JP2011168849A - Nickel powder and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide nickel powder with fine and uniform grain sizes which can be suitably used as the one for forming the internal electrode of a laminated ceramic capacitor, and a method for producing the same. <P>SOLUTION: The method for producing nickel powder includes: a step (A) of roasting nickel hydroxide in which the content of the group 2 elements in the Periodic Table is 0.002-1 mass% so as to be nickel oxide powder; and a step (B) of performing heating to a reducing temperature while holding the obtained nickel oxide powder (the object to be reduced) to ≤3 mm by a conversion thickness, and feeding a hydrogen-containing gas at a flow rate of ≥0.01 m/s to reduce nickel oxide powder. The nickel powder is obtained by the method for producing nickel powder, and has the average grain size of 0.2-0.4 μm. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to nickel powder and a method for producing the same, and more particularly to a nickel powder having a fine and uniform particle size that can be suitably used for forming an internal electrode of a multilayer ceramic capacitor and a method for producing the same.

  A multilayer ceramic capacitor (hereinafter also referred to as “MLCC”) is a small and high-capacity capacitor having a structure in which dielectric layers and internal electrodes are alternately stacked. Ceramic materials such as barium titanate are used for the dielectric layer, while noble metal materials have been used for the internal electrodes. System materials are the mainstream.

An MLCC using nickel powder for forming an internal electrode is generally manufactured by the following method.
That is, nickel powder and an organic solvent are kneaded together with various additives to produce a nickel paste, which is printed on a dielectric green sheet and dried. Next, a desired number of layers are laminated, thermocompression bonded, cut into a chip shape, and after debinding at a temperature of about 300 ° C., the internal electrode and the dielectric green sheet are baked at a temperature of several thousand hundred degrees. As a result, an external electrode made of nickel or the like is formed.

  The binder removal treatment is performed by heat treatment in an oxidizing atmosphere and burning the binder. Usually, a polyvinyl alcohol compound is used for the binder of the dielectric green sheet, and an ethyl cellulose compound is used for the binder of the nickel paste for forming the internal electrode. The atmosphere and temperature in the binder removal step are adjusted by controlling the combustion timing and the amount of generated gas.

  In this debinding step, if unintended gas is generated from the nickel powder, or if the nickel powder undergoes a significant volume change due to oxidation, there is a risk that cracking or delamination occurs in the MLCC. For this reason, the purity of the nickel powder is strictly controlled in the manufacturing process and the surface state is adjusted so that no significant volume change due to gas generation or oxidation occurs in this process. In addition, since the dielectric is a ceramic and the internal electrode is a metal, the amount of shrinkage during sintering is generally larger for the internal electrode and the melting point is lower for the metal. However, the internal electrode is lower. However, if there is a large difference between the amount of shrinkage during sintering and the sintering start temperature, holes or breaks occur in the sintered electrode and the electrode does not function. Accordingly, ceramic powder or the like is mixed in the nickel paste, and a small amount of other elements are added to the nickel powder itself to delay the sintering phenomenon.

  On the other hand, in this industry, with the aim of further reducing the size and increasing the capacity of MLCCs, the internal electrode and the thickness of the dielectric are being reduced and the number of layers is being increased. In a thin internal electrode, if the particle size of the nickel powder is large, the number of particles present in the electrode thickness direction is small, and the gaps between the particles are also large. Be encouraged. For this reason, the nickel powder for internal electrodes is also required to have a finer particle size. In addition, the thinned MLCC is required to contain no coarse particles because a short circuit occurs between electrodes when coarse nickel powder is mixed. However, if particles that are much finer than the average particle size are present, oxidation in the binder removal step and lowering of the sintering start temperature in the sintering step occur, so particles with extremely fine particle sizes may not be included. is important.

As described above, the most important for nickel powder for internal electrodes is not only that gas is not easily generated in the debinding process, but also that it is close to the sintering shrinkage characteristics of the dielectric, and that it has a fine and uniform particle size. It is considered as a required characteristic.
Under such circumstances, various nickel powders that are fine and free of coarse particles and methods for producing the same have been proposed.
First, nickel powder having an average particle size of 0.2 to 0.6 μm by vapor phase hydrogen reduction method of nickel chloride vapor, and the presence rate of coarse particles having a particle size of 2.5 times or more of the average particle size is the number. A nickel powder having a standard value of 0.1% or less has been proposed (for example, Patent Document 1).
Further, as a method for producing nickel powder having an average particle size of 0.1 to 1.0 μm, the nickel chloride vapor gas is used so that the content of nickel powder having a particle size of 2 μm or more is 700/1 million or less on a number basis. A method of classifying nickel powder obtained by a phase hydrogen reduction method or the like with a liquid cyclone or the like has been proposed (for example, Patent Document 2).

