JPH0249364B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing fine nickel and cobalt powders by a wet process, and more particularly, to a method for producing fine nickel and cobalt metal powders that have a small, uniform particle size distribution and are non-agglomerative. Powder is used not only in the powder metallurgy field but also in the electronic industry field.
It is being put into practical use as a paste material for electronic components, for example, in place of precious metals such as gold, silver, and palladium. Conventional manufacturing methods for obtaining nickel and cobalt fine powder include (1) thermal decomposition of nickel or cobalt carbonyl salts, and (2) reduction of nickel or cobalt oxides or salts with hydrogen or carbon at a temperature below their melting point. Method (3) The evaporation method in gas, in which nickel metal is evaporated and condensed in vacuum or inert gas, is widely known. Method (1) is a method that is widely practiced industrially, but the resulting nickel powder has a particle size of 0.5 to 10 μm.
The particle size distribution width is wide and the particle shape is not constant.Furthermore, in order to obtain the small particle size and particle size distribution width required in the electronics industry, it is necessary to crush,
It requires sieving and the yield of the product is poor. In addition, the method (2) has drawbacks such as the significant influence of the particle size and particle morphology of compounds such as oxides or salts, and the tendency to cause sintering of particles because the reaction is carried out at high temperatures. Furthermore, the method (3) has the disadvantage that the evaporation rate is controlled by temperature, atmospheric pressure, etc., the production capacity of fine metal powder is extremely low, and it is difficult to continuously produce a large amount of fine metal powder. In addition, the powder obtained by conventional wet methods such as electrochemical reduction and chemical reduction has a particle size distribution over a wide range of 0.5 to 200 μm, and at the same time, the particle shape is not constant. It requires further grinding and sieving. In addition, in the chemical reduction method, impurities such as phosphorus (P) and boron (B) are contained in an amount of several percent to several tens of percent, and the product yield is also low. The fine powders obtained by these wet methods generally have many processing problems, such as the fact that the smaller the particle size, the more difficult it is to recover them by normal filtration methods. The present invention was made to eliminate these drawbacks of conventional methods, and its purpose is to easily and freely control the particle size to 2 μm or less in diameter using a wet method and simple equipment, and to achieve a uniform particle size distribution with a small width. The object of the present invention is to provide a method for producing non-agglomerated, highly pure nickel and cobalt metal fine powders in large quantities and in high yield. As a result of various studies to achieve the above object, the present inventors have discovered that aqueous solutions of nickel sulfate, cobalt sulfate, nickel chloride, cobalt chloride, nickel nitrate, cobalt nitrate, etc. containing nickel or cobalt as ions (hereinafter referred to as nickel) Sodium borohydride (NaBH ₄ as well as Na ₂ B ₂ H ₆ ,
A general term for compounds with compositions that correspond to addition compounds of borohydride and Na, such as Na ₂ B ₄ H ₁₀ and Na ₂ B ₅ H ₉ . Hereinafter referred to as SBH. ) and hydrazine (NH ₂ NH ₂ )
are mixed and added at the same time to reduce the nickel or cobalt in the solution to metal fine powder aggregates, and then the metal fine powder aggregates are treated with glue, and then washed with alcohol.
The present invention was completed by discovering that by drying, a uniform, non-agglomerated, highly pure nickel and cobalt metal fine powder with a diameter of 2 μm or less and a narrow particle size distribution width can be obtained. That is, in the present invention, SBH and hydrazine are mixed and added to a nickel ion solution or a cobalt ion solution at the same time, the nickel or cobalt ions in the solution are returned to metal fine powder aggregates, and then the metal fine powder aggregates are mixed with glue. A method for producing fine nickel and cobalt powders, characterized in that after treatment, a fine metal powder dispersion is obtained by washing with alcohol and drying. In the method for producing fine nickel and cobalt powder according to the present invention, the pH of the nickel ion solution or cobalt ion solution is adjusted to 6.0 to 10, preferably by using a mineral acid such as caustic soda, caustic potash, ammonia, preferably ammonia, and a mineral acid such as sulfuric acid, preferably sulfuric acid. is kept at 8.0~9.5, and the temperature of the aqueous solution is kept at 30~9.5.
