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
  • B22F9/00—Making metallic powder or suspensions thereof
  • B22F9/02—Making metallic powder or suspensions thereof using physical processes
  • B22F9/04—Making metallic powder or suspensions thereof using physical processes starting from solid material, e.g. by crushing, grinding or milling
• • 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
  • B22F1/14—Treatment of metallic powder
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C27/00—Alloys based on rhenium or a refractory metal not mentioned in groups C22C14/00 or C22C16/00
  • C22C27/04—Alloys based on tungsten or molybdenum
• • 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
• • 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
  • 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
  • B22F1/054—Nanosized particles
• • 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
  • B22F2998/00—Supplementary information concerning processes or compositions relating to powder metallurgy
  • B22F2998/10—Processes characterised by the sequence of their steps

Definitions

• the present invention relates to a method for producing tungsten fine powder. More specifically, the present invention relates to a method for processing tungsten powder into a tungsten powder having a finer particle diameter that is useful for an electrolytic capacitor, and a method for producing tungsten fine powder using the method.
• capacitors used in these electronic devices are smaller and lighter, with larger capacitance and lower ESR (equivalent series resistance). ) Is required.
• an anode body of a capacitor made of a sintered body of valve action metal powder such as tantalum capable of anodization is anodized, and a dielectric layer made of these metal oxides is formed on the surface.
• An electrolytic capacitor has been proposed.
• Electrolytic capacitors that use tungsten as the valve metal and have a sintered body of tungsten powder as the anode body have the same volume of anode body using tantalum powder of the same particle size, compared to electrolytic capacitors that can be obtained with the same conversion voltage. Although a large capacity can be obtained, the leakage current (LC) is large and it has not been put to practical use as an electrolytic capacitor. In order to improve this, a capacitor using an alloy of tungsten and another metal has been studied. However, although the leakage current is somewhat improved, it has not been sufficient (Japanese Patent Laid-Open No. 2004-349658 (US6876083)). : Patent Document 1).
• Patent Document 2 Japanese Patent Laid-Open No. 2003-272959 discloses a capacitor using a tungsten foil electrode on which a dielectric layer selected from WO 3 , W 2 N, and WN 2 is formed. This is not a solution for the leakage current.
• Patent Document 3 International Publication No. 2004/055843 (US7154743) discloses an electrolytic capacitor using an anode selected from tantalum, niobium, titanium, and tungsten. There is no description of the specific examples used.
• the anode body for an electrolytic capacitor sintered after forming the tungsten powder has the same volume, the smaller the particle diameter of the tungsten powder, the larger the capacity of the anode body can be made. The smaller the particle size, the better, but the average particle size of commercially available tungsten powder is 0.5 to 20 ⁇ m.
• Tungsten powder can be produced by treating tungsten oxide, halide, ammonium salt or the like with a reducing agent such as hydrogen.
• a reducing agent such as hydrogen.
• the reduction rate is increased, there is a problem that a composite oxide is generated. Therefore, in order to produce a finer powder, the reduction rate must be slowed, resulting in a reduction in production efficiency and an increase in cost.
• a material having a wide explosion range, such as hydrogen gas must be handled by a complicated process having an expensive control device.
• An object of the present invention is to provide a tungsten powder processing method for obtaining a tungsten powder having a smaller particle size as a raw material for a capacitor having tungsten as an anode (hereinafter referred to as a tungsten capacitor), and a method for producing a tungsten fine powder using the method. It is to provide.
• the present inventors have found that a tungsten fine powder suitable for a tungsten capacitor can be obtained by electrolytic oxidation of the surface of currently available tungsten powder, and the present invention has been completed. did. That is, the present invention relates to the following tungsten powder refinement method and tungsten powder production method.
• Fine powder of tungsten powder characterized in that an oxide film is formed on the surface of tungsten powder particles by electrolytic oxidation while stirring the tungsten powder in an electrolytic solution, and the oxide film is removed with an alkaline aqueous solution.
• Method. [2] The method for finely pulverizing tungsten powder according to [1], wherein the removal of the oxide film with an alkaline aqueous solution includes mechanically removing a reaction product on the particle surface of the tungsten powder. [3] The tungsten powder thinning method according to item 1 or 2, wherein the electrolytic solution is an aqueous solution of a mineral acid.
• a method for producing a tungsten fine powder characterized in that a tungsten powder having an average particle size of 0.04 to 0.4 ⁇ m is obtained by a process including the method according to 1 to 6 above.
• the range of the average particle size ( ⁇ m), the true density (g / cm 3 ), and the BET specific surface area (m 2 / g) is in the range of 6 ⁇ 0.4 by the steps including the methods 1 to 6 above.
• a method for producing tungsten fine powder, characterized in that tungsten powder is obtained.