The above proposals are all based on the vapor phase hydrogen reduction method of nickel chloride vapor, but besides this, a method for producing nickel powder by a wet method in which the raw nickel salt is reduced in an aqueous solution is also proposed (for example, Patent Document 3). Here, the number of particles having a particle size of 1.5 times or more of the average particle size measured by laser diffraction scattering type particle size distribution measurement is 20% or less of the total particle number, and the particle size of 0.5 times or less of the average particle size. There is described a nickel powder in which the number of particles having a number is 5% or less of the total number of particles and the average primary particle diameter by SEM observation is 0.1 to 2 μm. This nickel powder is obtained by pulverizing raw nickel powder containing aggregates obtained by the wet method.
However, the nickel powder obtained by the gas phase hydrogen reduction method has good crystallinity and excellent characteristics, but the productivity is low and the cost is high. Moreover, classifying nickel powder obtained by a gas phase hydrogen reduction method or the like results in a worse yield and higher cost.
Moreover, even if the agglomerates obtained by the above wet method are pulverized, if the primary particle size before pulverization is not uniform, it is necessary to classify, and an increase in cost due to deterioration in yield is inevitable. When manufactured by a wet method, nickel powder having a relatively uniform particle diameter can be obtained, but the productivity is low and the cost is high.

Therefore, in order to produce nickel powder at a lower cost, the present applicant continuously added the nickel-containing solution to the slurry in the reaction vessel, while adding the alkaline solution to generate nickel hydroxide, The slurry is filtered, washed with water and dried to obtain nickel hydroxide, which is proposed to be heated and reduced at a reduction temperature of 400 to 550 ° C. using hydrogen as a reducing agent (Patent Document 4). Thereby, mass production of nickel powder became possible by heat reduction of nickel hydroxide, and the cost could be reduced, but there was a problem that it was difficult to obtain nickel powder having a fine and uniform particle diameter.
As described above, a method capable of mass-producing nickel powder having a fine and uniform particle size at a low cost has not yet been developed.

JP 11-189801 A JP 2001-73007 A JP 2001-247903 A JP 2003-213310 A

  An object of the present invention is to provide a nickel powder having a fine and uniform particle diameter and a method for producing the same in large quantities at a low cost in view of the problems of the prior art.

  The inventors of the present invention have made extensive studies to achieve the above object, roasting a specific nickel hydroxide powder to obtain a nickel oxide powder, and then reducing the reduced product made of nickel oxide to a thickness of 3 mm. While maintaining the following, a reducing gas is supplied to the surface at a specific flow rate and reduced by heating to obtain a fine and uniform nickel powder, which can be preferably used as a low-cost nickel powder for MLCC internal electrodes. As a result, the present invention has been completed.

  That is, according to the first invention of the present invention, the step of roasting nickel hydroxide powder having a content of Group 2 elements of the periodic table of 0.002 to 1% by mass to obtain nickel oxide powder (A And the obtained nickel oxide powder (reduced substance) is heated to the reduction temperature while maintaining the converted thickness at 3 mm or less, and the hydrogen-containing gas is supplied at a flow rate of 0.01 m / s or more. There is provided a method for producing nickel powder comprising the step (B) of reducing the powder.

According to a second invention of the present invention, there is provided a method for producing nickel powder characterized in that, in the first invention, the Group 2 element of the periodic table is magnesium in the step (A). .
According to the third invention of the present invention, in the first or second invention, in step (B), the hydrogen-containing gas is a mixed gas of hydrogen and an inert gas, and the hydrogen content is 10 to 10. A method for producing nickel powder characterized by being 50% by volume is provided.
According to the fourth invention of the present invention, in any one of the first to third inventions, in the step (B), the reduction temperature is 300 to 500 ° C. Is provided.

On the other hand, according to the fifth invention of the present invention, it is obtained by the nickel powder manufacturing method according to any one of the first to fourth inventions, and the average particle size is 0.2 to 0.4 μm. Nickel powder is provided.
According to a sixth aspect of the present invention, there is provided the nickel powder according to the fifth aspect, wherein the particle size distribution (D90) measured by observation with a scanning electron microscope is 1 μm or less.

  According to the present invention, specific nickel hydroxide is roasted to obtain nickel oxide, and the obtained nickel oxide is heated and reduced under specific conditions. And it can be manufactured easily. Further, the obtained nickel powder is particularly suitable for forming MLCC internal electrodes whose size and capacity are increasing, and has an extremely large industrial value.

  Hereinafter, the nickel powder of the present invention and the manufacturing method thereof will be described in detail.

1. Nickel powder manufacturing method The nickel powder manufacturing method of the present invention is a step of roasting nickel hydroxide powder having a content of Group 2 elements of the periodic table of 0.002 to 1% by mass to obtain nickel oxide powder. While maintaining (A) and the obtained nickel oxide powder (reduced substance) at a converted thickness of 3 mm or less, heating to a reduction temperature, supplying a hydrogen-containing gas at a flow rate of 0.01 m / s or more, It includes a step (B) of reducing nickel oxide powder. In the method for producing nickel powder of the present invention, the reduction conditions for nickel oxide are important.

  In the production method of the present invention, first, nickel hydroxide powder containing 0.002 to 1% by mass of Group 2 element (alkaline earth metal) of the periodic table must be used as the raw material powder. By adding Group 2 elements of the periodic table to the nickel hydroxide powder, to suppress the fusion of particles during the generation of nickel particles during reduction, to refine and spheroidize, and to further improve the smoothness of the particle surface It is. Although it does not restrict | limit especially as an alkaline-earth metal, It is preferable to use magnesium with a big effect of refinement | miniaturization and spheroidization.

