JP2015190043A - Wet manufacturing process of nickel powder - Google Patents

Wet manufacturing process of nickel powder Download PDF

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JP2015190043A
JP2015190043A JP2014070299A JP2014070299A JP2015190043A JP 2015190043 A JP2015190043 A JP 2015190043A JP 2014070299 A JP2014070299 A JP 2014070299A JP 2014070299 A JP2014070299 A JP 2014070299A JP 2015190043 A JP2015190043 A JP 2015190043A
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nickel powder
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nickel
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JP6135935B2 (en
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貴広 植田
Takahiro Ueda
貴広 植田
慎悟 村上
Shingo Murakami
慎悟 村上
行延　雅也
Masaya Yukinobu
雅也 行延
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Sumitomo Metal Mining Co Ltd
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Abstract

PROBLEM TO BE SOLVED: To provide a wet manufacturing process of nickel powder having high crystallinity with an extremely small content of coarse particles (e.g. particle diameter: 1 μm or more), applicable to an internal electrode of a multilayer ceramic capacitor with effective suppression of reduction in capacity drop and reduction in reliability of a capacitor.SOLUTION: The wet manufacturing process includes each of the steps of highly crystallizing raw material nickel powder made by a wet process and crushing the product. The raw material nickel powder has an average particle diameter of 0.3 μm or less and a crystallite diameter (CS: nm) of 40 nm or less. The step of high crystallization includes heat treating raw material nickel powder at a temperature of 250°C to 350°C in a reduction atmosphere for enlargement of crystallites to obtain nickel powder with a large crystallite diameter. The crushing step includes crushing the nickel powder having a large crystallite diameter obtained in the step of high crystallization, such that the nickel powder having a large crystallite diameter aggregated or sintered in the step of high crystallization is dispersed. The nickel powder by the wet process has an average particle diameter of 0.3 μm or less, and a crystallite diameter (CS: nm) of CS≥1.3×CS, with a proportion of coarse particles with a particle diameter of 1 μm or more in the total particle number of 50 ppm or less.

Description

本発明は、湿式ニッケル粉末の製造方法に関する。
詳しくは、積層セラミックコンデンサ（ｍｕｌｔｉｌａｙｅｒ ｃｅｒａｍｉｃ ｃａｐａｃｉｔｏｒｓ；ＭＬＣＣ）の内部電極に適用した場合に、コンデンサの容量低下や信頼性低下を効果的に抑制可能な、高い結晶性を有し、かつ粗大粒子（例えば、粒径１μｍ以上）の含有が極めて少ない、湿式ニッケル粉末の製造方法に関するものである。 The present invention relates to a method for producing wet nickel powder.
Specifically, when applied to an internal electrode of a multilayer ceramic capacitor (MLCC), it has high crystallinity and coarse particles (for example, capable of effectively suppressing a decrease in capacitance and reliability of the capacitor). In other words, the present invention relates to a method for producing wet nickel powder having a very small particle size of 1 μm or more.

従来から、ニッケル粉末は、厚膜導電体を作製するための導電ペーストの材料として使用されている。
この厚膜導電体は、電気回路の形成、積層セラミックコンデンサ及び多層セラミック基板等の積層セラミック部品の電極等に用いられている。特に、積層セラミックコンデンサでは、小型・高容量化の要求から高積層化が進み、そのために用いる導電ペーストの使用量も大幅に増加している。
このため、導電ペーストに使用する金属粉末としては、ＰｄやＡｇ−Ｐｄのような高価な貴金属の使用を避け、安価なニッケルなどの卑金属が主流となっている。 Conventionally, nickel powder has been used as a material for a conductive paste for producing a thick film conductor.
The thick film conductor is used for forming an electric circuit, an electrode of a multilayer ceramic component such as a multilayer ceramic capacitor and a multilayer ceramic substrate. In particular, in multilayer ceramic capacitors, the increase in the number of layers has progressed due to the demand for smaller size and higher capacity, and the amount of conductive paste used for that purpose has also increased significantly.
For this reason, as the metal powder used for the conductive paste, the use of expensive noble metals such as Pd and Ag-Pd is avoided, and inexpensive base metals such as nickel are mainly used.

この厚膜導電体が使用される積層セラミックコンデンサは、例えば、金属粉末にニッケル粉末を用いた場合は、次のような方法で製造される。
まず、ニッケル粉末と、エチルセルロース等の樹脂と、ターピネオール等の有機溶剤等とを混練して得られた導電ペーストを、誘電体グリーンシート（セラミックグリーンシート）上にスクリーン印刷・乾燥して内部電極用のニッケル塗膜を作製する。
次に、印刷された内部電極用のニッケル塗膜と誘電体グリーンシートが交互に重なるように積層し、圧着して積層体を作製する。 The multilayer ceramic capacitor in which this thick film conductor is used is manufactured by the following method, for example, when nickel powder is used as the metal powder.
First, a conductive paste obtained by kneading nickel powder, a resin such as ethyl cellulose, and an organic solvent such as terpineol is screen-printed and dried on a dielectric green sheet (ceramic green sheet) for internal electrodes. A nickel coating is prepared.
Next, the printed nickel electrode coating for internal electrodes and the dielectric green sheets are laminated so as to overlap each other, and pressed to produce a laminate.

その後、その積層体を所定の大きさにカットし、有機バインダとして使用したエチルセルロース等の樹脂の燃焼除去を行うための脱バインダ処理を行った後、１３００℃程度の高温焼成による誘電体、および内部電極（ニッケル膜）の焼結を進め、誘電体層と内部電極層が互いに積層したセラミック体を得る。そして、このセラミック体に外部電極を取り付け、積層セラミックコンデンサとする。
なお、上記積層体の脱バインダ処理は、ニッケル粉末が酸化しないように、極めて微量の酸素を含んだ雰囲気下にて行われる。 Thereafter, the laminate is cut into a predetermined size, and after performing a binder removal treatment for removing a resin such as ethyl cellulose used as an organic binder, a dielectric by high-temperature firing at about 1300 ° C., and an internal Sintering of the electrode (nickel film) proceeds to obtain a ceramic body in which the dielectric layer and the internal electrode layer are laminated together. And an external electrode is attached to this ceramic body, and it is set as a laminated ceramic capacitor.
Note that the binder removal treatment of the laminate is performed in an atmosphere containing a very small amount of oxygen so that the nickel powder is not oxidized.

ところで、近年、小型化及び大容量化が求められている積層セラミックコンデンサでは、それを構成する内部電極及び誘電体ともに、薄層化が進められている。特に、内部電極に使用されるニッケル粉末の粒径としては、０．３μｍ程度が主流となっており、一部の高積層タイプでは０．２μｍ程度のより微細なものも用いられている。   Incidentally, in recent years, in multilayer ceramic capacitors that are required to be reduced in size and increased in capacity, both internal electrodes and dielectrics constituting the same are being made thinner. In particular, the particle size of nickel powder used for the internal electrode is mainly about 0.3 μm, and in some high lamination types, finer ones of about 0.2 μm are also used.

このような内部電極の薄層化に伴い、いくつかの問題が顕在化しており、その一つが、積層セラミックコンデンサの容量低下である。
内部電極用のニッケル塗膜中のニッケル粉末の充填密度は粉末冶金における成形体の充填密度に比べてはるかに低く、しかも基板となる誘電体グリーンシート（セラミックグリーンシート）の焼結に伴う収縮量はニッケル膜の収縮に比べて小さいために、薄層化したニッケル膜では焼結の進行に伴ってニッケル膜が島状に途切れるという現象がより発生しやすくなる。
この内部電極（ニッケル膜）の途切れは、コンデンサの容量低下を引き起こすため、この途切れを抑制して高容量のコンデンサを得るためには、焼結時の収縮をできるだけ小さく抑えながら、緻密で薄い内部電極（ニッケル膜）を形成することが不可欠である。 As the internal electrodes are made thinner, several problems have become apparent, and one of them is a decrease in the capacity of the multilayer ceramic capacitor.
The packing density of nickel powder in the nickel coating for internal electrodes is much lower than the packing density of compacts in powder metallurgy, and the amount of shrinkage associated with sintering of the dielectric green sheet (ceramic green sheet) that becomes the substrate Is smaller than the shrinkage of the nickel film, the thinned nickel film is more likely to have a phenomenon that the nickel film breaks into islands as the sintering proceeds.
This internal electrode (nickel film) breakage causes a decrease in the capacitance of the capacitor. To obtain a high-capacitance capacitor by suppressing this breakage, the inner part is dense and thin while minimizing the shrinkage during sintering. It is essential to form an electrode (nickel film).

そのためには、ニッケル塗膜の密度（乾燥膜密度（ＤＦＤ：Ｄｒｙ Ｆｉｌｍ Ｄｅｎｓｉｔｙ））を高めること、ニッケル粉末の真比重を高めること、ニッケル粉末の急激な焼結を抑制すること、等の対策が必要である。   For that purpose, measures such as increasing the density of the nickel coating (Dry Film Density (DFD)), increasing the true specific gravity of the nickel powder, and suppressing rapid sintering of the nickel powder are required. is necessary.

そこで、ニッケル塗膜の密度を高める方法としては、一般に導電ペースト中のニッケル粉末の分散性を良くなるように、導電ペーストの配合組成（樹脂、分散剤、溶剤、等）を最適化する手法が用いられるため、ニッケル粉末自体の特性改善というよりも、導電ペーストの特性改善の側面が強い。
したがって、コンデンサの容量低下抑制に向けたニッケル粉末自体の特性改善としては、真比重を高めること、および、ニッケル粉末の急激な焼結を抑制すること、となるが、これらの双方に、ニッケル粉末の結晶性を高めこと（結晶子径を大きくすること）が有効と考えられている。 Therefore, as a method of increasing the density of the nickel coating film, there is generally a method of optimizing the composition of the conductive paste (resin, dispersant, solvent, etc.) so as to improve the dispersibility of the nickel powder in the conductive paste. Therefore, the characteristics improvement of the conductive paste is stronger than the characteristics improvement of the nickel powder itself.
Therefore, the improvement of the characteristics of the nickel powder itself for suppressing the capacity decrease of the capacitor is to increase the true specific gravity and to suppress the rapid sintering of the nickel powder. It is considered effective to increase the crystallinity (increase the crystallite diameter).

また、内部電極の薄層化に伴う他の問題点は、絶縁破壊による信頼性低下である。
内部電極の薄層化と同時に誘電体も薄層化されており、例えばニッケル膜に突起があると、その突起部分で誘電体層の層間距離が短くなって絶縁破壊が発生しやすくなる。これを抑制するためには、内部電極（ニッケル膜）の表面平滑性を高める必要があり、ニッケル粉末中の粗大粒子（例えば、粒径１μｍ以上）の低減、導電ペースト中でのニッケル粉末の分散性の向上、等の対策が必要である。 Another problem associated with the thinning of the internal electrode is a decrease in reliability due to dielectric breakdown.
At the same time as the internal electrode is thinned, the dielectric is also thinned. For example, if there is a protrusion on the nickel film, the interlayer distance of the dielectric layer is shortened at the protrusion and the dielectric breakdown is likely to occur. In order to suppress this, it is necessary to improve the surface smoothness of the internal electrode (nickel film), to reduce coarse particles (for example, a particle size of 1 μm or more) in the nickel powder, and to disperse the nickel powder in the conductive paste. Measures such as improvement of safety are necessary.

ここで、上記導電ペースト中でのニッケル粉末の分散性の向上は、表面平滑性の場合と同様に、導電ペーストの特性改善の側面が強いため、絶縁破壊による信頼性低下の抑制に向けた、ニッケル粉末自体の特性改善としては、ニッケル粉末中の粗大粒子（例えば、粒径１μｍ以上）を徹底的に低減することである。   Here, the improvement of the dispersibility of the nickel powder in the conductive paste is similar to the case of the surface smoothness, because the side of the improvement in the characteristics of the conductive paste is strong, so that the reduction in reliability due to dielectric breakdown was suppressed. An improvement in the characteristics of the nickel powder itself is to thoroughly reduce coarse particles (for example, a particle size of 1 μm or more) in the nickel powder.

ところで、上記内部電極に使用されるニッケル粉末の製造方法は、気相法（乾式法）と湿式法に大別される。
前者の気相法には、例えば塩化ニッケル等のニッケル化合物の蒸気を高温で還元性ガスにより還元する化学気相析出法（ＣＶＤ法）（例えば、特許文献１参照）、金属ニッケルの蒸気を気相中で凝縮させる物理気相析出法（ＰＶＤ法）、硝酸ニッケル等のニッケル化合物を水や有機溶媒に溶解または分散させた溶液または懸濁液を微細な液滴にし、その液滴を高温加熱して熱分解することでニッケル粉末を析出させる噴霧熱分解法（例えば、特許文献２参照）、等がある。 By the way, the manufacturing method of the nickel powder used for the internal electrode is roughly divided into a vapor phase method (dry method) and a wet method.
The former vapor phase method includes, for example, a chemical vapor deposition method (CVD method) in which a vapor of a nickel compound such as nickel chloride is reduced with a reducing gas at a high temperature (see, for example, Patent Document 1), and vapor of metallic nickel is vaporized. A physical vapor deposition method (PVD method) that condenses in a phase, or a solution or suspension in which a nickel compound such as nickel nitrate is dissolved or dispersed in water or an organic solvent is made into fine droplets, and the droplets are heated at high temperature. Then, there is a spray pyrolysis method (for example, see Patent Document 2) in which nickel powder is precipitated by pyrolysis.

一方、後者の湿式法には、例えばニッケル塩水溶液中からヒドラジン等の還元剤を用いてニッケル粒子を還元析出させてニッケル粉末を得る方法（例えば、特許文献３参照）等が知られている。   On the other hand, as the latter wet method, for example, a method in which nickel particles are reduced and precipitated from a nickel salt aqueous solution using a reducing agent such as hydrazine to obtain nickel powder (see, for example, Patent Document 3) is known.

気相法で得られるニッケル粉末（気相ニッケル粉末）は、数百度以上の高温プロセスでニッケル粒子が合成されるため、例えば粒径０．２〜０．３μｍだと結晶子径１００ｎｍ程度と大きくできるが、その製造方法ゆえに、どうしても粒度分布が大きくなって粗大粒子（例えば、粒径１μｍ以上）が多く含まれることは避けられない。
そこで、得られたニッケル粉末の精密分級（液体サイクロン、気流分級装置、等）を行い、粗大粒子を除去する方法（例えば、特許文献４参照）が試みられているが、例えばニッケル粉末の粒径が０．３μｍ以下（特に０．２μｍ以下）になってくると、粗大粒子の分級除去効率や製品歩留りが低下してくる問題がある。 The nickel powder obtained by the vapor phase method (vapor phase nickel powder) is synthesized by a high temperature process of several hundred degrees or more, and for example, when the particle size is 0.2 to 0.3 μm, the crystallite size is as large as about 100 nm. However, because of the manufacturing method, it is inevitable that the particle size distribution is increased and a large amount of coarse particles (for example, a particle size of 1 μm or more) is contained.
Therefore, a method (for example, see Patent Document 4) for removing coarse particles by performing precise classification (liquid cyclone, airflow classifier, etc.) of the obtained nickel powder has been tried. When the particle size becomes 0.3 μm or less (particularly 0.2 μm or less), there is a problem that the classification and removal efficiency of coarse particles and the product yield decrease.

