JP4978785B2 - Method for producing nickel powder - Google Patents

Description

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

  A multilayer ceramic capacitor (hereinafter referred to as “MLCC” for convenience of explanation) is a small and high-capacity capacitor having a structure in which dielectric layers and internal electrodes are alternately stacked. As the dielectric, a ceramic material typified by barium titanate is used. On the other hand, noble metal-based materials have been used for the internal electrodes, but in recent years, nickel-based materials have become the mainstream because of their low cost.

The outline of the production method of MLCC using nickel powder for internal electrode formation is as follows.
That is, a nickel paste produced by kneading nickel powder and an organic solvent together with various additives is printed on a dielectric green sheet and dried. Next, a desired number of layers are stacked, thermocompression bonded, cut into a chip shape, and after cutting, the binder is removed at a temperature of about 300 ° C., and then 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.

  In the binder removal step, a method of burning the binder by heat treatment in an oxidizing atmosphere is performed. A polyvinyl alcohol-based material is often used as the binder of the dielectric green sheet, and an ethylcellulose-based material is often used as the binder of the nickel paste for forming the internal electrode. The atmosphere and temperature in the debinding process are adjusted so as to control the combustion timing and the amount of generated gas.

  Nickel powder is required not to cause unintentional gas generation in this process or to cause a significant volume change due to oxidation. Has been adjusted. In addition, since the dielectric is a ceramic and the internal electrode is a metal, the shrinkage during sintering is generally larger in the internal electrode. In addition, since the melting point of the metal is lower, the sintering start temperature is lower for the internal electrode. Therefore, the same effect can be obtained by mixing ceramic powder or the like in the nickel paste to delay the sintering phenomenon, or adding a small amount of other elements to the nickel powder itself.

  On the other hand, MLCC manufacturers are working to reduce the thickness and increase the thickness of internal electrodes and dielectrics with the aim of further reducing the size and increasing the capacity of MLCCs. In the thinned internal electrode, if the particle size of the nickel powder is large, the number of particles existing in the electrode thickness direction is small, and the voids between the particles are also large. Occurs and does not function as an electrode. For this reason, the nickel powder used for the internal electrode is also required to have a finer particle size. Further, in the MLCC having a thin layer, when coarse nickel powder is mixed, a short circuit occurs between the electrodes, and it is required that coarse particles are not included. Furthermore, if particles that are significantly finer than the average particle size are present, oxidation in the binder removal process and lowering of the sintering start temperature in the sintering process occur, so it is also important that particles with extremely fine particle sizes are not included. It is.

  As described above, the nickel powder for internal electrodes is required to be less likely to generate gas in the debinding process and close to the sintering shrinkage characteristics of the dielectric. Is the most important requirement.

In order to solve the above problems, nickel powders produced by various methods and containing no coarse particles have been proposed.
For example, in Patent Document 1, the presence of coarse particles having an average particle size of 0.2 to 0.6 μm by vapor phase hydrogen reduction of nickel chloride vapor and having a particle size of 2.5 times or more the average particle size Nickel powder with a rate of 0.1% or less on the number basis has been proposed. Moreover, in patent document 2, it is nickel powder with an average particle diameter of 0.1-1.0 micrometer, Comprising: The nickel powder whose content rate of nickel powder with a particle diameter of 2 micrometers or more is 700/1 million or less on a number basis. It is disclosed that nickel powder obtained by vapor phase hydrogen reduction of nickel chloride vapor can be obtained by classification with a liquid cyclone or the like. Further, in Patent Document 3, 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 average particle size is 0.5%. Nickel powder has been proposed in which the number of particles having a particle size of twice or less is 5% or less of the total number of particles, and the average primary particle size by SEM observation is 0.1 to 2 μm. This nickel powder is obtained by a pulverization treatment using a nickel powder containing an aggregate obtained by a wet process in which a nickel salt is used as a raw material in an aqueous solution and the like as a raw powder.

