JP2020186154A - Large particle size nickel oxide powder and method for producing the same - Google Patents

Abstract

To provide a method for producing nickel oxide powder in which particle size and specific surface area are controlled within desired ranges.SOLUTION: A method for producing nickel oxide powder having the form of secondary particles in which primary particles are aggregated comprises a crystallization step of crystallizing particles mainly composed of nickel hydroxide by neutralizing an aqueous solution of nickel sulfate with an aqueous solution of alkali containing a hydroxide of an alkali metal as an alkali component such as sodium hydroxide, and a heat treatment step of heat-treating the particles mainly composed of the nickel hydroxide in a non-reducing atmosphere at an atmospheric temperature of 900°C or higher and lower than 1100°C to produce nickel oxide powder.SELECTED DRAWING: Figure 1

Description

The present invention relates to a large particle size nickel oxide powder having a low impurity grade and a method for producing the same, which is suitable as a material for electronic parts and an electrode material for a solid oxide fuel cell.

Generally, the nickel oxide powder is a nickel salt such as nickel sulfate, nickel nitrate, nickel carbonate, nickel hydroxide, or nickel metal powder, such as a rolling furnace such as a rotary kiln, a continuous furnace such as a pusher furnace, or a burner furnace. It is manufactured by charging it in a batch furnace and firing it in an oxidizing atmosphere. These nickel oxide powders are used not only for conventional materials for electronic parts, but also for electrodes for solid oxide fuel cells, which are expected as new power generation systems because they are excellent in terms of both low environmental load and energy saving. It has spread to various fields.

For example, in applications as materials for electronic parts, nickel oxide powder is widely used as a raw material for ferrite parts and the like produced by mixing nickel oxide powder with other materials such as iron oxide and zinc oxide and then sintering the powder. When a plurality of materials are mixed and fired to produce a composite metal oxide like this ferrite component, the production reaction is rate-determined by the diffusion reaction of the solid phase. Generally, fine powder is preferably used as the form of the raw material. On the other hand, in the application as a solid oxide fuel cell, it is used as a raw material for a sintered fuel electrode constituting the cell of the fuel cell. In this case, nickel oxide powder having a relatively large particle size may be mixed with the fine powder in order to secure the mechanical strength of the fuel electrode obtained by the sintering molding and to include voids through which the gas flows. There are many.

The mechanical strength of the fuel electrode obtained by the above sintering formation and the amount of voids included are generally in a trade-off relationship, and both of them improve the power generation characteristics and life of the cell stack of the solid oxide fuel cell. It becomes an important requirement in. Further, in solid oxide fuel cells and the like, it is required to reduce the grade of impurity elements contained in the nickel oxide powder as the raw material. Among the impurity elements, chlorine and sulfur may react with silver used for the electrodes to cause electrode deterioration and corrode the firing furnace, so it is desirable to reduce them as much as possible.

For example, in Patent Document 1, nickel sulfate as a raw material is charged into a kiln or the like and roasted in an oxidizing atmosphere at a roasting temperature of 950 to 1000 ° C. A method of producing nickel oxide powder by heat treatment in the second stage roasting for roasting has been proposed. According to the production method of Patent Document 1, it is described that nickel oxide fine powder having an average particle size controlled and a sulfur grade of 50 mass ppm or less can be obtained.

Further, Patent Document 2 describes a method for producing nickel oxide powder in which anhydrous nickel sulfate as a raw material is charged into a horizontal rotary production furnace and roasted at a maximum temperature of 900 to 1250 ° C. while forcibly introducing air. Has been proposed. It is described that the production method of Patent Document 2 can also reduce the impurity grade, and for example, a nickel oxide powder having a sulfur grade of 500 mass ppm or less can be obtained.

Japanese Unexamined Patent Publication No. 2001-032002 Japanese Unexamined Patent Publication No. 2004-189530

According to the production method of Patent Document 1 described above, nickel oxide powder having a low impurity grade can be obtained, but the production cost is high because heat treatment is required twice. Further, in any of the manufacturing methods of Patent Documents 1 and 2, since a large amount of exhaust gas containing SOx is generated during heat treatment, there is a problem that expensive abatement equipment is required for the abatement treatment. ing.

