High-pressure crystallization, advantages

Advantages of high pressure crystallization are simple control of process parameters, and a solvent-free system. 

Pure barium is a silvery-white metal, although contamination with nitrogen produces a yellowish color. The metal is relatively soft and ductile and may be worked readily. It is fairly volatile (though less so than magnesium), and this property is used to advantage in commercial production. Barium has a bcc crystal stmcture at atmospheric pressure, but undergoes soHd-state phase transformations at high pressures (2,3). Because of such transformations, barium exhibits pressure-induced superconductivity at sufftciendy low temperatures (4,5). 

Recently, the steady-state reaction kinetics of CO oxidation at high pressure over Ru , Rh " , Pt, Pd, and Ir single crystals have been studied in our laboratory. These studies have convincingly demonstrated the applicability and advantages of model single crystal studies, which combine UHV surface analysis techniques with high pressure kinetic measurements, in the elucidation of reaction mechanisms over supported catalysts. 

The advantages of using polychromatic radiation from a reactor source, coupled with Laue diffraction methods, have been investigated by McIntyre et al. for high-pressure studies [194]. Using a 0.5-mm crystal in a moissanite anvil pressure cell... 

Quartz Crystal Microbalance (QCM) in high pressure cell (Burgass et al., 2002 Mohammadi et al., 2003) Yes P, T (with P transducer, thermocouple in cell) Yes P, T vs. time Typically 6000 psi / diss. /diss Advantages mg samples so equilibration times (hence experimental time) reduced... 

Especially they took advantage of the endo-selectivity of the Diels-Alder reaction and the acceleration of rates by high pressures. The yield of the cyclic product 6, a solid with a mp > 300 C, increased to 20%. Good crystals for X-ray crystallography emerged from slow evaporation of a chloroform solution of 6. The X-ray crystal structure discloses the elegance of the molecular structure and reveals the clathrate-like inclusion of chloroform molecules between layers of 6. 

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