Classifications

• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
  • H05H1/00—Generating plasma; Handling plasma
  • H05H1/24—Generating plasma
  • H05H1/26—Plasma torches
  • H05H1/32—Plasma torches using an arc
  • H05H1/44—Plasma torches using an arc using more than one torch
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J12/00—Chemical processes in general for reacting gaseous media with gaseous media; Apparatus specially adapted therefor
  • B01J12/002—Chemical processes in general for reacting gaseous media with gaseous media; Apparatus specially adapted therefor carried out in the plasma state
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J19/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
  • B01J19/08—Processes employing the direct application of electric or wave energy, or particle radiation; Apparatus therefor
  • B01J19/087—Processes employing the direct application of electric or wave energy, or particle radiation; Apparatus therefor employing electric or magnetic energy
  • B01J19/088—Processes employing the direct application of electric or wave energy, or particle radiation; Apparatus therefor employing electric or magnetic energy giving rise to electric discharges
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J8/00—Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes
  • B01J8/08—Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes with moving particles
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05B—SPRAYING APPARATUS; ATOMISING APPARATUS; NOZZLES
  • B05B7/00—Spraying apparatus for discharge of liquids or other fluent materials from two or more sources, e.g. of liquid and air, of powder and gas
  • B05B7/16—Spraying apparatus for discharge of liquids or other fluent materials from two or more sources, e.g. of liquid and air, of powder and gas incorporating means for heating or cooling the material to be sprayed
  • B05B7/22—Spraying apparatus for discharge of liquids or other fluent materials from two or more sources, e.g. of liquid and air, of powder and gas incorporating means for heating or cooling the material to be sprayed electrically, magnetically or electromagnetically, e.g. by arc
  • B05B7/222—Spraying apparatus for discharge of liquids or other fluent materials from two or more sources, e.g. of liquid and air, of powder and gas incorporating means for heating or cooling the material to be sprayed electrically, magnetically or electromagnetically, e.g. by arc using an arc
  • B05B7/226—Spraying apparatus for discharge of liquids or other fluent materials from two or more sources, e.g. of liquid and air, of powder and gas incorporating means for heating or cooling the material to be sprayed electrically, magnetically or electromagnetically, e.g. by arc using an arc the material being originally a particulate material
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C4/00—Coating by spraying the coating material in the molten state, e.g. by flame, plasma or electric discharge
  • C23C4/12—Coating by spraying the coating material in the molten state, e.g. by flame, plasma or electric discharge characterised by the method of spraying
  • C23C4/131—Wire arc spraying
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
  • H01J37/32—Gas-filled discharge tubes
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
  • H05H1/00—Generating plasma; Handling plasma
  • H05H1/24—Generating plasma
  • H05H1/26—Plasma torches
  • H05H1/32—Plasma torches using an arc
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
  • H05H1/00—Generating plasma; Handling plasma
  • H05H1/24—Generating plasma
  • H05H1/26—Plasma torches
  • H05H1/32—Plasma torches using an arc
  • H05H1/34—Details, e.g. electrodes, nozzles
  • H05H1/36—Circuit arrangements
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
  • H05H1/00—Generating plasma; Handling plasma
  • H05H1/24—Generating plasma
  • H05H1/26—Plasma torches
  • H05H1/32—Plasma torches using an arc
  • H05H1/42—Plasma torches using an arc with provisions for introducing materials into the plasma, e.g. powder, liquid
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J2219/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
  • B01J2219/08—Processes employing the direct application of electric or wave energy, or particle radiation; Apparatus therefor
  • B01J2219/0894—Processes carried out in the presence of a plasma

Definitions

• the present invention relates to continuous plasma processing of materials, and more particularly to an apparatus and method for plasma processing which utilizes a gas injected in the center of a coalesced plasma column for obtaining desired heat transfer to the anode and/or particulate material processing.
• Thermal plasmas formed by arcs between a cathode and an anode, generate high temperatures and have an extremely active nature, and thus have attracted the interest of metallurgists and chemical synthesists for years.
