JPS63183101A - Production of metal-coated powder - Google Patents

Abstract

PURPOSE:To permit formation of a uniform and secure coating layer on the surface of base metal powder grains by pouring a soln. contg. a noble metal to the base metal powder grains charged into a reaction vessel and fluidizing the powder. CONSTITUTION:A coating material which is the noble metal such as copper mill scale 1 is fed to a dissolution tank 3 and is dissolved by sulfuric acid 5, etc., to form a copper sulfate soln. The soln. is passed through a filter 10 and is fed via a measuring tank 13 from a copper soln. storage tank 12 to the reaction vessel 14. The base metal powder grains such as iron powder 15 charged into the vessel 14 flows and reacts uniformly with the copper sulfate soln. and the continuous film of copper is formed on the surface of the individual iron powder grains 15. The copper-coated metal powder is fed to a magnetic separator 17, by which the copper-coated metal powder is separated from the soln. Said powder is then cleaned 19 and is fed to a vacuum dryer 21. The powder is further fed to a deoxidation heating s furnace 22 and is heated in a hydrogen atmosphere. Since the coating of the noble metal adheres uniformly to the individual metal particles, the metal-coated powder having excellent quality is obtd.

Description

[Detailed description of the invention] [Industrial application field] The present invention uses base metals such as iron, zinc, and aluminum as copper.

This invention relates to a method for producing metal-coated powder coated with precious metals such as silver and gold.

[Conventional technology]

In recent years, the materials used in powder metallurgy technology are not limited to the traditional iron and copper types, but also aluminum.

Various materials such as cemented carbide have been developed.

These materials are used in various fields depending on their properties, and are expected to grow significantly in the future.

This material for powder metallurgy is sintered into products, so
In order to improve sintering properties, a coating layer of copper or the like is formed on the metal powder grains that serve as the base material. This coating layer also provides a certain electrical conductivity to the resulting product, for example when copper is used.

As a conventional method for forming a metal coating layer on powder grains, for example, "Standard Metallurgy Course/Powder Metallurgy" (January 3, 1978)
As described on page 38 (published by Corona Publishing Co., Ltd.), the base metal powder to be coated is placed in a container containing an aqueous solution containing metal salts as a coating material. and,
By performing a substitution reaction between a metal salt in an aqueous solution and a base metal powder, the generated metal is deposited on the surface of the base metal powder.

[Problems that the invention attempts to solve]

In conventional coating methods that utilize such substitution reactions, although metal is deposited on the surface of the powder, the resulting coating layer is often unsatisfactory. As a result of research conducted by the present inventors, it was found that the substitution reaction when the coating layer is obtained in this manner differs depending on the powder.

For example, in the case where iron powder is coated with copper, the reaction between the prepared liquid and the iron powder occurs extremely quickly. This substitution reaction varies greatly depending on the properties of the metal powder. For example, the average particle diameter of iron powder used as a conductive filler is extremely small, ranging from 10 to 70 mm, and therefore the particle specific surface area is large, ranging from 0.03 to 0.2 m''/g.On the other hand, the iron powder used The amount of powder is 3% relative to the amount of copper present in the solution.
~20 times.

As the substitution reaction progresses in a state where the reaction interfacial area is large and the amount of iron powder is large, the copper salt in the solution, which is the coating material supply source, is consumed. Therefore, there is a difference in the amount of copper salt in the solution between the early, middle, and late stages of the iron powder artist, and this appears as a difference in the amount of copper coated. In extreme cases, no copper cladding may be formed in the final input.

Due to this decrease in copper salt concentration, even if a predetermined copper basis weight is secured as a whole, differences occur in the coating layer thickness of individual iron powders. When such metal-coated powder is used as a raw material for ordinary powder metallurgy or as a conductive filler in powder metallurgy, it becomes a fatal drawback.

In order to avoid this drawback, it is conceivable to suppress the rate of substitution reaction. However, if the reaction rate is suppressed, even if a uniform coating layer can be obtained, productivity will decrease and processing costs will increase, which is not preferable.

