WO2004067211A1 - Fine metal powder, process for producing the same, and conductive paste containing the fine metal powder - Google Patents

Fine metal powder, process for producing the same, and conductive paste containing the fine metal powder Download PDF

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Publication number
WO2004067211A1
WO2004067211A1 PCT/JP2004/000081 JP2004000081W WO2004067211A1 WO 2004067211 A1 WO2004067211 A1 WO 2004067211A1 JP 2004000081 W JP2004000081 W JP 2004000081W WO 2004067211 A1 WO2004067211 A1 WO 2004067211A1
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Prior art keywords
nickel
powder
metal
gas
fine powder
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PCT/JP2004/000081
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French (fr)
Japanese (ja)
Inventor
Mitsugu Yoshida
Koji Tokita
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Toho Titanium Co., Ltd.
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Publication of WO2004067211A1 publication Critical patent/WO2004067211A1/en

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES OR LIGHT-SENSITIVE DEVICES, OF THE ELECTROLYTIC TYPE
    • H01G4/00—Fixed capacitors; Processes of their manufacture
    • H01G4/002—Details
    • H01G4/005—Electrodes
    • H01G4/008—Selection of materials
    • H01G4/0085—Fried electrodes
    • 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
    • B22F1/145—Chemical treatment, e.g. passivation or decarburisation
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C8/06—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
    • C23C8/08—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases only one element being applied
    • C23C8/10—Oxidising
    • C23C8/12—Oxidising using elemental oxygen or ozone
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
    • H01B1/00—Conductors or conductive bodies characterised by the conductive materials; Selection of materials as conductors
    • H01B1/20—Conductive material dispersed in non-conductive organic material
    • H01B1/22—Conductive material dispersed in non-conductive organic material the conductive material comprising metals or alloys

Definitions

  • the present invention relates to fine powders of metals such as nickel, copper or silver suitable for a conductive paste used in, for example, electronic parts and the like, a method of producing the same, and fine powders of these metal powders.
  • the present invention relates to a conductive paste using the same, and particularly relates to a manufacturing technique for fine metal powder and the like having excellent sintering characteristics when used as an internal electrode of a laminated ceramic capacitor.
  • a multilayer ceramic capacitor is formed by alternately laminating ceramic dielectric layers and metal fine powder internal electrodes by laminating and sintering ceramic paste and metal fine powder paste.
  • Conductive metal fine powders such as nickel, copper, silver and the like are useful as materials for internal electrodes of laminated ceramic capacitors, and in particular, nickel fine powders have attracted attention in such applications.
  • multilayer ceramic capacitors are manufactured as follows. That is, a dielectric green sheet is produced by forming a paste in which a dielectric ceramic powder such as barium titanate is mixed with an organic binder into a sheet. On the other hand, a fine metal powder for the internal electrode is mixed with an organic solvent, an organic compound such as an organic binder, etc. to form a fine metal powder paste, which is printed on a dielectric green sheet and dried. After laminating this electrode layer coated dielectric green sheet, it is heated and pressed to form a laminated body, and processed into a desired shape.
  • a dielectric green sheet is produced by forming a paste in which a dielectric ceramic powder such as barium titanate is mixed with an organic binder into a sheet.
  • a fine metal powder for the internal electrode is mixed with an organic solvent, an organic compound such as an organic binder, etc. to form a fine metal powder paste, which is printed on a dielectric green sheet and dried. After laminating this electrode layer coated dielectric green sheet, it is heated and
  • the laminate is subjected to heat treatment (debinding treatment) in a weakly acidic atmosphere to remove organic components such as an organic binder, and then the temperature is around 130 ° C. or higher in a reducing atmosphere.
  • the outer electrode is baked on the outside of the dielectric ceramic layer to obtain a multilayer ceramic capacitor.
  • the binder removal treatment is performed in an oxidizing atmosphere in order to remove the organic compound. For this reason, the metal fine powder is oxidized during the binder removal processing to cause expansion of the volume. Furthermore, after the binder removal processing, the laminate is heated to a higher temperature for sintering, but this sintering is a reducing atmosphere. As it takes place in the metal fine powder is reduced and volume contraction occurs.
  • the volume change due to the expansion and contraction of the metal fine powder occurs due to the oxidation-reduction reaction.
  • the dielectric itself changes its volume due to sintering, but if the sintering start temperature of the metal fine powder used for the internal electrode is extremely lower than the sintering start temperature of the dielectric layer, The rapid contraction causes a volume change between the internal electrode layer and the dielectric layer to generate a defect called delamination. Since this delamination causes a decrease in capacitor capacity, there is a demand for a metal fine powder which has a high sintering start temperature and in which rapid sintering does not occur.
  • Japanese Patent Application Laid-Open No. 11 18017 proposes a technique for incorporating sulfur into nickel powder. ing.
  • the present invention it is possible to increase the sintering start temperature of the metal fine powder without containing sulfur in the above-mentioned nickel powder, and to suppress the generation of delamination,
  • the purpose is to provide the manufacturing method and the conductive paste.
  • the sintering start temperature of the metal fine powder That is, sintering is not started while the oxide film is present on the surface of the metal fine powder, but sintering of the metal powder is started when the oxide film is reduced to disappear as the firing temperature rises.
  • sintering usually starts at 200 to 300 ° C., it is not reduced even when heated to a temperature of 200 to 300 ° C. or higher. By forming such an oxide film, the generation of the above-mentioned delamination can be suppressed.
  • the present inventors have found that the oxide film produced by ozone gas starts to be reduced at a higher temperature compared to a normal oxide film. From the fact that this oxide film on the surface of metal powder It has been found that, if it is formed, it is possible to shift the sintering start temperature of the metal fine powder to a higher temperature range, thereby suppressing the occurrence of the above-mentioned delamination.
  • the present inventors have found that the metal fine powder having an oxide film formed by ozone gas has a sintering start temperature shifted to a higher temperature range compared to the conventional case, so the shrinkage rate of the metal fine powder at the time of sintering decreases. It has been found that this can also suppress the occurrence of the above-mentioned delamination.
  • the oxidation treatment with ozone gas can be performed at a lower temperature than the oxidation treatment using normal oxygen, the aggregation due to the sintering of the metal fine powder during the oxidation treatment is prevented.
  • the oxidation treatment with ozone gas can be performed at a lower temperature than the oxidation treatment using normal oxygen, the aggregation due to the sintering of the metal fine powder during the oxidation treatment is prevented.
  • the metal fine powder of the present invention is characterized by having an oxide film formed by ozone gas on the surface.
  • the sintering start temperature of the metal fine powder is shifted to a higher temperature range by delaying the loss due to reduction of the oxide film. Furthermore, by reducing the shrinkage rate of the metal powder during sintering, it is possible to suppress the delamination occurring between the internal electrode layer and the dielectric layer. Further, according to the present invention, the oxidation treatment in the low temperature range with ozone gas prevents the aggregation due to sintering of the metal fine powder during the oxidation treatment, and structural defects such as a short circuit of the internal electrode in the manufacturing process of the multilayer ceramic capacitor.
  • the metal fine powder of the present invention is mixed with an organic solvent, an organic binder such as an organic compound to form a metal fine powder paste and used as an internal electrode of a multilayer ceramic capacitor, the sintering start temperature is high. Therefore, the difference with the sintering start temperature of the dielectric is not large, the shrinkage ratio is low, the volume change with the dielectric is low, and the number of agglomerated particles is small. It is possible to suppress the occurrence of structural defects such as delamination, cracks, shorts of internal electrodes, and so on.
  • a multilayer ceramic capacitor Can realize the reduction of the thickness of the internal electrode and the reduction of resistance accompanying the miniaturization of the In such metal fine powder, it is desirable that the thickness of the oxide film be 1 to 10 nm. If the thickness of the oxide film is less than 1 nm, delay of loss due to reduction of the oxide film can not be sufficiently achieved. Therefore, the sintering start temperature of the metal powder is higher than that of the oxide film. As a result, the occurrence of the above-mentioned delamination can not be suppressed. In addition, when the thickness of the oxide film exceeds 10 nm, the sinterability of the metal fine powder is unfavorably lowered.
  • the thickness of the above-mentioned oxide film is preferably 2 to 10 nm, more preferably 2 to 5 nm, in order to make such prevention of occurrence of delamination and prevention of sintering more effective. Further preference is given.
  • metal fine powder is fine metal powder suitable for conductive paste filler such as nickel, copper and silver as metal fine powder of the present invention, and further, aluminum, titanium, chromium and manganese Fine powders of metals such as iron, cobalt and bismuth, fine powders of alloys of these, and the like can be mentioned.
  • nickel fine powder which is excellent in conductivity, can be fired in a reducing atmosphere, and is inexpensive is optimal.
  • the average particle size of the fine metal powder it is particularly desirable to set the average particle size of the fine metal powder to 1 m or less.
  • the average particle size exceeds 1 m, it is not preferable because structural defects such as a decrease in sinterability and a short circuit between internal electrodes of the multilayer ceramic capacitor are likely to occur.
  • the average particle size is excessively reduced, sintering and aggregation of the metal fine powders proceed during the oxidation process of the present invention. It is desirable to use 1 / im.
  • the ratio of the oxygen concentration of the metal fine powder to the thickness of the oxide film be 0.3 to 1.0.
  • the oxygen concentration means the oxygen concentration of the metal fine powder containing the oxide film
  • the thickness of the oxide film means that the center of the metal fine powder containing the oxide film is a virtual sphere. Mean the thickness of the oxide film measured in the radial direction. If the above ratio is less than 0.3, since the oxide film is easily reduced, the delay of the loss of the oxide film can not be sufficiently achieved.
  • the sintering start temperature of the metal fine powder Can not be transferred to a higher temperature range, and as a result, the occurrence of the above-mentioned delamination can not be suppressed.
  • the above ratio exceeds 1.0, the sinterability of the metal fine powder is lowered, which is not preferable.
  • the above ratio is preferably 0.3 to 0.8 nm, and 0.5 to 0.5 nm. It is further preferred that
  • the method for producing metal fine powder of the present invention is a method for advantageously producing the above-mentioned metal fine powder, wherein the metal fine powder is treated in a carbonic acid aqueous solution and then subjected to an oxidation treatment in an ozone gas atmosphere. , It is characterized by forming an oxide film on the surface.
  • the oxide film formed by the ozone gas is formed on the surface of the metal fine powder, whereby the sintering start temperature of the metal fine powder is determined by delaying loss due to reduction of the oxide film.
  • the oxidation treatment in the low temperature range with ozone gas prevents aggregation due to sintering between metal fine powders during oxidation treatment, and causes structural defects such as a short circuit of internal electrodes in the multilayer ceramic capacitor manufacturing process.
  • By suppressing the generation it is possible to realize the miniaturization of the multilayer ceramic capacitor and the reduction in thickness and resistance of the internal electrode accompanying the increase in capacity.
  • the oxidation treatment in an ozone concentration range of 1 to 20 vol%.
  • the oxidation treatment is performed at an ozone concentration of less than 1 V o 1%, a long time of oxidation treatment is necessary to obtain a strong oxide film that shifts the sintering start temperature to a high temperature region, which is practically useful. is not.
  • the oxidation treatment is performed at an ozone concentration of more than 20 vo 1%, the inside of the metal fine powder is easily oxidized, which tends to cause a decrease in sinterability, and the cost also becomes expensive. It is not practical.
  • the treatment in a carbonated aqueous solution is pH 5.
  • metal fine powder As nickel, and it is not practical because the cost ratio is not high, and the metal fine powder manufactured according to the above-mentioned production method is practical.
  • a powder By using a powder, a conductive paste can be obtained which can prevent the occurrence of the above-mentioned delamination when it is used for an electronic component or the like.
  • the metal fine powder produced by the method of producing a metal fine powder of the present invention may be a metal fine powder suitable for various uses such as a copper or silver paste filler, a titanium composite material, or a catalyst other than nickel. Powders can be mentioned, and furthermore, it is also possible to produce metal fine powders such as aluminum, titanium, chromium, manganese, iron, cobalt, platinum and bismuth.
  • the metal fine powder in the present invention can be produced by a known method such as a gas phase method or a liquid phase method, but in particular, it is possible to form a metal fine powder by bringing a metal chloride gas into contact with a reducing gas.
  • Phase reduction method, or spray pyrolysis method that thermally decomposes by spraying a pyrolytic metal compound This method is preferred in that the final particle size can be easily controlled, and spherical particles can be produced efficiently.
  • the vaporized nickel chloride gas is reacted with a reducing gas such as hydrogen, but even if solid nickel chloride is heated and evaporated, a salty nickel gas is generated. Good.
  • a reducing gas such as hydrogen
  • the metal nickel is brought into contact with the chlorine gas to continuously generate the nickel chloride gas, and the nickel chloride gas is directly used in the reduction step.
  • a preferred method is to supply and then contact with a reducing gas to continuously reduce the nickel chloride gas to produce a fine nickel powder.
  • the particle size of the fine nickel powder to be produced is determined by the conditions such as the partial pressure of the chloride digel gas and the temperature in the reduction step. According to the above method for producing fine nickel powder, nickel chloride gas is generated in an amount corresponding to the amount of chlorine gas supplied. Therefore, by controlling the amount of chlorine gas supplied, the amount of chlorinated Nigel gas supplied to the reduction step is The amount can be adjusted, and this can control the particle size of the fine nickel powder produced.
  • metal chloride gas is generated by the reaction of chlorine gas and metal, unlike the method of generating metal chloride gas by heating and evaporation of solid metal chloride, the use of carrier gas can be reduced. Depending on the manufacturing conditions, it may not be possible to use it. Therefore, in the gas phase reduction reaction, the manufacturing cost can be reduced by reducing the amount of carrier gas used and the heating energy associated therewith.
  • the partial pressure of nickel chloride gas in the reduction step can be controlled by mixing an inert gas with the nickel chloride gas generated in the chlorination step.
  • the particle size of the nickel powder can be controlled, thereby stabilizing the particle size of the nickel fine powder.
  • the particle size can be set arbitrarily.
  • the conditions for producing fine nickel powder by the above-mentioned vapor phase reduction method are:
  • the particle diameter of the starting material, ie, metal nickel is preferably in the form of particles, lumps, plates, etc. of about 5 to 20 mm, and its purity is preferably 9 9 5% or more is preferable.
  • This metallic nickel is first reacted with chlorine gas to form nickel chloride gas, and the temperature at that time is set to 800 ° C. or higher in order to allow the reaction to proceed sufficiently, and the melting point of nickel is 1 Lower the temperature to 4 5 3 ° C. In consideration of the reaction rate and the durability of the chlorination furnace, practically, the range of 900 ° t to 110 ° C is preferable.
  • the nickel chloride gas is directly supplied to the reduction step to cause a catalytic reaction with a reducing gas such as hydrogen gas, but an inert gas such as nitrogen or argon is mixed with 1 to 30 mol% of nickel chloride gas.
  • the mixed gas may be introduced into the reduction step.
  • chlorine gas can be supplied to the reduction step together or independently with nickel chloride gas.
  • the temperature of the reduction reaction may be a temperature sufficient to complete the reaction, but since it is easier to handle when producing a solid nickel powder, the melting point or less of nickel is preferable, considering the economics. 0 ° C. to 1 100 ° C. is practical.
