Helium gas jet

This process, originally designated as RSR (rapid solidification rate), was developed by Pratt and Whitney Aircraft Group and first operated in the late 1975 for the production of rapidly solidified nickel-base superalloy powders.[185][186] The major objective of the process is to achieve extremely high cooling rates in the atomized droplets via convective cooling in helium gas jets (dynamic helium quenching effects). Over the past decade, this technique has also been applied to the production of specialty aluminum alloy, steel, copper alloy, beryllium alloy, molybdenum, titanium alloy and sili-cide powders. The reactive metals (molybdenum and titanium) and... 

The catcher foil can take the form of a jet of rapidly moving gas, a helium jet. The atoms produced in a nuclear reaction recoil out of a thin target and are stopped in — 1 atm of helium gas in the target chamber. The gas contains an aerosol, typically... 

Fig. 2 (a) A schematic of plasma jet, (b) a plasma jet discharged with helium gas, (c) a plasma jet impinging to a human finger [20], (d) a plasma jet with a flexible dielectric tubing [21]. 

The alternative technique to TIRES is transient infrared transmission spectrometry (TIRTS). This technique is analogous to TIRES, but instead of the sample being at ambient temperature and being heated by the gas jet, the sample is above the ambient temperature and is cooled by a narrow jet of cold helium. Were the sample... 

The tank, attached to the wing tip of a jet aircraft, was purged with helium gas and filled with liquid hydrogen to about 90 of its capacity. Within 5 min after the tank was loaded and the necessary vent valves closed, the airplane was airborne. During the flight, the liquid-hydrogen tank pressure increased because of the heat leak into the tank and, when the maximum safe operating pressure... 

Several instniments have been developed for measuring kinetics at temperatures below that of liquid nitrogen [81]. Liquid helium cooled drift tubes and ion traps have been employed, but this apparatus is of limited use since most gases freeze at temperatures below about 80 K. Molecules can be maintained in the gas phase at low temperatures in a free jet expansion. The CRESU apparatus (acronym for the French translation of reaction kinetics at supersonic conditions) uses a Laval nozzle expansion to obtain temperatures of 8-160 K. The merged ion beam and molecular beam apparatus are described above. These teclmiques have provided important infonnation on reactions pertinent to interstellar-cloud chemistry as well as the temperature dependence of reactions in a regime not otherwise accessible. In particular, infonnation on ion-molecule collision rates as a ftmction of temperature has proven valuable m refining theoretical calculations. 

On the high-pressure side of the nozzle molecules may be seeded into the jet of helium or argon and are also cooled by the many collisions that take place. However, in discussing temperature in molecules, we must distinguish between translational, rotational and vibrational temperatures. The translational temperature is the same as that of the helium or argon carrier gas and may be less than 1 K. 

Figure 9.46 shows an example of a fluorescence excitation spectmm of hydrogen bonded dimers of x-tetrazine (1,2,4,5-tetraazabenzene). The pressure of x-tetrazine seeded into helium carrier gas at 4 atm pressure was about 0.001 atm. Expansion was through a 100 pm diameter nozzle. A high-resolution (0.005 cm ) dye laser crossed the supersonic jet 5 mm downstream from the nozzle. 

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