Silica aerogel composites with embedded fibres: a review on their preparation, properties and applications

Abstract

Silica aerogels are among the lightest solid materials but they are also very fragile. Fibres embedment is the most versatile and effective method to preserve a monolithic shape during drying, even at large scale, thus widening their applications.

Porous Materials for Applications in Energy and Environment

“…Initiating the sol-gel process with the hydrolysis of the alkoxide precursors in alcohol, followed by a condensation in the primary particles and evolving in the middle, that is, adding to form larger secondary particles that come together in a continuous network, by acid or alkaline catalysts, such as HCl or NH 4 OH. Primary particles have sizes of approximately 1 nm, while secondary particles are around 10 nm [38].…”

“…On the other hand, under alkaline conditions, the speed of hydrolysis is slow, and condensation occurs more quickly, causing hydrolyzed species to be easily consummated becoming larger and denser colloidal particles. Therefore, the aerogels obtained are lighter and with a higher pore volume [38]. This process has been paramount in the synthesis of aerogels of SiO 2 and TiO 2 [44,45].…”

“…Once the gelling point has been achieved, there are chemical reactions that still take place inside the gel, since it contains a significant number of unreacted species. That is, the liquid inside the pores contains small particles that can condense as monomers and bind to the three-dimensional network [38]. During aging, Ostwald maturation is also carried out, as small particles found in unreacted sites dissolve and precipitate over larger particles or condense into secondary particles or pore regions [38].…”

“…Aging is an important stage as it influences the microstructure, pore size, specific surface area, porosity, shrinkage volume, and/or aerogel shrinkage; this parameter has been studied by Rao [50]. Therefore, aging is defined as the continuous process of crosslinking, thickening, and strengthening of the three-dimensional network due to additional condensation [38].…”

“…In addition, it is the only 2D material that has a very high specific surface area, theoretically possessing a value of 2630 m 2 /g [34,35]. Another material that has attracted the attention of the scientific community is the aerogel, as it is a very light and porous, approximately 95-99% of its volume is made up of air, while the remnant is solid [36][37][38].…”