JPS589792B2 - Copper coating method on graphite particles - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a composite powder in which a copper coating layer is formed on the surface of graphite particles, and its purpose is to be used for various purposes such as metal graphite brushes, current collectors, brake materials, and building materials. The goal is to provide a method for producing raw material powder that can be used for.

The general method of coating graphite particles with copper by depositing copper on the surface of graphite particles can be summarized as electroless plating.

Graphite belongs to the non-metal category and is difficult to ionize in an aqueous solution, so it cannot directly participate in redox reactions.

Therefore, other substances that perform a reducing action are allowed to coexist in the system consisting of graphite and copper liquid.

This substance usually uses a metal such as iron, zinc, or aluminum, or a liquid reducing agent such as formalin, such as Fehling's solution.

In the conventional copper coating method using a metallic reducing agent, a large amount of reducing agent remains in the resulting powder, and unless an operation to remove the residual reducing agent is added, high purity copper coating graphite powder cannot be obtained, which complicates the manufacturing process. .

In addition, in the method using Fehring's solution, several types of auxiliary reagents are added in addition to copper salts as raw materials, but these auxiliary reagents are often expensive, and copper-coated graphite powder also has the disadvantage of being economically expensive. There is.

In the present invention, by adding copper salt crystals in an amount exceeding the solubility range with respect to the water content in the slurry to a slurry containing a mixture of graphite to be coated with copper and a reducing agent to reduce copper ions, graphite particles In addition to forming a copper coating layer on the surface, it is possible to reduce the rate of reducing agent mixed into the resulting powder, increase the copper coating rate on graphite particles, and adjust the copper content in the copper-coated graphite powder according to the purpose. Furthermore, even though the amount of reducing agent used is reduced compared to conventional methods, the residual copper concentration in the waste liquid can be reduced to ppm units, making waste liquid treatment easier. .

The method of the present invention will be explained in detail below.

The present invention, which relates to a method for coating graphite with copper, adds graphite powder to a certain amount of water, and optionally adds a surfactant that imparts hydrophilicity to the graphite.

Next, a copper ion reducing agent is introduced, and the reducing agent used is a metal whose ionization tendency is less noble than that of copper, such as zinc, iron, or aluminum.

Furthermore, copper salt crystals are added to the graphite reducing agent slurry that has been fluidized by mechanical stirring.

After the reaction is completed, the mixture is sieved, dehydrated, washed with water, and dried by conventional methods to obtain copper-coated graphite powder having the desired copper content.

The type of graphite applicable to the present invention is not particularly limited.

The shape of natural graphite is divided into scale-like, scale-like, and earth-like shapes, and when looking at the production system of artificial graphite, it is classified into coke-based, carbon black-based, pyrolytic graphite-based, organic material-based, etc.
Although graphite has a wide variety of shapes and production routes, each having its own unique characteristics, there is no need to consider any of these in the method according to the present invention.

Further, the particle size of the graphite powder is preferably such that it can flow in water or liquid by stirring.

Furthermore, although the present invention does not require activating the graphite surface by heating or the like as in conventional methods, the graphite must be wetted with water, and when applying a copper coating to graphite, which has poor hydrophilic properties, Organic or inorganic wetting agents may also be added.

As a reducing agent for copper ions, a metal whose ionization tendency is more base than copper is used.

Among the various metals that can be used, zinc, iron, aluminum, etc. are suitable from the viewpoint of economy and availability.

When considering the finish of the coated graphite powder, such as the copper coating rate, the progress of oxidation of the coated copper, and the treatment of manufacturing waste liquid, zinc and iron are most suitable.

These reactions are shown below.

Cu2++Zn=Cu+Zn2+...(1) Cu2+
+Fe=Cu+Fe2+...(2)3Cu2++2A
l=3Cu+2Al3+ (3) In the conventional method, that is, the method of coating graphite particles with copper from a copper salt solution having a concentration within the solubility range, the amount of reducing agent used is 1.1
The reaction rate remains at about 90% when the amount is approximately equivalent, and if the amount of residual copper in the manufacturing waste liquid is to be reduced to the ppm level, the amount of reducing agent used must be increased to 1.3 to 1.5 equivalents. Must be.

However, the large amount of reducing agent used is one of the factors that causes a large amount of reducing agent to remain in the produced powder, and it is necessary to add an operation for removing the residual reducing agent.