As a method for producing nickel oxide powder that suppresses the generation of exhaust gas containing SO _x , an aqueous solution containing a nickel salt such as nickel sulfate or nickel chloride is neutralized with an alkali such as an aqueous solution of sodium hydroxide to form nickel hydroxide particles. A method of crystallizing and roasting this has been proposed. In this manufacturing method, since the generation of exhaust gas containing substances derived from anionic components is small when the nickel hydroxide particles are roasted, the exhaust gas treatment equipment is unnecessary or a simple exhaust gas treatment equipment is sufficient, and the production is performed accordingly. It will be possible to keep costs down.

For example, nickel oxide powder is mixed with iron oxide or zinc oxide and sintered for use in ferrite parts as described above, and is mixed with solid electrolyte for use as an electrode material for solid oxide fuel cells. Used. In order to obtain desired properties as an electrode material for ferrite parts and solid oxide fuel cells during these mixing, a large particle size nickel oxide powder having a specific surface area adjusted within a predetermined range is required. I was sometimes asked.

The present invention has been made in view of the above circumstances, and is a nickel oxide powder in which the particle size and the specific surface area are controlled within a desired range, which is suitable as an electronic component material or an electrode material for a solid oxide fuel cell. And its manufacturing method.

In order to achieve the above object, the inventors have produced nickel oxide powder by roasting nickel hydroxide obtained by neutralizing a nickel salt aqueous solution as a production method that does not generate a large amount of exhaust gas that requires abatement treatment during heat treatment. As a result of intensive research focusing on the manufacturing method, nickel hydroxide obtained after neutralizing the nickel sulfate aqueous solution as a raw material with a specific alkaline aqueous solution to obtain particles containing nickel hydroxide as a main component. It has been found that nickel oxide powder having a particle size and a specific surface area within a specific range can be obtained by heat-treating the particles containing the above as a main component under predetermined conditions, and the present invention has been completed.

That is, the method for producing nickel oxide powder according to the present invention is a method for producing nickel oxide powder having the form of secondary particles in which primary particles are aggregated, and is a method for producing nickel oxide powder as an alkaline component with respect to an aqueous nickel sulfate solution. A crystallization step of neutralizing with an alkaline aqueous solution containing a hydroxide to crystallize the particles containing nickel hydroxide as a main component, and the particles containing nickel hydroxide as a main component at 900 ° C. in a non-reducing atmosphere. It is characterized by including a heat treatment step of producing nickel oxide powder by heat treatment at an atmospheric temperature of less than 1100 ° C.

Further, the nickel oxide powder according to the present invention is a nickel oxide powder having the form of secondary particles in which primary particles are aggregated, and the specific surface area measured by the BET method is 0.1 m ² / g or more and 1.0 m ² /. It is characterized in that it is less than g and the average particle size D50 of the secondary particles measured by a laser diffraction / scattering method is 5.0 μm or more and 20 μm or less.

According to the present invention, it is possible to easily obtain nickel oxide powder having a particle size and a specific surface area controlled within a specific range, which is suitable as an electronic component material such as a ferrite component or an electrode material for a solid oxide fuel cell. it can.

It is an SEM photograph of the nickel oxide powder of the sample 1 produced in the Example.

Hereinafter, a method for producing nickel oxide powder according to the embodiment of the present invention will be described. The method for producing nickel oxide powder according to the embodiment of the present invention is to neutralize a nickel salt aqueous solution with an alkaline aqueous solution and refer to particles containing nickel hydroxide as a main component (hereinafter, unless otherwise specified, nickel hydroxide particles. There is a crystallization step to obtain nickel oxide powder, and a heat treatment step to produce nickel oxide powder by heat-treating the obtained nickel hydroxide-based particles in a non-reducing atmosphere at an atmospheric temperature of 900 ° C. or higher and lower than 1100 ° C. It consists of.

The nickel oxide powder according to the embodiment of the present invention produced by such a production method has the form of secondary particles in which primary particles are aggregated, and the average particle size D50 of the secondary particles measured by a laser diffraction / scattering method. (The particle size that is 50% by volume integration of the amount of particles in the particle size distribution curve) is within the range of 5.0 μm or more and 20 μm or less, and the specific surface area measured by the BET method is 0.1 m ² / g or more and 1.0 m ² It is within the range of less than / g. In the present invention, "A or more and B or less" may be expressed as "A to B".