  Moreover, 0.005-0.5 mass% is preferable and, as for content of a periodic table group 2 element, it is more preferable that it is 0.01-0.1 mass%. When the Group 2 element of the periodic table is less than 0.002% by mass, the effect of refinement and smoothness improvement is not seen, and when it exceeds 1% by mass, the nickel quality of the resulting nickel powder is reduced, and the MLCC internal electrode The electrical resistance value of the capacitor becomes too large, leading to deterioration of the loss factor of the capacitor.

  Next, in the manufacturing method of the present invention, nickel hydroxide powder is oxidized and roasted in a non-reducing atmosphere to form nickel oxide powder, and this nickel oxide powder is subjected to reduction treatment under specific conditions. In general, in a reduction treatment under a reducing gas atmosphere, nickel oxide powder is reduced to produce nickel powder, but at this time, nickel fine powder is produced by metallization leaving the form of nickel oxide powder. Absent. That is, nickel oxide powder is reduced from the surface and becomes nickel powder with generation of fine nickel particles, and thus the nickel powder obtained in this way has high activity on the surface of the generated nickel fine powder. Therefore, compared to the case of other metal powders that are metallized while leaving the shape, the particles are more likely to aggregate or sinter. Furthermore, if hydrogen is used as the reducing gas in order to prevent contamination of nickel, which is easily bonded to carbon, a large amount of water vapor will be present in the atmosphere during the reduction, which will only hinder contact between the reducing gas and nickel oxide powder. Alternatively, the action of water vapor that agglomerates or sinters the metal particles is greater.

  Therefore, it is important to sufficiently supply a reducing gas, particularly hydrogen gas, during the reduction, and to discharge the generated water vapor out of the system. In order to improve the gas flow and sufficiently supply hydrogen gas and discharge water vapor, a method of reducing nickel oxide powder while flowing is effective, but in the case of reducing nickel oxide powder, nickel oxide powder is effective. Since the difference in fluidity between the powder and the nickel fine powder obtained by reduction is large, the nickel powder tends to be unevenly distributed, and is likely to be agglomerated or sintered nickel fine powder. For this reason, means for improving the supply of hydrogen gas and the discharge of water vapor are employed in a stationary reduction method.

  In the static reduction method described above, diffusion using a concentration gradient as a driving force is dominant in the supply of hydrogen into the stationary object and the removal of water vapor generated inside. Therefore, performing sufficient hydrogen supply and water vapor removal increases the diffusion amount of hydrogen and water vapor. Since the diffusion amount is determined by the diffusion rate and the distance, the diffusion amount can also be increased by controlling the temperature that affects the diffusion rate. However, since the adjustment range of the reduction temperature is determined by the finally required nickel particle size, reduction device, and reduction time, it is difficult to control the diffusion rate by the temperature because the restriction becomes large.

On the other hand, since the diffusion distance is governed by the shape of the stationary object and is not subject to the above restrictions, it is effective to increase the diffusion amount by the diffusion distance. In particular, the center part of the stationary object has the maximum diffusion distance and the minimum hydrogen supply and water vapor removal, so it is effective to shorten the distance. Therefore, the maximum diffusion distance may be controlled in order to suppress the aggregation or sintering of the particles with sufficient supply of hydrogen and removal of water vapor during reduction of nickel oxide.
This maximum diffusion distance is, for example, the thickness of the loaded nickel oxide powder when nickel oxide powder is loaded in a heat-resistant container and reduced gas is supplied only from the opening surface side. Moreover, when the material which can distribute | circulate gas is used for the bottom part of a heat-resistant container, the maximum diffusion distance becomes a half of the case where it is only from the said opening surface side. As can be seen from this, the maximum diffusion distance is not the layer thickness of the loaded nickel oxide powder, but the value obtained by dividing the volume of the loaded nickel oxide powder, that is, the reduction target made of nickel oxide powder, by the area in contact with the reducing gas. Will be dominated by. In the present invention, this concept is adopted as the converted thickness, and the reduced thickness of the reduction target is controlled to a specific value or less, thereby obtaining nickel powder having a fine and uniform particle diameter in the reduction treatment of nickel oxide. To do.

That is, in this invention, it is necessary to make the conversion thickness of the to-be-reduced object which consists of nickel oxide at the time of reduction | restoration into 3 mm or less. Here, the converted thickness means a value obtained by dividing the volume of the object to be reduced installed in the reducing apparatus by the area in contact with the reducing gas.
By setting the reduced thickness of the material to be reduced used for reduction to 3 mm or less, nickel powder having a fine and uniform particle diameter can be obtained by suppressing aggregation or sintering of particles in the whole material to be reduced. When the converted thickness exceeds 3 mm, the distance from the surface of the substance to be reduced becomes the maximum, and the resulting particles are agglomerated or sintered to produce coarse particles. In order to obtain the powder, a process such as classification is required in a subsequent process. The reduced thickness of the material to be reduced is preferably 2.5 mm or less, more preferably 2 mm or less.

