation performance. The as-prepared material displays that the average solar reflectance of the composite membrane is 96.07 % and the average infrared emissivity of the atmospheric window is 94.95 %. Notably, when the average solar radiation intensity is 885.56 W•m−2, the passive radiative cooling temperature during the day can reach 11.2 °C. Furthermore, this material has excellent self-cleaning and thermal insulation performance, making it a potential radiant cooling candidate in many fields.

Research progress of aerogel used in lithium-ion power batteries

In recent years, with the rapid development of clean energy vehicles (i.e., electric vehicles and hybrid electric vehicles) and electrochemical energy storage stations, safety accidents have significantly increased. However, the abuse conditions such as overheating, overcharging, mechanical abuse, short circuits, etc., can result in thermal runaway of lithium-ion batteries (LIBs). Severe thermal runaway can lead to battery fire and even explosion, thereby threatening the safety of personnel. The application of a few aerogels to the thermal insulation layer between the cells of the lithium-ion battery modules can strengthen the safety of batteries. Among many aerogels, oxide aerogels show excellent insulation and high-temperature resistance. Therefore, aerogels, especially oxide aerogels, have aroused widespread research interest. This paper introduces the mechanism of thermal runaway of LIBs and systematically reviews several important oxide aerogels and the derived composites, especially those based on SiO2, Al2O3, and ZrO2 aerogels. The mechanical strength and high-temperature resistance of those aerogels are discussed. The application of aerogel in LIBs is also investigated in detail, and the all-around effect is caused by the introduction of aerogel materials. In addition, the thermal protection safety strategy of aerogel thermal insulation layers is proposed. It is supposed that this review could enable readers to deepen their understanding of this field.

Gangue-Based SiO2 Aerogel Used for Pb(II) Adsorption in Wastewater and Mechanism Analysis

Gangue-Based SiO2 Aerogel Used for Pb(II) Adsorption in Wastewater and Mechanism Analysis

Study on physical properties and snow-melting performance of multilayer composite conductive-pervious concrete for improving the snow-melting efficiency and energy consumption of ECON

One of the most significant challenges facing transport networks in cold regions is snow accumulation on road surfaces. This can lead to traffic congestion and safety issues. While electrically conductive concrete (ECON) heated pavement systems (HPS) offer several advantages, including stability, and low environmental impact, they also present certain limitations, such as low snow-melting efficiency and high snow-melting energy consumption. In this study, a SiO2 aerogel mortar thermal-insulation layer and a self-compacting concrete structural layer were set underneath the reduced graphene oxide (RGO) composite conductive concrete, and the straight pervious channels were prefabricated, to reduce the snow-melting efficiency and energy consumption through the preparation of multilayer composite conductive-pervious concrete integrated specimen. The initial objective was to investigate the influence of SiO2 aerogel substitution rate on the mechanical properties and thermal conductivity of thermal-insulation mortar. Secondly, the impact of the thickness of the conductive layer and thermal-insulation layer on the mechanical properties of the integrated specimen was analyzed. Finally, the impact of SiO2 aerogel thermal-insulation mortar and straight pervious channels on the integrated specimen's snow-melting performance was evaluated through a snow-melting test, which assessed the efficiency and energy consumption of the snow-melting process. The results indicate that when the SiO2 aerogel substitution rate was 40 %, the thermal-insulation mortar exhibited favorable mechanical and thermal-insulation properties. The 5 cm conductive layer and the 1 cm thermal-insulation layer achieved good mechanical properties of the integrated specimen. In comparison to single-layer composite conductive concrete, the snow-melting time and energy consumption of multilayer composite conductive-pervious concrete integrated specimen were reduced by 23.05 % and 21.30 %, respectively. The straight pervious channels permit the immediate discharge of water produced by snow melting, thereby reducing the heat transfer from the snow-melting board to the water film. The setting of SiO2 aerogel thermal-insulation mortar enables the retention of heat for the heating of the snow-melting board and snow melting, which improves the snow-melting performance.

Preparation of High-Temperature Resistant Aerogels by Incorporating Aluminum Sol into Composite Silica Sources Using Ambient Pressure Drying.

To reduce production costs and enhance the high-temperature resistance of SiO2 aerogels, an aluminum-doped silica aerogel (ASA) was successfully prepared using the sol-gel method and atmospheric drying method. The composite silica sources included TEOS and inexpensive acidic silica sol, while the aluminum source was aluminum sol. The study investigated the influence of the molar ratio of acidic silica sol to TEOS, Al/Si, and calcination temperature on the composition, structure, and high-temperature resistance of the ASA. The results indicate that a sample with an acidic silica sol to TEOS molar ratio of 0.8 achieved a specific surface area of 683.204 m2·g-1. The Al/Si molar ratio significantly impacted the high-temperature resistance of the ASA, with the sample having a molar ratio of 0.02 Al/Si displaying the highest specific surface area of 705.956 m2·g-1 at 600 °C. Moreover, this surface area remained at 273.099 m2·g-1 after calcination at 1000 °C, notably higher than the sample without aluminum sol (16.082 m2·g-1). Mechanism analysis indicated that the addition of aluminum sol to the SiO2 aerogel inhibited phase transitions, and both acidic silica sol and aluminum sol particles enhanced the aerogel structure, contributing to a marked improvement in high-temperature resistance.

