Aerogel Particles Research Articles

Mixing and Packing of Fine Particles of Different Sizes

Two different approaches for mixing different sizes of fine particles without segregation and simultaneously increasing the packing density of the mixture are presented. The first application requires uniform mixing of 300 and 30 μm aluminum oxide particles acting as surrogates for the explosive RDX. The packing density needs to be as high as possible and the particles need to be well-mixed to prevent local hot spots. This was accomplished by adding moisture to uniformly mix the particles and then removing the moisture to increase the packing density. The second application requires mixing coarse (2.3 mm) and fine (65 μm) silica aerogel particles; the aerogels are very porous and light and have a very low thermal conductivity. Here we want to fill the voids between the coarse particles with fine particles so that the bulk (or packing) density of the mixture is increased, thereby further increasing their insulating properties. This was done by combining a negative pressure (vacuum) with an external force field, such as sound waves or vibration.

Design, simulation, and performance of a draft tube spout fluid bed coating system for aerogel particles

A draft tube spout fluid bed coating system was designed to coat porous aerogel particles in a size range from 0.1 to 2 mm in diameter. Its primary objective was to insure that just the outer surface of the particles was coated. The inner, pore surface area of the particles needed to remain open to preserve their insulating properties. This paper discusses the design, simulation, and experimental results we obtained on the actual coating of 1–3 mm particles. A conventional, pharmaceutical coating, Surelease®, was used as the coating material and the system successfully coated the particles without penetration of the coating material into the particles. The apparatus can be used to coat friable, low density particles as well as those of high density and is well suited for other coating applications including those in the pharmaceutical industry.

Effect of a uniaxially deformed aerogel on the orientation of the order parameter of superfluid 3He

The effect of a uniaxially deformed aerogel on the orientation of the order parameter of 3He has been analyzed with the inclusion of correlations in the positions of the particles forming the aerogel. The minimum strain for the B phase in the uniaxially stretched aerogel that can lead to the orientation of the orbital part of the order parameter different from the bulk case has been estimated. The orientational effect has been estimated for the A-like phase in the uniaxially compressed aerogel has been estimated. It has been shown that the dependence of the orientational effect on correlations in the mutual locations of the aerogel particles is stronger than that of the superconducting transition temperature.

Synthesis and Characterization of Nanocarbon-Supported Titanium Dioxide

AbstractIn this report, we describe recent efforts in fabricating new nanocarbon-supported titanium dioxide structures that exhibit high surface area and improved electrical conductivity. Nanocarbons consisting of single-walled carbon nanotubes and carbon aerogel nanoparticles were used to support titanium dioxide particles and produce monoliths with densities as low as 80 mg/cm 3. The electrical conductivity of the nanocarbon-supported titanium dioxide was dictated by the conductivity of the nanocarbon support while the pore structure was dominated by the titanium dioxide aerogel particles. The conductivity of the monoliths presented here was 72 S/m and the surface area was 203 m2/g.

Hypervelocity capture of particles in aerogel: Dependence on aerogel properties

Capture of high-speed (hypervelocity) particles in aerogel at ambient temperatures of 175–763 K is reported. This extends previous work which has mostly focussed on conducting experiments at ambient laboratory temperatures, even though aerogels are intended for use in cosmic dust capture cells in space environments which may experience a range of temperatures (e.g., the NASA Stardust mission which collected dust at 1.81 AU and putative Mars atmospheric sampling missions). No significant change in track length (normalised to impactor size) was found over the range 175–600 K, although at 763 K a significant reduction (30%) was found. By contrast, entrance hole diameter remained constant only up to 400 K, above this sudden changes of up to 50% were observed. Experiments were also carried out at normal laboratory temperature using a wide range of aerogel densities and particle sizes. It was found that track length normalised to particle size varies inversely with aerogel density. This is a power law dependence and not linear as previously reported, with longer tracks at lower densities. Glass projectiles (up to 100 μm size) were found to undergo a variety of degrees of damage during capture. In addition to the well known acquisition of a coating (partial or complete) of molten aerogel the mechanical damage includes pitting and meridian fractures. Larger (500 μm diameter) stainless steel spheres also showed damage during capture. In this case melting and ablation occurs, suggesting surficial temperatures during impact in excess of 1400 °C. The response of the aerogel itself to passage of particles through it is reported. The presence of fan-like fractures around the tracks is attributed to cone cracking similar to that in glasses of normal density, with the difference that here it is a repetitive process as the particles pass through the aerogel.

