aerogel (rus. аэрогель) — class of highly porous amorphous materials with bulk macrostructure where characteristic size of nanoelements is 4-10 nm; it is derived from agelin which theliquid component has been replaced with agas.

Description

There are well-known aerogels based on amorphous oxides: silicon dioxide SiO2, aluminium oxide Al2O3, oxides of Cr, Sn, W, Fe, Li, Na, Ca, Mg, Ba, Sb, Te, Ni, Ge, Zn, Mn and other elements. In addition, carbon nanotube aerogels have been created.

The SiO2-based aerogel is a branched three-dimensional cluster resembling a tree-like network of nanoparticles sized about 4 nm. The space between the clusters is filled with air. Since the characteristic size of such voids (~ 100 nm) is dozens of times higher than the cluster size, the material is very light. SiO2-based aerogels are usually formed by reacting tetraethylorthosilicate Si(OCH2CH3)4 with water, which is then removed from the resulting gel with ethanol.

Then, the gel is heated in an autoclave to supercritical temperatures and pressures and the evaporated ethanol is removed. Al2O3-based aerogels (spectrally pure hydrated amorphous aluminium oxyhydroxide AlOOH (Al2O3·H2O)) are obtained through the selective oxidation of gallium-aluminium or lead-aluminium melts. The same method is applied to obtain amorphous highly dispersed oxides of other metals.

Carbon aerogels are composed of nanoparticles that are covalently bonded together. They are electrically conductive and their large internal surface area (up to 800 m2 · g-1) enables their use in the manufacture of supercapacitors.

Unique properties of aerogels are their low density (0.002 to 0.25 g · cm-3), high specific surface area, low susceptibility to ageing and high sorption properties (they effectively absorb NO , NO2, CO, CO2, and unsaturated hydrocarbons). Aerogels of different compositions are used as heat and electrical insulation materials, nanodispersed additives to hybrid organo-inorganic composite materials, catalyst carriers and sorbents, and nano-filters.

Author

  • Gusev Alexander I.

Sources

  1. Gusev A. I. Nanomaterials, Nanostructures, and Nanotechnologies (in Russian) // Fizmatlit, Moscow (2007) - 416 pp.
  2. Gusev A. I., Rempel A. A. Nanocrystalline Materials. — Cambridge: Cambridge International Science Publishing, 2004. — 351 p.

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