JP3131075B2 - Purification method of ultrafine metal powder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrafine metal powder or a metal fine powder obtained by reducing a metal halide vapor in the gas phase (hereinafter, these are collectively referred to as ultrafine metal powder). And the removal of halogen.

[0002]

2. Description of the Related Art Halide remaining in ultrafine metal powder obtained by gas phase reduction of metal halide inhibits the rust resistance of ultrafine metal powder, and when metal ultrafine powder is used for conductive paste, for example. There are problems such as migration, and it is necessary to remove them.

[0003] Japanese Patent Application Laid-Open No. 60-67603 discloses a technique in which ultrafine metal powder obtained by a gas phase reduction method of a metal halide is washed with water to remove an attached halide. This technique requires a long processing time and is not applicable to halides that are not soluble in water. In addition, JP
JP-A-174807 also discloses a technique for washing ultrafine powders of metal and metal nitride obtained by gas-phase reduction of metal halides with water to remove unreacted halides and by-products. This technique also requires a long time for the treatment, and furthermore, it is reported that the peak of the X-ray has disappeared, but the concentration value is not described, but it is estimated to be about 0.1% or less.

Japanese Patent Application Laid-Open No. 61-48506 discloses that
A method is disclosed in which a metal obtained by gas phase reduction of a metal halide and a method of washing with a metal that dissolves a halide and a by-product in metal nitride fine particles are used. However, even in this method, there is a problem that the removal of impurities is such that the peak of X-rays disappears, and a long time is required for a thin acid, and a metal or a metal nitride powder itself is dissolved for a strong acid.

[0005] Japanese Patent Application Laid-Open No. 1-319610 discloses a technique for cleaning ultrafine metal powder obtained by gas phase reduction of a metal halide using aqueous ammonia. This technique is an improvement over the above-mentioned disadvantages of the conventional technique, and has a feature that the washing time is short, the technique can be applied to a halide that does not dissolve in water, and there is no dissolution loss of the metal itself due to washing.

[0006]

SUMMARY OF THE INVENTION The present invention relates to the removal of unreacted halide in ultrafine metal powder obtained by reducing the vapor of a metal halide in the gas phase.
It is an object of the present invention to provide a technique which is different from the technique of Japanese Patent Application Laid-Open No. 9610, and which has the same or better effects. That is, an efficient metal ultrafine powder purification method that requires a relatively short washing time, can be applied to a halide insoluble in water, and has almost no dissolution loss due to oxidation of the metal powder itself. It is a suggestion.

[0007]

SUMMARY OF THE INVENTION The present invention provides a method for producing a metal ultrafine powder obtained by reducing the vapor of a metal halide in the gas phase, using tartaric acid,
A method for purifying ultrafine metal powder, comprising washing with an aqueous solution of a chelating agent such as citric acid or EDTA to remove residual halide. In this case, it is preferable that the concentration of the chelating agent aqueous solution be 0.02 to 0.2 wt%. Further, by performing the cleaning in a non-oxidizing atmosphere, dissolution loss due to oxidation of the ultrafine metal powder itself can be reduced.

[0008] Generally, ultrafine metal powder and fine powder are distinguished by the particle size, but the ultrafine metal powder of the present invention includes general fine metal powder in its range.

[0009]

The metal ultrafine powder to which the method of the present invention can be applied includes Au, obtained by gas phase reduction of a metal halide,
Ag, Cu, Ni, Co, Fe, Mn, Cd, Cr, T
i, Pt, Pd, Ce, Al, Ca, Bi and the like. The halides of these metals form water-soluble chelates in aqueous chelating agents. Therefore, when the metal ultrafine powder obtained by vapor-phase reduction of the metal halide vapor is washed with an aqueous solution of a chelating agent, the metal halide in the metal ultrafine powder forms a water-soluble chelate, which is separated from the metal powder. Then, a purified metal powder can be easily obtained.

FIG. 1 shows a flow chart of the method for purifying ultrafine metal powder of the present invention. A chelating agent aqueous solution 2 is added to the untreated ultrafine metal powder 1. The aqueous solution of the chelating agent is preferably one from which dissolved oxygen has been sufficiently removed. Next, in the stirring and washing step 3, stirring and washing are performed for 1 to 20 minutes. As a cleaning method, ultrasonic or mechanical stirring is used, and the cleaning time is 10 minutes.
It is sufficient that the number of times of washing is about 1 minute or 2 times. Although washing may be performed more than twice, there is almost no necessity from the viewpoint of economy and the amount of residual halogen. When the stirring and cleaning treatments are performed in a non-oxidizing atmosphere, dissolution loss during cleaning can be reduced for Cu, Fe, Ni, and the like. However, A
With respect to precious metals such as g, Au, Pt, and Pd, removal of residual halide can be achieved without dissolution loss even in a non-oxidizing atmosphere. Examples of the non-oxidizing atmosphere include an inert gas such as Ar, He, and N ₂ , H ₂ , C
A reducing gas such as H _4, a non-oxidizing gas atmosphere such as a combustion exhaust gas, or a vacuum atmosphere can be used.

