JP6614034B2 - Nickel fine powder, method for producing nickel fine powder, nickel powder organic slurry and nickel paste - Google Patents

Description

  The present invention relates to a nickel fine powder, a method for producing a nickel fine powder, a nickel powder organic slurry, and a nickel paste that can be suitably used as a material for an internal electrode of a multilayer ceramic capacitor, for example.

  In general, nickel ultrafine powder used for an internal electrode of a multilayer ceramic capacitor (hereinafter also referred to as “MLCC”) is generally used by adding a binder such as an organic resin into a paste. The paste is applied in a thin layer on the ceramic green sheet by screen printing or the like. And about the laminated body which laminated | stacked the ceramic green sheet and the internal electrode layer several hundred, a degreasing process, a sintering process, and a baking process are performed, and a laminated ceramic capacitor is manufactured.

  In recent years, MLCCs are required to increase the number of laminated ceramic green sheets with internal electrode layers from several hundred to about 1000 layers in order to achieve a small size and large capacity. For this reason, studies have been made to reduce the thickness of the internal electrode layer from the conventional several micron level to the submicron level, and accordingly, the particle size of nickel powder, which is an electrode material for internal electrodes, has been reduced. ing.

  However, the nickel fine powder tends to suddenly cause thermal shrinkage at a temperature significantly lower than the temperature of the above-described firing step, and this tendency becomes more prominent as the nickel fine powder becomes finer. When the nickel fine powder undergoes thermal shrinkage, during the firing of the internal electrode, due to the difference in thermal shrinkage characteristics between the ceramic substrate and the metallic nickel fine powder, delamination or cracking of the nickel fine powder during firing Defects such as (cracking) occur.

  Further, in reducing the thickness of the internal electrode layer, a conductive paste having a small surface roughness, a high film density, and a stable viscosity is required. As the grain size of the paste becomes finer, the dispersibility in the conductive paste becomes worse and the paste viscosity becomes unstable.

  If the paste viscosity changes with time and becomes thicker, handling at the manufacturing site becomes difficult, long-term storage after processing into a conductive paste is difficult, and quality control and quality maintenance as a conductive paste used in the manufacture of electronic components, etc. The work spent on the process becomes complicated. As described above, the nickel fine powder is required to have dispersibility, which is a quality as a conductive paste, and a property capable of appropriately maintaining the viscosity.

  Here, a method of providing an appropriate oxide layer on the surface of nickel ultrafine powder is known in order to achieve both heat shrinkage resistance of nickel ultrafine powder and paste viscosity stabilization (for example, Patent Documents 1 to 3). ). Patent Documents 1 and 2 disclose conventional surface oxidation methods for nickel ultrafine powder.

  However, nickel ultrafine powder provided with an oxide layer by a conventional method is not sufficient in improving heat shrinkability and dispersibility and viscosity stability in a conductive paste. In particular, the ultrafine nickel powder synthesized by the liquid phase method has a narrow particle size distribution without classification and can synthesize nickel nanoparticles of 200 nm or less, but the surface area increases due to the smaller particle size. There is a risk of abnormal heat generation when exposed to the atmosphere. In addition, the heat generation generates nickel oxide and forms a strong aggregate.

  On the other hand, if the surface of nickel nanoparticles is subjected to an oxidation treatment in a water slurry, nickel hydroxide is generated simultaneously with the oxidation of the particle surface, resulting in deterioration of electrical characteristics when made into a nickel paste. It is not preferable as a material for an electrode. Furthermore, since the nickel ultrafine powder synthesized by the liquid phase method has a crystallite size smaller than that of a dry method such as a CVD method, there is a disadvantage that the heat shrinkage is poor.

  The behavior of such nickel fine powder is difficult to handle and may cause product defects. Therefore, for nickel nanoparticles synthesized by the liquid phase method, the particle surface condition is more There is a need for further improvement and improvement in heat shrinkability.

  Patent Document 4 discloses a technique for oxidizing the surface of nickel particles. Nickel powder produced by a liquid phase method is added to pure water to form a slurry, and then oxidized with hydrogen peroxide. This technical matter is disclosed.