Investigation of ionic conductivity of composite gel polymer electrolyte membranes based on P(VDF-HFP), LiClO 4 and silica aerogel for lithium ion battery

In the present investigation, a series of P(VDF-HFP)-based composite gel polymer electrolyte membranes using silica aerogel (SAG) as filler have been synthesized with varying the plasticizer-filler ratio, systematically. The maximum room temperature ionic conductivity is found to be 1.04 × 10 −2 S/cm. XRD and FTIR studies have been conducted to investigate the structural and interaction of different groups in the composite polymer electrolyte (CPE) membrane. Microstructural studies by SEM exhibit highly porous membrane due to presence of silica aerogel particles. DSC results confirm that with the additon of SiO 2 aerogel up to 4 wt.%, the glass transition temperature ( T g) and crystallinity decreases, but increases slightly when it crosses this limit.

Effect of reduction temperature on the preparation of zero-valent iron aerogels for trichloroethylene dechlorination

Zero-valent iron (ZVI) aerogels have been synthesized by sol-gel method and supercritical CO2 drying, followed by H2 reduction in the temperature range of 350–500 °C. When applied to trichloroethylene (TCE) dechlorination, the ZVI aerogel reduced at 370 °C showed the highest performance in the conditions employed in this study. Thus, the effect of reduction temperature in preparing ZVI aerogels has been investigated by several characterizations such as BET, XRD, TPR, and TEM analyses. As the reduction temperature decreased from 500 to 350 °C, the BET surface area of the resulting aerogels increased from 6 to 30 m2/g, whereas their Fe0 content decreased up to 64%. It was also found that H2 reduction at low temperatures such as 350 and 370 °C leads to the formation of ZVI aerogel particles consisting of both Fe0 and FeOx in the particle cores with a different amount ratio, where FeOx is a mixture of maghemite and magnetite. It is, therefore, suggested that reduction at 370 °C for ZVI aerogel preparation yielded particles homogeneously composed of Fe0 and FeOx in the amount ratio of 87/13, resulting in high TCE dechlorination rate. On the other hand, when Pd- and Ni-ZVI aerogels were prepared via cogellation and then applied for TCE dechlorination, we also observed a similar effect of reduction temperature. However, the reduction at 350 or 370 °C produced Pd- or Ni-ZVI aerogel particles in which Fe0 and Fe3O4 co-exist homogeneously. Since both Fe0 and Fe3O4 are advantageous in TCE dechlorination, the activities of Pd- and Ni-ZVI aerogels reduced at 350 °C were comparable to those of both aerogels reduced at 370 °C, although the former aerogels have less Fe0 content.

7Li NMR spectroscopy and ion conduction mechanism of composite gel polymer electrolyte: A comparative study with variation of salt and plasticizer with filler

Microporous composite gel polymer electrolyte (CGPE) has been prepared by incorporating the home-made silica aerogel (SAG) particles into the poly(vinylidene fluoride- co-hexafluoropropylene) (PVdF-HFP) copolymer/LiClO 4 matrix. The ionic transport behavior of the electrolyte is studied with various experimental techniques such as AC impedance, X-ray diffraction (XRD), infrared (IR) spectra, nuclear magnetic resonance (NMR), scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and thermogravimetric analyzer (TGA), etc. The results reveal that the SAG particles are well dispersed in the electrolytes and incorporate with the other components of the CGPEs. The solid-state 7Li NMR study has confirmed the interactions of lithium ion with SAG, polymer and plasticizers, causing to form the microporous structure and reduce the glass transition temperature and crystallinity, resulting in an increase in ionic conductivity of the CGPE. The best ionic conductivity (1.04 × 10 −2 S/cm at room temperature) is obtained from the composite polymer electrolyte containing 4 wt% of SAG, which is approximately four times higher than the ionic conductivity of the electrolyte without the filler.