  • the formed nickel powder is cooled.
  • the reduction reaction was completed to prevent the formation of secondary particles by aggregation of the primary particles of the formed nickel and to obtain a Nikkell powder of a desired particle diameter, the gas around 100 ° C. It is desirable to rapidly cool the stream to about 400-800 ° C. by blowing inert gas such as nitrogen gas. After that, the produced nickel powder is separated and recovered, for example, by bagfill Yuichi et al.
  • a thermally decomposable metal compound is used as a raw material, specifically, metal nitrates, sulfates, oxynitrates, oxysulfates, chlorides, It is one or more of an ammonium complex, a phosphate, a carboxylate, an alkoxy compound and the like.
  • the solution containing the nickel compound is sprayed to form fine droplets, and as the solvent at this time, water, alcohol, acetone, ether or the like is used.
  • the method of spraying is performed by a spraying method such as ultrasonic or double jet nozzle.
  • the heating temperature at this time is The temperature is higher than the temperature at which certain metal compounds are thermally decomposed, and preferably around the melting point of the metal.
  • an aqueous nickel solution containing nickel sulfate, nickel chloride or nickel complex is added to an alkali metal hydroxide such as sodium hydroxide or the like.
  • an alkali metal hydroxide such as sodium hydroxide or the like.
  • the metallic nickel powder thus produced is subjected to a unwinding treatment as necessary to obtain uniform particles.
  • FIG. 1 shows an apparatus for producing fine metal powder used in the present invention.
  • the chlorination step is preferably performed by a chlorination furnace 10 as shown in the figure.
  • a supply pipe 11 for supplying raw material metal nickel (M) is installed at the upper end face of the chlorination furnace 10.
  • a chlorine gas supply pipe 12 is connected to an upper portion of one of the chlorination furnaces 10, and an inert gas supply pipe 13 is connected to the lower side thereof.
  • a heating means 14 is disposed around the chlorination furnace 10, and a transfer pipe / nozzle 15 is connected to the other upper part of the chlorination furnace 10.
  • the chlorination furnace 10 may be vertical or horizontal, but is preferably vertical to uniformly carry out solid-gas contact reaction.
  • Chlorine gas is introduced from the chlorine gas supply pipe 12 continuously by measuring the flow rate.
  • the transfer pipe / nozzle 15 is connected to the upper end face of the reduction furnace 20 described later, and has a function of transferring nickel chloride gas or the like generated in the chlorination furnace 10 to the reduction furnace 20. Further, the lower end portion of the transfer pipe / nozzle 15 projects into the reduction furnace 20 and functions as a nickel chloride injection nozzle.
  • the form of metallic nickel (M), which is the starting material, does not matter, but from the viewpoint of contact efficiency and prevention of pressure drop rise, granular, coarse, plate-like, etc. with a particle size of about 5 mm to 20 mm are preferable.
  • the purity is generally 99.5% or more.
  • the bed height of the metallic nickel (M) in the chlorination furnace 10 is determined by the chlorine gas supply rate, the temperature in the chlorination furnace, the continuous operation time, the shape of the metallic nickel (M), etc. It may be appropriately set in a range sufficient for conversion to nickel gas.
  • the temperature in the chlorination furnace 10 should be 800.degree. C. or higher to promote the reaction sufficiently.
  • the temperature shall be 1483 ° C or less. In consideration of the reaction rate and the durability of the chlorination furnace 10, practically, the range of 900 ° (: to 110 ° C. is preferable.
  • the nickel chloride gas generated in the chlorination step is transferred as it is to the reduction furnace 20 by the transfer pipe / nozzle 15 and, in some cases, an inert gas such as nitrogen or argon from the inert gas supply pipe 13
  • the mixture is mixed with 1 mol% to 3% mol of 1 mol% to 3 moll of nickel chloride gas, and the mixed gas is transferred to a reduction furnace 20.
  • the preferable nickel chloride gas partial pressure in the mixed gas passing through the transfer pipe / nozzle 15 is in the range of 0.5 to 1.0 when the total pressure is 1.0, and in particular, the particle diameter is 0.21 to 11 1. In the case of producing fine nickel powder having a small particle size of 0.5 m, a partial pressure of about 0.6 to 0.9 is preferable.
  • the nickel chloride gas generated in the chlorination step is transferred to the reduction furnace 20 continuously.
  • the reduction step is preferably performed using a reduction furnace 20 as shown in FIG.
  • the reduction furnace 20 shown in the figure has a cylindrical shape, and reduction is performed in the upper half, and cooling is performed in the lower half.
  • the nozzle of the above-described transfer pipe / nozzle 15 (hereinafter simply referred to as the nozzle 15) is protruded downward.
  • a reducing gas supply pipe (hydrogen gas supply pipe) 21 is connected to the upper end face of the reduction furnace 20.
  • heating means 22 is disposed around the reduction furnace 20.
  • the nozzle 15 has a function of injecting nickel chloride gas (which may contain an inert gas) from the salt furnace 10 into the reduction furnace 20 at a preferable flow rate.
  • a downward light flame F similar to the combustion flame of gaseous fuel such as LPG is formed from the tip of the nozzle 15 Ru.
  • the amount of hydrogen gas supplied to the reduction furnace 20 is approximately 1.0 to 3.0 times the chemical equivalent of chloride / nickel gas, that is, the chemical equivalent of chlorine gas to be supplied to the chloride reactor 10. Preferably, it is about 1.1 to 2.5 times, but it is not limited to this.
  • the temperature of the reduction reaction may be a temperature sufficient to complete the reaction, but it is preferably below the melting point of nickel because it is easier to handle when producing a solid fine nickel powder. The above temperature is practically 900 ° C. to 1100 ° C. in consideration of the reaction rate, the durability of the reduction furnace 20, and the economy, but it is not particularly limited thereto.
  • the chlorine gas introduced into the chlorination furnace 10 becomes substantially the same molar amount of chloride nickel gas, which is used as the reduction material.
  • the particle size of the obtained nickel fine powder P is optimized by adjusting the linear velocity of the gas flow ejected from the tip of the nozzle 15 of the mixed gas of nickel chloride gas or chloride di-gel and inert gas. It is possible. That is, if the nozzle diameter is constant, the particle size of the nickel fine powder P generated in the reduction furnace 20 is adjusted to the desired range by adjusting the chlorine supply amount to the chlorination step and the inert gas supply amount. can do.
  • the preferable linear velocity of the gas flow at the tip of the nozzle 15 (the total of nickel chloride gas and inert gas (calculated value converted to the amount of gas supplied at the reduction temperature)) is 900 ° C. to 1100 ° (reduction temperature of
  • the linear linear velocity of hydrogen gas in the reduction furnace 20 in the reduction furnace 20 is about 1/50 to 1/300 of the ejection velocity of nickel chloride gas (linear velocity).
  • 1/80 to 1/250 is more preferable. Therefore, substantially salty nickel gas is injected from the nozzle 15 into a static hydrogen atmosphere.
  • the direction of the outlet of the reducing gas supply pipe 21 is preferably not directed to the bright flame F side.
  • hydrogen gas hydrogen sulfide gas and the like can be used as the reducing gas used to form the nickel fine powder, but in view of the effect on the formed fine nickel powder, Hydrogen gas is preferred.
  • the reduction reaction temperature range for contacting and reacting metal chloride complex gas with reducing gas is usually 900 to 1200 ° C., but 950 to 1100 ° C.
  • the layer preferably has a temperature of 980 to 1050 ° C.
  • the fine nickel powder produced in the reduction step is cooled in the space portion (lower portion) opposite to the nozzle 15 in the reduction furnace 20, as shown in FIG.
  • cooling is performed to the space portion below the tip of the bright flame F.
  • the cooling inert gas is blown from the gas supply pipe 23.
  • the term "cooling" as used in the present invention is an operation performed to stop or suppress the growth of nickel particles in the gas stream (including hydrochloric acid gas) generated by the reduction reaction, and specifically, the reduction reaction has been completed. It means an operation of rapidly cooling the gas flow around 100 ° C. to about 400 ° C. to 800 ° C. Of course, cooling can also be performed to a temperature lower than this.
  • the inert gas for cooling the produced nickel fine powder is not particularly limited as long as it does not affect the produced nickel fine powder, and nitrogen gas, argon gas and the like can be used. Among these, nitrogen gas is preferable because it is inexpensive. Furthermore, the supply amount of the inert gas for cooling is 5 N 1 Z minutes or more, preferably 10 to 50 N 1 / minute, per 1 g of the fine nickel powder usually produced. In addition, although the temperature of the inert gas to be supplied is usually 0 to 100 ° C., it is more effective when the temperature is 0 to 80 ° C.
  • the mixed gas of fine nickel powder P, hydrochloric acid gas and inert gas sequentially passed through the steps of chlorination, reduction and cooling is transferred to a recovery furnace (not shown) through a nozzle 24 in FIG. Then, fine nickel powder P is separated and recovered from the mixed gas.
  • a recovery furnace not shown
  • fine nickel powder P is separated and recovered from the mixed gas.
  • a bag filter for example, one or a combination of two or more of a bag filter, a collection and separation means in water, a collection and separation means in oil, and a magnetic separation means are suitable, but it is not limited thereto. Absent.
  • the fine nickel powder produced Before or after separation and recovery, the fine nickel powder produced may be washed with a solvent such as water or a monohydric alcohol having 1 to 4 carbon atoms, if necessary. Furthermore, if necessary, the nickel fine powder produced is subjected to hydrogen reduction treatment in a reducing atmosphere of hydrogen gas or hydrogen gas diluted with an inert gas to finely adjust the oxygen content in the nickel fine powder. It can also be done.
  • the hydrogen reduction treatment temperature is preferably 220 to 300 ° C, and more preferably 250 to 300 ° C.
  • the hydrogen reduction treatment time is 5 to 60 minutes.
  • the fine nickel powder of the present invention the fine nickel powder obtained by the above method is used.
  • the powder is treated in aqueous carbonate solution and then oxidized by heating in an ozone atmosphere.
  • carbon dioxide gas is blown into a fine metal powder slurry to obtain P
  • the oxidation treatment is carried out by putting the aqueous nickel powder obtained by the gas phase reduction method and then drying it into an oxidation furnace, heating it, and supplying ozone gas into the oxidation furnace.
  • the ozone gas can be supplied as a mixture with gases such as oxygen, air, carbon monoxide, carbon dioxide, water vapor, lower alcohols, etc. However, mixing with oxygen gas is more effective.
  • the ozone gas concentration is preferably in the range of 1 to 20 V o 1%, and more preferably 5 to 20 V o 1%.
  • the oxidation treatment temperature is suitably in the low temperature range of 200 to 250 ° C, preferably in the range of 220 to 230 ° C.
  • the oxidation treatment time may be appropriately selected within the range of 1 minute to 30 minutes so that the thickness of the oxide film becomes 1 to 10 nm according to the above-mentioned ozone gas concentration and oxidation treatment temperature.
  • the nickel fine powder obtained by the vapor phase reduction method absorbs moisture to form nickel hydroxide by leaving it in the air.
  • the dispersibility is reduced and the fine nickel powder is aggregated to increase coarse powder. It takes a long time for heat treatment to remove it. Therefore, in the case where the nickel fine powder obtained by the vapor phase reduction method is subjected to the oxidation treatment, it is preferable to carry out the above-mentioned oxidation treatment as quickly as possible.
  • the metal fine powder obtained as described above is suitable for use as a conductive paste or an electrode paste.
  • Such metal fine powder is mixed with an organic solvent and a binder to form a paste.
  • organic solvent organic vehicle
  • the binder an organic or inorganic binder is used, but it is preferable to use a polymer binder such as hydroxyethyl cellulose.
  • glass frits such as lead-based glass, zinc-based glass or cailic acid-based glass, and metal oxide fillers such as manganese oxide, magnesium oxide, bismuth oxide, etc. may be mixed when forming the paste, if necessary. It is also good.
  • an electrode is formed by coating and sintering on a base material such as ceramics by mixing these additives, an electrode having excellent adhesion to the base material and high conductivity can be formed. Improve the wettability of
  • plasticizers such as phthalic acid ester and stearic acid, and dispersants can be added to the paste.
  • the sintering start temperature is high, the shrinkage rate at sintering is low, and the coarse powder due to the aggregation of the metal fine powder is
  • metal fine powder By using such metal fine powder, it is possible to suppress structural defects such as delamination in the manufacturing process of the multilayer ceramic capacitor.
  • FIG. 1 is a view showing an apparatus for producing a metal fine powder used in the present invention.
  • chlorine gas is supplied from the chlorine gas supply pipe 12 into the salt furnace 10 to salt the metallic nickel to form a salt pot. It generated kelgas.
  • nitrogen gas of 10% (molar ratio) of the chlorine gas supply amount was supplied and mixed from an inert gas introduction pipe 13 provided on the lower side of the chlorination furnace 10. Then, a mixed gas of nickel chloride gas and nitrogen gas was introduced into the reduction furnace 20 through the nozzle 15.
  • a mixed gas of a nickel chloride gas and a nitrogen gas is heated by a heating device 22 to a reduction furnace 20 in which the atmosphere temperature in the furnace is set to a temperature of 1000 ° C.
  • the flow rate was introduced at 2.3 mZ seconds (converted to 1000 ° C.).
  • hydrogen gas is supplied from the reducing gas introduction pipe 41 provided at the upper end in the reduction furnace 20 into the reduction furnace 20 at a flow rate of 7 N 1 min to reduce the chloride nickel gas and reduce nickel. Fine powder P was obtained.
  • the fine nickel powder P produced in the reduction process was supplied at a cooling gas supply pipe 23 provided at the lower side of the reduction furnace 20 at 13.4 N 1 / min ⁇ g.
  • the fine nickel powder P was cooled by contacting with nitrogen gas.
  • the produced fine nickel powder P was introduced to a not-shown recovery furnace through the nozzle 24 together with chlorine gas and hydrochloric acid vapor.
  • the nitrogen gas, hydrochloric acid vapor and nickel fine powder P thus introduced into the recovery furnace from the nozzle 24 were introduced into a bag filter (not shown) to separate and recover the fine nickel fine powder. Then, the collected fine nickel powder P was washed with hot water, and carbon dioxide gas was blown into the fine nickel powder slurry to obtain pH 5.5, and the fine nickel powder was treated in a carbonated water solution for 60 minutes at normal temperature. .
  • the carbonic acid aqueous solution-treated nickel fine powder was dried and then oxidized.
  • the fine nickel powder P obtained by the vapor phase reduction method is placed in an oxidation furnace, the atmosphere temperature in the furnace is set to 200 ° C. by heating means, and ozone monooxygen mixed with 5 V 01% ozone gas from the oxidation gas supply pipe. Gas was introduced for 10 minutes to oxidize the fine nickel powder P to obtain a fine nickel powder.
  • the atmosphere temperature in the oxidation furnace is 250 ° C.
  • the ozone concentration in the ozone / oxygen mixed oxidation gas is 5 vo 1%
  • oxidation treatment was carried out for 30 minutes at a time of.
  • Example 1 A fine nickel powder P was produced in the same manner as in Example 1, and was subjected to oxidation treatment without treatment with an aqueous carbonate solution.