Therefore, the present invention aims to reduce the influence of the decrease in the concentration of metal salt in the solution, which is the coating material supply source, as the substitution reaction progresses, and quickly form a uniform coating layer on the surface of the metal powder particles. To do something for the purpose.

[Means for solving problems]

In order to achieve the purpose of the method for producing metal-coated powder of the present invention, a solution containing a noble metal is applied to the base metal powder charged in a reaction vessel at a flow rate such that the base metal powder exhibits a fluid state. The method is characterized in that the noble metal produced by a chemical reaction between the solution and the base metal powder is deposited on the surface of the base metal powder.

When injecting this noble metal-containing solution, stirring the base metal powder charged into the reaction vessel will further improve the reaction rate and ensure a uniform substitution reaction for each base metal powder. This is preferable from a practical standpoint. In addition, in order to further improve the reaction rate, it is necessary to add 20% of the solution containing the noble metal.
It is preferable to control the reaction temperature within a range of 100°C to 100°C, preferably 25 to 100°C. If this reaction temperature range is less than 20°C, the reaction rate will decrease;
When the temperature exceeds ℃, the reaction becomes too radical. As a result, the strength of the resulting coating deteriorates.

In addition, the concentration of metal salts in the solution can be increased by dividing the injection of the solution containing the noble metal into several parts and by discharging the solution after the reaction at each stage before injecting the solution in the next stage. This is an advantageous means to further reduce the influence of the drop.

Examples of solutions used here include those containing, for example, 20 g/l or more of copper and whose pH is maintained at 0.5 to 4.

Further, in the second invention, after dehydrating, washing, and drying the metal powder particles coated with the noble metal in this way,
20 minutes to 120 minutes in H2 gas atmosphere in the temperature range of 50℃
It is characterized by being processed separately.

[Effect]

That is, in contrast to the conventional method of introducing metal powder particles into a solution containing a metal salt, in the present invention, metal powder particles to be coated are first charged into a reaction vessel, and then the noble metal salts are added to the solution. A solution is injected. This solution is injected at such a flow rate that the previously charged metal powder particles exhibit a fluid state.

Therefore, the metal powder particles come into contact with the injected solution evenly. Furthermore, since the solution at this time is in an initial state where the noble metal salt serving as the coating material supply source has not been consumed, each metal powder particle undergoes a uniform substitution reaction.

By reversing the charging of the metal powder particles and the injection of the noble metal salt-containing solution in this way, the solution for forming the coating can be brought into contact with the metal powder particles under the same concentration conditions. Further, since the surface of the metal powder particles can be uniformly exposed to the noble metal salt-containing solution, the noble metal precipitated by the substitution reaction can be formed as a uniform coating on the surface of the metal powder particles. Since such a precipitation form is not greatly affected by the rate of substitution reaction, it is also possible to increase the reaction rate.

Film formation using this substitution reaction is carried out through an initial stage in which the noble metal is precipitated, and a second stage in which a new noble metal film is formed by penetrating the precipitated noble metal film. Due to both the precipitation and penetration effects, the layer thickness gradually increases to cover the entire surface of the metal powder particles. At this time, in the conventional coating method, a part of the metal powder comes into contact with the solution after the noble metal salt has been partially consumed, so the precious metal is deposited on the surface of the metal powder in the form of sparse dots or sponges. Easy to precipitate. In addition, the sponge layer becomes thick and is interposed between the metal powder particles and the noble metal layer on the outer surface, causing a significant deterioration in the strength of the coating on the outer surface. On the other hand, according to the present invention, since each metal powder comes into contact with a noble metal salt-containing solution of the same concentration in the initial state, the precipitated precious metal is formed in a continuous form with a uniform thickness on the surface of each metal powder. Forms a film.

Such a coating has the advantage that it has a uniform thickness, and since it is continuous, it also has excellent adhesive strength to the metal powder particles that are the base material.

