JPH11263625A - Production of anhydrous nickel chloride - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing anhydrous nickel chloride appropriate as the raw material to produce a metallic nickel fine powder for electronic material by chemical vapor deposition(CVD) for reducing the vapor of a nickel salt with hydrogen gas. SOLUTION: The crystal of nickel chloride hexahydrate is heat-treated at a temp. of 160-200 deg.C. In this case, the NiO content is effectively reduced by performing the heat treatment under reduced pressure. Further, in this method, the temp. increasing rate is effectively controlled so that the water of crystallization in the nickel chloride crystal is not dissociated as water but removed as vapor. By using this means, the anhydrous nickel chloride contg. 0.1-1% NiO is produced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing anhydrous nickel chloride suitable as a raw material for producing fine nickel metal powder for electronic materials by a CVD method.

[0002]

2. Description of the Related Art Methods for producing fine nickel powder are roughly classified into a dry method and a wet method. The characteristics of the fine nickel powder obtained by the dry method are high crystallinity, suitable for sintering at a relatively high temperature, and small in shrinkage during sintering. On the other hand, sintering of the nickel powder by the wet method starts at a relatively low temperature, and shrinkage during sintering is relatively large.

[0003] Nickel powder obtained by CVD, which is a kind of dry method, in which nickel chloride vapor is reduced by hydrogen, is suitable and used for internal electrodes of multilayer ceramic capacitors. The multilayer ceramic capacitor is formed by laminating a fine nickel powder into a paste, multi-layered as a green sheet, and sintered at a high temperature. At this time,
A weakly oxidizing atmosphere is used for debinding.

[0004] In the miniaturization and high lamination of ceramic capacitors, the required characteristics of nickel powder as an electrode material are becoming increasingly severe. Particularly, in the process of manufacturing a ceramic capacitor, when a dielectric and a nickel powder-containing paste that is an electrode material are laminated and sintered, the particle shape,
It has been found that the particle size, particle size distribution, dispersibility, fillability, and crystallinity affect the sintering characteristics and consequently greatly affect the product yield of the capacitor. In particular, it is becoming clear that the above-mentioned product yield is affected by the presence of abnormal coarse particles in the nickel powder.

[0005] In particular, the inventors have found that in the CVD method for reducing hydrogen of anhydrous nickel chloride by hydrogen, the incorporation of NiO contained in anhydrous nickel chloride into nickel powder is the main cause of coarse particles. SEM and TEM
Observed by observation. Therefore, to produce fine nickel metal powder by the CVD method, it is necessary to control the content of NiO in anhydrous nickel chloride used as a raw material. However, in the conventional method for producing anhydrous nickel chloride, that is, the method for drying hexahydrate of nickel chloride, nickel chloride is hydrolyzed when the nickel chloride crystal is dried, and the obtained nickel chloride Contains about 4 to 5% or more of NiO, which causes the above-described generation of coarse particles and further causes a reduction in product yield.

[0006]

SUMMARY OF THE INVENTION In view of the above circumstances, an object of the present invention is to provide a method for producing anhydrous nickel chloride suitable as a raw material when producing fine nickel metal powder by a CVD method. I do.

[0007]

In order to achieve the above-mentioned object, the present invention provides a method for producing hexachloride crystals of nickel chloride under atmospheric pressure.
A method for producing anhydrous nickel chloride having a NiO content of 0.1% or more and 1% or less, characterized by performing a heat treatment at a temperature of 160 ° C or more and 200 ° C or less.

Further, in the above method, the NiO content can be more effectively reduced by performing the heat treatment at a reduced pressure. Further, in the above method, it is effective to control the heating rate so that the water of crystallization in the nickel chloride crystal is not dissociated as water but is removed as vapor. By using the above means, it is possible to produce anhydrous nickel chloride having a NiO content of 0.1% or more and 1% or less.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The cause of abnormal coarse particles was investigated by SEM and TEM, and it was found that most of the abnormal coarse particles were NiO. Therefore, in order to produce nickel powder that does not contain abnormal coarse particles,
In the VD method, it is necessary to use anhydrous nickel chloride having a low NiO content.

The multilayer ceramic capacitor is used by laminating the above-mentioned fine nickel powder in the form of paste into a multilayer. In the high lamination region where the number of laminated layers of this capacitor is 200 or more, the thickness of the dielectric is about 1 to 2 microns, and if there is one or more coarse particles of 1 micron or more in 200, the dielectric is not sintered. Coarse particles penetrate the layer and cause a short circuit between the electrodes.

Therefore, when the mixing ratio of the coarse particles is 1/200 or less, the production yield of the multilayer ceramic capacitor can be improved. It is more preferable that the mixing ratio of the coarse particles is small, but reducing the mixing ratio to 1/400 or less is not an economical method from the present application.
To achieve the above object, the content of NiO should be 1%
It has been found effective to use the following anhydrous nickel chloride.

