Optimized synthesis of ambient pressure dried thermal insulating silica aerogel powder from non-ion exchanged water glass

Abstract

In order to make aerogel available for a wide application range, the synthesis complexity, use of hazardous components and high cost price need to be lowered. In this work, silica aerogel powders were obtained using water glass as a precursor, but without performing ion exchange resulting in a faster and easier synthesis. For this study, 6 and 8 wt% silica sols were prepared and the difference in properties of the resulting aerogels was investigated. A combined solvent exchange, silylation and washing out of sodium ions was carried out using a hexane:trimethylchlorosilane:isopropylalcohol solution. A molar ratio trimethylchlorosilane/pore water of only 0.11 was used. The resulting hydrophobic organogels were then dried at ambient pressure and temperature. The aerogel powder was finally dried in an oven at 150°C to remove the residual moist. No notable shrinkage was observed during and after drying for samples with 8 wt% silica. The obtained aerogel showed low density of around 100-120 kg/m 3 , high porosity of 93-94%, pore volume of 0.6-4.1 cm 3 /g, an average pore size of 32-50 nm, and a thermal conductivity of 23-25 mW m-1 K-1 , all depending on the weight percentage of silica and pH of the sol.

An asymmetric Salamo-based Zn complex supported on Fe3O4 MNPs: a novel heterogeneous nanocatalyst for the silyl protection and deprotection of alcohols under mild conditions

“…Besides, R 3 SiCl, MeSiN ¼ C(Me)OSiMe, Me 3 SiCl, or Me 3 SiOTf in the presence of base are the reagents applied in the traditional and conventional processes. 12,[21][22][23][24][25][26][27][28][29] Moreover, hexamethyldisilazane (HMDS) is a stable, commercially available and inexpensive reagent that can be used for the protection of hydroxy bearing compounds to trimethylsilyl ethers. [30][31][32] Its handling does not require special precautions, and the workup is not timeconsuming because the by-product of the reaction is ammonia, which is easily removed from the reaction medium.…”

Comparative study of a cubic, Kelvin and Weaire-Phelan unit cell for the prediction of the thermal conductivity of low density silica aerogels

“…The investigated beads, as described in [5], possess a certain overlap or relative contact length between their neighbors which is typically between 0.3-0.9 (30-90%). The existing gaseous pores, between these backbones, formed during the sol-gel process, typically, have dimensions of 10 -100 nm [6]. These two geometric characteristics are responsible for the low bulk densities (up to 3 kg.m -3 ) and the high specific surface areas.…”

Sodium silicate-derived aerogels: effect of processing parameters on their applications

“…69 Recently, thermal insulating aerogel powders modied with TMCS and HMDS with a thermal conductivity of 0.022 W m À1 K À1 were reported by Pooter et al in 2018. 70 Technically and economically viable forms of silica aerogels have been successfully commercialized by Aspen Aerogels, Inc. USA for over a decade. They offer high performance aerogel insulation blankets comprised of synthetic amorphous silica (SAS) over a wide range of products such as Pyrogel®, Cryogel® and Spacelo® aerogel blanket insulation.…”