WO2000067936A1 - Poudres metalliques obtenues par reduction d'oxides au moyen de magnesium gazeux - Google Patents

Poudres metalliques obtenues par reduction d'oxides au moyen de magnesium gazeux Download PDF

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Publication number
WO2000067936A1
WO2000067936A1 PCT/US1999/009772 US9909772W WO0067936A1 WO 2000067936 A1 WO2000067936 A1 WO 2000067936A1 US 9909772 W US9909772 W US 9909772W WO 0067936 A1 WO0067936 A1 WO 0067936A1
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WIPO (PCT)
Prior art keywords
powder
metal
oxide
tantalum
niobium
Prior art date
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PCT/US1999/009772
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English (en)
Inventor
Leonid N. Shekhter
Terrance B. Tripp
Leonid L. Lanin
Karlheinz Reichert
Oliver Thomas
Joachim Vieregge
Original Assignee
H.C. Starck, Inc.
H.C. Starck Gmbh & Co. Kg.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
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Publication date
Priority to BRPI9911008A priority Critical patent/BRPI9911008B1/pt
Priority to US09/445,331 priority patent/US6558447B1/en
Priority to BRPI9917635A priority patent/BRPI9917635B1/pt
Priority to PCT/US1999/009772 priority patent/WO2000067936A1/fr
Priority to JP2000616950A priority patent/JP4202609B2/ja
Priority to BR9911008-3A priority patent/BR9911008A/pt
Priority to UA2000126988A priority patent/UA67779C2/uk
Priority to CA2331707A priority patent/CA2331707C/fr
Application filed by H.C. Starck, Inc., H.C. Starck Gmbh & Co. Kg. filed Critical H.C. Starck, Inc.
Priority to AU58965/99A priority patent/AU757790B2/en
Priority to IL13906199A priority patent/IL139061A/en
Priority to DE69940030T priority patent/DE69940030D1/de
Priority to EP99946575A priority patent/EP1144147B8/fr
Publication of WO2000067936A1 publication Critical patent/WO2000067936A1/fr
Priority to HK02100530.5A priority patent/HK1039087B/zh

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
    • H01G9/00—Electrolytic capacitors, rectifiers, detectors, switching devices, light-sensitive or temperature-sensitive devices; Processes of their manufacture
    • H01G9/004—Details
    • H01G9/04—Electrodes or formation of dielectric layers thereon
    • H01G9/048—Electrodes or formation of dielectric layers thereon characterised by their structure
    • H01G9/052—Sintered electrodes
    • H01G9/0525—Powder therefor
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F9/00—Making metallic powder or suspensions thereof
    • B22F9/16—Making metallic powder or suspensions thereof using chemical processes
    • B22F9/18—Making metallic powder or suspensions thereof using chemical processes with reduction of metal compounds
    • B22F9/20—Making metallic powder or suspensions thereof using chemical processes with reduction of metal compounds starting from solid metal compounds
    • B22F9/22—Making metallic powder or suspensions thereof using chemical processes with reduction of metal compounds starting from solid metal compounds using gaseous reductors
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B34/00—Obtaining refractory metals
    • C22B34/20—Obtaining niobium, tantalum or vanadium
    • C22B34/24—Obtaining niobium or tantalum
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B5/00—General methods of reducing to metals
    • C22B5/02—Dry methods smelting of sulfides or formation of mattes
    • C22B5/04—Dry methods smelting of sulfides or formation of mattes by aluminium, other metals or silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B5/00—General methods of reducing to metals
    • C22B5/02—Dry methods smelting of sulfides or formation of mattes
    • C22B5/12—Dry methods smelting of sulfides or formation of mattes by gases

Definitions

  • This invention relates to the production of tantalum, niobium and other metal powders and their alloys by the reduction of the corresponding metal oxide with gaseous active metals such as Mg, Ca and other elemental and compound reducing materials, in gaseous form.
  • gaseous active metals such as Mg, Ca and other elemental and compound reducing materials
  • Tantalum and niobium are members of a group of metals that are difficult to isolate in the free state because of the stability of their compounds, especially some of their oxides.
  • a review of the methods developed to produce tantalum will serve to illustrate the history of a typical manufacturing process for these metals. Tantalum metal powder was first produced on a commercial scale in Germany at the beginning of the 20 th Century by the reduction of the double salt, potassium heptafluorotantalate (K 2 TaF 7 ) with sodium. Small pieces of sodium were mixed with the tantalum containing salt and sealed into a steel tube. The tube was heated at the top with a ring burner and, after ignition, the reduction proceeded quickly down the tube.
  • the reaction mixture was allowed to cool and the solid mass, consisting of tantalum metal powder, unreacted K 2 TaF 7 and sodium, and other products of the reduction was removed by hand using a chisel.
  • the mixture was crushed and then leached with dilute acid to separate the tantalum from the components.
  • the process was difficult to control, dangerous, and produced a coarse, contaminated powder, but nevertheless pointed the way to what became the principal means of production of high purity tantalum in later years.
  • Commercial production of tantalum metal in the United States began in the 1930's.
  • a molten mixture of K 2 TaF 7 containing tantalum oxide (Ta 2 O 5 ) was electrolyzed at 700°C in a steel retort. When the reduction was completed, the system was cooled and the solid mass removed from the electrolysis cell, and then crushed and leached to separate the coarse tantalum powder from the other reaction products.
  • the dendritic powder was not suitable for use directly in capacitor applications.
