JPS63297511A - Production of fine metal powder - Google Patents

Abstract

PURPOSE:To produce fine metal powder having unique electrical and magnetic characteristics by adding metal colloid to a bath contg. an inorg. metal salt or a complex salt and a reducing agent for the salt with stirring and by mixing them. CONSTITUTION:Metal colloid such as Pd colloid is added to a bath contg. an inorg. metal salt such as chloride or sulfate of Ni or Co or a complexing agent forming a complex salt such as ammonia, ethylene-diamine, pyrophosphate or citric acid and further contg. a reducing agent such as sodium hypophosphite, potassium hypophosphite or form-aldehyde and they are mixed. The Pd colloid acts as the nuclei of a catalyst and reduction reaction proceeds rapidly and uniformly around the nuclei, so useful metal powder having superior electrical and magnetic characteristics can stably be produced.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to the production of fine metal powder, and more specifically to the production of fine metal powder, in particular, the method of reducing the metal by mixing a metal colloid in a bath containing an inorganic metal salt or complex salt and its reducing agent. The main uses of the precipitated metal fine powder according to the present invention are magnetic fluids, magnetic recording materials, electromagnetic shielding materials, anisotropic or pressurized conductive rubber, plastic magnetism,
These include conductive paints and adhesives.

(Prior art) Methods for producing fine metal powder from a liquid phase are broadly divided into precipitation methods and solvent evaporation methods. Of these, precipitation methods further include coprecipitation methods, hydrolysis methods, homogeneous precipitation methods, and oxidative hydrolysis methods. , reduction method, etc. are known (Chemistry Review N0048.1985 Ultrafine Particles-
Science and Applications, p. 24).

However, in the precipitation method, the precipitate is generally gel-like and washed with water.

It has drawbacks such as difficulty in filtration and the presence of precipitants as impurities.

Silver and gold can also be produced by reduction reactions from metal salt solutions.

Colloids of precious metals such as platinum and palladium are produced by reduction methods, but in this case as well, they are difficult to separate from water, solidify during drying, and difficult to remove impurities. It should be noted that the production of fine metal powders with excellent electrical and magnetic properties using conventional precipitation methods has not yet been reported.

(Problems to be Solved by the Invention) As a result of intensive research into the production of new and useful metal fine powders that are easy to manufacture in a method of producing metal fine powders from a liquid phase by a reduction method, inorganic metal salts or We have discovered that by mixing a metal colloid with stirring into a bath containing a complex salt and its reducing agent, the above-mentioned drawbacks can be improved and a new and useful metal fine powder with excellent electrical and magnetic properties can be obtained. This led to the present invention.

(Means for Solving the Problems) The present invention is characterized in that, in the production of fine metal powder, a metal colloid is mixed into a bath containing an inorganic metal salt or complex salt and its reducing agent under stirring.

The method for producing fine metal powder according to the present invention will be explained in detail below.

In the present invention, in a bath containing an inorganic metal salt or a complex salt and its reducing agent (hereinafter referred to as a reducing bath), a metal colloid having a metal whose ionization direction is the same or smaller than that of the metal is mixed with stirring, Fine metal powder is obtained by reducing and precipitating the metal.

The above-mentioned inorganic metal salt is not particularly limited,
Although it can be selected as appropriate depending on the purpose of use, generally chloride,
Sulfates etc. are used. Complexing agents that form complex salts include ammonia, ethylenediamine, pyrophosphate, citric acid, and acetic acid.

Various organic acid salts, EDTA, etc. are used.

The reducing agent mentioned above is sodium hypophosphite.

Potassium hypophosphite, sodium hydride.

Hydrogenated potassium boron, hydrazine, formalin.

Examples include dimethylamine borane.

In the above reduction bath, PHa Sessan is added as necessary.

Those commonly used as components of electroless plating baths, such as PH buffers, stabilizers, and improvers, may be used as appropriate.

The metal in the metal colloid must have an ionization tendency that is the same or smaller than that of the metal constituting the metal salt or complex salt in order to perform reduction precipitation.

