Abstract: A waste-melting furnace includes a furnace body, a rotary heat-resistive vessel which is arranged inside the furnace body and into which waste is to be fed, and a transferred arc type torch plasma gun and a water-cooled electrode arranged above the rotary heat-resistive vessel, the plasma gun and electrode being opposed to each other.

Abstract: Method to equalize the temperature in a heating furnace (10) with a controlled-oxidization ambient, the furnace (10) comprising at least one insulated chamber (11) cooperating with a supporting and conveying surface defined by a plurality of rollers (12), the rollers (12) including rings (35) to bear slabs (19), a plurality of burners (18) being comprised in cooperation with the upper part of the furnace (10), whereas a plurality of aspiration intakes (21) is included in cooperation with the lower part of the furnace (10), the feed to the burners (18) being adjusted in such a way as to ensure a strongly oxidizing atmosphere within the furnace (10) so as to obtain a desired and controllable layer of scale on the surface of a slab (19) in the furnace (10), this strongly oxidizing atmosphere being conveyed so as to surround and lap continuously and evenly the whole periphery of the slab (19), the furnace (10) cooperating downstream with a descaling assembly (22) to remove the layer of scale thus formed.

Abstract: A plasma oscillator photonic energy water heater/steam boiler, establishes, amplifies and stores photonic energy in a plasma wherein resonance and temporary energy storage is maintained until energy is transferred on demand by thermal radiation and conduction of molecular kinetic energy to a heat exchanger having water to be heated therein. The chamber is a closed hollow internally reflective mirrored cylinder which includes parallel and optically resonant mirrored surfaces for sustaining a plasma oscillation within the container. A containerized molecular gas media is flooded with broad band electromagnetic radiation in order to create population inversions at the electron level in the gaseous atmosphere, and hence, store photonic energy in the plasma oscillator. Water in a heat exchanger immersed within the plasma is heated by thermal radiation energy transfer, and by conduction from a high molecular kinetic energy stored within the plasma.

Abstract: A reactor and method for the treatment of matter by plasma action. A plurality of electrode structures are positioned to define a reaction zone associated with the inter-electrode space. The inter-electrode space is conditioned (as by preionizing) and a series of discrete electrical discharges are produced throughout the reaction zone. In a preferred embodiment, the reaction zone is subjected to a sequence of discrete electrical discharges in a time interval less than the residence time of material to be treated within the reaction zone.

Abstract: A plasma melting furnace has a melting chamber having an anode torch and a cathode torch made of graphite and having a electric conductor disposed on the bottom thereof. When the furnace is operated, the anode torch, having an inflow of electrons, which forms an unstable plasma arc is contacted with the electric conductor and is not used, while the cathode torch, having an outflow of electrons, which forms a stable plasma arc, is utilized for heating, whereby the furnace can be stably and continuously operated. Thus, since the cathode torch which is used is not heated so much and the anode torch, which is liable to be heated to a great degree, is not used, the electrode consumption rate can be greatly reduced.

Abstract: A plasma arc melter which is equipped with at least two transferred arc plasma torches of opposite polarities is used to melt normal batch materials for producing glass, ceramics, refractories and other such materials and for the recycling, combustion and/or vitrifying incineration of waste materials. To enhance the stability of the plasma jets, the anode torch is positioned farther above the surface of the materials being processed than the cathode torch and the materials being processed are introduced into the melter so that the materials first pass beneath the cathode torch. An oxidizing gas can be introduced into the zone between the torches in the region of the plasma jets to enhance the combustion process. For waste materials with a high organic content, a plasma arc afterburner can be used to further treat the exhaust gases from the melter.

Abstract: The ash melting furnace disposes the combustion ash resulted from incineration of municipal or other sorts of waste by melting it utilizing as the main fuel the unburnt carbon contained in the ash itself. The ash melting furnace includes a stationary plasma torch which uses air for the working gas, and which is so placed facing the combustion ash heaped up within the furnace as to project its hot gas jet thereon. The furnace further includes a torch unit controller that actuates the plasma torch to secondarily heat and melt the ash.