JP 2000-169904 A JP 2001-049301 A JP 2014-122368 A Japanese Patent Laid-Open No. 11-343501

  The present invention has been proposed in view of such circumstances, has no agglomeration, has a sharp particle size distribution, has good heat shrinkage resistance, dispersibility when formed into a paste, and changes over time. An object of the present invention is to provide a nickel fine powder that has excellent viscosity stability and can be suitably used as a material for an internal electrode of a multilayer ceramic capacitor.

  This inventor repeated earnest examination in order to solve the subject mentioned above. As a result, the aqueous slurry containing nickel fine particles is replaced with an organic solvent, the obtained organic solvent slurry is subjected to an oxidation treatment, and then subjected to a heat treatment such as autoclave heating or microwave heating, The inventors have found that a nickel fine powder having no agglomeration, sharp particle size distribution, and good heat shrinkage can be obtained, and the present invention has been completed.

  (1) In the first invention of the present invention, the particle diameter is 200 nm or less, the primary particles are present in a ratio of 95% or more within an average particle diameter of ± 30%, and the surface is oxidized with a thickness of 1 nm or more. A nickel fine powder having an oxide film containing nickel and having a crystallite diameter of 140 Å (angstrom) or more and 300 Å or less.

  (2) The second invention of the present invention is a nickel fine powder having an average particle size of 100 nm or less in the first invention.

  (3) In the third invention of the present invention, the particle size is 200 nm or less in the organic solvent, the primary particles are present in a ratio of 95% or more within the average particle size ± 30%, and the thickness is 1 nm on the surface. This is a nickel powder organic slurry having the above oxide film containing nickel oxide and having a crystallite diameter of 140 Å (angstrom) or more and 300 Å or less, in which fine nickel powder is dispersed.

  (4) A fourth invention of the present invention is obtained by adding an organic solvent to an aqueous slurry of nickel fine particles having a particle diameter of 200 nm or less prepared by a liquid phase method, and substituting the organic solvent slurry. In addition, an oxidizing agent is added to the nickel organic solvent slurry to oxidize the surface of the nickel fine particles, and heat treatment is performed on the nickel organic solvent slurry after the oxidation treatment.

  (5) The fifth invention of the present invention is the method for producing fine nickel powder according to the fourth invention, wherein the nickel organic solvent slurry after the oxidation treatment is subjected to a heat treatment by an autoclave.

  (6) The sixth invention of the present invention is the method for producing fine nickel powder according to the fourth invention, wherein the nickel organic solvent slurry after the oxidation treatment is subjected to a heat treatment by microwaves.

  (7) A seventh invention of the present invention is the nickel fine powder manufacturing method according to any one of the fourth to sixth inventions, wherein the oxidizing agent is hydrogen peroxide.

  (8) According to an eighth aspect of the present invention, in any one of the fourth to seventh aspects, the amount of the oxidizing agent added is 0.1 ml / g or more with respect to the mass of the nickel fine particles. It is a manufacturing method of a fine powder.

  (9) A ninth invention of the present invention is a nickel paste for a multilayer ceramic capacitor internal electrode, comprising the nickel fine powder according to either the first or second invention.

  According to the present invention, there is no aggregation, the particle size distribution is sharp, the heat shrinkage is good, the dispersibility when pasted and the viscosity stability over time are excellent, and the internal electrode of the multilayer ceramic capacitor The nickel fine powder which can be used suitably as a material for use, and its manufacturing method can be provided.

It is a flowchart which shows the flow of the manufacturing process of nickel fine powder. It is a graph which shows the evaluation result of the thermal contraction characteristic of the nickel fine powder of Example 1 and Comparative Example 1.

  Hereinafter, a specific embodiment of the present invention (hereinafter referred to as “the present embodiment”) will be described in detail. In addition, this invention is not limited to the following embodiment, In the range which does not change the summary of this invention, it can change suitably.

<< 1. Nickel fine powder >>
The nickel fine powder according to the present embodiment has a particle size of 200 nm or less, and the primary particles are present in the range of an average particle size within ± 30% at a ratio of 95% or more and hardly contain aggregates. Is. Further, the nickel fine powder has an oxide film containing nickel oxide having a thickness of 1 nm or more on the surface thereof, and the crystallite diameter is 140 Å (angstrom) or more and 300 Å or less.

