JPH0543921A - Production of nickel fine powder - Google Patents

Abstract

PURPOSE:To obtain nickel fine powder having good diffusivity, small particle diameters and extremely narrow particle size distribution range by using basic nickel carbonate as a raw material in a method for reacting nickel containing solution with hydrazine, etc. CONSTITUTION:Dispersion liquid which basic nickel carbonate is dispersed in solvent, such as water to form is heated to the prescribed temp. and kept at at that temp. and hydrazine hydrate (or hydrazine) is added to it while stirring. Then, nickel complex is formed by solid-liquid reaction between basic nickel carbonate and hydrazine hydrate and nickel ions are deposited as metallic nickel by the reducing action of hydrazine hydrate. The basic nickel carbonate is produced by making water solution of soluble nickel (II) salt, such as nickel chloride interact with alkali carbonate. The product arbitrary composition represented by the general formula, whose NiCO3.yNi(OH)2.H2O, can be usually used, but that of <=50ppm impurity element concentration is preferable and if 50ppm is exceeded, the diffusivity of the formed nickel powder is decreased.

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 fine nickel powder, and more particularly to a method for producing fine nickel powder which is useful as an internal electrode material of a multilayer capacitor.

[0002]

2. Description of the Related Art In recent years, in order to reduce the production cost of a small-sized and large-capacity monolithic ceramic capacitor, non-reducing dielectric ceramics have been used by using a base metal such as nickel instead of a noble metal such as platinum or palladium as an internal electrode material. A multilayer ceramic capacitor using as a dielectric material is proposed in, for example, Japanese Patent Publication No. 56-46641, and as a method for producing the metallic nickel powder thereof, for example, Japanese Patent Laid-Open No. 53-
Japanese Patent No. 95165 proposes a method in which a hydrazine or a hydrazine compound is added to and mixed with a nickel-containing solution containing any one of nickel chloride, nickel carbonate, and nickel acetate, and the mixture is heated at a temperature of 100 ° C. or lower.

[0003]

However, the nickel powder produced by the above method has a wide particle size distribution range, and
Since the dispersibility in the binder is poor, there is a problem that when it is used as an internal electrode material of a multilayer capacitor, internal defects and deterioration of electric characteristics are caused.

Therefore, an object of the present invention is to obtain a fine metal nickel powder having a good dispersibility, a small particle size and an extremely narrow particle size distribution width.

[0005]

In order to solve the above-mentioned problems, the present invention is one in which hydrazine or hydrazine hydrate is added to a solvent containing basic nickel carbonate for reduction.

The basic nickel carbonate used in the present invention is, for example, water-soluble nickel (II) such as nickel chloride (NiCl ₂ ), nickel sulfate (NiSO ₄ ), nickel nitrate (Ni (NO ₃ ) ₂ ), and nickel acetate. ) Obtained by reacting an aqueous solution of salt with an alkali carbonate, and usually has the general formula:
An arbitrary composition represented by xNiCO ₃ · yNi (OH) ₂ · zH ₂ O can be used, but it is preferable to use one having an impurity element concentration of 50 ppm or less contained in basic nickel carbonate. .. This is because when the concentration of all impurity elements in basic nickel carbonate exceeds 50 ppm, the dispersibility of the nickel powder produced due to the influence of the impurity elements deteriorates. The basic nickel carbonate has an average particle size of 6-9.
Preference is given to using powders with a particle size distribution of 0.2 to 10 μm.

Any solvent can be used as the solvent as long as it can dissolve the reducing agent, but water is generally used. As the reducing agent, it is preferable to use hydrazine or hydrazine hydrate having a strong reducing action, and the reduction is usually performed at a bath temperature of 65 to 95 ° C., preferably
The temperature is maintained at 70 to 92 ° C. The basic nickel carbonate, solvent and reducing agent are in a molar ratio of 1: 15: 190-90.
It is mixed in a ratio of 1: 30: 230.

[0008]

[Function] When basic nickel carbonate is added to the solvent, the basic nickel carbonate powder is dispersed in the solvent, and the dispersion is heated and maintained at a predetermined temperature, and when hydrazine hydrate is added with stirring, the basic carbonate is added. A solid-liquid reaction between nickel and hydrazine hydrate produces a nickel complex salt, and the reducing action of hydrazine hydrate further reduces nickel ions to deposit metal nickel.

Examples will be described below.

[0010]

[Example] 15 mol of pure water was put into a reaction tank, and 20
Stir with a stirrer rotating at a speed of 0 to 300 rpm, while maintaining the bath temperature at 80 ° C, basic nickel carbonate (Ni
CO ₃ .2Ni (OH) ₂ .4H ₂ O, average particle size: 8.0 μm, particle size range: 0.2 to 10 μm) 1 mol and 190 mol of hydrazine hydrate were sequentially added, and nickel was added using an Ni ²⁺ ion checker. Hold until no ions are detected. In addition,
Impurity concentration in basic nickel carbonate is Fe <10ppm, M
g <10ppm, Ca <10ppm, Cu <10ppm, Na <50p
pm, Co <50 ppm, and total impurity concentration is 50 ppm or less.
Then, after cooling the reaction solution to room temperature, pure water is gently added to produce nickel powder, and the pH of the cleaning solution is adjusted to 7.0.
Wash to 8.0. After the nickel powder is filtered off, it is dried at 90 ° C. to obtain metallic nickel powder.

