History of Aerogels

Abstract

This chapter presents a historical account of the progressive development of the solid materials known as aerogels. The founding work of Kistler is first summarized. His precursory work attracted the attention of scientists who focused on the physics and chemistry of aerogels, reviewed in the second section. The latter studies allowed for the understanding of how a very high open porosity solid could be maintained when drying a gel and how some specific properties such as transparency or a hydrophobic character could be granted to these materials. In turn, a better knowledge of the scientific basis behind aerogels led to determining their technical characteristics and developing their applications, as addressed in the third section. The most recent developments summarized in the last section aim at a progressive transfer of these applications toward the industry. The Founding Studies by KistlerThe term aerogel was first introduced by Kistler in 1932 to designate gels in which the liquid was replaced with a gas, without collapsing the gel solid network [1]. While wet gels were previously dried by evaporation, Kistler applied a new supercritical drying technique, according to which the liquid that impregnated the gels was evacuated after being transformed to a supercritical fluid. In practice, supercritical drying consisted in heating a gel in an autoclave, until the pressure and temperature exceeded the critical temperature T c and pressure P c of the liquid entrapped in the gel pores.This procedure prevented the formation of liquid-vapor meniscuses at the exit of the gel pores, responsible for a mechanical tension in the liquid and a pressure on the pore walls, which induced gel shrinkage. Besides, a supercritical fluid can be evacuated as gas, which in the end lets the "dry solid skeleton" of the initial wet material. The dry samples that were obtained had a very open porous texture, similar to the one they had in their wet stage.Overall, aerogels designate dry gels with a very high relative or specific pore volume, although the value of these characteristics depends on the nature of the solid and no official convention really exists (Chap. 21). Typically, the relative pore volume is of the order of 90% in the most frequently studied silica aerogels [2]

Review of the Selected Carbon-Based Materials for Symmetric Supercapacitor Application

“…For instance, the gelation process of resorcinol and formaldehyde can be performed under alkaline or acid conditions. 58 Generally, the global market of supercapacitors was estimated to USD$115M in 1999, and it was predicted in those days that it may be doubled in 2004. 59 Estimations in 2010 indicated that the market would amount to USD$470M, USD$1.2B in 2015, and would eventually reach USD$5B in 2025.…”

Alümina aerojellerin fiziksel özellikleri üzerine yaşlandırma ve kurutma süresinin etkisi

“…Başka bir deyişle, süper kritik kurutma yöntemi, jel gözeneklerinin çıkışında sıvı-buhar ara yüzünün oluşmasını engeller. Sıvı-buhar ara yüzünün oluşması gözeneklerin çökmesine sebep olan 100-200 MPa kılcal basınçlara neden olur [10].…”

Thermal Insulation Properties of Electrospun Nanofibrous Layers

“…Literature searches on the subject of submicron fibers in thermal insulation reveal very limited fundamental or applied work using polymer nanofibers for thermal insulation applications. Silica aerogel is a highly porous material with pore diameters in the range of 2-50 nm [5,6]. The nanoporous structure of the silica aerogel having a high porosity above 90% makes the aerogel a highly thermal insulating materials with a super-low thermal conductivity as low as 0.013 W·m .…”