JPH0731873A - Prep aration of self-gradient-type composite particle - Google Patents

Abstract

PURPOSE:To prepare a self-gradient-type composite particle which has a continuous or discontinuous gradient distribution of a chemical composition or a crystal phase in a powder particle by injecting a raw material powder into a plasma generated under specific pressure and temperature conditions and allowing the powder to pass through the plasma. CONSTITUTION:A solid particle 7 is injected into a plasma 1 generated under conditions of from 1 torr to the atmospheric pressure and from 1000 deg.C to 1500 deg.C, and then is allowed to pass through the plasma 1. Consequently, a thermal and/or a chemical interaction is induced between the plasma 1 and the solid particle 7, so that the chemical composition or crystal phase of the powder particle is permitted to have a continuous or a discontinuous gradient structure.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing self-gradient composite particles. More specifically, the present invention relates to self-grading composite particles useful for manufacturing catalysts, sensors, structural materials, electromagnetic materials and the like, and a method for manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, attempts have been made to create composite particles having a new function by compensating for the defects of various constituent components by compounding the particles, and a method for producing the composite particles has been proposed. Much has been devised. Such composite particles are generally classified into two types: dispersion-type composite particles and coating-type composite particles. Among them, the dispersion-type composite particles are, for example, as shown in FIG. 1 (a), in a state where two or more kinds of particles (11) and (12) are uniformly or non-uniformly dispersed and mixed. It is manufactured by the mixing method.

On the other hand, the coated composite powder is, for example, as shown in FIG.
As illustrated in (b), it is a powder in which the surface of the particle is coated with a heterogeneous phase, and the inner component (13) and the outer component (1
It is composed of two or more phases of 4) and is generally manufactured by a wet method such as a sol-gel method or a chemical plating method. However, the dispersion-type composite particles produced by the mixing method are merely a physical mixture of two or more kinds of particles, and the interaction between the different components of the two or more kinds of particles is caused only by the contact of each particle surface. Therefore, it is difficult for the performance of the entire powder to exceed the additive performance of the constituents, and the functionality naturally has a limit.

On the other hand, the coated composite particles produced by a wet method such as a sol-gel method or a chemical plating method have a boundary structure between an inner component and a coating component. Therefore, unlike the dispersion-type composite particles, the contact area between different kinds of components increases, but it is not possible to expect the improvement of the composite function utilizing the interaction due to the chemical bond. There are naturally limits.

Therefore, as a composite particle which compensates for the drawbacks of the conventional composite particles and is further developed to have a high function, for example, a self-gradient type composite particle is considered as illustrated in FIG. 1 (c). In this self-gradient type composite particle, the chemical composition or crystal phase changes continuously from the inside of the particle toward the surface, and in the case of this self-gradient type composite particle, its functionality goes from the central part to the surface. It has a self-grading function that changes continuously or discontinuously. Therefore, by utilizing the functionality of the inner component and the surface component and the interaction of both components at the interface, the chemical functions of the sensor, catalyst, etc.
It is expected to realize electrical / magnetic functions and mechanical functionality such as toughness and strength.

However, although the self-gradient type composite particles are expected to realize the new functionality as described above, the manufacturing method thereof has not been established until now. The present invention has been made in view of the above circumstances, and provides a method for producing self-grading composite particles capable of overcoming the technical limitations of conventional composite particles and realizing new functionality. Is intended.

[0007]

In order to solve the above-mentioned problems, the present invention injects powder into a gas plasma generated at a temperature of 1000 ° C. or more and 15000 ° C. or less at a pressure of 1 Torr or more and atmospheric pressure or less. Provided is a method for producing a self-grading composite particle, which comprises producing a self-grading composite particle having a chemical composition or a crystal phase in a powder particle having a continuous or discontinuous gradient distribution.

[0008]

The present invention forms a powder by injecting a raw material powder into a gas plasma generated under the conditions of a pressure of 1 to 760 Torr and a temperature of 1000 to 15000 ° C. and passing the powder into the plasma. It has been completed based on the finding that a continuous phase or a discontinuous phase can be arbitrarily controlled from the inside of the particles to the surface, and a new method for producing gradient composite particles that enables this control. Is characterized by.

That is, in the present invention, attention is paid to the physical and chemical interaction between plasma and particles, and the particles are passed through the plasma generated under various conditions to be treated, whereby lattice defects of the particles are processed. Formation, the chemical reaction between the constituent atoms of the particles and the chemical species in the plasma, and the instantaneous freezing of the non-equilibrium state due to quenching continuously or discontinuously from the inside to the surface of the particles (chemical composition, crystalline or amorphous phase). Phase) and without coating etc. 1
The particles themselves are compounded.

Of course, in the present invention, various kinds of plasma such as high frequency plasma and direct current plasma can be used as the plasma. Gases for plasma generation and interaction with solid particles include rare gases such as argon and helium, organic substances such as hydrogen, nitrogen, oxygen, and hydrocarbons, and also water vapor, ammonia, diborane, silane, and the like. One or more hydrides can be used.