In this way, the diffusion amount can be controlled by the converted thickness, but it is difficult to obtain a nickel powder having a fine and uniform particle diameter only by controlling the converted thickness. Therefore, in the present invention, in addition to controlling the converted thickness, it is necessary that the flow rate of the reducing gas be 0.01 m / s or more on the surface of the material to be reduced.
Water vapor discharged from the inside of the reductant by diffusion exists on the reductant surface during the reduction. When the amount of water vapor increases, not only can the concentration gradient serving as the driving force for water vapor diffusion be sufficient, but also the supply of hydrogen to the surface of the substance to be reduced is hindered. Therefore, in the present invention, the flow rate of the reducing gas is set to 0.01 m / s or more, the water vapor diffused from the inside of the material to be reduced is removed, the concentration gradient is sufficient, and sufficient hydrogen is supplied. To be. Thereby, the supply of hydrogen and the removal of water vapor are ensured, and the nickel powder having a fine and uniform particle diameter can be obtained by suppressing the aggregation or sintering of the particles in the entire substance to be reduced.
When the flow rate of the reducing gas is less than 0.01 m / s, the removal of water vapor on the surface of the material to be reduced is not sufficient, and nickel powder having a fine and uniform particle diameter cannot be obtained. On the other hand, the upper limit of the flow velocity is not particularly limited, but for example, when nickel oxide powder is put in the mortar, depending on the shape of the mortar and the wind speed direction, if the flow velocity is too large, the powder may be scattered. Therefore, it is not preferable to exceed 1 m / s. The flow rate of the reducing gas is preferably 0.02 m / s or more, more preferably 0.03 m / s or more on the surface of the substance to be reduced.

  The flow rate may be adjusted by mixing an inert gas such as nitrogen with the hydrogen to be added, or may be adjusted by appropriately designing the shape in the reducing device, the shape of the substance to be reduced, and the like. When the hydrogen-containing gas is a mixed gas of hydrogen and an inert gas, the type of the inert gas is not particularly limited, but nitrogen gas is preferable in consideration of cost. The hydrogen content is preferably 10 to 50% by volume. When the hydrogen content is less than 10% by volume, the reduction reaction rate becomes slow, and aggregation or connection of nickel fine powder occurs. On the other hand, if the hydrogen content exceeds 50% by volume, the reaction proceeds rapidly and the amount of water vapor generated increases, which again causes aggregation or connection of nickel fine powder. The hydrogen content is more preferably 30 to 50% by volume.

Hereafter, the manufacturing method of this invention is demonstrated in order of a process.
(1) Step (A) Preparation of Nickel Hydroxide Powder In the present invention, nickel hydroxide powder containing 0.002 to 1% by mass of Group 2 element of the periodic table is used. Nickel hydroxide powder can be obtained by an ordinary known method. For example, nickel hydroxide powder can be obtained as a uniform precipitate by neutralizing and precipitating an aqueous solution of a water-soluble nickel salt such as nickel chloride or nickel sulfate by controlling the pH and keeping the precipitation rate constant.
The aqueous solution of the water-soluble nickel salt is not particularly limited, and an aqueous solution containing a water-soluble nickel salt such as nickel chloride, nickel sulfate, nickel nitrate, or nickel organic acid salt is used. It is preferable to use an aqueous nickel chloride salt solution from the viewpoint of environmental impact such as ease of wastewater treatment and cost.

On the other hand, the periodic table Group 2 element contained in the nickel hydroxide powder may be mixed in a nickel salt aqueous solution as a water-soluble substance such as a water-soluble salt and coprecipitated when nickel hydroxide is produced.
Although it does not specifically limit as said pH, 7-9.5 are preferable and 8-9 are more preferable. That is, if the pH is less than 7, the nickel salt may not be sufficiently neutralized. On the other hand, if the pH exceeds 9.5, fine colloidal nickel hydroxide particles are formed, and solid nickel particles are formed. Liquid separation becomes very difficult, and nickel oxide powder may be agglomerated or sintered by oxidation roasting in the next step, and the dispersibility of the finally obtained nickel fine powder may not be sufficient.
The method for neutralizing and precipitating is not particularly limited, and it is possible to produce a neutralized solution while adding a nickel salt aqueous solution and an alkaline aqueous solution by a double jet method in a sufficiently stirred reaction vessel. It is effective for obtaining nickel hydroxide with uniform characteristics. Here, pure water can be put in the reaction tank in advance, but it is more preferable to use the filtrate once adjusted for neutralization to a predetermined pH with an alkali.
The type of the alkaline aqueous solution is not particularly limited. For example, an aqueous solution of an alkali metal hydroxide such as an aqueous sodium hydroxide solution or an aqueous potassium hydroxide solution is preferable, and an aqueous sodium hydroxide solution in terms of availability and price. Is more preferable. In addition, although alkaline compounds, such as sodium hydroxide and potassium hydroxide, can be used directly instead of alkaline aqueous solution, care must be taken because precipitation may be uneven.

The reaction equipment for producing the nickel hydroxide powder is not particularly limited, and may be, for example, a known equipment that can perform pH control in a storage tank having a stirrer.
The nickel hydroxide precipitate produced by the neutralization treatment is recovered by dehydration by filtration to obtain a filter cake.
Here, as the filtration operation, it is preferable to use means capable of sufficiently reducing the residual chlorine concentration. For this reason, known techniques such as repulp washing, cross flow filtration washing, washing using an acid such as sulfuric acid, and the like are used.
The nickel hydroxide precipitate after washing is dried by a known method such as air drying or vacuum drying. Thereby, the nickel hydroxide powder containing 0.002-1 mass% of periodic table group 2 elements is obtained.