  • the oxidizing gas was oxygen gas for the oxidation treatment.
  • the oxidation treatment temperature and the oxidation treatment time were the same as in Example 1.
  • a fine nickel powder P was produced in the same manner as in Example 1, and was subjected to oxidation treatment without treatment with an aqueous carbonate solution.
  • the oxidizing gas was oxygen gas for the oxidation treatment.
  • the oxidation treatment temperature was 400 ° C., and the oxidation treatment time was 30 minutes.
  • the thickness of the oxide film of the metallic nickel fine powder, the oxygen concentration, the sintering start temperature, the shrinkage rate and the particle size distribution were measured by the following methods.
  • fine metallic nickel powder was directly sprinkled on a copper sheet mesh covered with a collodion film, and then carbon was vapor deposited to prepare a measurement sample.
  • the lattice image of the sample was observed using a 200 kV electrolytic radiation transmission electron microscope (HF- 200, manufactured by Hitachi, Ltd.) to measure the thickness of the oxide film on the surface of the metallic nickel fine powder. did.
  • Metallic nickel fine powder is filled in a capsule made of nickel, placed in a graphite crucible, heated to 500 ° C. under argon atmosphere, carbon monoxide generated at this time is quantified by IR, and metallic nickel fine is prepared. The oxygen concentration in the powder was determined.
  • shrinkage rate In the shrinkage rate curve obtained by the measurement of the sintering start temperature in the above 3), the shrinkage rate was defined as the weight loss rate when the temperature was raised to 500 ° C.
  • the sample is suspended in equinene (isopropyl alcohol 10%, ethanol 90%) using a particle size measuring instrument LS 230 (manufactured by Koru Yui Co., Ltd.), dispersed for 3 minutes with a homogenizer, and measured.
  • the particle diameter (D 50) at which the integrated value becomes 50% by volume in the distribution was determined.
  • Table 1 shows the measurement results of the oxide film thickness, oxygen concentration, sintering start temperature, shrinkage rate and particle size distribution of the fine nickel powder obtained in Examples 1 and 2 and Comparative Examples 1 and 2.
  • Oxide film density Ratio of oxygen concentration to oxide film thickness (oxygen concentration Z oxide film thickness)
  • the fine nickel powders obtained in Examples 1 and 2 are comparative examples 1 and 2 Compared with the fine nickel powder obtained in the above, the thickness of the oxide film was generally large, the oxygen content was also large, the sintering start temperature was also high, and the shrinkage was small. That is, it is understood that the nickel fine powder in each example is stronger than the nickel fine powder in each comparative example, and an oxide film sufficient to improve the sintering behavior can be obtained.
  • the particle size distribution of the obtained nickel fine powder (coarse particles Regarding the ratio (), each Example had a smaller value than each Comparative Example.
  • the large value relating to the particle size distribution in Comparative Example 2 is due to the long-time oxidation treatment at high temperature.
  • Example 1 50% by mass of the nickel fine powder oxidized with ozone gas obtained in Example 1, and 50% by mass of a vehicle comprising 5% by mass of acetyl cellulose and 5% by mass of terpioneel 9
  • the paste was prepared by kneading with three rolls, and this was applied to measure the film density.
  • the fine nickel powder obtained in Comparative Example 2 was oxidized using an oxygen gas, and had the same oxygen concentration as the oxide film of the same thickness as the fine nickel powder obtained in Example 1.
  • a paste was prepared in the same manner as in Example 3 and applied to measure the film density.
  • Table 2 shows the film density measurement results of the pastes obtained in Example 3 and Comparative Example 3.
  • the paste of Example 3 has a large film density and good dispersibility as compared with the paste of Comparative Example 3. Therefore, in the paste of Example 3, when used as an internal electrode of the multilayer ceramic capacitor, the effect of suppressing structural defects such as cracks and delamination can be obtained.
  • an oxide film is formed on the surface of the metal fine powder by ozone gas, and the loss due to the reduction of the oxide film is delayed, thereby starting the sintering of the metal fine powder.
  • the internal electrode layer and the dielectric layer are It is possible to suppress the delamination that occurs during the Therefore, the present invention is promising in that metal fine powders suitable for conductive pastes used for electronic parts and the like can be produced.

Abstract

A fine metal powder, a process for producing the powder, and a conductive paste. An oxide film is formed on the surface of a fine metal powder by the action of ozone gas to heighten the sintering initiation temperature for the fine metal powder. Thus, delamination can be inhibited.

Description

金属微粉末およびその製造方法ならびにこの金属微粉末を用いた導電ペースト 技術分野  Metal fine powder, method for producing the same, and conductive paste using the metal fine powder
本発明は、例えば電子部品等に使用される導電べ一ストに好適なニッケル、銅、 あるいは銀などの金属微粉末およびその製造方法、 ならびにこれらの金属微粉末 明  The present invention relates to fine powders of metals such as nickel, copper or silver suitable for a conductive paste used in, for example, electronic parts and the like, a method of producing the same, and fine powders of these metal powders.
を使用した導電ペーストに関し、 特に、 積層セラミックコンデンサの内部電極に 使用した場合に、 焼結特性に優れた金属微粉末等の製造技術に関する。 In particular, the present invention relates to a conductive paste using the same, and particularly relates to a manufacturing technique for fine metal powder and the like having excellent sintering characteristics when used as an internal electrode of a laminated ceramic capacitor.
書  book
背景技術 Background art
積層セラミックコンデンサは、 セラミックスのペーストと金属微粉末のペース トとを積層した後焼結することによって、 セラミックスの誘電体層と金属微粉末 の内部電極層とを交互に形成したものである。 ニッケル、 銅、 銀などの導電性の 金属微粉末は、 積層セラミックコンデンザの内部電極用材料として有用であり、 特にニッケル微粉末はこのような用途において注目されている。  A multilayer ceramic capacitor is formed by alternately laminating ceramic dielectric layers and metal fine powder internal electrodes by laminating and sintering ceramic paste and metal fine powder paste. Conductive metal fine powders such as nickel, copper, silver and the like are useful as materials for internal electrodes of laminated ceramic capacitors, and in particular, nickel fine powders have attracted attention in such applications.
一般に、 積層セラミックコンデンサは、 以下のようにして製造されている。 す なわち、 チタン酸バリゥムなどの誘電体セラミックス粉末を有機バインダと混合 したペーストをシート状に形成して誘電体グリーンシートを作製する。 一方、 内 部電極用の金属微粉末を有機溶剤、有機バインダ等の有機化合物と混合して金属 微粉末ペーストを形成し、 これを誘電体グリーンシート上に印刷し、 乾燥する。 この電極層塗布誘電体グリ一ンシートを積層後、 加熱圧着して積層体を形成し、 目的の形状に加工する。 次いで、 有機バインダ等の有機成分を除去するために弱 酸性雰囲気で積層体に加熱処理 （脱バインダ処理） を施し、 その後還元性雰囲気 中で、 1 3 0 0 °C前後、 あるいはそれ以上の温度で焼成し、 最後に誘電体セラミ ックス層の外側に外部電極を焼き付けて積層セラミックコンデンサを得る。  In general, multilayer ceramic capacitors are manufactured as follows. That is, a dielectric green sheet is produced by forming a paste in which a dielectric ceramic powder such as barium titanate is mixed with an organic binder into a sheet. On the other hand, a fine metal powder for the internal electrode is mixed with an organic solvent, an organic compound such as an organic binder, etc. to form a fine metal powder paste, which is printed on a dielectric green sheet and dried. After laminating this electrode layer coated dielectric green sheet, it is heated and pressed to form a laminated body, and processed into a desired shape. Next, the laminate is subjected to heat treatment (debinding treatment) in a weakly acidic atmosphere to remove organic components such as an organic binder, and then the temperature is around 130 ° C. or higher in a reducing atmosphere. Finally, the outer electrode is baked on the outside of the dielectric ceramic layer to obtain a multilayer ceramic capacitor.
上記のような積層セラミックコンデンザの製造においては、脱バインダ処理は、 有機化合物を除去するため、 酸化雰囲気中で行われる。 このため、 脱バインダ処 理中に金属微粉末は酸化されて体積の膨張が生じる。 さらに、 この脱バインダ処 理の後には、 積層体をさらに高温に加熱して焼結するが、 この焼結が還元雰囲気 中で行われるため、 金属微粉末は還元されて体積の収縮が生じる。 In the production of the multilayer ceramic condenser as described above, the binder removal treatment is performed in an oxidizing atmosphere in order to remove the organic compound. For this reason, the metal fine powder is oxidized during the binder removal processing to cause expansion of the volume. Furthermore, after the binder removal processing, the laminate is heated to a higher temperature for sintering, but this sintering is a reducing atmosphere. As it takes place in the metal fine powder is reduced and volume contraction occurs.
このように、 積層セラミックコンデンサの製造工程においては、酸化還元反応 により金属微粉末の膨張 ·収縮による体積変化が生じる。 一方、 誘電体自身も焼 結により体積が変化するが、 内部電極に用いた金属微粉末の焼結開始温度が誘電 体層の焼結開始温度よりも極端に低い場合には、 内部電極層の急激な収縮により、 内部電極層と誘電体層との間に体積変化が生じて、 デラミネ一ションと呼ばれる 欠陥が発生する。 このデラミネーシヨンは、 コンデンサ容量の低下を招くことか ら、焼結開始温度が高く、急激な焼結が起こらない金属微粉末が要望されている。 上記のような、 金属微粉末の焼結開始温度を高くするための方法として、 例え ば、 特開平 1 1一 8 0 8 1 7号公報には、 ニッケル粉に硫黄を含有させる技術が 提案されている。  As described above, in the manufacturing process of the multilayer ceramic capacitor, the volume change due to the expansion and contraction of the metal fine powder occurs due to the oxidation-reduction reaction. On the other hand, the dielectric itself changes its volume due to sintering, but if the sintering start temperature of the metal fine powder used for the internal electrode is extremely lower than the sintering start temperature of the dielectric layer, The rapid contraction causes a volume change between the internal electrode layer and the dielectric layer to generate a defect called delamination. Since this delamination causes a decrease in capacitor capacity, there is a demand for a metal fine powder which has a high sintering start temperature and in which rapid sintering does not occur. As a method for raising the sintering start temperature of the metal fine powder as described above, for example, Japanese Patent Application Laid-Open No. 11 18017 proposes a technique for incorporating sulfur into nickel powder. ing.
しかしながら、 上記した特許文献 1に記載されたニッケル粉の製造技術では、 焼結時に硫黄が誘電体層に拡散し、誘電体層の電気的特性を劣化させるおそれが ある。 発明の開示  However, in the nickel powder manufacturing technology described in Patent Document 1 described above, sulfur may diffuse into the dielectric layer during sintering, which may deteriorate the electrical characteristics of the dielectric layer. Disclosure of the invention
したがって、 本発明は、 上記したようなニッケル粉に硫黄を含有させずに、 金 属微粉末の焼結開始温度を高くして、デラミネーシヨンの発生を抑制することが できる、金属微粉末およびその製造方法ならびに導電べ一ストを提供することを 目的としている。  Therefore, according to the present invention, it is possible to increase the sintering start temperature of the metal fine powder without containing sulfur in the above-mentioned nickel powder, and to suppress the generation of delamination, The purpose is to provide the manufacturing method and the conductive paste.
金属微粉末の焼結開始温度に関しては、以下の事実が知られている。すなわち、 金属微粉末表面に酸化皮膜が存在する間は焼結が開始されないが、焼成温度の上 昇に伴い酸化皮膜が還元されて存在しなくなると、金属微粉末の焼結が開始され る。 例えば、 ニッケル微粉末の場合であれば、 通常 2 0 0〜3 0 0 °Cで焼結が始 まるので、 2 0 0〜3 0 0 °C以上の温度に加熱されても還元されない、 強固な酸 化皮膜を形成することで、上記デラミネーシヨンの発生を抑制することができる。 本発明者らは、 上記事実に基づき、 金属微粉末の酸化皮膜について鋭意研究を 重ねた結果、オゾンガスにより生成した酸化皮膜は、通常の酸化皮膜と比較して、 還元され始める温度がより高温であることから、 この酸化膜を金属微粉末の表面 に形成すれば、 金属微粉末の焼結開始温度をより高温域に移行することができ、 これにより上記デラミネーションの発生を抑制することができることを見出し た。 The following facts are known as to the sintering start temperature of the metal fine powder. That is, sintering is not started while the oxide film is present on the surface of the metal fine powder, but sintering of the metal powder is started when the oxide film is reduced to disappear as the firing temperature rises. For example, in the case of fine nickel powder, since sintering usually starts at 200 to 300 ° C., it is not reduced even when heated to a temperature of 200 to 300 ° C. or higher. By forming such an oxide film, the generation of the above-mentioned delamination can be suppressed. Based on the above facts, as a result of extensive research on the oxide film of metal fine powder, the present inventors have found that the oxide film produced by ozone gas starts to be reduced at a higher temperature compared to a normal oxide film. From the fact that this oxide film on the surface of metal powder It has been found that, if it is formed, it is possible to shift the sintering start temperature of the metal fine powder to a higher temperature range, thereby suppressing the occurrence of the above-mentioned delamination.
また、 本発明者らは、 オゾンガスにより生成した酸化皮膜を有する金属微粉末 は、 焼結開始温度が従来に比して高温域に移行するため、 焼結時における金属微 粉末の収縮率を減少させ、 これによつても上記デラミネ一ションの発生を抑制す ることができることを見出した。  Also, the present inventors have found that the metal fine powder having an oxide film formed by ozone gas has a sintering start temperature shifted to a higher temperature range compared to the conventional case, so the shrinkage rate of the metal fine powder at the time of sintering decreases. It has been found that this can also suppress the occurrence of the above-mentioned delamination.
さらに、 本発明者らは、 オゾンガスによる酸化処理は、 通常の酸素を使用した 酸化処理よりも低温で実施することができるため、酸化処理中の金属微粉末同士 の焼結による凝集が防止され、 積層セラミックコンデンサ製造工程における内部 電極の短絡等の構造欠陥の発生を抑制することにより、 積層セラミツクコンデン ザの小型化、 大容量化に伴う内部電極の薄層化、 低抵抗化にも寄与し得ることも 見いだした。 本発明はこれらの知見に基づいてなされたものである。  Furthermore, since the oxidation treatment with ozone gas can be performed at a lower temperature than the oxidation treatment using normal oxygen, the aggregation due to the sintering of the metal fine powder during the oxidation treatment is prevented. By suppressing the occurrence of structural defects such as short-circuiting of internal electrodes in the manufacturing process of multilayer ceramic capacitors, it can also contribute to thinning of internal electrodes and resistance reduction due to the miniaturization and increase in capacity of multilayer ceramic capacitors. I also found out. The present invention has been made based on these findings.
すなわち、 本発明の金属微粉末は、 表面にオゾンガスにより生成した酸化皮膜 を有することを特徴としている。  That is, the metal fine powder of the present invention is characterized by having an oxide film formed by ozone gas on the surface.