以上のように、気相ニッケル粉末は、結晶子径が大きいため、真比重が高く、かつニッケル粉末の急激な焼結を抑制でき、コンデンサの容量低下抑制には有効ではあるが、そのままでは粗大粒子が多いため、絶縁破壊によるコンデンサの信頼性低下を引き起こしやすい。   As described above, since the vapor phase nickel powder has a large crystallite size, it has a high true specific gravity and can suppress abrupt sintering of the nickel powder, which is effective for suppressing a decrease in the capacity of the capacitor. Because there are many particles, it tends to cause a decrease in the reliability of capacitors due to dielectric breakdown.

一方、湿式法で得られるニッケル粉末（湿式ニッケル粉末）は、その製造原理からして、粒度分布がシャープで含まれる粗大粒子（例えば、粒径１μｍ以上）を極めて少なくできるものの、数十度の低温プロセスのため、結晶子径４０ｎｍ以下程度のニッケル粒子しか得ることができなかった。   On the other hand, the nickel powder (wet nickel powder) obtained by the wet method can reduce the number of coarse particles having a sharp particle size distribution (for example, a particle size of 1 μm or more) from the manufacturing principle. Due to the low temperature process, only nickel particles having a crystallite diameter of about 40 nm or less could be obtained.

以上のように、湿式ニッケル粉末は、結晶子径が小さいため、真比重が低く、かつニッケル粉末の急激な焼結を生じやすいので、コンデンサの容量低下の引き起こしやすいものの、粗大粒子が少ないため、絶縁破壊によるコンデンサの信頼性低下を抑制できるという特徴がある。   As described above, the wet nickel powder has a small crystallite size, so the true specific gravity is low, and the nickel powder is likely to be rapidly sintered. There is a feature that a reduction in the reliability of the capacitor due to dielectric breakdown can be suppressed.

そこで、粗大粒子の少ない湿式ニッケル粉末において、粗大粒子の発生を伴わずにその結晶子径を増大させることができれば、コンデンサの容量低下や絶縁破壊による信頼性低下という課題を効果的に解消できるため、いくつかの試みがなされている。   Therefore, in wet nickel powder with few coarse particles, if the crystallite diameter can be increased without the generation of coarse particles, the problem of reduced capacitance due to capacitor and reduced reliability due to dielectric breakdown can be effectively solved. Several attempts have been made.

例えば、特許文献５では、湿式ニッケル粉末をＴｉやＳｉの添加処理後に非酸化性雰囲気中で４００〜６００℃で加熱保持し、結晶子径を３０ｎｍ（＝３００Å［オングストローム］）以上とすることが可能と記載されている（段落「００１０」参照）。
この特許文献５に開示されている実施例には、湿式ニッケル粉末の加熱処理による高結晶化の具体的な記載は全く見られないが、平均粒径０．５６〜０．５８μｍと非常に大きな湿式ニッケル粉末を対象としており、上記近年の内部電極の薄層化に対応することは難しい。 For example, in Patent Document 5, wet nickel powder is heated and held at 400 to 600 ° C. in a non-oxidizing atmosphere after the addition treatment of Ti and Si, and the crystallite diameter is set to 30 nm (= 300 Å [angstrom]) or more. It is described as possible (see paragraph “0010”).
In the examples disclosed in Patent Document 5, there is no specific description of high crystallization by heat treatment of wet nickel powder, but the average particle size is very large as 0.56 to 0.58 μm. It is intended for wet nickel powder, and it is difficult to cope with the recent thinning of internal electrodes.

さらに、これまで述べてきたように、近年の内部電極の薄層化に伴い、平均粒径０．３μｍ以下の微細な湿式ニッケル粉末が用いられるようになっており、湿式ニッケル粉末の熱処理温度を、特許文献５に記載の４００〜６００℃の加熱温度まで高くすると、ニッケル粒子同士が強く焼結して粗大粒子を形成するため好ましくないと考えられる。   Furthermore, as described above, with the recent thinning of internal electrodes, fine wet nickel powder having an average particle size of 0.3 μm or less is used, and the heat treatment temperature of the wet nickel powder is increased. When heating to 400 to 600 ° C. described in Patent Document 5, the nickel particles are strongly sintered to form coarse particles, which is considered not preferable.

また、特許文献５では、平均粒径０．５６〜０．５８μｍと非常に大きな湿式ニッケル粉末を対象としているためか、高結晶化のための加熱処理を行った場合において、その後の解砕処理の必要性が述べられていない。この点でも、加熱処理によって、平均粒径０．３μｍ以下の微細な湿式ニッケル粉末の高結晶化を図る場合の問題点が認識されていないことが明らかである。   Moreover, in patent document 5, since the average particle diameter of 0.56-0.58 micrometers is intended for very large wet nickel powder, or when the heat treatment for high crystallization is performed, the subsequent crushing treatment The need for is not stated. In this respect as well, it is apparent that no problem has been recognized in the case of achieving high crystallization of fine wet nickel powder having an average particle size of 0.3 μm or less by heat treatment.

さらに、特許文献５と同様に、湿式ニッケル粉末に加熱処理を施して、積層体の脱バインダ処理時の急激なガス発生の抑制や、内部電極（ニッケル膜）の焼結時の熱収縮速度の制御を行う方法も開示されている（特許文献６、非特許文献１参照）。   Furthermore, similarly to Patent Document 5, the wet nickel powder is subjected to heat treatment to suppress rapid gas generation during the binder removal treatment of the laminate, and the heat shrinkage rate during sintering of the internal electrode (nickel film). A method of performing control is also disclosed (see Patent Document 6 and Non-Patent Document 1).

特許文献６では、湿式ニッケル粉末を還元雰囲気中で１５０〜３５０℃の温度で熱処理してニッケル粉末の表面改質を行い、脱バインダ処理時の急激なガス発生の抑制を行うものであり、水素（Ｈ２）等の還元性ガス濃度は、ニッケル粉末表面の酸化物、水酸化物等の除去（ニッケルにまで還元）を十分に行なうために１体積％以上が必要と記載されている（段落「００２６」〜「００２７」参照）。 In Patent Document 6, wet nickel powder is heat-treated in a reducing atmosphere at a temperature of 150 to 350 ° C. to modify the surface of the nickel powder and suppress rapid gas generation during the debinding process. It is described that the concentration of the reducing gas such as (H 2 ) needs to be 1% by volume or more in order to sufficiently remove oxides, hydroxides and the like on the nickel powder surface (reduction to nickel) (paragraph). “0026” to “0027”).

この還元雰囲気中での熱処理の湿式ニッケル粉末の結晶子径に及ぼす影響については全く記載されておらず、実施例１では１５０℃の加熱温度の熱処理が行われているが、このような低温の熱処理では湿式ニッケル粉末の高結晶化が達成されないのは明らかであり、この点からも、特許文献６の熱処理が湿式ニッケル粉末の高結晶化を目的としていないことが判る。また、還元雰囲気中での加熱処理後に解砕処理が施されていない点は、特許文献５と同様である。   The effect of the heat treatment in the reducing atmosphere on the crystallite size of the wet nickel powder is not described at all. In Example 1, the heat treatment at a heating temperature of 150 ° C. is performed. It is clear that high crystallization of the wet nickel powder is not achieved by the heat treatment, and it can be seen from this point that the heat treatment of Patent Document 6 is not aimed at high crystallization of the wet nickel powder. Moreover, it is the same as that of patent document 5 that the crushing process is not performed after the heat treatment in a reducing atmosphere.

非特許文献１は、ディスプロシウムを含有する湿式ニッケル粉末により内部電極（ニッケル膜）の焼結時の熱収縮速度の制御を行うものであるが、特許文献６と同様に、湿式ニッケル粉末を還元雰囲気中で１５０〜３５０℃の温度で加熱処理してニッケル粉末の表面改質（表面状態変化、不純物除去）が行われている。
還元雰囲気に使用した水素（Ｈ２）等の還元性ガス濃度は、ニッケル粉末表面の状態変化や不純物除去を十分に行なうために１体積％以上が必要と記載されている。 Non-Patent Document 1 controls the heat shrinkage rate during sintering of an internal electrode (nickel film) with a wet nickel powder containing dysprosium. Nickel powder surface modification (surface state change, impurity removal) is performed by heat treatment at a temperature of 150 to 350 ° C. in a reducing atmosphere.
It is described that the concentration of reducing gas such as hydrogen (H 2 ) used in the reducing atmosphere is required to be 1% by volume or more in order to sufficiently change the state of the nickel powder surface and remove impurities.

さらに、上記加熱処理で生じるニッケル粉末の凝集をほぐすためにジェットミル等による解砕処理を施すことが記載されている。しかしながら、還元雰囲気中での加熱処理の湿式ニッケル粉末の結晶子径に及ぼす影響については全く記載されておらず、非特許文献１の加熱処理が湿式ニッケル粉末の高結晶化を目的としていないことは明らかである。   Further, it is described that a crushing process using a jet mill or the like is performed in order to loosen the aggregation of the nickel powder generated by the heat treatment. However, the effect of heat treatment in a reducing atmosphere on the crystallite size of wet nickel powder is not described at all, and that the heat treatment of Non-Patent Document 1 is not aimed at high crystallization of wet nickel powder. it is obvious.

特開平１１−８０８１７号公報Japanese Patent Laid-Open No. 11-80817 特開平１０−１０２１０８号公報JP-A-10-102108 特開２００５−２３３９５号公報JP 2005-23395 A 特開２００１−０７３００７号公報JP 2001-073007 A 特開２０００−１７８６０１号公報JP 2000-178601 A 特開２０１１−１４９０８０号公報JP 2011-149080 A

公技番号２０１２−５０３６９４Official technical number 2012-503694

このような状況の中で、本発明は、積層セラミックコンデンサの内部電極に適用した場合に、コンデンサの容量低下や信頼性低下を効果的に抑制可能な、高い結晶性を有し、かつ粗大粒子（例えば、粒径１μｍ以上）の含有が極めて少ない、湿式ニッケル粉末の製造方法を提供するものである。   Under such circumstances, the present invention has high crystallinity and coarse particles, which can effectively suppress the capacitance reduction and reliability reduction of the capacitor when applied to the internal electrode of the multilayer ceramic capacitor. The present invention provides a method for producing wet nickel powder that contains very little (for example, a particle size of 1 μm or more).

上記目的を達成するために、発明者らは、鋭意研究を行なったところ、平均粒径が小さく、かつ本質的に粗大粒子の含有割合の少ない湿式ニッケル粉末に対し、特定の条件で加熱処理する高結晶化工程、次いで、解砕工程を施すことで、高い結晶性を有し、かつ粗大粒子（例えば、粒径１μｍ以上）の含有が極めて少ない、湿式ニッケル粉末を得ることができることを見出し、本発明を完成したものである。   In order to achieve the above object, the inventors have conducted extensive research and heat-treat the wet nickel powder having a small average particle size and essentially a small content of coarse particles under specific conditions. By performing a high crystallization step and then a crushing step, it has been found that wet nickel powder having high crystallinity and containing very small particles (for example, a particle size of 1 μm or more) can be obtained. The present invention has been completed.

すなわち、上記の目的を達成するための本発明の第１の発明は、ニッケル塩溶液の還元反応法である湿式法を用いて作製した原料ニッケル粉末に、高結晶化工程、解砕工程の各工程を施して得られる湿式ニッケル粉末の製造方法であって、その原料ニッケル粉末は、０．３μｍ以下の平均粒径を有し、かつ結晶子径（ＣＳ１：ｎｍ）が４０ｎｍ以下で、その高結晶化工程が、原料ニッケル粉末を還元雰囲気中で２５０℃〜３５０℃の温度で熱処理して結晶子を増大させ、高結晶子径のニッケル粉末を得る工程であり、その解砕工程が、高結晶化工程で得られた高結晶子径のニッケル粉末に解砕処理を施して、高結晶化工程で凝集・焼結が生じた高結晶子径のニッケル粉末を分散させる工程で、得られた湿式ニッケル粉末は、０．３μｍ以下の平均粒径を有し、かつ結晶子径（ＣＳ２：ｎｍ）が、ＣＳ２≧１．３×ＣＳ１、であり、粒径１μｍ以上の粗大粒子の個数が全粒子個数の５０ｐｐｍ以下であることを特徴とする湿式ニッケル粉末の製造方法である。 That is, the first invention of the present invention for achieving the above object is that the raw nickel powder produced by using a wet method which is a reduction reaction method of a nickel salt solution is applied to each of the high crystallization step and the crushing step. A method for producing a wet nickel powder obtained by performing a process, wherein the raw material nickel powder has an average particle size of 0.3 μm or less and a crystallite size (CS 1 : nm) of 40 nm or less, The high crystallization process is a process in which the raw material nickel powder is heat-treated at a temperature of 250 ° C. to 350 ° C. in a reducing atmosphere to increase the crystallites to obtain a nickel powder having a high crystallite diameter. It is obtained by crushing the high crystallite diameter nickel powder obtained in the high crystallization process and dispersing the high crystallite diameter nickel powder that has been agglomerated and sintered in the high crystallization process. Wet nickel powder is 0.3 μm or less Has Hitoshitsubu diameter, and crystallite diameter (CS 2: nm) is, CS 2 ≧ 1.3 × CS 1 , a number of particle size 1μm or more coarse particles is less than 50ppm of the total grain number It is the manufacturing method of the wet nickel powder characterized by the above-mentioned.

本発明の第２の発明は、ニッケル塩溶液の還元反応法である湿式法を用いて作製した原料ニッケル粉末に、高結晶化工程、解砕工程の各工程を施して得られる湿式ニッケル粉末の製造方法であって、その原料ニッケル粉末は、０．３μｍ以下の平均粒径を有し、かつ結晶子径（ＣＳ１：ｎｍ）が４０ｎｍ以下で、その高結晶化工程が、原料ニッケル粉末を、不活性ガス雰囲気中で３００℃〜４００℃の温度（Ｔ１：℃）で熱処理して結晶子を増大させた後、還元雰囲気中で１５０〜３５０℃以下の温度（Ｔ２：℃、Ｔ２≦Ｔ１）で熱処理してニッケル粉末の酸素含有量を低減させる、高結晶子径のニッケル粉末を得る工程であり、その解砕工程が、高結晶化工程で得られた高結晶子径のニッケル粉末に解砕処理を施して、高結晶化工程で凝集・焼結が生じた高結晶子径のニッケル粉末を分散させる工程で、得られた湿式ニッケル粉末は、０．３μｍ以下の平均粒径を有し、かつ結晶子径（ＣＳ２：ｎｍ）が、ＣＳ２≧１．３×ＣＳ１、であり、粒径１μｍ以上の粗大粒子の個数が全粒子個数の５０ｐｐｍ以下であることを特徴とする湿式ニッケル粉末の製造方法である。 According to a second aspect of the present invention, there is provided a wet nickel powder obtained by subjecting a raw material nickel powder produced by a wet method, which is a reduction reaction method of a nickel salt solution, to a high crystallization step and a crushing step. The raw material nickel powder has an average particle diameter of 0.3 μm or less and a crystallite diameter (CS 1 : nm) of 40 nm or less. The crystallites are increased by heat treatment in an inert gas atmosphere at a temperature of 300 ° C. to 400 ° C. (T 1 : ° C.), and then a temperature of 150 to 350 ° C. or less (T 2 : ° C., T 2 ≦ T 1 ) to obtain a high crystallite diameter nickel powder that is heat-treated to reduce the oxygen content of the nickel powder, and the crushing process is a high crystallite diameter obtained in the high crystallization process. High crystallization process by crushing nickel powder In step aggregation and sintering dispersing nickel powder of high crystallite size resulting wet nickel powder obtained has an average particle size of less than or equal to 0.3 [mu] m, and the crystallite size (CS 2: nm) However, CS 2 ≧ 1.3 × CS 1 , and the number of coarse particles having a particle diameter of 1 μm or more is 50 ppm or less of the total number of particles.

