JP2005068531A - Metal powder production method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a metal powder production method which easily enables the surface of a metal powder to be coated with a desired oxide densely in a specified composition. <P>SOLUTION: The metal powder production method is used for producing a metal powder coated with an oxide comprising constituent elements of a dielectric material on the surface of the metal powder. The method comprises bringing a soluble compound and an alcohol into contact with the metal powder for forming the oxide comprising the constituent elements of the dielectric material, reacting the metal powder by contact with oxalic acid and ammonium oxalate to coat the surface of the metal powder with an oxalate, and firing the resultant metal powder. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  TECHNICAL FIELD The present invention relates to a method for producing metal powder, and in particular, a desired oxide is densely coated on the surface of metal powder when producing metal powder having characteristics suitable for an internal electrode material of a multilayer ceramic capacitor. It is related with the manufacturing method of the metal powder characterized.

  Conventionally, metal powder has been used as a wiring material such as a paste. As an example, various metal powders are used as an internal electrode material of a multilayer ceramic capacitor. This multilayer ceramic capacitor is made by laminating ceramic dielectrics and internal electrodes alternately in layers, pressing and firing them, and conventionally, noble metal powders such as platinum and palladium are used as internal electrode materials. However, in recent years, a technique using a base metal powder such as nickel has been developed.

  However, as a metal powder that is an internal electrode material, for example, using nickel powder, printing on a ceramic base material using a nickel paste, after stacking a plurality of the printed base materials and integrating them by thermocompression bonding, When heat firing is performed in a reducing atmosphere, nickel is oxidized during firing and nickel is diffused into the ceramic phase of the substrate. In addition, a difference in thermal shrinkage between the nickel paste and the ceramic substrate may cause defects such as delamination (delamination) and cracks during firing.

  In order to cope with such a problem of nickel paste, for example, it is known to coat the surface of nickel powder particles with an element constituting a dielectric material forming a ceramic substrate as an oxide. By coating the surface of the nickel powder with oxides of the constituent elements of the dielectric material, oxidation of nickel during firing can be prevented, and the thermal contraction rate of the nickel paste can be made closer to the ceramic substrate. Because.

  More specifically, nickel powder in which a composite oxide such as barium titanate and calcium zirconate is coated on the surface of nickel powder is known. As a method for producing such nickel powder, the structure of the dielectric material is used. It has been proposed that an element is coated as a hydroxide on the surface of nickel powder once, and then the hydroxide is reduced in a reducing atmosphere to coat the surface of nickel powder with an oxide (for example, Patent Document 1). reference).

JP 2001-192702 A

  According to the manufacturing method disclosed in Patent Document 1, although the desired oxide is coated on the surface of the nickel particles, the covering state is not very sufficient. That is, the oxide coated on the surface of the nickel particles is not in a dense state. Further, in the method of reducing the hydroxide, there is a tendency that when the oxide or the composite oxide having a predetermined composition is coated, the composition tends to be shifted. Furthermore, the yield during production is lowered due to the difficulty in obtaining nickel powder having a predetermined particle size due to the sintering of particles during reduction, and the ease of separation of hydroxide or oxide obtained by reduction. There is also a trend.

  The present invention has been made under the circumstances as described above, and provides a method for producing a metal powder that can easily coat a surface of a metal powder with a desired oxide densely and with a predetermined composition. In particular, the present invention provides a technique that makes it possible to produce metal powder having characteristics suitable for an internal electrode material of a multilayer ceramic capacitor.

  In order to achieve the above-mentioned problems, the present inventors have studied various methods from the viewpoint of whether a finer oxide can be coated on the surface of metal powder particles, and as a result, have come up with the present invention.