Removal of Oil from Water by Inverse Fluidization of Aerogels

Surface-treated hydrophobic aerogel (Nanogel) granules of sizes between 500 and 850 μm, 1.7 and 2.3 mm, and 0.5 and 2.3 mm are fluidized by a downward flow of oil-contaminated water in an inverse fluidization mode. Aerogel particles are nanostructured, extremely light and porous, have a very large surface area per unit mass, and are sufficiently robust to be fluidized. Their hydrophobic surface gives them a strong affinity for oil and other organic compounds, with the exclusion of water. These desirable properties make them an ideal sorbent or filter media for the removal of oil from wastewater. The hydrodynamic characteristics of inverse fluidized beds of aerogel granules of different size ranges were studied by measuring the pressure drop and bed expansion as a function of superficial velocity. The oil removal efficiency and capacity of the aerogel granules in the inverse fluidized bed were found to depend mainly on the size of the granules, the initial height of the bed (amount of powder used), the void fraction, and the fluid velocity. Among the advantages of the process are the extremely low energy consumption (low pressure drop) during oil removal and the large absorption capacity. Oil concentrations of about 2000 mg/L in water could be reduced to less than 10 mg/L by the inverse fluidization process.

Immobilization of lipase on methyl-modified silica aerogels by physical adsorption

In this work, methyl-modified silica aerogels, a new kind of macro-porous material with high porosity, were used as carriers to immobilize lipase by adsorption. SEM, TEM, nitrogen adsorption device, and thermogravimetric analysis were used to characterize the properties of modified aerogels. The surface area was 395.6m2/g, and the average pore diameter was 68.72nm. The contact angle of aerogel particles increased from 20.9° to 99.2° after methyl modification. Reaction characteristics of the material after enzyme loading were also discussed. The results showed that adsorption capacity could reach 67.42mg/g; and the maximal enzyme activity was 19.87μmolmin−1mg−1 (protein), and activity retention could reach 56.44%. It is worth mentioning that the amount of modified aerogels added had significant effects on the diameter of droplets and the mass transfer behavior of substrates in the reaction emulsion. Online microscope was used to visualize the droplets in the emulsion, where the aerogel particles were observed locating at the interface of oil and water. The average diameter of droplets reached the minimum when 0.06g of modified aerogels was added into the reaction emulsion which contained 10ml of oil and 10ml of phosphate buffer solution. The phenomenon was resulted from the wettability of methyl-modified silica aerogels.

Porous nanoarchitectures based on TiO 2 aerogels and Au particles as potential SERS sensor for monitoring of water quality

Encouraged by the environment friendly character of TiO 2 and the well-known affinity of a large variety of molecules to bind to the gold nanostructures surface we obtained novel porous nanoarchitectures based on TiO 2 aerogel and Au colloidal particles and tested their capability to detect contaminant species adsorbed from an aqueous solution on metallic nanoparticles surface. The efficiency of the composites prepared by various methods to detect pollutants from water by surface-enhanced Raman spectroscopy (SERS) was established by using thioacetamide, crystal violet and rhodamine 6G as test molecules and comparatively discussed. The lowest detectable concentrations were found to depend on the sample preparation method and the pollutant species type and were determined to be of around 10 −2 M for thioacetamide and in the range between 10 −5 and 10 −7 M for dye molecules off and under resonant excitation, respectively. The obtained results show the real potential of the prepared porous composites for further use in the development of new SERS-based sensors for monitoring of water quality.

Recovering the elemental composition of comet Wild 2 dust in five Stardust impact tracks and terminal particles in aerogel

Abstract— The elemental (non‐volatile) composition of five Stardust impact tracks and terminal particles left from capture of comet 81P/Wild 2 dust were mapped in a synchrotron X‐ray scanning microprobe with full fluorescence spectra at each pixel. Because aerogel includes background levels of several elements of interest, we employ a novel “dual threshold” approach to discriminate against background contaminants: an upper threshold, above which a spectrum contains cometary material plus aerogel and a lower threshold below which it contains only aerogel. The difference between normalized cometary‐plus‐background and background‐only spectra is attributable to cometary material. The few spectra in‐between are discarded since misallocation is detrimental: cometary material incorrectly placed in the background spectrum is later subtracted from the cometary spectrum, doubling the loss of reportable cometary material. This approach improves accuracy of composition quantification. We present the refined whole impact track and terminal particle elemental abundances for the five impact tracks. One track shows mass increases in Cr and Mn (1.4×), Cu, As and K (2×), Zn (4×), and total mass (13%) by dual thresholds compared to a single threshold. Major elements Fe and Ni are not significantly affected. The additional Cr arises from cometary material containing little Fe. We exclude Au intermixed with cometary material because it is found to be a localized surface contaminant carried by comet dust into an impact track. The dual threshold technique can be used in other situations where elements of interest in a small sample embedded in a matrix are also present in the matrix itself.