本発明の第３の発明は、第１または第２の発明における原料ニッケル粉末が、少なくとも有機硫黄化合物と無機硫黄化合物のいずれかで表面修飾されていることを特徴とする湿式ニッケル粉末の製造方法である。   According to a third aspect of the present invention, there is provided a method for producing wet nickel powder, characterized in that the raw material nickel powder in the first or second aspect is surface-modified with at least one of an organic sulfur compound and an inorganic sulfur compound. It is.

本発明の第４の発明は、第１〜第３の発明における還元性雰囲気が、水素ガスと不活性ガスの混合雰囲気であり、その混合雰囲気中の水素ガス濃度が０．１体積％を超え５．７体積％未満であることを特徴とする湿式ニッケル粉末の製造方法である。   In a fourth aspect of the present invention, the reducing atmosphere in the first to third aspects is a mixed atmosphere of hydrogen gas and inert gas, and the hydrogen gas concentration in the mixed atmosphere exceeds 0.1% by volume. It is a manufacturing method of the wet nickel powder characterized by being less than 5.7 volume%.

本発明の第５の発明は、第２および第４の発明における不活性ガスが、窒素ガス、希ガスの内のいずれか１種類以上であることを特徴とする湿式ニッケル粉末の製造方法である。   A fifth invention of the present invention is a method for producing wet nickel powder, wherein the inert gas in the second and fourth inventions is one or more of nitrogen gas and rare gas. .

本発明の第６の発明は、第１〜第５の発明における解砕工程が、湿式解砕工程または乾式解砕工程であることを特徴とする湿式ニッケル粉末の製造方法である。   6th invention of this invention is a manufacturing method of the wet nickel powder characterized by the crushing process in 1st-5th invention being a wet crushing process or a dry crushing process.

本発明の第７の発明は、第６の発明における湿式解砕工程が高圧衝突式分散機を用い、前記乾式解砕工程が気流式微粉砕機（ジェットミル）を用いて行われることを特徴とする湿式ニッケル粉末の製造方法である。   The seventh invention of the present invention is characterized in that the wet crushing step in the sixth invention is carried out using a high-pressure collision disperser, and the dry crushing step is carried out using an airflow type pulverizer (jet mill). This is a method for producing wet nickel powder.

本発明に係る湿式ニッケル粉末の製造方法によれば、高い結晶性を有し、かつ粗大粒子（例えば、粒径１μｍ以上）の含有が極めて少ない、湿式ニッケル粉末を得ることが可能となる。
そして、その湿式ニッケル粉末は、積層セラミックコンデンサの内部電極に適用した場合に、コンデンサの容量低下や信頼性低下を効果的に抑制できる顕著な効果を奏するものである。 According to the method for producing a wet nickel powder according to the present invention, it is possible to obtain a wet nickel powder having high crystallinity and containing an extremely small amount of coarse particles (for example, a particle size of 1 μm or more).
And when the wet nickel powder is applied to the internal electrode of the multilayer ceramic capacitor, it has a remarkable effect that can effectively suppress the capacity reduction and the reliability reduction of the capacitor.

以下、本発明の実施の形態について詳細に説明する。
本発明の湿式ニッケル粉末の製造方法では、湿式法（ニッケル塩溶液の還元反応法）を用いて作製した原料ニッケル粉末に、高結晶化工程、解砕工程の各工程を施すことにより、高い結晶性を有し、かつ粗大粒子（例えば、粒径１μｍ以上）の含有が極めて少ない、湿式ニッケル粉末を得ている。 Hereinafter, embodiments of the present invention will be described in detail.
In the method for producing wet nickel powder of the present invention, high crystallinity is obtained by subjecting raw material nickel powder produced by a wet method (reduction reaction method of nickel salt solution) to a high crystallization step and a crushing step. The wet nickel powder has excellent properties and has a very small content of coarse particles (for example, a particle size of 1 μm or more).

［原料ニッケル粉末］
本発明で用いる原料ニッケル粉末には、湿式法で作製されたニッケル粉末を用いる。
湿式法によるニッケル粉末の製造は、ニッケル塩水溶液に、必要に応じて錯化剤、分散剤、アルカリ成分を添加し、ヒドラジン等の還元剤によりニッケル粉末を晶析させて行うことができ、例えば、特許文献３や特許文献６に記載されるような公知の方法を利用することができる。
得られるニッケル粒子の形状は、晶析条件等にもよるが、一般的には、粒状、略球状、球状等である。また湿式法を用いるため、粒度分布がシャープで含まれる粗大粒子（例えば、粒径１μｍ以上）を極めて少なくでき、製品歩留りが高い。 [Raw material nickel powder]
The raw material nickel powder used in the present invention is a nickel powder produced by a wet method.
The production of nickel powder by a wet method can be performed by adding a complexing agent, a dispersing agent, an alkali component to a nickel salt aqueous solution as necessary, and crystallizing the nickel powder with a reducing agent such as hydrazine, for example, A known method as described in Patent Document 3 or Patent Document 6 can be used.
The shape of the obtained nickel particles is generally granular, substantially spherical, spherical or the like, although depending on crystallization conditions and the like. In addition, since the wet method is used, coarse particles (for example, a particle size of 1 μm or more) containing a sharp particle size distribution can be extremely reduced, and the product yield is high.

用いるニッケル塩水溶液は特に限定されるものではなく、例えば、塩化ニッケル、硝酸ニッケルおよび硫酸ニッケル等から選ばれる少なくとも１種類を含む水溶液を用いることができる。
錯化剤やアルカリ成分も特に限定されるものではなく、例えば錯化剤では、クエン酸、酒石酸等の有機多価カルボン酸やその塩（クエン酸ナトリウム、酒石酸ナトリウム等）が、アルカリ成分では水酸化ナトリウム（苛性ソーダ）、水酸化カリウム（苛性カリ）等が適用可能である。 The aqueous nickel salt solution to be used is not particularly limited, and for example, an aqueous solution containing at least one selected from nickel chloride, nickel nitrate, nickel sulfate and the like can be used.
The complexing agent and the alkali component are not particularly limited. For example, complexing agents include organic polyvalent carboxylic acids such as citric acid and tartaric acid and salts thereof (sodium citrate, sodium tartrate, etc.), and alkaline components include water. Sodium oxide (caustic soda), potassium hydroxide (caustic potash) and the like are applicable.

原料ニッケル粉末の平均粒径は、近年の内部電極（ニッケル膜）の薄層化に対応するため、０．３μｍ以下が必要であり、好ましくは、０．０５〜０．２μｍ、さらに好ましくは０．０７〜０．１８μｍである。
平均粒径が０．３μｍを超えると、薄層化された内部電極（ニッケル膜）において、内部電極各層のニッケル粒子の個数が減少してニッケル膜の連続性が損なわれ、内部電極（ニッケル膜）に突起が生じて平坦性が低下するなどの悪影響が生じるからである。 The average particle diameter of the raw material nickel powder needs to be 0.3 μm or less, preferably 0.05 to 0.2 μm, more preferably 0, in order to cope with the recent thinning of the internal electrode (nickel film). 0.07 to 0.18 μm.
When the average particle size exceeds 0.3 μm, the number of nickel particles in each internal electrode layer is reduced in the thinned internal electrode (nickel film), and the continuity of the nickel film is impaired. This is because there is an adverse effect such as the occurrence of protrusions on the surface and the flatness.

湿式法においてニッケル粉末の粒径を制御するには、このニッケル塩水溶液からのヒドラジン等の還元剤による晶析の過程で、ニッケルよりも還元されやすく、かつニッケルと固溶性の高い元素（Ｃｕ、Ａｕ、Ｐｔ、Ｐｄ、Ｒｈ等）またはそれらの化合物を核剤として用いる方法が知られており、それら既知の方法を活用すればよい。   In order to control the particle size of the nickel powder in the wet method, in the process of crystallization from a nickel salt aqueous solution with a reducing agent such as hydrazine, an element (Cu, Au, Pt, Pd, Rh, etc.) or their compounds are known as nucleating agents, and these known methods may be utilized.

上記核剤の活用例としては、例えば特許文献６に、アルカリ性水溶液中に分散したパラジウムと銀からなるコロイド粒子を核剤に用いて湿式ニッケル粉末を製造する方法が開示されているが、この方法に限定されるわけでなく、これ以外の既知の核剤を用いた粒径制御方法が適用可能である。 As an application example of the nucleating agent, for example, Patent Document 6 discloses a method of producing wet nickel powder using colloidal particles composed of palladium and silver dispersed in an alkaline aqueous solution as a nucleating agent. However, the particle size control method using other known nucleating agents is not limited thereto.

本発明の原料ニッケル粉末（湿式法で得られるニッケル粉末）は、前述したように、気相ニッケル粉末と異なり、粒度分布が狭く、例えば粒径１μｍ以上の粗大粒子（粒径の大きな単一粒子や連結粒子）が少ないという特長を有している。
ここで、原料ニッケル粉末（平均粒径０．３μｍ以下）における、粒径１．０μｍ以上の粗大粒子の割合はできるだけ小さい方が好ましいが、具体的には、全粒子個数の５０ｐｐｍ以下である。この程度の粗大粒子の割合であれば、湿式法における晶析条件等を最適化すれば、それ程達成は困難ではない。５０ｐｐｍを超えると、前述のように、内部電極（ニッケル膜）に突起が生じて、誘電体層の絶縁破壊を引き起しやすくなるため好ましくない。 As described above, the raw material nickel powder (nickel powder obtained by a wet method) of the present invention has a narrow particle size distribution unlike the vapor phase nickel powder, for example, coarse particles having a particle size of 1 μm or more (single particles having a large particle size). And connected particles).
Here, the ratio of coarse particles having a particle size of 1.0 μm or more in the raw nickel powder (average particle size of 0.3 μm or less) is preferably as small as possible, but specifically, it is 50 ppm or less of the total number of particles. With such a ratio of coarse particles, it is not so difficult to achieve by optimizing the crystallization conditions in the wet method. If it exceeds 50 ppm, as described above, protrusions are generated in the internal electrode (nickel film), and dielectric breakdown of the dielectric layer is likely to occur, which is not preferable.

また、原料ニッケル粉末（平均粒径０．３μｍ以下）の結晶子径（ＣＳ１：ｎｍ）は４０ｎｍ以下と、気相ニッケル粉末（平均粒径０．２〜０．３μｍ）の結晶子径１００ｎｍ程度と比べて小さいため、真比重が低目で、かつニッケル粉末の急激な焼結を生じやすいという欠点を有している。 In addition, the crystallite size (CS 1 : nm) of the raw material nickel powder (average particle size 0.3 μm or less) is 40 nm or less, and the crystallite size of the vapor phase nickel powder (average particle size 0.2 to 0.3 μm) is 100 nm. Since it is smaller than the degree, the true specific gravity is low, and it has the disadvantages that nickel powder is likely to be rapidly sintered.

原料ニッケル粉末は、晶析反応後にろ過等で固液分離され、洗浄後に、乾燥して得られるため、粒子表面は少なからず酸化されており、酸化ニッケル（ＮｉＯ）や水酸化ニッケル（Ｎｉ(ＯＨ)２）等が存在している。
原料ニッケル粉末の酸素含有量は、平均粒径や乾燥方法等にも依存するが、平均粒径０．２〜０．３μｍ程度であれば、通常、０．５〜１．５重量％程度の範囲内に収まる。ニッケル粉末の酸化が進んで酸素含有量が１．５重量％を超えてくると、積層セラミックコンデンサの焼結時にニッケル粉末の体積収縮が大きくなって、内部電極（ニッケル膜）が途切れて連続性が保てなくなり、さらにニッケル粉末表面のニッケル酸化物が還元・分解して発生するガスによって、コンデンサ内にクラックやデラミネーションを生じる可能性が高くなるため好ましくない。
なお、上記晶析反応後のろ過や乾燥の方法は、公知の方法を適宜選択すればよく、ろ過であれば、フィルタープレス、遠心分離機、デカンタ、等が、乾燥であれば、熱風乾燥、真空乾燥、凍結乾燥、噴霧乾燥、等が挙げられるが、これらに限定されない。 Since the raw material nickel powder is obtained by solid-liquid separation by filtration or the like after crystallization reaction, and drying after washing, the particle surface is oxidized a little, and nickel oxide (NiO) or nickel hydroxide (Ni (OH) ) 2 ) etc. exist.
The oxygen content of the raw material nickel powder depends on the average particle size, the drying method, etc., but if the average particle size is about 0.2 to 0.3 μm, it is usually about 0.5 to 1.5% by weight. Within the range. When the nickel powder is oxidized and the oxygen content exceeds 1.5% by weight, the volumetric shrinkage of the nickel powder increases during the sintering of the multilayer ceramic capacitor, and the internal electrode (nickel film) is interrupted and is continuous. Further, it is not preferable because a gas generated by reduction and decomposition of nickel oxide on the surface of the nickel powder becomes more likely to cause cracks and delamination in the capacitor.
The filtration and drying methods after the crystallization reaction may be appropriately selected from known methods. If filtration, filter press, centrifuge, decanter, etc. are dry, hot air drying, Examples include, but are not limited to, vacuum drying, freeze drying, spray drying, and the like.

ここで、原料ニッケル粉末は、少なくとも有機硫黄化合物と無機硫黄化合物のいずれかで表面修飾してもよい。上記表面修飾により、ニッケル粉末表面の触媒活性（導電ペーストに配合された樹脂の分解に対する触媒活性）が抑制されるため、内部電極（ニッケル膜）の焼結時に、その焼結性を改善する効果が期待できる。   Here, the raw material nickel powder may be surface-modified with at least one of an organic sulfur compound and an inorganic sulfur compound. The surface modification suppresses the catalytic activity on the nickel powder surface (catalytic activity for the decomposition of the resin blended in the conductive paste), so the effect of improving the sinterability when sintering the internal electrode (nickel film) Can be expected.