• High intensity arcs are used for welding, cutting, plasma spraying, lighting, interrupting high power circuits, melting and alloying, and producing ultra fine refractories in the form of particulate material. It is known that arc induced magnetohydrodynamic effects dominate a high intensity arc. Interaction of the arc current with the self magnetic fields gives rise to a pumping action, inducing jets or gas flows called a cathode jet and an anode jet. The action of such induced gas flows depends on the gap between the cathode and anode and on the current strength, and can substantially affect the total heat transfer to the anode.
• the present invention uses a multiple arc system, in the preferred form.
• electrical cir ⁇ uity is used as explained in an article by J.E. Harry and R. Knight entitled “Simultaneous Operation of Electric Arcs From The Same Supply", IEEE Trans Plasma Science, PS. 9(4) pp. 248-254 (1981), and also in an article "Power Supply Design For Multiple Discharge Arc Processes", published in the 6th International Symposium on Plasma Chemistry, Symposium Proceedings, Volume 1, pp. 150-155 (1983).
• plasma torch shall mean a device consisting of a thin stick-type cathode surrounded by a tube shaped anode with a nozzle at one end.
• a jet of plasma is emitted from the opening of the nozzle.
• a multiple source plasma generator arrange ⁇ ment as shown by a multiple cathode arrangement, has the plasma creating members positioned about a central axis.
• a gas nozzle is centered along the axis for feeding inert or reactive gases and/or particulate material from the top of the device downward toward the target surface.
• the location of the gas nozzle would be in the area in which the multiple cathodes are located and the nozzle would be directed downward toward the anode.
• the multiple arc arrangement is DC driven to provide a coalesced arc formed plasma column, and a flow of inert gas from the nozzle is directed through the column along its axis to enhance stability of the arc and to provide a means for continuous feeding of particulate matter into the plasma core for controlled processing of materials.
• controlling the flow of the forced gas results in the creation of a bell shaped arc that has a substantial area of contact with the anode to provide enhanced heat transfer to the anode without creating localized hot spots.
• the forced flow of gas from the central nozzle may be used as a means for injecting particulate material into the core of the multiple arcs so that inflight processing, such as melting and/or chemical reactions of the materials, is confined within the plasma. This results in higher processing efficiencies, and better control over the operations.
• a second embodiment comprises use of the invention as an arc plasma reactor through utilization of the interaction between forced gas flows and self-induced gas flows that are created in this type of device.
• the forced gas flows are externally applied convective gas flows in either or both the areas of the anode or cathodes.
• the self-induced flows are an electromagnetic pumping effect of gas from the cathode to the anode, called a cathode jet, and from the anode to the cathode, called an anode jet.
• the forced flow from the cathodes toward the anode, augmented by the cathode jets, may be used to counteract the anode jet and form a stagnation layer at a level between the cathodes and the anode.
• the stagnation region represents a region of high plasma temperature and relatively low gas velocities, which is ideally suited for plasma processing of particulate material.
• particulate material carried by the forced gas flows is entrained in the high temperature plasma and maintained in the stagnation region for a relatively long period of time to enhance proper formation of the process products.
• the processed particulate material is then discharged from the arc region laterally outwardly and can impinge against the sides of a furnace for collection.
• the forced gas can be inert or a reactant for processing the particulate material.
• the interaction of the self magnetic fields of the arc leads to a coalescence of the individual arcs into a single arc column.
• the coalescence occurs at some distance from the cathodes, so cathode-anode spacing is controlled to insure such coalescence.
• the stagnation layer will be at a location after the arcs have coalesced, and in a region which provides enhanced material processing.
