Plasma jet

Argon, helium, and their mixtures with other gases are used as the working fluids in plasma arc devices for producing plasma jets with temperatures in excess of 50,000 K. These devices are used for cutting metals and for spray coating of refractory alloys and ceramics (qv) (see Plasma technology). 

H. Bockborn and co-workers, "Production of Acetylene ia Premixed Flames and of Acetylene—Ethylene Mixtures," Chem. Ing. Pechnol. 44(14), 869 (1972). "Thermal Decomposition of Ethane ia a Plasma Jet," Rogyo Kagaku Zasshil4(9), 83 (1971). 

Plasma-jet diamond techniques yield growth rates of about 980 p.m/h (163,164). However, the rate of diamond deposition is still one to two orders of magnitude lower than the HP—HT technology, which is about 10,000 p.m/h (165). Diamond deposition rates of ca 1 p.m/s have been reported usiag laser-assisted techniques (166). This rate is comparable to the HP—HT synthesis. 

Hot RF and - DC plasma, are discharge, plasma jets Oxy-acetylene flames Low pressure microwave plasma, holt filament. Low pressure DC or RF glow discharge Thermal decomposition... 

Operation of the installation is as follows. The power supply (1) is connected to the plasma generator (4.5 kW) (2), which initiates a plasma jet by delivering plasma-forming gas (air, oxygen, nitrogen etc.). The solution is loaded onto the plasma by means of pneumatic nozzles (3) and dispersed using the same type of gas. 

Some workers have correlated experimental data in terms of k at the arithmetic mean temperature, and some at the temperature of the bulk plasma. Experimental validation of the true effective thermal conductivity is difficult because of the high temperatures, small particle sizes and variations in velocity and temperature in plasma jets. 

Ohtake, N., and Yashikawa, M., Diamond Film Preparation by Arc Discharge Plasma Jet Chemical Vapor Deposition in the Methane Atmosphere, / Electrochem. Soc., 137(2) 717-722(1990)... 

Kurihara, K., Sasaki, K., Kawarada, M., and Koshino, M., High Rate Synthesis of Diamond by DC Plasma Jet Chemical Vapor Deposition, Phys. Lett., 52(6) 437 38 (1988)... 

The plasma jet can be cooled rapidly just prior to coming in contact with the substrate by using a blast of cold inert gas fed into an annular fixture. Gaseous boron or phosphorus compounds can be introduced into the gas feed for the deposition of doped-semiconduc-tor diamond. 

Woodin, R. L., Bigelow, L. K., and Cann, G. L., Synthesis of Large Area Diamond Films by a Low Pressure DC Plasma Jet, mApplications of Diamond Films and Related Materials, (Y. Tzeng, et al., eds.), Elsevier Science Publishers, pp. 439-444(1991)... 

Hubicka, Z., Sicha, M., Pajasova, L., Soukup, L., Jastrabik, L., Chvostovd, D., and Wagner, T., CNx Coatings Deposited by Pulsed RF Supersonic Plasma Jet Hardness, Nitrogenation and Optical Properties, Surf. Coat. Technol., Vol. 142-144, 2001, pp. 681-687. 

Conversion of Methane to Hydrogen and Carbon black by D.C. Plasma Jet... 

Preparation of nitrogen-doped TiOi powder by plasma jet... 

It is necessary to supply a spray into the plasma jet, in order to excite the elements. This has presented some difficulty and it is a n stery to the author as to why the plasma jet has not been more widely applied for the analysis of sodium potassium, calcium and magnesium. It has the advantage of safety, in that one inert gas (argon) would be used, and high sensitivity. In addition, four elements, calcium, magnesium. 

An argon-hydrogen plasma is created in a dc thermal arc (cascaded arc) operated at high pressure 0.5 bar) [556, 559. 560] (the cascaded arc is also employed in IR ellipsometry, providing a well-defined source of intense IR radiation see Section 1.5.4 [343]). As the deposition chamber is at much lower pressure (0.1-0.3 mbar), a plasma jet is created, expanding into the deposition chamber. Near the plasma source silane is injected, and the active plasma species dissociate the silane into radicals and ions. These species can deposit on the substrate, which is positioned further downstream. 

If the reaction at 2500 °K may be considered as occurring at constant volume, determine the times corresponding to the two maxima. Note that the time in the plasma jet will be exceedingly small. 

Gulyaev and Polak [Kinetics and Catalysis, 6 (352), 1965] have studied the kinetics of the thermal decomposition of methane with a view toward developing a method for the commercial production of acetylene in a plasma jet. The following differential equations represent the time dependence of the concentrations of the major species of interest. 

Emission spectrometer incorporating a sample nebulizer, grating monochromator, photomultiplier detection system and microprocessor controller. Excitation by dc-arc plasma jet, or inductively coupled plasma. Laser excitation sometimes used. 

FIGURE 6.13 Schematic diagram of plasma spray deposition processing, (a) Radial injection of feedstock into plasma torch, showing partial entrainment of feed particles into the plasma jet and (b) axial injection of feedstock into plasma torch, showing more complete entrainment of feed particles into the plasma jet. 

Plasma-jet spraying Alloy powders are molten in a plasma jet and spray-quenched against a cold heat-conducting substrate (cooling rate about 109oC/s). 

TTie technique developed allows rapid and routine determination, both at trace and higher concentration levels, in either aqueous or non-aqueous solvents, of approximately 70 elements in the periodic table. It is fuUy automatic with aU the operations, including sampling and clean-out of the plasma jet, controlled by a microcomputer. Being able to control the time allowed for clean-out of the plasma jet is especially useful in the determination of elements which tend to cause memory effects in later samples. 

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