上記有機硫黄化合物と無機硫黄化合物には、公知の物質を適宜選択すればよく、有機硫黄化合物であれば、有機チオール化合物、有機スルフィド化合物、等が、無機硫黄化合物であれば、硫化水素ナトリウム、硫化水素アンモニウム、硫化ナトリウム、硫化アンモニウム、等が挙げられるが、これらに限定されない。   The organic sulfur compound and the inorganic sulfur compound may be appropriately selected from known substances. If the organic sulfur compound is an organic thiol compound, an organic sulfide compound, etc., and the inorganic sulfur compound is sodium hydrogen sulfide, Examples include, but are not limited to, ammonium hydrogen sulfide, sodium sulfide, ammonium sulfide, and the like.

また、上記有機硫黄化合物や無機硫黄化合物の表面修飾量は、原料ニッケル粉末（平均粒径０．３μｍ以下）に対し硫黄量換算で０．０５〜０．６質量％、好ましくは０．１〜０．４質量％が良い。
０．０５質量％未満では、原料ニッケル粉末の単位表面当りの硫黄化合物量が少なく、上記触媒活性抑制や焼結性の改善が不十分となる場合があり、一方、０．６質量％を超えると、原料ニッケル粉末の単位表面当りの硫黄化合物量が多くなりすぎて、積層セラミックコンデンサの製造工程において腐食ガスの発生等の別の問題が生じる可能性がある。 The surface modification amount of the organic sulfur compound or inorganic sulfur compound is 0.05 to 0.6% by mass, preferably 0.1 to 0.1% in terms of sulfur amount with respect to the raw material nickel powder (average particle size 0.3 μm or less). 0.4 mass% is good.
If it is less than 0.05% by mass, the amount of the sulfur compound per unit surface of the raw material nickel powder is small, and the above-mentioned catalytic activity suppression and improvement in sinterability may be insufficient. In addition, the amount of the sulfur compound per unit surface of the raw nickel powder becomes too large, which may cause another problem such as generation of corrosive gas in the manufacturing process of the multilayer ceramic capacitor.

［高結晶化工程］
本発明の高結晶化工程では、湿式法で得られた上記原料ニッケル粉末に特定の雰囲気と温度範囲での熱処理を施し、原料ニッケル粉末の結晶子を増大させて高結晶子径を有するニッケル粉末を得る工程である。
原料ニッケル粉末の結晶子径（ＣＳ１）は、この高結晶化工程により増大し、後述する解砕工程において若干低下するものの、最終的に得られる湿式ニッケル粉の結晶子径（ＣＳ２）は、ＣＳ２≧１．３×ＣＳ１、好ましくはＣＳ２≧１．７×ＣＳ１、より好ましくはＣＳ２≧２．０×ＣＳ１、で表される範囲まで到達させることができる。 [High crystallization process]
In the high crystallization process of the present invention, the raw material nickel powder obtained by the wet method is subjected to a heat treatment in a specific atmosphere and temperature range to increase the crystallites of the raw material nickel powder to have a high crystallite diameter. It is the process of obtaining.
Although the crystallite diameter (CS 1 ) of the raw material nickel powder is increased by this high crystallization process and slightly decreased in the crushing process described later, the crystallite diameter (CS 2 ) of the finally obtained wet nickel powder is , CS 2 ≧ 1.3 × CS 1 , preferably CS 2 ≧ 1.7 × CS 1 , more preferably CS 2 ≧ 2.0 × CS 1 .

本発明の高結晶化工程は、熱処理の雰囲気と温度範囲によって、以下の第１の実施形態と第２の実施形態に分けられる。
＜第１の実施形態＞
上記高結晶化工程における、第１の実施形態は、平均粒径が０．３μｍ以下で、かつ結晶子径（ＣＳ１：ｎｍ）が４０ｎｍ以下の原料ニッケル粉末を還元雰囲気中で２５０℃〜３５０℃の温度で熱処理し、原料ニッケル粉中の結晶子を増大させて高結晶子径のニッケル粉末を得るものである。 The high crystallization process of the present invention is divided into the following first and second embodiments depending on the atmosphere and temperature range of the heat treatment.
<First Embodiment>
In the high crystallization step, the first embodiment is such that a raw material nickel powder having an average particle size of 0.3 μm or less and a crystallite size (CS 1 : nm) of 40 nm or less is reduced to 250 ° C. to 350 ° C. in a reducing atmosphere. Heat treatment is performed at a temperature of 0 ° C. to increase the number of crystallites in the raw material nickel powder, thereby obtaining a nickel powder having a high crystallite diameter.

上記還元雰囲気は、水素ガスと不活性ガスの混合雰囲気が望ましく、不活性ガスとしては、窒素ガス（Ｎ２）、ヘリウム（Ｈｅ）、アルゴン（Ａｒ）等の希ガスのいずれか１種類以上が挙げられるが、中でも安価でかつ高純度品を得やすい窒素ガスが望ましい。 The reducing atmosphere is preferably a mixed atmosphere of hydrogen gas and inert gas, and the inert gas includes at least one kind of rare gas such as nitrogen gas (N 2 ), helium (He), argon (Ar), etc. Among them, nitrogen gas is preferable because it is inexpensive and easily obtains a high-purity product.

還元雰囲気（例えば、上記水素ガスと不活性ガスの混合雰囲気）を用いると、原料ニッケル粉末において、その結晶粒界近傍や微細な開空孔（オープンポア）内に極微量存在すると想定されるニッケル酸化物や水酸化ニッケル物等が還元除去（Ｎｉに還元）されるためか、原料ニッケル粉末の高結晶化（結晶子径増大）が促進されやすい。
一方で、原料ニッケル粉末表面に所定量存在するニッケル酸化物や水酸化ニッケル物等も同様に還元除去（Ｎｉに還元）されるが、これは、ニッケル粉末の酸素含有量が低下するという点では好ましい側面ではあるが、焼結抑制作用を有するニッケル酸化物や水酸化ニッケル物の除去により、ニッケル粒子同士が焼結（ネッキング）しやすくなって、粗大粒子の形成が促進される恐れがある。そのため、過度に還元性を高めた雰囲気（例えば高濃度の水素ガス含有する窒素ガス雰囲気等）は避けた方が良い。 When a reducing atmosphere (for example, a mixed atmosphere of hydrogen gas and inert gas described above) is used, nickel that is assumed to exist in a minute amount in the vicinity of crystal grain boundaries and in fine open pores (open pores) in the raw material nickel powder It is easy to promote high crystallization (increase in crystallite diameter) of the raw material nickel powder because oxides, nickel hydroxide, etc. are reduced and removed (reduced to Ni).
On the other hand, nickel oxide, nickel hydroxide, etc. present in a predetermined amount on the surface of the raw material nickel powder are similarly reduced and removed (reduced to Ni), but this is because the oxygen content of the nickel powder is reduced. Although it is a preferred aspect, the removal of nickel oxide or nickel hydroxide having a sintering inhibiting action may facilitate the sintering (necking) of the nickel particles, thereby promoting the formation of coarse particles. For this reason, it is better to avoid an atmosphere in which reducibility is excessively increased (for example, a nitrogen gas atmosphere containing a high concentration of hydrogen gas).

原料ニッケル粉末の酸素含有量は、還元雰囲気を用いる上記高結晶化工程を経ることで、粉末表面に存在するニッケル酸化物や水酸化ニッケル物等が還元除去（Ｎｉに還元）されるため、０．２〜０．５重量％程度低下する傾向にある（なお、高結晶化工程の完了に当たり、一旦還元されたニッケル粉末は、大気中に取り出す際に再酸化されている（徐々に酸化させて極薄の安定な酸化ニッケル被膜を形成する徐酸化処理が行われる））。   The oxygen content of the raw material nickel powder is 0 because nickel oxide, nickel hydroxide, etc. existing on the powder surface are reduced and removed (reduced to Ni) through the high crystallization process using a reducing atmosphere. (It should be noted that when the high crystallization process is completed, the nickel powder once reduced is re-oxidized when taken out into the atmosphere. A gradual oxidation process is performed to form a very thin and stable nickel oxide film)).

上記混合雰囲気中の水素ガス濃度は０．１体積％を超え５．７体積％未満、より好ましくは、０．１体積％を超え４.０体積％未満、さらに好ましくは０．２体積％以上１．０体積％未満である。
水素ガス濃度が０．１体積％以下だと、上記原料ニッケル粉末の高結晶化（結晶子径増大）の促進効果が薄れるため、望ましくない。一方、水素ガス濃度が５．７体積％未満だと、水素と窒素の混合ガス雰囲気では不燃性になるため、高結晶化工程の加熱装置（加熱炉）における取扱いがより簡便となり好ましい。
水素ガス濃度を５．７体積％以上にしても、高結晶化（結晶子径増大）の促進効果に変わりがなく、原料ニッケル粉末表面のニッケル酸化物や水酸化ニッケル物が除去されやすくなってニッケル粒子同士の焼結（ネッキング）の促進を招くだけである。 The hydrogen gas concentration in the mixed atmosphere is more than 0.1 volume% and less than 5.7 volume%, more preferably more than 0.1 volume% and less than 4.0 volume%, still more preferably 0.2 volume% or more. It is less than 1.0% by volume.
If the hydrogen gas concentration is 0.1% by volume or less, the effect of promoting high crystallization (increase in crystallite diameter) of the raw material nickel powder is reduced, which is not desirable. On the other hand, when the hydrogen gas concentration is less than 5.7% by volume, it becomes nonflammable in a mixed gas atmosphere of hydrogen and nitrogen, and therefore, handling in a heating apparatus (heating furnace) in a high crystallization process becomes easier and preferable.
Even when the hydrogen gas concentration is 5.7% by volume or more, the effect of promoting high crystallization (increase in crystallite diameter) remains the same, and the nickel oxide and nickel hydroxide on the surface of the raw material nickel powder are easily removed. It only promotes the sintering (nicking) of the nickel particles.

熱処理の加熱温度は２５０〜３５０℃、好ましくは３００〜３５０℃である。
熱温度が２５０℃未満だと、原料ニッケル粉末の高結晶化（結晶子径増大）が促進されず（ＣＳ２＜１．３×ＣＳ１）、好ましくない。また、加熱温度が３５０℃より高いと、高結晶化（結晶子径増大）は促進される（ＣＳ２≧１．３×ＣＳ１）ものの、原料ニッケル粉末同士の焼結（ネッキング）が進行して、次工程の解砕工程で分散しきれずに残存する粗大粒子が生じるため望ましくない。 The heating temperature of the heat treatment is 250 to 350 ° C, preferably 300 to 350 ° C.
When the heat temperature is less than 250 ° C., high crystallization (increase in crystallite diameter) of the raw material nickel powder is not promoted (CS 2 <1.3 × CS 1 ), which is not preferable. When the heating temperature is higher than 350 ° C., high crystallization (crystallite diameter increase) is promoted (CS 2 ≧ 1.3 × CS 1 ), but sintering (necking) between the raw material nickel powders proceeds. Then, coarse particles that remain without being dispersed in the crushing step of the next step are not desirable.

熱処理の加熱時間は、加熱温度にもよるが（加熱温度が高い程、加熱時間を短くできる）、高結晶化工程の処理効率を考慮すると、１０分〜４時間、好ましくは２０分〜３時間、さらに好ましくは３０分〜２時間である。
加熱時間が１０分未満だと、加熱時間が短すぎて原料ニッケル粉末の温度分布が大きくなって高結晶化（結晶子径増大）にバラツキが生じる可能性があり好ましくない。また、加熱時間が４時間を超えると、高結晶化工程の処理効率が著しく低下するため望ましくない。 The heating time of the heat treatment depends on the heating temperature (the higher the heating temperature, the shorter the heating time), but considering the processing efficiency of the high crystallization step, 10 minutes to 4 hours, preferably 20 minutes to 3 hours. More preferably, it is 30 minutes to 2 hours.
If the heating time is less than 10 minutes, the heating time is too short, the temperature distribution of the raw material nickel powder becomes large, and there is a possibility that high crystallization (crystallite diameter increase) may vary, which is not preferable. On the other hand, when the heating time exceeds 4 hours, the processing efficiency of the high crystallization step is remarkably lowered, which is not desirable.

＜第２の実施形態＞
高結晶化工程における、第２の実施形態は、平均粒径が０．３μｍ以下で、かつ結晶子径（ＣＳ１：ｎｍ）が４０ｎｍ以下の原料ニッケル粉末を不活性ガス雰囲気中で３００℃〜４００℃の温度（Ｔ１：℃）で熱処理して結晶子を増大させた後、還元雰囲気中で１５０〜３５０℃以下の温度（Ｔ２：℃、Ｔ２≦Ｔ１）で熱処理してニッケル粉末の酸素含有量を低減させて、高結晶子径のニッケル粉末を得るものである。 <Second Embodiment>
In the second embodiment of the high crystallization process, a raw material nickel powder having an average particle diameter of 0.3 μm or less and a crystallite diameter (CS 1 : nm) of 40 nm or less is obtained in an inert gas atmosphere at 300 ° C. to After heat treatment at a temperature of 400 ° C. (T 1 : ° C.) to increase crystallites, nickel is heat-treated at a temperature of 150 to 350 ° C. or less (T 2 : ° C., T 2 ≦ T 1 ) in a reducing atmosphere. By reducing the oxygen content of the powder, nickel powder having a high crystallite diameter is obtained.

上記不活性ガス雰囲気中の熱処理では、原料ニッケル粉末表面に所定量存在するニッケル酸化物や水酸化ニッケル物等が還元除去（Ｎｉに還元）されずに粉末表面に残存し、原料ニッケル粉末同士の焼結を抑制するため、前述した第１の実施形態の還元雰囲気での熱処理に比べ、加熱温度を高めることができ（第２の実施形態の加熱温度（Ｔ１）＝３００〜４００℃、第１の実施形態の加熱温度＝２５０〜３５０℃）、原料ニッケル粉末の高結晶化（結晶子径増大）を促進できる側面がある。 In the heat treatment in the above inert gas atmosphere, nickel oxide, nickel hydroxide, etc. existing in a predetermined amount on the surface of the raw material nickel powder remain on the surface of the powder without being reduced and removed (reduced to Ni). In order to suppress the sintering, the heating temperature can be increased as compared with the heat treatment in the reducing atmosphere of the first embodiment described above (heating temperature (T 1 ) of the second embodiment = 300 to 400 ° C., In one embodiment, the heating temperature is 250 to 350 ° C., and there is a side face that can promote high crystallization (increase in crystallite diameter) of the raw material nickel powder.

上記不活性ガスとしては、窒素ガス、ヘリウム（Ｈｅ）、アルゴン（Ａｒ）等の希ガスのいずれか１種類以上が挙げられるが、中でも安価でかつ高純度品を得やすい窒素ガスが望ましい。
不活性ガスに含まれる、不純物としての酸素ガス（Ｏ２）濃度は１０ｐｐｍ以下、好ましくは５ｐｐｍ以下、さらに好ましくは１ｐｐｍ以下がよい。酸素ガス濃度が１０ｐｐｍを超えると、不活性ガス雰囲気中の熱処理において、原料ニッケル粉末の酸化が進行し、粉末表面のニッケル酸化物等が過剰なまでに増加するため好ましくない。 Examples of the inert gas include one or more of nitrogen gas, rare gas such as helium (He), and argon (Ar). Among them, nitrogen gas is preferable because it is inexpensive and easily obtains a high-purity product.
The concentration of oxygen gas (O 2 ) as an impurity contained in the inert gas is 10 ppm or less, preferably 5 ppm or less, more preferably 1 ppm or less. When the oxygen gas concentration exceeds 10 ppm, the oxidation of the raw material nickel powder proceeds in the heat treatment in the inert gas atmosphere, and the nickel oxide and the like on the powder surface increase to an excessive amount, which is not preferable.

