MXPA01000176A - High temperature rotating vacuum kiln and method for heat treating solid particulate material under a vacuum - Google Patents

Abstract

A rotating vacuum kiln (1) and method for heat treating solid particulate material under vacuum conditions uses a rotating refractory metal cylindrical vessel (2) with a cool inlet zone (3), hot intermediate zone (6), and cool exit zone (7), with a first series of inner radiation shields (25) provided at the hot intermediate zone adjacent the cool inlet zone (5) and a second series of inner radiation shields (29) provided at the hot intermediate zone (6) adjacent the cool exit zone (7) to protect those two zones from the high temperatures in the hot intermediate zone. Heat for the hot intermediate zone of the cylindrical vessel is provided indirectly by electrical resistance heaters (35) that surround the vessel and outer radiation shields (37, 38) are provided about the heaters to direct heat to the cylindrical vessel.

Description

A HIGH TEMPERATURE ROTATING OVEN TO THE VACUUM AND THE METHOD OF TREATMENT OF MATERIAL IN SOLID PARTICLES BY VACUUM HEATING FIELD OF THE INVENTION The present invention relates to a rotary vacuum oven and to a method for the treatment of solid particulate material under high temperature and high vacuum conditions.

BACKGROUND OF THE INVENTION Solid particulate material must sometimes be vacuum treated at elevated temperatures in order to provide a desired product. In the manufacture of tantalum powders, for example, for use in capacitors, in one or more steps when processing the powder it is heat treated in a vacuum cooker. Such treatment should be used to remove residual impurities and to provide a flowable powder. A current processing system involves placing a stack of trays containing tantalum powder in a vacuum cooker and heating everything% the assembly of trays. After a comparatively short heat treatment, in such a batchwise treatment, the entire tray assembly is cooled and a small amount of air is admitted until a layer of tantalum oxide has formed on the surfaces of the powder particles. In order to avoid pyrophoric combustion of the powder after subsequent exposure to air. Such treatment consumes time and energy and requires expensive equipment. Also, the geometry of the fixed bed of the treatment results in material near the outside of the bed that heats up faster and to a greater degree than the material in the bed. middle part of the bed of the stack of trays. Thermal transfer is also slow. In addition, because the material on the outside of the bed is heated more than the inside, a non-uniform clumping may occur. A The non-uniform product can result in different portions of the load with different physical properties from those of another. If the material inside does not coalesce sufficiently, the resulting product is fragile and a large proportion of this material becomes dust during the subsequent handling of the product. Such dust or fine particles must be recycled for reprocessing. It is an object of the present invention to provide an apparatus for the high temperature treatment of solid particulate material, while under vacuum, by the use of a rotary kiln which will provide a more uniform thermally treated product. It is another object of the present invention to provide a method for the continuous high temperature treatment of solid particulate material, such as tantalum powder, while under vacuum, using a rotary kiln in order to provide a more uniform thermally treated product.

BRIEF DESCRIPTION OF THE INVENTION A vacuum rotary kiln has a revolving cylindrical refractory metal vessel that includes a cold inlet zone, a hot intermediate zone, and a cold outlet zone. A gaseous exhaust conduit extends through a front wall of the cylindrical vessel through the cold outlet zone and into the hot intermediate zone. An f >is provided The first series of internal radiation shields in the cylindrical vessel in the hot intermediate zone adjacent to the cold inlet zone, and a second series of internal radiation shields in the hot intermediate zone adjacent to the cold outlet zone is provided. A first vacuum housing includes a supply conduit that directs solid particulate material to the cold inlet region of the cylindrical vessel while it is under vacuum, while a second vacuum housing includes a discharging conduit to discharge the treated material from the cylindrical housing while it also finds emptiness. The solid particulate material is moved through the cylindrical refractory metal vessel by the use of screw passages attached to the inner surface of the vessel wall or when tilting the vessel in order to allow flow by gravity. The hot intermediate zone of the cylindrical vessel is indirectly heated by electric resistance heating bands which are provided, spaced from and through the hot intermediate zone, while the outer radiation shields surround the heating bands and the cylindrical vessel along the intermediate zone callente. The use of heating bands, radiation shields, and the first and second series of internal radiation shields, concentrate the heat in