(2) Step (A) Preparation of Nickel Oxide Powder Next, the nickel hydroxide powder is prepared by oxidizing and baking the nickel hydroxide powder in a non-reducing atmosphere.

  The roasting method is not particularly limited, and is a known method using a general roasting furnace such as a stationary roasting furnace, a rolling furnace, a burner furnace, a conveying continuous furnace, or a fluidized roasting furnace. It can be carried out. At this time, in order to obtain a fine nickel powder that is excellent in dispersibility and uniform, it is important to obtain a nickel oxide powder having uniform characteristics and sufficiently converted into a nickel oxide form. If the conversion to the nickel oxide form is insufficient, nickel hydroxide remains, water vapor is generated by the decomposition of nickel hydroxide during the subsequent reduction process, and aggregation or sintering occurs between the nickel particles. Therefore, nickel fine powder having excellent dispersibility cannot be obtained.

The roasting conditions are not particularly limited, and can be arbitrarily set according to the characteristics of the furnace so that characteristics such as the particle diameter of the target nickel fine powder can be obtained, but uniform processing is performed. Therefore, it is preferable to carry out in a gas stream.
There is no problem if the roasting atmosphere is in a non-reducing atmosphere, and an inert gas or an oxidizing gas is used as the atmosphere gas. However, using air as an oxidizing gas is cost and ease of handling. Is preferable.
The roasting temperature is not particularly limited and may be any temperature that can be sufficiently converted into the form of nickel oxide, but 350 to 550 in the case of a general static roasting furnace. It is preferable to set it as ° C, and it is more preferable to set it as 400-500 ° C. That is, when the roasting temperature is less than 350 ° C., the conversion to the nickel oxide form is not sufficient and nickel hydroxide may remain. On the other hand, when the roasting temperature exceeds 550 ° C., the nickel oxide powder is agglomerated or sintered, and the nickel fine powder particles obtained by the reduction treatment are coarsened and the dispersibility may not be sufficient.
The roasting time is not particularly limited, and the nickel hydroxide powder is sufficiently converted into the form of nickel oxide in consideration of the roasting temperature, the processing amount, the equipment to be used, etc. If you can leave. For example, it can be in the range of 1 to 5 hours.

(3) Step (B) Reduction treatment Thereafter, the reduction target made of nickel oxide is held at a converted thickness of 3 mm or less, a hydrogen-containing gas is used as the reduction gas, and the flow rate of the reduction gas is set to the surface of the reduction target. At a rate of 0.01 m / s or more, and nickel oxide is reduced by reducing nickel oxide.

  The production method of the present invention is characterized in that a reduction target made of nickel oxide is reduced while being reduced to a converted thickness of 3 mm or less. The to-be-reduced product means a load of nickel oxide powder to be subjected to reduction treatment. In addition to a load of nickel oxide powder in a mortar, a net-like container is filled with nickel oxide powder. Alternatively, nickel oxide powder may be granulated. The use of a net-like container or granulation is a preferable means because the area in contact with the reducing gas can be increased and the converted thickness can be reduced, and a large amount of nickel powder can be efficiently produced.

  The method of granulating the nickel oxide powder is not particularly limited, and suppresses variations in density and size of individual granulated bodies of nickel oxide powder as much as possible, and the particle diameter of the raw nickel oxide powder, It is preferable to avoid changes in the microstructure and the like. Therefore, a wet method is suitable as a granulation method, and for example, the following method can be used.

  First, a solvent such as nickel oxide powder and pure water is mixed and slurried so as to obtain properties such as viscosity suitable for molding. In the slurrying, a general kneader or a stirrer can be used. For example, any method such as a twin screw kneader or a rotation and revolution type stirrer can be used depending on the scale and characteristics.

Next, the obtained slurry is molded into a molded body. In molding, a general molding machine such as a single screw extrusion molding machine or a roll press machine can be used.
The shape of the granulated body is not particularly limited, and is preferably spherical, spheroidal or cylindrical in order to obtain the strength of the molded body or uniform reactivity with gas. The dimension of the granule is not particularly limited as long as the converted thickness is within a range of 3 mm or less, but after drying, for example, in the case of a sphere, the diameter is preferably 2 to 6 mm. In the case of a cylindrical shape, the diameter is preferably 2 to 6 mm and the length is preferably 2 to 50 mm. If the diameter of the granulated body after drying exceeds 10 mm, the reaction between the inside and outside of the granulated body may become non-uniform during the reduction reaction, resulting in variations in characteristics. On the other hand, when the diameter of the granulated body after drying is less than 2 mm, the gap between the granulated bodies is small, and it is difficult to reduce the flow rate of the reducing gas on the surface of the granulated body to 0.01 m / s or more during the reduction reaction. May be. In the case of a cylindrical shape, if the length is out of the above range, the granulated body may collapse during handling such as reduction treatment, causing dust generation.
In addition, the apparent density of the granulated body is not particularly limited, but is preferably 1 to ³ g / cm ³ after drying in order to promote the reduction reaction uniformly throughout the entire granulated body. When the apparent density of the granulated body exceeds ³ g / cm ³ , the reaction between the central portion and the outer peripheral portion of the granulated body may be uneven during the reduction reaction, resulting in variation in characteristics. On the other hand, if the apparent density of the granulated body is less than 1 g / cm ³ , sufficient strength cannot be obtained in the granulated body, the granulated body may collapse, and the granulation effect may not be sufficiently obtained. There is a possibility of dust generation due to collapse.
If molding is performed under certain conditions, changes in dimensions and apparent density before and after drying are stable.Consider the granulation conditions by performing a small amount of granulation in consideration of the solvent amount, shape, granulation pressure, etc. By determining, it is easy to control the size and apparent density after drying within the above range.