Moreover, in addition to the rapid formation of the coating layer,
Since the metal powder particles come into uniform contact with the precious metal salt-containing solution at the same concentration, the spongy coating formed between the metal powder particles and the noble metal layer on the outer surface of the same coating layer thickness can be made extremely thin. , the proportion of the spongy coating to the total thickness of the coating layer can be made extremely small. therefore,
It also becomes possible to freely control the total thickness of the coating layer while suppressing the formation of a spongy coating.

Further, in order to suppress the formation of this sponge layer and obtain a coating with excellent strength, it is preferable to divide the noble metal salt-containing solution and add it to the metal powder particles several times. For example, from the beginning of the reaction until the copper concentration drops by 20 g/l, the copper precipitated by a displacement reaction with metal powder forms a metallic film, but between 20 g/l and the concentration at the end of the reaction, Copper precipitated from a copper solution becomes spongy and has a weak film strength. If a batch method is adopted to overcome this drawback, a strong metallic copper coating is formed in a laminated form depending on the number of batches. As a result, copper-coated powder particles with excellent mechanical strength can be obtained.

〔Example〕

Hereinafter, the features of the present invention will be specifically explained using examples with reference to the drawings.

FIG. 1 is a diagram schematically showing the overall configuration of the apparatus used in this example.

This example is an example in which iron powder is used as the base metal powder and copper sulfate is used as the noble metal salt as the coating material supply source. In addition to iron powder, various metals or alloys such as aluminum, zinc, and tungsten are used as the base metal powder. On the other hand, as the noble metal salt, in addition to copper salts, silver nitrate, blue compounds, etc. can be used.

Solutions containing copper sulfate are prepared from precipitated steel (copper content approximately 80% by weight) recovered from the chloride volatilization pellet method of sintered ore, and copper mill scale generated during processing processes such as copper elongation. . These raw materials can be heated at 600 to 800℃ as necessary.
It is oxidized by heating. However, it goes without saying that the present invention is not limited to this. For example, a copper sulfate-containing solution can also be prepared from separately purified copper.

First, the copper mill scale 1 is sent to the dissolution tank 3 from the coated resource supply tank 2 in which the copper mill scale 1 is stored. Sulfuric acid 5 with a concentration of 70%, for example, stored in a sulfuric acid tank 4 is fed into the dissolution tank 3 by a pump 6 in order to dissolve the copper mill scale l.

The copper mill scale 1 is dissolved by the fed sulfuric acid 5, and a copper sulfate solution is produced. A pH meter 7 is provided in the dissolution tank 3 to adjust the hydrogen concentration of the copper sulfate solution, and the flow rate of industrial water 8 sent to the dissolution tank 3 is controlled based on the value detected by the pH meter 7. are doing. This pH can be adjusted by controlling the amount of sulfuric acid added. Furthermore, steam 9 is injected into the dissolution tank 3 as necessary, and the temperature of the copper sulfate solution obtained is maintained within a predetermined range by the steam 9.

In addition, as a copper salt, copper chloride is used instead of copper sulfate.

Copper solutions such as copper ammonia, copper acetate, copper nitrate, etc. can be used.

The copper sulfate solution prepared in the dissolution tank 3 is transferred to a filter 10 to remove undissolved components. Then the copper sulfate solution is
It is stored in the liquid preparation storage tank 12. In this example, two liquid preparation storage tanks 12 are provided, but the number of installed liquid storage tanks 12 can be adjusted as appropriate depending on the processing capacity of the entire apparatus. In addition,
The copper concentration of the copper sulfate solution in this liquid storage tank 12 is 10
It is preferable to select the processing conditions in the dissolution tank 3 so that the pH value is 0.5 to 4, more preferably 3 to 4 at g/1 or more, for example 40 g/j2.