the intermediate zone of the cylindrical vessel and shield the cold entry zone, the cold exit zone, and the associated mechanical equipment, such as drive equipment and support equipment, from the elevated temperatures of the hot intermediate zone. One method for heating a solid particulate material to elevated temperatures includes providing a rotatable cylindrical refractory metal vessel having a cold inlet zone, hot intermediate zone, and cold outlet zone, with a first series of internal radiation shields in the intermediate zone. hot adjacent to the cold inlet zone and a second series of internal radiation shields in the hot intermediate zone adjacent to the cold outlet zone. The solid particulate material is moved through the revolving cylindrical refractory metal vessel while it is under vacuum from the cold inlet zone and is heated to a temperature between about 1000 ° to 1700 ° C in the hot intermediate zone and then discharged of the cold exit zone of the revolving cylindrical vessel of the refractory metal.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be easily understood by reference to the following description of the embodiments thereof and the accompanying drawings, wherein: Figure 1 is a longitudinal sectional view of a rotary cylindrical metal refractory cup rotary vacuum oven of the present invention; Figure 2 is a longitudinal sectional view through another embodiment of a rotary vacuum oven of the present invention; Figure 3 is a view taken along lines 111-111 of Figure 2; Figure 4 is a view taken along lines IV-IV of Figure 2; and Figure 5 is a schematic view of the rotary vacuum oven of Figure 1 illustrating the systems for feeding and discharging vacuum material.

DETAILED DESCRIPTION OF THE PRESENT INVENTION The rotary vacuum oven of the present invention allows the heating of solid particulate material at an elevated temperature, to heat-treat or bind under high vacuum conditions. Referring now to the drawings, Figure 1 illustrates one embodiment of a rotary vacuum furnace 1 of the present invention having a rotating cylindrical vessel 2 having an inner wall 3 and an outer wall 4, the refractory cylindrical metal vessel 2 which it has a cold inlet zone 5, a hot intermediate zone 6, and a cold outlet zone 7. A means 8 is provided for charging a solid particulate material in the cold inlet zone 5 of the cylindrical vessel 2, such as a conduit feed 9, which feeds the material to a mixing and charging conduit 10 attached to the cylindrical vessel 2, which communicates with the cold inlet zone 5, the supply conduit 9 and the mixing and charging conduit 10 that is included in a first vacuum housing 11. The mixing and charging duct 10 includes an inclined wall 12 on the cylindrical vessel 2 that acts as a dam to prevent the solid particulate material from escaping from the mixing and charging duct. 10 instead of moving towards the cold inlet zone 5 of the cylindrical vessel 2, whose inclined wall 12 receives and includes the discharge end 13 of the supply conduit 9. The supply conduit 9 also has an outward flared cut 14 in the upper end to receive the solid particulate material. The cold exit zone 7 of the cylindrical vessel 2 has a front wall 15 with a gaseous exhaust conduit 16 passing through the wall 15, and a discharge conduit 17 communicating with the cylindrical vessel 2 in the exit zone cold 7, the discharge conduit 17 having an open receiving end 18 within the cold exit zone 7 for receiving the solid material thereof and a discharge end 19 for discharging the solid material therefrom. The discharge end 19 of the discharge conduit 17 is included in a second vacuum housing 20. Extending through the front wall 15 of the cylindrical vessel 2, the gaseous exhaust conduit 16 receives gases from the cylindrical vessel 2 and passes the same to a gaseous discharge conduit 21, while the gas discharge conduit 21 is connected to a vacuum line 22 which, in turn, is connected to a vacuum pump 23. The gaseous exhaust conduit 16 is preferably concentric with a ee a_ of the cylindrical vessel 2, extends through the cold exit zone 7, and has an open end 24 placed in the hot intermediate zone of the cylindrical vessel 2. A first series of interior radiation shields 25 is provided in the region hot intermediate 6 adjacent to the cold inlet zone 5 of the cylindrical vessel 2 in order to reduce the thermal flow of the hot intermediate zone 6 towards the cold inlet zone 5 of the cylindrical vessel 2. The first mere series of interior radiation shields 25 are secured to the interior wall 3, such as by gauges 27 (Figure 2) that extend to the interior wall and are welded, as in 28 to the inner wall 3. A second series of interior radiation shields 29 is provided in the hot intermediate zone 6 adjacent to the cold outlet zone 7 of the cylindrical vessel 2 in order to reduce the thermal flow from the zone intermediate 6 towards the cold exit zone 7. The second series of interior radiation shields 29 are secured to the exterior wall 31 of the gaseous exhaust duct 16, such as by welds 32. The second series of interior radiation shields 29 shields the