JPH0723488B2 - Method for producing fine metal powder - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing fine metal powder by applying a wet method,
More specifically, the present invention relates to a method for easily and inexpensively producing a fine metal powder having a fine powder particle size of 1 μm or less and a small variation in particle size.

(Prior Art) In recent years, fine metal powders have been used not only in the field of powder metallurgy but also in the field of electronic materials such as conductive pastes, conductive paints, antistatic materials and electromagnetic wave shielding materials. There is.

Generally, as a method for producing a fine metal powder, (1) a mechanical pulverization method including a ball mill, (2) molten metal is water,
Spraying method using gas or centrifugal force to scatter, (3) Gas evaporation method to agglomerate metal vaporized by heating in vacuum or inert gas, (4) Dust of metal powder by arc or plasma in active hydrogen The hydrogen activated plasma method, (5) electrolysis method, chemical reduction method and the like.

(Problems to be Solved by the Invention) Although the above methods (1) and (2) have been widely used in the field of powder metallurgy, the average particle size of the obtained metal powder is 10 μm or more. It is not suitable for electronic materials because it is large, its particle size distribution is wide, and its shape is not uniform. On the other hand, according to the methods (3) and (4), there is an advantage that a fine metal powder having a particle diameter of 1 μm or less can be easily obtained. However, these methods have the disadvantages that the control of conditions such as temperature and pressure is complicated, and that the device becomes complicated and large and the manufacturing cost increases. Furthermore (5)
Although the method of 1 has the advantage that metal powder can be manufactured at a low cost with a relatively small-scale facility, the width of the particle size distribution of the obtained powder is extremely wide, requiring a mechanical grinding step or sieving as a post-treatment. It had been.

The present invention has been made to solve the above problems,
An object of the present invention is to provide a method for easily and inexpensively producing a fine metal powder having an average particle size of 1 μm or less, a uniform shape, and maintaining the state of primary particles by a wet method, that is, a chemical reduction method. .

(Means for Solving the Problems) In order to achieve the above object, according to the present invention, “a metal ion is separated into an organic phase by adding an organic solvent as an extract to an aqueous solution containing the metal ion and then shaking. And a second extraction step of extracting metal ions into an aqueous phase by adding an aqueous reducing agent solution as an extract to the organic phase containing the metal ions and then shaking the mixture. In this second extraction step, the metal ions are extracted and simultaneously reduced to be precipitated as fine metal powder in the aqueous phase. "

In the production method of the present invention, the metal ion as a starting material is not particularly limited, but for example, chromium (Cr), manganese (Mn), iron (Fe), cobalt (C
o), nickel (Ni), copper (Cu), silver (Ag), gold (A
u), palladium (Pd), platinum (Pt), molybdenum (M
o), tungsten (W), rhenium (Re), ruthenium (Ru), osmium (Os), rhodium (Rh), iridium (Ir), cadmium (Cd), indium (In), antimony (Sb), bismuth (Sb) Ions of metals such as Bi), selenium (Se) and tellurium (Te) can be mentioned as preferable ones. These metals, for example, chloride,
An aqueous solution containing metal ions is prepared by dissolving it in water in the form of sulfate or nitrate.

First, in the first extraction step, metal ions are extracted into the organic phase from the aqueous solution containing the metal ions. The extract used at this time is not particularly limited as long as it is an organic solvent that is sparingly soluble in water, and can extract the metal ions at a high extraction rate, for example, naphthenic acid,
C9-C19 tertiary carboxylic acids and aliphatic series monocarboxylic acids; 1-aminonaphthalene trisulfonic acid,
Sulfonic acids such as dinonylnaphthalene sulfonic acid; Alkyl phosphoric acids such as di-2-ethylhexyl phosphoric acid;
Examples thereof include neutral phosphates such as tributyl phosphate; polymeric amines such as trioctylamine and methyldioctylamine. The carbon 9 to
Preferred examples of the tertiary carboxylic acid of 19 include Versatic Acid 9 to 11 and Versatic Acid 15 to 19 (all are trade names, tertiary carboxylic acid manufactured by Ciel Chemical Co., Ltd.).