• FIG. 1 is a schematic representation of a plasma generator of the present invention including a schematic representation of the electrical circuit used therewith;
• Figure 2 is a schematic side view of the. device of the present invention showing the type of arc shape (bell shape) obtained with the forced gas flow used with the center nozzle for enhancing heat transfer to the anode;
• Figure 3 is a representation of the device of the present invention showing the effects of reduced forced gas flow that provides a stagnation area in the plasma column between the anode and cathode for plasma reactor use;
• Figure 4 is a representation of the configuration of ' Figure 3 illustrating particulate processing when particles are injected through forced gas nozzles at both the anode and cathode ends of the plasma column;
• Figure 5 is a graph depicting typical results of operations of a device of the present invention illustrating the anode heat dissipation in the presence of an anode jet dominated mode of operation as shown in Figure 3, and illustrating the transition to a forced gas and cathode jet dominated mode of operation as shown in Figure 2 at two arc lengths, which illustrates the type o attachment of an arc to an anode at a standard current of 100 amps and at different gas flows; and
• Figure 6 is a graph representing the voltage characteristics of a device of the present invention at two different arc lengths, and at varying gas flows, plotting the voltage versus the gas flow with a standard current of 100 amps.
• plasma forming means are indicated generally at 10, and in the form shown include an anode 11, and as shown in the preferred embodiment, a plurality of cathodes 12, 13 and 14 spaced from the anode a desired distance, and supported in a suitable manner (not shown) . These can be supported in a frame that is suitably cooled, if necessary, and placed within the confines of a furnace, for example having walls indicated schematically at 20.
• a power supply 21 provides power to anode 11 through a line 22 and shunt current resistor 23, and then to anode 11.
• Each of the cathodes 12, 13 and 14 is connected to the negative terminal of the power supply 21 through a line 26, shunt current resistor 24, and stabilizing resistor 25, in series with the resistor 24.
• Cathodes 12, 13 and 14 are connected in parallel through line 26 to the negative side of power supply 21.
• the above identified electrical arrangement provides adequate stabilization of current flow for establishing an arc.
• the shunt current resistors provide a means of measuring current flow to monitor the operation of the device.
• the arcs are generally initiated using a high frequency spark at very close gaps, after which the cathodes can be moved away from the anode a _ desired amount to obtain the desired gap length.
• the anode 11 preferably is copper or other suitable material.
• the anode 11 can be water cooled to prevent it from being consumed or evaporated during operation.
• it is possible to maintain an uncooled molten anode inside a crucible. It is also possible to produce a coating on a substrate moving in the lateral direction which serves, at the same time, as an anode.
• the three cathodes 12, 13 and 14 are positioned 120° apart around a central axis 30 at an included angle along the longitudinal axes of the cathodes of substantially 45°, as shown in Figure 1.
• the central axis 30 is through the center of the anode 11, and the tips of the cathodes 12, 13 and 14 are spaced at a desired distance apart.
• a gas nozzle indicated generally at 32 is centered along the central axis 30 and positioned in front of cathode 13. As shown in Figure 2, nozzle 32 has a central opening 31 through which suitable inert or reactive gases can be directed down into the core of the plasma formed.
• the cathodes 12, 13 and 14 include suitable cathode holders or supports 34 and cathode tips 33.
• An arc is formed between the cathodes and the anode 35.
• cathode 13 is ' not shown but is understood to be positioned behind nozzle 32 as shown in Figure 1.
• the plasma column 39 formed by the arc is controlled and stabilized by providing a flow of gas through the central opening 31 of the nozzle 32 from a gas source 37 at a desired flow rate controlled by a valve 38.
• Valve 38 may be any suitable valve which permits varying the rate of gas flow.
• An inert gas such as argon may be used, and this will form a core 40 of material generally as outlined in the dotted lines.
• the arcs from each of the cathodes 12, 13 and 14 will coalesce approximately one-third of the way from the cathodes to the anode 35, the exact location depending on system parameters including cathode/anode geometry, current flow, and forced gas flows, in the bell-shaped form shown to broaden out the area of contact of the arc on the anode.
• the coalesced arcs form the plasma column 39.