熱処理の加熱温度（Ｔ１：℃）は３００〜４００℃、好ましくは３５０〜４００℃である。加熱温度（Ｔ１：℃）が３００℃未満だと、原料ニッケル粉末の高結晶化（結晶子径増大）が促進されず（ＣＳ２＜１．３×ＣＳ１）、好ましくない。また、加熱温度（Ｔ１：℃）が４００℃より高いと、高結晶化（結晶子径増大）は促進される（ＣＳ２≧１．３×ＣＳ１）ものの、原料ニッケル粉末同士の焼結（ネッキング）が進行して、次工程の解砕工程で分散しきれずに残存する粗大粒子が生じるため望ましくない。 The heating temperature (T 1 : ° C.) of the heat treatment is 300 to 400 ° C., preferably 350 to 400 ° C. When the heating temperature (T 1 : ° C.) is less than 300 ° C., high crystallization (increase in crystallite diameter) of the raw material nickel powder is not promoted (CS 2 <1.3 × CS 1 ), which is not preferable. Further, when the heating temperature (T 1 : ° C.) is higher than 400 ° C., high crystallization (crystallite diameter increase) is promoted (CS 2 ≧ 1.3 × CS 1 ), but sintering of raw material nickel powders is performed. (Necking) proceeds, and coarse particles remaining without being dispersed in the subsequent crushing step are generated, which is not desirable.

熱処理の加熱時間は、加熱温度にもよるが（加熱温度が高い程、加熱時間を短くできる）、高結晶化工程の処理効率を考慮すると、１０分〜４時間、好ましくは２０分〜３時間、さらに好ましくは３０分〜２時間である。
加熱時間が１０分未満だと、加熱時間が短すぎて原料ニッケル粉末の温度分布が大きくなって高結晶化（結晶子径増大）にバラツキが生じる可能性があり好ましくない。また、加熱時間が４時間を超えると、高結晶化工程の処理効率が著しく低下するため望ましくない。 The heating time of the heat treatment depends on the heating temperature (the higher the heating temperature, the shorter the heating time), but considering the processing efficiency of the high crystallization step, 10 minutes to 4 hours, preferably 20 minutes to 3 hours. More preferably, it is 30 minutes to 2 hours.
If the heating time is less than 10 minutes, the heating time is too short, the temperature distribution of the raw material nickel powder becomes large, and there is a possibility that high crystallization (crystallite diameter increase) may vary, which is not preferable. On the other hand, when the heating time exceeds 4 hours, the processing efficiency of the high crystallization step is remarkably lowered, which is not desirable.

第２の実施形態では、不活性ガス雰囲気中での熱処理で原料ニッケル粉末の高結晶化を図った後、引き続き、還元雰囲気中で１５０〜３５０℃以下の温度（Ｔ２：℃、Ｔ２≦Ｔ１）で熱処理し、ニッケル粉末表面に残存するニッケル酸化物等を還元除去（Ｎｉに還元）して、ニッケル粉末の酸素含有量を低減させる必要がある。 In the second embodiment, after high crystallization of the raw material nickel powder is achieved by heat treatment in an inert gas atmosphere, subsequently, a temperature of 150 to 350 ° C. or less (T 2 : ° C., T 2 ≦ T) in a reducing atmosphere. It is necessary to reduce the oxygen content of the nickel powder by performing heat treatment at T 1 ) and reducing and removing nickel oxide remaining on the nickel powder surface (reducing to Ni).

上記還元雰囲気は、水素ガスと不活性ガスの混合雰囲気が望ましく、不活性ガスとしては、窒素ガス（Ｎ２）、ヘリウム（Ｈｅ）、アルゴン（Ａｒ）等の希ガスのいずれか１種類以上が挙げられるが、中でも安価でかつ高純度品を得やすい窒素ガスが望ましい。 The reducing atmosphere is preferably a mixed atmosphere of hydrogen gas and inert gas, and the inert gas includes at least one kind of rare gas such as nitrogen gas (N 2 ), helium (He), argon (Ar), etc. Among them, nitrogen gas is preferable because it is inexpensive and easily obtains a high-purity product.

上記還元雰囲気中の水素ガス濃度は０．１体積％を超え５．７体積％未満、より好ましくは、０．５〜４．０体積％、さらに好ましくは１．０〜４．０体積％である。
水素ガス濃度が０．１体積％以下だと、ニッケル粉末表面に残存するニッケル酸化物等の還元除去（Ｎｉに還元）が不十分となるため望ましくない。一方、水素ガス濃度を５．７体積％以上にしても、ニッケル酸化物等の還元除去（Ｎｉに還元）の効率に著しい改善が見られる訳ではなく、また、水素と窒素の混合ガス雰囲気では不燃性の扱いにならなくなるため、必ずしも好ましいとは言えない。 The hydrogen gas concentration in the reducing atmosphere is more than 0.1% by volume and less than 5.7% by volume, more preferably 0.5 to 4.0% by volume, still more preferably 1.0 to 4.0% by volume. is there.
When the hydrogen gas concentration is 0.1% by volume or less, reduction removal (reduction to Ni) such as nickel oxide remaining on the surface of the nickel powder is not desirable. On the other hand, even when the hydrogen gas concentration is 5.7% by volume or more, there is no significant improvement in the efficiency of reduction removal (reduction to Ni) such as nickel oxide, and in a mixed gas atmosphere of hydrogen and nitrogen It is not necessarily preferable because it is not treated as nonflammable.

還元雰囲気中の熱処理の加熱温度（Ｔ２：℃、Ｔ２≦Ｔ１）は、１５０〜３５０℃以下、好ましくは２００〜３００℃である。加熱温度（Ｔ２：℃）が１５０℃未満だと、ニッケル粉末表面に残存するニッケル酸化物等の還元除去（Ｎｉに還元）が不十分となるため望ましくない。一方、加熱温度（Ｔ２：℃）が３５０℃より高いと、ニッケル粉末同士の焼結（ネッキング）が進行して、次工程の解砕工程で分散しきれずに残存する粗大粒子が生じるため望ましくない。また還元雰囲気中の熱処理の加熱温度（Ｔ２：℃）は不活性ガス雰囲気中熱処理の加熱温度（Ｔ１：℃）以下とする。 The heating temperature (T 2 : ° C., T 2 ≦ T 1 ) of the heat treatment in the reducing atmosphere is 150 to 350 ° C. or less, preferably 200 to 300 ° C. When the heating temperature (T 2 : ° C.) is less than 150 ° C., it is not desirable because reduction removal (reduction to Ni) of nickel oxide or the like remaining on the nickel powder surface becomes insufficient. On the other hand, when the heating temperature (T 2 : ° C.) is higher than 350 ° C., the sintering (necking) between the nickel powders proceeds, and coarse particles remaining without being dispersed in the subsequent crushing step are generated. Absent. The heating temperature (T 2 : ° C.) of the heat treatment in the reducing atmosphere is set to be equal to or lower than the heating temperature (T 1 : ° C.) of the heat treatment in the inert gas atmosphere.

還元雰囲気中の熱処理の加熱時間は、１０分〜４時間、好ましくは２０分〜３時間、さらに好ましくは３０分〜２時間である。加熱時間が１０分未満だと、加熱時間が短すぎて原料ニッケル粉末の温度分布が大きくなり、ニッケル粉末の酸素含有量の低減にバラツキが生じる可能性があり好ましくない。また、加熱時間が４時間を超えると、処理効率が著しく低下するため望ましくない。   The heating time of the heat treatment in the reducing atmosphere is 10 minutes to 4 hours, preferably 20 minutes to 3 hours, and more preferably 30 minutes to 2 hours. When the heating time is less than 10 minutes, the heating time is too short, the temperature distribution of the raw material nickel powder becomes large, and the reduction in the oxygen content of the nickel powder may cause variation, which is not preferable. On the other hand, if the heating time exceeds 4 hours, the processing efficiency is remarkably lowered, which is not desirable.

高結晶化工程の第２の実施形態におけるニッケル粉末の酸素含有量は、上記還元雰囲気中の熱処理により、粉末表面に存在するニッケル酸化物等が還元除去（Ｎｉに還元）されるため、原料ニッケル粉末に比べて、０．２〜０．５重量％程度低下する傾向にある。なお、高結晶化工程の完了に当たり、一旦還元されたニッケル粉末は、大気中に取り出す際に再酸化されている（徐々に酸化させて極薄の安定な酸化ニッケル被膜を形成する徐酸化処理が行われる）。   The oxygen content of the nickel powder in the second embodiment of the high crystallization process is that the nickel oxide, etc. present on the powder surface is reduced and removed (reduced to Ni) by the heat treatment in the reducing atmosphere. Compared to powder, it tends to decrease by about 0.2 to 0.5% by weight. Upon completion of the high crystallization process, the nickel powder once reduced is reoxidized when taken out into the atmosphere (gradual oxidation treatment that gradually oxidizes to form a very thin stable nickel oxide film is performed. Done).

上記高結晶化工程の第１の実施形態、および第２の実施形態において、還元雰囲気ガスや不活性ガスは、高結晶化工程で使用する加熱装置（加熱炉）に供給しながら用いられる。
加熱装置（加熱炉）としては、バッチ炉、ローラーハース炉、プッシャー炉などを用いることができるが、還元雰囲気および不活性ガス雰囲気で使用できるものであれば特に限定されない。 In the first embodiment and the second embodiment of the high crystallization process, the reducing atmosphere gas and the inert gas are used while being supplied to a heating apparatus (heating furnace) used in the high crystallization process.
As the heating device (heating furnace), a batch furnace, a roller hearth furnace, a pusher furnace, or the like can be used, but is not particularly limited as long as it can be used in a reducing atmosphere and an inert gas atmosphere.

［解砕工程］
本発明の解砕処理では、上記高結晶化工程で得られた高結晶子径のニッケル粉末に解砕処理を施して、高結晶化工程で緩やかな凝集・焼結が生じた高結晶子径のニッケル粉末を分散させる工程である。
前述の通り、原料ニッケル粉末（平均粒径０．３μｍ以下）における、粒径１．０μｍ以上の粗大粒子の全粒子個数に対する割合は５０ｐｐｍ以下のため、解砕工程を経ることによって、粒径１．０μｍ以上の粗大粒子の全粒子個数に対する割合は５０ｐｐｍ以下にする必要がある。 [Crushing process]
In the pulverization treatment of the present invention, the high crystallite diameter obtained by subjecting the nickel powder having a high crystallite diameter obtained in the high crystallization step to pulverization and causing gradual aggregation and sintering in the high crystallization step. In which nickel powder is dispersed.
As described above, the ratio of the coarse particles having a particle size of 1.0 μm or more in the raw material nickel powder (average particle size of 0.3 μm or less) to the total number of particles is 50 ppm or less. The ratio of coarse particles of 0.0 μm or more to the total number of particles needs to be 50 ppm or less.

上記解砕工程は、湿式解砕工程、乾式解砕工程のいずれでもよく、例えば、湿式解砕工程であれば高圧衝突式分散機等が、また乾式解砕工程であれば、気流式微粉砕機（ジェットミル）等、が挙げられるが、高結晶化工程で得られた高結晶子径のニッケル粉末における粒径１．０μｍ以上の粗大粒子の全粒子個数に対する割合は５０ｐｐｍ以下にできれば良く、これらに限定されない。   The crushing step may be either a wet crushing step or a dry crushing step. For example, a high-pressure collision disperser or the like is used in the wet crushing step, and an airflow fine crusher is used in the dry crushing step. (Jet mill), etc., but the ratio of the coarse particles having a particle size of 1.0 μm or more in the nickel powder having a high crystallite size obtained in the high crystallization step to the total number of particles may be 50 ppm or less. It is not limited to.

上記高圧衝突式分散機としては、例えばアルティマイザー（スギノマシン株式会社製）、マイクロフルイダイザー（みずほ工業株式会社製）、ナノマイザー（吉田機械工業株式会社製）等が挙げられ、気流式微粉砕機（ジェットミル）には、カウンター式ジェットミル、スパイラル式ジェットミル（日本ニューマチック工業株式会社、ホソカワミクロン株式会社）等が挙げられる。   Examples of the high-pressure collision disperser include an ultimateizer (manufactured by Sugino Machine Co., Ltd.), a microfluidizer (manufactured by Mizuho Kogyo Co., Ltd.), a nanomizer (manufactured by Yoshida Kikai Kogyo Co., Ltd.), and the like. Examples of the jet mill) include a counter type jet mill and a spiral type jet mill (Nippon Pneumatic Industrial Co., Ltd., Hosokawa Micron Co., Ltd.).

ここで、解砕工程でジェットミルを用いる場合を一例として説明する。
ジェットミルを用いた解砕処理のガス媒体には空気が一般的であるが、高結晶子径のニッケル粉末の平均粒径が０．３μｍ以下と小さく酸化しやすいこと、粉塵濃度が高まると粉塵爆発の可能性があること、等を考慮すると、不活性ガスを用いても良い。
なお、ニッケル粉末が微細化するほど凝集性が強くなるため、より強力な解砕力を与える必要があり、この点からすると、空気よりも軽いガス媒体を用いることが望ましく、具体的には、窒素ガス、ヘリウムガスが挙げられる。 Here, a case where a jet mill is used in the crushing step will be described as an example.
Air is generally used as a gas medium for pulverization using a jet mill, but the average particle diameter of nickel powder with a high crystallite diameter is as small as 0.3 μm or less and is easily oxidized. In consideration of the possibility of explosion, etc., an inert gas may be used.
In addition, since the cohesion becomes stronger as the nickel powder becomes finer, it is necessary to give a stronger crushing force. From this point of view, it is desirable to use a gas medium lighter than air, specifically, nitrogen gas. And helium gas.

解砕工程は、高結晶化工程で得られた高結晶子径のニッケル粉末を分散させて粗大粒子を低減・消失させる作用を有するが、それ以外にも、ニッケル粉末同士もしくはニッケル粉末と分散・粉砕機の機壁での擦れ合いによるニッケル粉末の表面平滑化の作用も有している（原料ニッケル粉末よりも平滑な表面が得られる）。
なお、解砕工程では、ニッケル粉末に大きな解砕力が印加されるため、高結晶化工程で高結晶化したニッケル粉末の結晶子径は若干低下する。例えば、ジェットミルを用いた解砕処理が施されると、ニッケル粉末の結晶子径は１〜２ｎｍ程度低下する。 The crushing step has the effect of reducing and eliminating coarse particles by dispersing the high crystallite diameter nickel powder obtained in the high crystallization step. It also has the effect of smoothing the surface of the nickel powder by rubbing at the machine wall of the pulverizer (a smoother surface can be obtained than the raw nickel powder).
In the crushing step, since a large crushing force is applied to the nickel powder, the crystallite diameter of the nickel powder highly crystallized in the high crystallization step slightly decreases. For example, if the crushing process using a jet mill is performed, the crystallite diameter of nickel powder will fall about 1-2 nm.