Bulbous tracks arising from hypervelocity capture in aerogel

Abstract— The capture of 81P/Wild 2 cometary particles in aerogel with a well‐defined impact velocity (6.1 km s−1) has provided a wealth of data concerning the composition of Jupiter‐family comets. To interpret this data we must understand the capture processes in the aerogel. A major category of tracks are those with bulbous cavities lined with particle fragments. We present a new model to account for the production of these “turnip”‐shaped impact cavities. The model uses a thermodynamic approach in order to account for the likely expansion of vapors from particles rich in volatile species. Volume measurements of some of the largest Stardust tracks analysed so far, together with theoretical considerations, indicate that for the majority of Stardust cometary aggregate particle impacts, fragmentation of relatively weak impactors (combined with radial expansion of the resulting subgrains) is the leading cause of bulbous track production, while volatile release of vapors played a secondary role.

Surface nature of nanoparticle zinc-titanium oxide aerogel catalysts

Nanoparticle zinc-titanium oxide materials were prepared by the aerogel approach. Their structure, surface state and reactivity were investigated. Zinc titanate powders formed at higher zinc loadings possessed a higher surface area and smaller particle size. X-ray photoelectron spectroscopy (XPS) revealed a stronger electronic interaction between Zn and Ti atoms in the mixed oxide structure and showed the formation of oxygen vacancy due to zinc doping into titania or zinc titanate matrices. The 8–45 nm aerogel particles were evaluated as catalysts for methanol oxidation in an ambient flow reactor. Carbon dioxide was favorably produced on the oxides with anion defects. Titanium based oxides exhibited a high selectivity to dimethyl ether, so that a strong Lewis acidic character suggested for the catalysts was associated primarily with the Ti 4+ center. Both methanol conversion and dimethyl ether formation rates increased with increasing the zinc content added to the oxide support. Results demonstrate that cubic zinc titanate phases produce new Lewis acid sites having also a higher reactivity and that the nature of the catalytic surface transforms from Lewis acidic to basic characters due to the presence of reactive oxygen vacancies.

Diffusion‐Controlled Oxygen Reduction on Multi‐Copper Oxidase‐Adsorbed Carbon Aerogel Electrodes without Mediator

AbstractBioelectrocatalytic reduction of O2 into water was archived at diffusion‐controlled rate by using enzymes (laccase from Trametes sp. and bilirubin oxidase from Myrothecium verrucaria, which belong to the family of multi‐copper oxidase) adsorbed on mesoporous carbon aerogel particle without a mediator. The current density was predominantly controlled by the diffusion of dissolved O2 in rotating‐disk electrode experiments, and reached a value as large as 10 mA cm–2 at 1 atm O2, 25 °C, and 8,000 rpm on the laccase‐adsorbed electrode. The overpotential of the bioelectrocatalytic reduction of O2 was 0.4–0.55 V smaller than that observed on a Pt disk electrode. Without any optimization, the laccase‐adsorbed biocathode showed stable current intensity of the O2 reduction in an air‐saturated buffer at least for 10 days under continuous flow system.

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.

