JP2008056948A - Pretreatment method for ceramic fine particle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pretreatment method for producing a fine particle which is easily refined when having collided with a substrate, by forming cracks in the fine particle without using a mechanical technique. <P>SOLUTION: The pretreatment method is applied to the ceramic fine particle that is used for forming a film on the substrate by using an AD method of dispersing the ceramic fine particles in a gas to form an aerosol, and jetting and colliding the aerosol against the substrate. The method includes applying thermal shock to the ceramic fine particles before forming the aerosol. The thermal shock is given by holding the ceramic fine particles at 500 to 1,100°C for 10 minutes or longer and then quenching them. The ceramic fine particle is a fine particle particularly of alumina. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a ceramic fine particle pretreatment method for forming a ceramic coating by dispersing ceramic fine particles in a gas by an aerosol deposition method (hereinafter referred to as AD method) and causing the aerosol to collide with a substrate.

As a method for forming a film on a substrate, there is a method for forming a film or structure of a brittle material called a fine particle beam deposition method or an AD method. In the AD method, an aerosol containing fine particles of a brittle material such as ceramics is ejected from a nozzle toward a base material, the fine particle collides with the base material, and the mechanical impact force is used to make a polycrystalline structure of the brittle material Is formed directly on the substrate. The fine particles that collide with the base material are refined to generate a new surface, and since the activity of the new surface is high, deposition proceeds and a polycrystalline structure such as a dense film is formed.
It is preferable to give cracks or the like to the fine particles so that the fine particles can be easily made fine at the time of collision with the substrate. As a pretreatment method for imparting cracks to fine particles, for example, there is a method of mechanically cracking with a ball mill, a jet mill or the like. Conventionally, a method of providing a classifying device and a crushing device as an AD method (see Patent Document 1) and the like have been disclosed.

However, in the actual production technique, there is a problem that the film forming speed is slow in the method of mechanically cracking. When a ball mill is used, a drying process is necessary because of wet mixing, but since it easily aggregates during drying, cracked primary particles cannot be easily obtained. Moreover, when using a jet mill, although it collects with a bag filter, since the fine powder deposited on the filter has aggregated, a primary particle cannot be obtained easily.
Therefore, there is a demand for a pretreatment method in which particles are cracked without using a mechanical method, and particles that can be easily refined at the time of collision are produced.
JP 2001-181859 A

  The present invention has been made to cope with such a problem, and an object of the present invention is to provide a pretreatment method for producing fine particles that are easy to be miniaturized at the time of collision by generating cracks in the fine particles without using a mechanical method. And

The ceramic fine particle pretreatment method of the present invention is the above-mentioned ceramic used for film formation by the AD method in which ceramic fine particles are dispersed in a gas to form an aerosol, and the aerosol is sprayed onto a substrate to collide with the film. A pretreatment method for fine particles, wherein the pretreatment method is a method in which a thermal shock is applied to the ceramic fine particles before the aerosolization.
The thermal shock is characterized in that the ceramic fine particles are held at 500 ° C. to 1100 ° C. for 10 minutes or more and then rapidly cooled.

The ceramic fine particles are alumina fine particles. The average particle size of the ceramic fine particles is 0.1 μm to 2 μm.
The gas is an inert gas containing argon, nitrogen, or helium.

The pretreatment method for ceramic fine particles according to the present invention is a method in which thermal shock is applied to the ceramic fine particles of the aerosol raw material used in the AD method, so that mechanical interparticle contact such as mixing and deposition does not occur. Aggregation of fine particles can be prevented, and cracks and stress strain due to thermal shock can be applied to the surface and inside of the fine particles. As a result, it becomes easy to miniaturize at the time of collision with the base material, and the film forming efficiency is improved.
In particular, by using alumina fine particles as ceramic fine particles and holding them at 500 ° C to 1100 ° C for 10 minutes or more as a thermal shock and then performing a rapid cooling treatment, cracks and stress strains due to thermal expansion and rapid thermal shrinkage are reduced. It can be given to alumina fine particles.

The ceramic fine particle pretreatment method of the present invention is a ceramic fine particle used for film formation by the AD method in which ceramic fine particles are dispersed in a gas to form an aerosol, and the aerosol is sprayed onto a substrate to collide with the film. (In particular, a thermal expansion coefficient of about 7.5 × 10 ⁻⁶ / ° C. and a melting point of about 1300 ° C.), which is a method of applying thermal shock to ceramic fine particles before aerosolization.
This thermal shock is a process of rapidly cooling after holding at 500 ° C. to 1100 ° C. for 10 minutes or more. In order to apply a thermal shock to the ceramic fine particles, the ceramic fine particles are put into a crucible or tray made of aluminum titanate that is resistant to thermal shock, and then left in an electric furnace at a temperature of 500 ° C. to 1100 ° C. for a certain period of time.
After leaving the crucible or tray out of the electric furnace, the ceramic fine particles can be given cracks and stress strain due to thermal shrinkage by rapid cooling. When it is less than 500 ° C., cracks and stress strains are slight, and when it exceeds 1100 ° C., particles are partially welded, which is not preferable. Even if it is 500 ° C to 1100 ° C, if it is less than 10 minutes, cracks and stress strains are minor and do not contribute to the improvement of film formation efficiency.