  The present invention relates to a method for producing a metal powder in which a metal powder surface is coated with an oxide composed of a constituent element of a dielectric material, and a soluble compound and an alcohol for forming the oxide composed of the constituent element of the dielectric material The metal powder was contacted with the powder and reacted with oxalic acid and ammonium oxalate to react with the oxalic oxide on the powder surface, and then the metal powder was baked. According to the method for producing a metal powder of the present invention, it is possible to densely coat an oxide on the particle surface, and it is possible to easily coat an oxide or composite oxide having a predetermined composition.

According to the method for producing metal powder according to the present invention, the constituent elements of the dielectric material are once coated on the surface of the metal powder in the form of single or composite oxide. Since this soot oxide is excellent in adhesion to the surface of the metal particles, it is presumed that the surface of the metal particles can be coated in a dense state as compared with the case of coating with a conventional hydroxide. That is, the surface of the metal powder particles is densely coated with the oxide by changing the soot oxide coated in a dense state with high adhesion to an oxide. For example, when zirconium (Zr) and calcium (Ca) are used as the constituent elements of the dielectric material, zirconium and calcium are once coated on the surface of the metal particles in the form of soot oxide. When the metal powder coated with these soot oxides is fired, these soot oxides become CaZrO ₃ composite oxides, and the surface of the metal powder particles is densely coated.

  In addition, according to the method for producing metal powder according to the present invention, the constituent elements of the dielectric material are firmly adhered to the surface of the metal powder particles as soot oxide, and the soot oxide is coated with the oxide as an oxide. There is no significant shift in the composition of the oxide. Furthermore, since the resulting oxide coating is dense, the metal powder is excellent in dispersibility and is less likely to agglomerate.

  In the method for producing a metal powder according to the present invention, as a method for bringing the metal powder into contact with a soluble compound for forming an oxide composed of a constituent element of a dielectric material and an alcohol, for example, the metal powder is poured into water. This can be realized by preparing a metal powder slurry, mixing a soluble compound for forming an oxide composed of a constituent element of a dielectric material, and alcohol into the metal powder slurry and stirring. And by adding an oxalic acid solution and an ammonium oxalate solution to the metal powder slurry thus obtained, the surface of the metal powder particles can be coated with a predetermined oxalate. Examples of the alcohol in the present invention include methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 2-methyl-1-propanol, 2-methyl-2-propanol, allyl alcohol, ethanolamine and the like. Although it can be used, methanol is preferred for practical use.

  And in the manufacturing method of the metal powder which concerns on this invention, it is preferable to give a mechanical effect | action to the baked metal powder. The mechanical action in the present invention refers to, for example, colliding powder particles by stirring and mixing metal powder. That is, the oxide is fixed to the surface of the metal particle by the collision energy when the metal particle coated with the oxide and the oxide particle collide with each other. More specifically, the mechanical action is applied to the metal powder and the oxide by mixing and stirring the dried metal powder using a wind circulator using centrifugal force or using a so-called ball mill. Can be given. By applying such a mechanical action, if the oxide is fixed, the aggregation of the metal powder can be prevented, and the uniform maintenance of the particle diameter of the metal powder can be easily realized.

  The firing treatment in the method for producing metal powder of the present invention is preferably heated to 300 to 600 ° C. in a non-oxidizing atmosphere. Examples of the non-oxidizing atmosphere include a nitrogen gas atmosphere and an argon gas atmosphere. When the firing temperature is less than 300 ° C., the soot oxide remains on the surface without being decomposed, and when it exceeds 600 ° C., the progress of the sintering becomes remarkable and the crushing becomes difficult.

  Furthermore, the constituent element of the dielectric material in the method for producing metal powder of the present invention is preferably selected from calcium, titanium, zirconium, barium, strontium, and yttrium. These elements constitute a ceramic dielectric, and by covering the surface of the metal powder as an oxide, it is possible to effectively realize prevention of oxidation of metal powder, delamination during firing, and generation of cracks. Because.