The physical properties of the obtained metallic nickel powder were measured, and the average particle diameter of the primary particles was 0.6 μm.
The spherical fine powder had a very narrow particle size distribution with a particle size range of 0.2 to 5.0. The tap density is 2.0 g / ml, the specific surface area is 2.4 m ² / g, the impurity concentration in the nickel fine powder is Al <10 ppm, Fe <10 ppm, Mg <10-50 ppm,
Ca <− and Cu <10 ppm.

47.5 wt% of the nickel powder and the dispersant 4.
0 wt% was mixed with 10.0 wt% of a vehicle prepared by kneading terpineol in ethyl cellulose for 30 to 60 minutes, then kneaded 2 to 4 times with a three-roll mill, and 38.5 wt% of the vehicle and terpineol were added and mixed. The viscosity is adjusted to 4.5 to 16 pa. And the specific gravity is 1.2 to 2.0.
A nickel paste is prepared by mixing for 0 to 60 minutes.

Using this nickel paste as a conductive paste for forming internal electrodes, a monolithic ceramic capacitor was manufactured by a conventional method. That is, first, according to the conventional method (Ba _0.98
Ca _0.02 ) _1.01 (Ti _0.84 Zr _0.16 ) O _{2 A} barium titanate-based dielectric ceramic calcinated powder was prepared, and 3 wt% of an organic binder was added thereto and wet mixed to prepare a ceramic green sheet. To get The nickel paste is applied to the surface of the ceramic green sheet by a screen printing method using a 325 to 400 mesh screen. After stacking a plurality of the ceramic green sheets so that one end of the coating film formed by the nickel paste is alternately exposed on the end surface of the laminate, and stacking the ceramic green sheets not coated with the nickel paste on the upper and lower sides, the whole Are pressure-bonded to form a laminated body. This laminated body is cut into a predetermined size to obtain a capacitor chip, and each chip is applied as an intermediate layer for joining with an external electrode by dipping each chip in a nickel paste. The nickel paste is of the same kind as the internal electrode forming nickel paste prepared for dipping. Next, the capacitor chip is fired at a temperature of 1250 ± 100 ° C. in a non-oxidizing atmosphere to obtain a capacitor unit having a nickel layer as a dielectric layer. A conductive paste containing Ag or Ag-Pd as a main component is applied to both ends of this unit so as to cover the respective bonding intermediate layers, and then heat-cured to form external electrodes, and nickel plating is performed on the external electrodes. Or tin plated,
Obtain a monolithic ceramic capacitor (rated voltage: 25V).

The rate of occurrence of crack defects due to thermal shock and the electrical characteristics of the obtained monolithic ceramic capacitor were measured, and the results shown in Table 1 were obtained.

The rate of occurrence of crack defects was determined by using several tens of monolithic ceramic capacitors as samples, immersing them in a molten solder bath at 240 ° C. for several seconds without preheating, and then naturally cooling them to room temperature. The cracks inside the sample were detected by ultrasonic flaw detection, and the ratio of the number of samples with internal cracks to the total number of samples was calculated. In addition, the insulation resistance deterioration time is measured by continuously measuring the insulation resistance between the external electrode terminals while applying a voltage (100 V) that is four times the rated power of the monolithic ceramic capacitor until the insulation resistance becomes 1 MΩ or less. It's time. Furthermore, the insulation resistance deterioration is determined to be no insulation resistance deterioration if the initial resistance value of the multilayer ceramic capacitor is measured with an IR meter and the insulation resistance value after applying a voltage of 100 V is the same as that of the conventional multilayer ceramic capacitor. did. For the dielectric breakdown voltage, apply a voltage to the external electrode terminals of the monolithic ceramic capacitor,
The current value between the electrode terminals is 1 when it is increased at 00V / sec.
The voltage value when it became mA or more was measured, and this was made into the dielectric breakdown voltage.

[0016]

[Table 1]

From the results shown in Table 1, when the nickel fine powder obtained by the method of the present invention is used, the occurrence rate of crack defects is reduced to about 1/7 that of the nickel powder obtained by the conventional method, and the electrical characteristics are reduced. It can be seen that deterioration of can be prevented.

[0018]

As described above, according to the present invention, basic nickel carbonate, in particular, basic nickel carbonate having a high purity and a specific particle size is used as a raw material to produce fine nickel powder by solid-liquid reaction. Since the average particle size of the primary particles is small, it is possible to obtain a spherical nickel fine powder having an extremely narrow particle size range of 0.2 to 5.0 μm, and it is possible to improve the dispersibility in the binder. It has an excellent effect.

Claims (3)

[Claims] 1. A method for producing fine nickel powder, which comprises adding hydrazine or hydrazine hydrate to a solvent containing basic nickel carbonate for reduction. 2. The method according to claim 1, wherein the concentration of the impurity element in the basic nickel carbonate is 50 ppm or less. 3. The method according to claim 1, wherein the reduction is carried out at a temperature in the range of 65 to 95 ° C.