  However, the nickel powder obtained by these proposals has a problem that the cost becomes high. Nickel powder obtained by the gas phase hydrogen reduction method has good crystallinity and excellent characteristics, but has low productivity and high cost. Moreover, classifying nickel powder obtained by a gas phase hydrogen reduction method or the like results in a worse yield and higher cost. Even if the agglomerates obtained by a wet method or the like are pulverized, if the primary particle diameter 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 size can be obtained, but the problem of low productivity and high cost cannot be solved.

  On the other hand, the low-cost nickel powder includes nickel powder obtained by heat reduction of nickel hydroxide. For example, in Patent Document 4, while adding a nickel-containing solution continuously to a slurry in a reaction vessel, an alkaline solution is added to form nickel hydroxide, and the slurry is filtered, washed with water, and dried. Thus, there is disclosed a production method for obtaining nickel powder by obtaining nickel hydroxide, using hydrogen as a reducing agent, and heating and reducing at a reduction temperature of 400 to 550 ° C. However, nickel powder obtained by heat reduction of nickel hydroxide can be mass-produced and is low in cost, but there is a problem that it is difficult to obtain nickel powder having a fine and uniform particle size.

As described above, a method for producing a large amount of nickel powder having a fine and uniform particle size at a low cost has not been developed yet.
JP 11-189801 A JP 2001-73007 A JP 2001-247903 A JP 2003-213310 A

The present invention has been made in view of the above-described conventional situation, and an object of the present invention is to provide a method for producing a large amount of nickel powder having a fine and uniform particle size at a low cost.

In order to solve the above problems, the present inventor conducted extensive research on a method for obtaining nickel powder by heat reduction of nickel hydroxide. Nickel oxide is obtained by roasting nickel hydroxide under specific conditions. In addition, the present inventors have found that a nickel powder having a fine and uniform particle diameter can be obtained at low cost by heating and reducing the obtained nickel oxide under specific conditions.
That is, the nickel powder manufacturing method according to the present invention is a nickel hydroxide powder obtained by roasting nickel hydroxide powder containing 0.002 to 1% by mass of alkaline earth metal, and reducing the obtained nickel oxide powder. In the powder production method, 0.02 to 0.4 liter / min of air is flowed with respect to 1 g of nickel hydroxide and roasted at a temperature of 250 to 500 ° C. to change the nickel hydroxide powder to nickel oxide powder. The obtained nickel oxide powder is made to flow into the nickel powder by flowing 0.01 to 0.2 liter / min of hydrogen with respect to 1 g of the nickel oxide powder and reducing it to a temperature of 300 to 500 ° C. is there.

Moreover, it is preferable that the nickel oxide obtained by the said baking of this invention satisfy | fills the following conditions for the mass reduction | decrease when heated in a reducing atmosphere.
0.5 ≦ (weight loss from room temperature to 400 ° C. (mass%)) / (weight loss from room temperature to 800 ° C. (mass%)) ≦ 1

  Furthermore, in the method for producing nickel powder according to the present invention, the alkaline earth metal contained in the nickel hydroxide powder is preferably magnesium, and furthermore, in the method for producing nickel powder according to the present invention, It is preferable that the average particle diameter of the obtained nickel powder is 0.2 to 0.4 μm.

  In the method of obtaining nickel powder by heating and reducing nickel hydroxide, the present invention obtains nickel oxide by baking nickel hydroxide under specific conditions, and heat-reducing the obtained nickel oxide under specific conditions. As a result, the nickel powder having a fine and uniform particle diameter can be produced in a large amount at a low cost. In addition, the nickel powder obtained by the method of the present invention is particularly suitable for forming MLCC internal electrodes whose size and capacity are increasing, and has an extremely large industrial value.