Next, the molded body is sufficiently dried to obtain a granulated body. When the granulated body is not sufficiently dried, water vapor is generated during the reduction treatment, and the aggregation or sintering of the nickel fine powder generated as described above is promoted, and the nickel fine powder having excellent dispersibility cannot be obtained.
The moisture content of the nickel oxide powder (granulated body) after drying is not particularly limited, but is preferably 5% by mass or less, and more preferably 3% by mass or less. When the water content exceeds 5% by mass, nickel fine powder having excellent dispersibility may not be obtained due to the influence of the generation of water vapor.
This drying method is not particularly limited, and a general stationary dryer may be used, or a vibration dryer may be used. The drying temperature and time are not particularly limited as long as the granule is sufficiently dried. For example, the drying temperature is preferably 60 to 200 ° C., and the drying time is appropriately determined in consideration of the drying temperature and the processing amount.

The dried granulate thus obtained is then subjected to reduction treatment in a furnace. The furnace is not particularly limited, but a stationary reduction furnace is preferable, and for example, a batch type atmosphere firing furnace, a conveyance type continuous furnace, or the like is used. A fluidized bed reducing furnace such as a kiln type is not necessarily not usable, but care must be taken because it tends to be agglomerated or sintered nickel powder as described above.
The treatment temperature and time of the reduction treatment conditions can be appropriately set according to the target particle diameter and the like.
The reduction temperature is not particularly limited, but in order to obtain fine nickel powder suitable for an internal electrode of MLCC, the reduction temperature is preferably 300 to 500 ° C. As the reduction temperature is higher and the reduction time is set longer, the particle size tends to increase. When the reduction temperature exceeds 500 ° C., aggregation or sintering of the nickel powder reduced during the reduction occurs, and as a result, a desired particle size may not be obtained with high accuracy. On the other hand, when the temperature is lower than 300 ° C., the reduction from nickel oxide to nickel is difficult to proceed, and a long time is required for the reduction, and the aggregation of the nickel powder may proceed. Therefore, in order to obtain nickel fine powder of 0.5 μm or less, which is a more preferable average particle diameter for the internal electrode, the reduction temperature is more preferably 380 to 420 ° C.
In addition, the reduction time is not particularly limited, and it may be a time necessary for all nickel oxide to be reduced to nickel depending on the amount of hydrogen flowing during reduction, the reduction temperature, and the amount of nickel oxide powder to be added. Good. It is preferable to control the time so as to obtain a desired particle diameter, and as with the above-described roasting of the nickel hydroxide powder, providing a uniform air flow as much as possible to obtain a uniform nickel fine powder. Therefore, it is preferable.

The nickel powder after reduction thus obtained has a fine and uniform particle size and very little aggregation between the particles, and can be easily dispersed including the granulated body. However, if agglomerated powder is generated during the process or foreign matter is mixed in during the process, the foreign matter may be removed by crushing or classification using a dry or wet centrifugal force or a filter. An apparatus is not specifically limited, The apparatus of a vibration sieve, a jet mill, and a cyclone type used for manufacture of normal nickel powder is used.
As described above, the method for producing nickel powder of the present invention is a relatively simple method of reducing nickel hydroxide produced by a wet method, does not have complicated steps, and has good dispersibility. Since uniform nickel fine powder is obtained, the manufacturing cost can be kept low.

2. Nickel powder obtained The nickel powder obtained by the production method of the present invention is fine, uniform and excellent in dispersibility, and is suitable as a material for electronic parts.
That is, as a specific characteristic, the average particle diameter is 0.2 to 0.6 μm. When the average particle size is less than 0.2 μm, in the case of MLCC internal electrode paste, the sintering temperature of nickel powder is low, so the difference in sintering behavior with dielectric ceramics is large, and the electrode breaks or peels off. Sometimes. On the other hand, if the average particle diameter exceeds 0.6 μm, the thinned internal electrode may cause holes or breaks in the sintered electrode, which is not preferable. Furthermore, the particle size distribution measured by observation with a scanning electron microscope preferably has a D90 (diameter equivalent to 90% under sieve by volume integration) of 1 μm or less. If D90 exceeds 1 μm, nickel powder may penetrate through the dielectric layer, causing a short circuit between the electrodes of the MLCC.

  Hereinafter, the present invention will be described in detail using examples, but the present invention is not limited to these examples.