  • the manufacturing process still requires the removal of the solid reaction products from the retort, separation of the tantalum powder from the salts by leaching, and treatments like agglomeration to improve the physical properties.
  • Most capacitor grade tantalum powders are also deoxidized with magnesium to minimize the oxygen content (Albrecht, W.W., Hoppe, H., Papp, V. and Wolf, R., US Patent 4537641, 1985).
  • Artifacts of preagglomeration of primary particles to secondary particle form and doping with materials to enhance capacitance are also known today.
  • niobium has only been used in the capacitor industry to a very minor extent, predominantly in areas of with lower quality requirements.
  • niobium oxide dielectric constant is about 1 ,5 times as high as that of a similar tantalum oxide layer, which should allow in principle, for higher capacitance of niobium capacitors, subject to considerations of stability and other factors.
  • the use of magnesium to deoxidize or reduce the oxygen content of tantalum metal is well known.
  • the process involves blending the metal powder with 1-3 percent magnesium and heating to achieve the reduction process.
  • the magnesium is in the molten state during a portion of the heating time.
  • the objective is to remove 1000-3000 ppm oxygen and only a low concentration of MgO is produced.
  • a much greater quantity of tantalum oxide is reduced a large quantity of magnesium oxide is generated.
  • the resulting mixture of magnesium, tantalum oxide and magnesium oxide can under conditions of poorly controlled temperature, form tantalum-magnesium-oxygen complexes that are difficult to separate from the tantalum metal.
  • Another object is to provide niobium/tantalum alloy powders of capacitor grade quality and morphology.
  • the oxide source should be substantially or preferably entirely in solid.
  • the oxide is provided in the form of a porous solid with high access throughout its mass by the gaseous reducing agent.
  • the metals that can be effectively produced singly or in multiples (co-produced) through the present invention are in the group of Ta, Nb, and Ta/Nb alloy, any of these alone or with further inclusion of added or co-produced Ti, Mo, V, W, Hf and/or Zr.
  • the metals can also be mixed or alloyed during or after production and/or formed into useful compounds of such metals.
  • the respective stable and unstable oxide forms of these metals can be used as sources.
  • Metal alloys may be produced from alloyed oxide precursors, e.g. resulting from coprecipitation of a suitable precursor for the oxide.
  • Vapor pressures of some of the reducing agents are given as follows:
  • the temperature of reduction varies significantly depending on the reducing agent used.
  • the temperature ranges for reduction of (Ta, Nb) oxide are: with Mg (gas) -800- l,100°C, Al (gas) - 1,100-1, 500°C, Li (gas) - 1,000- 1,400°C, Ba (gas) - 1,300-1,900°C.
  • One embodiment of the invention includes a first step of reducing an oxide source of selected metal(s) substantially to free 80-100% (by weight) of the metal values therein as primary powder particles, then leaching or other steps of hydrometallurgy to separate the metal from residual reducing agent oxide and other byproducts of the reduction reaction and from residual condensed reducing agent (optionally), followed by one or more deoxidation steps under less concentrated reagent conditions than in the first gross reduction step (and with better tolerance of molten state of the reducing agent), then further separation as might be needed.
  • the invention provides for a single stage reduction process for the production of metal powders as cited above, comprising the steps of:
  • reducing agents used in this reduction process of the first embodiment are Mg, Ca and/or their hydrides. Particularly preferred is Mg.
  • Nb and/or Ta metals optionally alloyed with each other and/or with alloying elements, selected from the group consisting of Ti, Mo,
  • a second embodiment of the invention provides for a two-stage reduction process, comprising the steps of:
  • the reducing metals and/or metal hydrides are brought into contact with the suboxide in gaseous form.
  • Preferred reducing metals in the second reduction step of this second embodiment are Mg and/or Ca and/or their hydrides. Particularly preferred is Mg.
  • Reduction temperature preferably (for Mg) is selected between 850°C up to normal boiling point (1150°C)
  • the process according to the present invention specifically has been developed to provide capacitor grade tantalum and niobium and tantalum nio- bium alloy powders and Ta/Nb materials or application of equivalent purity and/or morphology needs.
  • the greatest gap of the state of the art is filled in part by the availability of capacitor grade niobium enabled by this invention, but a segment of the tantalum art is also enhanced thereby.
  • the tantalum and/or niobium may be enhanced by alloying or compounding with other materials during the reduction reaction production of the tantalum/niobium or thereafter.
  • the reduction of oxides with gaseous reducing agents at least during the initial reduction phase allows for easy control of temperature during reduction to avoid excessive presintering. Furthermore, as compared to prior art proposals using liquid reducing metals, the controlled reduction with gaseous reducing metals does not lead to contamination of the reduced metal with the reducing metal by incorporation into the reduced metal lattice. It has been found that such contamination mainly occurs during the initial reduction of (in case of Nb) Nb 2 O 5 to NbO 2 . This at first appeared surprising because niobium suboxide (NbO ) contains only 20% less oxygen than niobium pentoxide (NbO 2 .5).
  • Preferred temperature during reduction with magnesium gas is between 900 and 1 100°C, particularly preferred between 900 and 1000°C.
  • Temperature may be increased up to 1200°C after at least 20% of the oxygen is removed to improve presintering.
  • the reduction of the pentoxide with hydrogen produces a suboxide which is already sintered with the formation of agglomerates comprising stable sintered bridges, which have a favorable structure for use as a capacitor material.
  • the reactors are preferably lined with molybdenum sheet or by a ceramic which is not reduced by H 2 , in order to prevent contamination.