cold exit zone 7 of the elevated temperatures of the hot intermediate zone 6 of the cylindrical vessel 2. A series of short screw passages 33 can be provided in the cold inlet zone 5, the hot intermediate zone 6 and the cold outlet zone 7 , secured to the inner wall 3 such as by welds 34, in order to move the solid material through the cylindrical refractory metal vessel. The hot intermediate zone 6 of the cylindrical vessel 2 is heated by the use of an indirect heat source, such as electrical resistance heating bands 35 which are spaced from and encircle the outer wall 4 of the cylindrical vessel 2. The bands of heating 35 extend along the length of the intermediate hot zone 6 and are energized by an electric current supplied from a source (not shown) through electric wires 36. In order to concentrate and direct the heat of the electrical heating bands 35 towards the outer wall 4 of the cylindrical vessel 2, at least one radiation shielding 37 and preferably a series of radiation shields 37a to 37f are provided, which are placed concentrically around and spaced from the bands of electrical heating 35 and the hot intermediate zone 6 of the cylindrical vessel 2 and enclose and include them. The radiation shields 37a-37f are included within a shield housing 38. The cold inlet zone 5 of the cylindrical vessel 2 can be provided with the series of short screw passages 33 of the inlet area which are secured to the wall interior 3, such as by welds 34, and extending from inner wall 3 and serving to move the solid particulate material from the mixing and charging duct 10 to the hot intermediate zone while a plurality of directed mixing flanges inwardly 39 can be provided on the inner wall 40 of the mixing and charging duct 10 to mix the solid particulate material fed thereto and charge it to the short screw passage of the inlet zone 33. Because the intermediate hot zone 6 of the cylindrical vessel 2, the heating bands 35 and the radiation shields 37 are contained in the shield housing 38 and the first series of rad shields. In the interior 25 and the second series of interior radiation shields 29 retain heat within the hot intermediate zone, water cooled coil cuts 41 can be used to include the outer wall 4 of the cold inlet zone 5 and the exit zone cold 7, and the coil cuts can be made from a less expensive ferrous alloy than a refractory metal such as is required for the cylindrical vessel 2. The cylindrical vessel 2 can be rotated such as by the use of an engine 42, which it has an ee 43 with gears 44"which engage with an annular gear 45 driven by the cylindrical beaker 2, with the gears 44 contained within the first vacuum housing 11 and the shaft 43 passing through a seal 46 secured in a wall of the accommodation. The front wall 15 of the cylindrical vessel 2 and the outer end 47 of the gaseous exhaust conduit 15 are also included in a third vacuum housing 48, with the discharge conduit 19 passing through the lower wall 49 of the third vacuum housing 48 towards the second vacuum housing 20. The gaseous exhaust conduit 16 preferably has a plurality of dampers 50 connected to the interior wall 51., such as by welds 52 which are displaced and spaced from one another along the horizontal axis a_ in order to provide a tortuous path for gases to flow therethrough. In order to maintain the interior 1 of the cylindrical vessel 2 under vacuum, while treating the solid particulate material therein, the vacuum source, the vacuum pump 23, pulls a vacuum through the vacuum line 22, the gas discharge conduit 21, the gaseous exhaust conduit 16, the interior i_ of the cylindrical vessel 2, the second vacuum housing 20, and the first vacuum housing 11, with seals and bearings provided where necessary in order to maintain the leaks within acceptable limits, as experts in the field know. To help maintain the vacuum in the system, and particularly the interior i_ of the cylindrical vessel 2, a series of hermetically sealed hoppers and leak-tight hoppers are provided, as shown in Figure 5. As illustrated schematically, for loading the cylindrical vessel 2, the solid particulate material to be treated is fed through a feed line 53, through a sealed inlet valve 54, to an initial feed duct 55, contained in a first feed housing 56 having a feeder 57 which cooperates with a second sealed valve 58. The second sealed valve 58 feeds a second feeder conduit 59 which is contained within a first blanked vacuum feed housing 60 which is connected through the line 61 to a vacuum source, such as pump 62, and which has a feeder 63 that cooperates with a third hermetic valve to 64. The third hermetic valve 64 is connected to an intermediate feed conduit 65 contained in an intermediate feed housing 66 having an intermediate element 67 and which cooperates with a fourth airtight valve 68. The fourth sealed valve 68 feeds to an additional supply conduit 69 which is contained in a housing 70 which is connected through line 71 to a vacuum source, such as pump 72, and which has a feeder 73 which cooperates with an airtight valve 74 which cooperates with the first housing 11 in order to feed solid