Classifications

• • 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
  • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
• • 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
  • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
  • B22F1/05—Metallic powder characterised by the size or surface area of the particles
  • B22F1/052—Metallic powder characterised by the size or surface area of the particles characterised by a mixture of particles of different sizes or by the particle size distribution
• • 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
  • C22C—ALLOYS
  • C22C1/00—Making non-ferrous alloys
  • C22C1/04—Making non-ferrous alloys by powder metallurgy
  • C22C1/045—Alloys based on refractory metals
• • 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
  • H01G9/042—Electrodes or formation of dielectric layers thereon characterised by the material
• • 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

Definitions

• the present invention relates to the production of tantalum-based solid electrolytic capacitors, in particular those having a high specific capacitance of above 70,000 ⁇ FV / g.
• the metallic carrier which at the same time represents the one capacitor electrode (anode), consists of a highly porous, sponge-like structure which is produced by pressing and sintering finely divided primary structures or already sponge-like secondary structures the stability of the compacts essential for further processing to the sintered body, the actual support structure or anode of the capacitor Carrier structure is electrolytically oxidized to the pentoxide ("formed"), wherein the thickness of the pentoxide layer by the maximum voltage of the elektro ⁇ lytic oxidation (“Formiernaps”) is determined.
• the counter electrode is formed by impregnating the sponge-like structure with manganese nitrate, which is thermally converted to manganese dioxide or with a liquid precursor of a polymer electrolyte and polymerization.
• the electrical contacts to the electrodes are represented on one side by a tantalum or niobium wire inserted in the mold before sintering and on the other side by the metallic capacitor sheath insulated against the wire.
• the strength with which the wire is sintered to the anode structure is another essential property for further processing to the capacitor.
• the capacitance C of a capacitor is calculated according to the following formula:
• the quality of such solid electrolytic capacitors depends essentially on the formation of the sponge-like anode structure, in particular the ramification of the open pore structures from larger to the finest pores.
• the sponge-like structure must still form a closed electrically conductive structure after formation of the insulator layer, which grows to one third into the original anode structure and grows up to two-thirds of it and on the other hand leave a contiguous open pore structure so that the cathode formed therein can completely contact the insulation layer surface.
• the sponge-like anode structure is thereby produced starting from finely divided primary and secondary structures by a generally multi-stage production of powder agglomerates, as well as pressing and sintering of the agglomerates, wherein excessive sintering by use of sintering dopants with nitrogen and / or phosphorus, formerly also Boron, silicon, sulfur, arsenic, is prevented.
• the partly too strongly reduced sintering activity for the purposes of agglomeration was counteracted by simultaneous reduction (deoxidizing agglomeration), in that an increased superficial atomic mobility was produced by the simultaneously occurring deoxidation reaction.
• the object of the invention is to expand the possibilities of compromises to be entered, i. to provide a powder for capacitor manufacturing that allows to produce capacitors with a wider range of characteristics or to produce capacitors with specific properties with less stringent process limitations.
• the invention relates to the according to tantalum powder, which consist of agglomerated primary particles with a minimum dimension of 0.2 to 0.8 microns, a specific surface area of 0.9 to 2.5 m 2 / g and a determined according to ASTM B 822 particle size distribution corresponding to a DIO value of 5 to 40 microns, a D50 value of 20 to 140 microns and a D90 value of 40 to 250 microns, wherein the powder is free of an effective content of sintering agents.
• Preferred tantalum powders according to the invention have a content of substances known for their sintering protection activity
• a content of foreign substances in the tantalum powders is effective as a sintering agent depends on the amount thereof as well as the way in which they are present in the powders. Thus, a superficial nitrogen content of 400 ppm can still be effective as a sintering protection agent, while a uniform doping via the volume of the powder particles is generally ineffective.
• the powders according to the invention are particularly preferably distinguished by the freedom of doping elements which are effective as a sintering-protecting agent, except in amounts of unavoidable impurities.
• tantalum powders according to the invention can be processed to form capacitors having a very low residual current, since the sintering protection doping according to the teaching of the prior art was also regularly used to reduce the residual current.
• Tantalum powders according to the invention after pressing into a cylindrical mold with a diameter of 5.1 mm and a length of 5.1 mm at a compacted density of 5.0 g / cm 3, have a crushing strength according to Chatillon of more than 4 kg, preferably more than 5 kg ,
• the invention also provides tantalum solid electrolytic capacitor anodes having a specific surface area of from 0.5 to 1 m 2 / g, which are substantially free of sintering inhibitors.