• the average particle diameter is 0.04 to 0.4 ⁇ m, and the product of the average particle diameter d ( ⁇ m), the true density M (g / cm 3 ), and the BET specific surface area S (m 2 / g) ( A tungsten powder having a dMS) value in the range of 6 ⁇ 0.4.
• a tungsten powder having a fine particle size and a substantially spherical particle shape suitable for an electrolytic capacitor is produced from tungsten powder that is currently commercially available or tungsten powder that can be produced by a known method. can do. Since the tungsten powder obtained by the present invention has a fine particle size, the capacity of the obtained capacitor is increased. Moreover, since the particle shape becomes closer to a sphere, the fluidity of the tungsten powder is improved. Therefore, it becomes easy to handle the powder in the granulated powder production process.
• the raw material tungsten powder to be finely divided is preferably one having an average particle diameter in the range of 0.1 to 10 ⁇ m.
• a method for obtaining the raw material tungsten powder in addition to commercially available products, those produced by known methods, for example, a method of pulverizing tungsten trioxide powder in a hydrogen atmosphere, or tungstic acid or tungsten halide with hydrogen, sodium, etc. It can obtain by selecting suitably the method etc. which reduce by. Moreover, what was obtained by selecting reduction conditions directly or through several processes from a tungsten containing mineral may be used.
• tungsten powder that has been pretreated by a chemical oxidation method is used as the raw material tungsten powder as described later, or the method of the present invention is applied. You may use the tungsten powder obtained by doing as raw material tungsten powder. By using the tungsten powder that has been subjected to the fine powdering process as the raw material tungsten powder, a tungsten powder having a smaller particle diameter can be obtained. For example, when application of the method of the present invention is repeated, tungsten powder having an average particle size of 0.04 ⁇ m or less can be obtained.
• the dielectric layer is formed by anodic oxidation
• the lower limit value of the particle size of tungsten powder used for the capacitor is at least twice the thickness of the dielectric layer to be formed. For example, when the rated voltage is 1.6 V, it is 0.04 ⁇ m or more. When the particle size is less than this, when anodization is performed, a sufficient conductive tungsten portion does not remain, making it difficult to form an anode of the electrolytic capacitor.
• the particle size of the tungsten powder is preferably 0.04 to 0.4 ⁇ m, more preferably 0.08 to 0.2 ⁇ m.
• the raw material tungsten powder used in the method of the present invention may contain impurities as long as the capacitor characteristics do not deteriorate, or elements such as silicon, nitrogen, carbon, boron, phosphorus, oxygen, etc. for improving the capacitor characteristics. It may be processed to include. However, the processing of the particle surface such as silicidation, nitridation, carbonization, or boride treatment, which will be described later, is preferably performed in a step after applying the present invention.
• the oxide film on the surface is removed and the tungsten powder refined
• Oxidation of the tungsten powder particle surface can be carried out by chemical oxidation or electrolytic oxidation, but the method of finely pulverizing using electrolytic oxidation (hereinafter referred to as electrolytic oxidation method) determines the amount of oxide film generated by the applied voltage during electrolytic oxidation. Therefore, it can be easily operated as compared with a method of finely pulverizing using chemical oxidation (hereinafter referred to as chemical oxidation method).
• the electrolytic oxidation method can be preferably applied to the production of finer tungsten powder that requires more accurate control of the amount of oxide film produced.
• Tungsten powder may be thinned only by electrolytic oxidation, but when relatively large particles (for example, average particle diameter of 1 ⁇ m or more) are finely divided, pretreatment by chemical oxidation is performed to some extent.
• the electrolytic oxidation method is applied after pulverization (for example, an average particle size of 0.5 ⁇ m or less), the applied voltage at the time of electrolytic oxidation can be kept low, so that the operation becomes easy.
• an electrolytic solution such as an aqueous solution of a mineral acid or a salt thereof can be used, but an aqueous mineral acid solution is preferable because washing after oxidation is easy.
• the mineral acid include phosphoric acid, nitric acid, hydrochloric acid, sulfuric acid, boric acid and the like, but phosphoric acid or boric acid aqueous solution is preferable in that a relatively defective oxide film is easily obtained and easily removed with an aqueous alkaline solution later.
• the concentration of the mineral acid aqueous solution is preferably 0.1 to 5% by mass. When the concentration becomes high, cleaning of tungsten powder, which is a subsequent process, becomes troublesome.
• the raw material tungsten powder is put into a metal container containing an electrolytic solution, and a predetermined voltage is applied under stirring with the metal stirring rod as the anode and the container as the cathode, preferably at room temperature.
• the boiling point of the aqueous solution more preferably 30 to 80 ° C., is preferably applied for 10 minutes to 100 hours, more preferably 1 to 10 hours for oxidation. At this time, it is carried out while replenishing the solvent component disappearing by evaporation if necessary.