[0012] Therefore, it has been found that, in the method for producing anhydrous nickel chloride, the NiO content in anhydrous nickel chloride can be reduced to 1% or less by heat treatment under atmospheric pressure to a temperature of 160 ° C to 200 ° C. . Furthermore, if the pressure is reduced during the heat treatment, for example, a heat treatment at a temperature of 160 ° C. or more and 200 ° C. or less under reduced pressure of 100 torr is more effective than heating at atmospheric pressure, and the NiO content is reduced to 0.1. It was found that it could be halved to 5%.

Further, the heating rate is controlled to a rate at which the water of crystallization in the nickel chloride crystal is removed as steam without dissociating as water, specifically, at a rate of 1 ° C./min to 20 ° C./min. The method was found to be effective. For example, 3
If the heating rate is 0 ° C./min or more, water of crystallization separates as water, and in extreme cases, ice may be locally generated by heat of evaporation, which is not preferable. At a heat treatment temperature of 160 ° C. or lower, it is difficult to remove water of crystallization of nickel chloride hexahydrate, and water of crystallization remains. Also, 2
When heated to 00 ° C., nickel chloride in the nickel chloride crystal and water cause a hydrolysis reaction to generate NiO.

If the NiO content is 1% or less, the mixing ratio of coarse particles can be reduced to the target of 1/200 or less.
In addition, the NiO content is 0.1%, and the mixing ratio of substantially coarse particles can be reduced to 1/400. Although it is preferable that the NiO content be further reduced, industrially, the method can be economically reduced to about 1/400 by this method.

[0015]

EXAMPLES (Example 1) A nickel chloride crystal was heated at a temperature of 180 under atmospheric pressure to remove water of crystallization. As a result, the quality of NiO in anhydrous nickel chloride was 1%. When fine nickel powder was produced by a CVD method using this anhydrous nickel chloride, the particle size was found to be 1 μm by SEM observation.
The mixing ratio of abnormal coarse particles of m or more was 1/200.

Example 2 Nickel chloride crystals were
Heat treatment was performed at a temperature of 180 ° C. or less under a vacuum of torr to remove water of crystallization. As a result, the quality of NiO in anhydrous nickel chloride was 0.5%. Fine nickel powder was produced by CVD using this anhydrous nickel chloride.
According to EM observation, the mixing ratio of abnormal coarse particles having a particle size of 1 μm or more was 1/300. (Example 3) In Example 2, the heating rate was further increased by 5 ° C.
/ Min, and heating was performed so that the degree of vacuum did not become 100 torr or more. As a result, the quality of NiO in the obtained anhydrous nickel chloride was 0.1%. When fine nickel powder was produced by CVD using this anhydrous nickel chloride, the mixing ratio of abnormal coarse particles having a particle diameter of 1 μm or more as observed by SEM was 1/400. (Comparative Example 1) A nickel chloride crystal was heated at 250 ° C under atmospheric pressure.
When the water of crystallization was removed by heating at a temperature of 5%, the NiO grade in anhydrous nickel chloride was 5%. When fine nickel powder was produced by CVD using this anhydrous nickel chloride, the mixing ratio of abnormal coarse particles having a particle size of 1 μm or more was 1/100 as observed by SEM.

(Comparative Example 2) A nickel chloride crystal was heated at a temperature of 150 ° C. under atmospheric pressure to remove water of crystallization. As a result, the NiO quality in anhydrous nickel chloride was 0.5%. Part of the water of crystallization remained, and the water content was 4%. When fine nickel powder was produced by a CVD method using this nickel chloride, the mixing ratio of abnormally large particles having a particle diameter of 1 μm or more as observed by SEM was 1/150.

[0018]

According to the method of the present invention, anhydrous nickel chloride suitable as a raw material for nickel powder by a CVD method can be produced.

Claims (3)

[Claims] 1. The method of claim 1, wherein the nickel chloride crystals are heated at atmospheric pressure to 160
A method for producing anhydrous nickel chloride having a NiO content of 0.1% or more and 1% or less, characterized by performing a heat treatment at a temperature of from 200C to 200C. 2. The pressure of nickel chloride crystal is reduced from atmospheric pressure.
A method for producing anhydrous nickel chloride having a NiO content of 0.1% or more and 1% or less, characterized by performing a heat treatment at a temperature of 160 ° C or more and 200 ° C or less. 3. The NiO content according to claim 1 or 2, wherein the temperature of the NiO crystal is controlled to a rate at which the water of crystallization in the nickel chloride crystal is not dissociated as water but removed as vapor.
A method for producing anhydrous nickel chloride of at least 1%.