JP2007126755A - Carbon-coated metal particle and method for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a special metal particle (carbon-coated metal particle) excellent in chemical resistance and oxidation resistance, and a method for manufacturing the same. <P>SOLUTION: The special metal particle is a carbon-coated metal particle wherein the surface of a pure metal particle is covered with a carbon coating. In the manufacturing method, the carbon-coated metal particle is obtained by subjecting a mixture of a particle of a metal oxide and a particle of a thermoplastic resin to a heat-treatment in an inert gas atmosphere and inducing liquid-phase carbonization of the thermoplastic resin to simultaneously promote reduction of the metal oxide and carbonization of the thermoplastic resin. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to special metal particles that can stably maintain the original characteristics of a metal material even in a harsh chemical environment, and that are particularly excellent in chemical resistance and oxidation resistance, and a method for producing the same.

  In general, metal materials gradually start electrochemical corrosion from the surface in an environment where they are in direct contact with air, water, chemicals, high-temperature gas, soil, etc., and especially corrosion caused by chemicals and oxidation progresses to a certain extent. It is remarkable. When such corrosion progresses, as a natural result, the original characteristics of the metal material are also impaired. Therefore, means for imparting chemical resistance and oxidation resistance are taken for various devices and apparatuses arranged in an environment where such corrosion and oxidation by chemicals are problematic.

  As such means, it is usually effective to form a thin film such as a metal or ceramic having excellent chemical resistance or oxidation resistance on the surface of a metal material (mechanical structural material) as a base material. Various forming methods have been proposed and implemented. For example, a vacuum deposition method, a sputtering method, an ion plating method, various CVD methods, a plasma method, and the like can be given.

  However, various devices and devices vary in shape, size, etc., especially for devices with complex shapes and devices with a large surface area, it is not possible to uniformly form a thin film of metal or ceramic on the surface. It is very difficult. Moreover, in order to carry out the above-described forming method, a large-scale forming apparatus is required, and further, there is a limit to the forming speed, so the productivity is very poor, and eventually, chemical resistance or oxidation resistance is imparted. There is also a problem that the cost of this becomes very high.

  Therefore, if the metal particles themselves can have chemical resistance and oxidation resistance at the stage of the metal particles before being used as a mechanical structural member, the metal particles themselves can have chemical resistance and oxidation resistance. From the standpoint of helping to solve this problem, a thin film of a heterogeneous material (a material with excellent environmental resistance) is formed on the surface of the metal particle, and the metal particle coated with such an environmental resistance material is used as a mechanical structural material ( The idea (technical idea) itself to be used as a raw material for secondary processed products has existed.

  However, there has been no means (practical means) that embodies the idea so far, and therefore, no practical metal particles with a thin film of an environmental resistant material formed on the surface have yet appeared. In the case of metal particles, the surface is in an active state, which makes it very difficult to handle, and it is considered that it is extremely difficult to form a thin film uniformly on the surface. Although the present inventors disclose the means (practical means) embodied for the first time here, the conventional idea (thought to form a thin film on the surface of a metal particle by the physical action from the outside) and Was completed based on completely different ideas.

  That is, the object of the present invention is to provide special metal particles excellent in chemical resistance and oxidation resistance, and to provide a production method capable of easily and efficiently obtaining the special metal particles. In the point.

  One aspect of the present invention that has achieved the above object is carbon-coated metal particles in which the surfaces of the metal particles are covered with a carbon film. Another invention is an invention of a method for producing the carbon-coated metal particles, wherein a mixture of metal oxide particles and thermoplastic resin particles is heat-treated in an inert gas atmosphere, and the thermoplastic resin is liquid-treated. The basic feature is phase carbonization.

  The inventors of the present invention have been researching on physical property improvement technologies such as carbon materials and carbon composite materials for some time, and in particular, as part of the development research of carbon-metal composite materials, the present inventors have also proposed the conventional idea described above. Various experiments have been conducted to find a means to realize the present invention, but satisfactory carbon-coated metal particles have not been obtained. Since it was judged that the main reason was the handling of active metal particles, it was decided to treat the particles as chemically stable metal oxides and reduce the metal oxides to form metal particles. At the same time, we conducted further experimental studies with the aim of developing a technology that could cover the surface of the metal particles whose shape had changed with a carbon coating.

  As a result, when the metal oxide particles are coated with a thermoplastic resin and heat-treated, the reduction of the metal oxide and the carbonization of the thermoplastic resin proceed at the same time, and the metal particles whose surface is covered with the carbon coating can be easily obtained. The present invention has been completed by finding out that it can be obtained.

  One of the present invention is special metal particles in which the surface of pure metal particles is uniformly covered with a carbon coating, so that the original characteristics of the metal (for example, paramagnetism, electrical conductivity, etc.) are stably maintained. However, metal particles having chemical resistance and oxidation resistance can be obtained. Therefore, by using this carbon-coated metal particle, surface protection structures (members) such as various shapes and sizes placed in environments where corrosion and oxidation by chemicals are a problem can be freely and easily performed. It can also be equipped.

  In addition, the production method of the present invention is completely different from the conventional idea (the idea of forming a thin film on the surface of metal particles by a physical action from the outside), that is, reduction of metal oxide and carbonization of thermoplastic resin. This is a method of uniformly covering the surface of pure metal particles with a carbon coating by simultaneously proceeding with the chemical action of the above, so there is no need for a large-scale thin film forming apparatus as in the past, and an existing baking apparatus is used. The special metal particles according to the present invention can be easily manufactured by using and controlling the operating conditions, and the special metal particles of the present invention can be obtained very simply and efficiently.