In the method for producing nickel powder of the present invention, roasting conditions for nickel hydroxide and reducing conditions for nickel oxide are important. In the present invention, the nickel oxide powder is completely reduced at a low temperature for a short time to obtain a uniform nickel powder having a desired particle size. Thus, in order to reduce at a low temperature for a short time, it is necessary to use nickel oxide that has low crystallinity, a small particle size, and is easily reduced.
In the present invention, nickel hydroxide powder obtained by flowing air at 0.02 to 0.4 liter / min to 1 g of nickel hydroxide and roasting at a temperature of 250 to 500 ° C. is used as nickel oxide powder. Furthermore, the obtained nickel oxide powder is made to flow into the nickel powder by flowing 0.01 to 0.2 liter / min of hydrogen with respect to 1 g of the nickel oxide powder and reducing it to a temperature of 300 to 500 ° C. It depends on the reason described.
First, nickel hydroxide powder containing alkaline earth metal is roasted at a temperature of 250 to 500 ° C. while flowing air of 0.02 to 0.4 liter / min with respect to 1 g of nickel hydroxide to obtain nickel oxide powder. Since the decomposition of nickel hydroxide into nickel oxide gradually proceeds when the amount of air flowing during roasting is less than 0.02 liter / min with respect to 1 g of nickel hydroxide, crystals of nickel oxide are obtained. On the other hand, when roasting at a temperature exceeding 500 ° C., sintering proceeds during roasting and coarse nickel oxide powder is formed.
Since the nickel oxide obtained in this way has grown crystals or has a coarse particle size, it needs to be reduced at a high temperature for a long time in order to reduce it. When reduction is performed at a high temperature for a long time, the grain growth of nickel powder proceeds, resulting in a coarse and non-uniform particle size.
Even if the amount of air flowing at the time of roasting exceeds 0.4 liter / min with respect to 1 g of nickel hydroxide, an effect of obtaining uniform fine nickel powder can be obtained, but there is no further improvement in the effect, and the cost increases. It only becomes. In addition, when a large amount of air is flowed, fine nickel oxide powder is scattered and the yield is also lowered. On the other hand, when the roasting temperature is less than 250 ° C., not only does roasting take a long time, but also the conversion from nickel hydroxide to nickel oxide does not proceed sufficiently, and the reduction proceeds non-uniformly during reduction, resulting in the growth of nickel powder grains. .
The roasting time is not particularly limited, and the time required for all the nickel hydroxide to be converted to nickel oxide depending on the amount of air flowing during roasting, the roasting temperature, and the amount of nickel hydroxide powder to be added. And it is sufficient. At this time, in order to lower the crystallinity, the baking time is preferably as short as possible.

Next, when the nickel oxide thus obtained is reduced in an atmosphere containing hydrogen, 0.01 to 0.2 liter / min of hydrogen is allowed to flow with respect to 1 g of nickel oxide at a temperature of 300 to 500 ° C. Reduce at temperature. At this time, only hydrogen gas may flow or a mixed gas of hydrogen gas and an inert gas such as nitrogen may flow. Here, when the amount of hydrogen flowing at the time of reduction is less than 0.01 liter / min with respect to 1 g of nickel oxide, grain reduction of nickel powder occurs because the reduction proceeds gradually, and uniform nickel powder with a desired particle diameter On the other hand, even if the amount of hydrogen exceeds 0.2 liter / min with respect to 1 g of nickel oxide, the effect of shortening the reduction necessary for obtaining a fine and uniform particle size of nickel powder However, there is no improvement in the amount of wasteful hydrogen, which only increases costs.
Moreover, the reduction temperature is limited to 300 to 500 ° C. When the reduction temperature exceeds 500 ° C., the reduced nickel powder is sintered during the reduction, and as a result, a desired particle size can be obtained with high accuracy. On the other hand, at a temperature 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 proceeds.
The reduction time is not particularly limited, and may be a time required for all the 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. It is preferable to control the time so that a desired particle size is obtained. The equipment used for roasting and reduction is not particularly limited as long as the atmosphere can be controlled. For example, a batch type atmospheric furnace, a batch type rotary kiln, a continuous roller hearth kiln, a continuous type pusher furnace, a continuous type rotary kiln, etc. may be used. it can.

