Papers by Keyword: Silica Aerogel

Abstract: The field of nanotechnology has seen rapid advancements over the last decade. Nanofiber production through the method of electrospinning is one of the attraction points in this area. The nanofibers, prepared with nano-sized additives, particularly with polymer, have an extensive range of usages. This study utilizes silica aerogels obtained by the sol-gel method due to their low density of 700-800 gr/m². Polycaprolactone (PCL)-Silica Aerogel Nanofibers were attained by adding 0.5%,1%, 2%and 4% of previously produced aerogels to the nanofibers formed by electrospinning. This paper correspondingly examined the differences between AC-CL and MET-CL solvent groups being utilized during the preparation of the solutions. In addition to this examination, series of material tests were conducted, such as tensile test, SEM, FTIR, DTA/TG, and BET. Overall, the resultant nanofibers with a property of high surface area can be utilized in the design of materials applied to many areas, including solar devices, solar pools, sensors, and capacitors.

Abstract: The article presents an investigation about effects of the synthesis conditions on the performance of silica aerogels. Tetraethyl orthosilicates (TEOS) were selected as the silicon source, and two acid-base catalysts were adopted to catalyze the reaction. CO₂ supercritical drying was used to drive out the solvent of alcohols in the wet gels. Semi-transparent monolithic and crack-free SiO₂ aerogels were successfully obtained. The solvents were prepared with a ratio of ethyl orthosilicate: absolute ethanol: H₂O:HCl:NH₃·H₂O=1:3:5:3×10^-3:4.8×10^-3.The single effects of solution pH, water volume, and aging temperature synthesized were investigated. The aerogels were characterized with SEM, specific surface area analysis, thermal constant analysis, thermogravimetric analysis, Raman spectroscopy analysis, N₂ adsorption-desorption analysis, and hydrophobic angle test. The as-synthesized silica aerogels have a porosity of 95.6%, a specific surface area of 756.9m²/g, an average pore diameter of 16.22nm, a density of 96.8kg/m², and a thermal conductivity of 0.02W/(m· K). Hydrophobic silica aerogels were also obtained.

Abstract: As its much lower thermal conductivity than other usual materials, Silica aerogel is a potentially efficient heat insulation material with the lowest bulk density. However, it is transparent for infrared light when used in high temperature. Herein, titanium oxide was added in the silica aerogel by in-situ blending. The dispersion property of titanium oxide particles, microstructure mechanical property, thermal conductivity, and thermal insulation were investigated. The results of this in-situ blending process indicated a potential application value in aerospace thermal protection industry.

Abstract: Silica aerogel is a nanostructured porous solid material. It has a low bulk density, low thermal conductivity and can be hydrophobic. In this work, hydrophobic silica gel, a material used to form aerogel, is used instead of its powder form to avoid ultrafine air particles pollution. It is used to surface modified materials to make the materials superhydrophobic and still withstand physical abrasion that ordinary aerogel would not able to do. The superhydrophobic silica aerogel coating was designed by mixing the hydrophobic gel with DOW CORNING^® 2405 resin as binder and varying DOWSIL^™ Z-6137 silane and tetraethyl orthosilicate (TEOS). The coating is characterized by the static contact angles (CA) and abrasion test. Scanning electron micrographs of different coating compositions were investigated. Results show that the hydrophobic gel mixed with resin and Z-6137 silane have contact angle >179º. Superhydrophobic silica aerogel coating can be utilized as material coatings for glass, fiber, polymer, etc.

Abstract: Synthesis of polyurethane foams (PUF) with silica aerogel nanoparticles is an efficient alternative to improve the mechanical and thermal properties of the foam owing to the outstanding thermal insulation properties of porous silica aerogel nanoparticles. Silica aerogel was added into polyurethane foams at different weight percent (0, 1, 3, 5 wt.%) to observe the changes in the material properties. To confirm the applicability of the synthesized PUF to the heat insulating material, compressive tests were carried out at ambient and cryogenic temperature (20, -163°C) and the thermal conductivities were measured according to wt.%. In addition, the cell microstructure was identified using FE-SEM to analyze the effect of silica aerogels on the foam morphologies. As a result of the experiment, it was confirmed that the mechanical strength and the heat insulation performance were improved in the polyurethane foam containing 1 wt.% of silica aerogel.

Abstract: Thermal degradation of the composite blend consisting unsaturated polyester resin, alumina trihydrate and silica aerogel was studied using thermal gravimetric analysis. Composite filled with silica aerogel show lower density and slightly improve the thermal stability of the pure polymer. The addition of alumina trihydrate slows down the degradation of the polymer due to the release of bond water while the combination of silica aerogel and alumina trihydrate in polyester matrix does not interrupt the function of alumina trihydrate due to inert properties of silica aerogel.

Abstract: In this experiment, silica sol was used as raw material, the mixture of ammonium chloride and ammonia was used as coagulant. After replacing the solvent with n-hexane, silica aerogel was obtained under the condition of normal pressure. The influence of sol pH and coagulating temperature on the gel time was studied. According to the SEM photographs, the influence of drying temperature from 30 °C to 60 °C on the microstructure of silica aerogel was analyzed. This study showed that when sol pH was 6.5, coagulating temperature was 80 °C and the concentration of ammonia was 0.4 mol/L, the gel time was the shortest. The average size of silica aerogel particles was 10-20 nm, the average size of apertures was 20-50 nm. When the drying temperature was 40 °C, the specific surface area was 402.41 m²/g, the pore volume was 2.33 cm³/g, the density was 0.18 g/cm³.

Abstract: 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, S_BET, 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.

Abstract: In this paper, a case study on replacing the existing insulating material (Mineral wool) by the Silica Aerogel in the main steam line (MSL) of the thermal power plant is presented.A sample length of 3 m in MSL was insulated with various thicknesses of silica aerogel, mineral wool and the combinations of mineral wool and silica aerogel. The heat loss in the sample length with different insulating material was calculated by carrying out field experiments. The results show that the silica aerogel is providing better insulation than the mineral wool. Nonetheless, the use of silica aerogel is expensive. To bring down the cost, hybrid insulation with the optimal thickness of silica aerogel + mineral wool + silica aerogel was suggested. This hybrid combination considerably reduced the heat loss and improved the thermal efficiency. The payback period for this implementation was reported.

Abstract: This review gives an idea of thermal conductivity and its dependent on several factor.