• the jet of gas coming from the nozzle 32 tends to stablize the plasma column 39 and keep it from dancing back and forth on the anode 35 as the arc is generated.
• the gas flow from the nozzle 32 will counteract the induced gas flow from the anode 35 toward the cathodes 12, 13 and 14, commonly known as the anode jet, and will assist or add to gas flows from the cathodes 12, 13 and 14 to the anode 35, called the cathode jets.
• the bell shaped end 39A of the plasma column 39 is obtained by having sufficient gas flow from the nozzle 32 along the core 40 of the plasma column 39 to overcome self- induced anode jets moving in direction from the anode 35 toward the cathodes 12, 13 and 14, and provide a net positive flow from the cathodes 12, 13 and 14 to the anode 35.
• the gas flowing from nozzle 32 may be inert for simple melting and/or vaporizing processes (e.g. coating, spherodization, etc.) or may be reactive for chemical transformations (e.g. reduction, coal gasification, etc.)
• particles (particulate matter) from a particle source indicated at 41 can be intermixed with the gas from the gas source 37. This particulate matter is thus injected into the plasma column 39 and is passed down through the column core 40, to intermix with the plasma and chemically react, or be heated in a desired manner.
• the particles can be carried in a gas stream from the source or dispersed in any suitable manner. If desired, the particles can be processed in the plasma column 39 and then either deposited as a coating on the material forming the anode 35 in the approximate area of contact between the plasma column and the anode or ejected as shown by arrows 42.
• injecting a suitable column of gas along an axis positioned between a plurality of cathodes stabilizes the plasma column, and adjusting the flow of such gas diffuses the plasma column at its base where it contacts the anode to provide a bell shaped, wide area of contact between the plasma and the anode.
• the self-induced flow of gases from the anode to the cathodes that would occur in the case of a constricted plasma column at the anode is overcome by the flow of the gas from the nozzle 32, augmented by the self-induced flow of gas from the cathodes to the anode.
• the flow from nozzle 32 can be adjusted with valve 38 between the gas source and the nozzle 32 to provide the desired bell shape.
• the nozzle 32 is a water cooled sleeve having a partition tube 46 surrounding the annular center tube 31, and the flow of water would be cool along the walls forming the center tube 31. The water flows back out along the outer walls of the nozzle to keep the nozzle material from deteriorating in the high temperature environment of the furnace.
• the same type of results can be obtained using a core gas flow for stabilization of plasma torch flows, if the cathodes are replaced with plasma torches.
• the anode 35 would remain an anode and the plasma jets from the torches would be flowing toward the surface of the anode 35.
• the plasma torches would be operating in the transferred arc mode, where the anodes of the torches are electrically disconnected after arc initiation.
• the use of a center inert gas core stabilizes the plasma flow, and provides for a wider area of contact of the plasma to the anode as well as providing the ability to control processing of particles from a source by having better control of the time for processing and the temperatures.
• FIG 3 a form of plasma column particularly useful for plasma processing is shown which can be obtained by regulating the gas flows through the valve 38.
• cathode 13 is not shown, but is positioned behind nozzle 32.
• Self-induced gas entrain ent from the anode 47 occurs, as previously mentioned, without a flow of gas from the nozzle 32, so that there will be a convective effect upward from the anode 47 toward the cathodes 12, 13 and 14 forming an "anode jet" indicated at 52.
• the anode jet can dominate the plasma flow and even result in the plasma column extending upwardly above the ends of the cathodes 12, 13 and 14 in a direction away from the anode 47.
• the plasma column indicated in this form of the invention at 50 will not extend above the ends of the cathodes.
• the anode 47 will be water cooled in a conventional manner for use in the apparatus of Figure 3, which forms a plasma reactor.
• the stagnation zone 51 may be moved axially in relation to the cathodes 12, 13 and 14 and anode 47 as desired by adjusting the parameters of operation including cathode/anode geometry, current flow, and forced gas flow.
