JPH01162701A - Method for refining copper super fine powder - Google Patents

Abstract

PURPOSE:To remove chrolide as contained impurity without sintering super fine powdery Cu by heating the super fine powdery Cu obtd. by hydrogen- reducing CuCl vapor in gas phase at the specific temp. in the vacuum. CONSTITUTION:In the super fine powdery Cu obtd. by gas-phase-reducing the CuC vapor in the hydrogen, the non-reducing CuCl remains and also O2 is contained at 0.5-5wt.% ratio. After packing, this impurity-contained super fine powdery Cu into a board 3 in a vacuum vessel 1, while vacuum-exhausting the inner part of the vessel 1 with a pump 6 providing a dust filter 4 and condensed part 5, it is heated with an electric furnace at outside of the vessel 1. As condition of treatment in this case, the inner part of the vacuum vessel 1 is made to vacuum at less than 10 torr under inert gas atmosphere of Ar, etc., and the heating temp. is made to temp. range of 350-500 deg.C. The contained Cl is removed without sintering the super fine powdery Cu and the high purity Cu fine powder is manufactured at low cost.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention is a method for removing chlorides contained as impurities from ultrafine copper powder produced by hydrogen reduction of cuprous chloride vapor in the gas phase. The present invention relates to a purification method.

(Prior Art) A method of purifying ultrafine metal powder by reducing metal halide vapor with hydrogen in the gas phase has high productivity, and the obtained ultrafine powder has excellent powder properties. However, this method has the disadvantage that contamination with chloride-based impurities cannot be avoided. Therefore, a wide range of methods have been attempted to reduce the chlorine content in ultrafine metal powder. H, Lampre et al.
y and R,L.

Riplay, Journal of Electr
chemical soc,,dan.

109 (1962)) reduced the chlorine content from 0.24% by weight to 0.04% by weight by heating ultrafine tungsten powder produced by hydrogen reduction of tungsten chloride at 800°C for 24 hours in a dry hydrogen atmosphere. I was able to reduce it. At this time, the specific surface area is 12 m/g to 6
．． It decreased to 49m/g. Although this method can reduce the chlorine content by heating in a hydrogen atmosphere, it also has the problem that the ultrafine powder is sintered and the powder particles also grow.

Also, JP-A-60-174807 and JP-A-61-
No. 48506 discloses a method of vacuum drying after solvent washing (with water and an acidic solvent, respectively) at room temperature in order to dechlorinate ultrafine powder while preventing oxidation and sintering. In terms of reducing the amount of unreacted halides,
This is insufficient because the X-ray peak of the by-product disappears.

Furthermore, Japanese Patent Publication No. 60-67603 describes a method in which ultrafine metal powder is washed with water to remove adhering halides, and then slowly oxidized with a gas containing a controlled amount of oxygen. The chlorine content of the fine powder is 2.43
% to 30 ppm or less, but the process was as follows: ■ Stirring sedimentation (
Pure water 317 times x lO times), ■ Moisture extraction (acetone 1.S
M! It consists of the following steps: vacuum drying, and slow oxidation (introducing air in stages in a vacuum), which uses a large amount of solvent and strictly controls oxidation during drying. There is a need to.

(Problems to be Solved by the Invention) As described above, a method for removing chloride-based impurities from ultrafine metal or ceramic powder produced by reacting metal chloride vapor with a reducing gas such as hydrogen or ammonia. Conventionally, dry methods using heating in a reducing atmosphere and wet methods using solvent washing have been attempted.
The former has the problem of sintering and coarsening of ultra-fine powder, while the latter has the problem of cost increase due to the use of a large amount of solvent and the complexity of the process.

Therefore, the present invention proposes a method using a -stage dry heating, which is more cost-effective than a wet method, for removing chloride-based impurities from copper superstarch, and which has been a problem in the past. The aim is to solve the problem of sintering and coarsening of ultrafine powder due to heating.