本発明によれば、 オゾンガスにより生成した酸化皮膜を金属微粉末の表面に形 成することにより、酸化被膜の還元による喪失の遅延によって金属微粉末の焼結 開始温度をより高温域に移行させ、 さらには焼結時における金属微粉末の収縮率 を減少させることに基づき、 内部電極層と誘電体層との間に発生するデラミネー シヨンを抑制することができる。 また、 本発明によれば、 オゾンガスによる低温 域での酸化処理により、酸化処理中の金属微粉末同士の焼結による凝集が防止さ れ、積層セラミックコンデンサ製造工程における内部電極の短絡等の構造欠陥の 発生を抑制する。 すなわち、 本発明の金属微粉末を有機溶媒、 有機バインダ等の 有機化合物と混合して金属微粉末ペーストを形成し、 積層セラミックコンデンサ の内部電極として使用した場合には、 焼結開始温度が高温であるため、 誘電体の 焼結開始温度との差が大きくないこと、 収縮率が低いため誘電体との間の体積変 化が低いこと、. さらには凝集粒子が少ないことから、 製造工程中におけるデラミ ネーシヨン、 クラック、 内部電極の短絡、 等の構造欠陥の発生を抑制することが できる。 したがって、 本発明の金属微粉末によれば、 積層セラミックコンデンサ の小型化、大容量ィヒに伴う内部電極の薄層化、低抵抗化を実現することができる。 このような金属微粉末においては、 酸化皮膜の厚みが、 l〜1 0 nmであるこ とが望ましい。 酸化被膜の厚みが 1 n m未満である場合には、 酸化被膜の還元に よる喪失の遅延を十分に達成することができず、 このため、 金属 ί救粉末の焼結開 始温度をより高温域に移行させることができず、 結果的に上記デラミネーシヨン 発生を抑制することができない。 また、 酸化被膜の厚みが 1 0 n mを超える場合 には、 金属微粉末の焼結性が低下するので好ましくない。 このようなデラミネ一 シヨン発生防止と焼結性の防止との双方をより実効あらしめるためには、 上記酸 化皮膜の厚みは 2〜1 0 nmであることが好ましく、 2〜5 n mであることがさ らに好ましい。 According to the present invention, by forming the oxide film formed by the ozone gas on the surface of the metal fine powder, the sintering start temperature of the metal fine powder is shifted to a higher temperature range by delaying the loss due to reduction of the oxide film. Furthermore, by reducing the shrinkage rate of the metal powder during sintering, it is possible to suppress the delamination occurring between the internal electrode layer and the dielectric layer. Further, according to the present invention, the oxidation treatment in the low temperature range with ozone gas prevents the aggregation due to sintering of the metal fine powder during the oxidation treatment, and structural defects such as a short circuit of the internal electrode in the manufacturing process of the multilayer ceramic capacitor. Suppress the occurrence of That is, when the metal fine powder of the present invention is mixed with an organic solvent, an organic binder such as an organic compound to form a metal fine powder paste and used as an internal electrode of a multilayer ceramic capacitor, the sintering start temperature is high. Therefore, the difference with the sintering start temperature of the dielectric is not large, the shrinkage ratio is low, the volume change with the dielectric is low, and the number of agglomerated particles is small. It is possible to suppress the occurrence of structural defects such as delamination, cracks, shorts of internal electrodes, and so on. Therefore, according to the metal powder of the present invention, a multilayer ceramic capacitor Can realize the reduction of the thickness of the internal electrode and the reduction of resistance accompanying the miniaturization of the In such metal fine powder, it is desirable that the thickness of the oxide film be 1 to 10 nm. If the thickness of the oxide film is less than 1 nm, delay of loss due to reduction of the oxide film can not be sufficiently achieved. Therefore, the sintering start temperature of the metal powder is higher than that of the oxide film. As a result, the occurrence of the above-mentioned delamination can not be suppressed. In addition, when the thickness of the oxide film exceeds 10 nm, the sinterability of the metal fine powder is unfavorably lowered. The thickness of the above-mentioned oxide film is preferably 2 to 10 nm, more preferably 2 to 5 nm, in order to make such prevention of occurrence of delamination and prevention of sintering more effective. Further preference is given.
また、上記金属微粉末においては、金属微粉末が本発明の金属微粉末としては、 ニッケル、 銅、 銀等の導電ペーストフイラ一に適した金属微粉末や、 さらには、 アルミニウム、 チタン、 クロム、 マンガン、 鉄、 コバルト、 ビスマス等の金属微 粉末及びこれらの合金微粉末等が挙げられる。積層セラミックコンデンサの内部 電極用として使用する場合、 導電性に優れ、 還元雰囲気での焼成が可能であり、 安価であるニッケル微粉末が最適である。  In the above metal fine powder, metal fine powder is fine metal powder suitable for conductive paste filler such as nickel, copper and silver as metal fine powder of the present invention, and further, aluminum, titanium, chromium and manganese Fine powders of metals such as iron, cobalt and bismuth, fine powders of alloys of these, and the like can be mentioned. When used as an internal electrode of a laminated ceramic capacitor, nickel fine powder which is excellent in conductivity, can be fired in a reducing atmosphere, and is inexpensive is optimal.
このような金属微粉末においては、 とくに金属微粉末の平均粒径を 1 m以下 とすることが望ましい。 上記平均粒径が 1 mを超える場合には、 焼結性の低下 や、 積層セラミックコンデンサの内部電極同士の短絡等の構造欠陥が生じ易くな るため好ましくない。 この焼結性の低下や構造欠陥の発生をより防止するために は、 金属微粉末の平均粒径を 0 . 5 以下とすることがさらに望ましい。 しか しながら、 上記平均粒径を過度に小さくした場合には、 本発明の酸化工程中に金 属微粉末同士の焼結、 凝集が進行することから、 上記平均粒径の下限値は、 0 . 1 /i mとすることが望ましい。  In such fine metal powder, it is particularly desirable to set the average particle size of the fine metal powder to 1 m or less. When the average particle size exceeds 1 m, it is not preferable because structural defects such as a decrease in sinterability and a short circuit between internal electrodes of the multilayer ceramic capacitor are likely to occur. In order to further prevent the decrease in the sinterability and the occurrence of structural defects, it is more desirable to set the average particle diameter of the metal fine powder to 0.5 or less. However, if the average particle size is excessively reduced, sintering and aggregation of the metal fine powders proceed during the oxidation process of the present invention. It is desirable to use 1 / im.
さらに、 このような金属微粉末においては、 金属微粉末の酸素濃度と酸化皮膜 厚みの比 （酸素濃度 Z酸化皮膜厚み） が 0 . 3〜1 . 0であることが望ましい。 ここでいう酸素濃度とは、 酸化被膜を含む金属微粉末の酸素濃度を意味し、 酸 化被膜の厚みとは、 酸化被膜を含む金属微粉末の形状を仮想球とした場合の、 そ の中心から径方向に測定した酸化被膜の厚みを意味する。 上記比が 0 . 3未満である場合には、，酸化被膜が還元され易いため、 酸化被膜 の上記喪失の遅延を十分に達成することができず、 このため、 金属微粉末の焼結 開始温度をより高温域に移行させることができず、結果的に上記デラミネーショ ン発生を抑制することができない。 また、 上記比が 1 . 0を超える場合には、 金 属微粉末の焼結性が低下するので好ましくない。 このようなデラミネーション発 生防止と焼結性の防止との双方をより実効あらしめるためには、 上記比は 0 . 3 〜0 . 8であることが好ましく、 0 . 3〜0 . 5 n mであることがさらに好まし い。 Furthermore, in such metal fine powder, it is desirable that the ratio of the oxygen concentration of the metal fine powder to the thickness of the oxide film (oxygen concentration Z oxide film thickness) be 0.3 to 1.0. Here, the oxygen concentration means the oxygen concentration of the metal fine powder containing the oxide film, and the thickness of the oxide film means that the center of the metal fine powder containing the oxide film is a virtual sphere. Mean the thickness of the oxide film measured in the radial direction. If the above ratio is less than 0.3, since the oxide film is easily reduced, the delay of the loss of the oxide film can not be sufficiently achieved. Therefore, the sintering start temperature of the metal fine powder Can not be transferred to a higher temperature range, and as a result, the occurrence of the above-mentioned delamination can not be suppressed. On the other hand, if the above ratio exceeds 1.0, the sinterability of the metal fine powder is lowered, which is not preferable. In order to make both such prevention of delamination occurrence and prevention of sinterability more effective, the above ratio is preferably 0.3 to 0.8 nm, and 0.5 to 0.5 nm. It is further preferred that
また本発明の金属微粉末の製造方法は、上記した金属微粉末を有利に製造する ための方法であって、 金属微粉末を炭酸水溶液中で処理し、 次いでオゾンガス雰 囲気中で酸化処理を施し、 表面に酸化皮膜を形成させることを特徴としている。 本発明の金属微粉末の製造方法によれば、オゾンガスにより生成した酸化皮膜 を金属微粉末の表面に形成することにより、酸化被膜の還元による喪失の遅延に よって金属微粉末の焼結開始温度をより高温域に移行させ、 さらには焼結時にお ける金属微粉末の収縮率を減少させることに基づき、 内部電極層と誘電体層との 間に発生するデラミネーションを抑制することができる。また、本発明によれば、 オゾンガスによる低温域での酸化処理により、酸化処理中の金属微粉末同士の焼 結による凝集が防止され、積層セラミックコンデンサ製造工程における内部電極 の短絡等の構造欠陥の発生を抑制することにより、積層セラミックコンデンサの 小型化、 大容量化に伴う内部電極の薄層化、 低抵抗化を実現することができる。 このような金属微粉末の製造方法においては、酸化処理を 2 0 0〜 2 5 0 の 温度範囲で行うことが望ましい。上記酸化処理を 2 0 0 °C未満の温度で行った場 合には、金属微粉末の焼結開始温度を高温にすることのできる酸化皮膜を形成す るには長時間の酸化処理が必要となり、 実用的ではない。 また、 2 5 0 °Cを超え る温度で行った場合には、金属微粉末の内部に至るまで酸化処理がなされてしま い、 焼結性の低下や、 積層セラミックコンデンサの内部電極の抵抗値の上昇等が 生じ、 好ましくない。 酸化被膜の形成時間をさらに短縮し、 かつ焼結性の低下を さらに防止するためには、酸化処理を 2 2 0〜2 3 0 °Cの温度範囲で行うことが さらに望ましい。 また、 上記金属微粉末の製造方法においては、 酸化処理を l〜2 0 v o l %の オゾン濃度範囲で行うことが望ましい。酸化処理を 1 V o 1 %未満のオゾン濃度 で行った場合には、 焼結開始温度を高温域に移行させる強固な酸化皮膜を得るた めに、 長時間の酸化処理が必要となり、 実用的ではない。 また、 酸化処理を 2 0 v o 1 %を超えるオゾン濃度で行った場合には、 金属微粉末の内部まで酸化され やすくなり焼結性の低下を引き起こし易くなるだけでなく、 コストも割高となる ため実用的ではない。 Further, the method for producing metal fine powder of the present invention is a method for advantageously producing the above-mentioned metal fine powder, wherein the metal fine powder is treated in a carbonic acid aqueous solution and then subjected to an oxidation treatment in an ozone gas atmosphere. , It is characterized by forming an oxide film on the surface. According to the method for producing metal fine powder of the present invention, the oxide film formed by the ozone gas is formed on the surface of the metal fine powder, whereby the sintering start temperature of the metal fine powder is determined by delaying loss due to reduction of the oxide film. It is possible to suppress the delamination between the internal electrode layer and the dielectric layer by shifting to a higher temperature range and further reducing the shrinkage rate of the metal fine powder at the time of sintering. Further, according to the present invention, the oxidation treatment in the low temperature range with ozone gas prevents aggregation due to sintering between metal fine powders during oxidation treatment, and causes structural defects such as a short circuit of internal electrodes in the multilayer ceramic capacitor manufacturing process. By suppressing the generation, it is possible to realize the miniaturization of the multilayer ceramic capacitor and the reduction in thickness and resistance of the internal electrode accompanying the increase in capacity. In the method of producing such metal fine powder, it is desirable to carry out the oxidation treatment in a temperature range of 200-250. When the above oxidation treatment is carried out at a temperature of less than 200 ° C., a long oxidation treatment is necessary to form an oxide film which can raise the sintering start temperature of the metal fine powder to a high temperature. And not practical. When the temperature is higher than 250 ° C., oxidation treatment is performed up to the inside of the metal fine powder, which lowers the sinterability and the resistance value of the internal electrode of the multilayer ceramic capacitor. Unfavorably cause rise in In order to further shorten the formation time of the oxide film and to further prevent the decrease in the sinterability, it is further desirable to carry out the oxidation treatment in a temperature range of 220 to 230 ° C. Further, in the method of producing the metal fine powder, it is desirable to carry out the oxidation treatment in an ozone concentration range of 1 to 20 vol%. When the oxidation treatment is performed at an ozone concentration of less than 1 V o 1%, a long time of oxidation treatment is necessary to obtain a strong oxide film that shifts the sintering start temperature to a high temperature region, which is practically useful. is not. In addition, when the oxidation treatment is performed at an ozone concentration of more than 20 vo 1%, the inside of the metal fine powder is easily oxidized, which tends to cause a decrease in sinterability, and the cost also becomes expensive. It is not practical.
また、上記金属微粉末の製造方法においては、炭酸水溶液中での処理を p H 5 . Moreover, in the method of producing the metal fine powder, the treatment in a carbonated aqueous solution is pH 5.
5〜6 . 5の範囲で行うことが望ましい。 炭酸水溶液中での処理を p H 5 . 5未 満で行つた場合には、 金属微粉末表面に不均一な酸化皮膜が生成し金属微粉末の 焼結性を低下させることになる。 また、 金属微粉末自体が溶解してしまい、 表面 の荒れが生じる。 P H 6 . 5を超えて行った場合には、 金属微粉末表面に付着、 もしくは吸着した水酸化物を除去することができず、乾燥後に残存した水酸化物 が不均一な酸化皮膜となる。 このような不利益をさらに防止するためには、 炭酸 水溶液中での処理を ρ Η 5 . 5〜6 . 0の範 Hで行うことが望ましい。 It is desirable to carry out in the range of 5 to 6.5. If the treatment in a carbonated aqueous solution is carried out below pH 5.5, a non-uniform oxide film will be formed on the surface of the metal fine powder, which will lower the sinterability of the metal fine powder. In addition, the fine metal powder itself dissolves, resulting in surface roughness. In the case of exceeding P H 6.5, the hydroxide attached or adsorbed to the surface of the metal fine powder can not be removed, and the hydroxide remaining after drying forms a non-uniform oxide film. In order to further prevent such disadvantages, it is desirable to carry out the treatment in a carbonated aqueous solution within the range H of Η 5.5 to 6.0.
さらに、 このような金属微粉末の製造方法においては、 金属微粉末を特にニッ ケルとすること力、 コスト力割高とならないことから実用的であり、 上記した製 造方法にしたがい製造された金属微粉末を用いることで、電子部品等に使用した 場合に、 上記デラミネ一ションの発生を防止することができる導電ペーストが得 られる。  Furthermore, in the method of producing such metal fine powder, it is practical to use metal fine powder as nickel, and it is not practical because the cost ratio is not high, and the metal fine powder manufactured according to the above-mentioned production method is practical. By using a powder, a conductive paste can be obtained which can prevent the occurrence of the above-mentioned delamination when it is used for an electronic component or the like.