However, in the method of introducing copper salt crystals exceeding the solubility range of the present invention, the amount of reducing agent used or the reaction formula is 1.01.
Even though only ~1.06 equivalents are required, the residual copper concentration in the manufacturing waste liquid is reduced to ppm units, the reaction rate is improved, and the rate of unreacted reducing agent mixed into the produced powder is about 0.3% or less. It is possible for the value to decrease.

The reducing agent can be of any external shape, such as square, rectangular, spherical, or even amorphous, and if its size is expressed in terms of surface area, it depends on the type of reducing agent, but it is generally 2 to 2.
Approximately 40 cm2/g is appropriate.

In the case of fine particles with a surface area of 40 cm2/g or more, the copper that is reduced and precipitated will coat the surface of the reducing agent itself instead of the graphite surface, and in the case of large particles with a surface area of 2 cm2/g or less, the reducing agent will not hold well in the solution. It is difficult to obtain a sufficient flow, and the copper precipitates on the surface of the graphite particles segregates. At the same time, copper precipitates on the surface of the reducing agent itself in the same way as when the reducing agent is 40 cm2/g or more. Therefore, the size of the reducing agent should be within the above range. It is desirable to size the particles within

As the copper salt crystal added as a copper source, salts with relatively high solubility, such as copper sulfate and copper chloride, are used.

The solubility of copper sulfate (CuSO4.5H2O) in water is 18.2 g/100 g solution in terms of anhydride at 25°C, and the solubility of copper chloride (CuCl2.2H2O) is 2.
43.6g/100g solution (calculated as anhydride) at 5℃
``Chemical Handbook'' published by Maruzen Co., Ltd. and edited by the Chemical Society of Japan).

The solubility of copper salts varies depending on the temperature of the solution, but the solubility in the present invention is taken based on the temperature of the water in which the copper salts are to be dissolved, and the amount of copper salts added is determined by the temperature of the water in which the copper salts are to be dissolved. The upper limit is determined by the copper content to be coated.

According to the method of the present invention, when copper salts are introduced into the reaction tank, a large amount of undissolved copper salt crystals will flow in the tank, but as the reaction progresses, the crystals will gradually dissolve and eventually It will be completely dissolved and all the copper will be coated with graphite.

In addition, the redox reaction is an exothermic reaction, and as the reaction progresses, the temperature of the solution rises, and depending on the amount of copper salts added, it reaches a boiling state. Dissolution progresses.

Note that the amount of copper salts added to the reaction tank may be sufficient as long as it satisfies the desired copper content of the resulting powder, but care must be taken that the copper salts and reducing agent will be produced through a substitution reaction. It is also necessary to take into account the solubility of salts such as zinc sulfate, iron sulfate or aluminum sulfate.

This is because the salts of these reducing agents are mixed into the produced powder, causing a decrease in the purity of the produced powder.

However, in this case, the generated powder can be removed by washing with water, hot water, or other methods.

In addition, the stirring reaction time is 20 to 60 minutes regardless of the type of reducing agent.
minutes is enough.

The copper-coated graphite thus obtained is made into a product powder through the usual dehydration, water washing, and drying steps.

Example 1 200 g of artificial graphite having the particle size distribution shown in Table 1 and 212 g of flower-like zinc having a surface area of about 3 cm2/g were added to 1.3 liters of tap water at 25°C, so that the graphite did not settle and the graphite did not settle. Stirring to the extent that the flower-shaped zinc flows (in this experimental device, 50°C
0 RPM, peripheral speed 126 m/min).

To this, 809 g of industrial copper sulfate (equivalent to 200 g of copper) was added with the aim of achieving a copper content of 50% in the copper-coated graphite.

The above amount of zinc is 1.0% of the amount required to reduce copper in sulfuric acid steel.
This corresponds to 0.03 equivalents.

After stirring for 40 minutes, the mixture was sieved through a standard sieve (28 mesh), and 24 g remained on the sieve.

The amount of filtrate obtained by suctioning and dehydrating the bottom of the sieve with a Puchner funnel was 1.34 liters, and the amount of residual copper was 0.2 ppm.

The copper coating amount of the copper-coated graphite was 47.53 w·t%, and the zinc content was 0.23 w·t%.

The residue on the standard sieve (28 mesh) consisted of zinc and copper, and the zinc content was 21.16 w·t%.

The particle size distribution of the copper-coated graphite powder produced is as shown in Table 2, and the percentage of copper coating on the graphite particles was 93.4% (934 particles out of 1000 particles) completely coated based on microscopic observation.

E. according to the attached photo. P. M. A. This figure shows the state of copper adhesion to the graphite surface.

Comparative Example 809 g of industrial copper sulfate (similar to Example 1) was added to 4 liters of tap water.
(equivalent to 200 liters of copper) was dissolved.