Since the reactivity of the nickel oxide powder is higher as it is finer as described above, it is desirable that the nickel oxide powder having the form of secondary particles has the primary particles having a relatively finely adjusted particle size aggregated. .. However, in the secondary particles in which fine primary particles are aggregated, when the contact area between the primary particles increases due to an increase in the heat treatment temperature, the above-mentioned reactivity decreases and generally the primary particles When the area of the contact portion between the two increases, the binding force of the contact portion is strengthened, so that the crushability may be lowered when crushing in the subsequent step if necessary. Therefore, in the nickel oxide powder having the form of secondary particles in which the primary particles are aggregated, in addition to the average particle size of the secondary particles, the specific surface area that can be expressed as an index of reactivity is the above-mentioned predetermined value. It is important to be adjusted within the range.

In the above crystallization step, it is important to use nickel sulfate as the raw material nickel salt aqueous solution. By using nickel sulfate, it is possible to obtain fine primary particles of nickel oxide even if the heat treatment temperature is raised in the heat treatment step of the subsequent step as compared with the case of using other nickel salts, and as a result, sulfur It is possible to produce nickel oxide powder in which fine primary particles having controlled impurity grades such as the above are aggregated.

By using nickel sulfate as a raw material in this way, the present inventors can suppress the influence of the heat treatment temperature on the particle size of the primary particles, and as a result, the particle size of the primary particles made of nickel oxide is fine. It was found that the sulfur grade can be controlled while maintaining the temperature. Furthermore, they have found that by controlling the heat treatment temperature within a predetermined range, the degree of aggregation due to sintering of the primary particles can be controlled, and the particle size and specific surface area of the secondary particles can be adjusted within a specific range. Moreover, since nickel chloride does not have to be used as a raw material in the above crystallization step, it is possible to obtain nickel oxide powder in which primary particles substantially containing no chlorine other than impurities inevitably contained in the raw material are aggregated. ..

The clear reason why fine nickel oxide primary particles can be obtained by the above method is unknown, but since the decomposition temperature of nickel sulfate is as high as 848 ° C., the particles containing nickel hydroxide crystallized by neutralization as the main component. It is considered that the sulfur component derived from nickel sulfate is involved as a sulfate on the surface or interface of the nickel oxide powder, which suppresses the sintering of nickel oxide powder to a high temperature. Further, if the heat treatment is performed at a temperature higher than the decomposition temperature of the nickel sulfate, the sulfur component is decomposed or volatilized, so that the sulfur grade of the nickel oxide powder after the heat treatment can be reduced.

In the heat treatment step after the crystallization step, the hydroxyl groups in the nickel hydroxide particles are desorbed to produce nickel oxide powder. At that time, by appropriately setting the heat treatment temperature, it is possible to control the particle size, specific surface area, and sulfur grade of the secondary particles in which the primary particle group is aggregated by sintering. Specifically, the atmospheric temperature of the particles containing nickel hydroxide as a main component during heat treatment is controlled to 900 ° C. or higher and lower than 1100 ° C., preferably 950 ° C. or higher and 1050 ° C. or lower. As a result, the sulfur grade of the nickel oxide powder is 100 mass ppm or less, the average particle size (D50) measured by the laser diffraction / scattering method is 5.0 μm or more and 20 μm or less, and the specific surface area measured by the BET method is 0.1 m ² /. It can be controlled to be greater than or equal to g and less than 1.0 m ² / g. Hereinafter, the method for producing nickel oxide powder according to the embodiment of the present invention will be described in detail for each step.

1. Crystallization step First, in the crystallization step, the nickel sulfate aqueous solution as a raw material is neutralized with an alkaline aqueous solution to generate particles containing nickel hydroxide as a main component. In the nickel sulfate aqueous solution used as this raw material, since the finally obtained nickel oxide powder is used as an electrode for electronic parts or solid oxide fuel cells, impurities contained in the raw material are contained in order to prevent corrosion thereof. It is desirable that the total of is less than 100 mass ppm.

The nickel concentration in the nickel sulfate aqueous solution is preferably 50 to 150 g / L in consideration of productivity. If this concentration is less than 50 g / L, the productivity will deteriorate. On the contrary, when this concentration exceeds 150 g / L, the anion concentration in the nickel sulfate aqueous solution becomes too high, and the sulfur grade in the produced nickel hydroxide becomes high, so that the impurities in the finally obtained nickel oxide powder are high. The quality may not be sufficiently low.