• what is necessary is just to set the voltage to apply according to the grade of desired fine powdering. When the applied voltage is further increased, the amount of oxide film is increased and the particle diameter can be further reduced. The specific voltage is obtained by a preliminary experiment.
• the applied voltage is preferably 100 V or less, more preferably 50 V or less, and if necessary, the pulverization operation may be repeated.
• the operation of removing the liquid by decantation or the like is repeated, and the tungsten powder is washed with a solvent such as water. The tungsten powder in this state changes from black to yellowish blue.
• the oxide film of tungsten powder with the oxidized surface obtained above is treated with an alkaline aqueous solution and at least chemically removed.
• the stirring is performed while mechanically removing the product generated on the surface of the tungsten particles by a device capable of strong stirring such as a homogenizer.
• a device capable of strong stirring such as a homogenizer.
• the alkaline solution for example, a sodium hydroxide aqueous solution, a potassium hydroxide aqueous solution, an aqueous ammonia or the like is used, and a sodium hydroxide aqueous solution or a potassium hydroxide aqueous solution is preferable.
• an alkaline aqueous solution is added to the tungsten powder whose surface is oxidized, and the mixture is stirred and allowed to stand. After removing the liquid by decantation, a solvent such as water is added, and the mixture is stirred and left to stand. Repeat a series of operations to be performed several times. By these operations, the tungsten powder becomes black, and the oxide formed on the surface is removed. Thereafter, it is dried by a vacuum dryer (for example, a temperature of 50 to 180 ° C. under reduced pressure at 104 to 102 Pa) and cooled to room temperature. Next, by gradually putting air so as not to ignite and taking it out into the air, a finely divided tungsten powder having a smaller particle size than that of the raw material tungsten powder can be obtained.
• a vacuum dryer for example, a temperature of 50 to 180 ° C. under reduced pressure at 104 to 102 Pa
• the raw material tungsten powder is dispersed by stirring or the like in an aqueous oxidizing agent solution, and the surface is oxidized by holding for a predetermined time.
• an apparatus capable of strong stirring such as a homogenizer.
• oxidation proceeds faster when oxidized at a high temperature.
• the oxidizing agent include manganese (VII) compounds such as permanganate; chromium (VI) compounds such as chromium trioxide, chromate and dichromate; perchloric acid, chlorous acid and hypochlorous acid.
• Halic acid compounds such as acids and their salts; peroxides such as hydrogen peroxide, diethyl peroxide, sodium peroxide, and lithium peroxide; peroxo acids such as peracetic acid and persulfate and their salts .
• peroxides such as hydrogen peroxide, diethyl peroxide, sodium peroxide, and lithium peroxide
• peroxo acids such as peracetic acid and persulfate and their salts .
• hydrogen peroxide and ammonium persulfate are preferable because they are easy to handle, stable as an oxidizing agent, and easily soluble in water.
• the concentration of the oxidizing agent in the aqueous solution is in a range from about 1% to the saturation solubility of the oxidizing agent. The oxidant concentration is appropriately determined by preliminary experiments.
• the oxidation time is from 1 hour to 1000 hours, preferably from 1 hour to 100 hours, and the oxidation temperature is from room temperature to the boiling point of the solvent, preferably from 50 ° C. to the boiling point of the solution.
• the tungsten powder is separated from the oxidation reaction solution by an operation such as decantation, and then washed by repeating a series of operations of adding to a solvent, stirring, standing, and decantation. In the tungsten powder in this state, the black color of the raw material is changed to yellowish blue, and it can be visually confirmed that the surface is oxidized.
• the solvent used in each step of the present invention is not limited to water and is selected from a mixed aqueous solution with a water-soluble organic solvent (for example, ethanol, methanol, etc.) from the viewpoint of powder dispersibility and decantation time. May be.
• a water-soluble organic solvent for example, ethanol, methanol, etc.
• the removal of the oxide film of the tungsten powder having the oxidized surface obtained as described above is performed in the same manner as the removal of the oxide film by the electrolytic oxidation method described above.
• a substantially spherical tungsten particle powder can be obtained unless the particle shape of the raw material tungsten powder is particularly high in anisotropy.
• the particles are spherical because the average particle diameter (d) ( ⁇ m), true density (M) (g / cm 3 ), and BET specific surface area (S) (m 2 / g) of the obtained tungsten powder are It can be confirmed by satisfying the following formula. That is, the product (d ⁇ S ⁇ M) (abbreviated as dSM) of the average particle diameter d ( ⁇ m), true density M (g / cm 3 ), and BET specific surface area S (m 2 / g) of the obtained tungsten powder.
• the obtained tungsten powder particles are substantially spherical.