The copper sulfate solution stored in the liquid preparation storage tank 12 is transferred to the pump 1.
1 to the reaction vessel 14 via the metering tank 13. The reaction vessel 14 is charged with iron powder 15 to be coated from an iron powder tank 16 prior to injection of the copper sulfate solution. Then, by pouring the copper sulfate solution onto the iron powder 15 from above, the iron powder 15 becomes fluid,
Reacts homogeneously with copper sulfate solution. As a result, individual iron powder 1
A continuous coating of copper is formed on the 5 surface.

In this example, a decarburized powder of 0.01 to 1 mm obtained by classifying and polishing converter dust was used as the metal powder iron powder 15. .

The particle size of the iron powder 15 treated according to the present invention is 0.005
It is preferable to be in the range of about 3 m+n.

As the reaction vessel 14 used for forming this film, there are a tilting rotary vessel such as a concrete mixer, and a counterflow type high speed mixer such as an Eirich mixer. Alternatively, the iron powder 15 and the copper sulfate solution can be brought into contact by forming the reaction vessel 14 in the shape of a horizontally spread pallet and blowing up the copper sulfate solution from the bottom surface of the pallet. The substitution reaction that forms this copper film is as follows.

Cu5O, +Fe-+Cu +FeSO4 In order to stabilize this reaction and improve the film forming effect, the copper sulfate solution is rapidly injected into the reaction vessel 14, and the falling energy of the copper sulfate solution removes the already loaded material in the reaction vessel 14. It is important to make the iron powder 15 contained in a fluid state. As a result, each of the 15 iron powder particles comes into even contact with the fresh copper sulfate solution, and a uniform noble metal coating is formed on each of the 15 iron powder particles. In order to create such a fluid state, the copper sulfate solution must be poured into the reaction vessel 1 at a flow rate of 3 m/sec or more.
It is desirable to inject at 4.

Note that the reaction vessel 14 is preferably equipped with appropriate stirring means. Such stirring means include one in which the reaction vessel 14 itself is rotated or vibrated, and one in which a rotating blade is inserted into the reaction vessel 14. This stirring means promotes the flow or transfer of the iron powder 15,
The interfacial reaction to the copper sulfate solution becomes more uniform.

In addition, in order to adjust the substitution reaction that precipitates the noble metal, the temperature of the copper sulfate solution is adjusted to 20°C to 100°C, more preferably 2°C.
It is preferable to control the temperature within the range of 5 to 100°C. As the temperature of the copper sulfate solution increases, the substitution reaction occurs rapidly, and as the temperature decreases, the reaction rate becomes slower. Therefore, for example, if the temperature of the solution rises beyond the appropriate temperature range for copper precipitation due to the reaction during copper solution production, the copper sulfate solution should be cooled by an appropriate cooling means before being poured into the reaction vessel 14. . Alternatively, the copper sulfate solution itself in the reaction vessel 14 can also be cooled. Moreover, when the temperature of the copper sulfate solution decreases and falls below the temperature range required for copper precipitation, steam 9 can be blown into the dissolution tank 3 to increase the temperature of the adjusted copper sulfate solution. Alternatively, the temperature can also be controlled by blowing steam into the reaction vessel 14.

Furthermore, it is also possible to maintain the copper sulfate solution at a temperature suitable for precipitation by adjusting the concentration of the copper sulfate solution. For example, when the temperature of the copper sulfate solution is high, the concentration of copper sulfate is reduced to suppress the amount of copper produced by the substitution reaction. On the other hand, if the solution temperature is low, the concentration of copper sulfate is increased.

By controlling the temperature or copper sulfate concentration of the copper sulfate solution in this manner, the reaction rate or reaction amount is controlled, and the desired copper coating is smoothly produced.