On the other hand, as the alkaline aqueous solution for neutralization, one containing an alkali metal hydroxide as an alkaline component is used in consideration of the amount of nickel remaining in the reaction solution. Sodium hydroxide and potassium hydroxide are preferable as the hydroxide of the alkali metal, and sodium hydroxide is more preferable in consideration of cost. Alkali may be added to the nickel sulfate solution in a solid state, but in the production method of the embodiment of the present invention, it is added in the form of an aqueous solution for ease of handling.

In the production method of the embodiment of the present invention, it is preferable that the above-mentioned alkaline aqueous solution for neutralization contains sodium carbonate as an alkaline component. As described above, since sodium carbonate is contained in the alkaline aqueous solution, the details are unknown, but the amount of sulfur components and alkali metal components such as sodium that are involved in the interface and surface of the nickel hydroxide particles generated by crystallization can be determined. Can be reduced. That is, when sodium carbonate is contained in a small amount as an alkaline component, the sulfur grade in the nickel hydroxide particles increases once, but as the mixing ratio of sodium carbonate increases, the sulfur grade decreases. On the other hand, the grade of alkali metals such as sodium in nickel hydroxide particles can be lowered by containing a small amount of sodium carbonate, but if the mixing ratio of sodium carbonate is too high, on the contrary, the quality of alkali metals such as sodium The dignity is high.

Therefore, in the production method of the embodiment of the present invention, when sodium carbonate is contained in the alkaline aqueous solution, the concentration of sodium carbonate in the alkaline aqueous solution is set to 0.4 to 0.8 mol / L. When the sodium carbonate concentration is less than 0.4 mol / L, the sulfur grade of the nickel hydroxide particles may be higher than that of the nickel hydroxide particles neutralized without containing sodium carbonate, and conversely, 0.8 mol. If it exceeds / L, the grade of the alkali metal such as sodium of the nickel hydroxide particles may be higher than that of the nickel hydroxide particles neutralized without containing sodium carbonate. Alkali metals such as sodium form a sulfate having a high melting point in the heat treatment step described later, which acts in a direction of inhibiting the decomposition and volatilization of the sulfur component. Therefore, if the alkali metal quality of the nickel hydroxide particles is high, The sulfur grade of the nickel oxide fine powder tends to be high.

The nickel hydroxide particles obtained by crystallization of the neutralization reaction can have a sulfur grade of 2% by mass or less. The lower limit of the sulfur grade is not particularly limited, but can be 0.5% by mass or more when the concentration of sodium carbonate in the alkaline aqueous solution is in the range of 0.4 mol / L or more and less than 0.8 mol / L. The sulfur grade can be preferably 1.0 to 2.0% by mass, and more preferably 1.2 to 1.8% by mass by appropriately adjusting the sodium carbonate concentration and the like. Further, in the above nickel hydroxide particles, the grade of total alkali metal such as sodium is 10 mass ppm or less, and by using nickel sulfate as a raw material, the chlorine grade is 50 mass ppm or less. The total alkali metal grade is the total grade of alkali metal elements such as sodium and potassium.

The nickel hydroxide particles obtained by crystallization of the neutralization reaction can further have a D90 of 60 μm or less measured by a laser diffraction / scattering method. The D90 of the nickel hydroxide particles can be preferably 50 μm or less by appropriately adjusting the heat treatment temperature and the like described above. The lower limit of D90 of the nickel hydroxide particles is not particularly limited, but usually 5 μm is the lower limit in the crystallization by the neutralization reaction.

In order to obtain nickel hydroxide particles having uniform characteristics with high productivity, a nickel sulfate aqueous solution and an alkaline aqueous solution as a nickel salt aqueous solution prepared in advance are added to a solution that is sufficiently stirred in the reaction vessel. The continuous crystallization method of adding by the so-called double jet method is effective. That is, instead of putting a predetermined amount of either a nickel salt aqueous solution or an alkaline aqueous solution in the reaction vessel and adding the other to neutralize the reaction vessel, the mixture is sufficiently stirred in the reaction vessel in advance. It is preferable to add the nickel salt aqueous solution and the alkaline aqueous solution to the liquid to be turbulent in the reaction layer simultaneously and continuously while continuing this stirring. As a result, the neutralization reaction can be carried out in a sufficiently mixed reaction solution, so that efficient crystallization is possible and productivity can be improved. In this case, it is preferable to use a liquid to be put in the reaction vessel in advance by adding the above alkaline component to pure water and adjusting the pH to a predetermined value.