The particle size distribution of the nickel powder was evaluated as follows.
Using a scanning electron microscope (JSM-5510, manufactured by JEOL Ltd.), a photograph of 10,000 times the nickel powder was taken, and the particle size of all particles that could be confirmed in one field of view was measured and statistically processed. The evaluation items were 50% equivalent diameter under sieve (D50: average diameter) and 90% equivalent diameter under sieve (D90).

Example 1
First, 100 g of nickel chloride hexahydrate (reagent grade 1, manufactured by Wako Pure Chemical Industries) and magnesium chloride hexahydrate (reagent grade 1 manufactured by Wako Pure Chemical Industries) 0.2 g (Mg content in nickel hydroxide of 0. 06 mass%) was dissolved in 250 mL of pure water to prepare an aqueous nickel chloride solution. Next, a solution obtained by dissolving 35.5 g of sodium hydroxide (reagent grade 1, manufactured by Wako Pure Chemical Industries, Ltd.) in 250 mL of pure water was added to the nickel chloride aqueous solution, and the generated hydroxide was filtered. Further, this was washed with 1 L of pure water and filtered again (hereinafter, this operation is referred to as “filtered water washing”). Similarly, after washing with filtered water four times, drying was performed at 150 ° C. for 48 hours with a box-type atmospheric dryer (DX601, manufactured by Yamato Kagaku) to obtain nickel hydroxide powder.
After crushing the obtained nickel hydroxide powder, nickel oxide powder was obtained by performing oxidative roasting in the air at 400 ° C. for 2 hours using a roller hearth kiln (desk kiln, manufactured by Noritake).
Furthermore, 12 g of the obtained nickel oxide powder was placed in a tubular atmosphere furnace having a diameter of 11 cm so as to have a thickness of 3 mm on a ceramic tray. Hydrogen gas equal to 0.1 liter / min per 1 g of nickel oxide powder and nitrogen gas in the same amount as hydrogen were mixed, distributed as a reducing gas, and held at 400 ° C. for 1 hour to obtain nickel powder. At this time, the flow rate of the reducing gas on the sample is 0.01 m / s. The obtained nickel powder was passed through a # 100 sieve, and the particle size of the nickel powder was evaluated by a scanning electron microscope (hereinafter, SEM).
Table 1 summarizes the results of measurement of the Mg addition amount, reduction conditions, and particle size in nickel hydroxide.

(Example 2)
Nickel powder was obtained and evaluated in the same manner as in Example 1 except that 0.1 g of magnesium chloride hexahydrate added to the nickel chloride aqueous solution was changed to 0.1 g (equivalent to Mg content of 0.02 mass% in nickel hydroxide). .
Table 1 also shows the Mg content in nickel hydroxide, roasting conditions and reducing conditions, and particle size measurement results.

(Example 3)
Nickel powder was obtained and evaluated in the same manner as in Example 1 except that the input amount of nitrogen was 0.2 liter / minute per 1 g of nickel oxide powder (total nitrogen of 2.4 liter / minute). The flow rate of the reducing gas on the sample at this time is 0.015 m / s.
Table 1 also shows the Mg content in nickel hydroxide, roasting conditions and reducing conditions, and particle size measurement results.

Example 4
Nickel powder was obtained and evaluated in the same manner as in Example 1 except that the input amount of nitrogen was 0.3 liter / minute per 1 g of nickel oxide powder (total nitrogen was 3.6 liter / minute). The flow rate of the reducing gas on the sample at this time is 0.02 m / s.
Table 1 also shows the Mg content in nickel hydroxide, roasting conditions and reducing conditions, and particle size measurement results.

(Example 5)
Nickel powder was obtained and evaluated in the same manner as in Example 1 except that 12 g of nickel oxide powder was placed on a ceramic tray to a thickness of 2.5 mm. Table 1 also shows the Mg content in nickel hydroxide, roasting conditions and reducing conditions, and particle size measurement results.

(Example 6)
Nickel powder was obtained and evaluated in the same manner as in Example 1 except that 12 g of nickel oxide powder was placed on a ceramic tray to a thickness of 2 mm.
Table 1 also shows the Mg content in nickel hydroxide, roasting conditions and reducing conditions, and particle size measurement results.

(Comparative Example 1)
Nickel powder was obtained and evaluated in the same manner as in Example 1 except that the nickel chloride aqueous solution was prepared only with nickel chloride hexahydrate. Table 1 also shows the Mg content in nickel hydroxide, roasting conditions and reducing conditions, and particle size measurement results.

(Comparative Example 2)
Nickel powder was obtained and evaluated in the same manner as in Example 1 except that the amount of nitrogen introduced was 0.06 liter / minute per 1 g of nickel oxide powder (total nitrogen was 0.7 liter / minute). At this time, the flow rate of the reducing gas on the sample is 0.008 m / s. Table 1 also shows the Mg content in nickel hydroxide, roasting conditions and reducing conditions, and particle size measurement results.

(Comparative Example 3)
Nickel powder was obtained and evaluated in the same manner as in Example 1 except that 12 g of nickel oxide powder was placed on a ceramic tray to a thickness of 3.5 mm. Table 1 also shows the Mg content in nickel hydroxide, roasting conditions and reducing conditions, and particle size measurement results.

