JP2000044843A - Coating material and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a coating material for graphite by which a zirconia powder or a yttria powder is coated so as to reduce the reactivity of the graphite when a molten metal has reactivity with the graphite or the graphite is used in a high-temperature oxidizing atmosphere, etc. SOLUTION: A yttria powder or a zirconia powder is used as a coating powder. The particle diameter range of fine particulate coating powder is 0.1-1.0 μm and the particle diameter range of small particulate coating powder is 1-10 μm. The particle diameter range of medium particulate coating powder is 10-40 μm and the mixing ratio of the respective powders is (10/20/70)-(30/40/30) wt.%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a ceramic (zirconia powder) for reducing the reactivity of graphite when the molten metal has a reactivity with graphite or when graphite is used in a high-temperature oxidizing atmosphere. Or yttria powder) and a method for producing the same.

[0002]

2. Description of the Related Art Graphite coating methods are used for various melting and casting processes, film forming processes on the premise of dissolving metals such as vacuum deposition, and heat-resistant members used in the atmosphere. is there.

[0003] In order to increase the corrosion resistance of graphite to molten metal, the method of coating the surface thereof with ceramics such as silicon carbide (SiC) includes a spraying method, a method of mixing an inorganic or organic binder and ceramic powder. Some are applied to the surface of graphite.

FIG. 4 shows a state in which a ceramic coating is formed on the surface of graphite by thermal spraying. As shown in the figure, a ceramic film such as silicon carbide (SiC) is sprayed on the surface of a graphite 12 having a large number of pores 11 to form a ceramic coating 13 on the surface of the graphite 12.

In addition to the above-described method, CVD (Chem
ical vapor deposition) method or CVR (Chemical
Some are coated by the Vapor Reaction) method.

[0006]

By the way, graphite is generally a material having releasability and has a property that ceramics hardly penetrate between graphite pores. Therefore, in the coating method by thermal spraying described above, the ceramics do not sufficiently penetrate into the pores 11 of the graphite 12, and the adhesion at the interface 14 between the surface of the graphite 12 and the ceramic coating 13 is low. Very weak. Therefore, when the graphite 12 having the ceramic coating 13 formed on the surface by thermal spraying is used, there is a problem that the graphite 12 and the ceramic coating 13 are thermally expanded or peeled off by cooling as the temperature is increased.

[0007] This is also apparent from a so-called tape peeling test. That is, this tape peeling test is a test for attaching a tape to the surface of the ceramic film 13 formed on the graphite 12 and checking whether the ceramic film 13 is peeled off from the graphite 12 together with the tape by the peeling operation. The graphite 1 on which the ceramic coating 13 is formed by the above-mentioned thermal spraying
In the case of No. 2, the ceramic coating 13 is easily peeled off by the tape peeling test, which is a problem.

On the other hand, the coating method using the CVD method or the like directly modifies the surface of graphite to form a ceramic film such as silicon carbide. However, in the CVD method, the film growth rate is low. In addition, there is a problem that the cost is high.

As described above, it is not easy to firmly adhere a ceramic material to the surface of a graphite component, and at present, no method has been established.

The present invention has been made to solve the above problems, and provides a coating material for graphite capable of forming a hard zirconia coating or a yttria coating which is inexpensive and excellent in heat resistance, and a method for producing the same. That is the task.

[0011]

A first coating material of the present invention for solving the above-mentioned problems comprises a coating powder of fine powder and small and medium coating powder obtained by grinding coarse particles. It is characterized by being blended.

In the second coating material of the present invention, the particle size range of the fine-particle coating powder is 0.1 to 1.0 μm, the particle size range of the small-particle coating powder is 1 to 10 μm, and The particle size range of the powder is 10 to 40 μm, and the respective mixing ratios are 10/20/70 to 30/4.
0/30% by weight.

A third coating material of the present invention is characterized in that, in the first or second coating material, the coating powder is zirconia powder or yttria powder.

On the other hand, the first method for producing a coating material according to the present invention is characterized in that fine zirconia powder is preliminarily dispersed using a dispersant and a dispersion medium, and then small and medium zirconia powders are mixed. And

A second method for producing a coating material according to the present invention is characterized in that fine yttria powder is preliminarily dispersed using a dispersant and a dispersion medium, and then small and medium yttria powders are mixed. .

[0016]

Embodiments of the present invention will be described below in detail.

The first coating material of the present invention is obtained by blending a coating powder of fine powder with small and medium coating powder obtained by grinding coarse particles. Is zirconia powder (zirconium oxide), yttria powder (zirconium oxide)
For example, a material suitable for coating the surface of graphite.