  In the present invention, the oxide coated on the surface of the metal particles may be a single oxide of a selected element, or a plurality may be selected to form a composite oxide. Specifically, there are calcium oxide, titanium oxide, zirconium oxide, barium oxide, strontium oxide, yttrium oxide as a single oxide, and barium titanate, calcium titanate, strontium titanate, zirconate as complex oxides. Examples thereof include perovskite complex oxides such as calcium.

  The above-described method for producing metal powder according to the present invention is particularly effective for nickel powder that is a paste material for internal electrodes, but other metal powders, for example, metal powders such as copper, silver, and palladium, nickel -It is also suitable for various alloy powders such as phosphorus alloy, nickel-cobalt alloy, silver-palladium alloy. When the present invention is applied to these metal powders, the production conditions may be appropriately determined in consideration of the type of each metal powder and the required powder characteristics.

  As described above, according to the metal powder manufacturing method of the present invention, the surface of the metal powder particles can be coated with a desired oxide densely and with a predetermined composition. In particular, when applied to metal powder such as nickel powder, a metal that can reliably prevent delamination and cracks that are likely to occur during firing in the production of multilayer ceramic capacitors, and diffusion of the metal powder component to the ceramic phase due to oxidation of the metal powder component Powder can be produced.

  Hereinafter, preferred embodiments of the present invention will be described based on examples and comparative examples.

  In Example 1, Examples 1-1 and 1-2 taking nickel powder as an example will be described. In Examples 1-1 and 1-2 and Comparative Example 1 described here, nickel powder obtained by hydrazine reduction of a nickel hydroxide slurry was used as a raw material.

Example 1-1 : First, 100 g of nickel powder as a raw material (primary average particle diameter of 0.29 μm by SEM observation) was added to 0.6 L of pure water and stirred to prepare a nickel powder slurry. A solution prepared by dissolving 1.86 g of calcium chloride and 5.4 g of zirconium chloride in 0.6 L of water and 1 L of methanol were added thereto and stirred.

A first solution in which 4.69 g of oxalic acid was dissolved in 0.2 L of pure water and a second solution in which 5.28 g of ammonium oxalate was dissolved in 0.2 L of pure water were prepared. And this 1st and 2nd solution was simultaneously added over about 1 hour to the nickel slurry produced as mentioned above. After completion of the addition, the liquid component was removed by filtration, followed by drying at 70 ° C. in the atmosphere. The powder particle surface of the nickel powder thus obtained was covered with CaC ₂ O ₄ and Zr (C ₂ O ₄ ) ₂ .

After drying, the nickel powder was baked for 20 minutes at 330 ° C. in a nitrogen gas atmosphere. And the nickel powder which finished the baking process was given a mechanical effect | action using the grinder (hybridizer), and the coating on the surface of a powder particle was fixed and stabilized. There was thus obtained nickel powder state composite oxide of calcium zirconate (CaZrO ₃₎ was coated on the granular surface.

Example 1-2 : As in Example 1-1, first, 100 g of nickel powder as a raw material (primary average particle diameter of 0.29 μm by SEM observation) was charged into 0.6 L of pure water and stirred. A nickel powder slurry was prepared. A solution obtained by dissolving 3.12 g of barium chloride and 4.56 g of potassium titanium oxalate in 0.6 L of water and 1 L of methanol were added thereto and stirred.

A first solution in which 4.69 g of oxalic acid was dissolved in 0.2 L of pure water and a second solution in which 5.28 g of ammonium oxalate was dissolved in 0.2 L of pure water were prepared. And this 1st and 2nd solution was simultaneously added over about 1 hour to the nickel slurry produced as mentioned above. After completion of the addition, the liquid component was removed by filtration, followed by drying at 70 ° C. in the atmosphere. The powder particle surface of the nickel powder thus obtained was covered with BaC ₂ O ₄ and Ti (C ₂ O ₄ ) ₂ .

After drying, this nickel powder was baked for 20 minutes at 300 ° C. in a nitrogen gas atmosphere. And the nickel powder which finished the baking process was given a mechanical effect | action using the grinder (hybridizer), and the coating on the surface of a powder particle was fixed and stabilized. In this way, nickel powder in a state in which the powder oxide surface was coated with a composite oxide of barium titanate (BaTiO ₃ ) having a perovskite structure was obtained.

