Supercritical fluids inorganic particles

Crystallization Solutes may be crystallized from supercritical fluids by temperature and/or pressure changes, and by the PCA process described above. In the rapid expansion from supercritical solution (BESS) process, a SCR containing a dissolved solute is expanded through a nozzle or orifice in less than 1 ms to form small particles or fibers. A variety of inorganic crystals have been formed naturally and synthetically in SCR water. 

By utilizing the rapid expansion of supercritical solutions, small-size particles can be produced from materials which are soluble in supercritical solvents. In this process, a solid is dissolved in a pressurized supercritical fluid and the solution is rapidly expanded to some lower pressure level which causes the solid to precipitate. This concept has been demonstrated for a wide variety of materials including polymers, dyes, pharmaceuticals and inorganic substances. 

F. Inorganic Particles Obtained Using Supercritical Fluids... 

Supercritical fluids have received considerable attention as solvents for the synthesis of ceramic or similar materials. One method applies thermal decomposition of precursors in a supercritical fluid, which is at the end of the reaction depressurized and removed from the system. After removal of the solvent, obtained inorganic material is typically in the form of micron or submicron particles. The second method uses supercritical fluid as a solvent and a reactant. In this case, the typical supercritical fluid is water, and the process is called hydrothermal synthesis. Inorganic solids obtained by the decomposition in the supercritical fluid or by the synthesis using supercritical reactant, are hsted in Tables 24.4 and Table 24.5, respectively. As it can be seen from the presented data different morphologies can be obtained on the micrometer or nanometer scale. 

Supercritical fluids (SCFs) offer the potential for a controlled solution environment because of the tunability of their properties by small changes in temperature and pressure. Indeed, near-critical water and supercritical water are obvious candidates as solvents in nanoparticle formation because water is the most commonly used solvent in conventional synthesis of inorganic particles. However, other solvents, such as carbon dioxide, can also be used. Several methods that take advantage of SCF behavior are described below. Not all have been employed in the production of magnetic nanoparticles. However, they represent a natural bridge between methods that are carried out mainly in the liquid state and those that are carried out in the gaseous state. 

Turk, M. (2010) Supercritical fluids as novel particle formation media 1. Application to the formation of organic and inorganic materials. Paper presented at the Proceedings of the 12th European Meeting on Supercritical Fluids, Graz, Austria. 

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