本発明の湿式ニッケル粉末の製造方法では、高結晶化工程の熱処理により高結晶子径のニッケル粉末に緩やかな凝集・焼結が生じて粗大粒子が形成された場合であっても、解砕工程で分散させて粗大粒子を低減・消失させているので、最終的に得られる湿式ニッケル粉末は、その平均粒径が、原料ニッケル粉末と同等の０．３μｍ以下となっている。   In the method for producing wet nickel powder of the present invention, even when coarse particles are formed due to mild agglomeration / sintering in nickel powder having a high crystallite size by heat treatment in the high crystallization step, the crushing step Since the coarse particles are reduced / disappeared by the dispersion, the wet nickel powder finally obtained has an average particle size of 0.3 μm or less, which is the same as that of the raw material nickel powder.

以下に、本発明の実施例を用いて詳細に説明するが、本発明は、これらの実施例によって何ら限定されるものではない。なお、ニッケル粉末の評価は以下のようにして行なった。   Hereinafter, the present invention will be described in detail using examples, but the present invention is not limited to these examples. The nickel powder was evaluated as follows.

［平均粒径］
走査型電子顕微鏡（ＳＥＭ、ＪＳＭ−５５１０、日本電子株式会社製）を用い、倍率１００００倍のＳＥＭ像（視野：縦９．６μｍ×横１２．８μｍ）の写真を得た。
このＳＥＭ像を画像解析ソフト（Ｍａｃ−Ｖｉｅｗ、株式会社マウンテック製）を用いて像内の粒子形状の全様が見える粒子の面積と個数を計測し、これらから各粒子の直径を求め平均値により算出した。 [Average particle size]
A scanning electron microscope (SEM, JSM-5510, manufactured by JEOL Ltd.) was used to obtain a photograph of an SEM image (field of view: vertical 9.6 μm × horizontal 12.8 μm) at a magnification of 10,000.
This SEM image is measured using image analysis software (Mac-View, manufactured by Mountec Co., Ltd.) to measure the area and number of particles in which the entire shape of the particle shape can be seen, and from these, the diameter of each particle is obtained and averaged. Calculated.

［粗大粒子の数］
走査型電子顕微鏡を用い、倍率５０００倍のＳＥＭ像（視野：縦１９．２μｍ×横２５．６μｍ）の写真を２０視野得る。この２０視野のＳＥＭ像を、画像解析ソフトを用いて像内の粒子形状の全様が見える粒子の面積と個数を計測し、これらから各粒子の直径を求め、直径が１．０μｍ以上のものを粗大粒子としてカウントした。 [Number of coarse particles]
Using a scanning electron microscope, 20 views of a SEM image (field of view: length 19.2 μm × width 25.6 μm) at a magnification of 5000 times are obtained. This SEM image of 20 fields of view is measured using the image analysis software to measure the area and number of particles in which the entire shape of the particles can be seen, and from these, the diameter of each particle is obtained. Were counted as coarse particles.

［ニッケル粉の酸素含有量］
ニッケル粉の酸素含有量は、分析装置（ＬＥＣＯ社製、ＴＣ４３６ＡＲ）にて測定した。 [Oxygen content of nickel powder]
The oxygen content of nickel powder was measured with an analyzer (manufactured by LECO, TC436AR).

［原料ニッケル粉末の作製］
以下に、湿式還元法を用いた原料ニッケル粉末作製の詳細を示す。
パラジウムと微量の銀とゼラチンからなるアルカリ性コロイド溶液に、アルカリ性のヒドラジン溶液を混合し、ニッケルを還元するためのアルカリ性コロイド溶液を作製した。
作製したアルカリ性コロイド溶液におけるパラジウム、銀、ゼラチンの含有量は、始液となるニッケル塩水溶液中のニッケルの全質量に対して、パラジウム：７．５質量ｐｐｍ、銀：０．０７５質量ｐｐｍ、ゼラチン：０．７５質量％とした。なお、溶液中のパラジウムおよび銀の含有量は、ＩＣＰ発光分光分析法により分析した。 [Production of raw material nickel powder]
Below, the detail of raw material nickel powder preparation using the wet reduction method is shown.
An alkaline hydrazine solution was mixed with an alkaline colloidal solution composed of palladium, a small amount of silver and gelatin to prepare an alkaline colloidal solution for reducing nickel.
The content of palladium, silver, and gelatin in the prepared alkaline colloidal solution is palladium: 7.5 mass ppm, silver: 0.075 mass ppm, gelatin with respect to the total mass of nickel in the nickel salt aqueous solution that is the starting solution. : 0.75% by mass. The contents of palladium and silver in the solution were analyzed by ICP emission spectroscopic analysis.

上記ニッケルを還元するためのアルカリ性コロイド溶液の作製は、具体的には、次のように行った。
先ず、純水３０Ｌに所定量のゼラチンを溶解させた後、ヒドラジンの濃度が０．０１５ｇ／Ｌとなるようにヒドラジンを混合し、ゼラチンとヒドラジンを含む溶液を作製した。
次に、純水と所定量のパラジウム塩と銀塩の１Ｌの混合溶液を作製し、先に作製したゼラチンとヒドラジンを含む溶液に滴下して、コロイド溶液を得た。 The production of the alkaline colloid solution for reducing the nickel was specifically performed as follows.
First, after a predetermined amount of gelatin was dissolved in 30 L of pure water, hydrazine was mixed so that the concentration of hydrazine was 0.015 g / L to prepare a solution containing gelatin and hydrazine.
Next, a 1 L mixed solution of pure water, a predetermined amount of palladium salt and silver salt was prepared and dropped into the previously prepared solution containing gelatin and hydrazine to obtain a colloidal solution.

このコロイド溶液に、水酸化ナトリウム水溶液を添加し、ｐＨを１０以上とした後、さらにヒドラジンをニッケル重量：ヒドラジン重量が１：３．７５となるまで添加して、パラジウムと微量の銀からなる複合コロイド粒子が混合されたアルカリ性ヒドラジン溶液を作製し、ニッケルを還元するためのアルカリ性コロイド溶液とした。なお、この時点で、全溶液量は、４０Ｌとなるように純水を更に添加した。   A sodium hydroxide aqueous solution is added to this colloidal solution to adjust the pH to 10 or more, and hydrazine is further added until the nickel weight: hydrazine weight becomes 1: 3.75, so that the composite composed of palladium and a small amount of silver is added. An alkaline hydrazine solution mixed with colloidal particles was prepared and used as an alkaline colloid solution for reducing nickel. At this time, pure water was further added so that the total amount of the solution was 40 L.

そして、このアルカリ性コロイド溶液に、ニッケル塩水溶液としてニッケル濃度が１００ｇ／Ｌの塩化ニッケル水溶液を２．５Ｌ滴下して、ニッケルの還元を行い、ニッケル粉末を合成し、ニッケル粉末を沈降させデカンテーションで上澄み液を取り除いた。   Then, 2.5 L of a nickel chloride aqueous solution having a nickel concentration of 100 g / L is dropped into this alkaline colloid solution as a nickel salt aqueous solution, nickel is reduced, nickel powder is synthesized, nickel powder is precipitated, and decantation is performed. The supernatant liquid was removed.

次に、上記上澄み液が取り除かれたニッケル粉末を含むスラリーを２５ｇ／Ｌになるように純水に添加し、さらに、ニッケル粉末に対して硫黄が０．０７５質量％になるように秤量した硫化水素ナトリウムを純水０．５リットルに溶解した溶液を、添加し３０分間攪拌した後に固液分離した。次いで、エタノールで洗浄した後、固液分離し、１５０℃で真空乾燥し、硫黄化合物で表面修飾された原料ニッケル粉末を得た。   Next, the slurry containing the nickel powder from which the supernatant liquid has been removed is added to pure water so as to have a concentration of 25 g / L, and further, sulfur is weighed so that the sulfur is 0.075% by mass with respect to the nickel powder. A solution prepared by dissolving sodium hydride in 0.5 liter of pure water was added and stirred for 30 minutes, followed by solid-liquid separation. Next, after washing with ethanol, solid-liquid separation was performed and vacuum drying was performed at 150 ° C. to obtain a raw material nickel powder whose surface was modified with a sulfur compound.

上記原料ニッケル粉末は、その平均粒径は０．２μｍ、結晶子径（ＣＳ１）は１５ｎｍ、酸素含有量は１．２重量％、粒径１．０μｍ以上の粗大粒子の全粒子個数に対する割合は３２ｐｐｍであった。 The raw material nickel powder has an average particle diameter of 0.2 μm, a crystallite diameter (CS 1 ) of 15 nm, an oxygen content of 1.2% by weight, and a ratio of coarse particles having a particle diameter of 1.0 μm or more to the total number of particles. Was 32 ppm.

次に、高結晶化工程として、上記原料ニッケル粉末に、水素ガスと窒素ガスの混合ガス（Ｈ２：０．２体積％、Ｎ２：９９．８体積％）からなる還元雰囲気中で、加熱温度３５０℃で加熱時間１時間の熱処理を施し、高結晶化したニッケル粉末を得た。 Next, as a high crystallization step, the raw material nickel powder is heated in a reducing atmosphere composed of a mixed gas of hydrogen gas and nitrogen gas (H 2 : 0.2% by volume, N 2 : 99.8% by volume). Heat treatment was performed at a temperature of 350 ° C. for 1 hour to obtain a highly crystallized nickel powder.

さらに、解砕工程として、上記高結晶化したニッケル粉末に、スパイラル式ジェットミル（日本ニューマチック株式会社製）による解砕処理を施して、実施例１に係る湿式ニッケル粉末を作製した。   Furthermore, as the crushing step, the highly crystallized nickel powder was subjected to crushing treatment by a spiral jet mill (manufactured by Nippon Pneumatic Co., Ltd.) to produce a wet nickel powder according to Example 1.

作製した湿式ニッケル粉末の平均粒径、結晶子径、粒径１．０μｍ以上の粗大粒子の全粒子個数に対する割合、酸素含有量、を測定し、その結果を表１に示す。   The average particle size, crystallite size, ratio of coarse particles having a particle size of 1.0 μm or more, and oxygen content of the prepared wet nickel powder were measured, and the results are shown in Table 1.

高結晶化工程として、原料ニッケル粉末に、水素ガスと窒素ガスの混合ガス（Ｈ２：０．９体積％、Ｎ２：９９．１体積％）からなる還元雰囲気中で、加熱温度３００℃で加熱時間１時間の熱処理を施した以外は、実施例１と同じ条件により実施例２に係る湿式ニッケル粉末を作製した。 As a high crystallization process, the raw material nickel powder was mixed with hydrogen gas and nitrogen gas (H 2 : 0.9 vol%, N 2 : 99.1 vol%) in a reducing atmosphere at a heating temperature of 300 ° C. A wet nickel powder according to Example 2 was produced under the same conditions as in Example 1 except that a heat treatment for 1 hour was performed.

作製した湿式ニッケル粉末の平均粒径、結晶子径、粒径１．０μｍ以上の粗大粒子の全粒子個数に対する割合、酸素含有量、を測定し、その結果を表１に示す。   The average particle size, crystallite size, ratio of coarse particles having a particle size of 1.0 μm or more, and oxygen content of the prepared wet nickel powder were measured, and the results are shown in Table 1.

高結晶化工程として、原料ニッケル粉末に、水素ガスと窒素ガスの混合ガス（Ｈ２：２．０体積％、Ｎ２：９８．０体積％）からなる還元雰囲気中で、加熱温度２５０℃で２時間の加熱時間の熱処理を施した以外は実施例１と同条件により実施例３に係る湿式ニッケル粉末を作製した。 As a high crystallization process, the raw material nickel powder is mixed with hydrogen gas and nitrogen gas (H 2 : 2.0% by volume, N 2 : 98.0% by volume) in a reducing atmosphere at a heating temperature of 250 ° C. A wet nickel powder according to Example 3 was produced under the same conditions as in Example 1 except that heat treatment was performed for 2 hours.

作製した湿式ニッケル粉末の平均粒径、結晶子径、粒径１．０μｍ以上の粗大粒子の全粒子個数に対する割合、酸素含有量、を測定し、その結果を表１に示す。   The average particle size, crystallite size, ratio of coarse particles having a particle size of 1.0 μm or more, and oxygen content of the prepared wet nickel powder were measured, and the results are shown in Table 1.

高結晶化工程として、原料ニッケル粉末に、窒素ガス（Ｏ２濃度：０．５ｐｐｍ）からなる不活性ガス雰囲気中で、加熱温度４００℃で加熱時間１時間、引き続いて、水素ガスと窒素ガスの混合ガス（Ｈ２：０．５体積％、Ｎ２：９９．５体積％）からなる還元雰囲気中で、加熱温度３００℃で加熱時間１時間の熱処理を施した以外は実施例１と同条件により実施例４に係る湿式ニッケル粉末を作製した。 As a high crystallization process, the raw material nickel powder is heated in an inert gas atmosphere consisting of nitrogen gas (O 2 concentration: 0.5 ppm) at a heating temperature of 400 ° C. for 1 hour, followed by hydrogen gas and nitrogen gas. The same conditions as in Example 1 except that heat treatment was performed at a heating temperature of 300 ° C. for 1 hour in a reducing atmosphere consisting of a mixed gas (H 2 : 0.5% by volume, N 2 : 99.5% by volume). Thus, a wet nickel powder according to Example 4 was produced.

作製した湿式ニッケル粉末の平均粒径、結晶子径、粒径１．０μｍ以上の粗大粒子の全粒子個数に対する割合、酸素含有量、を測定し、その結果を表１に示す。   The average particle size, crystallite size, ratio of coarse particles having a particle size of 1.0 μm or more, and oxygen content of the prepared wet nickel powder were measured, and the results are shown in Table 1.

高結晶化工程として、原料ニッケル粉末に、窒素ガス（Ｏ２濃度：１ｐｐｍ）からなる不活性ガス雰囲気中で、加熱温度３５０℃で加熱時間１時間、引き続いて、水素ガスと窒素ガスの混合ガス（Ｈ２：２．０体積％、Ｎ２：９８．０体積％）からなる還元雰囲気中で、加熱温度２５０℃で加熱時間１時間の熱処理を施した以外は実施例１と同条件により実施例５に係る湿式ニッケル粉末を作製した。 As a high crystallization process, the raw material nickel powder is mixed with hydrogen gas and nitrogen gas in an inert gas atmosphere consisting of nitrogen gas (O 2 concentration: 1 ppm) at a heating temperature of 350 ° C. for a heating time of 1 hour. (H 2 : 2.0% by volume, N 2 : 98.0% by volume) In a reducing atmosphere, the heat treatment was performed under the same conditions as in Example 1 except that heat treatment was performed at a heating temperature of 250 ° C. for 1 hour. A wet nickel powder according to Example 5 was prepared.