Abstract: An apparatus and method for the synthesis of ultra-free (submicron) ceramic carbides in a thermal plasma torch reactor using primarily silica, boron oxide, titanium dioxide or other oxides as metal sources and methane as a reductant. A plasma torch operated with both argon and helium as plasma gases and having methane as a primary carrier gas is connected to the plasma reactor for providing the heat necessary to carry out the reaction. A collection chamber with both interior and exterior cooling is connected to the reactor for quenching of the reactants. Cooling is provided to the torch, the reactor and the collection using coils, baffles and jackets.

Abstract: A drum is introduced into an interlock chamber and the interlock chamber is sealed. A door leading to a transition chamber is opened and the drum is moved into the transition chamber. The transition chamber is contained within a spool valve which includes a pair of drum grips. The drum grips are actuated to grasp the drum. The drum grips are rotatably coupled to an inner element of the spool valve. The inner element is rotated with respect to a housing and a drum manipulator grasps an end of the drum. The drum is displaced from the transition chamber toward a treatment chamber. The drum is cut into a desired shape and/or number of pieces with the drum and the material contained therein being deposited into the treatment chamber.

Abstract: A reactor for incinerating and melting materials such as waste and/or toxic materials has a containment housing inside of which an upright, open-ended drum is rotatably mounted. The drum is lined with refractory, forms a central discharge opening for the removal of incinerated and melted materials, and has an upright, outer wall. Incineration heat is supplied by a plasma torch which is mounted to the containment housing and extends into the drum. A steel throat ring concentric with the discharge opening is connected with the exterior of the drum; e.g. an outer drum wall, by grounding arms which extend non-radially; e.g. tangentially from a periphery of the throat ring to the inside surface of the drum wall, so that electric discharge from the torch to the upwardly oriented surfaces of the throat ring and the grounding arms is possible.

Abstract: The invention is directed to a plasma torch which projects into a container and is fastened at a supporting device and has a nozzle arranged at a burner lance, as well as a main electrode pipe with a main electrode arranged inside the burner lance, gaseous and liquid media as well as electric current being supplied to the main electrode via coaxially arranged pipes. An annular insulating member (21) is provided around the main electrode (10) in the region of its foot end and encloses the electrode (10) annularly, the casing (33) of the double-walled burner lance (30) which is held by the supporting device being fastened at this insulating member.

Abstract: A reactor and method for the treatment of matter by plasma action. A plurality of electrode structures are positioned to define a reaction zone associated with the inter-electrode space. The inter-electrode space is conditioned (as by preionizing) and a series of discrete electrical discharges are produced throughout the reaction zone. In a preferred embodiment, the reaction zone is subjected to a sequence of discrete electrical discharges in a time interval less than the residence time of material to be treated within the reaction zone.

Abstract: A method of treating waste material which involves creating a substantially continuous curtain of plasma and directing the material to be treated through that curtain. An electric arc is generated between two electrodes which are separated by an annular space, and the arc column is caused to rotate about the axis of that annular space so that a substantially uninterrupted curtain of plasma bridges the space and extends around the circumferential extent of the space. The direction of rotation of the arc column is generally transverse to the direction in which that column extends between the two electrodes, and material to be treated is fed through the curtain in a direction which is transverse to both the rotational direction and the direction of longitudinal extent of the arc column. One of the electrodes may be of cylindrical tubular form, in which event material to be treated is fed into the region of the arc through the axial bore of that electrode.

Abstract: An apparatus for producing fused silica includes at least one anodic plasma arc electrode and at least one cathodic plasma arc electrode adjustably arranged with respect to one another so that the plasma arcs formed thereby couple together to form a plasma arc coupling zone. A feedstock material is fed into a region between the electrodes or to a region near the electrodes where the plasma arc coupling zone is formed. A platform is located beneath the plasma arc coupling zone to receive the silica product which is formed in the plasma arc coupling zone. The platform may be rotated about its axis and move up and down along its axis. A cooling device also may be included with the platform. The plasma anode torch used in the apparatus includes a cylindrical nozzle with a non-consumable, copper, blunt ended electrode disposed therein. A channel is provided between the electrode and the nozzle wall to allow the plasma gas to pass through the torch.