First Example of Single‐Crystal Nanodiamonds Immobilized in Porous SiO2‐Aerogel Matrix: Synthesis and Characterization

A first composite material containing uniformly dispersed disaggregated detonation nanocrystalline diamonds (DNDs) in SiO2 aerogel matrix was prepared. The synthetic protocol included hydrolysis of tetramethyl orthosilicate (Si(OMe)4, TMOS) by hydrosol of surface carboxylated DNDs with a typical size of 4‐5 nm with DMSO serving as a cosolvent and a stabilizer of DND single crystals. Composite samples containing DNDs in silica aerogel matrix in concentration 1.0, 0.1 and 0.01% w/w were prepared at ambient temperature. HRTEM data revealed that DNDs nanocrystals were uniformly distributed in aerogel and did not form aggregates. Textural and optical composites’ properties were determined.

Preparation and characterization of micro-cellular melamine foam supported SiO2 aerogel for building thermal insulation

This study aims to complement the advantages of SiO2 aerogel and melamine foam (MF) to produce high-performance building insulation materials. The optimal sol–gel scheme was determined by controlling system temperature, water content, amount of ethanol and amount of acid-base catalyst (orthogonal experiment). The density and porosity of MF/SiO2 aerogel were regulated by adjusting aging time, aging temperature and type of aging agent. Furthermore, the effects of different volume fractions hydrophobic modifier on the surface free energy and wettability of MF/SiO2 aerogel were also investigated. The experiment results showed that the prepared MF/SiO2 aerogel satisfies requirements for low density (0.089 g/cm3), low thermal conductivity at room temperature (0.0256 W m−1·K−1), and excellent hydrophobic performance (the contact angle was 140.1°). Meanwhile, it was found that SiO2 aerogel was stably and uniformly distributed in the pores of the MF and effectively enhanced the mechanical property (a maximum compressive strength of 0.2058 MPa), heat-shielding performance, flame retardant property, and sound absorption capacity(αmax = 0.76, αave = 0.31).Therefore, the MF/SiO2 aerogel composites exhibit exceptional application potential in comparison to conventional building insulation materials (such as EPS, Rock wool board, etc.) due to their significantly low thermal conductivity and remarkable flame retardant properties.

Effect of γ-radiation on silica aerogel and composite material for thermal insulation applications in nuclear power pipeline

SiO2 aerogel and its composite materials are considered as promising high-temperature thermal insulation materials due to their high porosity, low density and low thermal conductivity. However, a major obstacle for their application in nuclear power systems is the currently insufficient mechanism of the radiation effect. This study therefore aimed to investigated the changes in the microstructure, hydrophobic properties and thermal insulation properties of aerogel and ultrafine glass fiber reinforced aerogel composite (uGF/SiO2 aerogel) before and after γ-radiation, and explore the mechanism of the γ-radiation effect of aerogel materials. With an increase in cumulative radiation dose, the microstructure of aerogel suffered significant radiation damage, causing a gradual increase in crystallinity and thermal conductivity. When the cumulative dose reached 1700 kGy, the nanoparticles in the aerogel agglomerated and crystallized significantly, leading to an approximately 30 % increase in thermal conductivity. Notably, at the radiation of 1700 kGy, the uGF/SiO2 aerogel exhibited excellent structure stability, with a thermal conductivity of 31.60 mW/m·K, which was 3.27 % higher than that of unirradiated sample. This indicated the uGF/SiO2 aerogel exhibited excellent thermal performance and thermal stability even after γ-radiation. The study on the radiation effect of aerogel materials offers valuable insights for the composition optimization of aerogel used in nuclear power applications.

Characterization of similar Marshak waves observed at the LMJ

We detail results of two experiments performed at the Laser Mégajoule (LMJ) facility aimed at studying similar supersonic Marshak waves propagating in a low-density SiO2 aerogel enclosed in metallic tubes. Similar means here that these two experiments, driven by the same input radiation temperature history, use purposely very different tubes in terms of length (L = 1200 or 2000 μm), diameter (2R = 1000 or 2000 μm), nature of the wall (gold or copper), and aerogel densities (ρ = 30 or 20 mg/cm3), yet the transit time and the radiation temperature of the fronts at the tube exit are the same for both shots. Marshak waves are characterized at the exit using simultaneously for the first time to our knowledge, a one dimensional soft x-ray imager from which the radiation front transit time and curvature are measured and also a broadband x-ray spectrometer to infer its temperature history. These constraining results are then successfully compared to those from simple analytical models [Cohen et al., Phys. Rev. Res. 2, 023007 (2020) and Hurricane et al., Phys. Plasmas 13, 113303 (2006)] and from the three dimensional Lagrangian radiation-hydrodynamics code TROLL to get information on x-ray energy losses. Controlled compensation effects between the length, diameter, and nature of the tubes (governing these losses) are such that the radiation temperature drop along the tubes is eventually the same for these two similar shots.