particulate material therefrom through an outward flared cut 14 to the supply conduit 9 and then to the cold inlet zone 5 of the cylindrical beaker 2. To discharge the solid particulate material of the cylindrical vessel 2, the treated material is fed by rotating the cylindrical vessel 2 towards the open end 18 of the discharge conduit 17 in the second vacuum housing 20, and through a first sealed discharge valve 75 in the intermediate discharge conduit 76 contained in a housing 77 having an intermediate discharge feeder 78 which cooperates with a second airtight discharge valve 79. The second valve The sealed discharge 79 feeds a second discharge conduit 80 which is contained in the discharged discharge housing 81 which has a discharge line 82 to reduce the volume in the discharged discharge housing 81 through the reduction valve 83 , and having a discharge feeder 84 which cooperates with the final discharge seal valve 85 to discharge the material from the system. The operation of the rotary kiln 1 of the present invention is as follows. With the motor 42 activated, the cylindrical vessel 2 is rotated by means of gears 44 engaging with the annular gear 45 and after activation of the vacuum pump, the system including the vacuum line 22, the gas discharge conduit 21 , the interior of the housing 50, the gaseous exhaust duct 16, the discharge duct 17, the interior of the second discharge housing 20, the interior? of the cylindrical vessel 2, the mixing and charging duct 10, and the interior of the First vacuum housing 8 is placed under vacuum as desired for a particular treatment. The electric heating bands 35 are activated to heat the hot intermediate zone 6 of the cylindrical vessel 2 to the desired temperature, while the radiation shields 31 retain such heating. In this step, the solid particulate to be treated is provided in an additional supply duct 69, with the interior of the housing 70, with the sealed valves 68 and 74 closed, subjected to a vacuum comparable to that found inside the cylindrical vessel 2. , by means of the vacuum pump 72. After opening the hermetic valve 74, the solid particulate material is fed by the feeder 73 to the supply duct 9 through the outward flared cut 14 and passes by gravity through the duct feed 9 to the mixing and charging duct 10. In the mixing and charging duct 10, which is connected to, and is rotating with, the cylindrical vessel 2, the solid particulate material is mixed, in contact with and drumming by the flanges 39 on the inner wall 40, while the inclined wall 12 prevents the material from escaping and drains the material towards the cold inlet zone 5 of the cylindrical vessel 2. The material solid ticulate in the cold inlet zone 5 moves through the short screw passages 33 of the inlet area towards, and through, the hot intermediate zone 6, and move it through the hot intermediate zone 6, while being heated the material at the desired temperature. The hot material is then transferred, via intermediate short screw passages 33, to the open receiving end 18 of the discharge duct 17, with the hot material then fed to the discharge duct 17 to the housing 20 for discharge of the system. During the operation of the rotary kiln, the first series of interior radiation shields 25 shields the cold inlet zone 5 from the high temperature of the hot intermediate zone 6, while the second series of interior radiation shields 29 shields the exit zone cold 7 of that elevated temperature. The present method uses the rotatable cylindrical refractory metal vessel 2 described above in the thermal treatment of the solid particulate material. The solid particulate material is charged, under vacuum, to the cold inlet zone 5 of the revolving cylindrical refractory metal vessel 2, which has a cold inlet zone 5, hot intermediate zone 6 and cold outlet zone 7, and a first series of radiation shields 25 in the hot intermediate zone 6 adjacent to the cold inlet zone 5, and a second series of radiation shields 29 in the hot intermediate zone 6 adjacent to the cold outlet zone 7. The solid particulate material is moves through the revolving cylindrical vessel of refractory metal 2 while it is under vacuum and heating in the hot intermediate zone 6a a temperature of between approximately 1000 ° to 1700 ° C in the intermediate hot zone 6 and is discharged after the exit zone Cold 7. The heat treatment of the solid particulate material according to the present invention is carried out under vacuum conditions and can be carried out in a vacuum below approximately 0.001 Torr and as low as approximately 10 ~ 4 Torr or below, with residence times in the warm intermediate zone 6 from about 0.3 to about 2.0 hours. With the use of the first and second series of radiation shields 25 and 29, with temperatures between about 1000 ° - 1700 ° C, preferably 1400 ° - 1600 ° C in the hot intermediate zone 6, temperatures in the area cold inlet 5 and cold outlet zone 7 would be approximately 300 ° C or below. When the tantalum powder is heat treated, for example, temperatures in the range of 1500 ° C in the hot intermediate zone 6 are required and the