Silica Aerogel Powder Research Articles

A fast synthesis of silica aerogel powders-based on water glass via ambient drying

In this paper, we report the experimental results of the silica aerogel powders prepared by water glass and ambient pressure drying within 4 h. Water glass was hydrolyzed in water using HCl as the acid catalyst. In order to reduce the consumption of modifier and preparation period, the new technological process of mechanical crushing and filtration was introduced and solvent exchange/surface modification process can be rapidly carried out in this way. Furthermore, we utilized water glass instead of NH3·H2O as base catalyst. To some extent, it avoided impurities into the aerogels. Base concentration proved to have a very important influence on the physical and chemical properties of aerogels. As a result, when the dilution ratio of water glass as base catalyst is 3, aerogels with well-developed mesoporous structure (mean pore size of ~ 20 nm) and super hydrophobicity (contact angle of ~ 162°) can be obtained.

Preparation of aerogel-eicosane microparticles for thermoregulatory coating on textile

Aerogel/eicosane microparticles were prepared by dispersing nanoporous silica aerogel powder in a liquid of phase change material (PCM), eicosane. Melt-infiltration (M), solvent-dissolving (D) and combined melt-dissolving (MD) for particle dispersion were investigated. Differential Scanning Calorimetric thermograph indicated that microparticle M has maximum heat capacity of 198J/g whereas the heat capacity of microparticles D and MD was found to be 139J/g and 144J/g, respectively. FT-IR and SEM analyses of the microparticles revealed that the eicosane infiltrated and coated the fine aerogel particles but the microparticles still remained in the powder form. The nanoporous aerogel structure held the infiltrated eicosane while the ultra-high specific surface area of silica aerogel kept the surrounding eicosane in situ by surface tension. Infrared thermal imaging showed that the eicosane did not drip out from the microparticles even at 120°C, whereas the pure PCM completely changed phase to fluid when heated. The developed microparticles provide ease of coating application in room temperature for thermal protective textiles. The coated fabric showed significantly improved thermal resistance over the speculated phase transition period of the PCM. This opens up the opportunity for the developed microparticles to be utilised as a thermal protective coating additive in a wide temperature range without melting or dripping out from the applied substrates.

Hydrophobic silica aerogels for oil spills clean-up, synthesis, characterization and preliminary performance evaluation

The most important requirements for surface water management include the availability of rapid and efficient specific adsorbents. This work presents synthesis, characterization and performance analysis of a novel silica aerogel for oil decontamination from surface water. Hydrophobic silica aerogel powders were synthesized by a rapid co-precursor method applying ambient pressure. An inexpensive aqueous sodium silicate solution was used as starting material, with hexamethyldisilazane (HMDS), tetraethyl orthosilicate and trimethylchlorosilane as organic co-precursors. The prepared silica aerogels were characterized by nitrogen adsorption/desorption technique (BET), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and contact angle measurements. Silica aerogel samples prepared using HMDS exhibited the highest BET surface area of about 936 m2/g, pore volume (1.715 cm3/g) and contact angle approaching 106°. The aerogels were then tested for oil adsorbing capacity in oil salt–water mixtures for oil spill clean-up applications. Preliminary oil adsorption experiments have shown that a maximum oil removal of 96 and 90 % using silica aerogel prepared from HMDS from saline and non-saline oily waste waters, respectively. Moreover, the minimization of the costly precursors permits a low-cost large scale production and economic oil spill clean-up applications.

Superhydrophobic hybrid aerogel powders from waterglass with distinctive applications

