Recrystallization Powerful method

Nonetheless, characterization of catalysts in reactive atmospheres by XRD is a powerful method for obtaining the basic information needed to determine structure-activity correlations. Many phenomena of structural deactivation, either by sintering or recrystallization, are accessible by XRD under reaction conditions. The practice of approximating reacting atmospheres by simple-to-handle proxies (hydrogen for hydrocarbons or dry gases instead of steam-loaded feeds) has to be abandoned. 

The application of supercritical fluids as anti-solvents is an alternative recrystallization technique for processing solids that are insoluble in SCF. This method exploits the ability of gases to dissolve in organic liquids and to lower the solvent power of the liquid for the compounds in solution, thus causing the solids to precipitate. 

Cables via the powder-in-tube (PIT) method The approach is especially suited to processing Bi-2223 into leads and cables for power applications. A silver or silver alloy tube, filled with the partially reacted precursor powders formulated to yield Bi-2223, is drawn down to a wire 1-2mm diameter. The wire is rolled into a tape if that is the required form, usually with a width-to-thickness ratio of approximately 10 1. The composite is then heated to 800-900 °C when the powder partially melts. The recrystallization process is controlled and the pure Bi-2223 phase develops with large grains oriented so that the Cu-O planes lie parallel to the silver surface to optimize Jc. 

Supercritical anti-solvent and related processes (GAS/SAS/ASES/SEDS) In these processes, the SCE is used as an antisolvent that causes precipitation of the substrate(s) dissolved initially in a liquid solvent. This general concept consists of decreasing the solvent power of a polar liquid solvent in which the substrate is dissolved, by saturating it with carbon dioxide in supercritical conditions, causing the substrate precipitation or recrystallization. Depending on the desired solid morphology, various methods of implementation are available ... 

On this basic concept different practical ways of performing the recrystallization process can be used. In the first method, to the solution is simply added the dense carbon dioxide. The volume of the solution increases several-fold in the presence of the antisolvent due to the decrease in density. This causes a concurrent decrease in solvent power the solutitm becomes supersaturated, and the solute precipitates, often as crystalline microparticles. This essentially batch process is normally termed gas antisolvent (GAS) [32]. 

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