  • the reduction time and reduction temperature should be selected so that at least 20% of the oxygen is removed from the pentoxide. Higher degrees of reduction are not harmful. However, it is generally not possible to reduce more than 60% of the oxygen within practicable time scales and at tolerable temperature.
  • the reduction product is preferably still held (annealed) for some time, most preferably for about 60 to 360 minutes, at a temperature above 1000°C. It appears that this enables that the new, dense, crystal structure can be formed and stabilized. Since the rate of reduction decreases very considerably with the degree of reduction, it is sufficient to heat the suboxide at the reduction temperature under hydrogen, optionally with a slight decrease in temperature. Reduction and annealing times of 2 to 6 hours within the temperature range from 1100 to 1500°C are typically sufficient.
  • reduction with hydrogen has the advantage that impurities such as F, CI and C, which are critical for capacitor applications, are reduced to less than 10 ppm, preferably less than 2 ppm.
  • the suboxide is subsequently cooled to room temperature ( ⁇ 100°C) in the reduction apparatus, the suboxide powder is mixed with finely divided powders of the reducing metals or metal hydrides and the mixture is heated under an inert gas to the reduction temperature of the second stage.
  • the reducing metals or metal hydrides are preferably used in a stoichiometric amount with respect to residual oxygen of the acid earth metal suboxide, and are most preferably used in an amount which is slightly in excess of the stoichiometric amount.
  • One particularly preferred procedure consists of using an agitated bed in the first stage and of carrying out the second stage, without intermediate cooling, in the same reactor by introducing the reducing metals or metal hydrides. If magnesium is used as the reducing metal, the magnesium is preferably introduced as magnesium gas, since in this manner the reaction to form metal powder can readily be controlled.
  • the metal is cooled, and the inert gas is subsequently passed through the reactor with a gradually increasing content of oxygen in order to deactivate the metal powder.
  • the oxides of the reducing metals are removed in the manner known in the art by washing with acids.
  • Tantalum and niobium pentoxides are preferably used in the form of finely divided powders.
  • the primary grain size of the pentoxide powders should approximately correspond to 2 to 3 times the desired primary grain size of the metal powders to be produced.
  • the pentoxide particles preferably consist of free-flowing agglomerates with average particle sizes of 20 to 1000 ⁇ m, including a specific preference of a narrower range of most preferably 50 to 300 ⁇ m particle size.
  • Reduction of niobium oxide with gaseous reducing agents can be conducted in an agitated or static bed, such as a rotary kiln, a fluidized bed, a rack kiln, or in a sliding batt kiln.
  • the bed depth should not exceed 5 to 15 cm, so that the reducing gas can penetrate the bed. Greater bed depths are possible if a bed packing is employed through which the gas flows from below.
  • a bed packing is employed through which the gas flows from below.
  • Niobium powders which are particularly preferred according to the invention are obtained in the form of agglomerated primary particles with a primary particle size of
  • the powders according to the invention exhibit outstanding flow properties and pressed strengths, which determine their processability to produce capacitors.
  • the agglomerates are characterized by stable sintered bridges, which ensure a favorable porosity after processing to form capacitors.
  • niobium powder according to the invention contains oxygen in amounts of 2500 to 4500 ppm/m 2 surface and is otherwise low in oxygen, up to 10,000 ppm nitrogen and up to 150 ppm carbon, and without taking into account a content of alloying metals has a maximum content of 350 ppm of other metals, wherein the metal content is mainly that of the reducing metal or of the hydrogenation catalyst metal.
  • the total content of other metals amounts to not more than 100 ppm.
  • the total content of F, CI, S is less than 10 ppm.
  • Capacitors can be produced from the niobium powders which are preferred according to the invention, immediately after deactivation and sieving through a sieve of mesh size 400 ⁇ m.
  • these capacitors After sintering at a pressed density of 3,5 g/cm 3 at 1100°C and forming at 40 V these capacitors have a specific capacitance of 80,000 to 250,000 ⁇ FV/g (as measured in phosphoric acid) and a specific leakage current density of less than 2 nA/ ⁇ FV. After sintering at 1 150°C and forming at 40 V, the specific capacitor capacitance is 40,000 to 150,000 ⁇ FV/g with a specific leakage current density of less than 1 nA/ ⁇ FV.
  • capacitors After sintering at 1250°C and forming at 40 V, capacitors are obtained which have a specific capacitor capacitance (as measured in phosphoric acid) of 30,000 to 80,000 ⁇ FV/g and a specific leakage current density of less than 1 nA/ ⁇ FV.
  • the niobium powders which are preferred according to the invention have a BET specific surface of 1.5 to 30 m 2 /g, preferably of 2 to 10 m 2 /g.
  • capacitors can be made from Nb/Ta-alloy powders in way that the capacitors have an appreciably higher specific capacitance obtained from capacitors made from pure Nb-and pure Ta-powers or anticipated for an alloy be simple linear interpolation.
  • Capacitances ( ⁇ FV) of capacitors with sintered Nb-powder anodes and sintered Ta-powder anodes having the same surface area are approximately equal. The reason is that the higher dielectric constant of the insulating niobium oxide layer (41 as compared to 26 of tantalum oxide) is compensated by the larger thickness of the oxide layer per volt (anodization voltage) formed during anodization.
  • the oxide layer thickness per volt of Nb is about twice as thick as that formed on Ta (about 1.8 nm/V in the case of Ta and about 3.75 nm/V in the case of Nb).
