JP2015160780A - Method of producing nickel oxide, and nickel oxide fine powder obtainable therefrom - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a method of producing nickel oxide fine powder that has a low impurity content and is particularly suitable as a material used for producing a solid oxide fuel cell having a low sulfur concentration; and nickel oxide fine powder.SOLUTION: A method of producing nickel oxide includes obtaining nickel fine powder by subjecting a metal nickel pellet group to electric discharge in ultrapure water under an AC voltage application, and roasting the nickel fine powder in an oxidizing atmosphere. The method produces nickel oxide fine powder having a sulfur content of 10 mass ppm or less, in which a value of D50 measured by laser scattering method is 0.5 μm or less.

Description

  The present invention relates to a method for producing nickel oxide, and more specifically, a nickel powder with extremely few impurities is generated by spark discharge of metallic nickel pellets in ultrapure water, and the nickel powder is highly purified by firing and pulverization. The present invention relates to a production method for obtaining fine nickel oxide powder and the fine nickel oxide powder.

  Solid oxide fuel cells are expected as a new power generation system from both environmental and energy perspectives. As a new power generation system that replaces nuclear power generation, a combined power generation system that combines thermal power generation and fuel cells is being put to practical use. ing. Nickel oxide fine powder is used as a fuel electrode material of the solid oxide fuel cell, and demand for nickel oxide fine powder is expected to increase further in the future. The nickel oxide fine powder used for this purpose is required to have a high purity because of problems such as durability.

  Many methods for producing nickel oxide have been proposed. For example, nickel oxide, nickel sulfate, nickel chloride, or nickel nitrate can be obtained by firing in an oxidizing atmosphere.

As a method for producing nickel hydroxide, it is manufactured by adding sodium hydroxide or the like to a solution containing a nickel salt such as nickel sulfate, nickel chloride or nickel nitrate to make it alkaline (for example, patent document). 1). According to Patent Document 1, ammonia is added to an aqueous solution containing a nickel salt to form a nickel-ammonium complex salt, and a caustic alkali is allowed to act on this to precipitate nickel hydroxide.

In such a method for obtaining nickel hydroxide, the principle is simple, but many steps are required for implementation, and sodium hydroxide is used to make the reaction solution alkaline. Since it becomes a residual impurity, not only a large amount of washing waste liquid is generated in the washing process, but also the waste liquid containing sodium nitrate or sulfate after the reaction needs to be treated.

  In addition, impurities remain even when nickel sulfate, nickel chloride, nickel nitrate, or the like is baked in an oxidizing atmosphere.

  For example, Patent Document 2 proposes a method of roasting nickel sulfate at a maximum temperature of 900 to 1200 ° C. while forcibly introducing air using a horizontal rotary manufacturing furnace. According to this method, fine nickel oxide powder having a sulfur quality of 500 mass ppm or less is obtained.

  On the other hand, there is also a method for producing nickel hydroxide by electrolysis from metallic nickel other than the method for producing nickel hydroxide by chemical precipitation as described above.

  For example, Patent Document 3 proposes a method of precipitating spherical nickel hydroxide by dissolving a nickel electrode at an anode. This method does not contain sulfur as an impurity, but electrolysis is carried out at a high pH value and temperature, and the pH is adjusted with an alkali metal hydroxide such as sodium hydroxide. Therefore, nickel hydroxide produced by this method is roasted. There is also concern that sodium may remain in the nickel oxide obtained.

Patent Document 4 describes a method for producing nickel fine powder by a vapor phase method. According to Patent Document 4, nickel chloride as a raw material is put in a crucible, heated and evaporated in an argon gas of 10 liters / minute so that the concentration (partial pressure) is 8.0 × 10 ⁻² , and the steam is downstream of the crucible. The nickel powder can be obtained by transporting to a reaction part set at 1050 ° C. (1323 K) located at, and contacting and mixing with hydrogen. However, even in this method, the nickel purity is 99.5% or more, and there is a concern that chlorine remains in particular.

On the other hand, if it is not fine powder, high-purity nickel can be easily produced by a method such as electrolytic purification. According to Patent Document 5, a nickel sulfate solution is used as an electrolytic solution, and a hydrohalic acid is added to the electrolytic solution for electrolytic purification, which is characterized by 5N (99.999 mass%) or more in a high purity nickel production method. It is said that the nickel can be obtained. However, the obtained nickel is not a fine powder, and nickel oxide powder cannot be obtained by roasting. Since nickel metal has ductility and malleability, fine powder cannot be obtained by a pulverization process applying general mechanical pressure.

JP-A-56-143671 JP 2004-189530 A Special Table 2002-544382 JP-A-8-246001 JP 2002-285372 A

  The methods of Patent Documents 1 to 4 have a problem that some impurities remain even if nickel oxide fine powder is produced. Moreover, although there exists a method of obtaining high purity nickel like patent document 5, a high purity fine powder cannot be obtained. The problem to be solved by the present invention is to provide a method for producing fine nickel oxide powder and a fine nickel oxide powder suitable as materials used in the production of a solid oxide fuel cell having a low impurity content and particularly a low sulfur concentration. For the purpose.