Abstract: An apparatus and method for the synthesis of ultra-free (submicron) ceramic carbides in a thermal plasma torch reactor using primarily silica, boron oxide, titanium dioxide or other oxides as metal sources and methane as a reductant. A plasma torch operated with both argon and helium as plasma gases and having methane as a primary carrier gas is connected to the plasma reactor for providing the heat necessary to carry out the reaction. A collection chamber with both interior and exterior cooling is connected to the reactor for quenching of the reactants. Cooling is provided to the torch, the reactor and the collection using coils, baffles and jackets.

Abstract: An arc is drawn between a movable electrode (E) (preferably graphite), and a fixed electrode (7) in a furnace when smelting metal oxides using a plasma. Shielding gas, e.g. N. is introduced into plenum (P) about the movable electrode (E) to prevent metal vapor from settling on the inner lining (3;9) of the furnace (1). The movable electrode (E) may be connected to a mast (30) on the furnace roof (4) to align that electrode (E) in its path through a hole (10) in the roof (4) into the furnace chamber (C).

Abstract: For disposal of waste material including water, volatile components and vitrifiable components, the waste material is heated in a dehydrator to remove the water, heated in a high-temperature dryer to vaporize hydrocarbon liquids, and then fed to the focus point of a primary plasma reactor where plasma arc jets are focused on the surface of a pool of the vitrifiable components. At the focus point the vitrifiable components are melted, and the volatile components are volatized. The melted vitrifiable components are received in a quench chamber where they solidify on a quench roller and are broken into chips and delivered to a receiving area. Heat from the quench chamber is transferred to the dehydrator and high-temperature dryer. The hydrocarbon liquids and volatized components are fed to a secondary plasma reactor where they are disassociated into their elemental components.

Abstract: An apparatus for low temperature plasma treatment of powder particles for modifying the surface properties thereof, comprising means for the creation of a low pressure zone and, in association therewith, at least one cascade arc torch generator to form a plasma torch which is directed into said low pressure zone, means for the supply by gravity of powder particles to be treated into said low pressure zone and conduit means for the removal of the treated powder particles from said low pressure zone, said cascade arc generator having an orientation such that said plasma torch enters said low pressure zone at a downward angle (.alpha.) to the horizontal of from about 15.degree. to about 60.degree., and said conduit means being directed away from said plasma torch at an upward angle (.beta.) to the horizontal of from about 15.degree. to about 80.degree.

Abstract: A housing has a pair of chambers separated by a vertical wall. A hearth is on one side of the wall in the housing and is adjacent to an orifice which allows a stream of material, such as molten metal to pass from one chamber to the other. A gas is caused to flow through the orifice counter to the material flow by placing the other chamber at a higher fluid pressure than the one chamber. A blower coupled to the chambers provides the differential pressure. Molten metal is collected in a crucible in the other chamber. The gas flow moves through the orifice and forces impurities on the surface of the material to flow in reverse in the one chamber before the flow passes through the orifice.

Abstract: A plasma ashing apparatus has a vacuum treatment chamber for receiving therein a substrate coated with a resist film, a reactive gas introduction pipe equipped with a plasma applicator, a vacuum exhaust pipe, a heating means for heating the substrate, and two pieces of electrodes disposed in parallel to each other. One of the electrodes is a substrate electrode and the other thereof is a circular counter electrode. These two electrodes are commonly connected to an RF power source to thereby constitute a cathode electrode. Multiple concentric perforations are formed in the counter electrode except for a rib portion. A central perforation is formed in the center of the counter electrode. The concentric perforations are formed at every distance, from the center, equivalent to a diameter of the central perforation, while leaving circular electrode surfaces corresponding in width to a radius of of the perforation.