  • the present invention can provide a surface related capacitance ( ⁇ FV/m 2 ) of alloy powder capacitors which is up to about 1.5 to 1.7 higher than the expected value from linear interpolation between Nb powder capacitors and Ta powder capacitors. This seems to indicate that oxide layer thickness per volt of anodization voltage of alloy powders of the invention is closer to that of Ta, whereas the dielectric constant of the oxide layer is closer to that of Nb.
  • the foregoing surprisingly high capacitance of the alloy may be associated with a different structural form of oxide of alloy components compared to structure of oxides on surfaces of pure Nb powders. Indeed, preliminary measurements have revealed that oxide layer growth of a 15 at. -%Ta — 85 at.-% Nb alloy is almost 2.75 nm/volt.
  • the present invention accordingly further comprises an alloy powder for use in the manufacture of electrolyte capacitors consisting primarily of niobium and containing up to 40 at-% of tantalum based on the total content of Nb and Ta.
  • Alloy powder in accordance with the present invention shall mean that the minor Ta-component shall be present in an amount greater than the amount of ordinary impurity of niobium metal, e.g. in an amount of more than 0.2% by weight (2000 ppm, corresponding to 2 at.-% for Ta).
  • the content of Ta is at least 2 at.-% of tantalum, particularly preferred at least 5 at.-% of tantalum, most preferably at least 12 at.-% of tantalum, based on the total content of Nb and Ta.
  • the content of tantalum in the alloy powders in accordance with the in- vention is less than 34 at.-% of tantalum.
  • the effect of capacitance increase is gradually increasing up to a ratio of Nb- to Ta-atoms of about 3. Higher than 25 at.- % Ta based on the total content of Nb and Ta does only slightly further increase the effect.
  • the alloy powders according to the invention preferably have BET-surfaces multi- plied with the alloy density of between 8 and 250 (m 2 /g) x (g/cm 3 ), particularly preferred between 15 and 80 (m 2 /g) x (g/cm 3 ).
  • the density of the alloy material may be calculated from the respective atomic ratio of Nb and Ta multiplied by the densities of Nb and Ta respectively.
  • the effect of capacitance increase of alloying is not limited to powders having the structure of agglomerated spherical grains. Accordingly the alloyed powders in accordance of the invention may have a morphology in the form agglomerated flakes preferably having have a BET-surface times density of between 8 and 45 (m 2 /g) x (g/cm 3 ).
  • Particularly preferred alloy powders are agglomerates of substantially spherical primary particles having a BET-surface times density of 15 to 60 (m 2 /g) x (g/cm 3 ).
  • the primary alloy powders (grains) may have mean diameters of between 100 to 1500 nm, preferrably 100 to 300 nm. Preferrably the deviation of diameter of primary particles from mean diameter is less than a factor 2 in both directions.
  • the agglomerate powders may have a mean particle size as determined in accordance with ASTM-B 822 (Mastersizer) as disclosed for niobium powders above.
  • Particularly preferred alloy powders have a ratio of Scott density and alloy density of between 1.5 and 3 (g/inch 3 )/(g/cm 3 ).
  • Any production method known in the art for the production of capacitor grade tantalum powder may be used, provided that a precursor is used which is an alloyed precursor containing niobium and tantalum approximately at the atomic ratio of Nb and Ta desired in the metal powder alloy instead of precursor containing tantalum alone.
  • Useful alloy precursors may be obtained from coprecipitation of (Nb, Ta)- compounds from aqueous solutions containing water soluble Nb- and Ta-compounds e.g. coprecipitation of (Nb, Ta)-oxyhydrate from aqueous solution of heptafluoro- complexes by the addition of ammonia and subsequent calcination of the oxhydrate to oxide.
  • Flaked powders may be obtained by electron beam melting of a blend of high purity tantalum and niobium oxides, reducing the molten ingot, hydriding the ingot at elevated temperature, and comminuting the brittle alloy, dehydriding the alloy powder and forming it into flakes.
  • the flakes are thereafter agglomerated by heating to 1 100 to 1400°C in the presence of a reducing metal such as Mg, optionally with doping with P and/or N.
  • This process for the manufacture of "ingot derived" powder is generally known from US- A 4,740,238 for the production of tantalum flaked powder and from WO 98/19811 for niobium flaked powder.
  • Nb-Ta-alloy powders having the morphology of agglomerated spherical grains are produced from mixed (Nb, Ta)-oxides by reduction with gaseous reducing agent as described herein.
  • the metal powders produced are suitable for use in electronic capacitors and other applications including, e.g. the production of complex electro-optical, superconductive and other metal and ceramic compounds, such as PMN structures and high temperatures form metals and oxide.
  • the invention comprises the said powders, the methods of producing such powders, certain derivative products made from such powders and methods for making such derivative products.
  • the capacitor usage can be accompanied by other known artifacts of capacitor production such as doping with agents to retard sinter densification or otherwise enhance end product capacitance, leakage and voltage breakdown.
  • the invention enables several distinct breakthroughs in several of its various fields of application.
  • FIGS. 1-4 show sketch outlines of processing systems for practice of the present invention
  • FIGS. 5A-12C are scanning electron micrographs (SEMs) of powders produced according to the present invention, including some SEMs of state of the art or comparison examples of metal powders made otherwise than in accordance with the present invention;
  • FIGS. 13 and 14 are flow charts illustrating diverse usages of the powder and derivatives.
  • FIG. 15 is a schematic representation of an end item according to usage as a capacitor (one of several forms of capacitor usage).
  • FIG. 16 is a trace of capacitance and surface area of Ta-Nb alloy powders in relation to alloy composition.
