JPH0243377A - Coating and surface treatment for fine particle - Google Patents

Abstract

PURPOSE:To form a uniform layer on fine particle surface or to apply a uniform surface treatment thereon by supplying gaseous raw materials under a reduced pressure into a reaction treatment chamber contg. the fine particles and keeping the fine particles fluidized, thereby depositing the reaction product of the gaseous raw materials on the fine particle surface. CONSTITUTION:The superfine particles having <=0.1mu grain size are put into the reaction treatment chamber 6 made of a heat and corrosion resistant material and while the particles are heated by a heating furnace 5, the gaseous raw materials are blown from a gas supplying system 2 into the chamber from the bottom. The supply rate of the gaseous raw materials is adjusted by a flow meter 4 to keep the superfine particles in the reaction chamber 6 fluidized and to form a stable fluidized bed 1. The thin layer of the oxide, carbide or nitride formed by the reaction of the gaseous raw materials is formed on the superfine particles to a uniform thickness by which the coating layer without having unequal thicknesses among the superfine particles is formed. The surface of the superfine particles is otherwise subjected to the uniform treatment such as oxidation or reduction.

Description

Detailed Description of the Invention (Field of Industrial Application) This invention is applied to powder materials that exhibit unique properties due to their small particle size, by giving them additional functions. This relates to coatings and surface treatments to expand the range.

(Prior Art) Japanese Patent Application Laid-Open No. 19185/1985 discloses that the purpose of chemical vapor deposition on the surface of fine particles to form a uniform thin film layer is as follows.
It is disclosed that fine particles are captured by a filter in a reaction tube of a CVD apparatus, and a thin film layer is formed while changing the state of capture of the fine particles by the filter.

However, in order to change the trapping state of fine particles,
The process of inverting the reaction tube requires complicated equipment, and since it is heated together with the filter, precipitation on the filter is unavoidable, which poses a problem in terms of the effective use of the precipitated substance. Also, substances precipitated on the filter due to inversion etc. are mixed in.

On the other hand, Metallurgical Transa
H in ction+ 13B625P (1982),
reported the results of using a normal pressure fluidized bed to form a Nb3Sn film on Nb seed particles by hydrogen reduction of chloride vapor. But in this case,
It can be seen that particles with a different shape from the seed particles are generated and a uniform coating cannot be obtained in the normal pressure fluidized bed.

The use of a fluidized bed has been attempted in the past in order to overcome the problem that the powder surface, which is difficult to come into contact with gas, is not coated when the target powder is left stationary in a reaction tube and coated. This indicates that there was a problem with the uniformity of the film.

(Problems to be Solved by the Invention) As described above, in the conventional method using a thermochemical reaction, surface treatment that is uniform over the entire surface of each particle, with no unevenness between particles, and without contamination with impurities. of,
There was a problem that it could not be done easily and efficiently.

(Means for Solving the Problems) In order to solve the above-mentioned problems, the present invention employs the following means.

That is, a fluidized bed is formed in a reduced pressure state by feeding gas into a layer of fine particles and simultaneously exhausting the gas in the layer using a vacuum pump.

At this time, by keeping the fluidized bed at a certain temperature and using a reactive gas as the fluidizing gas, a chemical reaction is caused within the fluidized bed, and the product is deposited on the surface of the fine particles, or the product is reacted on the surface to modify it. It is.

That is, the present invention is a method for coating and surface treating fine particles, which is characterized by performing a thermochemical reaction treatment while fluidizing the fine particles under reduced pressure.

By causing precipitation and surface reactions under reduced pressure, non-uniformity on the surface of each particle can be avoided, and by fluidizing the particles, the uniformity of the fluidized bed can be used to improve the particle size. This study focuses on the fact that it is possible to eliminate non-uniformity between the two.

Because the reaction rate is fast in gas-phase thermochemical reactions at normal pressure, uniform nucleation occurs to produce powder or non-uniform precipitation occurs on particle surfaces. However, in a gas phase thermochemical reaction under reduced pressure, the mean free path of the reacting gas becomes large and the reaction rate is suppressed, so that uniform precipitation occurs on the particle surface.

Furthermore, powder fluidized beds are normally operated at normal pressure, but this invention applies the fact that they are sufficiently fluidized even under reduced pressure, and that even ultrafine particles can be fluidized well. .

FIG. 1 shows an example of an apparatus to which the method of the present invention is applied.

Gas is fed into the fluidized bed 1 from a gas supply system 2, and at the same time it is evacuated using a vacuum pump 3.

The flow meter 4 is set at a gas flow rate at which the particles become fluidized in a certain reduced pressure state, and the fluidized state is maintained.

A reactive gas is used as the fluidizing gas, and the heating furnace 5
The fluidized bed 1 is set in a reaction treatment tank 6 made of a material having corrosion resistance and heat resistance to a temperature at which a thermochemical reaction can sufficiently proceed within the bed.