At the time of the neutralization reaction, it is preferable to adjust the pH of the reaction solution within the range of 8.3 to 9.0, and it is particularly preferable to keep the pH substantially constant within this range. When this pH is lower than 8.3, the concentration of anionic components such as sulfate ions remaining in the nickel hydroxide particles increases, which becomes a large amount of SOx during the heat treatment step in the subsequent step, and the furnace body. It is not preferable because it damages. On the contrary, when the pH is higher than 9.0, the obtained nickel hydroxide particles become too fine, which may make the subsequent filtration difficult. In addition, sintering proceeds too much in the heat treatment step of the subsequent step, and it may be difficult to obtain fine nickel oxide powder.

At pH 9.0 or lower, which is the preferred neutralization reaction condition described above, a small amount of nickel component may remain in the aqueous solution after the neutralization reaction. In this case, by raising the pH of the aqueous solution to about 10 after crystallization by the above neutralization, the concentration of nickel components in the filtrate discharged during the subsequent filtration, which will be described later, can be reduced. At the time of the above neutralization reaction, it is preferable to control the fluctuation range of pH so as to be as constant as possible within 0.2 in absolute value centering on the set value. If the fluctuation range of pH becomes larger than this, the impurity grade in the nickel hydroxide particles may increase, or the specific surface area of the nickel oxide powder produced in the heat treatment step of the subsequent step may decrease.

The liquid temperature during the neutralization reaction is not particularly limited and may be normal temperature, which is usually performed in the neutralization reaction, but the liquid temperature is preferably 50 to 70 ° C. in order to sufficiently grow the nickel hydroxide particles. .. By sufficiently growing the nickel hydroxide particles in this way, it is possible to prevent excessive inclusion of the sulfur component in the nickel hydroxide particles. In addition, it is possible to suppress the entrainment of impurities such as sodium in the nickel hydroxide particles, and it is possible to reduce the impurity grade of the finally obtained nickel oxide powder.

If the liquid temperature is less than 50 ° C., the growth of nickel hydroxide particles may be insufficient, and sulfur components and impurities may be more involved in nickel hydroxide. On the contrary, when this liquid temperature exceeds 70 ° C., the amount of evaporation of water increases, the concentration of impurities such as sulfur components in the aqueous solution increases, and the grade of impurities such as sulfur components in the generated nickel hydroxide particles becomes high. It may be expensive.

After the completion of the neutralization reaction, the slurry containing the nickel hydroxide particles produced by crystallization is filtered, and the nickel hydroxide particles are recovered in the form of a filtered cake. It is preferable to wash the recovered filtered cake before processing it in the heat treatment step of the next step. In this cleaning, so-called repulp cleaning is preferable, in which a cleaning liquid is added to form a slurry, the mixture is stirred and washed, and then the liquid is removed by solid-liquid separation such as filtration. Water is preferable as the cleaning liquid used for this repulp cleaning, and pure water is particularly preferable.

The mixing ratio of nickel hydroxide and water during the above-mentioned repulp washing is not particularly limited, and the mixing ratio is such that anions contained in the nickel salt, particularly sulfate ions and alkali metal components such as sodium can be sufficiently removed. Just do it. Specifically, in order to sufficiently reduce impurities such as residual anions and alkali metals and to disperse nickel hydroxide particles satisfactorily, it is preferable to mix 1 L of the cleaning liquid with 50 to 150 g of nickel hydroxide. It is more preferable to mix 1 L of the cleaning liquid with about 100 g of nickel hydroxide.

The cleaning time for repulp cleaning may be appropriately determined according to cleaning conditions such as the mixing ratio with the above cleaning liquid and the liquid temperature during cleaning so that residual impurities after cleaning are sufficiently reduced. If impurities such as anions and alkali metals are not sufficiently reduced by one repulp washing, it is preferable to repeat the repulp washing a plurality of times. In particular, since alkali metals such as sodium can hardly be removed in the heat treatment step of the next step, it is preferable to sufficiently remove them by this repulp washing. For example, impurities can be sufficiently removed by using pure water as the cleaning liquid, measuring the conductivity of the cleaning liquid after the repulp cleaning, and repeating the repulp cleaning until the conductivity becomes equal to or less than a predetermined conductivity. After filtering in the repulp washing, it is preferable to dry it if necessary.