Comparative Example 1 : For comparison, nickel powder was manufactured by a conventional manufacturing method in which coating is performed by reducing hydroxide to oxide. In the same manner as in Example 1-1, 100 g of nickel powder as a raw material (primary average particle diameter of 0.29 μm by SEM observation) was first added to 2 L of pure water and stirred to prepare a nickel powder slurry. Then, a first solution in which 6.0 g of zirconium chloride is dissolved in 0.2 L of pure water and a second solution in which 1.86 g of calcium chloride is dissolved in 0.2 L of pure water are prepared. Was simultaneously added to the nickel powder slurry over about one hour. Further, 0.1 L of a sodium hydroxide solution having a sodium hydroxide concentration of 45 g / L was added, and stirring was performed so that zirconium hydroxide and calcium hydroxide were coated on the nickel powder particle surface in a composite manner. Thereafter, the filtered nickel powder was baked for 20 minutes at 300 ° C. in a nitrogen gas atmosphere. In this way, nickel powder in a state in which the complex oxide of calcium zirconate (CaZrO ₃ ) was coated on the particle surface was obtained.

The nickel powders of Examples 1-1 and 1-2 and Comparative Example 1 obtained as described above were measured for weight cumulative particle size D ₅₀ and specific surface area by laser diffraction scattering type particle size distribution measurement. The results are shown in Table 1.

Although _{D 50} of Examples 1-1 and 1-2 in comparison with the _{D 50} of the untreated nickel powder has not changed too large, in the specific surface area of Examples 1-1 and 1-2 Untreated It was found that the value was nearly four times larger than that of nickel powder. Further, the nickel powder of Comparative Example 1 is considered to be in a state where a part of nickel on the nickel powder particle surface is exposed because the nickel powder particle surface is not sufficiently covered with the oxide particles, and its specific surface area. Is estimated to be small.

  And the pellet was formed with each nickel powder of the said Example and comparative example, and the thermal contraction rate was measured by heating from room temperature to 1200 degreeC in air | atmosphere atmosphere. Moreover, the TG curve was measured about each nickel powder, and the oxidation start temperature of each nickel powder was also specified. The results are shown in FIGS.

FIG. 1 shows the result of measuring the change in the thermal expansion coefficient of each nickel powder. This measurement was performed on Examples 1-1 and 1-2 and Comparative Example 1, and untreated nickel powder (raw material: described as “untreated powder” in FIG. 1) for reference. As a measurement sample, 0.5 g of each nickel powder was sampled, a pressure of 98 MPa was applied, and pellets having a diameter of 5 mm and a height of about 5 mm were used. Then, using a thermomechanical analysis (TMA) apparatus (TMA / SS6000 manufactured by Seiko Denshi Kogyo Co., Ltd.), the pellets were increased from room temperature to 10 ° C./min in a reducing atmosphere (1% H ₂ -99% N ₂ ). The shrinkage is measured continuously by heating to 1200 ° C. at a temperature rate.

  First, as shown in FIGS. 1A to 1C, it can be seen that untreated nickel powder starts to shrink around 400 ° C. and continuously shrinks to around 600 ° C.