As a result of intensive studies to achieve the above-mentioned object, the present inventors have made nickel by using high-purity metallic nickel having a size of 1 mm to 3 cm as a raw material and discharging it in pure water by applying an alternating voltage. The present inventors have found that high-purity nickel oxide can be obtained by obtaining fine powder and baking it in an oxidizing atmosphere.

  That is, the nickel oxide fine powder manufacturing method according to the first aspect of the present invention uses a high-purity metallic nickel pellet as a starting material, and discharges between nickel pellets by applying an alternating voltage in ultrapure water. This is a method for producing nickel oxide fine powder comprising a step of obtaining nickel fine powder and a step of firing the metal nickel fine powder at 600 ° C. or more and less than 950 ° C. in an oxidizing atmosphere.

  According to a second aspect of the present invention, the nickel oxide production method according to claim 1, wherein the nickel nickel pellet has a size of 1 mm to 3 cm and a high-purity nickel having a sulfur concentration of 10 mass ppm or less as a starting material. . Is provided.

  According to a third aspect of the present invention, there is provided the nickel oxide manufacturing method according to claim 1 or 2, wherein the AC power source used for discharging is a voltage of 10 kV to 40 kV and a frequency of 200 kHz to 600 kHz. Is done.

  Moreover, according to 4th invention of this invention, the manufacturing method of nickel oxide including the process of crushing nickel oxide further after the baking process of Claim 1 is provided.

According to the fifth aspect of the present invention, the sulfur content obtained in any one of the first to fourth aspects of the present invention is 10 ppm by mass or less, and the value of D50 measured by the laser scattering method is 0. There is provided a nickel oxide fine powder characterized by being not more than 0.5 μm.

  According to the present invention, high-purity nickel oxide fine powder can be obtained using high-purity nickel metal as a starting material. Since impurities are not mixed in the process, the purity can be the same as that of the starting material, and high-purity nickel oxide corresponding to the starting material can be obtained. The nickel oxide fine powder obtained by the present invention can reduce impurities and is suitable as an electrode material for a solid oxide fuel cell.

  In the present invention, the high-purity nickel as a starting material directly affects the purity of the final nickel oxide, so that it is preferable that the purity be as high as possible. As an electrode material of the solid oxide fuel cell, it is preferable that sulfur is not contained as much as possible, and electric nickel or the like can be suitably used. Some of them have a size of about 2 cm at the time of producing electronickel and can be used as they are, but if they are larger than 3 cm, they are processed to a size of 1 mm to 3 cm. If it is smaller than 1 mm, it takes too much cost, and if it is larger than 3 cm, the productivity of nickel particles by discharge becomes worse. More preferably, it is 5 mm to 1.5 cm. If the discharge voltage is lower than 10 kV, the productivity is poor, and if it is higher than 40 kV, the particle diameter becomes large, which is not preferable. If productivity and particle diameter are taken into account, 20 kV to 30 kV is an appropriate discharge voltage range. As with the discharge voltage, the frequency is related to the productivity and the particle size. If the frequency is lower than 200 kHz, the productivity is good, but the particle size becomes too large. If the frequency is higher than 600 kHz, the particle size becomes smaller, but the productivity Decreases. More preferably, it is 300 kHz to 400 kHz.

When the discharge is started, the nickel particles are dispersed in the water. Therefore, the nickel particles are recovered by adding water and overflowing, and if 1 to 3 cm of nickel as a raw material is reintroduced into the water, continuous operation is possible. . Further, if high purity nickel is used as the electrode material to be discharged, there is no path for impurities to be mixed in the production of nickel particles, and nickel particles having the same purity as the raw material nickel can be obtained. If this is fired in an oxidizing atmosphere, nickel oxide powder can be obtained. As a calcination temperature, 600 degreeC or more and less than 950 degreeC are preferable. If it is less than 600 degreeC, it may not be oxidized to the center part of particle | grains, but since particle | grains will sinter and coarsen by 950 degreeC or more, it is unpreferable. The firing time is sufficient for nickel to oxidize, but considering productivity, it is preferably about 1 to 5 hours, and if it exceeds 5 hours, sintering between the nickel oxide particles proceeds. This is not preferable because the particle size becomes coarser than necessary. The oxidizing atmosphere during the baking treatment may be an atmosphere in which metallic nickel is oxidized to nickel oxide, but an air atmosphere that is easy to handle is particularly preferable.

In rare cases, coarse particles may remain in the nickel particles obtained by discharge, and there may be particles that do not oxidize to the inside of nickel by firing in an oxidizing atmosphere and that contain nickel metal. Since it has magnetism, it can be removed with a magnet.