2. Heat treatment step In the heat treatment step, nickel oxide powder is produced by heat-treating the nickel hydroxide particles obtained in the above crystallization step in a non-reducing atmosphere. In this heat treatment, the ambient temperature is set within a temperature range of 900 ° C. or higher and lower than 1100 ° C., preferably within a temperature range of 950 ° C. or higher and 1050 ° C. or lower, and more preferably within a temperature range of 1000 ° C. or higher and 1050 ° C. or lower. In the present invention, the atmospheric temperature at the time of this heat treatment may be simply referred to as the heat treatment temperature.

Thus, by the ambient temperature during the heat treatment within a range of less than 900 ° C. or higher 1100 ° C., a specific surface area while suppressing the sulfur grade 0.1 m ² / g or more 1.0m in the range of less than ² / g Can be controlled. That is, as described above, since the heat treatment is performed at a temperature exceeding 848 ° C., which is the decomposition temperature of nickel sulfate, in this heat treatment step, the primary particle group having suppressed sulfur grade is aggregated by sintering. A morphological nickel oxide powder can be produced.

The higher the atmospheric temperature during the heat treatment, the more the sintering of the primary particles progresses and the secondary particles become denser, the mechanical strength of the particles improves, but the specific surface area decreases. In addition, the average particle size (D50) of the secondary particles tends to decrease as the sintering of the primary particles progresses. The method for producing nickel oxide powder according to the embodiment of the present invention does not require crushing the nickel oxide powder produced by this heat treatment step.

When the heat treatment temperature is 1100 ° C. or higher, the decomposition of the sulfur component proceeds too much, the above-mentioned effect of suppressing sintering becomes insufficient, and the promotion of sintering by temperature becomes remarkable. As a result, the bonding force of the sintering of the primary particles of nickel oxide obtained by the heat treatment is increased, and not only the specific surface area can be less than 0.1 m ² / g, but also the oxidation of the obtained secondary particles in the form of the secondary particles. When nickel powder is mixed with other materials and used as an electrode material for ferrite parts or solid oxide fuel cells, it may not be possible to adjust their characteristics.

On the contrary, when the heat treatment temperature is less than 900 ° C., the decomposition and volatilization of sulfur components such as sulfates are insufficient, and the sulfur components remain excessively in the nickel hydroxide particles, so that the oxidation generated by the heat treatment The sulfur grade of nickel powder may exceed 100 mass ppm. Further, the specific surface area of the obtained nickel oxide powder becomes higher than 1.0 m ² / g, or the nickel oxide powder is easily crushed when mixed with other materials, so that ferrite parts and solid oxides are oxidized. It may be difficult to adjust the characteristics of the electrode material of the solid fuel cell.

The atmosphere at the time of the above heat treatment is not particularly limited as long as it is a non-reducing atmosphere, but it is preferably an air atmosphere in consideration of economy. Further, since water vapor is generated by desorption of hydroxyl groups during the heat treatment, it is preferable to carry out the heat treatment in an air flow having a sufficient flow velocity so that the water vapor can be efficiently discharged. A general roasting furnace can be used as an apparatus for performing heat treatment in such an air flow. The heat treatment time can be appropriately set according to the heat treatment conditions such as the heat treatment temperature and the treatment amount. At that time, it is preferable to set the specific surface area of the nickel oxide powder finally obtained to be 0.1 m ² / g or more and less than 1.0 m ² / g.

In the method for producing the nickel oxide fine powder according to the embodiment of the present invention described above, since the nickel hydroxide produced by the wet method is heat-treated, almost no exhaust gas containing a large amount of SOx is generated. Therefore, there is no need for expensive exclusion equipment for abatement treatment. Further, since the number of heat treatments is only one, the manufacturing cost can be kept low.

3. Physical properties of nickel oxide powder Since the nickel oxide powder of the embodiment of the present invention produced by the above-mentioned production method is not crushed after heat treatment, the primary particles are aggregated by sintering to form secondary particles. It has a specific surface area of 0.1 m ² / g or more and less than 1.0 m ² / g. Since the nickel oxide powder has the form of secondary particles and has a specific surface area in this range, it can be satisfactorily mixed with other materials as described above to form ferrite parts or solid oxides. The characteristics of the electrode material of the fuel cell can be adjusted. Further, the nickel oxide powder according to the embodiment of the present invention can have a D50 of 5.0 μm or more and 20 μm or less measured by a laser diffraction / scattering method, and is more suitable 7.0 by appropriately adjusting the heat treatment temperature and the like described above. It can be ~ 15 μm.