Abstract: In a method for plasma ashing a resist film coated on a substrate, the temperature of the substrate is controlled initially at temperatures below that at which explosion of the resist film occurs until a surface portion of a resist film has been removed. Thereafter, the substrate temperature is increased to remove the remaining portions of the resist film. An apparatus for conducting the method includes a plurality of supports, which may be movably disposed within a vacuum treatment chamber for moving the substrate away from a source of heat and for moving the substrate into contact with the heating source.

Abstract: Chemical waste is burned in oxygen using an electric plasma flame to heat a stream of gas which contains at least 70% by weight oxygen. Liquid waste in fine droplet form is introduced into the gas stream via a two-fluid atomizer using a carrier gas also preferably oxygen. The total amount of oxygen present is at least 30% more than required for complete combustion of the liquid waste. The reaction mixture is maintained at a temperature of at least 1450.degree. C. for a time of at least 2 milliseconds prior to cooling rapidly of the reaction products to a temperature below 300.degree. C.

Abstract: The device described serves to supply processing gas to an ionic implanter isolated from its environment by an electrically conductive enclosure connected to earth. Said gases are supplied by intermediate containers arranged permanently inside the enclosure and periodically filled from gas sources arranged outside, via pipelines which are at least partly insulated and pass through the enclosure. Each phase of filling the containers which is effected during the periods when the implanter is stopped, is followed by a gas evacuation phase through said pipelines. The invention overcomes the problems relating to the replacement of gas cylinders arranged around the enclosure in conventional installations.

Abstract: A method of preparing a melt for mineral fibre production wherein a mixture of mineral fibre-forming raw materials is introduced into a shaft furnace and is heated to melting temperature by a plasma gas stream formed in a plasma torch and wherein waste material from mineral fibre production is introduced into the plasma gas stream by a rotatable screw conveyor mounted in a feed pipe, the melt formed in the shaft furnace is being discharged from the bottom of the furnace and passed to a fiberizing apparatus in which it is converted into mineral fibres.

Abstract: A method of producing finely divided particles or powder, vapor or fine droplets comprises the steps of heating and melting the starting raw material in a vessel having opposed reflecting surfaces, and ejecting the melted raw material from the vessel as heated finely divided particles or powder, vapor or fine droplets, by introducing a carrier gas into the vessel.

Abstract: A high temperature reaction apparatus and method employing radiation to heat and react on matter, such as one or more fluids containing one or more reaction materials in gaseous molecular and/or particulate form. In a preferred form, one or more high temperature plasmas as formed across one or more pairs of electrodes which define a single or a plurality of plasmas and a single or plural reaction zones. A stream or streams of fluid particles pass through such reaction zone or zones and all or select of the particles or molecules thereof are heated to a high temperature sufficient to effect a select chemical and/or physical reaction or a plurality of high temperature reactions involving a plurality of reaction products which are separated from each other downstream of the reaction zone or zones. The apparatus and a method may be used to separate select atoms from molecules of a gas or gases passed through the reaction zone or zones by breaking the bonds between the atoms of the molecules of the gas.

Abstract: An electric furnace comprising a container having electrically isolated wall segments useful for melting materials, particlularly ceramics, is disclosed.The electric fornace's side walls are constructed from electrically isolated segments, which cause electric current from a plasma torch to be concentrated on the material in the furnace to be melted rather than diverted to the walls of the furnace.

Abstract: In a smelting unit comprising an arc furnace and at least one shaft-like charging material preheater which is arranged laterally on the furnace vessel of the arc furnace and the interior of which is connected in a region adjoining its bottom to the interior of the furnace vessel by way of a connecting zone, and in addition burners open in the lower region of the charging material preheater, in a sump mode of operation after the tapping step, of the amount of charging material which is required for the next bath of molten material, a part thereof is charged directly into the furnace vessel in order to reduce the smelting time. That part of the charging material is preheated in a preheating chamber which is connected downstream of the charging material preheater.