Hybrid silica aerogel powders with enhanced superhydrophobicity and very high reaction yield were prepared by a fast co-precursor method at ambient pressure. An inexpensive aqueous sodium silicate solution was used as starting material (waterglass or WG), with hexamethyldisilazane (HMDZ) as organic co-precursor.The key for successfully achieving such high yields and superhydrophobicity was a systematic tuning of the synthesis parameters (co-precursors and acid catalyst molar ratios) and process conditions (stirring speed, stirring period, aging, washing and drying steps), in close correlation with the reaction mechanism. Using a minimum amount of organic co-precursor, a total yield of ∼80% in hybrid aerogels with high lipophilic/hydrophilic ratio, very high water contact angles (∼152±2°) and very low densities (∼0.120gcm−3) were obtained. The optimized synthesis conditions consist in HNO3:WG:HMDZ molar ratios of 1.5:1.0:1.5, stirring speed of 120rpm, only during addition of the catalyst and co-precursor, aging for 5min and washing with water before drying at atmospheric pressure.The minimization of the only costly precursor allows envisaging a low-cost large scale production and, moreover, the encapsulation of water droplets within aerogel powder allows proposing distinctive applications, such as water transport at a microscale level.

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.

Evolution of visible photoluminescence of Si quantum dots embedded in silicon oxide matrix

Abstract Photoluminescence properties of nc-Si/SiOx nanocomposites produced by pressing the mixture of the silica aerogel powder with the porous silicon have been studied. The transformation of emission spectra of Si quantum dots, its quantum yield and emission kinetics during the long time (few months) aging in ambient conditions and formation conditions (external pressure) were observed. The different behavior of short and long wave range emission of Si quantum dots embedded in silicon oxide matrix has been obtained. The observed blue-shifting (from 2.02 to 2.05 eV) of emission peak associated with the free exciton recombination in Si quantum dots at forming pressure increasing is explained by the reduction of average Si quantum dot dimension due to the breaking away the surface irregularities and smoothing of the Si nanoparticles surface. Effect of a strong increase in intensity (more than 1 order) and blue shifting of emission of Si quantum dots were discovered in nc-Si/SiOx nanocomposites at few months’ storage in ambient conditions. Such effects were explained in terms of both surface passivation and the carrier confinement. It was also confirmed by the fact that for aged composites the photoluminescence kinetics transforms by adding the stretched exponential term to the single exponential low.

Thermal Characterisation of Thermoset Polyester Resin Filled Recycle Expanded Polystyrene Composite with Aerogel and Alumina Additives

The preparation and characterization of Unsaturated Polyester Resin (UPR) filled recycled Expanded Polystyrene (EPS) composite systems were systematically investigated. Additives such as Alumina and silica aerogel powder were added to the composite for Infrared reflection and insulation enhancement. The effect of differing alumina weight percentage on the thermal properties, i.e. thermal conductivity and glass transition temperature, Tg were determined. The fabricated composite undergoes thermal analysis by using a DSC and a hand-held thermal probe, and characterized by a FTIR. There is little variation of the Tg across the samples tested. Specific heat capacity, cp from the DSC thermogram was significantly affected by incorporation of silica aerogel; 565 J/kgK compared to the unfilled sample result of 1706 kJ/kg. The thermal conductivity showed a minimum at 0.147 W m-1 K-1 from integrated silica aerogel only sample, and alumina addition increases the thermal conductivity above the minimum k value in the ranges 0.227-0.313 W m-1 K-1. Alternative Cp values from the thermal probe followed similar trend as the DSC Cp. Thermal diffusivity from the probe also showed an increase upon silica aerogel and alumina incorporation.

다공성 실리카 에어로겔을 이용한 복합단열재의 특성에 관한 연구

High porous silica aerogel/polyurethane polymer composite was manufactured by cross-linking polymeriza tion of polyurethane foaming process. The properties of microstructure, mechanical strength, and thermal properties were investigated for its various applications. The superhydrophobic silica aerogel powders were used for highly thermal insulation filler materials. The thermal conductivities can be resulted 0.07 W/mK to 0.13 W/mK, by decreasing the contents of silica aerogels in composite materials. It is found that the polymerization formulation by organic binders can be applied to heavy industires, building materials, and various industries.