  Such nickel fine powder has almost no aggregation, sharp particle size distribution, good heat shrinkage resistance, excellent dispersibility when pasted and stable viscosity over time. It can be suitably used as a material used for an internal electrode of a multilayer ceramic capacitor (MLCC) mounted on a form device such as a telephone.

  More specifically, the nickel fine powder according to the present embodiment has a particle size of 200 nm or less, preferably 100 nm or less. Thus, when it is a fine powder with a particle size of 200 nm or less, it can be suitably used as a material for the internal electrode of MLCC, and can effectively cope with the thinning of the internal electrode layer.

  Further, the nickel fine powder has primary particles present at a ratio of 95% or more in a range within ± 30% of the average particle diameter. Here, primary particles refer to unit particles observed with a scanning electron microscope (SEM), and do not mean so-called secondary particles formed by aggregation and bonding of unit particles. The average particle diameter is an average value obtained by measuring the particle diameters of primary particles of 100 nickel fine particles existing within a predetermined range of an observation image obtained by SEM. In addition, the abundance ratio of the primary particles can be obtained by measuring the number of 100 primary particles in the range of the average particle size ± 30% based on the average particle size obtained by SEM, for example. .

  The fact that the primary particles of nickel fine powder are present at a ratio of 95% or more within the range of ± 30% of the average particle size means that the particle size distribution is extremely sharp and the particle size is uniform. It is nickel fine powder, and it means that primary particles having a particle size of 200 nm or less exist in a dispersed state without agglomeration.

  According to such a nickel fine powder, since there are very few coarse particles including an aggregate, it is possible to prevent occurrence of a short circuit or the like in the internal electrode layers of the MLCC.

  Further, the nickel fine powder has an oxide film having a thickness (film thickness) of 1 nm or more, more preferably 5 nm or more on the particle surface. Specifically, the oxide film contains nickel oxide. As will be described in detail later, in the method for producing nickel fine powder according to the present embodiment, nickel fine particles (nickel organic solvent slurry) dispersed in an organic solvent are oxidized with an oxidizing agent such as hydrogen peroxide. Then, an oxide film of nickel oxide is generated on the surface. The thickness of the oxide film on the particle surface can be appropriately set according to the application. For MLCC, there is no particular limitation because there is a heat treatment step in a reducing atmosphere in the subsequent step. However, for example, the thickness may be about 20 nm or less as long as the conductivity is not affected.

  Thus, according to the nickel fine powder having an oxide film containing nickel oxide on the surface, even particles having a particle size of 200 nm or less can effectively prevent the particles from agglomerating. Aggregate generation can be prevented.

  Further, in this nickel fine powder, the crystallite diameter is 140 to 300 mm, preferably 170 to 250 mm. According to the nickel fine powder having such a crystallite diameter, thermal shrinkage can be suppressed, and occurrence of defects such as short circuit and delamination can be effectively prevented during sintering during the production of the internal electrode. Moreover, by having such a crystallite diameter and excellent heat shrinkage resistance, it is possible to prevent re-aggregation during sintering and maintain good dispersibility.

  The crystallite diameter can be obtained from a diffraction pattern obtained by an X-ray diffractometer based on the Scherrer method.

  In addition, as described above, the nickel fine powder according to the present embodiment is obtained by dispersing nickel fine particles in an organic solvent to form a nickel organic slurry and subjecting the slurry to oxidation treatment. Nickel formation can be prevented. Therefore, this nickel fine powder does not contain nickel hydroxide. In addition, confirmation of presence of nickel hydroxide can be performed by observation using SEM.

≪2. Nickel organic slurry, nickel paste >>
As described above, the nickel fine powder according to the present embodiment has a particle size of 200 nm or less, and the primary particles are present at a ratio of 95% or more in the range of the average particle size within ± 30%. It contains almost no aggregates. Further, the nickel fine powder has an oxide film containing nickel oxide having a thickness of 1 nm or more on the surface, and further has a crystallite diameter of 140 to 300 mm.