cylindrical refractory metal vessel 2 would be composed of a refractory metal, such as molybdenum, tantalum , tungsten, or a refractory metal alloy such as a molybdenum alloy containing small amounts of titanium and zirconium. The term refractory metal, as used herein, is used to designate a metal that will last for sufficient periods of time at temperatures in the range of up to about 1700 ° C without harmful effects. For example, where the tantalum is treated, the cylindrical vessel could be formed from a molybdenum alloy containing small amounts of titanium and zirconium, with an inner coating of tantalum which would contact the hot particulate material by being treated through the cylindrical vessel , and with passages of tantalum screws welded to the inner lining of the cylindrical vessel wall and welded by points to each other in order to avoid differential expansion problems. A preferred embodiment would be "TEM", which is a molybdenum alloy with about 0.5% by weight of titanium and 0.08% by weight of zirconium. A preferred coating material is tantalum when the tantalum powder is processed. Other powders can also be processed in the rotary vacuum oven according to the present invention. For example, other valve metal powders can be processed in a manner similar to that used in the processing of tantalum powder. The niobium powders can also be processed in the rotary vacuum oven according to the process of the present invention, similar to that used to process the tantalum powder. In accordance with the present invention, additives or impurities can be added to a particulate material before, during, and / or after the treatment of the material in the rotary vacuum oven of the present invention. Preferably, the impurities used to control the agglutination and / or agglomeration of the particulate material are mixed with the material before its introduction into the rotary vacuum oven. Instead one or more impurities can be added directly to the rotary kiln separated from the introduction of the particulate material to the kiln. If added directly to the furnace, the feeding device for the impurotator preferably operates under the same conditions as the high vacuum that exists inside the rotary kiln. For example, impur i f icatere s directly added to the furnace can be fed by a gravity feed system. The impuricants that can be used to control the agglutination and / or agglomeration of the particulate material treated with the rotary vacuum oven include phosphorus, nitrogen, carbon, silicon, boron, and sulfur and the like. These impurities, and the introduction of these impurities in the particulate material, are described in the U.S. Patent. No. 5,448,447 to Chang, which is incorporated herein in its entirety for reference. Phosphorus is a preferred impurity for tantalum, niobium, and other valve metal powders which agglutinate and agglomerate in the rotary vacuum oven of the present invention. The impurity can be provided in any variety of ways, liquid forms being preferred according to some embodiments of the present invention. If phosphorus is used as impurity, it is preferably supplied as phosphoric acid or in the powdered form of NH4PF6. The amount of impurifier to be added to the particulate material before or during the agglutination is preferably sufficient to control the agglutination and agglomeration of the particulate material and provide a particulate material with flowability without interfering noxiously with the performance of a capacitor made from the resulting treated material. For example, phosphorus impurities are preferably employed in an amount to achieve a final phosphorus content in the treated material of from about 50 or less to about 200 parts per million (ppm) or more by weight of elemental phosphorus based on the total weight of the treated material. Other ranges of phosphorus and nitrogen impuri fi ers are described in the U.S. Patent. No. 5448,447. If nitrogen is used as the impuritator, the impuritator can be added before, during, and / or after the treatment of the particulate material in the rotary vacuum furnace of the present invention. If it is provided in the form of nitrogen gas, the gas is preferably introduced in an upstream flow in relation to the flow of the particulate material through the rotary vacuum furnace. Preferably, no gaseous dopant is introduced into the rotary vacuum furnace during agglutination so that conditions are maintained at high vacuum inside the furnace. Nitrogen fouling can occur simultaneously with oxygen passivation after agglutination of a particulate material. The residence time of a particulate material to be treated in the cylindrical vessel 2 can be adjusted as desired by the degree of inclination, height and speed of rotation of the cylindrical vessel. In some cases, as shown in Figure 1, the use of bolt passages 33 should be avoided if the cylindrical vessel is placed at a downward angle from the cold inlet zone 5 to the cold exit zone 7 and the the material assumes its natural angle of erosion under the rotation, and the material will move the same through the cylindrical vessel.