以下、 本発明の好適な実施の形態について、 図面を参照してニッケル微粉末の 製造例をもとに詳細に説明する。 なお、 本発明金属微粉末の製造方法によって製 造される金属微粉末としては、 ニッケルの他に、 銅もしくは銀のペーストフイラ ―、チタン材の複合材、または触媒等の各種用途に適した金属微粉末が挙げられ、 さらにはアルミニウム、 チタン、 クロム、 マンガン、 鉄、 コバルト、 白金、 ビス マス等の金属微粉末の製造も可能である。本発明での金属微粉末は気相法や液相 法など公知の方法により製造することができるが、 特に金属物塩化物ガスと還元 性ガスとを接触させることにより金属微粉末を生成させる気相還元法、 あるいは 熱分解性の金属化合物を噴霧して熱分解する噴霧熱分解法が、 生成する金属微粉 末の粒子径を容易に制御することができ、 さらに球状の粒子が効率よく製造する ことができるという点において好ましい方法である。 Hereinafter, preferred embodiments of the present invention will be described in detail on the basis of production examples of nickel fine powder with reference to the drawings. The metal fine powder produced by the method of producing a metal fine powder of the present invention may be a metal fine powder suitable for various uses such as a copper or silver paste filler, a titanium composite material, or a catalyst other than nickel. Powders can be mentioned, and furthermore, it is also possible to produce metal fine powders such as aluminum, titanium, chromium, manganese, iron, cobalt, platinum and bismuth. The metal fine powder in the present invention can be produced by a known method such as a gas phase method or a liquid phase method, but in particular, it is possible to form a metal fine powder by bringing a metal chloride gas into contact with a reducing gas. Phase reduction method, or spray pyrolysis method that thermally decomposes by spraying a pyrolytic metal compound, This method is preferred in that the final particle size can be easily controlled, and spherical particles can be produced efficiently.
ニッケル微粉末気相還元法においては、 気化させた塩化ニッケルのガスと水素 等の還元性ガスとを反応させるが、 固体の塩化ニッケルを加熱し蒸発させて塩ィ匕 ニッケルガスを生成させてもよい。 し力 しながら、 塩ィヒニッケルの酸化または吸 湿防止またエネルギー効率を考慮すると、 金属ニッケルに塩素ガスを接触させて 塩ィ匕ニッケルガスを連続的に発生させ、 この塩化ニッケルガスを還元工程に直接 供給し、 次いで還元性ガスと接触させ塩ィ匕ニッケルガスを連続的に還元してニッ ケル微粉末を製造する方法が有利である。  In the fine nickel powder vapor phase reduction method, the vaporized nickel chloride gas is reacted with a reducing gas such as hydrogen, but even if solid nickel chloride is heated and evaporated, a salty nickel gas is generated. Good. In consideration of the oxidation or absorption prevention of the salt nickel and the energy efficiency, the metal nickel is brought into contact with the chlorine gas to continuously generate the nickel chloride gas, and the nickel chloride gas is directly used in the reduction step. A preferred method is to supply and then contact with a reducing gas to continuously reduce the nickel chloride gas to produce a fine nickel powder.
気相還元反応によるニッケル微粉末の製造過程では、塩ィ匕ニッケルガスと還元 性ガスとが接触した瞬間にニッケル原子が生成し、 ニッケル原子同士が衝突 ·凝 集することによって超微粒子が生成し、 成長してゆく。 そして、 還元工程での塩 化二ッゲルガスの分圧や温度等の条件によって、 生成されるニッケル微粉末の粒 径が決まる。 上記のようなニッケル微粉末の製造方法によれば、 塩素ガスの供給 量に応じた量の塩化ニッケルガスが発生するから、塩素ガスの供給量を制御する ことで還元工程へ供給する塩化ニッゲルガスの量を調整することができ、 これに よって生成するニッケル微粉末の粒径を制御することができる。 さらに、 金属塩 化物ガスは、 塩素ガスと金属との反応で発生するから、 固体金属塩化物の加熱蒸 発により金属塩化物ガスを発生させる方法と異なり、 キャリアガスの使用を少な くすることができるばカゝりでなく、 製造条件によっては使用しないことも可能で ある。 従って、 気相還元反応の方が、 キャリアガスの使用量低減とそれに伴う加 熱エネルギーの低減により、 製造コストの低減を図ることができる。  In the process of producing fine nickel powder by gas phase reduction reaction, nickel atoms are formed at the moment of contact between nickel chloride gas and reducing gas, and ultrafine particles are formed due to collision and condensation of nickel atoms. , Will grow. Then, the particle size of the fine nickel powder to be produced is determined by the conditions such as the partial pressure of the chloride digel gas and the temperature in the reduction step. According to the above method for producing fine nickel powder, nickel chloride gas is generated in an amount corresponding to the amount of chlorine gas supplied. Therefore, by controlling the amount of chlorine gas supplied, the amount of chlorinated Nigel gas supplied to the reduction step is The amount can be adjusted, and this can control the particle size of the fine nickel powder produced. Furthermore, since metal chloride gas is generated by the reaction of chlorine gas and metal, unlike the method of generating metal chloride gas by heating and evaporation of solid metal chloride, the use of carrier gas can be reduced. Depending on the manufacturing conditions, it may not be possible to use it. Therefore, in the gas phase reduction reaction, the manufacturing cost can be reduced by reducing the amount of carrier gas used and the heating energy associated therewith.
また、塩化工程で発生した塩化二ッケルガスに不活性ガスを混合することによ り、 還元工程における塩化ニッケルガスの分圧を制御することができる。 このよ うに、塩素ガスの供給量もしくは還元工程に供給する塩化ニッケルガスの分圧を 制御することにより、 二ッケル粉末の粒径を制御することができ、 よってニッケ ル微粉末の粒径を安定させることができるとともに、 粒径を任意に設定すること ができる。  In addition, the partial pressure of nickel chloride gas in the reduction step can be controlled by mixing an inert gas with the nickel chloride gas generated in the chlorination step. Thus, by controlling the chlorine gas supply amount or the partial pressure of the nickel chloride gas supplied to the reduction step, the particle size of the nickel powder can be controlled, thereby stabilizing the particle size of the nickel fine powder. The particle size can be set arbitrarily.
上記のような気相還元法によるニッケル微粉末の製造条件は、 平均粒径 1 m 以下になるように任意に設定するが、 例えば、 出発原料である金属ニッケルの粒 径は約 5〜2 0 mmの粒状、 塊状、 板状等が好ましく、 また、 その純度は慨して 9 9 . 5 %以上が好ましい。 この金属ニッケルを、 まず塩素ガスと反応させて塩 化ニッケルガスを生成させるが、 その際の温度は、 反応を十分進めるために 8 0 0 °C以上とし、 力、つニッケルの融点である 1 4 5 3 °C以下とする。 反応速度と塩 化炉の耐久性を考慮すると、実用的には 9 0 O t：〜 1 1 0 0 °Cの範囲が好ましい。 次いで、 この塩化ニッケルガスを還元工程に直接供給し、 水素ガス等の還元性ガ スと接触反応させるが、 窒素やアルゴン等の不活性ガスを、 塩化ニッケルガスに 対し 1〜3 0モル％混合し、 この混合ガスを還元工程に導入してもよい。 また、 塩化ニッケルガスと共にまたは独立に塩素ガスを還元工程に供給することもで きる。 このように塩素ガスを還元工程に供給することによって、 塩化ニッケルガ スの分圧が調整でき、生成するニッケル粉末の粒径を制御することが可能となる。 還元反応の温度は反応完結に十分な温度以上であればよいが、 固体状のニッケル 粉末を生成する方が、取扱いが容易であるので、ニッケルの融点以下が好ましく、 経済性を考慮すると 9 0 0 °C〜 1 1 0 0 °Cが実用的である。 The conditions for producing fine nickel powder by the above-mentioned vapor phase reduction method are: The particle diameter of the starting material, ie, metal nickel, is preferably in the form of particles, lumps, plates, etc. of about 5 to 20 mm, and its purity is preferably 9 9 5% or more is preferable. This metallic nickel is first reacted with chlorine gas to form nickel chloride gas, and the temperature at that time is set to 800 ° C. or higher in order to allow the reaction to proceed sufficiently, and the melting point of nickel is 1 Lower the temperature to 4 5 3 ° C. In consideration of the reaction rate and the durability of the chlorination furnace, practically, the range of 900 ° t to 110 ° C is preferable. Next, the nickel chloride gas is directly supplied to the reduction step to cause a catalytic reaction with a reducing gas such as hydrogen gas, but an inert gas such as nitrogen or argon is mixed with 1 to 30 mol% of nickel chloride gas. The mixed gas may be introduced into the reduction step. In addition, chlorine gas can be supplied to the reduction step together or independently with nickel chloride gas. By thus supplying chlorine gas to the reduction step, the partial pressure of the nickel chloride gas can be adjusted, and the particle size of the produced nickel powder can be controlled. The temperature of the reduction reaction may be a temperature sufficient to complete the reaction, but since it is easier to handle when producing a solid nickel powder, the melting point or less of nickel is preferable, considering the economics. 0 ° C. to 1 100 ° C. is practical.
このように還元反応を行ぃニッケル微粉末を生成させたら、次は生成ニッケル 粉末を冷却する。 冷却の際、 生成したニッケルの一次粒子同士の凝集による二次 粒子の生成を防止して所望の粒径の二ッケル粉末を得るために、還元反応を終え た 1 0 0 0 °C付近のガス流を 4 0 0〜8 0 0 °C程度まで窒素ガス等の不活性ガ スを吹き込むことにより急速冷却させることが望ましい。 その後、 生成したニッ ケル粉末を、 例えばバグフィル夕一等により分離、 回収する。  Thus, after the reduction reaction is performed to form a fine nickel powder, next, the formed nickel powder is cooled. At the time of cooling, the reduction reaction was completed to prevent the formation of secondary particles by aggregation of the primary particles of the formed nickel and to obtain a Nikkell powder of a desired particle diameter, the gas around 100 ° C. It is desirable to rapidly cool the stream to about 400-800 ° C. by blowing inert gas such as nitrogen gas. After that, the produced nickel powder is separated and recovered, for example, by bagfill Yuichi et al.
また、 噴霧熱分解法による金属微粉末の製造方法では、 熱分解性の金属化合物 を原料とするが、 具体的には、 金属の硝酸塩、 硫酸塩、 ォキシ硝酸塩、 ォキシ硫 酸塩、 塩化物、 アンモニゥム錯体、 リン酸塩、 カルボン酸塩、 アルコキシ化合物 などの 1種又は 2種以上である。 このニッケル化合物を含む溶液を噴霧して、 微 細な液滴を作るが、 このときの溶媒としては、 水、 アルコール、 アセトン、 エー テル等が用いられる。 また、 噴霧の方法は、 超音波又は二重ジェットノズル等の 噴霧方法により行う。 このようにして微細な液滴とし、 高温で加熱し金属化合物 を熱分解して、 金属微粉末を生成させる。 このときの加熱温度は、 使用される特 定の金属化合物が熱分解する温度以上であり、好ましくは金属の融点付近である。 液相法による金属微粉末の製造方法では、 例えばニッケル微粉末の製造では、 硫酸ニッケル、 塩ィ匕ニッケルあるいはニッケル錯体を含むニッケル水溶液を、 水 酸化ナトリウムなどのアルカリ金属水酸化物中に添加するなどして接触させ二 ッケル水酸化物を生成させ、次いでヒドラジンなどの還元剤でニッケル水酸化物 を還元し金属ニッケル粉末を得る。 このように生成した金属ニッケル粉末は、 均 一な粒子を得るために必要に応じて解碎処理する。 Also, in the method of producing fine metal powder by spray pyrolysis, although a thermally decomposable metal compound is used as a raw material, specifically, metal nitrates, sulfates, oxynitrates, oxysulfates, chlorides, It is one or more of an ammonium complex, a phosphate, a carboxylate, an alkoxy compound and the like. The solution containing the nickel compound is sprayed to form fine droplets, and as the solvent at this time, water, alcohol, acetone, ether or the like is used. In addition, the method of spraying is performed by a spraying method such as ultrasonic or double jet nozzle. In this way, it is formed into fine droplets and heated at high temperature to thermally decompose the metal compound to form a fine metal powder. The heating temperature at this time is The temperature is higher than the temperature at which certain metal compounds are thermally decomposed, and preferably around the melting point of the metal. In the method of producing fine metal powder by the liquid phase method, for example, in the production of fine nickel powder, an aqueous nickel solution containing nickel sulfate, nickel chloride or nickel complex is added to an alkali metal hydroxide such as sodium hydroxide or the like. Contact, etc. to form nickel hydroxide, and then reducing nickel hydroxide with a reducing agent such as hydrazine to obtain metallic nickel powder. The metallic nickel powder thus produced is subjected to a unwinding treatment as necessary to obtain uniform particles.
以下金属ニッケルに塩素ガスを接触させて塩化ニッケルガスを連続的に発生 させ、 この塩化ニッケルガスを還元性ガスと接触させ還元してニッケル微粉末を 製造する方法を例に挙げ、 より詳細に説明する。  Hereinafter, a method of producing nickel fine powder by contacting the metal nickel with chlorine gas to continuously generate nickel chloride gas and bringing the nickel chloride gas into contact with a reducing gas for reduction to produce a fine nickel powder will be described in more detail. Do.