  Since such nickel fine powder is free of aggregates and nickel fine particles having a particle size of 200 nm or less are well dispersed, the nickel fine powder is applied as a nickel paste using the nickel fine particles as a raw material. It can be set as the paste excellent in the subsequent dry film density. Further, there is no increase in paste viscosity due to aggregation of fine particles. Furthermore, it has excellent heat shrinkage resistance. Such a nickel paste can be suitably used as a paste for MLCC internal electrodes.

  Here, the nickel paste can be manufactured, for example, by putting nickel fine powder into pure water to form a water slurry, and kneading the water slurry with a vehicle made of an organic solvent and a binder resin. In addition, about the manufacturing method of nickel paste, it is not limited to this.

≪3. Manufacturing method of nickel fine powder >>
Next, the manufacturing method of the nickel fine powder which has the characteristics mentioned above is demonstrated.

  The method for producing nickel fine powder according to the present embodiment includes a step of adding an organic solvent to a slurry of nickel fine particles prepared by a liquid phase method and replacing the slurry, and a nickel organic solvent slurry obtained by replacing with an organic solvent. On the other hand, the method includes a step of oxidizing the surface of the nickel fine particles by adding an oxidizing agent and a step of performing a heat treatment on the nickel organic solvent slurry after the oxidation treatment.

  Below, this manufacturing method is divided into the following (A) process-(F) process, and is demonstrated in detail, respectively. That is, as shown in FIG. 1, this nickel fine powder production method includes (A) a step of producing nickel nanoparticles, (B) a step of replacing the aqueous slurry of nickel nanoparticles with an organic solvent, and (C) organic A step of oxidizing the nickel organic solvent slurry obtained by substitution with a solvent, (D) a step of heating the nickel organic solvent slurry after the oxidation treatment, (E) a step of storing as a nickel organic slurry, or (F) A step of vacuum-drying the nickel organic slurry and storing it as a dry powder.

[(A) Nickel Nanoparticle Production Process]
First, nickel nanoparticles (nickel fine particles) having a particle size of 200 nm or less are prepared as starting materials. In the present embodiment, nickel fine particles are produced by a liquid phase method, and the produced nickel fine particles are added to pure water to form an aqueous slurry of nickel fine particles.

  Specifically, examples of the liquid phase method include a wet reduction method using a reducing agent such as hydrazine with respect to a nickel salt solution containing a nickel salt compound. In addition, as an aqueous slurry of nickel fine particles produced by a liquid phase method, a nickel powder water slurry manufactured by Sumitomo Metal Mining Co., Ltd., standard name: NR707 (nickel ultrafine powder by wet reduction method, average particle size 70 nm), NR720 (Nickel ultrafine powder by a wet reduction method, average particle size 200 nm) is commercially available and can be used effectively.

[(B) Replacement step with organic solvent]
Next, an organic solvent is added to the obtained aqueous slurry of nickel fine particles (nickel water slurry) to perform a substitution treatment, thereby generating a “nickel organic solvent slurry” in which the nickel fine particles are dispersed in the organic solvent.

The organic solvent is not particularly limited as long as it can replace the nickel water slurry with an organic solvent slurry. Specifically, for example, terpineol, dihydroterpineol, dihydroterpineol acetate, isobornyl propionate, isobornyl isobutyrate, mineral spirit, No. 0 solvent, butyl carbitol, isobutyl acetate, methyl ethyl ketone, cyclohexane, hexane, Examples include ethanol, nonane, nonanol, decanol and the like. Further, aliphatic hydrocarbons represented by CnH _{2n + 2} , CnH _2n , CnH _2n-2 , aromatic hydrocarbons represented by CnH _2n-6 , and the like can be used. Specifically, dimethyloctane, ethylmethylcyclohexane Methylpropylcycloheptane, trimethylhexane, butylcyclohexane, tridecane, tetradecane, methylnonane, ethylmethylheptane, trimethyldecane, pentylcyclohexane, decane, undecane, dodecane and the like. These organic solvents can be used alone or in combination of two or more.

  Specifically, in the replacement treatment with the organic solvent, a predetermined amount of the organic solvent is added to the aqueous slurry of nickel fine particles, and lightly stirred to perform decantation. Such decantation is repeated three times, thereby replacing the nickel water slurry with the nickel organic solvent slurry.