Appropriate ones of these can be used as the reaction gas. The type of particles to be targeted is not particularly limited, but particles of oxide, non-oxide ceramic particles, metal, alloy, ceramic / metal, etc. are suitably selected. When the pressure is lower than 1 Torr or higher than atmospheric pressure, it becomes difficult to generate and stabilize plasma suitable for production, and the temperature is lower than 1000 ° C. or 1500.
The same applies when the temperature exceeds 0 ° C.

The particle diameter and injection amount, and further the gas supply amount are appropriately determined according to the intended particles. Of course, the type and structure of the reactor are not particularly limited. Furthermore, in the present invention, the reaction gas may be supplied to the plasma downstream portion.

The present invention will be described in detail below with reference to examples.

[0014]

EXAMPLES Example 1 Using the high frequency plasma reactor shown in FIG. 2, high frequency plasma was generated to produce a self-gradient composite powder. In this high-frequency plasma reactor, a high-frequency coil (2) is wound around a water-cooled structure plasma reaction tube (3), a sheath gas (5) and a plasma gas (6) are supplied from the upper part, and a reaction gas (8) is supplied from the lower part. It has a structure of supplying and further injecting the raw material powder and the carrier gas (7) from the powder injection probe (4). The reaction gas (8) does not have to be used depending on the type of raw material powder, and in fact, the reaction gas (8) was not used in this Example 1.

Using this reactor, argon and hydrogen were used as sheath gas (5) at 6 liter / min and 5 respectively.
At a feed rate of liter / min, and further at a feed rate of 6 liter / min of argon as plasma gas (6),
Each of them is supplied to the water-cooled structure plasma reaction tube (3), and high-frequency power of 50 kW is supplied to the high-frequency coil (2) to generate plasma (1) in the water-cooled structure plasma reaction tube (3) at a pressure of 200 Torr. It was

Argon was introduced as a carrier gas from the powder injection probe (4) at a supply rate of 4 liters / minute, and titanium carbide powder (composition TiC) having an average particle diameter of 1.3 μm was introduced.
_0.97 ) was injected into the plasma (1) at a supply rate of 5 g / min. As a result of observing the titanium carbide particles after the plasma treatment with a scanning electron microscope, it was confirmed that the particles were melted and spheroidized, for example, as illustrated in FIG. The particles had an average composition of TiC _{0.91 and} it was found that the pores of carbon sites of titanium carbide were generated by the plasma treatment. As a result of examining the change of the carbon content with the melting time by dissolving with hot concentrated sulfuric acid, the vacancy of the carbon site is 200 to
It was confirmed that it was generated in the portion of 300 nm, and the concentration thereof continuously decreased toward the inside. Example 2 The titanium carbide raw material powder used in Example 1 was injected into the plasma generated under the same conditions as in Example 1, and further 5 liters of ammonia gas was used as a reaction gas (8) downstream of the plasma (1). Injected radially at a feed rate of 1 / min to produce self-grading composite particles.

Composition analysis of the titanium carbide particles subjected to the plasma treatment revealed that the titanium carbide particles contained 2% by weight of nitrogen. It was dissolved in hot concentrated sulfuric acid and the time-dependent change in nitrogen content was investigated. When the nitrogen content of the titanium carbide particles after plasma treatment was about the same as that of the raw material powder, the particle diameters were compared. It was confirmed that the solid solution was present in the portion up to 300 nm, and the concentration thereof continuously decreased toward the inside. Example 3 In a plasma generated in the same manner as in Example 1, α-alumina powder having an average particle size of 1.5 μm was injected into a high frequency plasma reactor at a supply rate of 5 g / min to produce self-grading composite particles. did.

As a result of examining the α-alumina particles after the plasma treatment with a transmission electron microscope, it was found that the particles were spheroidized. Furthermore, the central portion was a mixture of γ phase and δ phase, the intermediate phase was the θ phase, It was confirmed that the vicinity of the surface was composed of α phase.

[0019]

As described above in detail, according to the present invention, it becomes possible to produce self-grading composite particles in which the chemical composition or crystal structure changes continuously or discontinuously from the central part of the particles to the surface, By utilizing these self-gradient composite particles, it is expected that completely new chemical, electromagnetic and mechanical functionalities will be realized.

[Brief description of drawings]

1 (a), (b) and (c) are schematic views of the structure of dispersion type, coating type and gradient type composite particles, respectively.

FIG. 2 is a schematic view illustrating a method for producing self-gradient composite particles by high-frequency plasma and an apparatus therefor according to the present invention.

FIG. 3 is a scanning electron micrograph image diagram of titanium carbide particles after plasma treatment as an example.

[Explanation of symbols]

 11 particles 12 particles 13 inner component 14 outer component 1 plasma 2 high frequency coil 3 water cooled structure plasma reaction tube 4 powder injection probe 5 sheath gas 6 plasma gas 7 powder and carrier gas 8 reaction gas

Claims (2)

[Claims] 1. At a pressure of 1 Torr or more and atmospheric pressure or less, 1
Powder is injected into a gas plasma generated at a temperature of 000 ° C. or higher and 15000 ° C. or lower to produce self-grading composite particles having a continuous or discontinuous gradient distribution in chemical composition or crystal phase in the powder particles. A method for producing self-grading composite particles, comprising: 2. The method for producing self-gradient composite particles according to claim 1, wherein a reaction gas is injected into the downstream portion of the plasma.