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1 2004

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Aerożele organiczne i węglowe

Brodzik K., Stolarski M., Walendziewski J.

Wiadomości Chemiczne

2004

[Z] 58, 7-8

637--660

Aerogels are solid, organic (carbon) and inorganic porous materials of the exceptional properties such as very large specific surface area, low bulk density, low thermal and electric conductivity and superporous structure, obtained by sol-gel process. Numerous potential applications of aerogels as catalysts and catalyst supports, adsorbents, sensors, insulators, Cherenkov detectors and many others attract attention of many research laboratories. This review demonstrates selected routes to obtain organic and carbon aerogels. A special attention is given to the materials obtained by polycondensation of resorcinol with formaldehyde (RF aerogels). Some basis of the sol-gel processes as well as the influence of solvent on gelation time and shrinkage of the RF aerogels is presented. In the next part of the review the effect of the base preparation parameters i.e., resorcinol to formaldehyde (R/F) molar ratio and resorcinol concentration in solvent on textural properties on the final aerogel is discussed. Sol section of this paper is finished with information on the effect of catalyst concentration on particle size and shrinkage. Gel section contains informations about gelation time and aerogel properties dependence on it. Further sections are focused on drying step of the obtained gel, often found as the most important for the sake of final product characteristics. The reason why the drying step is so important is that solvent must be removed without destroying the gel matrix. Solvent removal methods are described with some principles of supercritical (low- and high-temperature) and freeze drying. Product obtained after supercritical or freeze drying step is called aerogel or cryogel respectively. Finally the effect of carbonization parameters on the carbon aerogels properties is described. Effect of other organic aerogel precursors such as cresol, phenol, furfural, melamine, PVC, MDI used in the sol-gel process of the preparation procedure of organic and carbon aerogels is described. Finally, selected technical applications of the carbon aerogels are presented.