作製した湿式ニッケル粉末の平均粒径、結晶子径、粒径１．０μｍ以上の粗大粒子の全粒子個数に対する割合、酸素含有量、を測定し、その結果を表１に示す。   The average particle size, crystallite size, ratio of coarse particles having a particle size of 1.0 μm or more, and oxygen content of the prepared wet nickel powder were measured, and the results are shown in Table 1.

高結晶化工程として、原料ニッケル粉末に、窒素ガス（Ｏ２濃度：２ｐｐｍ）からなる不活性ガス雰囲気中で、加熱温度３００℃で加熱時間２時間、引き続いて、水素ガスと窒素ガスの混合ガス（Ｈ２：４．０体積％、Ｎ２：９６．０体積％）からなる還元雰囲気中で、加熱温度２００℃で加熱時間１時間の熱処理を施した以外は実施例１と同条件により実施例６に係る湿式ニッケル粉末を作製した。 As a high crystallization process, the raw material nickel powder is mixed with hydrogen gas and nitrogen gas in an inert gas atmosphere composed of nitrogen gas (O 2 concentration: 2 ppm) at a heating temperature of 300 ° C. for a heating time of 2 hours. (Equivalent to Example 1 except that heat treatment was performed at a heating temperature of 200 ° C. for 1 hour in a reducing atmosphere consisting of (H 2 : 4.0% by volume, N 2 : 96.0% by volume)). A wet nickel powder according to Example 6 was prepared.

作製した湿式ニッケル粉末の平均粒径、結晶子径、粒径１．０μｍ以上の粗大粒子の全粒子個数に対する割合、酸素含有量、を測定し、その結果を表１に示す。   The average particle size, crystallite size, ratio of coarse particles having a particle size of 1.0 μm or more, and oxygen content of the prepared wet nickel powder were measured, and the results are shown in Table 1.

［原料ニッケル粉末の作製］
以下に、湿式還元法を用いた原料ニッケル粉末作製の詳細を示す。
パラジウムと微量の銀とゼラチンからなるアルカリ性コロイド溶液に、アルカリ性のヒドラジン溶液を混合し、ニッケルを還元するためのアルカリ性コロイド溶液を作製した。
作製したアルカリ性コロイド溶液におけるパラジウム、銀、ゼラチンの含有量は、始液となるニッケル塩水溶液中のニッケルの全質量に対して、パラジウム：１７質量ｐｐｍ、銀：０．１７質量ｐｐｍ、ゼラチン：１．７質量％とした。なお、溶液中のパラジウムおよび銀の含有量は、ＩＣＰ発光分光分析法により分析した。 [Production of raw material nickel powder]
Below, the detail of raw material nickel powder preparation using the wet reduction method is shown.
An alkaline hydrazine solution was mixed with an alkaline colloidal solution composed of palladium, a small amount of silver and gelatin to prepare an alkaline colloidal solution for reducing nickel.
The contents of palladium, silver, and gelatin in the prepared alkaline colloidal solution are as follows: palladium: 17 mass ppm, silver: 0.17 mass ppm, gelatin: 1 with respect to the total mass of nickel in the nickel salt aqueous solution as the starting solution. 0.7% by mass. The contents of palladium and silver in the solution were analyzed by ICP emission spectroscopic analysis.

上記ニッケルを還元するためのアルカリ性コロイド溶液の作製は、具体的には、次のように行った。
先ず、純水３０Ｌに所定量のゼラチンを溶解させた後、ヒドラジンの濃度が０．０５ｇ／Ｌとなるようにヒドラジンを混合し、ゼラチンとヒドラジンを含む溶液を作製した。
次に、純水と所定量のパラジウム塩と銀塩の１Ｌの混合溶液を作製し、先に作製したゼラチンとヒドラジンを含む溶液に滴下して、コロイド溶液を得た。 The production of the alkaline colloid solution for reducing the nickel was specifically performed as follows.
First, after a predetermined amount of gelatin was dissolved in 30 L of pure water, hydrazine was mixed so that the concentration of hydrazine was 0.05 g / L to prepare a solution containing gelatin and hydrazine.
Next, a 1 L mixed solution of pure water, a predetermined amount of palladium salt and silver salt was prepared and dropped into the previously prepared solution containing gelatin and hydrazine to obtain a colloidal solution.

このコロイド溶液に、水酸化ナトリウム水溶液を添加し、ｐＨを１０以上とした後、さらにヒドラジンをニッケル重量：ヒドラジン重量が１：３．７５となるまで添加して、パラジウムと微量の銀からなる複合コロイド粒子が混合されたアルカリ性ヒドラジン溶液を作製し、ニッケルを還元するためのアルカリ性コロイド溶液とした。なお、この時点で、全溶液量は、４０Ｌとなるように純水を更に添加した。   A sodium hydroxide aqueous solution is added to this colloidal solution to adjust the pH to 10 or more, and hydrazine is further added until the nickel weight: hydrazine weight becomes 1: 3.75, so that the composite composed of palladium and a small amount of silver is added. An alkaline hydrazine solution mixed with colloidal particles was prepared and used as an alkaline colloid solution for reducing nickel. At this time, pure water was further added so that the total amount of the solution was 40 L.

そして、このアルカリ性コロイド溶液に、ニッケル塩水溶液としてニッケル濃度が１００ｇ／Ｌの塩化ニッケル水溶液を２．５Ｌ滴下して、ニッケルの還元を行い、ニッケル粉末を合成し、ニッケル粉末を沈降させデカンテーションで上澄み液を取り除いた。   Then, 2.5 L of a nickel chloride aqueous solution having a nickel concentration of 100 g / L is dropped into this alkaline colloid solution as a nickel salt aqueous solution, nickel is reduced, nickel powder is synthesized, nickel powder is precipitated, and decantation is performed. The supernatant liquid was removed.

次に、上記上澄み液が取り除かれたニッケル粉末を含むスラリーを２５ｇ／Ｌになるように純水に添加し、さらに、ニッケル粉末に対して硫黄が０．１質量％になるように秤量した硫化水素ナトリウムを純水０．５リットルに溶解した溶液を、添加し３０分間攪拌した後に固液分離した。次いで、エタノールで洗浄した後、固液分離し、１５０℃で真空乾燥し、硫黄化合物で表面修飾された原料ニッケル粉末を得た。   Next, the slurry containing the nickel powder from which the supernatant liquid has been removed is added to pure water so as to have a concentration of 25 g / L, and further, sulfur is weighed so that the sulfur is 0.1% by mass with respect to the nickel powder. A solution prepared by dissolving sodium hydride in 0.5 liter of pure water was added and stirred for 30 minutes, followed by solid-liquid separation. Next, after washing with ethanol, solid-liquid separation was performed and vacuum drying was performed at 150 ° C. to obtain a raw material nickel powder whose surface was modified with a sulfur compound.

上記原料ニッケル粉末は、その平均粒径は０．１５μｍ、結晶子径（ＣＳ１）は１４．５ｎｍ、酸素含有量は１．５重量％、粒径１．０μｍ以上の粗大粒子の全粒子個数に対する割合は２８ｐｐｍであった。 The raw material nickel powder has an average particle size of 0.15 μm, a crystallite size (CS 1 ) of 14.5 nm, an oxygen content of 1.5% by weight, and the total number of coarse particles having a particle size of 1.0 μm or more. The ratio to was 28 ppm.

次に、高結晶化工程として、上記原料ニッケル粉末に、窒素ガス（Ｏ２濃度：０．５ｐｐｍ）からなる不活性ガス雰囲気中で、加熱温度３５０℃で加熱時間１時間、引き続いて、水素ガスと窒素ガスの混合ガス（Ｈ２：２．０体積％、Ｎ２：９８．０体積％）からなる還元雰囲気中で、加熱温度２５０℃で加熱時間１時間の熱処理を施し、高結晶化したニッケル粉末を得た。 Next, as a high crystallization step, the raw material nickel powder is subjected to hydrogen gas in an inert gas atmosphere composed of nitrogen gas (O 2 concentration: 0.5 ppm) at a heating temperature of 350 ° C. for a heating time of 1 hour. In a reducing atmosphere consisting of a mixed gas of nitrogen and nitrogen gas (H 2 : 2.0% by volume, N 2 : 98.0% by volume), heat treatment was performed at a heating temperature of 250 ° C. for a heating time of 1 hour to achieve high crystallization. Nickel powder was obtained.

さらに、解砕工程として、上記高結晶化したニッケル粉末に、スパイラル式ジェットミル（日本ニューマチック株式会社製）による解砕処理を施して、実施例７に係る湿式ニッケル粉末を作製した。   Furthermore, as a crushing step, the highly crystallized nickel powder was subjected to a crushing treatment by a spiral jet mill (manufactured by Nippon Pneumatic Co., Ltd.) to produce a wet nickel powder according to Example 7.

作製した湿式ニッケル粉末の平均粒径、結晶子径、粒径１．０μｍ以上の粗大粒子の全粒子個数に対する割合、酸素含有量、を測定し、その結果を表１に示す。   The average particle size, crystallite size, ratio of coarse particles having a particle size of 1.0 μm or more, and oxygen content of the prepared wet nickel powder were measured, and the results are shown in Table 1.

（比較例１）
高結晶化工程として、原料ニッケル粉末に、水素ガスと窒素ガスの混合ガス（Ｈ２：０．２体積％、Ｎ２：９９．８体積％）からなる還元雰囲気中で、加熱温度４００℃で加熱時間１時間の熱処理を施した以外は実施例１と同条件により比較例１に係る湿式ニッケル粉末を作製した。 (Comparative Example 1)
As a high crystallization process, the raw material nickel powder is mixed with hydrogen gas and nitrogen gas (H 2 : 0.2% by volume, N 2 : 99.8% by volume) in a reducing atmosphere at a heating temperature of 400 ° C. A wet nickel powder according to Comparative Example 1 was produced under the same conditions as in Example 1 except that the heat treatment was performed for 1 hour.

作製した湿式ニッケル粉末の平均粒径、結晶子径、粒径１．０μｍ以上の粗大粒子の全粒子個数に対する割合、酸素含有量、を測定し、その結果を表１に示す。   The average particle size, crystallite size, ratio of coarse particles having a particle size of 1.0 μm or more, and oxygen content of the prepared wet nickel powder were measured, and the results are shown in Table 1.

（比較例２）
高結晶化工程として、原料ニッケル粉末に、水素ガスと窒素ガスの混合ガス（Ｈ２：２．０体積％、Ｎ２：９８．０体積％）からなる還元雰囲気中で、加熱温度２００℃で加熱時間２時間の熱処理を施した以外は実施例１と同条件により比較例２に係る湿式ニッケル粉末を作製した。 (Comparative Example 2)
As a high crystallization process, the raw material nickel powder is mixed with hydrogen gas and nitrogen gas (H 2 : 2.0% by volume, N 2 : 98.0% by volume) in a reducing atmosphere at a heating temperature of 200 ° C. A wet nickel powder according to Comparative Example 2 was produced under the same conditions as in Example 1 except that the heat treatment was performed for 2 hours.

作製した湿式ニッケル粉末の平均粒径、結晶子径、粒径１．０μｍ以上の粗大粒子の全粒子個数に対する割合、酸素含有量、を測定し、その結果を表１に示す。
（比較例３） The average particle size, crystallite size, ratio of coarse particles having a particle size of 1.0 μm or more, and oxygen content of the prepared wet nickel powder were measured, and the results are shown in Table 1.
(Comparative Example 3)

高結晶化工程として、原料ニッケル粉末に、窒素ガス（Ｏ２濃度：０．５ｐｐｍ）からなる不活性ガス雰囲気中で、加熱温度４５０℃で加熱時間１時間、引き続いて、水素ガスと窒素ガスの混合ガス（Ｈ２：０．５体積％、Ｎ２：９９．５体積％）からなる還元雰囲気中で、加熱温度３００℃で加熱時間１時間の熱処理を施した以外は実施例１と同条件により比較例３に係る湿式ニッケル粉末を作製した。 As a high crystallization process, the raw material nickel powder was heated in an inert gas atmosphere consisting of nitrogen gas (O 2 concentration: 0.5 ppm) at a heating temperature of 450 ° C. for 1 hour, followed by hydrogen gas and nitrogen gas. The same conditions as in Example 1 except that heat treatment was performed at a heating temperature of 300 ° C. for 1 hour in a reducing atmosphere consisting of a mixed gas (H 2 : 0.5% by volume, N 2 : 99.5% by volume). Thus, a wet nickel powder according to Comparative Example 3 was produced.

作製した湿式ニッケル粉末の平均粒径、結晶子径、粒径１．０μｍ以上の粗大粒子の全粒子個数に対する割合、酸素含有量、を測定し、その結果を表１に示す。
（比較例４） The average particle size, crystallite size, ratio of coarse particles having a particle size of 1.0 μm or more, and oxygen content of the prepared wet nickel powder were measured, and the results are shown in Table 1.
(Comparative Example 4)

高結晶化工程として、原料ニッケル粉末に、窒素ガス（Ｏ２濃度：１ｐｐｍ）からなる不活性ガス雰囲気中で、加熱温度２５０℃で加熱時間２時間、引き続いて、水素ガスと窒素ガスの混合ガス（Ｈ２：４．０体積％、Ｎ２：９６．０体積％）からなる還元雰囲気中で、加熱温度２００℃で加熱時間１時間の熱処理を施した以外は実施例１と同条件により比較例４に係る湿式ニッケル粉末を作製した。 As a high crystallization process, raw material nickel powder is mixed with hydrogen gas and nitrogen gas in an inert gas atmosphere consisting of nitrogen gas (O 2 concentration: 1 ppm) at a heating temperature of 250 ° C. for a heating time of 2 hours. Comparison was made under the same conditions as in Example 1 except that heat treatment was performed at a heating temperature of 200 ° C. for 1 hour in a reducing atmosphere consisting of (H 2 : 4.0% by volume, N 2 : 96.0% by volume). A wet nickel powder according to Example 4 was prepared.

作製した湿式ニッケル粉末の平均粒径、結晶子径、粒径１．０μｍ以上の粗大粒子の全粒子個数に対する割合、酸素含有量、を測定し、その結果を表１に示す。   The average particle size, crystallite size, ratio of coarse particles having a particle size of 1.0 μm or more, and oxygen content of the prepared wet nickel powder were measured, and the results are shown in Table 1.

（比較例５）
高結晶化したニッケル粉末に解砕処理を施さなかった以外は実施例１と同条件により比較例５に係る湿式ニッケル粉末を作製した。 (Comparative Example 5)
A wet nickel powder according to Comparative Example 5 was produced under the same conditions as in Example 1 except that the highly crystallized nickel powder was not crushed.

作製した湿式ニッケル粉末の平均粒径、結晶子径、粒径１．０μｍ以上の粗大粒子の全粒子個数に対する割合、酸素含有量、を測定し、その結果を表１に示す。
（比較例６） The average particle size, crystallite size, ratio of coarse particles having a particle size of 1.0 μm or more, and oxygen content of the prepared wet nickel powder were measured, and the results are shown in Table 1.
(Comparative Example 6)

高結晶化したニッケル粉末に解砕処理を施さなかった以外は実施例４と同条件により比較例６に係る湿式ニッケル粉末を作製した。   A wet nickel powder according to Comparative Example 6 was produced under the same conditions as in Example 4 except that the highly crystallized nickel powder was not crushed.

