JPH0348244B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to the production of fine metal powder, and more specifically, the present invention relates to the production of a novel and useful fine metal powder, in which a metal colloid is mixed in a bath containing a metal complex salt and its reducing agent, and the metal is reduced and precipitated. Regarding manufacturing. The main uses of the metal fine powder according to the present invention are magnetic fluids, magnetic recording materials, electromagnetic shielding materials, anisotropic or pressurized conductive rubbers, plastic magnets, conductive paints, adhesives, and the like. (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 No.
48, 1985 Ultrafine Particles - Science and Applications p. 24). However, the precipitation method has drawbacks such as the precipitate is generally gel-like and difficult to wash with water and filter, and the precipitant is mixed in as an impurity. In addition, silver, gold, and
Colloids of precious metals such as platinum and palladium are produced by reduction methods, but in this case as well, it is difficult to separate them from water, they solidify during drying, and it is difficult to remove impurities. A method in which a metal colloid containing the same metal as the precipitated metal is used as a core is known in the case of gold (Japanese Patent Publication No. 57-61088).
However, in the case of precipitation of metal ions such as nickel and cobalt, which have a relatively strong ionization tendency, it is difficult for colloids of the same metal to exist stably in an aqueous system. Furthermore, methods using palladium cations (Japanese Unexamined Patent Publication No. 133796/1982) and palladium chloride solution (Japanese Patent Publication No. 29239/1983) as catalysts in the reduction-deposition reaction are also known; The possible palladium cations, or the palladium metal precipitated therefrom, do not act as nuclei, but rather constitute a component of the alloy. Furthermore, in Japanese Patent Publication No. 41-4567, metallic nickel powder is used as a core in the examples, but this metallic powder is not necessarily required in principle, and in order to precipitate metallic nickel fine powder, Even finer nickel metal powder is required as the core, but it is difficult to obtain such fine nickel metal powder. It should be noted that the production of metal powder 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 manufacturing metal fine powders from a liquid phase by a reduction method, metal complex salts and their By mixing a metal colloid with stirring in a bath containing a reducing agent, the above-mentioned drawbacks can be improved and a new useful metal fine powder with metal colloid as a core and having excellent electrical and magnetic properties can be obtained. This discovery 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 a metal complex salt and its reducing agent under stirring. The method for producing fine metal powder according to the present invention will be described in detail below. In the present invention, a metal colloid having a metal different from the metal and having the same or smaller ionization tendency than the metal is mixed in a bath containing a metal complex salt and its reducing agent (hereinafter referred to as a reduction bath) with stirring. , the metal is reduced and precipitated to obtain a fine metal powder. The above-mentioned metal complex salts are not particularly limited and are appropriately selected depending on the purpose of use, but are generally formed using inorganic metal salts such as chlorides and sulfates of iron, cobalt, and nickel, and complexing agents. be done,
As the complexing agent for forming a complex salt, ammonia, ethylenediamine, pyrophosphate, citric acid, acetic acid, various organic acid salts, EDTA, etc. are used. The above reducing agent includes sodium hypophosphite,
Potassium hypophosphite, sodium boron hydroxide,
Examples include potassium borohydride, hydrazine, formalin, and dimethylamine borane. In the above reduction bath, a PH regulator, PH
Buffers, stabilizers, modifiers, and other commonly used components of electroless plating baths 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 complex 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. As an example, regarding the production of palladium colloid, for example,
It is described in Publication No. 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, according to the present invention, metal fine powders with different electrical and magnetic properties can be easily produced by selecting metal atoms in the metal complex salt, or by using two or more types in combination, and by changing the production conditions. . (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, making it impossible to obtain metal fine powder. 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 Production of cobalt-phosphorus reduction bath (alkali sodium hydroxide) 0.05 mol of cobalt chloride, sodium hypophosphite
Contains 0.2 mol, sodium tartrate 0.5 mol, and boric acid 0.5 mol, pH adjusted with sodium hydroxide.