[(C) Step of performing oxidation treatment]
Next, the obtained nickel organic solvent slurry, that is, nickel fine particles dispersed in the organic solvent is subjected to an oxidation treatment with an oxidizing agent. By this oxidation treatment, an oxide film containing nickel oxide is generated on the surface of the nickel fine particles.

  The oxidizing agent is not particularly limited, and hydrogen peroxide, ozone, or the like can be used. However, it is preferable to use hydrogen peroxide from the viewpoint of low cost and easy handling.

  Specifically, in this oxidation treatment, an oxidizing agent such as hydrogen peroxide is gradually added to the nickel organic solvent slurry and stirred. For example, when hydrogen peroxide is used as the oxidizing agent, it is preferable to add hydrogen peroxide at a rate of 0.1 ml / g or more with respect to 1 g of nickel fine particles present in the nickel organic solvent slurry. It is more preferable to add at a rate of 1 ml / g or more.

  When the amount of hydrogen peroxide added is less than 0.1 ml / g with respect to 1 g of nickel fine particles, an oxide film is formed on the surface of the nickel fine particles, but an extremely thin oxide film with a thickness of less than 1 nm is formed. there is a possibility. Thereby, aggregation may occur in the obtained nickel fine powder. The upper limit of the addition amount is not particularly limited, but is preferably about 20 ml / g or less, more preferably about 10 ml / g or less with respect to 1 g of nickel fine particles. If the amount of hydrogen peroxide added is more than 20 ml / g, it is sufficient as an oxide film, but is costly and inefficient.

  Thus, in the nickel fine powder manufacturing method according to the present embodiment, nickel fine particles are subjected to an oxidation treatment to form an oxide film, and the oxidation treatment is dispersed in an organic solvent. Is important to do. Thereby, aggregation at the time of drying of the nickel fine powder obtained can be prevented more effectively. Moreover, generation | occurrence | production of nickel hydroxide can be prevented.

[(D) Step of performing heat treatment]
Next, the nickel organic solvent slurry after the oxidation treatment is subjected to heat treatment. By this heat treatment, the crystallite diameter of the nickel fine particles in the slurry can be increased, and a nickel organic slurry with improved heat shrinkage resistance can be obtained. Specifically, nickel fine particles having a crystallite diameter of 140 mm or more can be obtained.

  Although it does not specifically limit as a method of heat processing, For example, heat processing (henceforth "autoclave processing") by the autoclave for about 1 hour-about 5 hours is performed on the conditions of the temperature of about 150 to 250 degreeC. it can. By performing the autoclave treatment in this way, a slurry having an improved crystallite diameter can be obtained while the powder surface is wet without evaporating the organic solvent in the slurry.

  Moreover, as a heat treatment other than the autoclave treatment, for example, a heat treatment using microwaves is also a simple method and effective. Specifically, the nickel organic solvent slurry after the oxidation treatment is heated by irradiating microwaves, for example, for about 0.1 to 1 hour. Note that in the heat treatment using microwaves, an effect equivalent to that of performing the above-described autoclave treatment for 1 hour can be obtained by short-time microwave irradiation of about 0.1 hours.

[(E) Step of storing as nickel organic slurry]
As described above, by performing an oxidation treatment with an oxidizing agent such as hydrogen peroxide, a slurry of nickel fine particles having an oxide film containing nickel oxide on the surface can be obtained. Further, by subjecting the nickel organic solvent slurry after the oxidation treatment to a heat treatment, the crystallite diameter of the nickel fine particles can be increased to 140 mm or more, and the nickel fine particles (nickel fine powder) having improved heat shrinkage resistance A slurry is obtained. Here, the slurry of the nickel fine powder after the heat treatment is referred to as “nickel organic slurry”.

  The nickel organic slurry thus produced can be stored as it is. Moreover, a nickel paste can be manufactured using the nickel organic slurry as a raw material as it is, that is, without using a dry powder. Specifically, for example, a nickel paste can be produced by using a stored nickel organic slurry as a raw material and adding and kneading it to a vehicle composed of an organic solvent and a binder resin.

  In the present embodiment, since the oxide film containing nickel oxide is formed on the surface of the nickel fine particles by the oxidation treatment described above, the aggregation of the nickel fine particles is suppressed even in the obtained nickel organic slurry. And coarsening of the nickel fine powder can be prevented. Moreover, it can be set as the nickel fine powder which improved the heat-resistant shrinkage property by the crystallite diameter of the nickel fine particle becoming large by the heat processing mentioned above.