Further, the nickel oxide powder of the embodiment of the present invention does not include a step of mixing chlorine other than being mixed as an unavoidable impurity from the raw material, so that the chlorine grade is extremely low. In addition, the sulfur grade is controlled and the alkali metal grade represented by sodium is low. Specifically, the sulfur grade is 100 mass ppm or less, preferably 50 mass ppm or less, the chlorine grade is 50 mass ppm or less, preferably 20 mass ppm or less, and the sodium grade is 20 mass ppm or less, preferably 20 mass ppm or less. Has a total alkali metal grade of 20 mass ppm or less.

Since the nickel oxide powder of the embodiment of the present invention has the above physical properties and impurities, it is suitable as a material for electronic parts, particularly for ferrite parts, and a material for electrodes of solid oxide fuel cells. As a material for electrodes of solid oxide fuel cells, it is said that the sulfur grade is preferably 100 mass ppm or less. Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

Nickel hydroxide particles are generated by a continuous crystallization method in which a nickel sulfate aqueous solution and an alkaline aqueous solution are added to an alkaline aqueous solution previously placed in a reaction vessel by a double jet method, and then the obtained nickel hydroxide particles are non-reduced. Heat treatment was performed in a sexual atmosphere to produce nickel oxide powder having the form of large-sized secondary particles in which the primary particles were aggregated. Specifically, first, 4 L of an alkaline aqueous solution adjusted to pH 8.5 by adding sodium carbonate and sodium hydroxide to pure water is filled in a reaction tank having an effective capacity of 4 L with a stirrer having a baffle plate and an overflow port. , Stirred well. The amount of sodium carbonate added to the alkaline aqueous solution was adjusted so that the sodium carbonate concentration was 0.4 mol / L.

Next, nickel sulfate was dissolved in pure water to prepare a nickel sulfate aqueous solution having a nickel concentration of 120 g / L. Further, an alkaline aqueous solution for addition was prepared by dissolving sodium carbonate and sodium hydroxide as alkaline components in pure water prepared separately. The concentration of sodium carbonate in this alkaline aqueous solution for addition was 0.4 mol / L, which was the same as the concentration of sodium carbonate in the above-mentioned alkaline aqueous solution first filled in the reaction vessel.

The above nickel sulfate aqueous solution for addition and the alkaline aqueous solution for addition were added simultaneously and continuously to the alkaline aqueous solution stirred in the reaction vessel to prepare a reaction solution. At that time, the pH of the reaction solution was adjusted to be centered on 8.5 and the fluctuation range was adjusted to be within 0.2 in absolute value. Nickel hydroxide particles were continuously generated by this continuous crystallization method.

By supplying the nickel sulfate aqueous solution for addition to the reaction tank at a flow rate of 5 mL / min, the residence time of the generated nickel hydroxide particles, that is, the nickel hydroxide particles discharged by overflowing the effective capacity of the reaction tank can be obtained. The value divided by the extraction flow rate of the contained slurry was adjusted to about 3 hours. At this time, the nickel sulfate aqueous solution for addition and the alkaline aqueous solution for addition are both in a turbulent state at the two mixed portions of the reaction liquid in the reaction tank, which is the supply destination from the two supply nozzles. I was able to visually confirm that it was. Further, in this reaction vessel, the liquid temperature during the neutralization reaction was adjusted to 60 ° C., and the stirring blade of the stirrer was rotated at 700 rpm for stirring.

A slurry containing nickel hydroxide particles discharged from the overflow port of the reaction vessel was collected, introduced into a nutche covered with filter paper, and filtered to obtain a filtered cake. The slurry prepared by adding pure water to the filtered cake was held for 30 minutes with stirring, and then the repulp washing, which was filtered with Nutche in the same manner as above, was repeated 10 times. The filtered cake containing the nickel hydroxide particles after washing was charged into a blower dryer and dried in an air atmosphere at 130 ° C. for 24 hours to obtain nickel hydroxide particles.

The obtained nickel hydroxide particles were placed in an atmospheric firing furnace and heat-treated in the atmosphere at an atmospheric temperature of 995 ° C. for 7 hours. In this way, the nickel oxide powder of Sample 1 was obtained. When the nickel oxide powder of the obtained sample 1 was observed with a scanning electron microscope (SEM), it was confirmed that the primary particles had the form of secondary particles aggregated by sintering as shown in FIG. ..