Furthermore, in order to maintain the metal colloid stably for a long period of time, it is desirable to include a surfactant or a water-soluble polymer. - For example, the production of palladium colloid is described in, for example, Japanese Patent Application Laid-Open No. 61-207666.

In the present invention, in order to produce metal fine powder with excellent electrical and magnetic properties, it is necessary to mix the metal colloids with stirring, and furthermore, stirring in the presence of a magnetic field further improves the electrical and magnetic properties. can be improved.

Furthermore, in the present invention, fine metal powders with different electrical and magnetic properties can be easily produced by selecting metal atoms in inorganic metal salts or complex salts, or by using two or more types in combination, and by changing production conditions. Can be done.

(Function) The metal colloid acts as a catalyst nucleus, and the reduction reaction proceeds quickly, stably and uniformly around the colloid nucleus, so that the precipitated metal can be obtained in the form of a uniform fine powder.

Note that if a metal colloid is not mixed, the reduction reaction will not proceed or the metal will stick to the reactor wall, so that no fine metal powder will be obtained.

The present invention will be described below with reference to Examples, but the present invention is in no way limited by these Examples.

Example 1 Cobal chloride) 0. 05 mol, sodium hypophosphite 0. 2 mol, sodium tartrate 0, 5 mo
1, and 0.5 mol of boric acid, and the pH was adjusted to 9.0 with sodium hydroxide to obtain an aqueous solution with a total volume of 11.

Palladium colloid: 0.5 mmol of palladium chloride was dissolved in 25 ml of an aqueous solution containing 2.5 mmol of sodium chloride, and then diluted to 940 ml with distilled water. While vigorously stirring this aqueous solution, 10 ml of an aqueous solution containing 0.1 g of stearyltrimethylammonium chloride was added, and then 50 ml of an aqueous solution containing 'l, Q mmol of sodium borohydride was added dropwise to form a blackish-brown transparent solution. Palladium colloid was obtained.

When 200 ml of the above cobalt-phosphorus reduction bath (0.01 mol as cobalt atom and 20 ml of the above palladium colloid solution (1 mmol of O, O as palladium atom) dissolved in 2 g of sodium hypophosphite are mixed with vigorous stirring for 20 minutes, the turbidity is reduced. A certain metal fine powder mixture was obtained. After leaving it for a while and making the metal fine powder coagulate R (magnetization treatment) with a strong magnet from outside the vessel wall, the supernatant liquid was discarded by decantation, and the turnip water was poured. The washing operation with acetone and the replacement operation with acetone were repeated.Then, it was dehydrated and
It was dried using a hot air dryer at 0°C to obtain a fine metal powder.

Table 1 shows the properties of the obtained metal fine powder.

Example 2 The same operation as in Example 1 was performed except that stirring using a magnetic stirrer was employed. Table 1 shows the properties of the obtained metal fine powder.

Example 3 In the production of palladium colloid, the same operation as in Example 1 was carried out without using stearyltrimethylammonium chloride (surfactant) and before metal palladium aggregated. Table 1 shows the properties of the obtained metal fine powder.

Example 4 In producing palladium colloid, the same operation as in Example 1 was performed except that 0.1 g of polyvinyl alcohol (molecule 1L 1800) was used instead of stearyltrimethylammonium chloride. Table 1 shows the properties of the obtained metal fine powder.

Example 5 0.05 mol of anhydrous nickel chloride was dissolved in 0.5 mol of ammonia aqueous solution, 800 ml of 0.05 mol of sodium hypophosphite was added, and then P of the solution was removed with concentrated hydrochloric acid.
Adjust the H to 8.9, add distilled water and the total is 17! Closed.

The same operation as in Example 1 was carried out, except that in 200 ml of this nickel-phosphorus reducing bath, 1 mol of O, O (as a nickel atom) was used instead of the cobalt-phosphorus reducing bath.

Table 1 shows the properties of the obtained metal fine powder.