(Comparative Example 4)
Except that 12 g of nickel oxide powder was placed on a ceramic tray to a thickness of 3.5 mm, and the amount of nitrogen input was 0.3 liter / minute per gram of nickel oxide powder (total nitrogen of 3.6 liter / minute), In the same manner as in Example 1, nickel powder was obtained and evaluated. At this time, the flow rate of the reducing gas on the sample is 0.02 m / s. Table 1 also shows the Mg content in nickel hydroxide, roasting conditions and reducing conditions, and particle size measurement results.

(Example 7)
240 g of nickel chloride hexahydrate (reagent grade 1, manufactured by Wako Pure Chemical Industries) and magnesium chloride hexahydrate (reagent grade 1, manufactured by Wako Pure Chemical Industries) 0.33 g (Mg content in nickel hydroxide 0.04 mass) %) Was dissolved in 250 mL of pure water to prepare an aqueous nickel chloride solution. After washing in the same manner as in Example 1, oxidation roasting was performed to obtain nickel oxide powder.
To 120 g of the obtained nickel oxide powder, 42 ml of pure water was added and mixed with a rotating / revolving mixer to obtain a clay-like slurry. This operation was repeated to prepare 4 kg of pure water slurry of nickel oxide, granulated using a uniaxial granulator (Akira Kiko, model AX-75), and then dried at 120 ° C. with a stationary dryer. Nickel oxide granules were obtained. Here, a screen having a diameter of 4 mm was used for molding.
The dimensions of the obtained cylindrical granule after drying were about 3.8 mm in diameter and about 5 mm to about 20 mm in length. Moreover, the apparent density was 2.2 g / cm < ³ > and the moisture content was 2 mass%. The granulated body was prepared to have a length of about 5 mm as a raw material.
A honeycomb brick through which gas can flow is fixed at the position of the central portion of the heating zone in an alumina tube having an inner diameter of φ43 mm installed in a vertical tubular furnace so that there is no gap between the inner surface of the alumina tube, and a 150 mesh nickel mesh is fixed on the honeycomb brick. And 40 g of the granulated material was loaded on a nickel net. The granulated body had the same diameter as the alumina tube inner diameter, the height was about 22 mm, and the converted thickness was 0.8 mm.
Next, while flowing a 30% by volume hydrogen-nitrogen mixed gas as a reducing gas from the lower surface side of the loaded nickel oxide powder granule at a flow rate of 1.0 liter / min, hold at 390 ° C. for 1.5 hours. Nickel powder was obtained. The obtained nickel powder was evaluated in the same manner as in Example 1. In addition, since the granulated body is filled and loaded in the alumina tube, all the reducing gas flows through the gaps between the granulated bodies, and the flow rate of the reducing gas is 0.027 m / s.
Table 1 also shows the Mg content in nickel hydroxide, roasting conditions and reducing conditions, and particle size measurement results.

(Example 8)
Nickel powder was obtained and evaluated in the same manner as in Example 7 except that the reduction temperature was 400 ° C. Table 1 also shows the Mg content in nickel hydroxide, roasting conditions and reducing conditions, and particle size measurement results.

Example 9
Nickel powder was obtained and evaluated in the same manner as in Example 7 except that the reduction temperature was 430 ° C. Table 1 also shows the Mg content in nickel hydroxide, roasting conditions and reducing conditions, and particle size measurement results.

  As is apparent from the results shown in Table 1, the nickel powders of the examples obtained by the production method of the present invention have a sharp particle size distribution with an average particle size (D50) of 0.4 to 0.5 μm. It has been. On the other hand, in the nickel powders of Comparative Examples 1 to 4, the average particle diameter (D50) is large, or even if D50 is the same, D90 is larger and coarser nickel powder is included than in the examples. Recognize. Therefore, it turns out that the nickel powder of a comparative example is not preferable as nickel powder for MLCC internal electrodes since coarse particles are contained.

  Since the nickel powder obtained by the present invention has a fine and uniform particle size and is low in cost, it is suitable for use as an electronic component, particularly for forming MLCC internal electrodes whose size and capacity are increasing. And its industrial value is extremely high.

Claims (6)

  A step (A) of roasting nickel hydroxide powder having a content of Group 2 element of the periodic table of 0.002 to 1% by mass to form nickel oxide powder, and the obtained nickel oxide powder (reduced substance) ) Is reduced to a temperature of 3 mm or less, and heated to a reduction temperature, and a hydrogen-containing gas is supplied at a flow rate of 0.01 m / s or more to reduce nickel oxide powder (B). A method for producing nickel powder.   2. The method for producing nickel powder according to claim 1, wherein in the step (A), the Group 2 element of the periodic table is magnesium.   The nickel powder according to claim 1 or 2, wherein in the step (B), the hydrogen-containing gas is a mixed gas of hydrogen and an inert gas, and the hydrogen content is 10 to 50% by volume. Production method.   The method for producing nickel powder according to any one of claims 1 to 3, wherein in the step (B), the reduction temperature is 300 to 500 ° C.   Nickel powder obtained by the method for producing nickel powder according to any one of claims 1 to 4, having an average particle size of 0.2 to 0.4 µm.   The nickel powder according to claim 5, wherein the particle size distribution (D90) measured by observation with a scanning electron microscope is 1 µm or less.