It is maintained at 90°C, preferably 40 to 80°C, and the molar ratio (SBH/NiorCo, hydrazine/NiorCo) to the nickel or cobalt content in the aqueous solution is 1.25 × 10 ^-3 to 0.125, preferably 2.5 × 10 ^-3 ~0.05
An aqueous solution of SBH and 0.5 to 2.5, preferably 1.0 to 2.0, of hydrazine is added.
By this operation, the nickel or cobalt in the aqueous solution is reduced to fine metal powder aggregates, and solid-liquid separation can be easily performed in a short time by natural gravity or reduced pressure without using any supernatant or coagulant. After the solid-liquid separated nickel or cobalt metal fine powder aggregate held in a filter is washed with glue, alcohol is added and washed to obtain a nickel or cobalt metal fine powder dispersion. The glue used in this operation is treated in the form of an aqueous solution with a concentration of 0.5 to 5 g/g/g/g/g/g, and is added in an amount of 0.1 to 5 percent by weight based on the amount of fine nickel or cobalt metal powder. Subsequently, after washing excess glue with water, alcohol is added to remove the water by displacement. The alcohol may be any alcohol as long as it displaces water, but methanol and ethanol are preferred. The metal fine powder dispersion obtained in this way can be dried at a temperature of 60 to 90℃30 using an ordinary drying method without using special drying methods such as vacuum drying or freeze drying.
By drying for ~60 minutes, a uniform fine powder with a diameter of 2 μm or less and a narrow particle size distribution width can be obtained. In the reduction reaction, the concentration of the nickel or cobalt ion solution is not particularly limited, but from the viewpoint of the amount of liquid to be handled and reaction control, the concentration is between 0.5 and 0.5.
4.0 mol/ is preferable. According to the method of the present invention as described above, fine nickel and cobalt metal powders with a diameter of 2 μm or less, which has been difficult to produce in the past, can be easily produced in large quantities at high yields using simple equipment by a wet method compared to a dry method. It has an excellent effect in that it can be manufactured, and furthermore, the obtained metal fine powder is a uniform non-agglomerated powder with a narrow particle size distribution width, a specific surface area of 1 to 10 m ² /g, and a purity of 99.5%.
It also has the above excellent properties and can be used in the electronic industry. Hereinafter, the present invention will be explained in more detail based on Examples and Comparative Examples, but the present invention is not limited to these Examples. Example 1 Dissolve nickel sulfate (NiSO ₄ 6H ₂ O) in water,
The pH in the solution was adjusted with ammonia (NH ₄ OH) and sulfuric acid (H ₂ SO ₄ ). On the other hand, an aqueous hydrazine solution in which SBH and hydrazine were mixed and dissolved in water was added while maintaining the pH and reaction temperature as shown in Table 1, and the nickel in the aqueous solution was reduced to fine metal powder aggregates. In this case, the amount and concentration of the nickel sulfate aqueous solution,
Amount of mixed and added SBH and hydrazine (mol)
and SBH/Ni molar ratio, hydrazine/Ni molar ratio,
The hydrazine concentration in the hydrazine aqueous solution, PH, and reaction temperature conditions were changed as shown in Table 1, and Test No.
I did 5.

[Table] The slurry containing metal fine powder aggregates generated in the following process was passed through a natural gravity filter, and the nickel fine powder aggregates retained in the filter were washed with water → Glue solution 1 with a concentration of 2 g/ After carrying out the following processes: passing through a liquid, washing with water, passing through a methanol (CH ₃ OH) 1, a fine nickel powder was obtained which was dried at 80° C. for 60 minutes. Table 2 shows the amount of fine powder obtained in each test example and its characteristic values.

[Table] *2 Observation using a scanning electron microscope Ni obtained from Table 2 and attached Test No. 1
20000x scanning electron microscope reference photo of fine powder No.1
As is obvious, the specific surface area is large and the average particle size is
Observation using a scanning electron microscope showed that the particle size distribution was less than 2μ, and it was found to be a uniform, non-agglomerated fine nickel powder with a very small particle size distribution width. Example 2 Cobalt sulfate (CoSO ₄ 7H ₂ O) was dissolved in water, and the pH of the solution was adjusted to 9.0 with aqueous ammonia (NH ₄ OH) and sulfuric acid (H ₂ SO ₄ ) to give a cobalt concentration of 0.5 mol/. SBH6.25× in aqueous solution 5
10 ^-2 mol (SBH/CO molar ratio 2.5 x 10 ^-2 ) and 5 mol hydrazine (hydrazine/CO molar ratio 2.0) were mixed, and an aqueous solution with a hydrazine concentration of 20% by weight dissolved in water was reacted at pH 9.0. The cobalt was added while maintaining the temperature at 70° C. to reduce cobalt to metal fine powder aggregates, and then the same treatment as in Example 1 was performed to obtain 145 g of cobalt fine powder. The Co purity is 99.5%, the specific surface area is 2.2 m ² /g, and the average particle size is 0.5 μm, and the particle size range is 0.4 to 0.6 μm when observed with a scanning electron microscope.