These organic substances are diluted before use. The diluent to be used is not particularly limited as long as it dissolves these organic substances and is hardly soluble in water, and examples thereof include kerosene, toluene, benzene, chloroform, cyclohexane, carbon tetrachloride and the like. One of these may be used alone, or two or more of them may be used in combination. The dilution ratio is preferably 5 to 100 times, for example.

The first extraction step is performed by adding the above-mentioned extraction liquid to the above-mentioned aqueous solution containing metal ions and shaking the solution, and the metal ions in the aqueous solution are extracted into the organic phase by this step.

The subsequent second extraction step is a step of so-called back-extracting the metal ions into the aqueous phase from the organic phase in which the metal ions are dissolved as described above. In this step, an aqueous solution of a reducing agent is used as the extraction liquid to extract the metal ions and at the same time reduce the metal ions to deposit them in the aqueous phase as fine metal powder.

Known reducing agents can be used, for example, hydrazine, sodium borohydride, dimethylamine borane, formalin, formic acid, sodium hypophosphite, and hydrogen peroxide are preferable. . These reducing agents may be used alone or in combination of two or more.

In this step, when a reducing agent aqueous solution, that is, a reducing extract is added to the organic phase and shaken, fine bubbles are generated in the liquid, and the particle size of the metal fine powder deposited by the action of the fine bubbles is almost the same. The powder is controlled to be constant and the shape of the powder is close to a sphere. Furthermore, since each of the produced metal fine powders has an extremely thin film of an organic solvent on the surface thereof, the dispersibility in the aqueous phase is good, and the occurrence of secondary aggregation and the like is effectively prevented.

Thus, in order to recover the fine metal powder precipitated in the aqueous phase, first, the liquid is filtered, and then the powder is washed with a solvent that is compatible with the organic solvent, for example, ethanol, methanol, acetone, ether, and the like. It is preferable to remove the organic solvent film on the surface.

(Example) Example 1 34 g of silver nitrate (AgNO ₃ ) was dissolved in 1 of water to prepare an aqueous solution containing 0.2 M of silver ion (Ag ⁺ ). This aqueous solution was placed in a separating funnel, and a solution 1 having a concentration of 0.2 M obtained by diluting naphthenic acid with kerosene was further added as an extract and shaken. Ammonia water was added at the time of shaking to adjust the pH of the liquid to 9 or more, and Ag ⁺ ions were extracted into the organic phase (first extraction step). At this time, the extraction rate was 80% or more. Then, the lower aqueous phase of the separating funnel was removed.
The organic phase was washed with water and then dehydrated with anhydrous sodium sulfate.

Next, 0.005 M sodium borohydride (NaBH ₄ ) aqueous solution 1 was added to this separating funnel as a reducing extract and shaken (second extracting step). After shaking, it was confirmed that the aqueous phase became silver brown at the stage where the liquid was separated into two layers, and silver ions were extracted and reduced at the same time as the aqueous phase. The powder obtained by filtering the obtained aqueous phase was washed with ethanol (powder yield: about 1.3 g). This powder was silver brown, and it was confirmed from the X-ray diffraction pattern that it was a silver crystal. Furthermore, as a result of observing this powder with a scanning electron microscope, it was confirmed that the powder was a very uniform fine powder having an average particle diameter of about 0.2 μm and a substantially spherical shape. The specific surface area of this powder was 6.07 m ² / g (by BET method).

In the second extraction step, the silver-brown powder remaining in the organic phase was filtered, allowed to stand in ethanol for 24 hours, and then ultrasonically washed. As a result, the organic film covering the powder was removed, and uniform fine powder with good dispersibility was obtained as in the above.