Optical, electrical and magnetic properties of transparent, n‐type conductive Zn0.90−xV0.10Alx O thin films elaborated from aerogel nanoparticles

AbstractVanadium–aluminium co‐doped ZnO thin films have been grown by rf‐magnetron sputtering of Zn0.90−x V0.10Alx O (x = 0.01 to 0.03) aerogel nanoparticles. Even though the films were deposited at room temperature they were of good crystal quality and showed c‐axis texturing normal to the film surface. The films are highly transparent in the visible with a transmittance higher than 90%. The highest conductivity of 5.103 Ω−1 cm−1 is obtained for 1% Al doping. The incorporation of V, a notoriously difficult dopant in ZnO, is confirmed by the observation of different absorption bands near 800 nm which we attribute to intracenter transitions of Zn substituted V2+. The magnetic properties of the aerogel particles have been studied by electron paramagnetic resonance (EPR) spectroscopy. No evidence for a ferromagnetic phase is found contrary to theoretical predictions. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Sorption of lead, mercury and cadmium ions in multi-component system using carbon aerogel as adsorbent

In the present study, adsorption of three metal ions Pb(II), Hg(II) and Cd(II) on carbon aerogel a new form of activated carbon has been investigated in mono- and multi-component (binary and tertiary) system. Batch experiments were also carried out for mono- and multi-component systems with varying metal ion concentration (mg/l) to investigate the competitive adsorption characteristics. Many adsorbents have been studied for their adsorption properties pertaining to mono-component solutions of metal ions. However, to treat wastewater with new materials, their performance needs to be ascertained in multi-component system. The scanning electron micrographs (SEM) and EDAX spectrum of carbon aerogel surfaces before and after the adsorbent was equilibrated with the metal ion solution clearly establishes the presence of the metal ions and some surface modifications can be observed on the carbon aerogel particles adsorption with (i) surface chemistry of the pellets on the surface of carbon aerogel and (ii) inside layers of the carbon aerogel. Applicability of the isotherm models namely Freundlich and Langmuir to predict the equilibrium uptake of Pb(II), Hg(II) and Cd(II) in mono-component, binary and tertiary system has also been tested. Langmuir and Freundlich models are found to generally represent the experimental though but not consistently.

Thermodynamics and kinetics of adsorption of bis(2,2,6,6-tetramethyl-3,5-heptanedionato) (1,5-cyclooctadiene) ruthenium (II) on carbon aerogel from supercritical CO 2 solution

The thermodynamics and kinetics of adsorption of bis(2,2,6,6-tetramethyl-3,5-heptanedionato) (1,5-cyclooctadiene) ruthenium (II) (Ru(cod)(tmhd) 2) on carbon aerogel particles from supercritical carbon dioxide was investigated. The particles had an approximate radius of 1 mm and average pore size of 22 nm. The adsorption isotherms were measured at different temperatures and pressures, thus at different supercritical fluid densities. It was observed that at constant temperature, adsorbed amount ( q) decreased with the increasing scCO 2 density or pressure at a particular concentration in the fluid phase. The adsorption isotherms were best represented by the Modified Langmuir Model. The maximum uptakes were reached at concentrations considerably less than the solubility of Ru(cod)(tmhd) 2 in scCO 2 and were found to correspond to monolayer coverage of all the accessible surface of the carbon aerogels as determined by BET measurements. The kinetics of adsorption could be modeled using a model consisting of coupled ODEs based on diffusion in the pore volume and assuming local equilibrium at the adsorbent—fluid interface within the pores. Various simulations of the model were made in order to investigate the effect of isotherm parameters, particle size and pore size of carbon aerogel particles on the kinetics of adsorption. It was observed that in order to prepare Ru(cod)(tmhd) 2 impregnated carbon aerogel particles larger than 5 mm with a radially uniform metal distribution which are used as catalysts in industrial applications, one has to take into consideration the long diffusion time. The pore size of the carbon aerogel particles is also very important for the adsorption process. As the pore size starts to approach the solute size, the time to reach equilibrium starts to increase significantly.

Processing and compressive properties of aerogel/epoxy composites

Abstract Aerogels are ultra-lightweight materials composed of almost 99.98 vol.% of porosity and present excellent opportunities for developing lightweight composite materials. Special properties such as electrical insulation and controlled dielectric constant can be generated in such composites. Ultra-low density and hydrophobic nature of aerogels make it difficult to mix them in epoxy resins. The present research is aimed at developing fabrication methods for aerogel/epoxy composites. The development of such methods requires encapsulating the aerogel particles in epoxy resin without infiltrating them. Compression tests are conducted on these composites and their deformation and fracture behavior is studied. The composites are found to have compressive failure strain of over 25%. It is observed that the higher density composites showed higher compressive modulus but lower yield strength. The reduction in the yield strength is attributed to the early crack initiation in these specimens.