A. 塩化工程  A. Chlorination process
第 1図は、 本発明に使用する金属微粉末を製造するための装置である。 塩化工 程は、 同図に示すような塩化炉 1 0によって行うと好適である。 塩化炉 1 0の上 端面には原料金属ニッケル（M)を供給するための供給管 1 1が設置されている。 また、 塩化炉 1 0の一の上側部には塩素ガス供給管 1 2が接続され、 その下側部 には不活性ガス供給管 1 3が接続されている。塩化炉 1 0の周囲には加熱手段 1 4が配置され、 塩化炉 1 0の他の上側部には、 移送管兼ノズル 1 5が接続されて いる。 塩化炉 1 0は、 縦型、 横型を問わないが、 固体一ガス接触反応を均一に行 うためには縦型が好ましい。塩素ガスは、 流量計測して連続的に塩素ガス供給管 1 2から導入される。移送管兼ノズル 1 5は、 後述する還元炉 2 0上端面に接続 され、塩化炉 1 0で発生する塩化ニッケルガス等を還元炉 2 0へ移送する機能を 有する。 また、 移送管兼ノズル 1 5の下端部は、 還元炉 2 0内に突出して塩化二 ッケル噴出ノズルとして機能する。 出発原料である金属ニッケル （M) の形態は 問わないが、 接触効率、 圧力損失上昇防止の観点から、 粒径約 5 mm〜2 0 mm の粒状、 粗状、 板状などが好ましく、 またその純度は概して 9 9 . 5 %以上が好 ましい。 塩化炉 1 0内の金属ニッケル （M) の充填層高は、 塩素ガス供給速度、 塩化炉内温度、 連続運転時間、 金属ニッケル （M) の形状などをもとに、 供給塩 素ガスが塩化ニッケルガスに変換されるに十分な範囲に適宜設定すればよい。塩 化炉 1 0内の温度は、 反応を十分進めるために 8 0 0 °C以上とし、 ニッケルの融 点である 1 4 8 3 °C以下とする。反応速度および塩化炉 1 0の耐久性を考慮する と、 実用的には 9 0 0 ° (：〜 1 1 0 0 °Cの範囲が好ましい。 FIG. 1 shows an apparatus for producing fine metal powder used in the present invention. The chlorination step is preferably performed by a chlorination furnace 10 as shown in the figure. At the upper end face of the chlorination furnace 10, a supply pipe 11 for supplying raw material metal nickel (M) is installed. Further, a chlorine gas supply pipe 12 is connected to an upper portion of one of the chlorination furnaces 10, and an inert gas supply pipe 13 is connected to the lower side thereof. A heating means 14 is disposed around the chlorination furnace 10, and a transfer pipe / nozzle 15 is connected to the other upper part of the chlorination furnace 10. The chlorination furnace 10 may be vertical or horizontal, but is preferably vertical to uniformly carry out solid-gas contact reaction. Chlorine gas is introduced from the chlorine gas supply pipe 12 continuously by measuring the flow rate. The transfer pipe / nozzle 15 is connected to the upper end face of the reduction furnace 20 described later, and has a function of transferring nickel chloride gas or the like generated in the chlorination furnace 10 to the reduction furnace 20. Further, the lower end portion of the transfer pipe / nozzle 15 projects into the reduction furnace 20 and functions as a nickel chloride injection nozzle. The form of metallic nickel (M), which is the starting material, does not matter, but from the viewpoint of contact efficiency and prevention of pressure drop rise, granular, coarse, plate-like, etc. with a particle size of about 5 mm to 20 mm are preferable. The purity is generally 99.5% or more. The bed height of the metallic nickel (M) in the chlorination furnace 10 is determined by the chlorine gas supply rate, the temperature in the chlorination furnace, the continuous operation time, the shape of the metallic nickel (M), etc. It may be appropriately set in a range sufficient for conversion to nickel gas. The temperature in the chlorination furnace 10 should be 800.degree. C. or higher to promote the reaction sufficiently. The temperature shall be 1483 ° C or less. In consideration of the reaction rate and the durability of the chlorination furnace 10, practically, the range of 900 ° (: to 110 ° C. is preferable.
本発明の金属微粉末の製造方法においては、 金属ニッケル （M) が充填された 塩化炉 1 0への塩素ガスの連続供給は、塩化ニッケルガスの連続発生をもたらす。 そして、 塩素ガス供給量力塩化ニッケルガスの発生量を支配するから、 後述する 還元反応を支配し、その結果、目的とする製品ニッケル微粉末が生産可能になる。 なお、 塩素ガス供給については以下の還元工程において具体的に説明する。  In the method for producing metal fine powder of the present invention, continuous supply of chlorine gas to the chlorination furnace 10 filled with metallic nickel (M) leads to continuous generation of nickel chloride gas. And, since the amount of chlorine gas supply controls the amount of generation of nickel chloride gas, it controls the reduction reaction described later, and as a result, it becomes possible to produce the desired product fine nickel powder. The chlorine gas supply will be specifically described in the following reduction step.
塩化工程で発生した塩化ニッケルガスは、そのまま移送管兼ノズル 1 5により 還元炉 2 0に移送する力、、場合によっては不活性ガス供給管 1 3から窒素やアル ゴンなどの不活性ガスを、塩ィ匕ニッケルガスに対し 1 m o 1 %〜3 O m o 1 %混 合し、 この混合ガスを還元炉 2 0に移送する。移送管兼ノズル 1 5を通過する混 合ガス中の好ましい塩化ニッケルガス分圧は、 全圧を 1 . 0としたときに 0 . 5 〜1 . 0の範囲、 とりわけ粒径 0 . 2 111〜0 . 5 mといった小粒径のニッケ ル微粉末を製造する場合には、 分圧 0 . 6〜0 . 9程度が好適である。  The nickel chloride gas generated in the chlorination step is transferred as it is to the reduction furnace 20 by the transfer pipe / nozzle 15 and, in some cases, an inert gas such as nitrogen or argon from the inert gas supply pipe 13 The mixture is mixed with 1 mol% to 3% mol of 1 mol% to 3 moll of nickel chloride gas, and the mixed gas is transferred to a reduction furnace 20. The preferable nickel chloride gas partial pressure in the mixed gas passing through the transfer pipe / nozzle 15 is in the range of 0.5 to 1.0 when the total pressure is 1.0, and in particular, the particle diameter is 0.21 to 11 1. In the case of producing fine nickel powder having a small particle size of 0.5 m, a partial pressure of about 0.6 to 0.9 is preferable.
B . 還元工程 B. Reduction process
塩化工程で発生した塩化ニッケルガスは、 連続的に還元炉 2 0に移送される。 還元工程は、 第 1図に示すような還元炉 2 0を用いて行うことが望ましい。 同図 に示した還元炉 2 0は、 円筒状をなし、 その上半部で還元を行い、 その下半部で 冷却を行う。還元炉 2 0の上端部には、上述した移送管兼ノズル 1 5のノズル（以 下、 単にノズル 1 5と称する） が下方へ突出させられている。 また、 還元炉 2 0 の上端面には、 還元性ガス供給管 （水素ガス供給管） 2 1が接続されている。 ま た、 還元炉 2 0の周囲には加熱手段 2 2が配置されている。 ノズル 1 5は、 塩ィ匕 炉 1 0から還元炉 2 0内へ塩化ニッケルガス（不活性ガスを含む場合がある）を、 好ましい流速で噴出する機能を有する。  The nickel chloride gas generated in the chlorination step is transferred to the reduction furnace 20 continuously. The reduction step is preferably performed using a reduction furnace 20 as shown in FIG. The reduction furnace 20 shown in the figure has a cylindrical shape, and reduction is performed in the upper half, and cooling is performed in the lower half. At the upper end of the reduction furnace 20, the nozzle of the above-described transfer pipe / nozzle 15 (hereinafter simply referred to as the nozzle 15) is protruded downward. Further, a reducing gas supply pipe (hydrogen gas supply pipe) 21 is connected to the upper end face of the reduction furnace 20. Further, heating means 22 is disposed around the reduction furnace 20. The nozzle 15 has a function of injecting nickel chloride gas (which may contain an inert gas) from the salt furnace 10 into the reduction furnace 20 at a preferable flow rate.
塩ィ匕ニッケルガスと水素ガスとによる還元反応が進行する際には、 ノズル 1 5 の先端部からは、 L P Gなどの気体燃料の燃焼炎に似た下方に延びた輝炎 Fが形 成される。 還元炉 2 0への水素ガス供給量は、 塩ィ匕ニッケルガスの化学当量、 す なわち、 塩ィヒ炉 1 0へ供給する塩素ガスの化学当量の 1 . 0〜3 . 0倍程度、 好 ましくは 1 . 1〜2 . 5倍程度であるが、 これに限定するものではない。 また、 還元反応の温度は反応完結に十分な温度以上であればよいが、 固体状のニッケル 微粉末を生成する方が取扱いが容易であるので、ニッケルの融点以下が好ましい。 また、 上記温度は反応速度、 還元炉 20の耐久性、 経済性を考慮すると 900°C 〜1100°Cが実用的であるが、 特にこれに限るものではない。 When the reduction reaction between chloride nickel gas and hydrogen gas proceeds, a downward light flame F similar to the combustion flame of gaseous fuel such as LPG is formed from the tip of the nozzle 15 Ru. The amount of hydrogen gas supplied to the reduction furnace 20 is approximately 1.0 to 3.0 times the chemical equivalent of chloride / nickel gas, that is, the chemical equivalent of chlorine gas to be supplied to the chloride reactor 10. Preferably, it is about 1.1 to 2.5 times, but it is not limited to this. Also, The temperature of the reduction reaction may be a temperature sufficient to complete the reaction, but it is preferably below the melting point of nickel because it is easier to handle when producing a solid fine nickel powder. The above temperature is practically 900 ° C. to 1100 ° C. in consideration of the reaction rate, the durability of the reduction furnace 20, and the economy, but it is not particularly limited thereto.
上述のとおり、 塩化炉 10に導入された塩素ガスは、 実質的に同モル量の塩ィ匕 ニッケルガスとなり、 これが還元原料とされる。 塩化ニッケルガスもしくは塩ィ匕 二ッゲルと不活性ガスとの混合ガスのノズル 15先端から噴出されるガス流の 線速度を調整することにより、得られるニッケル微粉末 Pの粒径を適切化するこ とができる。 すなわち、 ノズル径が一定であれば、 塩化工程への塩素供給量と不 活性ガス供給量とを調整することによって、還元炉 20で生成されるニッケル微 粉末 Pの粒径を目的の範囲に調整することができる。  As described above, the chlorine gas introduced into the chlorination furnace 10 becomes substantially the same molar amount of chloride nickel gas, which is used as the reduction material. The particle size of the obtained nickel fine powder P is optimized by adjusting the linear velocity of the gas flow ejected from the tip of the nozzle 15 of the mixed gas of nickel chloride gas or chloride di-gel and inert gas. It is possible. That is, if the nozzle diameter is constant, the particle size of the nickel fine powder P generated in the reduction furnace 20 is adjusted to the desired range by adjusting the chlorine supply amount to the chlorination step and the inert gas supply amount. can do.
ノズル 15先端における好ましいガス流の線速度（塩化ニッケルガスおよび不 活性ガスの合計 （還元温度でのガス供給量に換算した計算値)） は、 900°C〜 1100°(の還元温度にぉぃて約1111 秒〜3 OmZ秒に設定される。水素ガス の還元炉 20内での軸方向の線速度は、 塩化ニッケルガスの噴出速度 〈線速度） の 1/50〜： 1/300程度が好ましく、 1/80〜： 1/250がすることがさ らに好ましい。 したがって、 実質的には静的水素雰囲気中へ塩ィヒニッケルガスが ノズル 15から噴射されることとなる。  The preferable linear velocity of the gas flow at the tip of the nozzle 15 (the total of nickel chloride gas and inert gas (calculated value converted to the amount of gas supplied at the reduction temperature)) is 900 ° C. to 1100 ° (reduction temperature of The linear linear velocity of hydrogen gas in the reduction furnace 20 in the reduction furnace 20 is about 1/50 to 1/300 of the ejection velocity of nickel chloride gas (linear velocity). Preferably, 1/80 to 1/250 is more preferable. Therefore, substantially salty nickel gas is injected from the nozzle 15 into a static hydrogen atmosphere.
なお、 還元性ガス供給管 21の出口の方向は、 輝炎 F側へ向けないことが好ま しい。 また、 ニッケル微粉末を生成する際に用いる還元性ガスとしては、 以上に 示した水素ガスの他に硫化水素ガス等を用いることができるが、 生成したエッケ ル微粉末への影響を考慮すると、 水素ガスが好適である。 さらに、 ニッケル微粉 末を製造する場合における金属塩ィ匕物ガスと還元性ガスとを接触、反応させる還 元反応温度領域は、 通常 900〜 1200 °Cであるが、 950〜 1100 °C、一 層好ましくは 980〜1050°Cである。  The direction of the outlet of the reducing gas supply pipe 21 is preferably not directed to the bright flame F side. In addition to the hydrogen gas shown above, hydrogen sulfide gas and the like can be used as the reducing gas used to form the nickel fine powder, but in view of the effect on the formed fine nickel powder, Hydrogen gas is preferred. Furthermore, in the case of producing nickel fine powder, the reduction reaction temperature range for contacting and reacting metal chloride complex gas with reducing gas is usually 900 to 1200 ° C., but 950 to 1100 ° C. The layer preferably has a temperature of 980 to 1050 ° C.
C. 冷却工程 C. Cooling process
還元工程で生成したニッケル微粉末は、 第 1図に示すように、 還元炉 20内の ノズル 15と反対側の空間部分 （下方部分） において冷却される。 冷却を行うた めの好ましい例として、 当実施形態では、 輝炎 F先端から下方の空間部分に冷却 ガス供給管 2 3から冷却用不活性ガスを吹き込むように構成されている。 なお、 本発明でいう冷却とは、 還元反応で生成したガス流 （塩酸ガスを含む） における 二ッケル粒子の成長を停止もしくは抑制するために行う操作であり、具体的には 還元反応を終えた 1 0 0 0 °C付近のガス流を 4 0 0 °C〜8 0 0 °C程度まで急速 冷却させる操作を意味する。 もちろんこれ以下の温度まで冷却を行うこともでき る。 The fine nickel powder produced in the reduction step is cooled in the space portion (lower portion) opposite to the nozzle 15 in the reduction furnace 20, as shown in FIG. As a preferred example for performing cooling, in the present embodiment, cooling is performed to the space portion below the tip of the bright flame F. The cooling inert gas is blown from the gas supply pipe 23. The term "cooling" as used in the present invention is an operation performed to stop or suppress the growth of nickel particles in the gas stream (including hydrochloric acid gas) generated by the reduction reaction, and specifically, the reduction reaction has been completed. It means an operation of rapidly cooling the gas flow around 100 ° C. to about 400 ° C. to 800 ° C. Of course, cooling can also be performed to a temperature lower than this.
生成したニッケル微粉末を冷却するための不活性ガスとしては、 生成したニッ ケル微粉末に影響の無いものであれば特に限定されないが、 窒素ガス、 アルゴン ガス等を用いることができる。 この中でも、 窒素ガスが安価であるため好適であ る。 さらに、 冷却用不活性ガスの供給量は、 通常生成されるニッケル微粉末 1 g 当り、 5 N 1 Z分以上、 好ましくは 1 0〜 5 0 N 1 /分である。 なお、 供給する 不活性ガスの温度は、 通常 0〜 1 0 0 °Cであるが、 0〜 8 0 °Cとした場合にはよ り効果的である。  The inert gas for cooling the produced nickel fine powder is not particularly limited as long as it does not affect the produced nickel fine powder, and nitrogen gas, argon gas and the like can be used. Among these, nitrogen gas is preferable because it is inexpensive. Furthermore, the supply amount of the inert gas for cooling is 5 N 1 Z minutes or more, preferably 10 to 50 N 1 / minute, per 1 g of the fine nickel powder usually produced. In addition, although the temperature of the inert gas to be supplied is usually 0 to 100 ° C., it is more effective when the temperature is 0 to 80 ° C.
D . 回収工程  D. Recovery process
塩化、還元および冷却の各工程を順次に経たニッケル微粉末 Pと塩酸ガスおよ び不活性ガスの混合ガスは、 第 1図のノズル 2 4を経て、 回収炉 （図示せず） に 移送され、 そこで混合ガスからニッケル微粉末 Pが分離回収される。 分離回収に は、 例えば、 バグフィルタ、 水中捕集分離手段、 油中捕集分離手段および磁気分 離手段の 1種または 2種以上の組合せが好適であるが、 これに限定されるもので はない。  The mixed gas of fine nickel powder P, hydrochloric acid gas and inert gas sequentially passed through the steps of chlorination, reduction and cooling is transferred to a recovery furnace (not shown) through a nozzle 24 in FIG. Then, fine nickel powder P is separated and recovered from the mixed gas. For separation and recovery, for example, one or a combination of two or more of a bag filter, a collection and separation means in water, a collection and separation means in oil, and a magnetic separation means are suitable, but it is not limited thereto. Absent.