Fluidized Bed Drying Effect on the Aerogel Powder Synthesis

A fluidized bed drying approach was utilized to the synthesis of water glass based silica aerogel powders. The effects of the fluidized bed drying conditions such as the superficial velocity and temperature of hot air and bead size as well as bead/wet-gel ratio, on the physical properties such as tapping density and productivity of the aerogel powders were systematically investigated. The experimental results showed that the amount of beads mixed with wet-gels in the fluidized bed column has the most profound impact on the fluidization efficiency, greatly enhancing the yield of the aerogel powders up to 98% with a proper bead/wet-gel weight ratio as compared to 72% without using beads. No significant change was observed in the tapping density over a wide range of the fluidized drying condition. Consequently the fluidized bed drying approach shows a good promise as an alternative route for the large-scale production of the aerogel powders.

Heat insulation properties of silica aerogel/glass fiber composites fabricated by press forming

Silica aerogel/glass fiber composites were fabricated by press forming of silica aerogel powders and dispersed glass fibers. Due to the nano porous structure, silica aerogel showed low gas thermal conductivity and solid thermal conductivity. By adding the glass fibers, the strength of the composites was improved but the heat insulation property was deteriorated. The thermal conductivities of the composites with 20wt.% glass fibers at 300°C and 600°C were 0.025W/(m K) and 0.030W/(m K), respectively. As opacifier, the addition of TiO2 decreased the radiative thermal conductivity abruptly, especially at high temperatures. At 700°C, it decreased from 0.041W/(m K) to 0.030W/(m K) after 20wt.% TiO2 powders were added.

High discharge capacity solid composite polymer electrolyte lithium battery

In this study, a series of nanocomposite polymer electrolytes (CPEs), PAN/LiClO4/SAP, with high conductivity are prepared based on polyacrylonitrile (PAN), LiClO4 and low content of the silica aerogel powder (SAP) prepared by the sol–gel method with ionic liquid (IL) as the template. The effect of addition of SAP on the properties of the CPEs is investigated by FTIR, AC impedance, linear sweep voltagrams and cyclic voltammetry measurements as well as the charge–discharge performance. It is found that the ionic conductivity of the CPE is significantly improved by addition of SAP. The maximum ambient ionic conductivity of CPEs is about 12.5 times higher than that without addition of SAP. The results of the voltammetry measurements of CPE-3, which contained 3wt% of SAP, show that the anodic and cathodic peaks are well maintained after 100 cycles, showing excellent electrochemical stability and cyclability over the potential range between 0V and 4V vs. Li/Li+. Besides, the room temperature discharge capacity measured at 0.5C for the coin cell based on CPE-3 is 120mAhg−1 and the capacity is retained after 20 cycles discharge, indicating the potential for practical use. This is perhaps the first report of the room temperature charge–discharge performance on the solid composite polymer electrolyte to the best of our knowledge.

Photoluminescence properties of silica aerogel/porous silicon nanocomposites

The luminescent properties of nanocomposite pellets based on silica aerogel and porous Si powder are studied depending on the ratio of chemical compounds. The photoluminescence of nanocomposites is characterized by a red–orange band related to silicon nanoparticles and a blue–green band related to silica aerogel with close values of decay time and activation energy. Remarkable tuning of nanocomposites' photoluminescence spectra in the RGB region is established allowing their use as promising phosphor materials for light-emitting diodes. The outgoing spectra of pellet photoluminescence are guided by the chemical composition ratio, porous Si and silica aerogel technology, and the storage time in ambient atmosphere. It was shown that using the silica aerogel as a dielectric matrix considerably increases the stability of photoluminescence yield of silicon nanoparticles.

Preparation of silica aerogel from oil shale ash by fluidized bed drying

The silica aerogel with high specific surface area and large pore volume was successfully synthesized using oil shale ash (OSA) via ambient pressure drying. The oil shale ash was burned and leached by sulfuric acid solution, and then was extracted using sodium hydroxide solution to produce a sodium silicate solution. The solution was neutralized with sulfuric acid solution to form a silica gel. After washing with water, the solvent exchange with n-hexane, and the surface modification with hexamethyldisilazane (HMDZ), the aged gel was dried by fluidization technique and also using a furnace to yield silica aerogels. The physical and textural properties of the resultant silica aerogels were investigated and discussed. The results have been compared with silica aerogel powders dried in a furnace. From the results, it is clear that the properties of silica powders obtained in fluidized bed are superior to that of powders dried in the furnace. Using fluidization technique, it could produce silica aerogel powders with low tapping density of 0.0775 g/cm 3, high specific surface area (789 m 2/g) and cumulative pore volume of 2.77 cm 3/g.