When it is desired to further reduce the nickel oxide particles after removing the coarse particles, the particle size can be adjusted by crushing treatment. Regarding the crushing treatment, a treatment using a medium such as a ball mill or a bead mill is also possible, but in that case, impurities may be mixed from the medium. Therefore, in order to prevent impurities from entering from the media, it is preferable to crush the nickel oxide particles by colliding them without using the media. As a method of crushing particles by colliding them, for example, use of a jet mill such as a nanogrinding mill commercially available from Tokuju Kogakusho Co., Ltd. is preferable. Even in the case of pulverization using a jet mill, dry pulverization is preferably performed because wet pulverization causes agglomeration during drying and deteriorates the particle size distribution.

  The nickel oxide fine powder of the present invention obtained by the above-described process has a sulfur content of 10 mass ppm or less and a D50 measured by a laser scattering method of 0.5 μm or less. In consideration of the handleability of the fine powder, D50 is preferably 0.05 to 0.5 μm, more preferably 0.1 to 0.5 μm.

  Thus, the nickel oxide fine powder of the present invention is extremely suitable as an electrode material for a solid oxide fuel cell because it has a very small impurity content and is composed of fine particles.

  EXAMPLES Hereinafter, although this invention is demonstrated using an Example, this invention is not limited only by an Example.

The following examples illustrate the invention in more detail. In addition, the analysis of sulfur in Examples and Comparative Examples was performed by a carbon sulfur analyzer manufactured by LECO.

Further, the particle diameter of the nickel oxide fine powder was measured by a laser scattering method, and the particle diameter D50 at a volume integration of 50% was determined from the particle size distribution. The specific surface area was determined by the BET method using nitrogen gas adsorption.
Example 1

  For the high-purity nickel starting material, 500 g of handy nickel Handy-E (Sumitomo Metal Mining Co., Ltd .: sulfur content 10 ppm) having a diameter of about 17 mm was introduced into 200 L of pure water, and 20 kV using an electric nickel electrode. And discharging at 300 kHz for 2 hours to obtain a suspension of nickel particles. This suspension was concentrated by decantation to give a 2 L slurry, and after filtering the slurry, 125 g of nickel particles were obtained by vacuum drying. Since the nickel particles were agglomerated, they were crushed with a shaker mixer and then classified with a 212 μm sieve. 5 g of the nickel particles under the sieve were put in an alumina mortar and fired at 900 ° C. for 2 hours in a muffle furnace. At this time, air was introduced into the furnace in an amount of 5 L / min to create an oxidizing atmosphere. Next, the nickel metal incompletely oxidized was removed with a magnet.

The obtained nickel oxide fine powder was pulverized by a nano grinding mill (manufactured by Deoksugaku Kosakusho) under the conditions of a pusher nozzle pressure of 1.0 MPa and a grinding pressure of 0.9 MPa to obtain a nickel oxide fine powder.
(Comparative Example 1)

  A nickel oxide fine powder was obtained in the same manner as in Example 1 except that the starting material was commercially available nickel (diameter 2 mm, length approximately 2 mm, sulfur content 1000 ppm).

The sulfur content of the nickel oxide fine powder obtained in Example 1 and Comparative Example 1, D50 and specific surface area by particle size distribution measurement are shown in Table 1 below.

  As can be seen from the above results, the nickel oxide fine powder of Example 1, which is an example of the present invention, has a low sulfur content of 10 ppm and is suitable as an electrode material for a solid oxide fuel cell.

On the other hand, the nickel oxide fine powders of Comparative Examples 1 and 2 have a high sulfur content and are difficult to use as electrode materials for solid oxide fuel cells.

  According to the present invention, nickel oxide having extremely small impurities and a particle size distribution D50 having an average particle diameter of 0.5 μm or less can be produced. For example, a nickel oxide fine powder suitable for a solid oxide fuel cell can be obtained. It is done.

Claims (5)

Starting with high-purity metallic nickel pellets and applying alternating voltage in ultrapure water to discharge between nickel pellets to obtain fine metallic nickel powder, in an oxidizing atmosphere at 600 ° C. or higher and lower than 950 ° C. A method for producing a nickel oxide fine powder comprising a step of firing the metal nickel fine powder. The method for producing nickel oxide according to claim 1, wherein the starting material is high-purity nickel having a metal nickel pellet size of 1 mm to 3 cm and a sulfur concentration of 10 mass ppm or less. The method for producing nickel oxide according to claim 1, wherein the AC power source used for the discharge is a voltage of 10 kV to 40 kV and a frequency of 200 kHz to 600 kHz. The manufacturing method of nickel oxide including the process of crushing a nickel oxide further after the baking process of Claim 1. A nickel oxide fine powder obtained by the method of claims 1 to 4, having a sulfur content of 10 mass ppm or less and a D50 value of 0.5 µm or less measured by a laser scattering method.