As a method for rapid cooling, there are methods such as (1) applying cold air to a crucible and tray containing ceramic fine particles subjected to predetermined heat treatment, (2) immersing in cooling water, and (3) placing in a low temperature bath. .
In the case of a normal crucible (alumina, zirconia, carbon), it breaks when quenched, but the crucible made of aluminum titanate is excellent in thermal shock resistance, so it does not break. As a commercially available aluminum titanate crucible, for example, a record manufactured by Aucera Corporation can be used.

The ceramic fine particles to be subjected to the pretreatment method of the present invention are arbitrary ceramic fine particles that are used as an aerosol raw material. Examples of such ceramic fine particles include oxides such as alumina, zirconia, and titania, and fine particles such as silicon carbide and silicon nitride. In the high-purity grades of the respective ceramics, it is preferable to use alumina fine particles because the one with a smaller true specific gravity is more easily aerosolized.
In addition to ceramic fine particles, the same effect can be obtained by carrying out the pretreatment of the present invention on fine particles of brittle materials having strong cleavage properties such as silicon and germanium.

  The AD method can realize bonding between fine particles at room temperature, and does not cause deterioration of physical properties due to transformation of raw material ceramics due to exposure to high temperature. For example, even if α-alumina with excellent insulating properties is used, the thermal spraying method transforms to γ-alumina and lowers the insulating properties. Therefore, it is necessary to increase the film thickness. Since the film can be formed with high α alumina, a ceramic layer having high insulation can be obtained without increasing the film thickness.

  The average particle size of the ceramic fine particles to be subjected to the pretreatment method of the present invention is preferably 0.1 μm to 2 μm. If it is less than 0.1 μm, it is easy to agglomerate and aerosolization is difficult, and if it exceeds 2 μm, film formation by AD method cannot be performed (film growth does not occur). In the present invention, the average particle diameter is a value measured by Nikkiso Co., Ltd .: Laser type particle size analyzer Microtrac MT3000.

A film forming method using ceramic fine particles treated by the pretreatment method of the present invention as an aerosol raw material will be described with reference to FIG. FIG. 1 is a view showing a film forming apparatus in the case of forming a ceramic film on the outer diameter surface of a bearing outer ring as a base material by the AD method.
As shown in FIG. 1, a ceramic film forming apparatus 1 using an AD method includes a vacuum chamber 2 and an aerosol generator 8. In the vacuum chamber 2, an outer ring 4 that is a base material on which a ceramic film is to be formed and an aerosol injection nozzle 9 are disposed. The inside of the vacuum chamber 2 is depressurized by the vacuum pump 3. In order to prevent mixing of ceramic fine particles, a fine particle filter 10 is provided immediately before the vacuum pump 3.
The aerosol injection nozzle 9 injects ceramic fine particles from the tip of a nozzle having an opening such as a rectangle onto the outer ring 4 that is a base material. In addition, the aerosol injection nozzle 9 may be one or plural. The aerosol injection nozzle 9 may be configured to be displaceable in the vacuum chamber 2.

In the aerosol generator 8, ceramic fine particles subjected to thermal shock by the pretreatment method of the present invention are put, and a carrier gas is supplied from the gas supply facility 7 to the aerosol generator 8, and the ceramic fine particles and the carrier gas are included. Form an aerosol. Usable carrier gases include inert gases such as argon, nitrogen and helium.
The aerosol is supplied from the aerosol generator 8 to the aerosol injection nozzle 9. The aerosol is sprayed from the fixed aerosol injection nozzle 9 onto the outer ring 4 rotating at a predetermined number of revolutions (A in the figure) by the object rotating motor 6, and a ceramic film is applied to the outer diameter surface of the outer ring 4. Overlapped and formed. At the same time, the outer ring 4 is moved in the axial direction by the positioning XY table 5 (B in the figure), so that a film is uniformly formed in the XY direction of the outer ring 4.
Here, since the raw material ceramic fine particles are preliminarily subjected to thermal shock before being aerosolized and are given minute cracks and stress strains, they are easily miniaturized at the time of collision with the outer ring 4 which is the base material. A film can be easily formed on a curved surface such as the above.