After the washing, in a filtration step 4, the purified powder and the water-soluble chelate (filtrate 5) are separated in a non-oxidizing gas by suction filtration or the like. The filtered purified metal powder 7 is dried in a non-oxidizing atmosphere in a drying step 6 and then stored in a non-oxidizing gas or vacuum.

[0012]

【Example】

Example 1 Purification of ultrafine copper powder (average particle size: 0.2 μm) obtained by gas-phase hydrogen reduction of copper chloride was performed according to the flow of FIG. 1. 0.02wt% to 10g of unrefined powder in air
100 cc of an EDTA aqueous solution was added, and stirring and washing were performed twice for 10 minutes by ultrasonic washing. After stirring and washing, suction filtration and drying in a vacuum are performed, so that the chlorine content is 2.
It decreased from 5% to 0.01%. The oxygen content is 0.1
2% became 6%. The dissolution of the copper powder itself in the aqueous chelating agent solution was 14%.

Example 2 In purifying the same ultrafine copper powder as used in Example 1, a 0.02 wt% aqueous solution of EDTA with 10 g of unpurified powder removed of dissolved oxygen in an N ₂ gas atmosphere. 100
Stirring and washing with ultrasonic waves at cc were performed twice at 10 minutes / time. The chlorine content was reduced from 2.5% to 10 ppm or less, and the oxygen content was reduced from 0.2% to 0.3%. No elution of the copper powder itself was observed.

Example 3 In the purification of the same copper ultrafine powder as used in Example 1, 100 cc of a 0.05 wt% tartaric acid aqueous solution obtained by removing dissolved oxygen from 10 g of unpurified powder in an N ₂ gas atmosphere was used. Stirring and washing with ultrasonic waves were performed twice at 10 minutes / time. The chlorine content was reduced from 2.5% to 10 ppm or less, and no elution of the copper powder itself was observed.

Example 4 In the purification of ultrafine nickel powder (average particle diameter 0.4 μm) obtained by hydrogen reduction of nickel chloride, 0.1% of dissolved pure oxygen was removed from 10 g of unpurified powder in an Ar atmosphere. 100 ml of tartaric acid aqueous solution, ultrasonic stirring and washing 10
Treated twice per minute. Chlorine content from 1.2% to 10%
ppm, the oxygen content is reduced from 0.2 % to 0.2 %
And did not change. Elution of the nickel powder itself was not observed.

Comparative Example 1 The same ultrafine copper powder as used in Example 1 was washed with water. 100 g of pure water from which dissolved oxygen has been removed per 1 g of unpurified powder
cc was added, and the mixture was stirred and washed 30 minutes / times × 5 times by ultrasonic cleaning in an Ar atmosphere, suction-filtered, and then vacuum-dried. The chlorine content dropped only from 2.5% to 0.7%.

Comparative Example 2 The same copper ultrafine powder as used in Example 1 was washed with hydrochloric acid. To 2.5 g of the unpurified powder, 100 cc of 2N hydrochloric acid from which dissolved oxygen had been removed was added, ultrasonic cleaning was performed for 40 minutes, followed by washing with 500 cc of pure water, suction filtration, and vacuum drying. In this way, the chlorine content dropped only from 2.5% to 0.4%.

[0018]

According to the present invention, unreacted halide in ultrafine metal powder produced by gas phase reduction of metal halide can be efficiently removed in a short time to an extremely low concentration. In addition, metal oxidation and elution can be suppressed to a minimum.

[Brief description of the drawings]

FIG. 1 is a flowchart showing a cleaning step of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ultrafine metal powder 2 Chelating agent aqueous solution 3 Stirring and washing process 4 Filtration process 5 Filtrate 6 Drying process 7 Purified metal powder

──────────────────────────────────────────────────の Continuing from the front page (72) Inventor Hiroyuki Ishikawa 1 Kawasaki-cho, Chuo-ku, Chiba Kawasaki Steel Corp. Technical Research Division (58) Fields investigated (Int. Cl. ⁷ , DB name) B22F 9 / 28

Claims (2)

(57) [Claims] 1. A method for purifying an ultrafine metal powder, comprising washing an ultrafine metal powder obtained by vapor-phase reduction of a metal halide vapor with an aqueous solution of a chelating agent to remove residual halide. 2. The method for purifying ultrafine metal powder according to claim 1, wherein the cleaning is performed in a non-oxidizing atmosphere.