Example 6 In Example 5, palladium colloid liquid IQml (
The same operation as in Example 5 was performed except that the palladium atoms were O, OO5 mmol) and stirring with a magneto stirrer was used. Table 1 shows the properties of the obtained metal fine powder.

Example 7 Nickel chloride 0. 05 mol, sodium hypophosphite 0. 2 mol, sodium tartrate 0.5 mol and boric acid 0.5 mol, the pH was adjusted to 9.0 with sodium hydroxide, and the total volume was 1! An aqueous solution of was obtained.

0.0025 mol as nickel atoms in 50 ml of the above nickel-Liet reducing bath) and 150 ml of the cobalt-phosphorus reducing bath of Example 1 (0.0075 mol as cobalt atoms)
The following operations were carried out in the same manner as in the Examples using two types of reducing baths (1). Table 1 shows the properties of the obtained metal fine powder.

However, the resistance value measured by the tester is determined by placing the tester needles at 7n intervals.
Measurement was made using a contact portion with a length of 5. The magnet used was a special strong magnet provided by Aoyama Special Steel Co., Ltd. (2-9-11 Shinkawa, Chuo-ku, Tokyo).

As is clear from Table 1, the metal fine powders obtained by the method of the present invention are oriented in the presence of a magnetic field and exhibit unique electrical and magnetic properties. From Example 2, it can be seen that the electric and magnetic properties are significantly improved by stirring in the presence of a magnetic field.

From Examples 5 and 6, the electrical properties were further improved by changing the metal of the inorganic metal salt from cobalt to nickel.
It is also seen that fine metal powders with different magnetic properties can be easily obtained by changing the manufacturing conditions.

From Example 7, when two types of metal salts are used together,
A fine metal powder with unique electrical and magnetic properties was obtained. Although not shown in the data, when the fine powders of Examples 1 to 7 were compressed, the tester needles were able to swing even in the absence of a magnetic field.

In addition, it was found that the electrical properties of the fine powder that was not subjected to magnetization treatment (non-magnetized) were extremely unstable. The reason for this is
This is thought to be because the fine powder becomes magnetized within a few hours under the influence of the earth's magnetic field. Also, when measuring the electrical resistance of non-magnetized fine powder with a tester, the needle moves momentarily, but then stops moving. The reason for this is thought to be that a current flows through the fine powder and it becomes magnetized.

Considering the properties of the obtained fine powder and the above-mentioned considerations, it is thought that when magnetic fine powder is magnetized, repulsion occurs between the fine powders and gaps are created. This repulsion is thought to be caused by thermal fluctuations in the spin of atoms within the fine powder (Ninomiya, Nakao, and Yotsuya hypotheses).

According to this hypothesis, it is possible to explain the production of magnetic fluid from magnetic fine powder and the abnormality of the electromagnetic properties in the examples.

If the cobalt-phosphorus fine powder is left in water for a long time, the color will turn black and the tester needle will not touch it even if it is oriented with a magnet or the fine powder is compressed. This seems to be because the surface of the fine powder is oxidized.

(Effects of the Invention) The metal fine powder according to the present invention has unique electrical and magnetic properties that were previously unknown, and by utilizing these excellent properties, it is expected that it will be used in many applications. , 1 In addition, it is extremely easy to manufacture, and by changing the manufacturing conditions, it is easy to obtain fine metal powders with different electrical and magnetic properties, so it has various excellent properties. It is possible to provide a new and extremely useful fine metal powder.

Claims (3)

[Claims] (1) In a bath containing an inorganic metal salt or complex salt and its reducing agent, a metal colloid having a metal with the same or smaller ionization tendency than the metal is mixed with stirring, and the metal is reduced and precipitated into a fine powder. A method for producing fine metal powder, characterized in that it obtains a fine metal powder. (2) The method for producing fine metal powder according to claim 1, characterized in that stirring is performed in the presence of a magnetic field. (3) The method for producing fine metal powder according to claim 1, characterized in that two or more types of inorganic metal salts or complex salts are used.