  In the method for producing nickel powder according to the present invention, the nickel oxide obtained by the roasting has the mass reduction when heated in a reducing atmosphere as described above, that is, the weight loss of 0.5 ≦ (room temperature to 400 ° C. (mass %)) / (Weight loss from room temperature to 800 ° C. (mass%)) ≦ 1 is preferably satisfied.

  In the present invention, the mass reduction when heated in the reducing atmosphere indicates the amount of oxygen in the nickel oxide reduced by the reduction, and the weight loss (% by mass) from room temperature to 800 ° C. was completely reduced. The oxygen content at the time, and the weight loss (mass%) from room temperature to 400 ° C. indicates the oxygen content reduced at 400 ° C. or less. That is, the ratio of (weight loss from room temperature to 400 ° C. (mass%)) / (weight loss from room temperature to 800 ° C. (mass%)) (hereinafter referred to as heat loss ratio) is the ratio of nickel oxide reduced at 400 ° C. or less. It is shown.

The method for producing nickel powder according to the present invention is characterized in that reduction is performed at a low temperature, and nickel oxide that satisfies the above conditions can be reduced at a low temperature. Accordingly, the heat loss ratio is preferably 0.5 to 1. That is, when the thermal weight loss ratio is less than 0.5, the amount of nickel oxide powder reduced at a temperature exceeding 400 ° C. increases, and the grain growth of the nickel powder obtained by reduction proceeds, which is coarse and uneven in particle size. It can be a thing. Accordingly, it is preferable that the amount of nickel oxide reduced at a temperature of 400 ° C. or less is large, and even if all nickel oxide is reduced, there is no problem, and thus the heat loss ratio can be in a range up to 1.
In addition, the reducing atmosphere in the case of measuring a heat loss ratio is not specifically limited, For example, the mixed gas of reducing gas and inert gas, such as 2 volume% hydrogen-nitrogen mixed gas, is used. Moreover, the apparatus used for the measurement may be a commonly used thermal analysis apparatus, and the measurement conditions may be those recommended for normal measurement.

  The nickel hydroxide powder used in the method for producing nickel powder according to the present invention can be obtained by an ordinary known method. For example, nickel hydroxide powder obtained by neutralizing and precipitating an aqueous solution of a water-soluble nickel salt such as nickel chloride or nickel sulfate by pH control can be used. The alkaline earth metal contained in the nickel hydroxide powder may be mixed with a nickel salt aqueous solution as a water-soluble substance such as a water-soluble salt and coprecipitated when nickel hydroxide is produced. There is no particular limitation on the reaction equipment for producing the nickel hydroxide powder, and any equipment that is normally used may be used, for example, as long as the pH can be controlled in a storage tank having a stirrer.

  The alkaline earth metal contained in the nickel hydroxide powder is effective in reducing the size and spheroidization of the particles when the nickel particles are produced during the reduction, and further improving the smoothness of the particle surface. The content of alkaline earth metal in nickel hydroxide is 0.002 to 1% by mass. When the alkaline earth metal is less than 0.002% by mass, the effect of refinement and improvement in smoothness is not observed. When the alkaline earth metal content exceeds 1% by mass, the electrical resistance of the electrode becomes too large when used as an MLCC internal electrode due to the decrease in nickel quality of the resulting nickel powder, and the loss factor of the capacitor Invite the deterioration.

  The nickel powder obtained by roasting and reduction of the nickel hydroxide has a fine and uniform particle size and very little aggregation between the particles. For the purpose of removing foreign substances mixed in the process, crushing or classification using a dry or wet centrifugal force or a filter may be performed. The apparatus to be used is not particularly limited, and a jet mill or a cyclone type apparatus that is used for producing ordinary nickel powder is used.