[(F) Process of giving dry treatment to dry powder]
Moreover, about the nickel organic slurry obtained by making it above, it can be set as dry powder by performing a drying process further.

  Specifically, the drying method is not particularly limited. For example, the solvent component in the slurry is dried and evaporated by performing vacuum drying for about 3 hours to 15 hours under conditions of a temperature of about 70 ° C. to 150 ° C. Dry powder (nickel fine powder) can be obtained.

  In this embodiment, since the oxide film containing nickel oxide is formed on the surface of the nickel fine particles by the above-described oxidation treatment, aggregation due to the drying can be suppressed even when a drying treatment such as vacuum drying is performed. Further, coarsening of the nickel fine powder can be prevented.

  In addition, in the nickel fine powder which is the dry powder obtained in this way, for example, the nickel fine powder can be put into pure water and used as a water slurry to be a raw material for producing nickel paste.

  EXAMPLES Hereinafter, examples of the present invention will be shown and described in more detail, but the present invention is not limited to the following examples.

[Example 1]
≪Manufacture of nickel organic slurry≫
(Preparation of nickel nanopowder)
First, 1000 g (standard name: NR707, nickel ultrafine powder by wet reduction method, average particle size 70 nm) prepared by Sumitomo Metal Mining Co., Ltd. was prepared as a starting material.

(Substitution with organic solvent)
Next, ethylene glycol was prepared as an organic solvent, 1000 g of the organic solvent was put into a nickel powder water slurry, and decantation was performed with gentle stirring. This decantation was repeated three times to replace the nickel water slurry with an organic solvent slurry to produce a nickel organic solvent slurry.

(Oxidation treatment)
Next, 200 ml of hydrogen peroxide (1 ml / g with respect to 1 g of nickel fine particles in the slurry) was gradually added to 1000 g of nickel organic solvent slurry (solvent amount 80%) obtained by organic solvent substitution. Then, oxidation treatment was performed with stirring. As a result, a nickel organic slurry was obtained in which an oxide film was formed on the surface of the nickel fine particles in the slurry.

(Heat treatment)
Next, the nickel organic solvent slurry after the oxidation treatment was put into a vacuum dryer, and heat treatment was performed by an autoclave at a temperature of 200 ° C. for 3 hours. Thereby, the nickel organic slurry containing the nickel fine powder in which the oxide film was formed on the surface and the crystallite diameter was improved was obtained.

(Vacuum drying process)
Subsequently, in order to obtain a dry powder from the obtained nickel organic slurry, the slurry was put into a vacuum dryer, and vacuum drying was performed under conditions of a temperature of 60 ° C. for 3 hours. By this vacuum drying treatment, a dry powder of nickel fine powder was obtained.

≪Evaluation≫
(Evaluation of aggregation of nickel fine powder in nickel organic slurry)
The obtained nickel organic slurry was evaluated for agglomeration of nickel fine powder. Specifically, the nickel organic slurry was mixed and stirred for 2 minutes at a rotational speed of a peripheral speed of 10 m / s using an Excel auto homogenizer (manufactured by Nippon Seiki Co., Ltd.). Thereafter, filtration under reduced pressure was performed with a 0.1 μm filter paper, and nickel fine powder remaining on the filter paper was confirmed. When nickel fine particles having an average particle diameter of 70 nm are used as a starting material, filtration is performed under reduced pressure using a 0.1 μm filter paper, and when nickel fine particles having an average particle diameter of 200 nm are used, a 0.3 μm filter paper is used. And vacuum filtered.

  After filtration under reduced pressure, the case where almost no nickel fine powder remained on the filter paper was evaluated as having good dispersibility (“good”) without aggregation. On the other hand, when most of the nickel fine powder remained on the filter paper, it was evaluated that aggregation occurred and the dispersibility was poor (“bad”).

(Average particle size and abundance of primary particles)
The obtained dry powder (nickel fine powder) was observed using a scanning electron microscope (SEM), and the particle size of 100 primary particles existing within a predetermined range of the SEM observation image was measured. The average particle size was taken. Moreover, based on the average particle diameter, the ratio which exists in the range of the average particle diameter +/- 30% among 100 primary particles was calculated | required.

