Characterization Of Silica Aerogels Research Articles

Synthesis and Characterization of Silica Aerogel from Rice Husk with Ambient Pressure Drying Method

Rice husk has become global concern due to the environmental problem since it has been dumped and open burned that contributed to the emissions of carbon dioxide to the atmosphere. Therefore, utilization of rice husk to other useable product such as silica aerogel for adsorption has been study recently due to the silica content in rice husk is about 60% and this material is sustainable and cost effective. Silica aerogel was prepared from rice husk ash and dried by using ambient pressure drying method with addition of tetraethyl orthosilicate (TEOS) due to its capability to prevent the gel from crack and increase the porosity of gel to increase the capacity of adsorption process. The silica aerogel was further characterized by using Fourier Transform Infrared spectroscopy (FTIR), Elemental Anaylzer (EA) and Scanning Electron Microscopic (SEM). The results show that the silica aerogel was successfully synthesized using rice husk ash. The FTIR studies reveal that silica aerogel produced consist of amorphous silica with Si-O-Si bonding and stretching’s. From EA analysis, the carbon in the rice husk decreasing when turn into silica aerogel due to the burning of carbon content in the preparation of silica. The SEM studies confirm that the silica aerogel has a porous structure and has ability to for the application adsorption process such as carbon dioxide adsorption, methylene blue adsorption and others application.

Aerogel, a high performance material for thermal insulation - A brief overview of the building applications

In this paper data regarding the utilization of aerogel as a promising material for thermal insulation of the residential and commercial buildings are presented. Also, research work and developments in synthesis, properties and characterization of silica aerogels will be addressed. Aerogel is a synthetic porous ultralight material derived from a gel in which the liquid component of the gel has been replaced with a gas. The result is a solid with extremely low density and low thermal conductivity. Sol-gel is the most used method of preparation. Aerogel melts at 1200ºC and the thermal conductivity is almost 0. Is a solid material with the smallest density because contains about 99.8% air. This material has almost unlimited potential, believing that they might find application in most human activities and areas. Aerogel insulation is a good choice because nearly neutralizes all three methods of heat transfer: convection, conduction and radiation. The resistance to convective transfer is given by the fact that air does not circulate in the material structure. The resistance to thermal transfer by conduction is given by the majority of gaseous components. If using a carbon based gel, a high resistance to radiation transfer is obtained. Therefore, the most used aerogel for thermal insulation is the silica aerogel with carbon as nanostructured material. The high price makes it currently inaccessible and less used material. But, inevitably, the aerogel will quickly become one of the most attractive materials in the future.

Preparation and characterization of silica aerogels from by-product silicon tetrachloride under ambient pressure drying

The by-product silicon tetrachloride (SiCl4) was usually obtained from polysilicon industry and was a cheaper alternative precursor. An economic method to produce silica aerogel using silicon tetrachloride under ambient pressure drying was presented in this work, which can also solve the pollution problem during the by-product silicon tetrachloride treatment process. The prepared aerogel samples were characterized by scanning electron microscopy, Brunauer-Emmett-Teller analysis, thermal conductivity analysis, contact angle test, Fourier transform infrared spectroscopy and thermogravimetric analysis. It was found that the molar ratio of H2O/SiCl4 could affect the properties of aerogels seriously. The density and thermal conductivity first decreased and then increased as the molar ratio increased from 13 to 32. The porosity showed an opposite trend with the density. Silica aerogel with high specific surface area (856.7 m2/g), low density (0.077 m3/g) and low thermal conductivity (0.0213 W/m·k) were obtained at the optimal conditions when the molar ratio was 25. The resulting aerogel is also mesoporous material with super hydrophobicity and have a huge application in thermal insulation field.

Synthesis and characterization of silica aerogel as a promising drug carrier system

In the past years, use of aerogel in drug carrier systems has been of great interest among researchers because of its amorphous structure, significant porosity, and other special properties. In this study, the effects of physical characteristics of silica aerogels on the efficient medical application are investigated. To this end, silica aerogels with several densities were synthesized by using a two-stage sol-gel procedure and dilution by acetonitrile in gelation step. Physical characteristics of produced silica aerogels were analyzed by BET and BJH methods. Results reveal that the pore diameter and the surface area of silica aerogel are functions of its density. Using supercritical CO2 method, the efficiency of drug (Ketoprofen) loading on aerogels with respect to aerogel density was investigated. Cell viability and cell growth on silica aerogels were evaluated by MTT assay and SEM analysis, respectively. The drug-loaded materials were characterized by using of FT-IR, XRD, UV-Spectroscopy, and FE-SEM analysis. Results show that the effective density of silica aerogel for a drug carrier system is 0.12 g/cm3.

