High-pressure cell Subject

The high-pressure cells and temperature control units are similar to the ones described by Betts and Bright (29). Samples for analysis were prepared by directly pipetting the appropriate amount of stock solution into the cell. To remove residual alcohol solvent, the optical cell was placed in a heated oven (60 °C) for several hrs. The cell was then removed from the oven, connected to the high-pressure pumping system (29), and a vacuum (50 pm Hg) maintained on the entire system for 10-15 minutes. The system was then charged with CF3H and pressurized to the desired value with the pump (Isco, model SFC-500). Typically, we performed experiments at 10 /xM PRODAN and there was no evidence for primary or secondary interfilter effects. HPLC analysis of PRODAN subjected to supercritical solvents showed no evidence of decomposition or additional components. 

There was no effect on the turnover number (Table 2) when the Fe(lll) sample was argon ion bombarded on both sides for varying lengths of time before some of the catalytic runs. In order to test for the possibility that the stainless-steel high-pressure cell was catalyzit the reaction, the Fe(111) crystal was replaced by a platinum sample of similar dimensions in order to reproduce, as closely as possible, the heat transfer between the crystal and the cell walls. When subjected to the usual synthesis reaction conditions at 773 K for many minutes, the platinum sample and cell walls produced no anunonia either as detected in the PID or as background gas in the mass spectrum after the cell was reopened to the UHV chamber. 

Sodium borohydride is marketed in powdered or pellet form, and in solution, for use in fuel cells. Boron nitride can withstand temperatures of up to 650°C (1,202°E) when subjected to high pressures and temperatures, it forms cubic crystals whose hardness rivals that of diamond. Boron carbide, produced by reacting coke and boric acid at 2,600°C (4,712°E), is a highly refractory material and one of the hardest substances known. It has both abrasive and abrasion-resistant applications, and is used in nuclear shielding, see ALSO Davy, Humphry Gay-Lussac, Joseph-Louis Nuclear Chemistry. 

Because many surface probes require high vacuum during their application, most surface science instruments are also equipped with high-pressure or environmental cells. The sample to be analyzed is first subjected to the usual high-pressure and/or high-temperature conditions encountered during reactions in the environmental cell. Then it is transferred into the evacuated chamber where the surface probe is located for surface analysis. One such apparatus is shown in Figure 1.13. 

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