  • Example 1 (comparison) A mixture of Ta 2 O5 and magnesium was loaded into a tantalum tray and covered with tantalum foil. The magnesium stoichiometry was 109% of that required to completely reduce the tantalum oxide. The mixture was heated at 1000° for six hours in an argon atmosphere. The mixture was not agitated during the reduction process. After cooling, the products were passivated by programmed addition of oxygen. The result of the reduction process was a black spongy material that was difficult to break up. The product was leached with dilute mineral acid to remove the magnesium oxide, dried and screened. The yield of the coarse (+40 mesh) material was high at 25 percent.
  • a bed (3) of 200 grams of tantalum pentoxide was placed on a porous tantalum plate 4 suspended above magnesium metal chips (5) contained in a tantalum boat.
  • the container was covered with a tantalum lid and placed in a sealed retort with argon (Ar) passed through the sealed volume via nozzle (6).
  • the product mixture was passivated by introducing argon-oxygen mixtures, containing 2, 4, 8, 15 inches (Hg, partial pressure) of O 2 (g), respectively, into the furnace. Each mixture was in contact with powder for 30 minutes. The hold time for the last passivation with air was 60 minutes.
  • the magnesium oxide was separated from the tantalum powder by leaching with dilute sulfuric acid and then rinsed with high purity water to remove acid residues.
  • the product was a free flowing, powder.
  • Samples of the product (designated as Ta GR-2D) are shown in scanning electron micrographs (SEMs) at FIGS. 5A, 5B, 5C at 15,700, 30,900 and 60,300 magnifications, respectively, taken in an electron microscope operated at 15 kilovolts.
  • SEMs scanning electron micrographs
  • FIGS. 5D and 5E which are 70,000 magnification (x) SEMs of tantalum powder made by sodium reduction.
  • Properties of the tantalum powder of FIGS. 5 A, 5B, 5C are given in Table 2.1, below.
  • FIG. 2 shows a flash reactor 20 with a vertical tube surrounded by a heater 24, a feed source 25 of metal oxide and a source 26 of reducing agent (e.g. Mg) vapor (mixed in argon), an argon outlet 26' and a collector 28 for metal and oxide of the reducing agent.
  • Valves VI, V2 are provided. Particles of the oxide drop through the tube and are flash reduced.
  • FIG.3 shows a rotary kiln 30 with an inclined rotating tube 32, heater 34, oxide hopper 35, gas source (reducing agent and diluent, e.g. argon) and outlet 36, 36', and collector 38 for metal and reducing agent oxide.
  • FIG.4 shows a multiple hearth furnace 40 with a retort 42 containing rotary trays 43 and splined paddles, 43 and splined paddles, 43, heater 44, oxide source 45, gas source and exit 46, 46' and collector 48.
  • Still other forms of reactors such as conventional per se fluid bed furnace reactors or Contop, KIVCET types can be used.
  • Tantalum powder with surface area of 57,000 cm 2 /gm made according to the procedure in Example 2 was deoxidized by blending the powder with 2 W/W% Mg and heating at 850°C for two hours in an argon atmosphere. Separation of reducing agent source and oxide is not necessary in this follow up deoxidation step.
  • the deoxidized powder was allowed to cool and then passivated, leached, and dried.
  • a SEM (100,000 x) of the deoxidized (finished) powder appears at FIG. 7A and a SEM (70,000 x) of finished sodium reduced powders appears at FIG. 7B. the morphology differences are apparent.
  • the powder was pressed into pellets weighing 0.14 grams at a press density of 5.0 g/cc.
  • a SEM of the further deoxidized powder is given at FIG. 6.
  • the pellets were sintered in vacuum at 1200°C for 20 minutes.
  • the pellets were anodized to 30 volts in 0.1 volume percent (V/V%) H 3 PO 4 solution at 80°C.
  • the formation current density was 100 mA/gm and the hold time at the formation voltage was two hours.
  • the average capacitance of the anodized pellets wasl05, 000 ⁇ F (VVgm and the leakage current measured after five minutes application of 21V was 0.1 nA/ ⁇ F (V).
  • Example 3 Powder with surface area of 133,000 cm /gm and bulk density of 27.3 g/m 3 made as described in Example 2 was treated as in Example 3. A SEM (56,600 x) of the finished powder appears at FIG. 7C. Pellets made from the deoxidized powder were anodized to 16V using the conditions in Example 3. The average capacitance of the anodized pellets was 160,000 ⁇ F (V)/gm.
  • the capacitance of the anodized pellets was 27,500 ⁇ F (V)/gm and the leakage was 0.43 nA/ ⁇ F (V).
  • the primary powder was deoxidized at 850°C for two hours. 4 W/W% Mg and 1 W/W% NH C1 were added. MgO was leached with mineral acid. Then the powder was doped at 200 ppm P by adding the equivalent amount of NH H 2 PO . The powder was deoxidized for the second time at 850°C for two hours and then nitrided at 325°C by adding a gaseous mixture containing 80% argon and 20% nitrogen. Some properties of the finished powder are given in Table 6.2, below.
  • Pellets were made from the powder at a press density of 5.0 gm/cc.
  • the sintered pellets were anodized at 80°C to 16 volts in 0.1 W/W% H 3 PO 4 solution. Capacitances and leakages as a function of sintering temperature are given in Table 6.3, below.
  • Potassium heptafluoroniobate (K 2 NbF 7 ) was reduced with sodium using a stirred reactor molten salt process similar to the ones described by Hellier et al. and Hildreth et al, US patent 5,442,978.