The feeding of the cylindrical vessel 2 is carried out by feeding the solid particulate material through the feed line 53 and through the open valve 54 towards the hopper or initial supply conduit 55 at atmospheric pressure. The valve 54 is then closed and the material is transferred through the feeder 57 through the open valve 58 to the second supply conduit. With valve 58 and valve 64 in closed position, a partial vacuum is provided in housing 59 through line 61 by activating the pump in vacuum 62. When the desired partial vacuum is reached, valve 64 is opened. and the feeder 63 feeds the material to the intermediate transfer supply conduit 65. The valve 64 is then closed and the valve 68 is opened, and the material, under partial vacuum, is fed by the intermediate feeder 67 to an additional supply conduit. 69. With the valves and with the vacuum pump 72 activated, a vacuum is applied that approaches the desired high vacuum in the cylindrical vessel and the feeder 73 is used to discharge the material to the supply conduit 9 through the flared cut 14 In the heat treatment of tantalum powder, a vacuum in the cylindrical refractory metal vessel of approximately 0.001 Torr or below shall be provided. During the discharge of the treated material from the cylindrical vessel, an inverse procedure is carried out, in which the solids treated from the cylindrical vessel are discharged therefrom through the discharge conduit into a second vacuum housing 20. With the second valve When the discharge valve 79 is closed, the first discharge valve opens and the material is fed into the intermediate discharge conduit 76. The first discharge valve 75 is then closed and the second discharge valve 79 is opened as the material is fed. by the intermediate discharge feeder 78 to the second discharge conduit 80. With the final discharge valve 85 in the closed position, then the second discharge valve 79 is closed and the vacuum is released through the line 82 and the valve of reduction 83. The material must be discharged in a rotating drum (not shown) at atmospheric pressure where the cooling and activation will take place. With the vacuum released, and a small amount of air injected to form an oxidized coating on the material, the final discharge valve can then be opened and the treated material removed for use.

Claims (22)

1. CLAIMS Having described the invention as an antecedent, what is claimed as property is contained in the following indications: 1. A rotary vacuum oven caterized because it comprises: a revolving cylindrical refractory metal vessel having inner and outer walls, an entrance area cold, a hot intermediate zone and a cold exit zone; means for charging the solid particulate material for heating in said cold inlet zone while it is under vacuum; means for discharging said material after heating said cold exit zone while it is under vacuum; means for moving the solid particulate in one direction of the loading means towards the discharge means; a first series of interior radiation shields in the cylindrical vessel in said hot intermediate zone, adjacent to said cold inlet zone, and a second series of interior radiation shields in said hot intermediate zone adjacent said cold discharge zone; a gaseous exhaust duct extending towards said cold exit zone and at least partially towards said hot intermediate zone to remove the gases and vaporized material thereof; means for indirectly heating said hot intermediate zone; and radiation shields surrounding the cylindrical refractory metal vessel along said hot intermediate zone.
2. 2. The rotary vacuum oven according to claim 1, characterized in that said first series of internal radiation shields are converted into the inner wall of said cylindrical refractory metal vessel.
3. 3. The rotary vacuum oven according to claim 1, characterized in that said second series of internal radiation shields is connected to an outer surface of said gaseous exhaust conduit.
4. The rotary vacuum oven according to claim 1, characterized in that said means for moving the particulate material in a direction of the loading means towards the discharge means comprises a series of bolt passages attached to the inner wall of the cylindrical vessel.
5. 5. The rotary vacuum oven according to the rei indication 1, characterized in that said gaseous exhaust conduit extends towards said hot intermediate zone and said second series of screw passages extending from the inner wall of said cylindrical vessel to a place closely adjacent an outer wall of said gaseous exhaust conduit.
6. 6. The rotary vacuum oven according to claim 1, characterized in that said means for heating said hot intermediate zone comprises electric resistance heaters spaced from and around the outer wall of said indipendent vessel.
7. 7. The rotatable vacuum oven according to claim 6, characterized in that said radiation shields are a plurality of radiation shields which are spaced from each other and spaced from and enclosing and include said electric resistance heaters.