Recent Advances in Research on the Synthetic Fiber Based Silica Aerogel Nanocomposites.

The presented paper contains a brief review on the synthesis and characterization of silica aerogels and its nanocomposites with nanofibers and fibers based on a literature study over the past twenty years and my own research. Particular attention is focused on carbon fiber-based silica aerogel nanocomposites. Silica aerogel is brittle in nature, therefore, it is necessary to improve this drawback, e.g., by polymer modification or fiber additives. Nevertheless, there are very few articles in the literature devoted to the synthesis of silica aerogel/fiber nanocomposites, especially those focusing on carbon fibers and nanofibers. Carbon fibers are very interesting materials, namely due to their special properties: high conductivity, high mechanical properties in relation to very low bulk densities, high thermal stability, and chemical resistance in the silica aerogel matrix, which can help enhance silica aerogel applications in the future.

Fabrication and Characterization of Silica Aerogel @Polystyrene Composite Beads by Suspension Polymerization

In this study, the powder of hydrophobic silica aerogel remaining nanopore by ambient pressure drying was successfully introduced into polystyrene beads during suspension polymerization. nanosilica powder without nanopore was also used. Pure polystyrene, silica aerogel/polystyrene (PS) and nanosilica/polystyrene beads were fabricated, respectively. The structure and properties of silica aerogel @PS composite beads were characterized by SEM, EDS, TG-DSC and FT-IR. The results of TG-DSC, FT-IR and EDS show silica aerogel is located in the PS beads, but it is difficult to be observed by SEM because of its low content. The introduction of silica and silica aerogel both decrease the transparency of PS beads. Silica aerogel loosen the microstructure of PS beads.

Preparation and characterization of silica aerogels from diatomite via ambient pressure drying

The silica aerogels were successfully fabricated under ambient pressure from diatomite. The influence of different dilution ratios of diatomite filtrate on physical properties of aerogels were studied. The microstructure, surface functional groups, thermal stability, morphology and mechanical properties of silica aerogels based on diatomite were investigated by BET adsorption, FT-IR, DTA-TG, FESEM, TEM, and nanoindentation methods. The results indicate that the filtrate diluted with distilled water in a proportion of 1: 2 could give silica aerogels in the largest size with highest transparency. The obtained aerogels with density of 0.122–0.203 g/m3 and specific surface area of 655.5–790.7 m2/g are crack free amorphous solids and exhibited a sponge-like structure. Moreover, the peak pore size resided at 9 nm. The initial aerogels were hydrophobic, when being heat-treated around 400°C, the aerogels were transformed into hydrophilic ones. The obtained aerogel has good mechanical properties.

Preparation and Characterization of Silica Aerogel Immobilized with Cyanex 301 for Extraction of Zn(II)

A new solid phase extractant silica aerogel immobilized with Cyanex 301 {bis (2,4,4-trimethylpentyl) dithiophosphinic acid} (SAWC) was prepared via a sol-gel method and investigated for the extraction of Zn (II) from aqueous solution by a batch extraction technique. It is found that SAWC can extract about 100% zinc at equilibrium pH 1.7. Prepared SAWC was characterized by FT-IR, BET, EDX and SEM which proved the presence of Cyanex 301 into silica aerogel. Moreover, the material is also easily regenerated and reused in the subsequent removal of Zn (II) in five cycles. Therefore, it could be concluded that it may perform as a solid phase extractant in the extraction of metal ions from the aqueous solution.

Preparation and characterization of silica aerogels from oil shale ash

The silica aerogels were successfully synthesized using oil shale ash which is a by-product of oil shale processing via ambient pressure drying. The physical and textural properties of the silica aerogels have been investigated and discussed. The results showed that the organic modification of hydrogels was a crucial step during the processing which preserved mesopores in ambient pressure drying. The unmodified hydrogel underwent tremendous shrinkage during the drying and yielded microporous silica aerogel. Using this novel route, it could produce silica aerogel with low tapping density of 0.074 g/cm 3, high specific surface (909 m 2/g) and cumulative pore volume of 2.54 cm 3/g. From the industrial point of view, the present process is quite suitable for a large scale production of powdered silica aerogel. Furthermore, it provides a new way to solve the problem of oil shale ash pollution.

