Supercritical drying technique

Aerogels are solid materials that consist of a highly porous network of micro-sized and meso-sized pores. The pores of an aerogel can frequently account for over 90% of the volume when the density of the aerogel is about 0.05 gcm. In general, aerogels are prepared by a supercritical drying technique, i.e., a sol-gel process, to remove the solvent from a gel. The process is conducted in a way that no solvent evaporation can occur. Thus no contraction occurs. 

More recently. Ye et al. proposed a new sol—gel method combined with a supercritical drying technique for the synthesis of nanocomposite electrocatalysts for ORR. They claimed that their method had a structure-preserving ability and favored a nanoscale mixing of the constituents, and then could produce a remarkably homogeneous solution. The chemical, physical, and morphological properties of catalysts produced using this sol—gel... 

Hu Y, Mackenzie J D (1992) Rubber-Uke elasticity of organically modified silicates. J Mater Sci 27 4415-4420 Novak B M, Auerbach D, Verrier C (1994) Low-density, mutually interpenetrating organic-inorganic composite materials via supercritically drying techniques. Chem Mater 6 282-286... 

Several companies tried to commercialize aerogel from 1950 to 1990, but ultimately failed due to the high manufacturing costs, limited batch production, and the dangers of using the supercritical drying technique with flammable solvents. 

There is disagreement within the aerogel community about the definitions of aerogel materials. Some definitions include porosity restrictions such as mesoporosity requirements (2-20 nm), others require supercritical drying techniques, and some include density restrictions. Even measuring these properties can lead to uncertainties and controversy. 

Ambient Preparations. Economic and safely considerations have provided a strong motivation for the development of techniques that can produce aerogel-like materials at ambient conditions, i.e., without supercritical drying. The strategy is to minimize the deleterious effect of capillary pressure which is given by ... 

Three different MgO samples were used in the experiments. AP-MgO with a surface area of 385 m2/g was prepared by a sol-gel technique involving high-temperature supercritical drying described in detail earlier.4,13 CP-MgO (281 m2/g) was obtained by decomposition of Mg(OH)2 prepared by hydration of commercial MgO. In both cases the final preparation step was overnight evacuation at 500°C followed by storage under ambient conditions. Their performance was compared to that of a commercial low surface area sample CM-MgO (10 m2/g). 

Drying techniques have been explored for pharmaceutical biopolymer formulations drying with the aid of a supercritical fluid is especially attractive for reasons of mild process conditions, cost-effectiveness, possible sterilizing properties of supercritical carbon dioxide, capability of producing microparticulate protein powders, and feasibility of scaling up. 

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