Liquid-nitrogen-based cooling system

In both cases, the Au nanoparticles behave as molecular crystals in respect that they can be dissolved, precipitated, and redispersed in solvents without change in properties. The first method is based on a reduction process carried out in an inverse micelle system. The second synthetic route involves vaporization of a metal under vacuum and co-deposition of the atoms with the vapors of a solvent on the walls of a reactor cooled to liquid nitrogen temperature (77 K). Nucleation and growth of the nanoparticles take place during the warm-up stage. This procedure is known as the solvated metal atom dispersion (SMAD) method. 

The absorption at the mercury wavelength (2537 A) occurs in the gas cell 12 sec after the heating cycle is initiated. The absorption is recorded in arbitrary imits, and the maximum height is noted. After the response has retiumed to the initial base line (60 sec), the heating is stopped, and the column is cooled in air for 30 sec. The U-tube is then returned to the liquid nitrogen bath. The carrier gas flow is set to 0.5 l./min, and the system is ready for the mercury spike additions. Total time for this operation is 9 min. Except for the stannous chloride addition, the system blank is established in a manner identical to the sample determination. 

Cooling systems designed for routine use on x-ray diffractometers are almost exclusively based on the gas-stream principle, where the sample temperature is controlled with a stream of gas, usually dry nitrogen. Contemporary commercial low-temperature attachments allow reasonably easy temperature control in the range from near liquid nitrogen temperature to about room temperature. 

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