8. 8. The rotary vacuum oven according to claim 1, characterized in that the interior of said cylindrical vessel is kept under vacuum by a vacuum pump which cooperates through a housing with said gaseous exhaust conduit.
9. 9. A rotary vacuum oven according to claim 1, characterized in that it includes a first housing which includes a charging conduit attached to said cylindrical vessel and which feeds the solid particulate material towards said cylindrical vessel in the cold entry zone of said vessel cylindrical.
10. A rotary vacuum oven according to claim 9, characterized in that it includes an inclined wall in said loading duct in said inlet area surrounding the discharge end of a feed duct, and a plurality of inwardly directed mixing flanges. on the inner wall of said loading conduit between said inclined wall and said cold inlet zone.
11. 11. A rotary vacuum oven according to the indication 1, characterized in that said means for discharging said solid material, after heating, from said cold outlet zone includes a discharge conduit having an open receiving end in said cold outlet zone and a discharge end that discharges said solid material into said outlet. a download hosting.
12. A rotary vacuum oven according to claim 1, characterized in that it includes a plurality of interconnected and hermetic feed hoppers to which the solid particulate material to be treated is fed and through which said particulate material passes while it is subjected to a increased vacuum before being charged to a feed conduit for said cylindrical vessel.
13. 13. A rotary vacuum oven according to claim 1, characterized in that it includes a plurality of interconnected and hermetic discharge hoppers through which passes the material discharged from said cylindrical vessel while it is subjected to a vacuum reduction before discharging of the same
14. 14. A rotary vacuum oven according to claim 1, characterized in that said refractory metal of the cylindrical beaker is a molybdenum alloy containing small amounts of titanium and zirconium.
15. 15. A rotary vacuum oven according to claim 14, characterized in that an inner tantalum coating is provided on the inner wall of said cylindrical vessel, and the tantalum composite screw passages are welded to said tantalum coating.
16. 16. A rotary vacuum oven characterized in that it comprises: a revolving cylindrical refractory metal vessel having inner and outer walls, a cold inlet zone, a hot intermediate zone and a cold outlet zone; means for charging the solid particulate material for heating in said cold inlet zone while it is under vacuum; means for discharging said material after heating said cold exit zone while it is under vacuum; a series -% of internal radiation shields attached to the inner wall of the cylindrical vessel, in said hot intermediate zone, adjacent to said zone, of cold entry; a second series of radiation shields placed in the cylindrical vessel in said hot intermediate zone, adjacent to said cold outlet zone; series of bolt passages attached to the inner wall of the cylindrical vessel adapted to move the solid particulate material in a direction from the loading means to said discharge means; a gaseous exhaust duct extending towards said cold exit zone and at least partially towards said hot intermediate zone to extract the gases and the vaporized material thereof; electric resistance heaters that are spaced from and around the outer wall of said cylindrical vessel along the hot intermediate zone; and a plurality of outer radiation shields which are spaced apart from one another and spaced from, and which encircle and radially include the electric resistance heaters.
17. 17. A method for heating a solid particulate material at a temperature of 1000 ° to 1700 ° C under vacuum characterized in that it comprises: producing a rotating cylindrical refractory metal vessel having inner and outer walls, a cold inlet zone, an intermediate zone hot, and a cold outlet zone, a first series of interior radiation shields in said hot intermediate zone adjacent to said cold inlet zone and a second series of interior radiation shields in said hot intermediate zone adjacent to said cold outlet zone; moving the solid particulate material through said revolving cylindrical refractory metal vessel while it is under vacuum; heating said solid particulate material at a temperature of 1000 ° to 1700 ° C in said hot intermediate zone; and discharging said heated solid particulate material from said heated solid particulate material from said cold exit zone.
18. 18. The method according to the indication 17, characterized in that said vacuum is at 0.001 Torr or below.
19. 19. The method according to claim 17, characterized in that said solid particulate material is tantalum powder.
20. The method according to claim 19, characterized in that said vacuum is at 0.001 Torr or below.
21. The method according to claim 19, characterized in that the residence time of said tantalum powder in the hot intermediate zone is between about 0.3 to 2.0 hours.
22. 22. The method according to the rei indication 19, characterized in that said temperature is from approximately 1400 ° to approximately 1600 ° C.