If the temperature of the copper sulfate solution that is brought into contact with the iron powder 15 is below 20°C, the rate of the substitution reaction that precipitates copper will not be sufficient;
The obtained copper coating becomes spongy. Such a copper coating has poor adhesive strength and easily peels off from the iron powder 15 particles. On the other hand, the temperature of the copper sulfate solution is 100℃
When the reaction rate exceeds 1, the reaction rate is rapid and peeling of the coating layer is likely to occur. For this reason, the temperature of the copper sulfate solution is
It is preferable to maintain the temperature in the range of 20 to 100°C.

In addition, the concentration of the copper sulfate solution is 10 g/l in terms of copper.
It is preferable that it is above. When this concentration is less than 10 g/l, the supply of copper necessary for coating is not sufficient, and the resulting copper coating takes on a spongy shape and has low coating strength.

The amount of the copper sulfate solution injected into the iron powder 15 in the reaction vessel 14 is maintained at a value corresponding to the amount of metal powder that provides a desired adhesion amount, taking into consideration the ratio of the amount of copper-coated metal powder. For example, when controlling the thickness of the coating to be thin, the total amount of copper and/or
Or increase the amount of metal powder. Also, if you want to make it thicker,
Increase the total amount of copper and/or reduce the amount of metal powder.

Furthermore, when injecting the copper sulfate solution, it is preferable to divide the copper sulfate solution containing the amount of copper necessary to form the target coating amount into a plurality of parts and inject the divided parts into the iron powder 15 in multiple stages. That is, after reacting the injected copper sulfate solution with the iron powder 15 for a predetermined time, the reacted solution is discharged, and then the second
Perform step injection of copper sulfate solution. By repeating the injection and discharging of the copper sulfate solution several times in this way, the frequency of the iron powder 15 coming into contact with the solution with the initial copper sulfate concentration increases, and the strong coating layer that is initially formed is spread over several layers. It will be done. As a result, the mechanical strength of the coating layer increases.

Since this substitution reaction occurs extremely rapidly, there is no need to use a special activator or the like. In this respect as well, the present invention is superior in terms of cost.

The obtained copper-coated metal powder is sent to the magnetic separator 17 together with the reacted solution. In this magnetic separator 17 , the copper-coated metal powder is attracted to a magnetic drum, separated from the solution, and sent to a conveyor 18 . During this process, the copper-coated metal powder
It is washed with washing water 19. The copper-coated metal powder thus separated from the iron sulfate solution or waste liquid is sent to a vacuum dryer 21 by a conveyor 20 such as a pallet.

During these dehydration, washing, and drying processes, the copper coating layer is coated with 1-20%
% of copper oxide is produced. In order to remove this oxide and improve the mechanical strength of the coating layer, the copper-coated metal powder dried in the vacuum dryer 21 is further sent to a deoxidizing heating furnace 22 and heated in a hydrogen atmosphere. This deoxidation treatment was carried out at 500°C.
By continuing in the temperature range of ~850°C for 20 minutes to 120 minutes, a copper-coated metal powder having characteristics of metallic copper powder is obtained.

Next, the deoxidized copper-coated metal powder is vacuum packed 23
After that, it is carried out as a product 24.

On the other hand, the reacted solution from which the copper-coated metal powder has been separated by the magnetic separator 17 is collected in a waste liquid tank 25 and returned to the sulfuric acid factory 27 by a waste liquid pump 26. Further, the solution 28 in which some powder components are suspended is collected together with the washing water 19 in a waste liquid tank 29, and is returned to the dissolution tank 3 by a pump 30.

Tables 1 to 3 show the results when copper coating was applied to iron powder and sponge iron obtained by decarburizing converter dust, in comparison with conventional methods. As is clear from these tables,
The coating layer obtained by the present invention is excellent in both coverage and peel strength. In addition, the coating layer is
Because it forms a uniform coating on each particle, it is used as a copper-coated metal powder of excellent quality.

(See the margins of this page below.) Figure 2 shows the temperature and concentration of the copper sulfate solution used to coat iron powder obtained by decarburizing dust discharged from a non-combustion converter. It is a graph showing the influence of the copper coating on the coverage rate and degree of peeling. As is clear from this figure, by maintaining proper temperature and concentration, a strong coating can be obtained with high coverage. However, the coverage was measured qualitatively and quantitatively on the cross section of the coating layer by electron beam projection, and the degree of peeling was measured by a Rattle type test using a rotating container.