The nickel powder obtained by the method for producing nickel powder according to the present invention as described above preferably has an average particle size of 0.2 to 0.4 μm. That is, when the average particle size is less than 0.2 μm, when used as a paste for MLCC internal electrodes, the sintering temperature of nickel powder is low, so the difference in sintering behavior with dielectric ceramics is large, and the electrodes are interrupted. On the other hand, if the average particle diameter exceeds 0.4 μm, the thinned internal electrode may cause holes or breaks in the sintered electrode, which is not preferable. is there.
[Example]

Hereinafter, the present invention will be described in detail using examples, but the present invention is not limited to these examples. The nickel powder was evaluated as follows.
(1) Particle size: A 10,000 times photograph was taken with a scanning electron microscope (JSM-5510, manufactured by JEOL), and the particle size of all the particles that could be confirmed in one field of view was measured and statistically processed. The evaluation items were 10% equivalent diameter under sieve (D10), 50% equivalent diameter under sieve (D50: average diameter), and 90% equivalent diameter under sieve (D90).
(2) Thermal weight loss ratio: Thermal weight from room temperature to 800 ° C. at a heating rate of 10 ° C./min in a 2% by volume hydrogen-nitrogen mixed gas atmosphere using a thermal analyzer (TG-DTA2000SA, manufactured by MAC). The change was measured and calculated by calculating (weight loss up to 400 ° C. (mass%)) / (weight reduction up to 800 ° C. (mass%)).

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: 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.
After pulverizing the obtained nickel hydroxide, the air flow rate was 0.2 liter / min per 1 g of dried nickel hydroxide powder using a batch-type atmosphere furnace (tubular furnace, manufactured by Irie Seisakusho) at 450 ° C. for 6 hours. The nickel oxide powder was obtained by holding and baking.
The heat loss ratio of the obtained nickel oxide powder was determined by a thermal analyzer. Further, the nickel oxide powder is held at 450 ° C. for 1 hour in a batch type atmosphere furnace in which the same amount of nitrogen gas as 0.1 liter / min of nickel oxide powder is mixed and flowed for 1 hour. Obtained. The obtained nickel powder was passed through a # 100 sieve, and the particle size of the nickel powder was measured with a scanning electron microscope (hereinafter, SEM).
Table 1 summarizes the Mg addition amount in nickel hydroxide, roasting conditions and reduction conditions, heat loss ratio, and particle size measurement results.

A nickel powder was obtained 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). The particle size was measured after passing through a # 100 sieve.
Table 1 also shows the Mg content in the nickel hydroxide, roasting conditions and reducing conditions, heat loss ratio, and particle size measurement results in this example.

Nickel powder was obtained in the same manner as in Example 1 except that the roasting conditions were changed to 280 ° C. for 48 hours, and the particle size was measured after passing through a # 100 sieve.
Table 1 also shows the Mg content in the nickel hydroxide, roasting conditions and reducing conditions, heat loss ratio, and particle size measurement results in this example.

Nickel powder was obtained in the same manner as in Example 1 except that the roasting conditions were 490 ° C. for 2 hours, and the particle size was measured after passing through a # 100 sieve.
Table 1 also shows the Mg content in the nickel hydroxide, roasting conditions and reducing conditions, heat loss ratio, and particle size measurement results in this example.

Nickel powder was obtained in the same manner as in Example 1 except that the air flow rate during roasting was set to 0.02 liter / min, and the particle size was measured after passing through a # 100 sieve.
Table 1 also shows the Mg content in the nickel hydroxide, roasting conditions and reducing conditions, heat loss ratio, and particle size measurement results in this example.

Nickel powder was obtained in the same manner as in Example 1 except that the air flow rate at the time of roasting was 0.4 liter / minute, and the particle size was measured after passing through a # 100 sieve.
Table 1 also shows the Mg content in the nickel hydroxide, roasting conditions and reducing conditions, heat loss ratio, and particle size measurement results in this example.

Nickel powder was obtained in the same manner as in Example 1 except that the reducing condition was changed to 300 ° C. for 3 hours, and the particle size was measured after passing through a # 100 sieve.
Table 1 also shows the Mg content in the nickel hydroxide, roasting conditions and reducing conditions, heat loss ratio, and particle size measurement results in this example.