作製した湿式ニッケル粉末の平均粒径、結晶子径、粒径１．０μｍ以上の粗大粒子の全粒子個数に対する割合、酸素含有量、を測定し、その結果を表１に示す。   The average particle size, crystallite size, ratio of coarse particles having a particle size of 1.0 μm or more, and oxygen content of the prepared wet nickel powder were measured, and the results are shown in Table 1.

Figure 2015190043
Figure 2015190043

表１からも明らかなように、実施例１〜３と比較例１、２、５とを比べると、いずれも原料ニッケル粉末は、平均粒径が０．３μｍ以下で、かつ結晶子径（ＣＳ１：ｎｍ）が４０ｎｍ以下であるが、原料ニッケル粉末に、還元雰囲気中で２５０℃〜３５０℃の温度で熱処理して高結晶子径のニッケル粉末を得る高結晶化工程、および高結晶子径のニッケル粉末を分散させる解砕工程を施して得られた実施例１〜３の湿式ニッケル粉末は、平均粒径が０．３μｍ以下で、高い結晶子径（ＣＳ２：ｎｍ）を有し（ＣＳ２≧１．３×ＣＳ１）、かつ粒径１μｍ以上の粗大粒子の割合も少ないことが判る。 As is apparent from Table 1, when Examples 1 to 3 and Comparative Examples 1, 2, and 5 are compared, the raw material nickel powder has an average particle size of 0.3 μm or less and a crystallite size (CS 1 : nm) is 40 nm or less, a high crystallization step for obtaining a high crystallite diameter nickel powder by heat-treating the raw material nickel powder at a temperature of 250 ° C. to 350 ° C. in a reducing atmosphere, and a high crystallite diameter The wet nickel powders of Examples 1 to 3 obtained by carrying out the crushing step of dispersing the nickel powders had an average particle size of 0.3 μm or less and a high crystallite size (CS 2 : nm) ( It can be seen that CS 2 ≧ 1.3 × CS 1 ) and the proportion of coarse particles having a particle size of 1 μm or more is small.

一方、還元雰囲気中で所定温度の範囲外（２５０℃未満、または３５０℃超）で熱処理して高結晶子径のニッケル粉末を得る高結晶化工程、および高結晶子径のニッケル粉末を分散させる解砕工程を施して得られた比較例１、比較例２、および還元雰囲気中で２５０℃〜３５０℃の温度で熱処理して高結晶子径のニッケル粉末を得る高結晶化工程のみ施し、高結晶子径のニッケル粉末を分散させる解砕工程を施さずに得られた比較例５の湿式ニッケル粉末は、比較例１、５では、粒径１μｍ以上の粗大粒子の割合が多く、比較例２では結晶子径の増大が不十分（ＣＳ２＜１．３×ＣＳ１）であることが判る。 On the other hand, a high crystallization process for obtaining a high crystallite diameter nickel powder by heat treatment outside a predetermined temperature range (less than 250 ° C. or over 350 ° C.) in a reducing atmosphere, and dispersing the high crystallite diameter nickel powder Only Comparative Example 1 and Comparative Example 2 obtained by performing the crushing step, and only the high crystallization step of obtaining a high crystallite diameter nickel powder by heat treatment at a temperature of 250 ° C. to 350 ° C. in a reducing atmosphere, The wet nickel powder of Comparative Example 5 obtained without performing the crushing step of dispersing the nickel powder having a crystallite size has a large proportion of coarse particles having a particle diameter of 1 μm or more in Comparative Examples 1 and 5, and Comparative Example 2 Then, it turns out that the increase in crystallite diameter is insufficient (CS 2 <1.3 × CS 1 ).

次に、実施例４〜７と比較例３、４、６とを比べると、いずれも原料ニッケル粉末は、平均粒径が０．３μｍ以下で、かつ結晶子径（ＣＳ１：ｎｍ）が４０ｎｍ以下であるが、原料ニッケル粉末に、不活性ガス雰囲気中で３００℃〜４００℃の温度（Ｔ１：℃）で熱処理して結晶子を増大させた後、還元雰囲気中で１５０〜３５０℃（Ｔ２：℃、Ｔ２≦Ｔ１）の温度で熱処理してニッケル粉末の酸素含有量を低減させて高結晶子径のニッケル粉末を得る高結晶化工程、および高結晶子径のニッケル粉末を分散させる解砕工程を施して得られた実施例４〜７の湿式ニッケル粉末は、平均粒径が０．３μｍ以下で、高い結晶子径（ＣＳ２：ｎｍ）を有し（ＣＳ２≧１．３×ＣＳ１）、かつ粒径１μｍ以上の粗大粒子の割合も少ないことが判る。 Next, when Examples 4 to 7 and Comparative Examples 3, 4, and 6 are compared, the raw material nickel powder has an average particle diameter of 0.3 μm or less and a crystallite diameter (CS 1 : nm) of 40 nm. As described below, the raw material nickel powder was heat-treated in an inert gas atmosphere at a temperature of 300 ° C. to 400 ° C. (T 1 : ° C.) to increase crystallites, and then in a reducing atmosphere, 150 to 350 ° C. ( A high crystallization step of obtaining a high crystallite diameter nickel powder by reducing the oxygen content of the nickel powder by heat treatment at a temperature of T 2 : ° C., T 2 ≦ T 1 ), and a high crystallite diameter nickel powder The wet nickel powders of Examples 4 to 7 obtained by carrying out the crushing step for dispersion have an average particle size of 0.3 μm or less and a high crystallite size (CS 2 : nm) (CS 2 ≧ 1). .3 × CS 1), and that the smaller the proportion of the particle size 1μm or more coarse particles That.

一方、不活性ガス雰囲気中で所定温度（Ｔ１：℃）の範囲外（３００℃未満、または４００℃超）で熱処理して結晶子を増大させた後、還元雰囲気中で１５０〜３５０℃（Ｔ２：℃、Ｔ２≦Ｔ１）の温度で熱処理してニッケル粉末の酸素含有量を低減させて高結晶子径のニッケル粉末を得る高結晶化工程、および高結晶子径のニッケル粉末を分散させる解砕工程を施して得られた比較例３、比較例４、および不活性ガス雰囲気中で３００℃〜４００℃の温度（Ｔ１：℃）で熱処理して結晶子を増大させた後、還元雰囲気中で１５０〜３５０℃（Ｔ２：℃、Ｔ２≦Ｔ１）の温度で熱処理してニッケル粉末の酸素含有量を低減させて高結晶子径のニッケル粉末を得る高結晶化工程のみ施し、高結晶子径のニッケル粉末を分散させる解砕工程を施さずに得られた比較例６の湿式ニッケル粉末は、比較例３、６では、粒径１μｍ以上の粗大粒子の割合が多く、比較例４では結晶子径の増大が不十分（ＣＳ２＜１．３×ＣＳ１）であることが判る。 On the other hand, after increasing the crystallite by heat treatment outside the range of a predetermined temperature (T 1 : ° C.) in an inert gas atmosphere (less than 300 ° C. or more than 400 ° C.), 150 to 350 ° C. ( A high crystallization step of obtaining a high crystallite diameter nickel powder by reducing the oxygen content of the nickel powder by heat treatment at a temperature of T 2 : ° C., T 2 ≦ T 1 ), and a high crystallite diameter nickel powder After heat treatment at a temperature of 300 ° C. to 400 ° C. (T 1 : ° C.) in an inert gas atmosphere after increasing the crystallites in Comparative Example 3 and Comparative Example 4 obtained by performing the crushing step of dispersing A high crystallization step of obtaining nickel powder having a high crystallite diameter by reducing the oxygen content of the nickel powder by heat treatment at a temperature of 150 to 350 ° C. (T 2 : ° C., T 2 ≦ T 1 ) in a reducing atmosphere. Crushing to disperse high crystallite diameter nickel powder The wet nickel powder of Comparative Example 6 obtained without performing the process has a large proportion of coarse particles having a particle diameter of 1 μm or more in Comparative Examples 3 and 6, and in Comparative Example 4, the increase in crystallite diameter is insufficient (CS 2 <1.3 × CS 1 ).

Claims (7)

ニッケル塩溶液の還元反応法である湿式法を用いて作製した原料ニッケル粉末に、高結晶化工程、解砕工程の各工程を施して得られる湿式ニッケル粉末の製造方法であって、
前記原料ニッケル粉末が、平均粒径が０．３μｍ以下、かつ結晶子径（ＣＳ１：ｎｍ）が４０ｎｍ以下で、
前記高結晶化工程が、前記原料ニッケル粉末を還元雰囲気中で２５０℃〜３５０℃の温度で熱処理して結晶子を増大させて高結晶子径のニッケル粉末を得る工程、
前記解砕工程が、前記高結晶化工程で得られた高結晶子径のニッケル粉末に解砕処理を施して、高結晶化工程で凝集・焼結が生じた高結晶子径のニッケル粉末を分散させる工程、
前記湿式ニッケル粉末が、０．３μｍ以下の平均粒径を有し、
かつ結晶子径（ＣＳ２：ｎｍ）は、ＣＳ２≧１．３×ＣＳ１、で、
粒径１μｍ以上の粗大粒子の全粒子個数に対する割合が５０ｐｐｍ以下であることを特徴とする湿式ニッケル粉末の製造方法。 A method for producing a wet nickel powder obtained by subjecting a raw material nickel powder produced using a wet method, which is a reduction reaction method of a nickel salt solution, to a high crystallization step and a crushing step,
The raw material nickel powder has an average particle size of 0.3 μm or less and a crystallite size (CS 1 : nm) of 40 nm or less,
The high crystallization step is a step of heat-treating the raw material nickel powder at a temperature of 250 ° C. to 350 ° C. in a reducing atmosphere to increase crystallites to obtain a high crystallite diameter nickel powder;
In the crushing step, the high crystallite size nickel powder obtained in the high crystallization step is subjected to crushing treatment, and the high crystallite size nickel powder in which aggregation and sintering have occurred in the high crystallization step is obtained. Dispersing step,
The wet nickel powder has an average particle size of 0.3 μm or less;
The crystallite diameter (CS 2 : nm) is CS 2 ≧ 1.3 × CS 1 ,
A method for producing wet nickel powder, wherein the ratio of coarse particles having a particle diameter of 1 μm or more to the total number of particles is 50 ppm or less. ニッケル塩溶液の還元反応法である湿式法を用いて作製した原料ニッケル粉末に、高結晶化工程、解砕工程の各工程を施して得られる湿式ニッケル粉末の製造方法であって、
前記原料ニッケル粉末が、０．３μｍ以下の平均粒径を有し、かつ結晶子径（ＣＳ１：ｎｍ）が４０ｎｍ以下で、
前記高結晶化工程が、前記原料ニッケル粉末を、不活性ガス雰囲気中で３００℃〜４００℃の温度（Ｔ１：℃）で熱処理して結晶子を増大させた後、還元雰囲気中で１５０〜３５０℃（Ｔ２：℃、Ｔ２≦Ｔ１）の温度で熱処理してニッケル粉末の酸素含有量を低減させる、高結晶子径のニッケル粉末を得る工程、
前記解砕工程が、前記高結晶化工程で得られた高結晶子径のニッケル粉末に解砕処理を施して、高結晶化工程で凝集・焼結が生じた高結晶子径のニッケル粉末を分散させる工程、
前記湿式ニッケル粉末が、０．３μｍ以下の平均粒径を有し、
かつ結晶子径（ＣＳ２：ｎｍ）が、ＣＳ２≧１．３×ＣＳ１、で、
粒径１μｍ以上の粗大粒子の全粒子個数に対する割合が５０ｐｐｍ以下であることを特徴とする湿式ニッケル粉末の製造方法。 A method for producing a wet nickel powder obtained by subjecting a raw material nickel powder produced using a wet method, which is a reduction reaction method of a nickel salt solution, to a high crystallization step and a crushing step,
The raw material nickel powder has an average particle diameter of 0.3 μm or less and a crystallite diameter (CS 1 : nm) of 40 nm or less,
In the high crystallization step, the raw material nickel powder is heat-treated at a temperature of 300 ° C. to 400 ° C. (T 1 : ° C.) in an inert gas atmosphere to increase crystallites, and then in a reducing atmosphere, 150 to A step of obtaining nickel powder having a high crystallite diameter by heat treatment at a temperature of 350 ° C. (T 2 : ° C., T 2 ≦ T 1 ) to reduce the oxygen content of the nickel powder;
In the crushing step, the high crystallite size nickel powder obtained in the high crystallization step is subjected to crushing treatment, and the high crystallite size nickel powder in which aggregation and sintering have occurred in the high crystallization step is obtained. Dispersing step,
The wet nickel powder has an average particle size of 0.3 μm or less;
And the crystallite diameter (CS 2 : nm) is CS 2 ≧ 1.3 × CS 1 ,
A method for producing wet nickel powder, wherein the ratio of coarse particles having a particle diameter of 1 μm or more to the total number of particles is 50 ppm or less. 前記原料ニッケル粉末が、少なくとも有機硫黄化合物と無機硫黄化合物のいずれかで表面修飾されていることを特徴とする請求項１または２に記載の湿式ニッケル粉末の製造方法。   The method for producing wet nickel powder according to claim 1 or 2, wherein the raw material nickel powder is surface-modified with at least one of an organic sulfur compound and an inorganic sulfur compound. 前記還元性雰囲気が、水素ガスと不活性ガスの混合雰囲気であり、該混合雰囲気中の水素ガス濃度が０．１体積％を超え５．７体積％未満であることを特徴とする請求項１〜３のいずれか１項に記載の湿式ニッケル粉末の製造方法。   2. The reducing atmosphere is a mixed atmosphere of hydrogen gas and inert gas, and a hydrogen gas concentration in the mixed atmosphere is more than 0.1 volume% and less than 5.7 volume%. The manufacturing method of the wet nickel powder of any one of -3. 前記不活性ガスが、窒素ガス、希ガスの内のいずれか１種類以上であることを特徴とする請求項２または４に記載の湿式ニッケル粉末の製造方法。   The method for producing wet nickel powder according to claim 2 or 4, wherein the inert gas is at least one of nitrogen gas and rare gas. 前記解砕工程が、湿式解砕工程または乾式解砕工程であることを特徴とする請求項１〜５のいずれか１項に記載の湿式ニッケル粉末の製造方法。   The said crushing process is a wet crushing process or a dry-type crushing process, The manufacturing method of the wet nickel powder of any one of Claims 1-5 characterized by the above-mentioned. 前記湿式解砕工程が高圧衝突式分散機を用い、前記乾式解砕工程が気流式微粉砕機（ジェットミル）を用いて行われることを特徴とする請求項６に記載の湿式ニッケル粉末の製造方法。   The method for producing wet nickel powder according to claim 6, wherein the wet crushing step is performed using a high-pressure impingement disperser, and the dry crushing step is performed using an airflow fine pulverizer (jet mill). .
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