JP2554213B2 - Method for producing spherical nickel ultrafine powder - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing spherical nickel ultrafine powder suitable for a conductive paste filler used in electronic parts and the like.

[0002]

2. Description of the Related Art The particle size distribution is narrow and the average particle size is 0.1 to several μ.
In the range of m, the ultrafine metal powder having spherical particles has a good paste property, and when used for forming a conductor of an electronic circuit, it is possible to form a fine pattern or a thin layer of the conductor. There is an increasing demand for such powders.

For example, a monolithic ceramic capacitor is manufactured by alternately laminating ceramic dielectrics and internal electrodes in layers, press-bonding them and firing them to integrate them. In this case, the dielectric ceramics are fired as the material of the internal electrodes. It is necessary to use expensive noble metals such as Pt and Pd that do not melt at the temperature that binds them and that does not decompose or reduce the dielectric ceramics and that does not oxidize even when fired in an atmosphere with a high oxygen partial pressure. It was an obstacle to capacity reduction and price reduction.

However, in recent years, in order to use a base metal such as Ni for the internal electrode, it does not become a semiconductor even if it is fired in a low oxygen partial pressure or a reducing atmosphere, and has a sufficient specific resistance and excellent dielectric characteristics as a dielectric for a capacitor. Has been developed. On the other hand, on the other hand, the miniaturization and large capacity of components have advanced, and it has become necessary to reduce the thickness and resistance of internal electrodes.

By the way, the thickness of the internal electrode is limited by the particle diameter of the filler in the paste used. That is, it cannot be made thinner than the particle size. Therefore, it suffices to use a filler powder with a small particle size, but even with a powder having an average particle size of less than 1 μm, the filler is not sufficiently filled when the internal electrode paste is printed and the density is low, so there are many voids after firing, There is a problem that the resistance becomes high, and delamination often occurs during firing.

However, conventionally, it has been impossible to inexpensively manufacture a large amount of spherical nickel ultrafine powder which meets such severe conditions. As a conventional method for producing ultrafine nickel powder, as disclosed in Japanese Patent Publication No. 59-7765, a velocity difference is provided between a metal halide vapor gas flow and a reducing gas flow, and a specific gravity difference between the gases is used. Then, there is known a method of producing ultrafine metal powder by growing nuclei generated in the interface unstable region.

In this case, however, the fine nickel powder produced particles having a crystal habit such as a cubic shape, and when used as a paste filler, there was a problem of filling property. In addition, as a method for producing fine nickel powder, as disclosed in Japanese Patent Publication No. 2-49364, a method of adding a reducing agent such as sodium borohydride to an aqueous solution containing nickel ions and performing reductive precipitation is known. There is.

In this case, various reducing agents are required, and the operating conditions are complicated. Further, the so-called reduction precipitation method is a batch method, and it is difficult to make the production continuous. In addition, there is a carbonyl method as a method for producing nickel and iron fine powders, but the powder obtained by this method has a large particle size and cannot satisfy the demand for fine patterning or thinning of the conductor portion.

Recently, the gas phase chemical reaction methods disclosed in JP-A-62-63604 and JP-A-62-188709 have been developed. This method vaporizes a metal halide,
When this is sent to the reaction part by its own vapor pressure or by using an inert gas as a carrier and the metal halide vapor and reducing gas (hydrogen etc.) are contacted and mixed in the reaction part, immediately the metal powder in the gas Is reduced / precipitated and then discharged from the outlet together with the gas. Therefore, the raw material metal halide can be continuously supplied, and the produced powder can be continuously recovered.

However, unlike the case of the copper powder in JP-A-62-63604 and the silver powder in JP-A-62-188709, in the case of nickel powder, particles having crystal habits such as cubes and octahedra. Was generated, and there was a problem in the filling property when used as a paste filler.

[0011]

In view of the above-mentioned conventional techniques, the present invention aims to provide an inexpensive method for producing spherical nickel ultrafine powder having an average particle size in the range of 0.2 to 1 μm. It is what

[0012]

The present invention provides a method for producing fine nickel powder by a chemical reaction between nickel chloride vapor and hydrogen, wherein the vapor concentration (partial pressure) of nickel chloride is 0.05 to 0.3, and 1004 ℃ (1277K) or higher 1453
A method for producing spherical nickel ultrafine powder, characterized by chemically reacting at a temperature lower than ℃ (1726K).

[0013]

[Operation] The present invention utilizes a gas phase chemical reaction method. In this method, using a reactor 1 as shown in FIG. 1, nickel chloride, which is a raw material, is put into a quartz boat 3 of an evaporation section 2 and then evaporated, and the evaporated nickel chloride gas is transported to a reaction section 5 together with an argon gas 4, and the reactor central The hydrogen 7 supplied from the nozzle 6 is brought into contact with and mixed with the hydrogen 7 to cause a reaction. The temperature of the reaction part is measured by a thermocouple 8 protected by a quartz tube. Then, the generated nickel fine powder passes through the cooling unit 9 together with the gas,
Collected with a cylindrical filter paper.