Nickel powder was obtained in the same manner as in Example 1 except that the reducing condition was changed to 500 ° C. for 0.5 hour, and the particle size was measured after passing through a # 100 sieve.
Table 1 also shows the Mg content in the nickel hydroxide, roasting conditions and reducing conditions, heat loss ratio, and particle size measurement results in this example.

Nickel powder was obtained in the same manner as in Example 1 except that the flow rate of hydrogen gas flowing at the time of reduction was 0.01 liters / minute and the mixture was mixed with the same amount of nitrogen gas and the reduction time was 3 hours. The particle size was measured after passing through a # 100 sieve.
Table 1 also shows the Mg content in the nickel hydroxide, roasting conditions and reducing conditions, heat loss ratio, and particle size measurement results in this example.

Nickel powder was obtained in the same manner as in Example 1 except that the flow rate of hydrogen gas flowing at the time of reduction was 0.2 liter / min, and the mixture was flowed with the same amount of nitrogen gas, and this was passed through a # 100 sieve. Later, the particle size was measured.
Table 1 also shows the Mg content in the nickel hydroxide, roasting conditions and reducing conditions, heat loss ratio, and particle size measurement results in this example.

100 kg of nickel chloride hexahydrate (manufactured by Sumitomo Metal Mining) and magnesium chloride hexahydrate (reagent grade, manufactured by Wako Pure Chemical Industries) 200 g (equivalent to Mg content of 0.06% by mass in nickel hydroxide) 250 L of pure water A nickel chloride aqueous solution was prepared. A solution prepared by dissolving 35.5 kg of sodium hydroxide (reagent 1 grade, manufactured by Wako Pure Chemical Industries, Ltd.) in 250 L of pure water is added to an aqueous nickel chloride solution, the formed hydroxide is filtered, and this is filtered through 100 L of pure water. Washed with water. Thereafter, after washing with filtered water four times in the same manner, drying was performed at 150 ° C. for 48 hours with a box-type atmospheric dryer (TD-B-10HH, manufactured by Temperature Equipment Laboratory) to obtain nickel hydroxide. After the obtained nickel hydroxide was crushed, the nickel oxide powder was roasted at 470 ° C. for 2 hours using a continuous pusher kiln in which an air flow rate of 0.02 liter / min per 1 g of the dried nickel hydroxide powder was flowed. Got. The heat loss ratio of the obtained nickel oxide powder was determined by a thermal analyzer. Further, the nickel oxide powder was mixed at 450 ° C. for 1 hour using a continuous pusher kiln in which hydrogen gas of 0.05 liter / min and nitrogen gas of 0.02 liter / min were mixed and flowed per gram of nickel oxide powder. Reduction was performed to obtain nickel powder.
The obtained nickel powder was passed through a # 100 sieve, and the particle size of the nickel powder was measured with a scanning electron microscope (hereinafter, SEM). Table 1 also shows the Mg addition amount in nickel hydroxide, roasting conditions and reduction conditions, heat loss ratio, and particle size measurement results.
[Comparative Example 1]

Nickel powder was obtained in the same manner as in Example 1 except that the nickel chloride aqueous solution was adjusted only with nickel chloride hexahydrate, and the particle size was measured after passing through a # 100 sieve.
Table 1 also shows the Mg content, roasting and reducing conditions, heat loss ratio, and particle size measurement results in nickel hydroxide in this comparative example.
[Comparative Example 2]

Nickel powder was obtained in the same manner as in Example 1 except that the air flow rate at the time of roasting was changed to 0.01 l / min, and the particle size was measured after passing through a # 100 sieve.
Table 1 also shows the Mg content, roasting and reducing conditions, heat loss ratio, and particle size measurement results in nickel hydroxide in this comparative example.
[Comparative Example 3]

Nickel powder was obtained in the same manner as in Example 1 except that roasting conditions were changed to 170 ° C. for 48 hours, and the particle size was measured after passing through a # 100 sieve.
Table 1 also shows the Mg content, roasting and reducing conditions, heat loss ratio, and particle size measurement results in nickel hydroxide in this comparative example.
[Comparative Example 4]