• the primary means of controlling the location of the stagnation zone is through adjusting valve 38 to change the forced gas flow through nozzle 32. While in this mode of operation there is a small area of arc contact on the anode that causes localized heating, the anode is additionally cooled by the self-induced anode flow 52 along the anode surface.
• the arrangement shown in Figure 4 can be used to process particulate matter 54.
• Particulate matter from a particle source 41 is introduced into the gas flow in the nozzle 32 and is thereby carried down into the plasma column 50.
• small amounts of gas from self-induced flow at the anode will be moving upwardly as previously explained.
• Additional particles can be injected into the anode jet gas flow 52 from the anode to cathode with nozzles indicated at 56 lying parallel to the surface of anode 47. These additional particles then will move up into the plasma column 50 along with the self-induced anode jet flow so that the center core of the plasma column will be filled with particles 54 as illustrated in Figure 4.
• the particles 54 then will be capable of being processed by the plasma for a period of time that is longer than that which is possible without the stagnation zone 51 generated by the forced gas flow from nozzle 32 in combination with the cathode jets 60 and anode jet 52.
• the process is used to cause the particles to change in character, for example, forming spheres from irregularly shaped particles. Additional chemical reactions can take place or the particles can be broken into fine powders depending on the reaction with the plasma column.
• the side walls 20 of the furnace will be bombarded with the processed particles 54A and may be used to collect the materials being processed, utilizing both the forced gas flow from the nozzle 32 and the natural pumping action of the plasma column 50.
• the particulate material is injected into the plasma column 50 by the pumping action of either or both the cathode jets 60 and anode jet 52, aided by the forced gas flows in nozzles 32 and 56.
• These pumping actions and forced gas flows overcome the effect of the high temperature gradients, as well as the high viscosity of the plasma, which otherwise inhibit the injection of particles.
• the geometry of the multiple cathode arrangement as shown in Figure 4 also enhances the injection of particles by feeding particles into a region where they are constrained by the noncoalesced plasmas resulting from the individual cathodes and hence are injected into the coalesced plasma core.
• the pumping action also permits feeding particles in both directions from the cathode and the anode, and the processed product is ejected radially at the stagnation region.
• the heat dissipated at the anode can be made to increase significantly where there is a diffused bell attachment of the arc or plasma column, such as that shown in Figure 2.
• the stagnation region or disk can be formed at a chosen location above the anode.
• a forced gas flow from nozzle 32 in the range of 10 to 12 grams per minute resulted in a change from the spot attachment of the plasma column to the anode, as shown in Figure 3, to a diffused bell-shaped attachment, as shown in Figure 2.
• a reasonable arc length is desired, and the voltage levels at 100 amps current ranged from approximately 13 volts for the five millimeter arc length, to about 30 volts for the longer arc length of 40 millimeters. At arc lengths between these extremes the voltage is also between these values, and varies somewhat.
• the stagnation region is formed at lower gas flows.
• the gas flows can be adjusted to obtain the desired results for a given arc length and a given arc current.
• Current also can be varied as desired to obtain the desired attachment point.
• Figure 6 is a graph generally illustrating the effect of various gas flows from the nozzle 32 on the voltage levels to maintain a current of 100 amps to each of the cathodes. This shows the various voltage levels that are produced by the conditions illustrated in Figure 5, in presence of an anode jet, at particular currents for two different arc lengths and shows the approximate region, as marked on Figure 5, of formation of the diffuse bell attachment to the anode at different gas flows.
• the use of the three cathodes adds stability to the coalesced arc, and provides for a large plasma volume through which the particles may pass for treatment.
• the arc voltage generally increases with increasing forced gas flow rate from nozzle 32 at each arc length. As the gas flow from the nozzle 32 increases, the cooling effect on the plasma becomes stronger. This cooling of the plasma increases the resistance of the arc and the arc voltage must rise to compensate.
• the voltage characteristics, generally speaking, of the triple cathode arc are similar to those found in conventional single cathode arcs, and because the forced gas from the nozzle 32 acts as an artificial cold cathode jet, the forced gas aids in the stabilization of the arc.