  In addition, it was found that the nickel powder of Example 1-1 (FIG. 1A) hardly contracted even near 500 ° C. and contracted from around 800 ° C. The shrinkage rate at 500 ° C. was −0.95% in Example 1-1 and −8.79% for the untreated nickel powder, so it was confirmed that there was a large difference in shrinkage rate. Then, it was found that the nickel powder of Example 1-2 (FIG. 1B) did not shrink much even near 600 ° C., and greatly shrunk from around 750 ° C. The shrinkage rate at 500 ° C. was −0.998% in Example 2, and the untreated nickel powder was −8.79%, so it was confirmed that there was a large difference in shrinkage rate. Furthermore, it was found that the nickel powder of Comparative Example 1 (FIG. 1C) began to shrink gradually from around 400 ° C. and contracted at a substantially constant rate up to 1200 ° C. The shrinkage rate at 500 ° C. is −1.96% in Comparative Example 1 and −8.79% in untreated nickel powder, and Comparative Example 1 is more than Examples 1-1 and 1-2. It was confirmed that the shrinkage rate was obviously large. From the above results, compared with the nickel powder of Comparative Example 1 according to the conventional manufacturing method, the nickel powders of Examples 1-1 and 1-2 have heat resistance shrinkage around 500 ° C. to 800 ° C. Turned out to be expensive.

  Next, the measurement result of the TG curve shown in FIG. 2 will be described. This TG curve measurement was also performed on the untreated nickel powder (raw material: described as “untreated powder” in FIG. 2) as examples and comparative examples and for reference. This measurement was performed using a differential thermogravimetric simultaneous measurement device (TG / DTA / SS6300 manufactured by Seiko Denshi Kogyo Co., Ltd.). 15 mg of each nickel powder was sampled and placed in a φ5 mm alumina cell. This cell was placed in the apparatus and heated from room temperature to 1000 ° C. at a rate of 5 ° C./min while circulating 150 mL / min of air. Thus, the increment of oxidized weight was measured continuously.

  As shown in FIGS. 2 (A ′) and (B ′), when the untreated nickel powder is compared with Examples 1-1 and 1-2, the untreated nickel powder changes in weight from a lower temperature range. You can see that Further, the nickel powder of Comparative Example 1 in FIG.

  As can be seen from FIG. 2 (A '), it was confirmed that Example 1-1 began to change from a temperature range higher than that of the untreated nickel powder. The degree of oxidation at 350 ° C. was found to be 1.2% in Example 1-1 and 2.76% for the untreated nickel powder. That is, it became clear that the nickel powder of Example 1-1 was less likely to be oxidized. Further, as shown in FIG. 2 (B '), it was confirmed that Example 1-2 also began to change in weight from a temperature range higher than that of the untreated nickel powder. The degree of oxidation at 350 ° C. was 1.07% in Example 2 and 2.76% in the untreated nickel powder, which revealed that there was a large difference in the degree of oxidation. Therefore, it was clearly found that the nickel powder of Example 1-2 was less likely to be oxidized. Furthermore, in Comparative Example 1 in FIG. 2 (C ′), it was confirmed that the weight started to change from a temperature range higher than that of the untreated nickel powder. The degree of oxidation at 350 ° C. was 2.00% in Comparative Example 1. From this, it was found that the nickel powders of Examples 1-1 and 1-2 were superior in oxidation resistance as compared with Comparative Example 1.

  Then, in this Example 2, the case regarding copper powder is demonstrated. In Example 2 described here, copper powder obtained by hydrazine reduction of copper sulfate was used as a raw material.

Example 2 : As in Example 1-1, first, 100 g of raw material copper powder (primary average particle diameter of 0.50 μm by SEM observation) was added to 0.6 L of pure water, followed by stirring. A slurry was prepared. A solution obtained by dissolving 3.12 g of barium chloride and 4.56 g of potassium titanium oxalate in 0.6 L of water and 1 L of methanol were added thereto and stirred.

A first solution in which 4.69 g of oxalic acid was dissolved in 0.2 L of pure water and a second solution in which 5.28 g of ammonium oxalate was dissolved in 0.2 L of pure water were prepared. And this 1st and 2nd solution was simultaneously added over about 1 hour to the copper powder slurry produced as mentioned above. After completion of the addition, the liquid component was removed by filtration, followed by drying at 70 ° C. in the atmosphere. The powder particle surface of the copper powder thus obtained was covered with BaC ₂ O ₄ and Ti (C ₂ O ₄ ) ₂ .