(Means for Solving the Problems) The method for refining ultrafine copper powder of the present invention is produced by reducing cuprous chloride vapor with hydrogen in the gas phase, contains chloride as an impurity, and has a total oxygen content of Ultrafine copper powder in the range of 0.5 to 5% by weight was heated at 350°C in a vacuum of 10 Torr or less.
It is characterized in that the chloride is removed while suppressing sintering of the ultrafine copper powder by heat treatment at a temperature below 500°C.

In the conventional dry method, in order to remove chloride-based impurities by reduction, the surface oxide film of the ultrafine powder itself was also reduced at the same time, so sintering and coarse graining due to activation of the powder surface were inevitable. .

The present inventors focused on the fact that metal chlorides generally have a high vapor pressure as a method for removing chloride-based impurities other than reduction, and investigated a method for removing them by evaporation and exhaust. As a result, it was discovered that the generated chloride vapor could be quickly removed by increasing its vapor pressure through heating and simultaneously keeping the heating system in a vacuum.

More importantly, we have found that it is effective to oxidize the surface to some extent in order to prevent the ultrafine particles from becoming coarse due to sintering during heating.

An example of the apparatus used in the present invention is the apparatus shown in FIG. In the figure, vacuum vessel l is electric furnace 2
The ultrafine copper powder filled in a sample loading boat 3 provided in a vacuum container 1 is heated and held while being evacuated by a pump 6 equipped with a dust filter 4 and an agglomerating section 5. To purge the container and create an inert atmosphere before and after heating, the main valve 7 connected to the pump is closed, and argon gas is introduced using the argon gas leak valve 8, the introduction valve 9, and the flow meter 10. A vacuum gauge 11 monitors the degree of vacuum inside the container. The thermocouple 12 is used to control the electric furnace 20 heating element.

13 is a pump leak valve.

Next, the conditions for purification treatment (degree of vacuum, heating temperature, time) will be described. The inventors have confirmed, using means such as X-ray analysis, that the main form of chloride-based impurities in ultrafine copper powder obtained by hydrogen reduction of cuprous chloride is CuC1. C
The vapor pressure of uCl is log P CuCL-EH56/T + 11.2, according to Physical Properties Constant I, edited by the Society of Chemical Engineers.
35, for example, about 1 between 200°C and 500°C.
Increases from O-bTorr to 4.8Torr. By creating a reduced pressure state close to the vapor pressure at each heating and holding temperature, the partial pressure of CuC1 in the exhaust gas can be increased. It is not easy to obtain a high vacuum in a heated state. Further, in order to increase the vapor pressure of CuCl and increase the evaporation rate, treatment at high temperature is desired, but at high temperature, sintering of ultrafine powder and coarsening proceed.

Therefore, the relationship between the degree of vacuum and the heating temperature is important.

Chlorine content obtained by hydrogen reduction of cuprous chloride 1.4
6% by weight, oxygen content 1.6% by weight, about I
Heat treatment temperature, post-treatment chlorine content, and specific surface area change rate (post-treatment specific surface area SA/treatment front surface area) after heating and holding treatment for 240 minutes in a Torr vacuum
Figure 2 shows the relationship between

In the figure, almost no sintering of the ultrafine powder is seen in the treatment at 200°C, but the chlorine content after treatment is large. 200
PCuCL at °C is 9.8 X 10-'Torr
This is because when processing is performed at the ultimate vacuum degree of I Torr during heating, the CuC1 partial pressure is small, and chlorides cannot be sufficiently removed by heating for 240 minutes. At 500°C, the chlorine content after treatment is small, but sintering of the ultrafine powder progresses, and the specific surface area after treatment is about 50% of that before treatment.

The sintering of ultrafine powder is more pronounced at high temperatures, but at the same temperature, the lower the oxygen content in ultrafine powder, the more sintering progresses. Figure 3 summarizes the rate of change in specific surface area after the body fine powders with various oxygen contents obtained by the above method were held at 450° C. for 240 minutes in a vacuum of about I Torr.

