Electric heating – Metal heating – By arc
Patent
1997-04-08
1999-02-23
Paschall, Mark H.
Electric heating
Metal heating
By arc
21912141, 21912159, 156345, 20429837, B23K 1000
Patent
active
058747052
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to method of and apparatus for producing a plasma substantially at or above atmospheric pressure using microwave energy.
The use of microwave generated plasma has found a wide range of applications in the synthesis of new materials and in materials surface engineering. For instance, U.S. Pat. No. 4,897,285, U.S. Pat. No. 4,664,937 and U.S. Pat. No. 4,893,584 disclose methods of depositing films or coatings onto a substrate using microwave generated plasma. However, the microwave generated plasma in the prior art is produced using sophisticated equipment requiring a high intensity microwave field and a low plasma pressure environment. The requirement for such sophisticated equipment and the necessity for the use of vacuum techniques has led to a high capital cost of microwave processes.
A microwave plasma apparatus is disclosed in EP-A-0435591 in which a methane gas is contained within a microwave field for conversion to acetylene, ethylene and hydrogen. Electrically conductive elongate particles are placed and maintained in the field to act as plasma initiators and catalysts for the reaction. This arrangement suffers from the disadvantage that the initiators fouled during the reaction and as disclosed in EP-A-0436363 they require regeneration.
The object of the present invention is to provide a simpler and cheaper microwave-plasma apparatus and a method of generating a plasma using microwave energy which does not require the maintenance of a low pressure in the vessel or the use of such catalysts to sustain a plasma substantially at or above atmospheric pressure.
SUMMARY OF THE INVENTION
The present invention provides a microwave-plasma apparatus for producing a plasma substantially at or above atmospheric pressure, comprising a vessel for containing gas substantially at or above atmospheric pressure and a plasma once initiated, means for radiating microwave energy into said vessel to produce a plasma therein; and means for initiating said plasma; wherein said vessel is shaped to confine said plasma in a volume to prevent dissipation of said plasma once initiated, and said means for radiating microwave energy includes power control means to control the power level of the microwave energy to sustain said plasma once initiated.
The present invention also provides a method of producing a plasma substantially at or above atmospheric pressure using microwave energy, the method comprising the steps of radiating microwave energy into a vessel containing a gas to initiate a plasma therein; confining said plasma in a volume in said vessel to prevent dissipation of said plasma; radiating further microwave energy into said vessel to sustain said plasma, wherein the radiation of further microwave energy is controlled to control the power level of the microwave energy to sustain said plasma once initiated.
The present invention is thus able to sustain a plasma substantially at or above atmospheric pressure after it has been initiated, by confining the plasma in a volume to prevent its dissipation and controlling the application of microwave power to the plasma. In order to sustain the plasma it is necessary to keep the microwave power density high enough to sustain the plasma. Therefore, the microwave power cannot be pulsed in such a manner that the microwave power is switched off for a long enough period for the plasma to extinguish since this will require the re-initiation of the plasma. The plasma is therefore preferably sustained by the continuous application of microwave energy, although the applied microwave energy can be pulsed so long as the off part of the duty cycle is not too long.
In order to provide an arrangement for the continuous feeding of gas into the microwave plasma, the microwave plasma apparatus preferably includes inlet means for introducing gas into the vessel and exhaust means for removing exhaust gas from the vessel.
The vessel is preferably substantially spherical and formed of a refractory material. The material is conveniently a dielectric non-conductive mat
REFERENCES:
patent: 3577207 (1971-05-01), Kirjushin
patent: 4609808 (1986-09-01), Bloyet et al.
patent: 4883570 (1989-11-01), Efthimion et al.
patent: 5023056 (1991-06-01), Aklufi et al.
patent: 5205912 (1993-04-01), Murphy
patent: 5270515 (1993-12-01), Long
patent: 5468296 (1995-11-01), Patrick et al.
patent: 5565118 (1996-10-01), Asquith et al.
EA Technology Limited
Paschall Mark H.
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