  • the diluent salt was sodium chloride and the reactor was made from Inconel alloy.
  • the niobium metal powder was separated from the salt matrix by leaching with dilute nitric acid (HNO 3 ) and then rinsing with water. Selected physical and chemical properties are given in Table 7.1, below.
  • the very high concentrations of the metallic elements, nickel, iron and chromium make the powders unsuitable for use as capacitor grade material.
  • the contamination resulted because of the inherent corrosive nature of the K 2 NbF 7 . This property makes the sodium reduction process unsuitable for making capacitor grade niobium powder.
  • Example 2 Two hundred grams of niobium pentoxide was reduced as described in Example 2. The resulting product was a free flowing black powder and had a surface area of 200,800 cm 2 /gm. The passivated product was leached with dilute nitric acid solution to remove magnesium oxide and residual magnesium and then with high purity water to remove residual acid. This material was blended with ten (10.0) W/W% Mg and deoxidized at 850°C for two hours. Physical and chemical properties of the powder are listed in table 8.1, below. The powder was doped with 100 ppm P as described in Example 3. Table 8.1
  • FIGS. 8A and 8B SEMs (70,000 x) appear at FIGS. 8A and 8B, respectively, for niobium powders produced by liquid sodium (Ex. 7) and magnesium gas (Ex. 8) reduction. Note the clustering of small particles as barnacles on large ones is much more pronounced in FIG. 8B than in 8 A.
  • FIGS. 8C, 8D are SEMs (2,000 x) of, respectively niobium powder as produced by sodium reduction and magnesium gas reduction.
  • the niobium powder produced by liquid sodium reduction has large (>700 nm) joined (300 nm+) grains protruding and facets that give the product a blocky shape and fine grain material (order of 10 nm, but some up to 75 nm) as barnacles while the niobium powder produced by magnesium gas reduction has a base grain size of about 400 nm and many smaller grains of about 20 nm thereon many of which smaller grains are themselves agglomerates of up to 100 nm in size.
  • Pellets weighing 0.14 gm were prepared from the niobium powder produced in Example 8. The pellets were anodized in 0.1 V/V% H 3 PO 4 solution at 80°C. The current density was 100 mA/gm and the hold time at the formation voltage was two hours. Electrical results as a function of pellet press density, formation voltage and sintering temperature are given in Table 9.1, below.
  • Niobium oxide was reduced with gaseous magnesium as described in Example 8.
  • the resulting powder was deoxidized twice. During the first deoxidation, 2.0 W/W% NH C1 was added to the charge to nitride the powder. The deoxidation conditions were 850°C for two hours with 7.0 W/W% Mg. After leaching and drying, the powder was doped with 200 ppm P. The second deoxidation was carried out at 850°C for two hours using 2.5 W/W% Mg. The finished powder has a surface area of 22,000 cm 2 /gm and good flowability.
  • Table 10.1 below. Pellets were anodized to 16 volts in 0.1 V/N% H 3 PO 4 solution at 80°C using a current density of 100 r-iA/g and a two-hour hold. The electrical properties are given in Table 10.2, below.
  • the Nb 2 O 5 used had a particle size of 1.7 ⁇ m as determined by FSSS (Fisher Sub Sieve Sizer) and comprised the following contents of impurities:
  • the suboxide obtained had a composition corresponding to NbO 2 .
  • the product was placed on a fine-mesh grid under which a crucible was situated which contained magnesium in 1.1 times the stoichiometric amount with respect to the oxygen content of the suboxide.
  • the arrangement comprising the grid and crucible was treated for 6 hours at 1000°C under an argon protective gas.
  • the magnesium evaporated and reacted with the overlying suboxide.
  • the kiln was subsequently cooled ( ⁇ 100°C) and air was gradually introduced in order to passivate the surface of the metal powder.
  • the product was washed with sulfuric acid until magnesium could no longer be detected in the filtrate, and thereafter was washed until neutral with deionized water and dried.
  • the primary grain size was determined visually as about 500 nm.
  • the Scott bulk density was 15.5 g/inch 3 .
  • the BET specific surface was 6.08 m 2 /g.
  • the pressed strength of the anodes was 6.37 kg.
  • the anodes were formed at 80°C in an electrolyte containing 0.1 % by volume of H 3 P0 4 at a current density of 100/150 mA at the voltage given in Table 11.1 and the capacitor characteristics were determined; see Table 11.1 Table 11.1
  • Example 11 was repeated, with the difference that the temperature in the first reduction stage was 1300°C.
  • the metal powder had the following properties:
  • the pressed strength was extremely high:
  • niobium pentoxide Three batches of niobium pentoxide were treated for 4 hours under hydrogen at 1100°C, 1300°C or 1500°C, under conditions which were otherwise the same.
  • a (Nb x , Ta ] . x ) 2 O 5 precursor is prepared by coprecipitation of (Nb, Ta)-oxyhydrate from mixed aqueous solution of niobium and tantalum heptafluorocomplexes by the addition of ammonia with stirring and subsequent calcination of the oxyhydrate to oxide.
  • the suboxide was placed on a fine mesh grid under which a crucible was situated which contained magnesium in 1 ,2 times the stoichiometric amount with respect to the oxygen content of the suboxide.
  • the arrangement comprising grid and crucible was treated for 6 hours at 1000°C under an argon protective gas.
  • the kiln was subsequently cooled to below 100°C and air was gradually introduced in order to passivate the surface of the metal powder.
