JPS59104404A - Preparation of copper powder by hydrogen reduction - Google Patents

Abstract

PURPOSE:To obtain a fine and uniform hardly oxidized crystalline copper powder with high purity, by a method wherein bismuth is added to an aqueous copper sulfate solution in a specific amount or more and hydrogen gas is introduced into said solution under pressure to perform reduction reaction. CONSTITUTION:An aqueous copper sulfate solution is subjected to hydrogen reduction to prepare a copper powder. The copper concn. in the aqueous copper sulfate solution is set to 10-90g/l (especially 20-40g/l) and 0.05g/l or more (expecially 0.05-1g/l) of bismuth is added to said solution. Bismuth is pref. added in the form of bismuth sulfate. Hydrogen gas is introduced into the resulting solution under pressure to perform reduction reaction to form a crystalline fine copper powder. The reaction temp. at this time is 120-250 deg.C and hydrogen partial pressure is 3-200kg/cm<2>.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for producing fine copper powder by reducing an aqueous copper sulfate solution with hydrogen.

Conventional technology Conventionally, methods for producing copper powder include molten metal spraying, mechanical crushing,
Electrolytic methods are known as typical methods, and hydrogen reduction methods have also been proposed in recent years.

In the molten metal atomization method, a trickle of molten copper metal flows out from a water hole, and a compressed gas or a water jet is applied to the molten metal copper to make it into a spray state and disperse it finely.At the same time, it is cooled and solidified to form copper. This method consists of obtaining powder, but in this method, the force applied to make the molten copper into a spray state and disperse it finely is short, so the resulting copper powder is said to be less likely to become fine powder. There are drawbacks.

In addition, the mechanical pulverization method consists of pulverizing deposited copper by electrolytic method or metallic copper obtained by gas reduction method using a ball mill, vibration mill, etc., and the operation is relatively hourly and the cost of pulverization is low. Although it has the advantage of having a low floor, it is easy for impurities caused by wear of the crusher to get mixed into the crushed metal copper during crushing, and in addition, it is easy to cause oxidation during crushing, so the resulting copper powder It has the disadvantage that a decrease in purity is unavoidable.

Next, the electrolytic method consists of collecting the copper powder deposited on the multi-cathode by copper electrolysis, washing it, dehydrating it, vacuum drying it, and then sieving it.

However, the copper powder obtained by this method tends to have a high oxygen content, and in addition, there is a problem that the electrolyte remains in the gaps between the copper powder particles, causing changes in the copper powder over time. It will be done.

In addition, in the method of producing copper powder by reducing a copper-containing aqueous solution such as a copper sulfate aqueous solution with a reducing gas such as hydrogen, although the purity of the copper powder obtained is relatively high, There are problems in that the deposited copper particles aggregate with each other and tend to adhere to the inner wall of the reactor for reduction.

Furthermore, since fine copper powder generally has a large specific surface area and is in an active state, it is very easily oxidized, so it is important to take measures to prevent oxidation in the production of copper powder.

Purpose of the Invention The present invention was made in view of the above-mentioned current situation in the production of copper powder. The object of the present invention is to provide a method that can be advantageously produced by a reduction method.

The present invention will be explained in detail below.

Structure of the Invention The structural feature of the invention is that bismuth is added to an aqueous solution of copper sulfate.
．． By adding 0.05 gA or more and introducing hydrogen gas under pressure to carry out the reduction reaction, it is possible to produce crystalline fine copper powder.

That is, in the present invention, when producing copper powder by reducing an aqueous copper sulfate solution with hydrogen, if bismuth is added to the aqueous solution, crystalline copper particles are generated.

Furthermore, this method is based on the knowledge that fine copper powder with high purity and consisting of uniform particles with little mutual aggregation of particles can be obtained. Incidentally, such a function of bismuth is thought to be due to the fact that bismuth acts as a catalyst during copper nucleation and nucleus growth from an aqueous copper sulfate solution.

