Supercritical fluids drying

Zhang, J.C., Li, Q. and Cao, W.L. (2005) Preparation of Ti02-MoOj nanocomposite photo-catalyst by supercritical fluid dry method. Journal of Environmental Sciences, 17 (China), 350-352. 

The PCA process uses supercritical fluid drying to help preserve fine microstructures in the material. Supercritical fluid drying is a technique that has been used for many years to dry biological materials and, more recently, aerogels (qv). The original solvent is replaced by exchange with a supercritical fluid, such as C02, and the system is depressurized above the critical temperature of the SCF. SCFs have no vapor—liquid interface. Thus fine microstructures are... 

Tachiwaki, T., Takase, Y., Sugimoto, J., Oda, M., Kawanaka, S. An experimental study of supercritical fluid drying of Y-Ba-Cu oxides powder from aqueous alcohol suspension using carbon dioxide. Part. Sci. Technol. 16,109-124,1998... 

Kazarian SG. Application of FTIR spectroscopy to supercritical fluid drying, extraction and impregnation. Appl Spectrosc Rev 1997 32 301-348. 

Leventis, N, Palczer A, McCorkle L, Zhang G, Sotiriou-Leventis C (2005) Nanoengineered silica-polymer composite aerogels with no need for supercritical fluid drying. J Sol-Gel Sci Tech 35 99-105. 

In analogy to their resorcinol-formaldehyde homologues, polyurethane wet gels are synthesized by polycondensation. Subsequently, aerogels are commonly obtained by supercritical fluid drying of the organic wet gels [23]. 

Recently, much attention has been paid to the preparation of nanometer particle catalysts. Several methods have been developed to prepare nanometer particles. The liquid phase method could be better for the preparation of catalyst with nanometer size [1]. A main problem for this preparation process is how the aggregation of fine particles can be avoided, espedsdly at the dr3dng step. The key is to reduce surface tension. Alcoholate method was developed for it in which alcoholate hydrolysis instead of aqueous solution to make the sol(gel) was used to avoid surface tension, i.e. avoid vapor-liquid interface freeze drying method, in which the solution is first firozen and then sublimated to remove it, and supercritical fluid drying method, in which the solvent is solved in a supercritical fluid to remove it, were also developed. Although these methods have successfully reduced or avoided the effect of surface tension, the preparation cost including raw material, special equipment and time is increased. 

The preparation of ultrafine Sn02 by the supercritical fluid drying technique (SCFDT)... 

Nanometer size SnOg was prepared with a sol-gel process followed by supercritical fluid drying. Their structure, particle size and spedflc surface area were characterized by XRD, TEM and nitrogen adsorption method. The effect of the preparation parameters is also discussed. 

Currently, the supercritical drying process is the best solution to avoid such capillary forces. With the supercritical fluid drying, it is possible to move from the liquid phase via the supercritical fluid directly to the gas phase without touching the two-phase area. With optimized drying parameters, capillary forces can be avoided and nanoporous structures are maintained [55-57]. 

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