  • the product was washed with sulfuric acid until magnesium could no longer be detected in the filtrate, and thereafter washed until neutral with deionized water and dried.
  • the primary grain size as determined visually was roughly 450 nm.
  • BET specific surface was 6.4 m 2 /g, Scott density 15.1 g/in 3 , particle size (FSSS) was 0.87 ⁇ m.
  • Anodes with a diameter of 2.94 mm, a length of 3.2 mm and a pressed density of 3.23 g/cm 3 were produced from the alloy powder by sintering on a niobium wire for 20 minutes at 1150°C. Sintered density was 3.42 g/cm 3 .
  • the electrodes were anodized in an electrolyte containing 0.25% of H 3 P0 4 until a final voltage of 40 V.
  • the capacitor characteristics were determined by using a 10% H 3 PO 4 aqueous solution as follows: Capacitance: 209117 ⁇ FV/g, Leakage current: 0.55 nA/ ⁇ Fg.
  • the primary grain size as determined visually was roughly 400 nm.
  • BET specific surface was 3.9 m 2 /g, Scott density 17.86 g/in 3 , particle size (FSSS) was 2.95 ⁇ m, Hall Flow 27.0 s.
  • Anodes with a diameter of 2.99 mm, a length of 3.23 mm and a pressed density of 3.05 g/cm 3 were produced from the alloy powder by sintering on a niobium wire for 20 minutes at 1,150°C. Sintered density was 3.43 g/cm 3 .
  • the electrodes were anodized in an electrolyte containing 0.25% of H 3 PO until a final voltage of 40 V.
  • the capacitor characteristics were determined by using a 10%H 3 PO 4 aqueous solution as follows: Capacitance: 290173 ⁇ FV/g, Leakage current: 0.44 nA/ ⁇ Fg.
  • Tantalum hydroxide was precipitated from an aqueous tantalum fluorocomplex solution by addition of ammonia.
  • FSSS Fisher Sub Sieve Sizer
  • BET specific surface area
  • Fig. 9A -9C SEM-pictures
  • the retort was evacuated, filled with argon and heated to 950°C for 12 hours. After cooling to below 100°C, and passivation the product was leached with an aqueous solution containing 23 wt.-% sulfuric acid and 5.5 wt.-% hydrogen peroxide and thereafter washed with water until neutral. The product was dried over night at 50°C and screened ⁇ 400 ⁇ m.
  • the tantalum powder showed the following analytical data:
  • FSSS Average particle size
  • Scott bulk density
  • BET surface 2,20 m 2 /g
  • the powder was soaked with gentle stirring with NH H 2 PO 4 -solution containing 1 mg P per ml, dried over night at 50°C for doping with 150 ppm P and screened ⁇ 400 ⁇ m.
  • Capacitor anodes were prepared from 0.047 g of Ta-powder each at pressed density of 5.0 g/cm 3 by sintering at 1260°C with 10 minutes holding time.
  • Forming current density was 150 mA/g with 0,1 wt.-% H 3 PO 4 solution as forming electrolyte at 85°C until final voltage of 16 V which was held for 100 minutes. Test results:
  • High purity optical grade Ta 2 O 5 was calcined first at 1700°C for 4 hours and thereafter for 16 hours at 900°C to provide for more compact and coarser precursor particles.
  • Physical properties of the pentoxide powder are:
  • FSSS Average particle size: 20 ⁇ m bulk density (Scott): 39 g/inch 3
  • the oxide powder was reduced to metal as described in example 16, however at 1000°C for 6 hours.
  • Capacitor anodes were prepared and anodized as in example 16.
  • the present process appears to represent the only demonstrated way of making high quality chemically reduced niobium powder.
  • the reduction of the metal oxide with a gaseous reacting agent, such as magnesium, as shown herein is thus particularly suitable for producing powders useable as metal-metal oxide capacitor substrates.
  • a gaseous reacting agent such as magnesium
  • the reduction process was carried out with the metal oxide in a bed in contact with a source of magnesium gas, the reduction can take place in a fluidized bed, rotary kiln, flash reactor, multiple hearth or similar systems provided the magnesium or other reducing agent is in the gaseous state.
  • the process will also work with other metal oxides or metal oxide mixtures for which the reduction reaction with gaseous magnesium or other reducing agent has a negative Gibbs free energy change.
  • the present invention further for the first time demonstrates the superiority of Ta-Nb alloy powders for use in the production of capacitors.
  • Fig. 16 shows the ratio of maximum obtainable capacitance ( ⁇ FV/g) and BET- surface of powder (m /g) in relation to the alloy composition.
  • a and C represent pure Ta-, Nb-powders, respectively, as measured in present Example 16.
  • B represents the highest known values of pure Ta powder capacitors as disclosed in Examples 2, 5 and 7 of WO 98/37249.
  • Line 1 represents expectable values for alloy powder capacitors from linear interpolation from pure Ta, and Nb powder capacitors.
  • E represents a Active Nb-powder capacitor wherein the insulating oxide layer has the same thickness per volt as in Ta powder capacitors, however, the dielectric constant of niobium oxide differs.
  • Line 11 represents linear interpolation between B and E.
  • D represents a measured value of 25 wt.-% Ta/75 wt.-% Nb alloy powder capacitor as presented in present Example 15.
  • Curve III represents the estimated dependency of capacitance on alloy composition of alloy powder capacitors in accordance with
  • FIG. 13 is a block diagram of steps for achieving an electrolytic capacitor usage of the invention.