The growth of particles in the gas phase chemical reaction method is considered as follows [Journal of Powder Engineering Vol. 21, 759-767].
(1984)]. At the moment when the metal halide vapor and the reducing gas come into contact with each other, a monomer of a metal atom or a cluster is produced, and ultrafine particles are produced by collisional aggregation of the monomer. Further, particle growth occurs due to collision and coalescence.

The ultrafine particles are generally spherical, but nickel is often a polyhedron. In particular, when the particles are in a relatively coarse region, the surface energy ratio also decreases, and the powder often has a crystal habit. In particular, when the particle size of nickel is larger than about 0.2 μm, cubic and octahedral crystal grains having clear crystal habit tend to be formed. Therefore, as a result of detailed investigation of the reaction generation of nickel fine powder, the present inventor set the nickel chloride vapor concentration (partial pressure in the supply gas excluding hydrogen) to 0.05 or more, and the reaction / powder generation temperature in absolute temperature. 0.74 times the melting point of nickel (1726K), that is, 1004 ℃ (1277K)
It was found that a spherical powder can be obtained with the above K) and the present invention has been completed.

It is speculated that the temperature dependence of the shape is related to the reaction rate, that is, the formation rate of the metal atom or the monomer of the cluster, being influenced by the temperature. In other words, it is considered that the growth rate of particles influences the shape. Further, it can be construed that the higher the temperature, the more anisotropic the growth of the particles becomes, so that the particles are likely to grow spherically. It is considered that the concentration dependence of the shape is related to the influence of the uniform nucleation rate on the concentration. In this case as well, it is understood that it depends on the growth rate of the particles as well as the temperature.

When the reaction is carried out, for example, in a reaction tube heated in an electric furnace, this reaction is an exothermic reaction. Therefore, if the set temperature of the electric furnace is lower than the above-specified temperature, as long as it can be compensated by the exothermic reaction, The purpose of spheroidization can be achieved. That is, in the vapor phase chemical reaction method, it is important to control the temperature at which the formation of metal monomers by reaction and the particle growth by collision / coalescence occur.

The upper limit of the reaction temperature is the melting point of nickel 1453 ° C.
Limited to less than (1726K). This is because at the melting point or higher, the produced particles are present in the form of droplets, so that particles that grow abnormally huge may be generated, the particle size distribution is broadened, and the adhesion to the wall of the reactor is increased. The upper limit of nickel chloride vapor concentration (partial pressure) in the evaporator is limited to 0.3. If the concentration exceeds 0.3, the particle size becomes coarse and the desired particle size cannot be obtained. Further, if it becomes coarse, crystal habit tends to occur.

The lower limit of the nickel chloride vapor concentration (partial pressure) is limited to 0.05. If the concentration is less than 0.05, grain growth is slow and crystal habit is likely to occur. Next, the present invention will be described in more detail based on examples.

[0020]

【Example】

Example 1 using a reactor 1 as shown in FIG. 1, placed 10g of nickel chloride in the raw material in a quartz boat 3 evaporators 2, 2l / min Concentration argon gas 4 (partial pressure) is 5.0 × 10 ^- Evaporated to ² . This raw material mixed gas was transported to the reaction section 5 set at 1030 ° C. (0.755 times the melting point of nickel at absolute temperature) and brought into contact with and mixed with hydrogen supplied from the reaction central nozzle 6 at a rate of 1 l / min to cause a reaction. Let When the temperature of the reaction part was measured by a thermocouple 8 protected by a quartz tube, it was 1065 ° C.
(0.775 times that of the previous year). The generated nickel powder passed through the cooling section 9 together with the gas, and was then collected by a cylindrical filter paper.
The specific surface area of this produced powder was 3.2 m ² / g, and it was a spherical powder having an average particle size of 0.21 μm as observed by an electron microscope. FIG. 2 shows an electron micrograph of the nickel powder obtained in this example. It can be seen that the nickel powder has a nearly spherical shape.

Example 2 Nickel powder was produced under the same conditions as in Example 1, except that the temperature set for the reaction section was 960 ° C. (0.714 times the melting point of nickel at the absolute temperature). When measured with thermocouple 8
It increased to 1004 ℃ (0.74 times). The specific surface area of the generated nickel powder was 3.7 m ² / g, and it was a spherical powder having an average particle size of 0.18 μm as observed by an electron microscope. The electron micrograph is shown in FIG.

Example 3 In Example 1, the reaction part set temperature was 960 ° C. (0.714 times the nickel melting point in absolute temperature) and the concentration (partial pressure) was 8.0 × 10 5.
Nickel powder was produced under the same conditions except that the value was ^-2 . When measured with a thermocouple 8, the temperature rose to 1006 ° C (0.74 times the same). The specific surface area of the generated nickel powder was 3.0 m ² / g, and it was a spherical powder having an average particle size of 0.22 μm as observed by an electron microscope.