Especially when using reactive gases that are liquid at room temperature,
The carrier gas is passed through a vaporizer 7 that is kept warm or heated, and is led to the fluidized bed 1 via a pipe 8 that is kept warm.

In the case of surface coating, reaction products from a thermochemical reaction within the fluidized bed are deposited on the surface of the fine particles.

Also, in the case of surface modification, a thermochemical reaction occurs on the surface of the fine particles, but since the fine particles are in a fluid state, uniform modification is applied to all particles.

A filter 9 is attached to the downstream side of the fluidized bed 1 in order to capture particles flying out from within the fluidized bed.

Note that 10 in the figure is a trap provided to protect the vacuum pump 3.

The powder used in the method of this invention may be any type of fine particles (several tens of microns or less) or ultrafine particles of 0.1 microns or less. Further, as the reactive gas, hydrogen or carbon oxide is used to reduce the particle surface, oxygen or water vapor is used for oxidation, methane gas is used for carbonization, and nitrogen or ammonia gas is used for nitridation. In addition to these gases, metal chlorides such as titanium tetrachloride and silicon tetrachloride, organometallic compounds, etc. are used for the coating treatment, and the surface precipitation resulting from the reaction between them and the reactive gas is utilized.

(Function) The apparatus to which the method of the present invention is applied has no moving parts (and is easy to operate, and since the CVD reaction occurs only on the surface of the particles, there is no possibility that precipitated substances will be mixed in as powder). It has the advantage of not being

Hereinafter, a detailed description will be given based on examples.

(Example) Example-1) Ultrafine particles of titanium dioxide (TiO□) (average particle size 0.0
34 μm) as shown in Fig. 1 (area approximately 3c+n2
), Ar/TiCl4/ NL/L (ratio,
t:i:i:i) (flow rate 0.04 per minute
pV (atmospheric pressure equivalent value) was introduced into the fluidized bed 1 at 40 Torr and fluidized. The fluidizing gas velocity at 40 Torr was 4 cm/s' (actual value).

On the other hand, by keeping the fluidized bed 1 at 1100°C using an electric furnace, a reaction expressed by the following formula % is caused, and T is applied to the surface of the TiO□ particles.
iN was precipitated. The nitrogen content of the obtained particles was 8.0
%, which showed a constant value regardless of the sample.

In addition, as a result of surface analysis by ESCA, the seed particle T
0 (oxygen) of iO□ was hardly detected.

Further, EMT observation confirmed that spherical particles were 1 to 1.3 times larger than TiO□ particles.

Example-2) Ultrafine particles of silicon monoxide (SiO□) (average particle size 0.0
5 μm) using the same equipment as in Example-1),
C14/CH4 (1:1:1) mixed gas (flow rate 0.
2 pV, > SiC at 1300°C at 10 Torr
Coated. The C content of the obtained particles was 7.1%
It was constant regardless of the sample.

In addition, as a result of surface analysis by ESCA, the seed particles S
0 (oxygen) of iO□ was hardly detected.

Further, EMT observation confirmed that spherical particles were 1 to 1.3 times larger than SiO□ particles.

Example 3) Ti fine powder (average particle size 2 μm) was nitrided. The gas used was nitriding gas, mixed 1:1 with Ar gas and heated to 20 Torr.
The mixture was fluidized and reacted at 800°C. The N content of the obtained powder was 3.0%, which was constant regardless of the sample.

Comparative Example-1) Ti was added to the surface of TiO□ ultrafine particles under the same conditions as Example-1).
N was precipitated. However, instead of a fluidized bed, a quartz tube was placed horizontally in the reactor, the surroundings of which were heated in an electric furnace, and a quartz boat was placed in the reactor and filled with TiO2 powder. 1
After processing for an hour, the hoard was removed and the powder was analyzed. The N content of the powder was 12% near the surface and 4% at the bottom of the port. This method shows that the thickness of the coating layer varies depending on the processing position.

Comparative Example 2) Ti0z ultrafine particles were fluidized using the same apparatus as in Example 1) at the same temperature and gas composition. However, the reaction was caused at a pressure cuff of 60 Torr and surface coating treatment was performed. When the powder after the treatment was observed with a transmission electron microscope, many particles with shapes and crystal habits completely different from those of the spherical TiO□ used were observed. This is TiN generated from homogenization.
Ti precipitated unevenly on the particle and TiO□ particle surface
This is thought to be due to N, and it was found that uniform coating treatment was difficult in a normal pressure fluidized bed.

(Effects of the Invention) The method of the present invention makes it possible to easily and efficiently perform surface treatment (coating, modification) that is homogeneous over the entire surface of each fine particle, has no unevenness between particles, and is free from contamination with impurities.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing the procedure for coating and surface treating fine particles by thermochemical reaction in a fluidized state under reduced pressure according to the present invention. 1...Fluidized bed 3...Vacuum pump 5...Heating furnace

Claims (1)

[Claims] 1. A method for coating and surface treatment of fine particles, which comprises performing a thermochemical reaction treatment while fluidizing the fine particles under reduced pressure.