Ultralow Density Silica Aerogels Research Articles

Effect of silica aerogel – Aluminium trihydroxide hybrid filler on the physio-mechanical and thermal decomposition behaviour of unsaturated polyester resin composite

Aluminum trihydroxide (ATH) is an eco-friendly and economical additive used in polymers as a flame retardant (FR), but its low thermal stability has become an important issue that is critical in determining the fire protection and thermal stability of the composites. The present study was an attempt to enhance the thermal stability of ATH to some extent by combining it with nano-porous silica known as silica aerogel (SA) as a hybrid FR filler in unsaturated polyester resin (UPR). Ultra-low density SA (0.07 g/cm3) in the form of fine particles was extracted from renewable resources (i.e. rice husk), through a sol-gel process, surface modification and dried at atmospheric pressure. From our findings, it is found that the addition of the hybrid filler into UPR results in interesting properties such as lightweight, flame retardancy and enhanced thermal stability whose properties cannot be gained by composites with single filler. From thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and gas analysis using Fourier transform infrared spectroscopy (FTIR); it is evident that doping the ATH with SA helps to improve the thermal stability via synergistic effect, by extending the ATH decomposition process over a wider temperature range. As a result, the UPR filled with SA/ATH hybrid demonstrates higher thermal stability when compared to the composites filled with only ATH or SA. Furthermore, the SA/ATH hybrid also provides sufficient flame retardancy in UPR as evaluate by ASTM D635-14 (UL–94) horizontal burning test. For mechanical properties, a sharp increase in tensile strength was observed for UPR filled with ATH or SA while the addition of SA/ATH hybrid filler only slightly increases the tensile properties of UPR due to particle agglomerations and porosities.

STXM-XANES analyses of Murchison meteorite samples captured by aerogel after hypervelocity impacts: A potential implication of organic matter degradation for micrometeoroid collection experiments

Author(s): Kebukawa, Y; Okudaira, K; Yabuta, H; Hasegawa, S; Tabata, M; Furukawa, Y; Ito, M; Nakato, A; David Kilcoyne, AL; Kobayashi, K; Yokobori, SI; Imai, E; Kawaguchi, Y; Yano, H; Yamagishi, A | Abstract: The Tanpopo mission is an astrobiology space experiment at the Japanese Experiment Module (JEM) 'Kibo' on the International Space Station (ISS). One of the sub-divided themes of the Tanpopo mission is for the intact capture of organic bearing micrometeoroids in low Earth orbit using ultralow density silica aerogel (0.01 g/cm 3 ). In order to evaluate damage to organic matter in micrometeoroids during hyper velocity impacts into the aerogel, Murchison meteorite powdered samples, analogs of organic bearing micrometeoroids, were fired into flight-grade silica aerogel (0.01 g/cm 3 ) using a two-stage light-gas gun with velocities of 4.4 and 5.9 km/s. The recovered Murchison grains were analyzed using scanning transmission X-ray microscopy/X-ray absorption near edge structure (STXM/XANES), transmission electron microscopy (TEM) and nanoscale secondary ion mass spectrometry (NanoSIMS). TEM observation did not show significant modifications of the recovered Murchison grains. Carbon-XANES spectra, however, showed a large depletion of the organic matter after the 5.9 km/s impact, but no such effects nor any significant hydrogen isotopic fractionation were observed after the 4.4 km/s impact.

Synthesis and Characterization of Silica Aerogel Materials Doped with TiO<sub>2</sub> Powder for Thermal Insulation

Super insulation and hydrophobic silica-based aerogels doped with TiO2 powder (8wt %) were successfully synthesized by using cost effective processing from Tetraeth oxysilane (TEOS). After aging and washing of wet gel, surface modification were modified using trimethylchlorosilane (TMCS) via one-step solvent exchange and surface modification. And the proper molar ratio of TMCS to pore water is 0.02. The microstructure and morphology of the ultralow density silica aerogels were characterized by the specific surface area, SBET, SEM, and the pore size distribution techniques. From the results, the obtained aerogel doped with TiO2 powder exhibited excellent physical properties with less than 10% volume shrinkage, extremely high specific surface area (652 m2/g) and super hydrophobicity (contact angle of~145°). It should be noted that TiO2 powders are physically embedded by SiO2 aerogel, and there is an obvious Ti–O–Ti and Si–O–Si bonding group based on structural analysis. The thermal properties of silica aerogel were determined using the Hot Disk device, composite aerogel exhibited thermal conductivities of 0.0426 W/m·K at 700°C, TiO2 powders effectively suppressed the intensified thermal radiations at high temperatures to achieve ultralow thermal conductivities. These results have important implications for designing novel structure of porous materials of high performance for silica aerogels.

Fluorescence imaging of microbe-containing particles shot from a two-stage Light-gas gun into an aerogel.