  • the steps comprise reduction of metal oxide with gaseous reducing agent; separation of reduction agent oxide from a mass of resultant metal; breakdown to powder form and/or primary powder particle size; classification; optionally, presinter to establish agglomerated secondary particles (controlled mechanical methods and control of original reduction or separation steps also being affective to establish agglomerates); deoxidation to reduce the oxygen concentration; compaction of primary or secondary particles to a porous coherent mass by cold isostatic pressing with or without use of compacting binders or lubricants; sintering to a porous anode form (which can be an elongated cylindrical, or slab or of a short length from such as a chip); anode lead attachment by embedding in the anode before sintering or welding to the sintered anode compact; forming the exposed metal surfaces within the porous anode by electrolytic oxidation to establish a dielectric oxide layer; solid electrode impregn
  • FIG. 14 is a block diagram collectively illustrating production of some of the other derivative products and uses of the invention including use of the powders as slips, in molding and loose pack form for further reaction and/or consolidation by way of sintering, hot isostatic pressing (H.I. P.) or in sinter/H.I.P. methods.
  • the powders per se and/or as consolidated can be used in making composites, in combustion, in chemical synthesis (as reactants) or in catalysis, in alloying (e.g. ferrometallurgy) and in coatings.
  • the consolidated powders can be used to make mill products and fabricated parts.
  • the end use products made using the gas reduction produced powders will resemble state of the art powders made with state of the art (e.g. reduced) powders and in other instances the products will be novel and have unique physical, chemical or electrical characteristics resulting from the unique forms as described herein of the powders produced by reduction by gaseous reducing agents.
  • the mill products and fabricated parts manufacture can involve remelting, casting, annealing, dispersion strengthening and other well known per se artifacts.
  • the end products made through further reaction of the metal powders can include high purity oxides, nitrides, suicides and still further derivatives such as complex ceramics used in ferroelectrics and in optical applications, e.g. perovskite structure PMW compounds.

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Abstract

L'invention concerne une poudre métallique de Ta et/ou Nb, avec un ou plusieurs des métaux sélectionnés dans le groupe constitué par Ta, Nb, Ti, Mo, W, V, Zr et Hf. Une fine poudre s'obtient par la réduction d'oxydes métalliques par contact avec un agent de réduction gazeux, de préférence un métal terreux alcalin, jusqu'à réduction quasi complète, lixiviation, nouvelle réduction et agglomération. La poudre ainsi produite peut être agglomérée par frittage sous forme d'anode de condensateur et traitée à d'autres fins.
PCT/US1999/009772 1998-05-06 1999-05-05 Poudres metalliques obtenues par reduction d'oxides au moyen de magnesium gazeux WO2000067936A1 (fr)

Priority Applications (13)

Application Number Priority Date Filing Date Title
UA2000126988A UA67779C2 (uk) 1998-05-06 1999-05-05 Спосіб отримання металевих порошків, вибраних з групи, що складається з танталу і ніобію і з їх сплаву, та порошок, отриманий цим способом
BRPI9917635A BRPI9917635B1 (pt) 1998-05-06 1999-05-05 pó de nióbio na forma de partículas aglomeradas primárias e método para a obtenção de um anodo de capacitor
PCT/US1999/009772 WO2000067936A1 (fr) 1998-05-06 1999-05-05 Poudres metalliques obtenues par reduction d'oxides au moyen de magnesium gazeux
JP2000616950A JP4202609B2 (ja) 1998-05-06 1999-05-05 気体状マグネシウムを用いる酸化物の還元により製造される金属粉末
BR9911008-3A BR9911008A (pt) 1998-05-06 1999-05-05 Pós de metal produzidos através da redução dos óxidos com magnésio gasoso
BRPI9911008A BRPI9911008B1 (pt) 1998-05-06 1999-05-05 processo para a produção de capacitor de pós de metal, pó de nióbio, anodo de capacitor, pó de liga para uso na fabricação de capacitores eletrolíticos, processo para a fabricação de pó de liga
CA2331707A CA2331707C (fr) 1998-05-06 1999-05-05 Reduction de poudre d'oxyde de nb ou de ta par metal gazeux leger ou l'un de ses hydrures
US09/445,331 US6558447B1 (en) 1999-05-05 1999-05-05 Metal powders produced by the reduction of the oxides with gaseous magnesium
AU58965/99A AU757790B2 (en) 1998-05-06 1999-05-05 Metal powders produced by the reduction of the oxides with gaseous magnesium
IL13906199A IL139061A (en) 1998-05-06 1999-05-05 Metal powders produced by the reduction of the oxides with gaseous magnesium
DE69940030T DE69940030D1 (de) 1998-05-06 1999-05-05 VERFAHREN ZUR HERSTELLUNG VON METALLPULVERN DURCH REDUKTION VON OXIDEN, Nb UND Nb-Ta PULVER UND DAMIT HERGESTELLTE KONDENSATORANODE
EP99946575A EP1144147B8 (fr) 1998-05-06 1999-05-05 PROCEDE DE FABRICATION DE POUDRES METALLIQUES PAR REDUCTION D'OXIDES, POUDRES DE Nb ET Nb-Ta ET ANODE DE CONDENSATEUR OBTENUE
HK02100530.5A HK1039087B (zh) 1998-05-06 2002-01-23 金屬粉末的製備方法

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
US09/073,488 1998-05-06
DE19831280.6 1998-07-13
PCT/US1999/009772 WO2000067936A1 (fr) 1998-05-06 1999-05-05 Poudres metalliques obtenues par reduction d'oxides au moyen de magnesium gazeux

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