Abstract: A furnace for producing a melt for mineral wool production includes a shaft for preheating and melting of the raw material. A water-cooled grate is disposed in the bottom portion of the shaft, which supports a bed of ceramic filling bodies as well as the raw material. A combustion chamber is disposed underneath the shaft, which has a bottom portion for collecting the melt dripping from the shaft and an outlet for melt tapping. At least one main burner is disposed in the combustion chamber. Auxiliary burners are disposed above the grate. The bottom surface of the combustion chamber is larger, preferably 20 to 400% larger, than the transverse cross-sectional area of the shaft.

Abstract: A heating device including a body comprised of two or more strata of electrically conductive refractory particles, a supporting element of a refractory material between adjacent strata and an arrangement for passing an electrical current through the body.

Abstract: The instant invention relates to the use of hollow silicon carbide beams as refractory in substantially closed open-arc furnaces used for the carbothermic reduction of metal oxides. The silicon carbide beams are used in areas of the furnace which are exposed to temperatures higher than those tolerated by standard refractories, said areas requiring, in addition, stability to oxidation and reduction type chemical reactions and sufficient electrical resistance to minimize arcing from the exposed electrode. In addition, the invention relates to the use of silicon carbide beams in a two-stage, open-arc furnace for the carbothermic reduction of silicon dioxide to silicon metal.

Abstract: There is disclosed an arc reactor for treating a material in powder form conductive at very high temperatures, the reactor comprising a vertical electrically insulated sleeve cylindrical in shape, an upper electrode coaxially mounted with the sleeve at its upper end, a bottom electrode cooperating with the upper electrode, injectors for injecting a gas tangentially into the sleeve in order to create a vortex inside the same, a feed mechanism for introducing the powder material inside the sleeve near its upper end, so as to form a uniform cylindrical curtain of particles falling down into the sleeve, the particles being centrifugally projected against the internal wall of the sleeve by the vortex and entirely covering the internal wall while they are being simultaneously treated by the arc column, a crucible positioned under the sleeve to collect the treated particles in molten form that drip down from the sleeve, the molten material in use being in conductive contact with the bottom electrode, and a drive sys

Abstract: Excavatged landfill material is treated in a plasma fired cupola in a process wherein hazardous material such as PCB's are volatilized and consumed in an afterburner above the cupola and hazardous materials containing heavy metals are fixed in vitreous material made molten within the cupola and resulting in a non-leachable solid product.

Abstract: A method and device for forming a modifiable closed volume (16) by means of an extensible and retractable tubular element (16) fixed around the orifice of a sleeve (3) closed by a valve (5) on the upstream side of the valve, and detachably fixed around the nose (12) of the torch (4), and balancing the pressure in the volume (16) on the upstream side of the valve with the pressure prevailing on the downstream side of the valve by a device (20, S), opening the valve and reducing the volume (16) by advancing to the mounted position the nose (12) of the torch and locking the torch (4) on a sealing element (7) of the sleeve.

Abstract: The device for mounting and withdrawing a plasma torch in an apparatus at high pressure and temperature comprises in combination: at least one circular sealing element (2) interposed between the inner surface of a sleeve (3) and a nose (12) of the torch (4) and surrounding the nose, devices (6, 13) for balancing the pressures on each side of a valve (5) within the sleeve, and devices (18,23) for cooling the sealing element. The devices for balancing the pressures on each side of the valve comprise a communication pipe (6) by-passing the valve (5) and a tap valve (13) inserted in the pipe.

Abstract: A method of reducing "fall back" contamination caused by high intensity heating of metals is taught. Splatter, vapor droplets and particulate matter resulting from the high intensity heating is repelled to avoid return to the melt. An electric field is established above the heating zone to repel the vapor droplets and particles from at least one charged electrode disposed above the surface where high intensity heat is applied to a metal surface.