  In addition, when polyvinyl chloride is used as the thermoplastic resin, a carbon film covering the metal particles can be obtained with a more uniform film thickness and a smoother surface, which improves chemical resistance and oxidation resistance. Can be expected. Furthermore, if a general-purpose argon gas is used as an inert gas that flows during the heat treatment, it can contribute to a reduction in manufacturing cost.

In the present invention, typical examples of the metal oxide include Fe ₃ O ₄ , Fe ₂ O ₃ , CoO, Co ₃ O ₄ , NiO, Cu ₂ O, and CuO. Further, the size of the metal oxide particles is not particularly limited, but considering the versatility, those having an average particle size of 10 to 100 μm are desirable.

  On the other hand, the thermoplastic resin is not particularly limited, but polyvinyl chloride (PVC) is desirable in view of the advantage that unevenness is hardly generated in the coating film when the metal oxide particles are coated. In addition, the size of the thermoplastic resin particles is sufficient. The thickness of the carbon coating layer of the target carbon-coated metal particles is sufficient if the carbon coating layer is about 5 μm thick because of the denseness of the carbon coating layer. Therefore, the size of the particles may be sufficient as long as the coating layer having a thickness of about 5 μm is formed almost uniformly and surely. For example, when the metal oxide particles are about 10 to 100 μm, they are preferably about 100 to 200 μm.

  The mixing ratio of the thermoplastic resin particles to the metal oxide particles is preferably about 20 to 80% by weight. If the amount is less than 20% by weight, the resin does not sufficiently spread over the entire metal oxide particles, and a uniform coating layer cannot be obtained. This is because the film thickness becomes too large and internal stress tends to occur in the coating itself.

  The mixture of metal oxide particles and thermoplastic resin obtained so as to satisfy the above conditions was placed in an inert gas atmosphere, and then heated at a heating rate of 50 to 500 ° C./hr, and 800 to 1500 After reaching ° C, hold for a period of time. The so-called firing operation is performed, but before this firing operation is completed, the metal oxide is reduced to metal particles, and at the same time, the thermoplastic resin undergoes liquid phase carbonization, and finally the reduced metal. The surface of the particles is covered with a carbon film of about 3 to 20 μm.

Hereinafter, the present invention will be specifically described based on examples.
(Example)
50 g of Fe ₃ O ₄ particles (average particle size is about 50 μm) are put in a plastic container, and 43% by weight of PVC powder (average particle size is 100 to 200 μm) is added, and then the container is closed for 10 minutes. The two were mixed uniformly by mechanical rocking. Next, the mixed powder is placed in an electric furnace, and while the argon gas is allowed to flow in the furnace, the temperature in the furnace is increased at a rate of 500 ° C./hr, reaches 1000 ° C., and is held for 1 hour for heat treatment. Went.

Although the periphery of the heat-treated powder is uniformly covered with carbon of about 10 μm in thickness, the powder is all magnetic, and some powders are used as samples for X-ray diffraction. The components of the metal particles were analyzed. The results are shown in the peak diagram of the middle part of FIG. 1 (X-ray diffraction diagram) (expressed as “Example” in the figure). According to this, since all the metal particles inside the powder are α-Fe, the metal oxide (Fe ₃ O ₄ ) is sufficiently reduced and pure metal particles (α-Fe), that is, active. It turns out that it is a metal particle.

(Comparative example)
Except for using only Fe ₃ O ₄ particles (average particle size is about 50 μm) as a raw material, the same heat treatment operation as in the above example was performed, and the heat treated powder was subjected to X-ray diffraction in the same manner as in the example. Component analysis of the heat-treated powder was performed. The results are shown in the lower part of FIG. 1 (X-ray diffraction diagram), which is a peak diagram (expressed as “Comparative Example” in the figure).
As is apparent from this figure, only the heat treatment of the _Fe 3 _{O 4} particles alone, it is seen that only _Fe 3 _{O 4} is partially reduced _α-Fe 2 _{O 3} is formed. 1 is an X-ray diffraction peak diagram of Fe ₃ O ₄ particles (normal temperature).

An X-ray diffraction diagram for the metal oxides used in Examples and Comparative Example (Fe 3 _{O 4),} metal oxides untreated carbon coated metal particles obtained according to the method of the present invention, only the metal oxide It is the figure which showed the X-ray-diffraction peak about each of the metal oxide obtained by heat processing in the upper stage, the middle stage, and the lower stage.

Claims (4)

  A carbon-coated metal particle, wherein the surface of the pure metal particle is covered with a carbon film having a thickness of 3 to 20 μm.   The surface of pure metal particles having a thickness of 3 is characterized in that a mixture of metal oxide particles and thermoplastic resin particles is heat-treated in an inert gas atmosphere, and the thermoplastic resin is liquid-phase carbonized. A method for producing carbon-coated metal particles covered with a carbon film of ˜20 μm.   The method for producing carbon-coated metal particles according to claim 2, wherein the thermoplastic resin is polyvinyl chloride.   The method for producing carbon-coated metal particles according to claim 2 or 3, wherein the inert gas is argon gas.

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