From the above experimental results, when heating and holding is performed in a vacuum with a pressure of 10 Torr or less, it is possible to remove CuCl by evaporation by heating to 350°C or more and less than 500°C and increasing the CuCl vapor pressure. If the total oxygen content of the fine powder is 0.5 to 5% by weight, sintering can be relatively suppressed.

Hereinafter, the present invention will be explained in more detail with reference to Examples.

(Example) Example 1 Fine body powder produced by gas-phase hydrogen reduction of cuprous chloride (
The chlorine content was reduced from 1.46 wt.% to below 0.01 wt.% by holding 3 g (oxygen content 1.6 wt.%) at 450° C. for 240 minutes in a vacuum of about I Torr. At this time, the specific surface area of the powder after treatment was 5.2 N/g, which was almost unchanged from 5.:M/g before heating.

Example 2 3 g of body fine powder (oxygen content 1.8% by weight) produced by the same method as above was heated to 450°C in a vacuum of about 5 Torr for 6 hours.
By holding for 0 minutes, the chlorine content was reduced from 1.49% by weight to 0.08% by weight. At this time, the specific surface area is 5
．． It only decreased from 5%/g to 5.1 m/g.

Example 3 Body fine powder produced by the same method as above (oxygen content 4% by weight)
) 3g was heated to 400℃ for 24 hours in a vacuum of 2 Torr or less.
By holding for 0 minutes, the chlorine content was reduced from 2.9% by weight to 0.05% by weight, and at this time, there was almost no change in the specific surface area.

Example 4 About 7 To
The chlorine content was reduced from 6.0% by weight to 0.02% by weight by holding it at 480°C for 120 minutes in a vacuum of RR, and the specific surface area after treatment was 2.56 m2/g.

Comparative Example 1 5 g of body fine powder (oxygen content: 4.4% by weight) produced by hydrogen reduction of cuprous chloride was held at 530° C. for 240 minutes in a vacuum of about I Torr, resulting in a specific surface area of 3. It decreased significantly from .58 m”/g to 0.43 m2/g.

Comparative Example 2 A fine body powder (oxygen content: 1.8% by weight, chlorine content: 1.5% by weight) produced by the same method as above was held at 300° C. for 240 minutes in a vacuum of about 3 Torr. Although there was almost no change in the specific surface area, the chlorine content remained at 0.5% by weight after treatment.

(Effects of the Invention) Sintering and coarsening can be suppressed by heat-treating the body fine powder produced by gas-phase hydrogen reduction of copper chloride in a vacuum at a constant temperature using the method according to the present invention. It has become possible to purify it easily and at low cost.

This makes it possible to obtain high-purity body part fine powder with a low chlorine content.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing a heating device accompanied by vacuum evacuation for heating the body part fine powder in a vacuum and evaporating and discharging chloride as an impurity. FIG. 2 shows the method according to the present invention in which the body powder produced by gas-phase hydrogen reduction of cuprous chloride vapor was heated from 200°C to 530°C.
The effect of treatment temperature on the chlorine content after treatment and specific surface area change rate (specific surface area after treatment SA/treatment front surface area) when purified for dechlorination by holding at each temperature up to ℃ for 240 minutes. This is a graph showing the influence of FIG. 3 is a graph showing the influence of oxygen content on the rate of change in specific surface area when body fine powders with various oxygen contents obtained by the above method were each held at 450°C for 240 minutes. . 1...Vacuum container 2...Electric furnace 3...Sample loading boat 4...Filter 5...Agglomeration section
6... Pump 7... Main valve
8... Ar gas leak valve 9... Ar gas introduction valve IO... Ar gas introduction flow meter 11... Vacuum gauge 12... Thermocouple 13.
・・Pump leak valve

Claims (1)

[Claims] Contains chloride as an impurity and has a total oxygen content of 0.5-5
The method is characterized in that the chloride is removed while suppressing sintering of the ultrafine copper powder by heat-treating the ultrafine copper powder in the range of % by weight to 350°C or more and less than 500°C in a vacuum of 10 Torr or less. A method for refining ultrafine copper powder.