Abstract: A method and apparatus for heating molten steel in a steel making operation is disclosed, and which includes a refractory lined vessel having an open top, a removable cover adapted to overlie the top, and at least one plasma arc torch mounted so as to extend through the cover at an angle of about 60.degree.. The arc gas for the torch includes a substantial percentage of nitrogen, which permits a higher power level as compared to conventionally used argon, and the mass flow rate of the arc gas is maintained at a sufficiently high level to produce a continuous blast of gas which impinges at an angle upon any slag formed on the surface of the molten steel with sufficient force to move the slag and expose the underlying molten steel. As a result, the attachment of the arc to the underlying molten steel is facilitated, and the impingement of the gas contributes to the mixing of the steel to avoid heat stratification.

Abstract: An improved plasma torch having a rugged configuration, which is easier to start, and which eliminates the need for fragile and possibly metal contaminating insulators from the lower end of the plasma torch. To prevent double arcing from occurring and to enable the elimination of costly insulators from the nozzle area, the electrode and nozzle of the plasma torch of a first embodiment of the present invention are rotated as a unit at a speed in the range of 0 to 400 rpm. In a second embodiment of the invention, the nozzle assembly rotates relative to the electrode which is normally stationary. The electrode and nozzle could rotate in opposite directions as well. When the nozzle assembly is rotated, the resident arc time would be of such short duration due to the spinning of the nozzle that serious damage to the nozzle would not occur.

Abstract: A system and method for conditioning and recycling inert gases which are used in a plasma furnace. The method comprises the steps of receiving the gas that is output from the plasma furnace and cooling the gas to a desired temperature. Substantially all the dust is removed from the gas and then the gas is compressed to the desired pressure using an oil-flooded screw compressor. Any oil which is introduced by the compressor is removed from the gas and an alarm is provided to signal a high oil level. Substantially all water vapor in the gas is removed and the gas is filtered to remove any remaining dust and small particulates. The amounts of water vapor and oxygen in the gas are monitored. The gas is then recycled to the plasma furnace.

Abstract: A method of continuously overheating large volumes of gas wherein a gas flow is heated in a cylindrical pipe by means of an electric arc generated between two electrodes arranged in the pipe and axially spaced from each other, the gas being introduced in the tube at a speed of 15-100 m/s and supplied with a quantity of energy amounting to 0.1-0.5 kWh/m.sup.3.

Abstract: An auxiliary plasma arc fed by an auxiliary circuit serves for igniting a plasma arc, fed by a main circuit, of a plasma burner provided in a metallurgical furnace vessel.To increase the service lives of the burners, the electrode of the plasma burner and the melting stock charged in the furnace vessel are applied to the auxiliary circuit, with the main circuit switched off, and an auxiliary plasma arc is ignited between the plasma burner and the melting stock, whereupon the plasma burner is moved back from the melting stock, thereby lengthening the auxiliary plasma arc, and subsequently the main circuit is applied to the plasma burner and to the melting stock, and the plasma arc is ignited.

Abstract: An improved plasma arc reactor is provided with variably positionable electrodes, including a cylindrical anode electrode having an inner, frustoconical cavity providing a reaction chamber and a spherical cathode ball electrode mounted therein. Between these electrodes an arc discharge is induced and sustained to heat and ionize an inert gas to produce an arc plasma for refining raw material introduced into the reaction chamber. A magnetic induction coil is mounted around the outer diameter of the anode electrode to thereby establish a magnetic field to rotate the arc discharge and plasma within the reaction chamber.

Abstract: A plant for the production of steel from scrap and optionally fluxes includes a shaft furnace section having a bottom to receive a liquid sump of premelt and heating means laterally entering into the lower part of its interior. A hearth type furnace section is integrally connected with the shaft furnace section, into which the premelt is transferable from the shaft furnace section.