• the value of dMS of the tungsten powder obtained by the present invention is usually in the range of 6 ⁇ 0.4.
• the tungsten powder obtained by applying the method of the present invention can be used as a raw material tungsten powder to obtain a tungsten powder composed of particles close to a true sphere.
• the dielectric layer formed on the surface of particles close to a spherical shape has a substantially uniform curvature, and there is no deterioration because there is no portion that bends with a small curvature that tends to concentrate stress. As a result, a capacitor with better LC characteristics can be obtained.
• the tungsten powder produced by the method of the present invention may be directly sintered to form a sintered body, or alternatively, the powder granulated into granules of about 10 to 300 ⁇ m may be sintered to form a sintered body. . Granulated ones are easier to handle and easier to keep ESR low. Further, the tungsten powder produced by the method of the present invention is subjected to silicidation, nitridation, carbonization, or boride treatment, and a part of the tungsten particle surface is tungsten silicide, tungsten nitride, tungsten carbide, and boride. A tungsten powder containing at least one selected from tungsten may be used.
• these processes can also be applied at the stage when the granulated powder or sintered body is obtained.
• This sintered body is used as one electrode (anode), and an electrolytic capacitor is produced with a dielectric interposed between the counter electrode (cathode).
• the particle diameter, specific surface area, and true density were measured by the following methods.
• the particle size was measured by laser diffraction scattering method using HRA9320-X100 manufactured by Microtrack, and the particle size value (D 50 ; ⁇ m) corresponding to 50% by volume was calculated as the average particle size. (D).
• this measurement method is a measurement method of the secondary particle size, the dispersibility of the tungsten powder is good to some extent, and therefore the measurement result can be a value close to the primary particle size. Therefore, the measurement result may be substantially regarded as the primary particle diameter, and applied to the above-described equation (1) to determine the particle shape.
• the specific surface area (S; m 2 / g) was measured by BET method using NOVA2000E (SYSMEX).
• the true density (M; g / cm 3 ) was measured by a pycnometer method (20 ° C.).
• Example 1 200 g of tungsten powder having an average particle diameter of 1 ⁇ m obtained by hydrogen reduction of ammonium tungstate was put into 500 mL of distilled water in which 5% by mass of ammonium persulfate was dissolved, and a homogenizer NS-51 manufactured by Microtech Nichion Co., Ltd. was used. And stirred at 50 ° C. for 24 hours. Meanwhile, continued to replenish the evaporating water. After allowing the powder to settle for 17 hours at room temperature, the liquid was removed by decantation. Further, 200 mL of distilled water was added, and the mixture was stirred for 5 minutes with the same homogenizer. After standing for several hours, the liquid was removed by decantation.
• tungsten powder containing water after decantation 100 g of powder alone was transferred to a separately prepared stainless steel container, and 300 mL of 1% by mass phosphoric acid aqueous solution was added as an electrolytic solution.
• a stainless steel stirring bar (4 cm long stainless steel wings are installed at the bottom of the bar, 90 degrees apart from each other) is placed in the electrolyte, and the stirring bar is used as the anode.
• 20 V was applied using the container as a cathode, and electrolytic oxidation was performed while stirring at 50 ° C. for 5 hours at a rotation speed of 100 rpm. Meanwhile, continued to replenish the evaporating water.
• the tungsten powder in this state was black and the oxide formed on the surface was removed. Thereafter, a part of the powder was transferred to a vacuum dryer, dried at 50 ° C. under reduced pressure, and then returned to room temperature. Next, air was gradually introduced so as not to ignite, and was taken out into the air.
• the produced powder had an average particle size (d) of 0.2 ⁇ m, a specific surface area (S) of 1.5 m 2 / g, and a true density (M) of 19.3.
• the resulting powder had an average particle size, specific surface area, and true density product (dMS) of 5.8.
• Example 2 The electrolyte solution of Example 1 was used as a mixed solution of 100 mL of 1.5 mass% boric acid methanol and 350 mL of water instead of 300 mL of 1 mass% phosphoric acid water.
• the decantation liquid was a mixed liquid of methanol and water at the same ratio.
• methanol continued to be replenished during electrolytic oxidation.
• tungsten powder was obtained in the same manner as in Example 1.
• the produced powder had an average particle size (d) of 0.16 ⁇ m, a specific surface area (S) of 2.0 m 2 / g, and a true density (M) of 19.3.
• the average particle size, specific surface area, and true density product (dMS) of the obtained powder was 6.2.
• the product of average particle diameter, specific surface area, and true density (dMS) was in the range of approximately 6 ⁇ 0.2, and it was confirmed that the particle shape was approximately spherical. .

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• 2012
  • 2012-08-29 WO PCT/JP2012/071761 patent/WO2013080617A1/ja not_active Ceased
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