Bismuth added to the copper sulfate aqueous solution in the present invention is preferably used in the form of a bismuth compound, and the valence of bismuth in the bismuth compound may be either trivalent or pentavalent, and the form of the compound may be a salt form, etc. It may be arbitrary, but
If anions other than sulfuric acid are not added to the system, they may be added in the form of bismuth sulfate, for example. The amount of bismuth added to the above aqueous solution needs to be 0.051/l as bismuth, and the above-mentioned effect is observed from around this addition amount, and as the addition concentration increases, the above-mentioned The effect will also be greater. However, if the concentration of bismuth in the above aqueous solution exceeds 1.0 Fl/l, white bismuth salt precipitates will be mixed into the produced copper powder, so in reality, the concentration of bismuth added should be 0.0 Fl/l. 05-1. O
It is preferable to use Fl/l.

The copper concentration in the copper sulfate aqueous solution used in the present invention is 10 to 90
g/mu, preferably 20 to 40 f//l, and as the copper concentration increases, the effect of adding bismuth decreases, and the crystallinity of copper particles precipitated by reduction is lost. At the same time, it should be noted that copper particles tend to agglomerate.In the present invention, hydrogen gas is introduced under pressure into a copper sulfate aqueous solution to which bismuth has been added as described above to carry out a reduction reaction. is the reaction temperature during the reduction reaction of 1
The temperature is preferably 20 to 250 C, preferably 150 to 180 C, and the partial pressure of hydrogen gas is 3 to 200 to 9/1, preferably 5 to 20 molar. In addition, the optimal conditions for this reaction temperature and partial pressure of hydrogen gas vary depending on the copper concentration in the copper sulfate aqueous solution, the free sulfuric acid concentration, the type of reaction equipment, and the target particle size of copper powder, so in practice, It is recommended to take these factors into consideration when making a selection.

Incidentally, in general, as the reaction temperature and hydrogen gas partial pressure increase, copper nucleation from the aqueous solution becomes easier, so fine copper powder is less likely to be produced.In particular, when the reaction temperature is high, the reaction rate becomes faster. Although high yields can be obtained in a short period of time, it should be noted that on the other hand, agglomeration of copper powder particles with each other and growth of dendrites in the copper powder may occur.

In addition, in the hydrogen reduction reaction of the present invention, sulfuric acid is produced as the reaction progresses, and the concentration of free sulfuric acid in the aqueous solution gradually increases, and when the concentration exceeds 5001/l, the reduction reaction rate becomes extremely slow. It is necessary to pay close attention to monitoring the sulfuric acid concentration in the aqueous solution during the reaction period.

As mentioned above, the rate of the reduction reaction is affected by the concentration of free sulfuric acid, and copper powder with better crystallinity can be obtained when the concentration is lower. It is preferable to stop the reaction before the sulfuric acid concentration becomes too high, or to neutralize the aqueous solution as appropriate.

Furthermore, in carrying out the present invention, a pressure vessel such as an autoclave is used to store a copper sulfate aqueous solution to which a required amount of bismuth has been added, and hydrogen gas is blown into the solution at a predetermined temperature and pressure to carry out a reduction reaction while stirring. When using a batch method in which copper powder is produced by performing a reduction reaction, the particle size of the copper powder produced by the reaction increases as the reaction time progresses, so the reduction reaction is completed in a trench. In order to recover fine copper powder with the desired particle size, the reaction is stopped at an appropriate reduction rate by taking into account reaction conditions such as copper concentration in the aqueous solution, reaction temperature, and partial pressure of hydrogen gas. It is better to make it .

Further, in order to carry out the present invention in a continuous manner, for example, a copper sulfate aqueous solution to which a required amount of bismuth has been added is continuously supplied to a pressure vessel, and the supply amount is adjusted so that a predetermined reduction rate is maintained. The solution containing the copper powder produced by the reaction is continuously taken out from the container. In this case, the aqueous solution may be supplied from one end of the container and hydrogen gas and water vapor as a heating source may be introduced in parallel, or hydrogen gas and water vapor may be introduced from the other end of the container so that they flow counter-currently with the aqueous solution. The aqueous solution is brought into contact with the hydrogen gas and water vapor to ensure sufficient contact with the hydrogen gas and water vapor.