Example 1
Put 100 g of alumina fine particles (manufactured by Sumitomo Chemical Co., Ltd .: trade name AKP-50, average particle size 0.2 μm, coefficient of thermal expansion 7.5 × 10 ⁻⁶ / ° C.) in a crucible (manufactured by OSELA: Recogit) and 500 in a thermostatic chamber. After maintaining at 10 ° C. for 10 minutes, a pretreatment was performed by applying cold air to rapidly cool to room temperature (20 ° C.). The pretreated fine particles are put in the aerosol generator shown in Fig. 1, and alumina fine particles are deposited by AD method on the surface of a bearing steel SUJ2 test substrate (length 30 mm x width 30 mm, thickness 3 mm) mounted in a vacuum chamber. Using, a ceramic coating was formed for 5 minutes.
The AD method uses a positioning XY table to inject an aerosol of alumina fine particles through a nozzle with an opening size of 10 mm x 0.3 mm under a reduced pressure of 100 Pa or less onto a test substrate moving at 6 mm / min. A film of × 10 mm was formed. Nitrogen gas was used as the carrier gas, and the particle velocity was controlled by the carrier gas flow rate.
The film thickness of the obtained film was measured and the film forming conditions were evaluated. The results are shown in Table 1. The film formation rate (μm · cm / min) means the thickness (μm) of the film formed per scan distance of 1 cm per minute. The film thickness was measured using a contact-type surface shape measuring instrument (manufactured by Nippon Vacuum Technology Co., Ltd .: Decak3030).

Example 2
The same procedure as in Example 1 was carried out except that the alumina fine particles held at 700 ° C. for 10 minutes in Example 1 were subjected to a pretreatment that was immersed in cooling water and rapidly cooled to room temperature instead of applying cold air. The film thickness of the film was measured and the film forming conditions were evaluated. The results are also shown in Table 1.

Example 3
The coating film obtained in the same manner as in Example 1 except that the alumina fine particles held at 1100 ° C. for 10 minutes in Example 1 were subjected to a pretreatment in which they were placed in a low temperature bath and rapidly cooled to room temperature instead of applying cold air. The film thickness was measured and the film forming conditions were evaluated. The results are also shown in Table 1.

Comparative Example 1
A coating was formed in the same manner as in Example 1 except that the pretreatment for applying thermal shock to the alumina fine particles in Example 1 was not performed.
The film thickness of the obtained film was measured and the film forming conditions were evaluated. The results are also shown in Table 1.

表１に示すように各実施例から良好な成膜条件はアルミナ微粒子に施す前処理条件が 500℃〜1100℃に 10分間以上保持した後、急冷する処理であればよいことがわかる。

As shown in Table 1, it can be seen from each example that favorable film forming conditions may be those in which the pretreatment conditions applied to the alumina fine particles are kept at 500 ° C. to 1100 ° C. for 10 minutes or more and then rapidly cooled.

  Since the pretreatment method of the present invention is a process of applying a thermal shock to the ceramic fine particles, mechanical inter-particle contact such as mixing and deposition does not occur, so that mechanical ceramic fine particle aggregation can be prevented and the surface of the fine particles can be prevented. In addition, cracks and stress strain can be imparted to the inside. As a result, it becomes easy to miniaturize at the time of collision with the base material, and the film forming efficiency is improved. Therefore, mass productivity is improved, and it can be suitably used when forming a ceramic coating on various members required for heat and abrasion resistance, durability, corrosion resistance and insulation resistance used in various industrial machines.

It is a figure which shows the ceramic film formation apparatus by AD method

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Ceramic film formation apparatus 2 Vacuum chamber 3 Vacuum pump 4 Outer ring 5 XY table for positioning 6 Motor for object rotation 7 Gas supply equipment 8 Aerosol generator 9 Aerosol injection nozzle 10 Fine particle filter

Claims (5)

A method for pretreating ceramic fine particles used for film formation by an aerosol deposition method in which ceramic fine particles are dispersed in a gas to be aerosolized, and the aerosol is sprayed onto a substrate to collide with the film.
The pretreatment method for ceramic fine particles is a method in which a thermal shock is applied to the ceramic fine particles before the aerosolization.   2. The pretreatment method of ceramic fine particles according to claim 1, wherein the thermal shock is a treatment in which the ceramic fine particles are held at 500 ° C. to 1100 ° C. for 10 minutes or more and then rapidly cooled.   3. The pretreatment method for ceramic fine particles according to claim 1, wherein the ceramic fine particles are alumina fine particles.   4. The pretreatment method for ceramic fine particles according to claim 1, wherein the average particle size of the ceramic fine particles is 0.1 to 2 [mu] m.   The pretreatment method for ceramic fine particles according to any one of claims 1 to 4, wherein the gas is an inert gas containing argon, nitrogen, or helium.

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