また、 分離回収前または後に、 必要に応じて生成したニッケル微粉末を水、 炭 素数 1〜4の 1価アルコール等の溶媒で洗浄することもできる。 さらには、 必要 に応じて生成したニッケル微粉末を、水素ガスあるいは不活性ガスで希釈された 水素ガスの還元性雰囲気下にて水素還元処理し、 ニッケル微粉末中の酸素含有量 を微調整することもできる。水素還元処理温度は 2 2 0〜3 0 0 °Cであることが 好ましく、 2 5 0〜 3 0 0 °Cであれはさらに好ましい。 水素還元処理時間は 5〜 6 0分である。  Before or after separation and recovery, the fine nickel powder produced may be washed with a solvent such as water or a monohydric alcohol having 1 to 4 carbon atoms, if necessary. Furthermore, if necessary, the nickel fine powder produced is subjected to hydrogen reduction treatment in a reducing atmosphere of hydrogen gas or hydrogen gas diluted with an inert gas to finely adjust the oxygen content in the nickel fine powder. It can also be done. The hydrogen reduction treatment temperature is preferably 220 to 300 ° C, and more preferably 250 to 300 ° C. The hydrogen reduction treatment time is 5 to 60 minutes.
E . 酸化処理工程  E. Oxidation process
本発明におけるニッケル微粉末では、 上記のような方法で得られたニッケル微 粉末を炭酸水溶液中で処理し、 次いでオゾン雰囲気中で加熱して酸化処理する。 炭酸水溶液処理は、金属二ッケル微粉末スラリー中に炭酸ガスを吹き込んで PIn the fine nickel powder of the present invention, the fine nickel powder obtained by the above method is used. The powder is treated in aqueous carbonate solution and then oxidized by heating in an ozone atmosphere. In the aqueous carbonate solution treatment, carbon dioxide gas is blown into a fine metal powder slurry to obtain P
H 5 . 5〜6 . 5とし、 炭酸水溶液として常温で 6 0分処理を行った。 H 5.55 to 6.5 and treated as a carbonated aqueous solution at room temperature for 60 minutes.
酸化処理は、 気相還元法によって得られ、 炭酸水溶液処理を施した後に乾燥し たニッケル微粉末を、 酸化炉内に入れて加熱し、 該酸化炉内にオゾンガスを供給 することによって実施される。 オゾンガスは、 酸素、 空気、 一酸化炭素、 二酸化 炭素等のガスや、水蒸気、低級アルコール等と混合して供給することができるが、 酸素ガスとの混合がより効果的である。オゾンガス濃度は 1〜2 0 V o 1 %の範 囲であることが好適であるが、 より好ましくは 5〜 2 0 V o 1 %である。酸化処 理温度は、 2 0 0〜2 5 0 °Cの低温度領域であることが好適であり， 好ましくは 2 2 0〜2 3 0 °Cの範囲である。酸化処理時間は、 前述のオゾンガス濃度と酸化 処理温度に応じて、酸化皮膜の厚みが 1〜1 0 n mとなるように 1分〜 3 0分の 範囲内で適宜選択すればよい。  The oxidation treatment is carried out by putting the aqueous nickel powder obtained by the gas phase reduction method and then drying it into an oxidation furnace, heating it, and supplying ozone gas into the oxidation furnace. . The ozone gas can be supplied as a mixture with gases such as oxygen, air, carbon monoxide, carbon dioxide, water vapor, lower alcohols, etc. However, mixing with oxygen gas is more effective. The ozone gas concentration is preferably in the range of 1 to 20 V o 1%, and more preferably 5 to 20 V o 1%. The oxidation treatment temperature is suitably in the low temperature range of 200 to 250 ° C, preferably in the range of 220 to 230 ° C. The oxidation treatment time may be appropriately selected within the range of 1 minute to 30 minutes so that the thickness of the oxide film becomes 1 to 10 nm according to the above-mentioned ozone gas concentration and oxidation treatment temperature.
気相還元法によって得られたニッケル微粉末は、大気中に放置しておくことに より、 水分を吸収して水酸化ニッケルを生成する。 このようなニッケル微粉末を 有機溶媒等と混合してニッケルペーストとした場合は、分散性が低下しニッケル 微粉末同士が凝集して粗粉が増加してしまうことになるため、 7K酸化ニッケルを 除去するための熱処理に長時間を費やすことになる。 したがって、 気相還元法に よって得られたニッケル微粉末に対して酸化処理を施す場合、 出来るだけ速やか に上記の酸化処理を行うことが好ましい。  The nickel fine powder obtained by the vapor phase reduction method absorbs moisture to form nickel hydroxide by leaving it in the air. When such fine nickel powder is mixed with an organic solvent or the like to form a nickel paste, the dispersibility is reduced and the fine nickel powder is aggregated to increase coarse powder. It takes a long time for heat treatment to remove it. Therefore, in the case where the nickel fine powder obtained by the vapor phase reduction method is subjected to the oxidation treatment, it is preferable to carry out the above-mentioned oxidation treatment as quickly as possible.
酸化処理後は、 必要に応じて水素雰囲気、 もしくは不活性ガスで希釈された水 素ガス雰囲気中で水素還元処理を行い、 ニッケル微粉末中の酸素含有量を微調整 することも可能である。  After the oxidation treatment, it is also possible to finely adjust the oxygen content in the fine nickel powder by carrying out a hydrogen reduction treatment in a hydrogen atmosphere or a hydrogen gas atmosphere diluted with an inert gas as necessary.
E . 導電ペーストの作製 E. Preparation of conductive paste
上記のようにして得られた金属微粉末は、導電ペーストあるいは電極形成用べ 一ストに好適である。 このような金属微粉末は、 有機溶媒およびバインダと混鍊 してペーストを形成する。 有機溶媒 （有機ビヒクル） としては、 従来の導体ぺー ストに用いられているものを使用すれば足り、 例えば、 ェチルセルロース、 ェチ レングリコール、 トルエン、 キシレン、 ミネラルオイル、 ブチルカルビトール、 ターピネオール等の高沸点有機溶媒を用いることができる。バインダとしては有 機また無機バインダが用いられるが、 ェチルセルロースなどの高分子バインダを 用いることが好ましい。 The metal fine powder obtained as described above is suitable for use as a conductive paste or an electrode paste. Such metal fine powder is mixed with an organic solvent and a binder to form a paste. As the organic solvent (organic vehicle), it is sufficient to use those used in conventional conductor pastes, for example, diethyl cellulose, ethylene glycol, toluene, xylene, mineral oil, butyl carbitol, A high boiling point organic solvent such as terpineol can be used. As the binder, an organic or inorganic binder is used, but it is preferable to use a polymer binder such as hydroxyethyl cellulose.
また、 必要に応じて鉛系 ラス、 亜鉛系ガラスあるいはケィ酸系ガラスなどの ガラスフリットや、 酸化マンガン、 酸化マグネシウム、 酸化ビスマなどの金属酸 化物フイラなどを、 ペーストを形成する際に混合してもよい。 これらの添加物を 混合することによってセラミックスなどの基材に塗布、 焼結して電極を形成した 際、 基材との密着性に優れ伝導性の高い電極を形成することができ、 また半田と の濡れ性を向上させる。 その他、 フタル酸エステルゃステアリン酸などの可塑剤 や、 分散剤などをペーストに添加することができる。  In addition, glass frits such as lead-based glass, zinc-based glass or cailic acid-based glass, and metal oxide fillers such as manganese oxide, magnesium oxide, bismuth oxide, etc. may be mixed when forming the paste, if necessary. It is also good. When an electrode is formed by coating and sintering on a base material such as ceramics by mixing these additives, an electrode having excellent adhesion to the base material and high conductivity can be formed. Improve the wettability of In addition, plasticizers such as phthalic acid ester and stearic acid, and dispersants can be added to the paste.
以上のように、 金属微粉末の表面にオゾンガスによる強固な酸化皮膜を形成す ることにより、 焼結開始温度が高く、 焼結時の収縮率が低く、 金属微粉末同士の 凝集による粗粉が少なく、 また、 有機溶媒等と混合して金属べ一ストにした際の 分散性に優れる、 積層セラミツクコンデンサの内部電極用としてふさわしい機能 を有する金属微粉末を得ることができる。 このような金属微粉末を使用すること により、 積層セラミックコンデンサ製造工程におけるデラミネ一ション等の構造 欠陥を抑制することが可能となる。 図面の簡単な説明  As described above, by forming a strong oxide film with ozone gas on the surface of the metal fine powder, the sintering start temperature is high, the shrinkage rate at sintering is low, and the coarse powder due to the aggregation of the metal fine powder is In addition, it is possible to obtain a fine metal powder having a function suitable for use as an internal electrode of a laminated ceramic capacitor, which is excellent in dispersibility when mixed with an organic solvent or the like to form a metal-based material. By using such metal fine powder, it is possible to suppress structural defects such as delamination in the manufacturing process of the multilayer ceramic capacitor. Brief description of the drawings
第 1図は、本発明に使用する金属微粉末を製造するための装^を示す図である。 発明を実施するための最良の形態  FIG. 1 is a view showing an apparatus for producing a metal fine powder used in the present invention. BEST MODE FOR CARRYING OUT THE INVENTION
以下、 本発明の実施例により、 本発明の効果を明らかにする。  Hereinafter, the effects of the present invention will be clarified by examples of the present invention.
二ッケル粉の焼結開始温度評価 Evaluation of sintering start temperature of nicker powder
[実施例 1 ]  [Example 1]
第 1図に示す金属ニッケル微粉末製造装置の塩化炉 1 0内に、 出発原料である 平均粒径 5 mmの金属二ッケル微粉末を原料供給管 1 1から充填するとともに、 加熱手段 1 4により炉内雰囲気温度を 1 1 0 0 °Cとする。 次いで、 塩素ガス供給 管 1 2から塩素ガスを塩ィヒ炉 1 0内に供給し、 金属ニッケルを塩ィ匕して塩ィヒニッ ケルガスを発生させた。 この塩化ニッケルガスに、 塩化炉 1 0の下側部に設けら れた不活性ガス導入管 1 3から塩素ガス供給量の 1 0 % (モル比） の窒素ガスを 供給して混合した。 そして、 塩化ニッケルガスと窒素ガスの混合ガスをノズル 1 5を介して還元炉 2 0に導入した。 In the chlorination furnace 10 of the apparatus for producing fine nickel metal powder shown in FIG. 1, a fine powder of metal di-nickel having an average particle diameter of 5 mm, which is a starting material, is filled from a raw material supply pipe 11 and The furnace ambient temperature is set to 1 100 ° C. Next, chlorine gas is supplied from the chlorine gas supply pipe 12 into the salt furnace 10 to salt the metallic nickel to form a salt pot. It generated kelgas. To this nickel chloride gas, nitrogen gas of 10% (molar ratio) of the chlorine gas supply amount was supplied and mixed from an inert gas introduction pipe 13 provided on the lower side of the chlorination furnace 10. Then, a mixed gas of nickel chloride gas and nitrogen gas was introduced into the reduction furnace 20 through the nozzle 15.
次いで、 還元工程として、 塩ィ匕ニッケルガスと窒素ガスとの混合ガスを加熱手 段 2 2により 1 0 0 0 °Cの炉内雰囲気温度とされた還元炉 2 0に、 ノズル 1 5か ら流速 2 . 3 mZ秒 （1 0 0 0 °C換算） で導入した。 同時に還元炉 2 0内の上端 部に設けられた還元性ガス導入管 4 1から水素ガスを流速 7 N 1ノ分で還元炉 2 0内に供給して塩ィ匕ニッケルガスを還元し、 ニッケル微粉末 Pを得た。  Next, as a reduction step, a mixed gas of a nickel chloride gas and a nitrogen gas is heated by a heating device 22 to a reduction furnace 20 in which the atmosphere temperature in the furnace is set to a temperature of 1000 ° C. The flow rate was introduced at 2.3 mZ seconds (converted to 1000 ° C.). At the same time, hydrogen gas is supplied from the reducing gas introduction pipe 41 provided at the upper end in the reduction furnace 20 into the reduction furnace 20 at a flow rate of 7 N 1 min to reduce the chloride nickel gas and reduce nickel. Fine powder P was obtained.
さらに、 冷却工程として、 還元工程にて生成したニッケル微粉末 Pに、 還元炉 2 0下側部に設けられた冷却ガス供給管 2 3から 1 6 . 4 N 1 /分 · gで供給し た窒素ガスを接触させ、 ニッケル微粉末 Pを冷却した。 そして、 生成したニッケ ル微粉末 Pを塩素ガス及び塩酸蒸気とともにノズル 2 4を介して図示しない回 収炉に導いた。  Furthermore, as a cooling process, the fine nickel powder P produced in the reduction process was supplied at a cooling gas supply pipe 23 provided at the lower side of the reduction furnace 20 at 13.4 N 1 / min · g. The fine nickel powder P was cooled by contacting with nitrogen gas. Then, the produced fine nickel powder P was introduced to a not-shown recovery furnace through the nozzle 24 together with chlorine gas and hydrochloric acid vapor.
このようにノズル 2 4から回収炉に導かれた窒素ガス、 塩酸蒸気、 およびニッ ケル微粉末 Pを図示しないバグフィルタに導き、 二ッケル微粉末を分離回収した。 そして、 回収したニッケル微粉末 Pを湯洗洗浄し、 'ニッケル微粉末スラリー中に 炭酸ガスを吹き込んで p H 5 . 5とし、 常温下においてニッケル微粉末を炭酸水 溶液中で 6 0分処理した。  The nitrogen gas, hydrochloric acid vapor and nickel fine powder P thus introduced into the recovery furnace from the nozzle 24 were introduced into a bag filter (not shown) to separate and recover the fine nickel fine powder. Then, the collected fine nickel powder P was washed with hot water, and carbon dioxide gas was blown into the fine nickel powder slurry to obtain pH 5.5, and the fine nickel powder was treated in a carbonated water solution for 60 minutes at normal temperature. .
炭酸水溶液処理したニッケル微粉末を乾燥した後、 酸化処理した。 気相還元法 で得られたニッケル微粉末 Pを酸化炉に入れ、加熱手段にて炉内雰囲気温度を 2 0 0 °Cとし、酸化ガス供給管からオゾンガス 5 V 0 1 %含有オゾン一酸素混合ガ スを 1 0分間導入してニッケル微粉末 Pを酸化処理し、製品ニッケル微粉末を得 た。  The carbonic acid aqueous solution-treated nickel fine powder was dried and then oxidized. The fine nickel powder P obtained by the vapor phase reduction method is placed in an oxidation furnace, the atmosphere temperature in the furnace is set to 200 ° C. by heating means, and ozone monooxygen mixed with 5 V 01% ozone gas from the oxidation gas supply pipe. Gas was introduced for 10 minutes to oxidize the fine nickel powder P to obtain a fine nickel powder.