9.0 to obtain an aqueous solution with a total volume of 1. Manufacture of palladium colloid 0.5 mmol of palladium chloride and 2.5 mmol of sodium chloride
It was dissolved in 25 ml of an aqueous solution containing mmol 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, followed by 50 ml of an aqueous solution containing 2.0 mmol of sodium borohydride.
was added dropwise to obtain a blackish brown transparent palladium colloid. 200ml of the above cobalt-phosphorus reduction bath (0.01mol as cobalt atom, 2g of sodium hypophosphite)
When 20 ml of the above palladium colloid solution (0.01 mmol as palladium atoms) was mixed with vigorous stirring for 20 minutes, a cloudy metal fine powder mixture was obtained. After leaving it for a while and coagulating and precipitating the fine metal powder (magnetization treatment) using a strong magnet from outside the vessel wall, discard the supernatant liquid by decantation.
The washing operation with distilled water and the replacement operation with acetone were repeated. The mixture was then dehydrated and dried in a hot air dryer at 100°C to obtain 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 carried out except that 0.1 g of polyvinyl alcohol (molecular weight 1800) was used instead of stearyltrimethylammonium chloride. Table 1 shows the properties of the obtained metal fine powder. Example 5 Production of nickel-phosphorus reduction bath (alkali ammonium hydroxide) 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 the solution was diluted with concentrated hydrochloric acid. PH
Adjust to 8.9 and add distilled water to bring the total volume to 1. The same operation as in Example 1 was carried out, except that 200 ml of this nickel-phosphorus reducing bath (0.01 mol in terms of nickel atoms) was used instead of the cobalt-phosphorous reducing bath. Table 1 shows the properties of the obtained metal fine powder. Example 6 In Example 5, the palladium colloid liquid was
ml (0.005 mmol as palladium atom),
The same operation as in Example 5 was performed except that stirring using a magnetic stirrer was employed. Table 1 shows the properties of the obtained metal fine powder. Example 7 Production of nickel-phosphorus reduction bath (sodium hydroxide alkali) Nickel chloride 0.05 mol, sodium hypophosphite
0.2mol, sodium tartrate 0.5mol and boric acid
Contains 0.5mol, pH 9.0 with sodium hydroxide
An aqueous solution having a total volume of 1 was obtained. 50 ml of the above nickel-phosphorus reducing bath (0.0025 mol as a nickel atom) and 150 ml of the cobalt-phosphorus reducing bath of Example 1 (0.0075 mol as a cobalt atom)
The following operations were carried out in the same manner as in the Examples using two types of reducing baths. Table 1 shows the properties of the obtained metal fine powder. Example 8 Production of silver colloid While vigorously stirring a solution of 0.5 mmol of silver nitrate () dissolved in 940 ml of distilled water, an aqueous solution 10 containing 0.1 g of stearyltrimethylammonium chloride was added.
ml and 50 ml of an aqueous solution containing 2.0 mmol of sodium borohydride were sequentially added, the color of the solution suddenly changed to yellowish brown, and a homogeneous transparent silver colloid with a pH of 9.6 was obtained. In Example 1, 20 ml of palladium colloid solution
The same operation was carried out except that 20 ml of the above silver colloid solution was used instead. Table 1 shows the properties of the obtained metal fine powder.

[Table] 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 all exhibit unique electric 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. Examples 5 and 6 show that by changing the metal of the metal complex salt from cobalt to nickel, the electrical properties are further improved, and by changing the manufacturing conditions, fine metal powders with different magnetic properties can be easily obtained. . From Example 7, fine metal powder having unique electrical and magnetic properties was also obtained when two types of metal complex salts were used together. Although not shown in the data,
When the fine powders of Examples 1 to 7 were compressed, the needles of the tester 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 thought to be that the fine powder becomes magnetized within a few hours under the influence of earth's magnetism. 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 (Nikan, 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 not known in the past, and by utilizing these excellent properties, it is expected to be applied to many uses. 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. It is possible to provide extremely useful fine metal powders.

Claims (1)

[Scope of Claims] 1. A metal colloid having a metal different from the metal and having the same or smaller ionization tendency than the metal is mixed in a bath containing a metal complex salt and its reducing agent with stirring, A method for producing fine metal powder, the method comprising obtaining a fine powder by reducing and precipitating the metal. 2. The method for producing fine metal powder according to claim 1, wherein the 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 metal complex salts are used.