Example 4 In Example 1, the reaction part set temperature was 1000 ° C. (0.74 times the nickel melting point in absolute temperature) and the concentration (partial pressure) was 8.5 × 10 ^−2.
Nickel powder was manufactured under the same conditions except that When measured with a thermocouple 8, the temperature rose to 1053 ° C (0.77 times the same). The specific surface area of the generated nickel powder was 2.9 m ² / g, and it was a spherical powder having an average particle size of 0.23 μm as observed by an electron microscope.

Example 5 In Example 1, the reaction part set temperature was 1050 ° C. (0.767 times the nickel melting point in absolute temperature), and the concentration (partial pressure) was 3.0 × 10 5.
Nickel powder was produced under the same conditions except that ^-1 was used. When measured with a thermocouple 8, the temperature rose to 1120 ° C (0.81 times the same). The specific surface area of the generated nickel powder was 0.9 m ² / g, and it was a spherical powder having an average particle size of 0.8 μm as observed by an electron microscope.

Comparative Example 1 Nickel powder was produced under the same conditions as in Example 1 except that the reaction part set temperature was 950 ° C. (0.71 times the nickel melting point in absolute temperature) and the concentration (partial pressure) was 4.5 × 10 ^−2. did. Thermocouple 8
When measured by, the temperature rose to 995 ℃ (0.73 times higher). The specific surface area of the generated nickel powder was 3.6 m ² / g, and it was a powder having a crystal habit such as a cube and an octahedron having an average particle size of 0.2 μm as observed by an electron microscope. The electron micrograph is shown in FIG.

Comparative Example 2 Nickel powder was produced under the same conditions as in Example 1, except that the reaction part set temperature was 950 ° C. (0.71 times the nickel melting point in absolute temperature) and the concentration (partial pressure) was 8.0 × 10 ^−2. did. Thermocouple 8
When measured by, the temperature rose to 998 ℃ (0.78 times higher). The specific surface area of the generated nickel powder was 3.4 m ² / g, and it was a powder having a crystal habit such as a cube and an octahedron having an average particle size of 0.2 μm as observed by an electron microscope.

Comparative Example 3 Nickel powder was produced under the same conditions as in Example 1, except that the reaction part set temperature was 1000 ° C. (0.74 times the nickel melting point in absolute temperature) and the concentration (partial pressure) was 4.5 × 10 ^−2. did. Thermocouple 8
When measured by, the temperature rose to 1042 ℃ (0.76 times the same). The specific surface area of the generated nickel powder was 3.4 m ² / g, and it was a powder having a crystal habit such as a cube and an octahedron having an average particle size of 0.2 μm as observed by an electron microscope.

Comparative Example 4 In Example 1, the reaction part set temperature was 1100 ° C. (0.795 times the melting point of nickel in absolute temperature) and the concentration (partial pressure) was 3.6 × 10 ^−1.
Nickel powder was manufactured under the same conditions except that When measured with a thermocouple 8, the temperature rose to 1160 ° C (0.83 times the same). The specific surface area of the generated nickel powder was 1.0 m ² / g, and it was a powder having a crystal habit such as a cube and an octahedron having an average particle diameter of 0.8 μm as observed by an electron microscope.

[0029]

EFFECTS OF THE INVENTION According to the present invention, it has excellent performance as a conductive paste filler, and can form fine patterns and thin layers of the conductor portion of electronic parts. Ultrafine nickel powder in the range of ˜1 μm can be manufactured at low cost.

[Brief description of drawings]

FIG. 1 is a schematic view of a reactor that can be suitably used for carrying out the present invention.

2 is a micrograph showing a particle structure of nickel ultrafine powder produced by the method of the present invention shown in Example 1. FIG.

3 is a micrograph showing the particle structure of nickel ultrafine powder produced by the method of the present invention shown in Example 2. FIG.

FIG. 4 is a micrograph showing a particle structure of nickel ultrafine powder produced in Comparative Example 1.

FIG. 5 is a graph showing the relationship between the nickel chloride vapor concentration and reaction temperature in the nickel chloride vaporization section and the shape of nickel particles in each of the examples and comparative examples.

[Explanation of symbols]

 1 Reactor 2 Evaporator 3 Quartz Boat 4 Argon Gas 5 Reaction 6 Central Nozzle 7 Hydrogen Gas 8 Thermocouple 9 Cooling

Claims (1)

(57) [Claims] 1. A method for producing fine nickel powder by a chemical reaction between nickel chloride vapor and hydrogen, wherein the nickel chloride vapor concentration (partial pressure) in the nickel chloride vaporizing section is 0.05 to 0.
3. A method for producing ultrafine spherical nickel powder, which comprises chemically reacting at a temperature of 1004 ° C. (1277 K) or more and less than 1453 ° C. (1726 K).