Example 2 145 g of nickel nitrate (Ni (NO ₃ ) ₂ .6H ₂ O) was dissolved in 1 water to prepare an aqueous solution containing 0.5 M nickel ion (Ni ²⁺ ). This aqueous solution was placed in a separating funnel, and Versatica cyside 10 was diluted with toluene as a liquid extract, and solution 1 having a concentration of 0.5 M was added and shaken. Ammonia water was added during shaking to adjust the pH of the solution to 9 or more, and Ni ²⁺ ions were extracted into the organic phase (first extraction step). At this time, the extraction rate was 85% or more. Then, the lower aqueous phase of the separating funnel was removed, the organic phase was washed with water, and then dehydrated with anhydrous sodium sulfate (Na ₂ SO ₄ ).

Next, 2 l of a 0.01 M dimethylamineborane ((CH ₃ ) ₂ HN.BH ₃ ) aqueous solution was added to the separating funnel as a reducing extract, and the mixture was shaken (second extracting step). 2 liquid after shaking
It was confirmed that the aqueous phase became black at the stage of separating into layers, and that Ni ²⁺ ions were extracted into the aqueous phase and simultaneously reduced.
The powder obtained by filtering the obtained aqueous phase was washed with ethanol (powder yield: about 20 g). This powder has an average particle size of about 0.2
It was confirmed to be a very uniform fine powder having a size of μm and a substantially spherical shape. The specific surface area was 6.11 m ² / g (by BET method).

(Effect of the Invention) As described above, according to the production method of the present invention, a first extraction step of extracting metal ions into an organic phase from an aqueous solution containing metal ions using an organic solvent as an extraction liquid, and this metal A second extraction step of extracting metal ions into an aqueous phase from an organic phase containing ions using a reducing agent aqueous solution as an extraction liquid;
In this second extraction step, since the metal ions were extracted and simultaneously reduced and deposited in the aqueous phase as fine metal powder, the obtained fine metal powder had an average particle size of 1 μm.
Below, it becomes a nearly spherical and extremely uniform one. Furthermore, the dispersed state is good, and secondary aggregation does not occur. Further, since the equipment and the like are simple, it has an advantage that it can be mass-produced at low cost.

Claims (7)

[Claims] 1. A first extraction step of extracting a metal ion into an organic phase by adding an organic solvent as an extraction liquid to an aqueous solution containing the metal ion and then shaking the organic phase containing the metal ion, The method comprises a second extraction step of extracting metal ions into an aqueous phase by adding an aqueous reducing agent solution as an extraction liquid and then shaking the mixture. In the second extraction step, the metal ions are extracted and simultaneously reduced to give water. A method for producing fine metal powder, which comprises depositing fine metal powder in the phase. 2. The metal ions are chromium, manganese,
Iron, cobalt, nickel, copper, silver, gold, palladium, platinum, molybdenum, tungsten, rhenium, ruthenium, osmium, rhodium, iridium, cadmium,
The method for producing a fine metal powder according to claim 1, wherein the ion is at least one kind of ion selected from the group consisting of indium, antimony, bismuth, selenium, and tellurium. 3. The organic solvent is an organic carboxylic acid, a sulfonic acid, an alkylphosphoric acid, a neutral phosphoric acid ester,
The method for producing fine metal powder according to claim 1, which is obtained by diluting at least one selected from polymeric amines. 4. The metal fine particles according to claim 3, wherein the diluent is at least one selected from kerosene, toluene, benzene, xylene, chloroform, cyclohexane, and carbon tetrachloride. Powder manufacturing method. 5. The reducing agent is at least one selected from the group consisting of hydrazine, sodium borohydride, dimethylamine borane, formalin, formic acid, sodium hypophosphite and hydrogen peroxide. The method for producing fine metal powder according to claim 1. 6. The method for producing fine metal powder according to claim 1, wherein the deposited fine metal powder is washed with a solvent compatible with an organic solvent. 7. The metal fine powder according to claim 6, wherein the solvent compatible with the organic solvent is at least one selected from ethanol, methanol, acetone and ether. Manufacturing method.