Figure 3 shows that iron powder obtained by decarburizing dust discharged from a non-combustion converter has a copper equivalent concentration of 45 g.
/ When coating using the copper sulfate solution of 1, the copper sulfate solution is injected into the iron powder charged in the reaction vessel 14 (
In Figure 3, this is expressed as “with stirring”)
2 is a graph showing the effect of coating in comparison with the case where static iron powder is coated.

As is clear from FIG. 3, the coverage according to this example is extremely high compared to the conventional method. That is,
It can be seen that the method of the present invention is extremely excellent as a coating means. Furthermore, by adding agitation that induces fluidization and transfer of the metal powder particles, in combination with reverse addition of the solution, the coverage can be significantly improved.

Moreover, the degree of peeling showed a low value in the case of this example, indicating that the film was strong and stable.

Although the effect of stirring on the degree of peeling itself is small, as mentioned above, although stirring significantly increased the coverage, it did improve the peeling resistance of the resulting film, in other words, the strength of the film. When considering this, the effect of stirring is significant.

〔Effect of the invention〕

As explained above, in the present invention, base metal powder particles are first charged into a reaction vessel, and a solution containing a noble metal salt is injected into the reaction vessel. is made into a fluid state, and in this state a substitution reaction is carried out in which precious metals are precipitated. As a result, a uniform and strong film is formed, and the amount of the film can be easily controlled. Further, the noble metal coating formed in this manner is of excellent quality because it is evenly adhered to each particle. For example, if the obtained coated powder is made into a product having a predetermined shape by powder metallurgy, the properties of the product will be uniform.

Furthermore, by utilizing the conductivity of the coating layer, it can also be used as an excellent conductive paint.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the overall configuration of the apparatus used to carry out the method of the present invention, and Figure 2 shows the influence of the temperature and concentration of the copper sulfate solution used in the examples on the coating layer. FIG. 3 is a graph specifically showing the effect of the present invention in comparison with the case where the substitution reaction is performed while standing still. Patent applicant: Nippon Steel Corporation (and one other person)
Masato Kobori (and 2 others)
Name) Figure 2,! [('C) Figure 3

Claims (1)

[Claims] 1. A solution containing a noble metal is injected into the base metal powder charged in a reaction container at a flow rate such that the base metal powder exhibits a fluid state, and the solution and the base metal powder are mixed together. A method for producing a metal-coated powder, characterized in that a noble metal produced by a chemical reaction during the process is deposited on the surface of the base metal powder. 2. A method for producing metal-coated powder, characterized in that the base metal powder particles according to claim 1 are in an agitated state. 3. A method for producing a metal-coated powder, characterized in that the reaction temperature of the solution containing the noble metal according to claim 1 is controlled within the reaction temperature range of 20 to 100°C. 4. The noble metal-containing solution according to claim 1 contains 10 g/l or more of copper and has a pH of 0.5 to 0.5.
4. A method for producing a metal-coated powder, characterized in that the metal-coated powder is maintained at a temperature of 4. 5. Injecting the solution containing the noble metal as described in claim 1 in several steps, and discharging the solution after the reaction in each step, before injecting the solution in the next step. A method for producing metal-coated powder characterized by: 6. A solution containing a noble metal is injected into the base metal powder charged in a reaction container at a flow rate that causes the base metal powder to exhibit a fluid state, and a chemical reaction between the solution and the base metal powder causes a chemical reaction between the solution and the base metal powder. Precipitating the generated noble metal on the surface of the base metal,
Next, after dehydrating, washing and drying this, the
A method for producing a metal-coated powder, characterized by processing for 20 minutes to 120 minutes in an H_2 gas atmosphere in the temperature range of °C.