Further, nickel oxide powders of Samples 2 and 3 were produced in the same manner as in Sample 1 except that the atmospheric temperature at the time of heat treatment was changed to 1030 ° C. and 985 ° C., respectively. When the nickel oxide powders of Samples 2 and 3 were observed by SEM, it was confirmed that the primary particles all had the form of secondary particles aggregated by sintering.

For a comparative example, nickel oxide fine powders of Samples 4 and 5 were produced in the same manner as in Sample 1 except that the atmospheric temperature during the heat treatment was changed to 1130 ° C and 890 ° C, respectively, instead of 995 ° C. When the nickel oxide powders of Samples 4 and 5 were observed by SEM, it was confirmed that the primary particles all had the form of secondary particles aggregated by sintering.

The chlorine grade, sulfur grade and sodium grade were analyzed for the nickel oxide powders of the above samples 1 to 5. For chlorine grade, each sample is dissolved in nitrate under microwave irradiation in a closed container that can suppress the volatilization of chlorine, silver nitrate is added to precipitate silver chloride, and the chlorine in the obtained precipitate is fluorescent X-ray. The analysis was performed by evaluation by the calibration curve method using a quantitative analyzer (Magic manufactured by PANalytical). The sulfur grade was analyzed using an ICP emission spectrophotometer (SPS-3000 manufactured by Seiko Corporation) after dissolving each sample in nitric acid. The sodium grade was analyzed by dissolving each sample in nitric acid and then evaluating it using an atomic absorption spectrophotometer (Z-2300 manufactured by Hitachi High-Tech).

Further, the average particle size and the specific surface area of the nickel oxide powders of Samples 1 to 5 were measured. The average particle size was determined as the average particle size D50 at a volume integration of 50% from the particle size distribution obtained by measuring by the laser diffraction / scattering method. The specific surface area was determined by the BET method by adsorbing nitrogen gas. The sulfur (S) grade, chlorine (Cl) grade, sodium (Na) grade, specific surface area, and average particle size D50 of the nickel oxide powders of these samples 1 to 5 are shown in Table 1 below.

As can be seen from Table 1 above, the nickel oxide powders of Samples 1 to 3 produced by the production method satisfying the requirements of the present invention all have a specific surface area in the range of 0.1 m ² / g or more and less than 1.0 m ² / g. The average particle size D50 was in the range of 5.0 μm or more and 20 μm or less. On the other hand, the nickel oxide powders of Samples 4 to 5 produced by the production method not satisfying the requirements of the present invention had an average particle size D50 within the range of 5.0 μm or more and 20 μm or less, but all had a specific surface area of 0. It was out of the range of .1 m ² / g or more and less than 1.0 m ² / g. Except for the sulfur grade of 20 mass of sample 3 and the sulfur grade of 70 mass ppm of sample 5, the nickel oxide powders of samples 1 to 5 had an impurity grade of less than 10 mass ppm.

Claims (5)

A method for producing nickel oxide powder having the form of secondary particles in which primary particles are aggregated. Nickel sulfate aqueous solution is neutralized with an alkaline aqueous solution containing an alkali metal hydroxide as an alkaline component to obtain water. A crystallization step of crystallizing particles containing nickel oxide as a main component and a heat treatment of the particles containing nickel hydroxide as a main component in a non-reducing atmosphere at an atmospheric temperature of 900 ° C. or higher and lower than 1100 ° C. A method for producing nickel oxide powder, which comprises a heat treatment step for producing. The method for producing nickel oxide powder according to claim 1, wherein the alkaline aqueous solution contains sodium carbonate in an amount of 0.4 to 0.8 mol / L. The method for producing nickel oxide powder according to claim 2, wherein the alkali metal hydroxide is sodium hydroxide. A nickel oxide powder in the form of secondary particles formed by aggregation of primary particles, the specific surface area measured by the BET method is less than 0.1 m 2 / ^g or more 1.0 m 2 / ^g, a laser diffraction scattering method A nickel oxide powder characterized in that the measured average particle size D50 of the secondary particles is 5.0 μm or more and 20 μm or less. The nickel oxide powder according to claim 4, wherein the sulfur grade is 100 mass ppm or less, the chlorine grade is 50 mass ppm or less, and the total alkali metal grade is 20 mass ppm or less.