After drying, this copper powder was baked for 20 minutes at 300 ° C. in a nitrogen gas atmosphere. And the copper powder which finished the baking process gave the mechanical effect | action using the grinding | pulverization apparatus (hybridizer), and adhered and stabilized the coating on the surface of a powder grain. In this way, copper powder was obtained in a state in which the powder oxide surface was coated with a composite oxide of barium titanate (BaTiO ₃ ) having a perovskite structure.

About Example 2, the untreated copper powder obtained as described above, the weight cumulative particle diameter D ₅₀ and the specific surface area were measured by laser diffraction scattering particle size distribution measurement. The results are shown in Table 2.

In the specific surface area of to Example 2 compared to the D ₅₀ of the untreated copper powder was found to have a large value 6 times more than the untreated copper powder.

  And the pellet was formed with each copper powder of the said Example and comparative example, and the thermal contraction rate was measured by heating from room temperature to 1000 degreeC in air | atmosphere atmosphere. Moreover, the TG curve was measured about each copper powder, and the oxidation start temperature of each copper powder was also specified. The result is shown in FIG.

  FIG. 3D shows the result of measuring the change in the thermal expansion coefficient of each copper powder. This measurement was performed on Example 2, untreated copper powder. The measurement sample and measurement conditions are the same as in the case of the nickel powder of Example 1, and are omitted (however, the measurement temperature is room temperature to 1000 ° C.).

  First, as shown in FIG. 3D, the untreated copper powder started to shrink from around 600 ° C. On the other hand, it was found that the copper powder of Example 2 hardly contracted even at around 600 ° C. and began to shrink from around 800 ° C. The shrinkage rate at 750 ° C. was 0.11% in Example 2 and 7.98% of the untreated copper powder, so it was confirmed that there was a large difference in shrinkage rate. From this result, it was confirmed that the copper powder of the present Example 2 has high heat shrinkage resistance on the low temperature side of about 600 ° C.

  Next, the measurement result of the TG curve shown in FIG. This TG curve measurement was also performed on Example 2, untreated copper powder. This measurement is omitted because it is the same as in Example 1 (however, the measurement temperature is room temperature to 800 ° C.).

  As shown in FIG. 3 (D ′), when the untreated copper powder was compared with Example 2, it was found that the untreated copper powder had a change in weight from a lower temperature range. Moreover, it was confirmed that Example 2 starts changing from a temperature range higher than that of untreated copper powder. The degree of oxidation at 350 ° C. was 2.25% in Example 2 and 5.45% for the untreated copper powder, so it was found that there was a large difference in the degree of oxidation. Therefore, it was clearly clarified that the copper powder of Example 2 was less likely to be oxidized.

The thermal expansion coefficient change measurement graph of each nickel powder. TG measurement graph of each nickel powder. The thermal expansion coefficient change measurement graph and TG measurement graph of copper powder.

Claims (5)

In the method for producing metal powder in which the metal powder surface is coated with an oxide composed of a constituent element of a dielectric material,
Contacting the metal powder with a soluble compound and alcohol for forming an oxide composed of the constituent elements of the dielectric material,
After coating the succinate on the surface of the granules by reacting the metal powder with oxalic acid and ammonium oxalate,
A method for producing a metal powder, comprising subjecting the metal powder to a firing treatment. The method for producing metal powder according to claim 1, wherein the metal powder after firing is subjected to mechanical action. The method for producing metal powder according to claim 1 or 2, wherein the baking treatment is performed by heating to 300 to 600 ° C in a non-oxidizing atmosphere. The method for producing a metal powder according to any one of claims 1 to 3, wherein the constituent element of the dielectric material is selected from calcium, titanium, zirconium, barium, strontium, and yttrium. The method for producing metal powder according to any one of claims 1 to 4, wherein the metal powder is formed from any one of nickel or nickel alloy, silver or silver alloy, copper or copper alloy, palladium or palladium alloy. .

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