Nickel powder was obtained in the same manner as in Example 1 except that roasting conditions were set at 600 ° C. for 2 hours, and the particle size was measured after passing through a # 100 sieve.
Table 1 also shows the Mg content, roasting and reducing conditions, heat loss ratio, and particle size measurement results in nickel hydroxide in this comparative example.
[Comparative Example 5]

Nickel powder was obtained in the same manner as in Example 1 except that the flow rate of hydrogen gas flowing at the time of reduction was 0.005 liters / minute and mixed with the same amount of nitrogen gas, and this was passed through a # 100 sieve. The particle size was measured.
Table 1 also shows the Mg content, roasting and reducing conditions, heat loss ratio, and particle size measurement results in nickel hydroxide in this comparative example.
[Comparative Example 6]

Nickel powder was obtained in the same manner as in Example 1 except that the reducing condition was set at 250 ° C. for 3 hours, and the particle size was measured after passing through a # 100 sieve.
Table 1 also shows the Mg content, roasting and reducing conditions, heat loss ratio, and particle size measurement results in nickel hydroxide in this comparative example.
[Comparative Example 7]

Nickel powder was obtained in the same manner as in Example 1 except that the reduction condition was 600 ° C. for 0.5 hour, and the particle size was measured after passing through a # 100 sieve.
Table 1 also shows the Mg content, roasting and reducing conditions, heat loss ratio, and particle size measurement results in nickel hydroxide in this comparative example.

  As is clear from the above examples, the nickel powder of the example obtained by the production method according to the present invention had an average particle size (D50) of 0.2 to 0.4 μm and a sharp particle size distribution. On the other hand, in the nickel powders of Comparative Examples 1, 2, and 7, it can be seen that the average particle diameter is larger than 0.4 μm, or that D90 is larger than that of the example and coarse nickel powder is included. In addition, in the nickel powders of Comparative Examples 3 to 6, although the average particle diameter is 0.2 to 0.4 μm, D10 is fine, so extremely fine particles are included, and D90 is large, and thus coarse particles. It can be seen that is included. Therefore, it can be seen that the nickel powder of the comparative example is not preferable as the nickel powder for MLCC internal electrodes because it contains extremely fine particles or coarse particles.

  In the method of obtaining nickel powder by heating and reducing nickel hydroxide, the present invention obtains nickel oxide by baking nickel hydroxide under specific conditions, and heat-reducing the obtained nickel oxide under specific conditions. As a result, the nickel powder having a fine and uniform particle diameter can be produced in a large amount at a low cost. In addition, the fine and uniform nickel powder obtained by the method of the present invention is particularly suitable for forming MLCC internal electrodes whose size and capacity are increasing, and its industrial value is extremely large.

Claims (4)

  In a nickel powder manufacturing method for roasting nickel hydroxide powder containing 0.002 to 1% by mass of an alkaline earth metal to obtain nickel oxide powder, and reducing the obtained nickel oxide powder, 1 g of nickel hydroxide The nickel hydroxide powder obtained by flowing air at 0.02 to 0.4 liter / min and roasting at a temperature of 250 to 500 ° C. is used as nickel oxide powder, and the obtained nickel oxide powder is used as the nickel oxide powder. A method for producing nickel powder, characterized in that 0.01 to 0.2 liter / min of hydrogen is supplied to 1 g of powder and reduced to a temperature of 300 to 500 ° C. to obtain nickel powder. The method for producing nickel powder according to claim 1, wherein the mass reduction of nickel oxide obtained by roasting satisfies the following condition when heated in a reducing atmosphere.
0.5 ≦ (weight loss from room temperature to 400 ° C. (mass%)) / (weight loss from room temperature to 800 ° C. (mass%)) ≦ 1   3. The method for producing nickel powder according to claim 1, wherein the alkaline earth metal contained in the nickel hydroxide powder is magnesium.   The average particle diameter of the obtained nickel powder is 0.2-0.4 micrometer, The manufacturing method of the nickel powder of any one of Claims 1-3 characterized by the above-mentioned.