(Presence or absence of nickel hydroxide)
The presence or absence of nickel hydroxide was confirmed by SEM observation of the obtained dry powder (nickel fine powder). The case where the occurrence of nickel hydroxide was confirmed was evaluated as “present”, and the case where it was not confirmed was evaluated as “absent”.

(Dry powder aggregation evaluation)
Moreover, the generation | occurrence | production of the aggregation of the nickel fine powder was confirmed by SEM observation of the obtained dry powder (nickel fine powder). The case where the occurrence of aggregation was confirmed was evaluated as “present”, and the case where the aggregation was not confirmed was evaluated as “absent”. In addition, although agglomeration was confirmed a little, what was judged to have hardly occurred was evaluated as “almost none”.

(Oxide film thickness)
Moreover, the film thickness of the oxide film which consists of nickel oxide in the obtained dry powder (nickel fine powder) was measured by energy dispersive X-ray analysis (EDS analysis). Specifically, the nickel amount and the oxygen amount were measured by EDS analysis, and the oxide film thickness was determined by oxidation conversion from the obtained numerical values.

(Evaluation of crystallite diameter)
Further, the crystallite diameter of the obtained dry powder (nickel fine powder) was determined by the Scherrer method using the (111) plane peak obtained from the 2θ-θ scan of X-ray diffraction. In addition, the half-value width and peak position of a diffraction peak employ | adopted the result of having performed the K (alpha) 1-K (alpha) 2 separation process about the peak.

(Evaluation of heat shrinkage characteristics)
The obtained dry powder (nickel fine powder) was compression-molded into a cylindrical shape, and the change in the thickness of the sample was measured when the molded sample was heated under the following conditions.
Measurement model: TMA4000SA (manufactured by Netch Japan Co., Ltd.)
・ Raising rate: 5 ° C / min
-Temperature range: room temperature to 1000 ° C
・ Load: 5g
_{Atmosphere: 2vol% -H 2 / N 2} , 200mL / min

  FIG. 2 is a graph showing the evaluation results of the heat shrinkage characteristics of the nickel fine powders of Example 1 and Comparative Example 1. In this graph, the horizontal axis indicates the temperature (unit: ° C.), and the vertical axis indicates the rate of change in thickness of the molded sample (unit:%).

[Example 2]
A nickel organic slurry was produced in the same manner as in Example 1 except that the temperature condition in the heat treatment was 150 ° C. The obtained nickel organic slurry and its dry powder were evaluated in the same manner as in Example 1.

[Example 3]
A nickel organic slurry was produced in the same manner as in Example 1 except that the temperature condition in the heat treatment was 250 ° C. The obtained nickel organic slurry and its dry powder were evaluated in the same manner as in Example 1.

[Example 4]
A nickel organic slurry was produced in the same manner as in Example 1 except that the treatment time in the heat treatment was 1 hour. The obtained nickel organic slurry and its dry powder were evaluated in the same manner as in Example 1.

[Example 5]
A nickel organic slurry was produced in the same manner as in Example 1 except that the treatment time in the heat treatment was 5 hours. The obtained nickel organic slurry and its dry powder were evaluated in the same manner as in Example 1.

[Example 6]
A nickel organic slurry was produced in the same manner as in Example 1 except that the heat treatment method was changed to a microwave method and the heat treatment time was changed to 6 minutes. The obtained nickel organic slurry and its dry powder were evaluated in the same manner as in Example 1.

[Example 7]
200 nm ultrafine nickel powder (nickel powder slurry standard name: NR720 manufactured by Sumitomo Metal Mining Co., Ltd .: nickel ultrafine powder by wet reduction method, average particle size 200 nm) prepared by a liquid phase method was used as a starting material. A nickel organic slurry was produced in the same manner as in Example 1 except that. The obtained nickel organic slurry and its dry powder were evaluated in the same manner as in Example 1.

[Comparative Example 1]
In Comparative Example 1, the replacement with the organic solvent was not performed, and the oxidation treatment was performed in the state of the nickel water slurry. Other than that was the same as Example 1. Then, the obtained nickel water slurry and its dry powder were evaluated in the same manner as in Example 1.