• the flow from the anode to cathode causes the disk of plasma at the stagnation region 51 spaced from the anode.
• the anode jet dominated mode is indicated at low gas flows for the different arc lengths shown there, and the diffused bell attachment of the anode occurs where the greatest amount of heat is shown to be dissipated for a given amount of power. It should be noted that for some limited values of current, voltage, and distance of cathodes, the stagnation zone 51 shown i .
• Figures 3 and 4 occurs as a result of the cathode jet alone without forced gas flow through nozzle 32; however, the flow through nozzle 32 allows creation of the stagnation zone for a much greater range of current, voltage, and distance of cathodes and in any event provides for greater control over the creation and location of the stagnation zone.
• the forced gas flow through nozzle 32 under typical operating conditions is approximately five times higher than the self-induced flow of the cathode jets.
• the presence of a self-induced cathode jet 60 depends in part upon the shape of the cathode tip. If the cathode tip is blunt, rather than a fine or sharp tip, the cathode jet is reduced and it is possible to operate in an anode jet dominated mode where the anode jet is in the full reverse flow.
• An anode jet flow in the opposite direction of the electron flow, aids the positive ion flow.
• the anode jet is forced downward toward the anode by the combination of the forced gas flow and cathode jets, the flow favors the electron flow, resulting in lower arc voltages.
• an anode jet, and a flow in the reverse direction are impinging upon each other, a high potential drop is needed to push the particles through the stagnation layer.
• the anode jet hinders heat transfer to the anode as a result of the flow along the anode and up through the plasma column.
• the anode jet mode should be avoided, and as shown in Figure 5, for example, a sufficient flow of gas from the cathode should be provided through the central core to provide the diffuse bell attachment to the anode.
• the flows are in the anode jet mode, and the forced flow through the nozzle 32 is selected to form a stagnation zone, the ability to inject particles at both the anode and through the central nozzle is present, and the processing of the particles in the stagnation zone at the plasma provides for greater length of time of particle processing, higher heats, and in many instances greater efficiency.
• Varying the current provides an additional means of control over the formation and location of the stagnation zone.
• Lower currents reduce the intensity of the cathode jets and hence will allow the stagnation zone to move somewhat closer to the cathodes; however, as noted above, the effect of the cathode jets are significantly less than the effect of the forced flow of gas.
• the position of the stagnation region can be adjusted by regulating the pressure through the cathode forced gas nozzle 32, as well as the anode forced gas nozzles 56.
• the carrier gas used for injection of particulate matter into the arc may be inert or it may represent a chemical reactant depending on the desired reaction in the plasma.
• This device may be used for physical as well as for chemical processing.
• Physical processing may, for example, include spheroidization of irregularly shaped powder particles, production of ultrafine powders (for example silica) and densification of conglomerates.
• Chemical processing includes the decomposition of compounds (for example toxic wastes), the synthesis of carbides, nitrides and refractory metal oxides, the production of chemical compounds and alloys using solids, liquids or gases as starting materials. Radial ejection of the products from the hot plasma zone provides for a fast quench of the products which may be further enhanced by imping ent of the products on water cooled walls or by entrainment of the products into water cooled channels.
• the injection nozzles 56 project radially from the axis of the plasma column, and perhaps six or so equally spaced nozzles would be used around the axis.
• the particles from nozzles 56 will generally be conveyed in a gaseous fluid in a known manner.
• the device will work with only one cathode, the use of three cathodes provides for better control and better action.
• the device will also work with modifications including the height of the gas nozzle relative to the cathode tips, the rotation of the entire multiple arc plasma torch assembly in any direction, and different anode geometries such as stick anodes, ring anodes, or anode crucibles.
• the particle injection occurs at a point equal to or below the cathode tips to prevent cathode degradation.

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• 1985
  • 1985-09-25 JP JP60504179A patent/JPS62500290A/ja active Pending
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