The Plasma Arc

A plasma may be defined as a gas containing a relatively large number of ions and free electrons. To produce a plasma, an energy source is required and for analytical atomic spectroscopy three different excitation methods have been used. They are (1) a dc arc, (2) radiofrequency energy coupled through a microwave cavity, and (3) radiofrequency energy inductively coupled to the plasma. 

FIGURE 5-10. Basic diagram of a plasma jet excitation source. [Courtesy Spex Industries, Inc.] 

FIGURE 5-12. Photograph of a dc-arc-excited plasma excitation source. [From a Ph.D. dissertation by S. E. Valente, Kansas State University.] 

The dc-excited plasmas are characterized by (1) high electronic temperatures, (2) good stability, (3) low detection limits, (4) linear calibration curves over a large concentration range, and (5) reduced interference effects from other elements in the plasma. They also have higher background. 

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Residuals Produced The plasma arc process produces ash which may require post treatment to make it suitable for disposal. The wet, scrubber blowdown may require treatment prior to disposal. 

The plasma torch is usually mounted on a circular end wall. The torch is aligned in such a way that waste material falls into the hot zone of the plasma arc. The torch cathode and anode are cooled by forced water flow. In addition, auxiliary cooling of the anode with air can be incorporated in the plasma torch. 

The Ba.C) N, nanotubes and fullerene-like structures have been synthesized by various laboratories in recent years. The most popular method is the plasma arc technique. The first report on the synthesis of BN nanotubes was by Zettl and coworkers (55). Since BN is an insulator, a composite anode was prepared from a tungsten rod with an empty bore in the center, which was stuffed with a pressed hexagonal BN powder. For the cathode, a water-cooled Cu rod was used. The collected gray soot contained limited amount of multi wall BN nanotubes. It is possible that in this case, the tungsten serves also as a catalyst. By perfecting this method, macroscopic amounts of double-wall BN nanotubes of a uniform diameter (2 nm)... 

Figure 10.27 A photograph of a screw in a PTA welding lathe a) natural gas burners are heating the screw billet to a temperature of about 400 to 430 °C, and b) the plasma arc of the PTA welder is visible in this photograph (courtesy of Jeffrey A. Kuhman of Glycon Corporation)...

The cycle times are important as this determines the length of time that the plasma arc Is being formed. When the voltage drops at the end of a half cycle, the arc will cease. Thus the cycle time acts as a timing switch for the arc. 

The Plasma Arc Centrifugal Treatment (PACT) is a thermal process that uses a plasma torch to treat hazardous wastes. In the presence of oxygen, the torch heats wastes to approximately... 

The plasma arc is a recent development, with a potential of high intensity and efficiency. By using photosensitizers, visible light or laser beams may also be employed. 

Apparatus. Plasma Jet. A section of the plasma arc gun is shown in Figure 1. A direct current arc was struck between the thoriated tungsten rod, which acted as the cathode, and the copper tube anode. Both electrodes were... 

Using nuclear-based electricity to power the plasma-arc reforming process saves fossil fuels. 

Very high temperatures (>3 000°C) are generated inside the plasma-arc reforming units. The energy, which is generated inside the plasma reformer, is not dependent on the chemical reaction. 

The need for fundamental information such as reaction mechanisms, catalysis, and kinetics and for new approaches such as the plasma arc... 

Plasma arc technology has been used successfully in Europe to destroy chemical warfare material but has not been permitted in the United States. Currendy, PMCD is optimistic that it will have little difficulty in obtaining a permit. They have identified several plasma arc firms in this country that have operational units, but none has destroyed a CW-related waste stream. If the ACWA program does not develop a continuous SCWO system that is cost-effective for use on the quantities of materiel to be destroyed in the nonstockpile program and if a permit for the plasma arc technology cannot be obtained in time, the Army may be forced to incinerate its waste streams to comply with the CWC treaty deadline of April 2007... 

A plasma arc may also initiate cross-linking in a paint film. The high temperatures produced in the interior of the plasma arc are transmitted only to a small extent to the paint film. 

BN and B cCj,N2 nanotubes and fullerene-like structures have been synthesized by various laboratories in recent years. The most popular methods are the plasma arc and laser ablation techniques. The first report on the synthesis of BN nanotubes, using the arc-discharge technique, was by the Zettl group [85, 86]. Because... 

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