Cost-effective preparation of pre-oxygenated PAN fiber composite SiO2 aerogel felt with excellent mechanical and thermal insulation properties

Silica aerogel is an attractive thermal insulation material due to its low thermal conductivity, light weight and non-combustible inorganic properties, but its inherent brittleness and high production cost hinder its practical application on a large scale. Herein, the high-performance pre-oxidized polyacrylonitrile fiber composite silica aerogel felt (PPAF-SiO2) was successfully prepared by a cost-effective combustion drying technique for the first time. The results show that the PPAF-SiO2 has the feature of lightweight, good flexibility, and its heat resistance, hydrophobicity, and specific surface area are significantly improved. Due to the further polymerization of fiber structure molecules caused by combustion, the tensile strength of the PPAF-SiO2 is increased by 81.9 % to 1.71 MPa. More importantly, due to the high proportion of silica aerogel in felt, its thermal conductivity can be reduced to 0.02 W/(m·K), which is lower than most aerogel composite materials. Moreover, the thermal insulation performance of the PPAF-SiO2 was further confirmed by the infrared thermal imager from room temperature to 300 ℃. In addition, the innovative drying mechanism based on the combustion flame model was proposed. Finally, compared with traditional physical drying technologies in terms of drying time and drying conditions, the combustion drying technology shows great advantages in drying efficiency, energy consumption and equipment investment, which greatly reduces production costs. The combustion drying technology opens up a promisingly method for high efficiency, low energy consumption, and low cost preparation of silica aerogel composites.

Effects of silica aerogel particles on performance of the coatings for new energy vehicle battery packs

In order to reach the fire protection standard for new energy vehicle battery packs, the incorporation of SiO2 aerogel particles as a functional filler in the nitrogen and phosphorus fire-retardant system is necessary due to the inadequate mechanical properties. The effects of SiO2 aerogel on the properties of the coatings for the electric car battery pack were investigated by fire protection test, thermogravimetric analysis, limited oxygen index, UL-94 vertical test, combustion test, mechanical properties test, and weathering resistance test. The backside temperature fireproof coatings containing 1.5% SiO2 aerogel was effectively reduced to 250.2 ± 0.1 °C and the residual weight of the coating reached 32.61 ± 0.01%. The composition and structure of the carbon layer were analyzed further. Especially, the weight loss percentage of the fireproof coating is only 5.87 ± 0.02% in the water resistance test. However, excessive SiO2 aerogel decreased the performances of fireproof coatings.

Thermal conductivity test and model modification of SiO2 aerogel composites based on heat flow meter method

In the composition of thermal protection system, lightweight and efficient super thermal insulation materials-aerogel and its composites have been paid more and more attention and applied in recent years. The heat transfer of aerogel composites is more complicated due to the influence of micro-scale additives, fiber distribution and coupling heat transfer of various heat transfer modes, so it is urgent to calculate the effective thermal conductivity (ETC) accurately. According to the variation law of gas, solid, gas–solid coupling and radiation thermal conductivity with temperature and pressure, the thermal conductivity test is conducted based on the heat flow meter method, so as to the mathematical models of thermal conductivity are modified. The modified models take into account the influence of various micro-scale additives, which can accurately and quickly calculate the ETC of aerogel composites under different working conditions. The questions that different aerogel composites need to reconstruct structural models and the existing theoretical formulas are inaccurate in calculating ETC are solved. This paper is of great theoretical value to accurately predict the thermal insulation performance of aerogel composites.

Wearable thermoelectric cooler encapsulated with low thermal conductivity filler and honeycomb structure for high cooling effect

Thermoelectric coolers (TEC) based on Peltier effect has been widely used in small scale cold storage because of its zero emission, and high efficiency, while wearable thermoelectric coolers (WTEC) for personal temperature management is garnered tremendous scientific attention. For out-of-plane structured WTEC using inorganic TE materials encapsuled in flexibility substrate, on the one hand, encapsulating materials are required to have low thermal conductivity, high reliability and high flexibility, and on the other hand, heat dissipation of devices is required to be lightweight, portable and efficient. For this reason, we propose a composite material synthesised from SiO2 aerogel, hollow glass beads (HGB) and polydimethylsiloxane (PDMS) as a filler, which takes advantage of the low thermal conductivity of (0.094 W/mK) to increase the temperature difference in the encapsulation layer of the device, and moreover performs the fabrication of honeycomb holes, which further reduces the thermal conductivity of the encapsulation layer and at the same time brings a certain degree of compression resistance to the device. Radiative cooling (RC) films synthesised using hexagonal boron nitride (HBN) and PDMS for lowering the temperature of the hot side in outdoor environments without additional energy consumption, providing heat dissipation at the hot side. Honeycomb wearable thermoelectric cooler (HWTEC) proposed in this work deliver high cooling temperature difference of 9.1 °C and 6.5 °C indoor and outdoor through human wear. Our work represents an important step in the development of flexible TE devices and is believed to have promising future applications in personal thermal management, e-skin and smart textiles.

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.