It was found that the powder was uniform with a narrow particle size distribution. A scanning electron micrograph of the obtained Co fine powder at a magnification of 20,000 times is attached as reference photograph No. 2. Comparative Example 1 Concentration adjusted in the same manner as Examples 1 and 2
0.5 mol/, 1.875 mol of SBH (SBH/Ni or Co molar ratio 0.75) or hydrazine 5 mol (Hydrazine/Ni or Co molar ratio 2.0) in nickel ion aqueous solution or cobalt ion aqueous solution 5 with pH 9.0
While maintaining the reaction temperature at 60° C., SBH and hydrazine were added individually, and the resulting powder slurry was treated in the same manner as in Example 1 to obtain powder. As a result of X-ray diffraction and chemical analysis of each powder,
When SBH was added alone to the nickel ion aqueous solution, the produced Ni powder showed a mixed peak of Ni ⁰ and Ni ₂ B, and the Ni content was 90% and the B content was 5%. similarly
Even when SBH was added alone to an aqueous cobalt ion solution, the resulting Co powder was a mixture of metal cobalt and cobalt holide, with a Co grade of 86% and a B grade of 4%. When hydrazine was added alone to an aqueous nickel solution or an aqueous cobalt ion solution, the powders produced were nickel hydrazine sulfate and cobalt hydrazine sulfate, respectively. That is, it is shown that simultaneous addition of SBH and hydrazine to a solution containing Ni ions or Co ions is essential in order to achieve the object of the present invention. Comparative Example 2 Nickel or cobalt fine powder aggregates produced in the same manner as Test No. 1 and Example 2 of Example 1 were simply washed with water without being treated with glue and/or alcohol, and then heated at 80°C. After drying for 240 minutes, 145 g and 146 g of nickel or cobalt fine powder were obtained, respectively. As a result of X-ray diffraction and scanning electron microscopy observation of the resulting fine powder, an oxide peak was observed, and at the same time, it was significantly agglomerated and solidified, and was not easily dispersed even by ultrasonic dispersion. That is, from this result, it can be seen that glue and/or alcohol treatment is necessary to achieve the object of the present invention. As is clear from the above examples and comparative examples, the method for producing fine nickel and cobalt powders according to the present invention has superior properties to fine powders obtained by conventional wet methods, and can be produced in large quantities at high yields using simple equipment. It is an extremely useful invention as it can be manufactured using

Claims (1)

[Claims] 1. Metal fine powder obtained by simultaneously adding sodium borohydride and hydrazine to an aqueous solution containing nickel ions or cobalt ions, reducing the nickel or cobalt in the aqueous solution to metal fine powder aggregates. A method for producing fine nickel and cobalt powder, which comprises treating the aggregates with glue, washing with alcohol, and drying to obtain a fine metal powder dispersion. 2 During the above reduction, the pH of the aqueous solution was adjusted to 6.0 to 10, and the temperature
The method for producing fine nickel and cobalt powder according to claim 1, wherein the temperature is maintained at 30 to 90°C. 3. When adding the sodium borohydride and hydrazine together, the molar ratio of sodium borohydride to the nickel or cobalt content in the aqueous solution is 1.25 x 10 ^-3 to 0.125, and the molar ratio of hydrazine is 0.5 to 2.5. A method for producing fine nickel and cobalt powder according to claim 1, characterized in that: 4 The metal fine powder aggregates are mixed with a glue concentration of 0.5 to 5 g/
2. The method for producing fine nickel and cobalt powder according to claim 1, wherein 0.1 to 5% by weight of the fine nickel or cobalt powder is added to an aqueous solution of the fine powder and washed.