Comparison of some physical properties of silica aerogel monoliths synthesized by different precursors (original) (raw)

A COMPREHENSIVE REVIEW ON SILICA AEROGEL

Silica Aerogel is a nano-structured material that is also known as “frozen smoke” or “blue smoke,” which is a lighter, low density, low dielectric constant, highly porous, and super-dried material, and it has many substantial properties and most exceptional property is its high thermal insulation. However, this research focuses on Silica Aerogel (SA) synthesis, characterization, properties, and its comparison with experimental results. Several precursors can be used for producing aerogels and its precursor is responsible for the properties of aerogel. Different silicon alkoxide precursors are either tetramethoxysilane (TMOS) or tetraethoxysilane (TEOS). TEOS is often preferred because it is cheap and less hazardous. The process for aerogel synthesis is known as “The Sol-Gel” method. After making the solution, it is converted into a waxy gel and after the gelation, the gel is transformed to a solid network by a drying process. Several drying procedures are used to transform the gel into a solid network like the widely used supercritical drying (SCD), or ambient pressure drying (APD). Modern research on silica aerogel is still in progress to improve its thermal, mechanical, and optical efficiency by introducing hybrid aerogels. For the determination of various properties of silica aerogel several characterization techniques are used such as for its external and internal structure, pore size, and morphology SEM, TEM, and AFM are used. Other techniques like XRD, Raman spectroscopy, FTIR, NMR, and thermal gravimetric analysis, etc., are also used to measure different properties. This research theoretically includes the predicted properties of silica aerogels and its comparison with experimental results. Mostly all the properties are discussed in chapter IV and the last section is all about the applications of silica aerogels in various fields.

An Overview of Silica Aerogels

2000

In recent years, silica aerogels have attracted more and more attention due to their surprising properties and their existing and potential applications in wide variety technological areas. Silica aerogel is a nanostructured material with high specific surface area, high porosity, low dielectric constant, low density and outstanding heat insulation properties. Release of some active ingredients from the aerogel-drug formulation is

Silica Aerogel: Synthesis and Applications

Journal of Nanomaterials, 2010

Silica aerogels have drawn a lot of interest both in science and technology because of their low bulk density (up to 95% of their volume is air), hydrophobicity, low thermal conductivity, high surface area, and optical transparency. Aerogels are synthesized from molecular precursors by sol-gel processing. Special drying techniques must be applied to replace the pore liquid with air while maintaining the solid network. Supercritical drying is most common; however, recently developed methods allow removal of the liquid at atmospheric pressure after chemical modification of the inner surface of the gels, leaving only a porous silica network filled with air. Therefore, by considering the surprising properties of aerogels, the present review addresses synthesis of silica aerogels by the sol-gel method, as well as drying techniques and applications in current industrial development and scientific research. tion and its development. In the 1930s, Samuel Stephens Kistler first produced silica aerogels by formulating the idea of replacing the liquid phase by a gas with only a slight shrinkage of the gel. He prepared aerogels from many other materials, including alumina, tungsten oxide, ferric oxide, tin oxide, nickel tartarate, cellulose, cellulose nitrate, gelatin, agar, egg albumen, and rubber, which are out of scope of the discussion. Kistler's method involves tedious and timeconsuming procedures, and as such there was no follow-up interest in the field of aerogels until 1968 when rediscovery of aerogels took place by a team of researchers headed by Professor S. J. Teichner at the University Claude, Bernard, Lyon, France. They substantially simplified the procedure by carrying out the sol-gel transition in a solvent, which was then removed at supercritical conditions. The first Cerenkov radiation detector based on silica aerogels was developed in 1974 by Cantin et al. Since then, aerogels have been used or considered for use in laser experiments, sensors, thermal insulation, waste management, for molten metals, for optics and light guides, electronic devices, capacitors, imaging devices, catalysts, pesticides, and cosmic dust collection. More recently, several groups around the 2 Journal of Nanomaterials world began working in the field of silica aerogels for the various applications mentioned above. Strictly speaking, to understand silica aerogels, it is necessary to first understand sol-gel chemistry and related physicochemical aspects. In the following, we shall discuss sol-gel chemistry, synthetic strategy of silica aerogels, and some recent developments in applications of aerogels.