Synthesis of water‐glass‐based silica aerogel powder via with and without squeezing of hydrogels

AbstractThe present article describes the synthesis of water‐glass‐based silica aerogel powder via coprecursor method, using with and without squeezing, in drying technique. The present research was aimed to develop a simple, cost‐effective, and rapid drying process, i.e., squeezing through sol–gel synthesis. The physical and textural properties of the aerogel powder synthesized with and without squeezing process via ambient pressure drying (APD) have been studied and compared. For characterization of aerogel powder, we employed Brunauer, Emmett, and Teller, Barrett‐Joyner‐Halenda, and field emission scanning electron microscope techniques. The experimental results showed that the properties of the aerogel powder obtained by squeezing are superior to those dried in a furnace one. The squeeze‐dried aerogel powder exhibited lower tapping density (0.126 g/cm3) than furnace dried. Furthermore, textural investigations revealed that the aerogel powder has high‐specific surface area (752.3 m2/g), high porosity, low shrinkage, and uniform pore size distribution, which is obtained by squeezing process via APD. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Influence of silica aerogel on the properties of polyethylene oxide-based nanocomposite polymer electrolytes for lithium battery

In this study, a series of nanocomposite polymer electrolytes (NCPEs) with high conductivity and lithium ion transference number, PEO/LiClO 4/SAP, were prepared from high molecular weight polyethylene oxide (PEO), LiClO 4 and low content of homemade silica aerogel powder (SAP), which had higher surface area and pore volume than the conventional silica particle. From the SEM images it was found that the SAP nanoparticles were well dispersed in the PEO polymer electrolyte matrix. The characterization and interactions in the CPEs were studied by DSC, XRD, FT-IR and 7Li NMR analysis. The ac impedance results showed that the ionic conductivity of the CPE was significantly improved by the addition of the as-prepared SAP. The maximum ambient ionic conductivity obtained from the CPE with EO/Li = 6 and 2 wt.% of SAP (O6A2) was about threefold higher than that of the corresponding polymer electrolyte without SAP (O6). In addition, the lithium ion transference number ( t +) of O6A2 at 70 °C was as high as 0.67, which was also three times higher than that of O6 and has not been previously reported for the PEO–LiX-based polymer electrolytes.

A continuous production process for silica aerogel powders based on sodium silicate by fluidized bed drying of wet-gel slurry

The present study described a continuous process for the production of hydrophobic silica aerogel powders based on an inexpensive precursor such as sodium silicate. Fluidization technique was employed for the drying of wet-gel slurry at an ambient pressure. The fluidization column was fed with the silylated wet-gel slurry in a continuous mode and the fluidization was carried out at 220 °C. The aerogel powder collected in Trap-I was fluidized twice at room temperature in order to separate the lighter aerogel particles from the first trap. The tapping density of the aerogel powder decreased from 0.09 to 0.05 g/cm 3 for Trap-II, however, the microstructure did not differ significantly. Using this process, hydrophobic silica aerogel powders exhibiting tapping density as low as 0.05 g/cm 3, high specific surface area of 783 m 2/g and cumulative pore volume of 1.79 cm 3/g have been obtained. The aerogels were characterized by Field-Emission Scanning Electron Microscopy (FE-SEM), BET specific surface area, N 2 physisorption isotherms, pore size distribution and particle size analyses. The results have been compared with aerogel powders obtained by ambient pressure drying of the wet-gel slurry in a furnace.