Silica aerogel; synthesis, properties and characterization

Abstract In recent years, silica aerogels have attracted increasingly more attention due to their extraordinary properties and their existing and potential applications in wide variety technological areas. Silica aerogel is a nanostructured material with high specific surface area, high porosity, low density, low dielectric constant and excellent heat insulation properties. Many research works have been carried out concerning aerogel production and characterization. In this review paper, research work and developments in synthesis, properties and characterization of silica aerogels will be addressed. Particular attention is paid to drying which is a critical step in aerogel synthesis and makes the production of this material more economical and commercial.

Effect of supercritical drying conditions in ethanol on the structural and textural properties of silica aerogels

Research on the preparation and characterization of silica aerogels has focused mainly on transparency and monolithicity. In this paper, we address the effect of supercritical drying conditions in ethanol on the shrinkage and porous texture of aerogels. The variables studied included the initial amount of ethanol added to the reactor, initial pressure of N2, heating rate and stabilization time above supercritical conditions. The starting material was an alcogel obtained by the sol–gel process in acidic media. All aerogels were amorphous. In general, skeletal density increased when the initial amount of ethanol added into the body of the autoclave was decreased and the volume fraction of porosity was above 91%. According to infrared spectra, skeletal SiO2 network was independent of supercritical drying conditions. N2 adsorption isotherms identify the macroporous character of aerogels, which was confirmed by SEM and TEM. Specific surface area significantly increased when the initial volume of ethanol added to the reactor was increased and the stabilization time above supercritical conditions decreased, whereas surface area decreased when autoclave pre-pressurization was increased.

Synthesis and characterization of silica aerogels by a novel fast ambient pressure drying process

Using cheap waterglass as silica source, silica aerogels were synthesized via a novel fast ambient drying by using an ethanol/trimethylchlorosilane (TMCS)/Heptane solution for modification of the wet gel. One-step solvent exchange and surface modification were simultaneously progressed by immersing the hydrogel in EtOH/TMCS/Heptane solution, in which TMCS reacting with pore water and Si–OH group on the surface of the gel, with ethanol and heptane helping to decrease the rate of TMCS reacting with pore water and extrude water from gel pores. The synthesized silica aerogel was a light and crack-free solid, with the density of 0.128–0.136 g/cm 3 and 93.8–94.2% porosity. The microstructure, morphology and properties of the aerogels were studied by FTIR, SEM, TEM and BET measurement. The results indicate that silica aerogels exhibit a sponge structure with uniform nano-particle and pores size distribution. The specific surface areas of silica aerogels are 559–618 m 2/g. And there is an obvious Si–CH 3 group on the surface of the silica aerogel.

Characterization of silica aerogel with the atomic force microscope and SAXS

The tapping atomic force microscope is the most convenient atomic force microscope mode to provide 3D surface measurements of mechanically weak materials like aerogels (dried with CO 2 at supercritical condition) down to the nanometer scale. The paper illustrates the variation of particle size as function of the water ratio in the precursor polyethoxydisiloxane. When the water ratio in the hydrolysis process is increased, the particle size of the samples decreases, which explains the shift of Rayleigh scattering in the UV region. For image interpretation, power spectrum analysis is introduced as a technique to compare the atomic force microscope images presented in the reciprocal space with scattering results. The radially averaged power spectrum of the images is in good agreement with the scattering data. The convolution of texture features with the atomic force microscope tip is quite important for structural features in the vicinity of the tip size.

Effect of gel parameters on monolithicity and density of silica aerogels

As part of continuing investigation of the preparation and characterization of silica aerogels, detailed experimental results on monolithicity and density of the aerogels as a function of catalysts and their concentrations, molar ratios of tetraethylorthosilicate (TEOS), ethanol (EtOH) and H2O, gel pH and gel ageing, are reported. With large concentrations of catalysts, lower and higher aged alcogels have been found to produce opaque, cracked and highdensity silica aerogels; however, good-quality monolithic, transparent and low-density aerogels have been obtained at lower catalyst concentration (0. 01n HCl) with alcogel ageing periods between 9 and 30 days. The best quality silica aerogels, in terms of transparency and monolithicity, have been obtained using TEOS∶EtOH∶H2O in the molar ratio of 1∶5∶8.

Optical Characterization of Silica Aerogel

ABSTRACTTwo optical methods are described for mapping the local variations of refractive index within monoliths of porous silica aerogel. One is an interferometrie measurement that produces “iso-index” fringes in a two dimensional image; an orthogonal view gives the third dimension information. The other method uses the deflection of a He-Ne laser beam to map the gradient index within a sample. The quantification of the measurements is described and the accuracy of the results is discussed.