The solution containing copper powder thus obtained is subjected to solid-liquid separation using a sieve such as a cyclone or a carowell cone to recover the copper powder.

5 In the present invention, polyamine,
It is also possible to add known anti-agglomerating agents such as polyacrylic acid to the aqueous copper sulfate solution along with bismuth.

As shown above, according to the present invention, crystalline high-purity copper powder that is difficult to oxidize and has a fine uniform particle size can be advantageously produced, so it can be used for paints, conductive pastes, etc. that utilize the reflectance of crystal planes. It becomes possible to provide copper powder suitable for use in the electronic industry field.

EXAMPLES The present invention will be explained in more detail with reference to Examples below.

Example In this example, the copper concentration in the copper sulfate aqueous solution is 161! /1.

321/l and 50 to 4, and the free sulfuric acid concentration to 0.
Bismuth monosulfate was added to each of the aqueous solutions adjusted to 50'/l, 50'/l and 200'/l.
0.06 #, phrase, 0.1 F, phrase and 0 as squares
．． 51 added at each concentration were charged into an autoclave, and x40c, t60c and 185
A reduction reaction is carried out by introducing hydrogen gas at a partial pressure of 10 kg/crl and 20 kg at a temperature of This figure shows the relationship between conditions such as the reduction rate, the particle size and crystal shape of the copper powder obtained, and the cohesiveness of the particles. ``In the process of the above reduction reaction, the reaction solution was taken out, filtered, dried, and sieved to recover copper powder.

The results are shown in Table 1.

As shown in Table 1, all of the obtained copper powders were particles with developed crystal faces having a low facet index of the cubic system, except those in which the reaction progressed and the reduction rate reached 91. The agglomeration of the particles is small or weak, and the average particle size also varies depending on the composition of the aqueous copper sulfate solution and the reaction conditions, but on average it can be said to be fine, about 0.3 to 0.0
．． A 5μ cubic crystal is also included.

Next, for reference, the attached drawing is an electron micrograph of the copper powder obtained in Test A3 in Table 1 and the copper powder obtained by reacting under the same conditions as Test 163 (comparative example) except that bismuth was not added. 1 (present invention) and FIG. 2 (comparative example).

As seen in this attached drawing, the copper powder obtained by hydrogen reduction of a copper sulfate aqueous solution to which sibismuth has been added according to the present invention has less agglomeration among its particles, whereas the above aqueous solution without bismuth It can be seen that the surface of the powdered copper powder obtained by similar hydrogen reduction has a rounded surface and the particles are agglomerated with each other. Furthermore, when the copper powder obtained in the present invention was left at room temperature in a natural atmosphere, no oxidation of the copper powder was observed even after 24 hours had passed. In the copper powder of the comparative example, significant discoloration was observed due to oxidation after 24 hours.

[Brief explanation of drawings]

Fig. 1 shows an example of an electron micrograph of copper powder obtained according to the present invention, and Fig. 2 shows an electron micrograph of copper powder obtained by hydrogen reduction of a copper sulfate aqueous solution without adding bismuth. This is an example of a photograph.

Claims (3)

[Claims] (1) In the method of producing copper powder by reducing a copper sulfate aqueous solution with hydrogen, bismuth is added to the copper sulfate aqueous solution with Q, 051/l.
By adding the above and introducing hydrogen gas under pressure to cause a reduction reaction. A method for producing copper powder characterized by producing crystalline fine copper powder. (2) The manufacturing method according to claim 1, wherein the copper concentration in the copper sulfate aqueous solution is 10 to 9 ON. (3) Addition concentration of bismuth is 0.05 to 1.09/l
The manufacturing method according to claim 1 or 2.