Superhydrophobic silica aerogel powders with simultaneous surface modification, solvent exchange and sodium ion removal from hydrogels

We report a novel method for the rapid synthesis of superhydrophobic silica aerogel powders based on an inexpensive precursor such as sodium silicate via ambient pressure drying. The sodium silicate was directly polymerized without prior ion exchange by the addition of nitric acid and hexamethyldisilazane (HMDS) to yield silylated hydrogels. The indispensable steps such as surface modification, solvent exchange and sodium ion removal were simultaneously accomplished in one-step by immersing the silylated hydrogel in a non-polar solvent such as n-hexane. The organic modification in the aqueous phase, i.e. in the hydrogel essentially led to the displacement of pore water and simultaneous intrusion of n-hexane transformed the hydrogel into an organo-gel. During this process, sodium ions present in the hydrogel were removed with the displaced pore water. Using this process, it was possible to produce superhydrophobic silica aerogel powders with contact angle as high as 150°, very low tapping density of 0.08 g/cm 3, high specific surface area (778 m 2/g) and cumulative pore volume of 2.34 cm 3/g. The total processing time of the aerogel powders could be restricted to 5 h. The textural properties of the aerogel powders have been investigated and discussed.

A cost-effective and fast synthesis of nanoporous SiO 2 aerogel powders using water-glass via ambient pressure drying route

Considering the need for large-scale production of silica aerogel powders, the present research was aimed to develop a simple, cost-effective and rapid process based on water-glass precursor via ambient pressure drying (APD) route. It has been shown that the surface chemical modification of hydrogels can rapidly be carried out with extremely low doses (e.g. 5 g of hexamethyldisilazane ( HMDS) for 100 g of hydrogel) of HMDS by a co-precursor method which makes this process quite cost-effective. The surface modification in the aqueous phase essentially resulted in the displacement of the pore water and the simultaneous one-step solvent exchange using n-hexane converted the hydrogel into an organo-gel in 3 h and thus the total processing time of the aerogel powder production via APD could drastically be reduced to 5 h. The solvent n-hexane could be recollected during the drying stage and it does not add much to the material cost. The aerogel powders with tapping densities and specific surface areas in the range of 0.100–0.309 g/cm 3 and 473–776 m 2/g, respectively, could be synthesized using this novel route. The surface modification of the aerogel powders was explored by means of X-ray photoelectron spectroscopy (XPS) in conjunction with the Fourier transform infrared (FT-IR) spectroscopy. The textural investigations revealed that the aerogel powders with a wide variation in their pore size distributions and average pore diameters can easily be synthesized by varying the silica content in the sol.

Aerogel: Space exploration applications

The unique physical properties of aerogel have proven to be enabling to a variety of both flight and proposed space exploration missions. The extremely low density and highly porous nature of aerogel makes it suitable for stopping high velocity particles, as a highly efficient thermal barrier, and as a porous medium for the containment of cryogenic fluids. The use of silica aerogel as a hypervelocity particle capture and return media for the Stardust Mission has drawn the attention of many in the space exploration community. Aerogel is currently being used as the thermal insulation material in the 2003 Mars Exploration Rovers. The SCIM (Sample Collection for the Investigation of Mars) and the STEP (Satellite Test of the Equivalence Principle) Missions are both proposed space exploration missions, in which, the use of aerogel is critical to their overall design and success. Composite materials comprised of silica aerogel and oxide powders are under development for use in a new generation of thermoelectric devices that are planned for use in many future space exploration mission designs. Work is currently ongoing in the development and production of non-silicate and composite aerogels to extend the range of useful applications envisioned for aerogel in future space exploration projects.

Investigation of stack materials for miniature thermoacoustic engines

In a thermoacoustic engine one of the most critical components is the stack that interacts thermally with a sound field. Its effective surface area determines directly the cooling power and efficiency while the thermal properties determine the losses. Moreover, as the engines are miniaturized, stack performance on a small scale becomes a limiting factor, especially when a stack length of 1000 μ or less has to maintain temperature differences of around 30°C. We have investigated as stack material cotton wool, glass wool, ceramics, silica aerogel, carbon fibers, and carbon powder by measuring flow resistance at high acoustic frequencies, 4–20 kHz, and thermal transport properties. The mechanical properties and ease of machining to small dimensions, of the order of 1 μ, have been studied. In selecting the ideal material for very small devices, a compromise needs to be made between thermoacoustic and mechanical properties. [Work supported by ONR.]