• the invention further solid electrolytic capacitors with an inventive anode / g, a specific capacity of 40,000 to 150,000 ufv, preferably to 150,000 ufv / g 70,000.
• A denotes the cross-sectional contour (dashed line) of two sintered primary particles with the sintering bridge D.
• the sintering bridge In the case of agglomeration in the presence of In the case of sintering protection with phosphorus or nitrogen (FIG. 1), the sintering bridge has a relatively large notch, whereas in the case of the (inventive) agglomeration without sintering protection doping (FIG.
• the sintering bridge notch is "lost."
• the area of contact formed by the sintering bridge represented by the double arrows D of the primary particles in FIG. 2 is about 3 times as large as in FIG. 1.
• the region shown in gray indicates the pentoxide layer after the anodization, which amounts to approximately 1 / 3 of their thickness perpendicular to the surface (dashed line) hineinge ⁇ grow into the original metal structure and et wa 2/3 has outgrown this.
• Anodes prepared from the powders of the present invention have extremely low specific residual currents and excellent voltage breakdown strength. The reason for this may possibly also be explained from FIGS. 1 and 2. While a “seam” is formed between the two primary particles during the growth of the pentoxide layer at the sintered protective sintered anode (FIG. 1), where the growth boundaries of the two particles grow together, this is in the case of the invention 2), but such a "growth seam” is an enrichment point for impurities and stacking faults in the atomic range and thus the basis for leakage or residual flows or overspill perforations.
• the starting tantalum pentoxide was prepared in a manner known per se by reacting a tantalum fluoric acid with ammonia solution, separating, washing and drying the precipitated tantalum hydroxide, calcining the hydroxide in air and sieving the product to less than 600 .mu.m and then stabilizing under argon at 1700 0 C over 4 hours as well as crushing and sieving produced.
• the starting tantalum pentoxide is placed on a braid of tantalum wire in a tantalum sheet lined furnace above a crucible containing 1.1 times the stoichiometric amount (based on the oxygen content of the pentoxide) of magnesium.
• the furnace has a heater and below the magnesium-containing crucible on a gas inlet opening and above the Tantalpentoxid thoroughlyung a gas outlet opening.
• the furnace is purged with argon. During the reduction argon flows slowly under normal pressure through the furnace. After completion of the reaction and cooling of the furnace, oxygen is gradually added to the furnace to passivate the metal powder.
• the magnesium oxide formed is removed by washing with sulfuric acid and then demineralized water to neutrality.
• the powder After reduction, the powder has an average primary particle size of about 0.2 ⁇ m determined from SEM images, a BET specific surface area of 2.3 m 2 / g and a particle size distribution according to ASTM B 822 corresponding to D10 of 16, 3 ⁇ m, D50 of 31, 7 ⁇ m and D90 of 93, 2 ⁇ m.
• Part of the powder is doped by soaking with phosphoric acid solution and drying with 150 ppm phosphorus.
• both phosphorus-doped and non-doped samples of the tantalum powder are first deoxidized by adding the 1.5-fold stoichiometric amount of magnesium turnings and heating for two hours to the deoxidation temperature given in Table 1 and rubbed after cooling through a sieve of mesh size 300 microns ,
• FSSS means the mean grain diameter determined by Fisher Sub Sieve Sizer according to ASTM B 330.
• the compression strength was determined on a powder compact of 5.1 mm in length and 5.1 mm in diameter with a nip density of 5.0 g / cm 3 with a Chatillon force gauge.
• BET denotes the specific surface area determined by the known method according to Brunauer, Emmet and Teller.
• the "flow-through” (“Hall-flow”) indicates the flow time in seconds of 25 g of powder through a 1/10 "hopper according to ASTM B 213.
• Mastersizer D10, D50 and D90 designate the 10, 50 and 90 mass percentiles of the particle size distribution of the powder determined according to ASTM B 822 with the Malvern MasterSizer S ⁇ instrument by laser diffraction once without and once with ultrasound treatment.
• compacts of dimension 3 mm in diameter and 3.96 mm in length are produced with a compressed density of 5.0 g / cm 3 , wherein a tantalum wire of 0.2 mm diameter inserted as a contact wire into the press die before filling the powder axially has been.
• the compacts are sintered in the high vacuum to anodes at the sintering temperature indicated in the table for 10 minutes.
• the “wire tensile strength” was determined as follows: The anode wire is inserted through the opening of 0.25 mm diameter of a holding plate and the free end is clamped in the holding clamp of a Chatillon force gauge ,
• the anode bodies are immersed in 0, l-% phosphoric acid and formed at a current limited to 150 mA current up to a forming voltage of 30 V. After dropping the current, the voltage is maintained for one hour.
• a cathode of 18% strength sulfuric acid is used. It was measured with an alternating voltage of 120 Hz.

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• Engineering & Computer Science (AREA)
• Power Engineering (AREA)
• Microelectronics & Electronic Packaging (AREA)
• Chemical & Material Sciences (AREA)
• Materials Engineering (AREA)
• Organic Chemistry (AREA)
• Metallurgy (AREA)
• Mechanical Engineering (AREA)
• Manufacturing & Machinery (AREA)
• Powder Metallurgy (AREA)
• Manufacture Of Metal Powder And Suspensions Thereof (AREA)
• Manufacture And Refinement Of Metals (AREA)
• Conductive Materials (AREA)
• Battery Electrode And Active Subsutance (AREA)
• Inorganic Compounds Of Heavy Metals (AREA)

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