JPH04323310A - Manufacturing method of metal fine powder - Google Patents

Abstract

PURPOSE:To easily produce a fine metal powder having a specified grain shape by forming the complex of the metal dissolved in an aq. solvent contg. acid with a base, adjusting the soln. to specified pH and then adding a reducing agent at a specified temp. CONSTITUTION:One or more kinds of metal, alloy and metallic salt as the raw material are dissolved in an aq. solvent contg. acid such as hydrochloric acid and acetic acid. The metal concn. in the soln. is controlled to about 0.05-100g/l in accordance with the grain diameter of the depositing fine metal powder. A base such as ammonia forming the complex of the metal in the raw material is then added to the soln. to adjust the soln. to about pH8-11. The grain size distribution can be adjusted by the pH value. The soln. is kept at a specified temp. corresponding to the desired shape of the fine metal powder to be obtained, and a reducing agent such as hydrazine is added to deposit the fine metal powder. In this case, a globular fine metal grain is obtained at the soln. temp. of 10-30 deg.C, and a polyhedral fine metal powder is obtained at the soln. temp. of >=50 deg.C.

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 metal powder having a predetermined particle shape.

0002

2. Description of the Related Art Fine metal powder is mixed into conductive pastes for printing electronic circuits, electromagnetic shielding paints, plastic pellets for injection molding of electromagnetic shielding moldings, and the like. Regarding fine metal powders used in such fields, it is desirable to use fine metal powders with spherical particle shapes in view of printing suitability, coating suitability, moldability, etc. However, from the viewpoint of conductivity and electromagnetic shielding properties, it is desirable that the grains have a polyhedral shape in order to achieve close contact between the particles of the metal fine powder. Therefore, fine metal powder with spherical grain shape and fine metal powder with polyhedral grain shape are often used as a mixture. In addition, in the field of powder metallurgy, in which a sintered compact is obtained by sintering a compact made of fine metal powder, various methods are used to adjust the sintering temperature, the firing temperature, and the packing density and surface smoothness of the sintered compact. There is a demand for fine metal powder with a specific particle shape.

Conventionally, in the production method of this type of metal fine powder, metal or metal salt is dissolved in an acidic aqueous solvent, neutralized with a base, and then reduced with a reducing agent to obtain metal fine powder. Wet methods of precipitation are provided.

0004

[Problems to be Solved by the Invention] However, in the conventional wet method described above, it is difficult to arbitrarily adjust the particle shape.

[0005]

[Means for Solving the Problems] As a means for solving the above-mentioned conventional problems, the present invention provides one or more raw materials selected from the group consisting of metals, alloys, and metal salts in an aqueous solvent containing an acid. Step 1 of dissolving in the solution Step 2 of adjusting the pH value to a predetermined value by adding a base that forms a complex of the metal or metal constituting the alloy to the solution
After H adjustment, a reducing agent is added to precipitate the metal fine powder while maintaining the temperature at a predetermined temperature depending on the desired shape of the metal fine powder obtained. Step 3. The metal fine powder consists of the above steps 1, 2, and 3. The present invention provides a method for manufacturing. The invention will be explained in detail below.

[0006] Examples of metals constituting raw materials or alloys used in the present invention include Ag, Pd, and C.
d, Co, Fe, Ni, Sn, Pb, Pt, Au, Cu
It includes all metals, alloys, and compounds conventionally used in fields such as conductive pastes, electromagnetic shielding paints, electromagnetic shielding moldings, and powder metallurgy. Metal salts as raw materials used in the present invention include, for example, salts of inorganic or organic acids such as hydrochlorides, sulfates, nitrates, carbonates, and acetates of metals constituting the metals, alloys, or compounds listed above. All are included. In the present invention, the above-mentioned metal and/or the above-mentioned alloy and the above-mentioned metal salt may be used in combination, or two or more types may be mixed.

In step 1, one or more raw materials selected from the group consisting of the metals, alloys and metal salts mentioned above are dissolved in an aqueous solvent containing an acid. The above-mentioned acid-containing aqueous solvent is an aqueous solvent containing an inorganic or organic acid such as hydrochloric acid, sulfuric acid, acetic acid, etc. The aqueous solvent may be water alone, or water combined with methanol, ethanol, isopropanol, ethylene glycol, propylene glycol, etc. A mixed solvent prepared by mixing a predetermined amount of water-miscible organic solvents such as , acetone, and tetrahydrofuran is used.

[0008] In the above step 1, the metal concentration in the solution is applied in a wide range, for example, from 0.05 to 100 g/l, and the particle size of the precipitated metal fine powder can be adjusted depending on the metal concentration. That is, as the metal concentration of the solution increases, the particle size of the obtained metal fine powder increases. In addition, in order to perform step 1 efficiently, it is necessary to first dissolve one or more raw materials selected from the group consisting of metals, alloys, and metal salts in a concentrated acid solution, and then dilute it to a predetermined concentration. desirable. If a concentrated solution is used, the above raw materials will dissolve quickly.

In step 2, a base that forms a complex of the metal or metal constituting the alloy is added to the solution to adjust the pH to a predetermined value. Examples of the base include ammonia or amines such as dimethylamine, triethylamine, diisopropylamine, triethanolamine, and diisopropanolamine.

[0010] In the above step 2, the desirable pH value range is 8-11, more preferably 9-11. In the present invention, it has been found that in the above pH value range, when the pH value is low, the particle size distribution becomes wide, and when the pH value is high, the particle size distribution becomes narrow. Therefore, by adjusting the pH value, the breadth of the particle size distribution can be adjusted. Therefore, if it is desired to obtain fine metal powder with uniform particle size, the pH value in step 2 may be increased. However, if the pH value is 11 or more, the shape of the metal fine powder will not only be spherical but also irregularly shaped such as flakes, so it is desirable to keep the pH value at 11 or less.