Abstract: A method and apparatus for heating molten steel in a steel making operation is disclosed, and which includes a refractory lined vessel having an open top, a removable cover adapted to overlie the top, and at least one plasma arc torch mounted so as to extend through the cover at an angle of about 60.degree.. The arc gas for the torch includes a substantial percentage of nitrogen, which permits a higher power level as compared to conventionally used argon, and the mass flow rate of the arc gas is maintained at a sufficiently high level to produce a continuous blast of gas which impinges at an angle upon any slag formed on the surface of the molten steel with sufficient force to move the slag and expose the underlying molten steel. As a result, the attachment of the arc to the underlying molten steel is facilitated, and the impingement of the gas contributes to the mixing of the steel to avoid heat stratification.

Abstract: A plasma burner comprises an electrode holder which carries a tubular outer electrode and a coaxially arranged central electrode, and an electrical current supply source, which can be coupled via current feeders to the outer and central electrodes respectively. Also a device is provided for feeding gas into the region of the electrodes, between which an arc is produced for plasma formation. The tubular outer electrode has a first cooled, arc-inactive tube section, consisting of electrically conductive metal, and an adjoining second arc-active uncooled tube section, which consists of heat-resistant and electrically conductive material, and which is releasably connected to the first tube section. The arc passes between the second tube section and the neighboring arc-active section of the coaxial central electrode.

Abstract: The invention relates to a device for facilitating the connection of burners, especially plasma generators, to reactor tuyeres in vertical furnaces for metal oxide reduction with simultaneous sealing of the vertical furnace, composed of a sealing ring (13) with a unit for the supply of a protective gas (10, 17, 18, 19). In this case the sealing ring (13) is constructed radially movable in a seat (12).

Abstract: A furnace for the sintering of refractory or ceramic materials using plasma heated gases. The furnace comprises a sintering chamber with strategic positioning of the plasma torch inlets and exhaust outlet, a furnace temperature controlling device during sintering so that the article being sintered does not decompose. The devices which can be used for controlling the temperature of the furnace during sintering include: (1) Tangential injection of a secondary colder gas stream into the hot primary plasma gas stream; (2) Utilization of a plasma torch or torches which can be temperature controlled to achieve stable and lower plasma gas temperatures; and (3) Introduction of a secondary cooler gas directly into the furnace sintering chamber.

Abstract: A process for the sintering of silicon carbide refractory or ceramic articles using plasma arc gases. In the process of the invention, a formed silicon carbide article is heated in a plasma fired furnace to a sintering temperature of between 2000.degree. C.-2500.degree. C. at a heating rate of 300.degree. C./hr-2000.degree. C./hr, and held at the sintering temperature for 0.1-2 hours. The enthalpy of the plasma gas is 2000 BTU/lb-4000 BTU/lb, when nitrogen is used as the plasma gas. The total cycle time for the process of the invention, including cooling and loading, is 1.5-20 hours. Silicon carbide articles, produced in accordance with the invention, have high strength, high density, high corrosion resistance and high dimensional stability.

Abstract: An improved process for sintering extruded powder shapes comprising drying or calcining an extruded shape in a microwave furnace and rapid sintering the shape in a plasma fired furnace. Alternatively, calcining or drying may take place within a furnace heated by the plasma furnace's exhaust. The process of the invention is especially useful for silicon carbide extruded materials and for tubular shapes. This process significantly reduces sintering times and costs. Use of the process yields a high strength sintered product.

Abstract: A system to prevent, retard or reverse the decomposition of silicon carbide articles during high temperature plasma sintering. Preferably, the system comprises sintering a silicon carbide refractory or ceramic green body in a closed sintering environment, such as a covered crucible, with strategic placement of the plasma torch or torches, exhaust outlet and crucibles. As sintering proceeds, a silicon vapor pressure builds up within the crucible, retarding the decomposition of the silicon carbide body. The plasma torch, exhaust outlet, and crucibles are positioned so that buoyant convective flow is maximized to increase the heat transfer and energy efficiency. In another embodiment, a "sacrificial" source of silicon carbide is placed into the sintering furnace. The silicon carbide in the sacrificial source starts to decompose before the silicon carbide refractory or ceramic article, creating a supersaturated atmosphere of silicon vapor species in the furnace.