[Comparative Example 2]
In Comparative Example 2, the replacement with the organic solvent was not performed, and the oxidation treatment was performed in the state of the nickel water slurry, and then the heat treatment by the microwave was performed on the nickel water slurry. Other than that was the same as Example 1. Then, the obtained nickel water slurry and its dry powder were evaluated in the same manner as in Example 1.

  Table 1 below shows the production conditions for the nickel organic slurries obtained in Examples 1 to 6 and Comparative Examples 1 and 2, and Table 2 below summarizes the evaluation results. FIG. 2 shows the evaluation results of the heat shrinkage characteristics of the nickel fine powders of Example 1 and Comparative Example 1.

  As shown in Table 1, the nickel fine powders obtained in Examples 1 to 7 did not aggregate even in the nickel organic slurry and had good dispersibility. In addition, it was confirmed that the dried powder hardly agglomerates and an oxide film having a thickness of 1 nm or more was formed and oxidized. Moreover, generation | occurrence | production of nickel hydroxide was not confirmed. Furthermore, the growth of the crystallite diameter was confirmed. From these facts, the obtained nickel fine powder has a small particle size and is preferable as a material for the internal electrode of the multilayer ceramic capacitor.

  On the other hand, in Comparative Examples 1 and 2, it was confirmed that a 5 nm oxide film was formed on the obtained dry powder and was oxidized, but aggregation occurred. Moreover, generation | occurrence | production of nickel hydroxide was also confirmed. Also, the crystallite diameter was smaller than that of the example. As a result of SEM observation, it was confirmed that nickel hydroxide was frequently generated, so that the crystallite diameter was reduced. From these facts, the obtained nickel fine powder was unpreferable for use as a material such as an internal electrode of a multilayer ceramic capacitor.

  Here, in FIG. 2, the result of the heat contraction behavior of the nickel fine powder obtained in each of Example 1 and Comparative Example 1 is shown. As shown in FIG. 2, it can be seen that the nickel fine powder of Example 1 has a lower thermal shrinkage rate and a higher shrinkage start temperature compared to Comparative Example 1, and this also indicates that the heat resistance is high. It can be seen that it is excellent in shrinkage and is suitable as a material for the internal electrode of the multilayer ceramic capacitor.

Claims (9)

The particle size is 200 nm or less,
The primary particles are present in a ratio of 95% or more within the average particle size ± 30%,
Having an oxide film containing nickel oxide having a thickness of 1 nm or more on the surface;
Nickel fine powder having a crystallite diameter of 140 Å (angstrom) or more and 179 Å or less. The nickel fine powder according to claim 1, wherein the average particle size is 100 nm or less. In organic solvent,
The particle size is 200 nm or less, the primary particles are present in a ratio of 95% or more within the average particle size ± 30%, the surface has an oxide film containing nickel oxide having a thickness of 1 nm or more, and the crystallite diameter Nickel powder organic slurry in which nickel fine powder is dispersed, having a particle size of 140 Å (angstrom) or more and 179 Å or less. An organic solvent is added to an aqueous slurry of nickel fine particles having a particle diameter of 200 nm or less prepared by a liquid phase method, and the slurry is replaced with the slurry of the organic solvent.
An oxidizing agent is added to the nickel organic solvent slurry obtained by the substitution to oxidize the surface of the nickel fine particles,
The manufacturing method of the nickel fine powder which heat-processes with respect to the nickel organic solvent slurry after an oxidation process. The manufacturing method of the nickel fine powder of Claim 4 which heat-processes with an autoclave with respect to the nickel organic solvent slurry after an oxidation process. The manufacturing method of the nickel fine powder of Claim 4 which heat-processes with a microwave with respect to the nickel organic solvent slurry after an oxidation process. The method for producing nickel fine powder according to any one of claims 4 to 6, wherein the oxidizing agent is hydrogen peroxide. The method for producing a nickel fine powder according to any one of claims 4 to 7, wherein an addition amount of the oxidizing agent is 0.1 ml / g or more with respect to a mass of the nickel fine particles. A nickel paste for a multilayer ceramic capacitor internal electrode, comprising the nickel fine powder according to claim 1.

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