We have proposed an experiment (the Tanpopo mission) to capture microbes on the Japan Experimental Module of the International Space Station. An ultra low-density silica aerogel will be exposed to space for more than 1year. After retrieving the aerogel, particle tracks and particles found in it will be visualized by fluorescence microscopy after staining it with a DNA-specific fluorescence dye. In preparation for this study, we simulated particle trapping in an aerogel so that methods could be developed to visualize the particles and their tracks. During the Tanpopo mission, particles that have an orbital velocity of ~8km/s are expected to collide with the aerogel. To simulate these collisions, we shot Deinococcus radiodurans-containing Lucentite particles into the aerogel from a two-stage light-gas gun (acceleration 4.2km/s). The shapes of the captured particles, and their tracks and entrance holes were recorded with a microscope/camera system for further analysis. The size distribution of the captured particles was smaller than the original distribution, suggesting that the particles had fragmented. We were able to distinguish between microbial DNA and inorganic compounds after staining the aerogel with the DNA-specific fluorescence dye SYBR green I as the fluorescence of the stained DNA and the autofluorescence of the inorganic particles decay at different rates. The developed methods are suitable to determine if microbes exist at the International Space Station altitude.

Preparation and Characterization of Ultralow Density Silica Aerogels by Acetonitrile Supercritical Drying

This paper deals with the synthesis of ultralow density silica aerogels using tetramethyl orthosilicate (TMOS) as the precursor via sol-gel process followed by supercritical drying using acetonitrile solvent extraction. Ultralow density silica aerogels with 6 mg/cc of density was made for the molar ratio by this method. The microstructure and morphology of the ultralow density silica aerogels was characterized by the specific surface area, SBET, SEM, and the pore size distribution techniques. The results show that the ultralow density silica aerogel has the high specific surface area of 812m2/g. Thermal conductivities at desired temperatures were analyzed by the transient plane heat source method. Thermal conductivity coefficients of silica aerogel monoliths changed from 0.024 to 0.043W/ (m K) as temperature increased to 400°C, revealed an excellent heat insulation effect during thermal process.

Studies of mobile dust in scrape-off layer plasmas using silica aerogel collectors

Dust capture with ultralow density silica aerogel collectors is a new method, which allows time resolved in situ capture of dust particles in the scrape-off layers of fusion devices, without substantially damaging the particles. Particle composition and morphology, particle flux densities and particle velocity distributions can be determined through appropriate analysis of the aerogel surfaces after exposure. The method has been applied in comparative studies of intrinsic dust in the TEXTOR tokamak and in the Extrap T2R reversed field pinch. The analysis methods have been mainly optical microscopy and SEM. The method is shown to be applicable in both devices and the results are tentatively compared between the two plasma devices, which are very different in terms of edge plasma conditions, time scale, geometry and wall materials.

Ultralow density, hollow silica foams produced through interfacial reaction and their exceptional properties for environmental and energy applications

We report a novel, facile, and reproducible method for large-scale production of highly porous, hollow silica foams (hollow spheres) with a robust ultrathin shell of several nanometres through a simple, one-step, bubble-controlled, interfacial hydrolysis reaction. This material has exceptional properties, including ultralow density (0.028 g cm−3, approaching 99% porosity), good thermal stability up to 1000 °C, an exceptionally high capacity for oil uptake from mixed solvents (up to 25.6 cm3 g−1), and a very low thermal conductivity comparable to ultralow density silica aerogels.

Ultralow density silica aerogels prepared with PEDS

This paper deals with the synthesis of ultralow density silica aerogels using polyethoxydisiloxanes (PEDS) as the precursor via sol–gel process followed by supercritical drying using ethanol solvent extraction. Ultralow density silica aerogels with 5 mg/cc of density were made for the molar ratio by this method. A remarkable reduction in the gelation time was observed by the effect of the catalyst NH4OH at room temperature. The microstructure and morphology of the ultralow density silica aerogels were characterized by the specific surface area, SBET, SEM, TEM and the pore size distribution techniques. The results show that the diameter of the silica particles is about 13 nm and the pore size of the silica aerogels is about several nm. The specific surface area of the silica aerogel is 339 m2/g and the specific surface area, pore volume and average pore diameter decrease with increasing density of the silica aerogel.

Ultralow density silica aerogels by alcohol supercritical drying

Synthesis of ultralow density aerogels requires full transformation of diluted monomers into solid. Shrinkage during ageing and supercritical drying must be controlled as low as possible. Reported investigations deal with achievement in the optimisation of the two-step process parameters performed using classical acid and basic steps. Acid step involves the formation of partially hydrolysed and partially condensed silica mixture in ethanol. Different compositions of tetraethoxysilane, ethanol and hydrochloric acid (TEOS:ETOH:HCl) have been prepared to provide suitable gelling time and to enhance mechanical properties of final gels. Supercritical drying was performed using modified solutions mixtures which prevent silica dissolution. Under these conditions gel texture is preserved as demonstrated by the low shrinkage. This route permits positioning of uncracked transparent aerogels with densities lower than 3 kg/m 3. Specific surface area values are in the range of usual aerogels. Therefore, because of their unusual large pores, specific surface area decreases with density.