[実施例 2 ]  [Example 2]
実施例 1と同様に製造したニッケル微粉末 Pを酸化工程で酸化するにあたり、 酸化炉内雰囲気温度を 2 5 0 °C, オゾン一酸素混合酸化ガス中のオゾン濃度を 5 v o 1 %、 酸化処理時間 3 0分間、 として酸化処理を実施した。  In oxidizing the fine nickel powder P produced in the same manner as in Example 1 in the oxidation step, the atmosphere temperature in the oxidation furnace is 250 ° C., the ozone concentration in the ozone / oxygen mixed oxidation gas is 5 vo 1%, oxidation treatment The oxidation treatment was carried out for 30 minutes at a time of.
[比較例 1 ] 実施例 1と同様にニッケル微粉末 Pを製造し、炭酸水溶液処理は実施せずに酸 化処理を施した。 酸化処理するにあたり、 酸化ガスを酸素ガスとした。 また、 酸 化処理温度、 酸化処理時間は実施例 1と同一条件で行った。 [Comparative example 1] A fine nickel powder P was produced in the same manner as in Example 1, and was subjected to oxidation treatment without treatment with an aqueous carbonate solution. The oxidizing gas was oxygen gas for the oxidation treatment. The oxidation treatment temperature and the oxidation treatment time were the same as in Example 1.
[比較例 2 ]  [Comparative example 2]
実施例 1と同様にニッケル微粉末 Pを製造し、炭酸水溶液処理は実施せずに酸 化処理を施した。 酸化処理するにあたり、 酸化ガスを酸素ガスとした。 さらに、 実施例 1で得られたニッケル微粉末と同じ厚みの酸化皮膜と酸素濃度を有する ようにするため、 酸化処理温度を 4 0 0 °C、 酸化処理時間 3 0分間で実施した。 上記実施例 1 , 2および比較例 1， 2にっき、 金属ニッケル微粉末の酸化皮膜 厚み、 酸素濃度、 焼結開始温度、 収縮率および粒度分布を下記の方法により測定 した。  A fine nickel powder P was produced in the same manner as in Example 1, and was subjected to oxidation treatment without treatment with an aqueous carbonate solution. The oxidizing gas was oxygen gas for the oxidation treatment. Furthermore, in order to have the same thickness of oxide film and oxygen concentration as the fine nickel powder obtained in Example 1, the oxidation treatment temperature was 400 ° C., and the oxidation treatment time was 30 minutes. In Examples 1 and 2 and Comparative Examples 1 and 2, the thickness of the oxide film of the metallic nickel fine powder, the oxygen concentration, the sintering start temperature, the shrinkage rate and the particle size distribution were measured by the following methods.
1 ) 酸化皮膜厚み  1) Oxide film thickness
まず、金属ニッケル微粉末をコロジオン膜を張った銅製シートメッシュ上に直 接振りかけ、 その後カーボンを蒸着させ測定試料を作製した。 次いで、 2 0 0 k V電解放射型透過電子顕微鏡 （H F— 2 0 0 0、 日立製作所製） を用いて測定試 料の格子像を観察し、 金属ニッケル微粉末表面の酸化皮膜厚さを測定した。 First, fine metallic nickel powder was directly sprinkled on a copper sheet mesh covered with a collodion film, and then carbon was vapor deposited to prepare a measurement sample. Next, the lattice image of the sample was observed using a 200 kV electrolytic radiation transmission electron microscope (HF- 200, manufactured by Hitachi, Ltd.) to measure the thickness of the oxide film on the surface of the metallic nickel fine powder. did.
2 ) 酸素濃度 2) Oxygen concentration
金属ニッケル微粉末をニッケル製のカプセルに充填し、 これを黒鉛ルツポに入 れ、 アルゴン雰囲気下で 5 0 0 °Cに加熱し、 このとき発生した一酸化炭素を I R により定量し、 金属ニッケル微粉末中の酸素濃度を求めた。  Metallic nickel fine powder is filled in a capsule made of nickel, placed in a graphite crucible, heated to 500 ° C. under argon atmosphere, carbon monoxide generated at this time is quantified by IR, and metallic nickel fine is prepared. The oxygen concentration in the powder was determined.
3 ) 焼結開始温度  3) Sintering start temperature
金属ニッケル微粉末 l g , 樟脳 3重量％、 アセトン 3重量％を混合し、 内径 5 mm, 高さ 1 0 mmの円柱状金属に充填し、 面圧 1トンの荷重をかけて試験ピー スを作製した。 この試験ピースの焼結開始温度の測定を、 熱膨張収縮挙動測定装 置 （TMA— 8 3 1 0、 株式会社リガク社製） を用いて、 弱還元性雰囲気 （1 . 5 %水素一 9 8 . 5 %窒素混合ガス） 雰囲気の下、 昇温速度 5 °CZ分の条件で行 つた。 上記測定で得られた収縮率曲線にて、 1 %収縮した時点における温度をも つて焼結開始温度とした。  Metallic nickel fine powder lg, 3% by weight of camphor and 3% by weight of acetone were mixed, filled in a cylindrical metal with an inner diameter of 5 mm and a height of 10 mm, and a load of 1 ton of surface pressure was applied to prepare a test piece did. The measurement of the sintering start temperature of this test piece was carried out using a thermal expansion / contraction behavior measuring device (TMA-830, manufactured by Rigaku Corporation) under a weak reducing atmosphere (1.5% hydrogen and 9 8 Under a 5% nitrogen mixed gas atmosphere, the temperature was raised at a rate of 5 ° C for Z minutes. In the shrinkage rate curve obtained by the above measurement, the temperature at the time of 1% shrinkage was taken as the sintering start temperature.
4 ) 収縮率 上記 3 ) の焼結開始温度測定で得た収縮率曲線において、 5 0 0 °Cまで昇温し た時点における重量減少率をもつて収縮率とした。 4) Shrinkage rate In the shrinkage rate curve obtained by the measurement of the sintering start temperature in the above 3), the shrinkage rate was defined as the weight loss rate when the temperature was raised to 500 ° C.
5 ) 粒度分布  5) Particle size distribution
粒度測定器 L S 2 3 0 (コール夕一社製） を用い、 試料をェキネン （イソプロピ ルアルコール 1 0 %、 エタノール 9 0 %) に懸濁させホモジナイザーにて 3分間 分散させて測定し、 積算粒度分布において積算値が 5 0体積％となる粒子径 （D 5 0 ) を求めた。  The sample is suspended in equinene (isopropyl alcohol 10%, ethanol 90%) using a particle size measuring instrument LS 230 (manufactured by Koru Yui Co., Ltd.), dispersed for 3 minutes with a homogenizer, and measured. The particle diameter (D 50) at which the integrated value becomes 50% by volume in the distribution was determined.
第 1表に、 実施例 1、 2および比較例 1、 2で得られたニッケル微粉末の酸 化皮膜厚み、酸素濃度、焼結開始温度、収縮率および粒度分布の測定結果を示す。  Table 1 shows the measurement results of the oxide film thickness, oxygen concentration, sintering start temperature, shrinkage rate and particle size distribution of the fine nickel powder obtained in Examples 1 and 2 and Comparative Examples 1 and 2.
Figure imgf000018_0001
Figure imgf000018_0001
*) 酸化皮膜密度：酸素濃度と酸化皮膜厚みの比 （酸素濃度 Z酸化皮膜厚み) 第 1表から明らかなように、実施例 1 , 2において得られたニッケル微粉末は、 比較例 1 , 2において得られたニッケル微粉末に比して、 酸化皮膜厚さ力概して 大きく、 酸素含有量も多いものであり、 焼結開始温度も高く、 収縮率は小さいも のであった。 すなわち、 各実施例におけるニッケル微粉末は各比較例における二 ッケル微粉末に比して、強固で焼結挙動を改善するのに十分な酸化皮膜を得るこ とができることが判る。 なお、 得られたニッケル微粉末の粒度分布 （粗大粒子の 割合） については、 各実施例は各比較例に比して小さい値となっていた。 特に比 較例 2において粒度分布に関する値が大きいのは、 高温で長時間酸化処理したた めである。 *) Oxide film density: Ratio of oxygen concentration to oxide film thickness (oxygen concentration Z oxide film thickness) As is clear from Table 1, the fine nickel powders obtained in Examples 1 and 2 are comparative examples 1 and 2 Compared with the fine nickel powder obtained in the above, the thickness of the oxide film was generally large, the oxygen content was also large, the sintering start temperature was also high, and the shrinkage was small. That is, it is understood that the nickel fine powder in each example is stronger than the nickel fine powder in each comparative example, and an oxide film sufficient to improve the sintering behavior can be obtained. In addition, the particle size distribution of the obtained nickel fine powder (coarse particles Regarding the ratio (), each Example had a smaller value than each Comparative Example. In particular, the large value relating to the particle size distribution in Comparative Example 2 is due to the long-time oxidation treatment at high temperature.
二ッケルペーストの分散性評価 Evaluation of dispersibility of Nikkoru paste
[実施例 3 ]  [Example 3]
実施例 1で得られた、 オゾンガスで酸化処理されたニッケル微粉末の 5 0質 量％と、 ェチルセルロース 5質量％とターピオネール 9 5質量％とからなるビヒ クル 5 0質量％とを 3本ロールで混練してペーストを作製し、 'これを塗布して膜 密度を測定した。  50% by mass of the nickel fine powder oxidized with ozone gas obtained in Example 1, and 50% by mass of a vehicle comprising 5% by mass of acetyl cellulose and 5% by mass of terpioneel 9 The paste was prepared by kneading with three rolls, and this was applied to measure the film density.
[比較例 3 ]  [Comparative example 3]
比較例 2で得られたニッケル微粉末であって、 酸素ガスで酸化処理され、 実施 例 1で得られたニッケル微粉末と同じ厚みの酸化皮膜と同じ酸素濃度を有する ニッケル微粉末を使用して、 実施例 3と同様にペーストを作製し、 これを塗布し て膜密度を測定した。  The fine nickel powder obtained in Comparative Example 2 was oxidized using an oxygen gas, and had the same oxygen concentration as the oxide film of the same thickness as the fine nickel powder obtained in Example 1. A paste was prepared in the same manner as in Example 3 and applied to measure the film density.
第 2表に、 実施例 3および比較例 3で得られたペーストの膜密度測定結果を示 す。  Table 2 shows the film density measurement results of the pastes obtained in Example 3 and Comparative Example 3.
第 2表 Table 2
Figure imgf000019_0001
第 2表によれば、 実施例 3のペーストは、 比較例 3のペーストに比して膜密度 が大きく、分散性の良好であることが判る。このため、実施例 3のペーストでは、 積層セラミックコンデンサの内部電極として使用した場合、 クラック、 デラミネ —ション等の構造欠陥の抑制効果が得られる。
Figure imgf000019_0001
According to Table 2, it is understood that the paste of Example 3 has a large film density and good dispersibility as compared with the paste of Comparative Example 3. Therefore, in the paste of Example 3, when used as an internal electrode of the multilayer ceramic capacitor, the effect of suppressing structural defects such as cracks and delamination can be obtained.
以上説明したように、 本発明の金属微粉末の製造技術によれば、 金属微粉末の 表面にオゾンガスにより酸化皮膜を形成して、酸化被膜の還元による喪失の遅延 によって金属微粉末の焼結開始温度をより高温域に移行させ、 さらには焼結時に おける金属微粉末の収縮率を減少させることに基づき、 内部電極層と誘電体層と の間に発生するデラミネーシヨンを抑制することができる。 よって、 本発明は、 電子部品等に使用される導電ペーストに好適な金属微粉末を製造することがで きる点で有望である。 As described above, according to the metal fine powder production technology of the present invention, an oxide film is formed on the surface of the metal fine powder by ozone gas, and the loss due to the reduction of the oxide film is delayed, thereby starting the sintering of the metal fine powder. By transferring the temperature to a higher temperature range and further reducing the shrinkage of the metal powder during sintering, the internal electrode layer and the dielectric layer are It is possible to suppress the delamination that occurs during the Therefore, the present invention is promising in that metal fine powders suitable for conductive pastes used for electronic parts and the like can be produced.

Claims

1. 表面に、 オゾンガスにより生成した酸化皮膜を有することを特徴とする金 属微粉末。 1. A fine metal powder characterized by having an oxide film produced by ozone gas on the surface.
2. 前記酸化皮膜の厚みが、 1〜1 Onmであることを特徴とする請求項 1に 2. The thickness of the oxide film is 1 to 1 O nm.
一卩一盲  A glance
記載の金属微粉末。 の Metal fine powder as described. of
3. 前記金属微粉末がニッケル微粉末であることを特徵とする請求項 1または 2に記載の金属微粉末。  3. The metal fine powder according to claim 1 or 2, characterized in that the metal fine powder is a nickel fine powder.
囲  Range
4. 前記金属微粉末の平均粒径が 1 m以下であることを特徴とする請求項 1 〜 3のいずれかに記載の金属微粉末。 4. The fine metal powder according to any one of claims 1 to 3, wherein the mean particle size of the fine metal powder is 1 m or less.
5. 前記金属微粉末の酸素濃度と酸化皮膜厚みの比（酸素濃度 Z酸化皮膜厚み） が 0. 3〜1. 0であることを特徴とする請求項 1〜4のいずれかに記載の金属 微粉末。 5. The metal according to any one of claims 1 to 4, wherein the ratio of the oxygen concentration to the oxide film thickness (oxygen concentration Z oxide film thickness) of the metal fine powder is from 0.3 to 1.0. Fine powder.
6. 金属微粉末を炭酸水溶液中で処理し、 次いでオゾンガス雰囲気中で酸化処 理を施し、表面に酸化皮膜を形成させることを特徴とする金属微粉末の製造方法。 6. A method of producing a metal powder, wherein the metal powder is treated in a carbonic acid aqueous solution and then oxidized in an ozone gas atmosphere to form an oxide film on the surface.
7. 前記酸化処理を 200〜250°Cの温度範囲で行うことを特徴とする請求 項 6に記載の金属微粉末の製造方法。 7. The method for producing a metal fine powder according to claim 6, wherein the oxidation treatment is performed in a temperature range of 200 to 250 ° C.
8. 前記酸化処理を 1〜20 vo 1 %のオゾン濃度範囲で行うことを特徴とす る請求項 6または 7に記載の金属微粉末の製造方法。 8. The method for producing metal fine powder according to claim 6 or 7, wherein the oxidation treatment is performed in an ozone concentration range of 1 to 20 vo 1%.
9. 前記炭酸水溶液中での処理を ρΗ 5· 5〜6. 5の範囲で行うことを特徴 とする請求項 6〜 8のいずれかに記載の金属微粉末の製造方法。 9. The method for producing a metal fine powder according to any one of claims 6 to 8, wherein the treatment in the carbonated aqueous solution is performed in the range of Η5 · 5 to 6.5.
1 0 . 前記金属微粉末がニッケルであることを特徴とする請求項 6〜9のいず れかに記載の金属微粉末の製造方法。 10. The method for producing a metal powder according to any one of claims 6 to 9, wherein the metal powder is nickel.
1 1 . 請求項 1に記載の金属微粉末を用いてなる導電ペースト。  1 1. A conductive paste using the metal fine powder according to claim 1.
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