[0011] In step 3, a reducing agent is added to the solution adjusted to a predetermined pH value. Reducing agents used at this time include organic reducing agents such as hydrazine, ascorbic acid, and glucose, and inorganic reducing agents such as sodium thiosulfate and sodium hyposulfite, but desirably, a reducing agent such as hydrazine that does not contain metal elements is used. used.

[0012] Although heat is generated in the above-mentioned reduction step, it has been found in the present invention that the particle shape of the fine metal powder can be adjusted by adjusting the temperature of the reduction step. That is, when the temperature is 50°C or higher, metal fine particles having a polyhedral shape are obtained, and when the temperature is 30°C
In the following, metal fine particles having a spherical particle shape are obtained. Further, at around 40° C., a fine metal powder containing a mixture of spherical particles and polyhedral particles is obtained. However, if the temperature drops below 10°C, the reduction reaction will not proceed smoothly. Therefore, the above reduction step is 1
It is desirable to carry out the process at a temperature of 0°C or higher. In step 3, the metal is reduced and precipitated from the solution. In this case, the metal is obtained as a fine powder having a predetermined particle size distribution depending on the pH value in step 2. The obtained metal fine powder is separated from the solvent by filtration, centrifugation, etc., washed with water, and mixed with methanol,
Wash with a water-miscible solvent such as ethanol or isopropanol, and then dry.

[0013]

[Operation] In step 3, the LaMer model is provided as the mechanism by which the metal is reduced from the solution and precipitated as particles. That is, when the metal salt is reduced to a metal in the reduction reaction in step 3, the metal is precipitated into the solution. According to the LaMer model, the nucleus of the particle precipitates first, and then the suspended atoms around the nucleus attach to the surface of the nucleus and move toward the stabilization position on the surface of the nucleus. At this point, the particles combine with the nuclear surface and particle growth occurs. However, at low temperatures, the mobility of atoms decreases, and atoms are captured and bonded to the nuclear surface before they reach a stable position on the nuclear surface.

That is, at high temperatures (eg, 50° C. or higher), the atoms have sufficient mobility to reach stable positions on the nuclear surface, so that the particles have a polyhedral crystal shape, and at low temperatures (eg, 3
(below 0°C), atoms cannot reach the stabilizing position on the nuclear surface, and random amorphous particles, ie, spherical particles, are precipitated.

[0015]

【Example】

[Example 1] An Ag--Pd alloy was prepared so that the weight ratio of Ag:Pd was 7:3, and the alloy was dissolved with (2+1) nitric acid. The alloy concentration of the solution at this time is Ag
+Pd is adjusted to 400g/l. The concentrated solution was then diluted with water to give 10% Ag + Pd.
Adjust to 0 g/l (Step 1). Add 20% by weight aqueous ammonia to the above solution to adjust the pH to 9 (
Step 2). After adjusting the pH, maintain the liquid temperature at a predetermined temperature and add 43cc of hydrazine per 100g of Ag + Pd.
is added to perform reduction (Step 3). The addition rate of hydrazine at this time is 1 cc/min. Thus Ag:Pd
Ag-Pd co-precipitated metal fine powder with a weight ratio of =7:3 is obtained. The Ag-Pd fine powder is filtered and washed with water, then with isopropanol, and then dried in a nitrogen stream. The relationship between the particle size distribution of the obtained Ag-Pd fine powder and the reduction temperature in step 3 is shown in FIG. According to FIG. 1, it can be seen that the particle size distribution becomes narrower as the liquid temperature becomes lower.

Furthermore, Table 1 shows the relationship between the particle shape of the obtained Ag--Pd fine powder and the reduction temperature in step 3.

[Table 1] According to Table 1, when the reduction temperature is 30°C or lower, a fine powder with a spherical grain shape is obtained, at 40°C a mixed fine powder with a spherical grain shape and a polyhedral grain shape is obtained, and at a reduction temperature of 50°C or higher, a mixed fine powder with a spherical grain shape and a polyhedral grain shape is obtained. It can be seen that a fine powder having a polyhedral grain shape is obtained.

As described above, according to the present invention, by adjusting the reduction temperature in step 3, it is possible to easily obtain fine metal powder having a desired particle shape.

Note that this example does not limit the present invention, and water-miscible solvents other than isopropanol, such as methanol and ethanol, may be used alone or in combination for washing the fine metal powder. The fine metal powder may not be dried in a nitrogen stream, but may be dried under reduced pressure.

[0019]

[Effects of the Invention] Therefore, according to the present invention, particles having a desired shape can be obtained by simple means.

[0020]

[Brief explanation of drawings]

FIG. 1 is a graph showing the relationship between the reduction temperature in Step 3 and the particle size distribution of the obtained fine metal powder.

Claims (3)

[Claims] Claim 1: Step 1 of dissolving one or more raw materials selected from the group consisting of metals, alloys, and metal salts in an acid-containing aqueous solvent; A complex of the metals constituting the metal or alloy is added to the solution. Step 2 of adjusting the pH value to a predetermined value by adding a base that forms
After H adjustment, a reducing agent is added to precipitate the metal fine powder while maintaining it at a predetermined temperature depending on the desired shape of the obtained metal fine powder.Step 3: It is characterized by comprising the above steps 1, 2, and 3. Method for producing fine metal powder 2. A method for producing fine metal powder, characterized in that in step 3, the temperature is adjusted to 10 to 30°C for the purpose of obtaining spherical fine metal particles. 3. A method for producing fine metal powder, characterized in that in step 3, the temperature is adjusted to 50° C. or higher for the purpose of obtaining polyhedral fine metal particles.