In this case, the copper sulfate was completely dissolved and no undissolved crystals remained.

Add 200g of artificial graphite and 212g of flower-like zinc to this,
The mixture was stirred at 500 RPM (peripheral speed 126 m/min) for 40 minutes.

After sieving through a standard sieve (28 mesh), the bottom of the sieve was suctioned and dehydrated to obtain a filtrate of 4.05 liters, with a residual copper concentration of 17
．． 99g/l, the copper content in the coated graphite powder under the sieve is 3
It was 8.35 w·t%.

Example 2 50 liters of artificial graphite similar to Table 1 in 4.5 liters of tap water at 25°C
0 g and a surface area of about 10 cm2/g (iron content 98.9%), and stirred to the extent that the graphite does not settle and the iron pieces flow (in this experimental device, at 700 RPM, speed of 176 m/min).

The iron used as the reducing agent was ordinary industrial steel material that did not contain additives such as Cr and Ni.

To this, 2020 g of industrial copper sulfate (equivalent to 500 g of copper) was added to aim for a copper content of 50% in the copper-coated graphite powder.

This amount of iron is 1.0 of the amount required to reduce copper in copper sulfate.
This corresponds to 6 equivalents.

After stirring for 30 minutes, the mixture was sieved through a standard sieve (28 mesh), and 85 g remained on the sieve.

The amount of liquid obtained by suctioning and dehydrating the bottom of the sieve with a Buchner funnel is 4
．． At 8 liters, the residual copper concentration was 1.7 ppm.

The copper content of the copper-coated graphite powder was 46.73 w·t%, and the iron content was 0.25 w·t%.

The iron content of the residue on the sieve was 28.22 w·t%.

Further, the percentage of copper coating on the graphite particles was 90.5% (905 particles out of 1000 particles) that were completely coated.

Example 3 30 artificial graphite similar to Table 1 in 1.5 liters of tap water at 25°C
0g and a surface area of about 40cm2/g (aluminum content 99.2%) 45
g, and stirred to such an extent that the graphite does not settle and the aluminum pieces flow (in this experimental device, the speed was 450 RPM and the circumferential speed was 1).
13m/min).

To this, 1214 g of industrial copper sulfate (equivalent to 300 g of copper) and 20 mg of common salt were added to make the reducing agent active, aiming at a copper content of 50% in the copper-coated graphite powder.

This amount of aluminum corresponds to 1.04 equivalents of the amount required to reduce copper in copper sulfate.

After stirring for 50 minutes, the mixture was sieved through a standard sieve (28 mesh), and 44 g remained on the sieve.

The amount of liquid obtained by suctioning and dehydrating the bottom of the sieve with a Buchner funnel is 1
．． 6l, the residual copper concentration is 4. It was 6 ppm.

The copper content of the copper-coated graphite was 46.13 w·t%, and the aluminum content was 0.17 w·t%.

The aluminum content of the residue on the sieve was 2.57 wt%.

Further, the percentage of copper coating on the graphite particles was 84.5% (845 out of 1000 particles) which were completely coated.

Example 4 Similar to Example 1, an experiment was conducted to produce coated graphite with a copper content of 80% using zinc as a reducing agent.

The procedure was the same as in Example 1 except that 50 g of artificial graphite was used.

At this time, 21 g remained on the standard sieve.

The amount of filtrate was 1.37 liters, and the amount of residual copper was 3.4 ppm.

The copper content of the copper-coated graphite was 78.30 w·t%, and the zinc content was 0.34 w·t%.

The zinc content of the residue on the sieve was 24.76 w·t%, and the percentage of copper coating on the graphite particles was 92.6% (926 particles out of 1000 particles), which was completely coated by microscopic observation.

Claims (1)

[Scope of Claims] 1. In the method of forming a copper coating layer on the surface of graphite particles, in order to reduce the graphite to be coated and copper ions, a metal whose ionization tendency is more base than copper and whose surface area is 2 to 40 cm is used.
m2/g of reducing agent is added to the slurry in an amount exceeding the solubility relative to the water content in the slurry, and the content of the reducing agent is equal to the amount of copper in the added copper salt crystals. 1. A method of coating copper on graphite particles, characterized in that the amount is 1.01 to 1.06 equivalents to that of graphite particles. 2. The method for coating graphite particles with copper according to claim 1, wherein when adding the steel salt crystals, stirring is performed to an extent that the graphite in the slurry does not settle and the reducing agent flows.