Hereinafter, the contents of the present invention will be described using zirconia powder as an example of a coating material.

The coating material comprising zirconia powder as a main component of the present invention forms a densely packed structure of particles by adding fine zirconia powder to coarse zirconia powder, thereby providing a dense coating having high adhesion strength. Material. Here, the coarse zirconia powder in the present invention refers to a powder having a mean particle size of 50 μm (10 to 80 μm) as a raw material. The average particle size of the coating powder is 10 to 40 μm. In the present invention, the medium zirconia powder is set to 10 to 40 μm,
This is because if the particle size is too large to exceed 40 μm, it is too coarse to be practical. Further, the fine zirconia powder has a thickness of 0.1 to 1.0 μm, but if it is less than 0.1 μm, it cannot be practically used, which is not preferable.
In the present invention, the small-grain zirconia powder has a particle size range of about 1.0 to 10 μm between the fine grains and the medium grains, but is not limited to this range. As described above, the finely packed structure at the time of filling can be optimized by combining zirconia powder having a particle size in a predetermined range with a predetermined combination.

The mixing ratio of the coating material of the present invention is as follows:
As will be shown in the examples below, 10-30% by weight of fine-grained coating powder (0.1-1.0 μm), 20-40% by weight of small-sized coating powder (1-10 μm) and medium 70 to 3 particles of coated powder (10 to 40 μm)
It is preferably 0% by weight. This is because, if it exceeds the above range, the zirconia film coated on the graphite is likely to peel off.

Further, in order to form the above-mentioned zirconia powder densely packed structure, it is necessary to pay attention to the formulation of zirconia which is a fine powder. That is, zirconia, which is a fine powder, is an aggregated powder that is usually supplied as a dry product, and therefore, the target characteristics cannot be obtained by using such an aggregated powder as it is. That is, since the particles for coating are generally supplied as dry powder, it is necessary to make the supplied dry powder into a slurry suitable for coating. In particular, since the fine particles are supplied as a dry powder with strong agglomeration, an operation for separating the agglomeration is required. If such an operation is not performed, the fine particles also act as agglomerated particles, so that they act in a large state as particles, and as a result, a densely packed structure cannot be formed.

Therefore, in the present invention, fine zirconia fine particles are added to the base zirconia coarse particles from the viewpoint of fine packing, so that fine packing can be performed. At this time, the fine zirconia fine particles are sufficiently dispersed, and the small and medium zirconia powder obtained by dividing the coarse particles into the slurry processed to a shape close to the primary particles is added to obtain a high solid content and filling property. A high slurry is preferred. The primary particles are the minimum units of the size of the particles constituting the primary particles. Normally small particles (submicron)
Is usually secondary aggregated, and this is used as primary particles by a dispersion treatment. The high solids concentration refers to a solid having a high solids concentration such as a solid concentration of 40 mol% or more in the slurry.

As described above, by combining particles having different particle size ranges of fine powder, small particles, and medium particles,
Small particles enter the gaps between the medium-sized particles in the relatively large particle size range, and the fine particles enter the gaps between the small particles, thereby forming a coating having a close-packed structure.

Here, the selection of the solvent and the dispersant for forming the slurry is important, and the order of mixing the powders is important.

First, fine particles are sufficiently dispersed in a dispersant and a solvent using a ball mill or another dispersing method such as an attritor, and then small and medium powders are added. Viscosity suitable for

The coating slurry thus treated enters into small pores on the graphite surface and generates an anchor effect to increase the bonding force. At the same time, the particles are finely packed at the same time as the drying, so that the drying shrinkage and the heat treatment shrinkage are extremely low. Become smaller.

After drying, although the coated body has a strong binding force, particles may be peeled off when water or the like adheres. For this reason, by performing heat treatment at a temperature of 1000 to 1200 ° C. for several hours, the fine particles are strongly sintered, the above-described peeling is prevented, and the bonding portion has a strong adhesive force.

In order to obtain a high solid content, a combination of a powder and a dispersion medium is important. For example, when water is used as the dispersion medium, as the dispersant, for example, polycarboxylic acid, polyacrylic acid, or the like can be used.

When the slurry has a high solid content, bubbles enter during mixing of the slurry and are fixed in such a state that they do not come out. Therefore, it is desirable to perform a vacuum defoaming treatment before use.

The coating material thus obtained is
After being applied to the joint, it is dried to have a strong adhesive force.

[0031]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of the present invention;

As zirconia, 8 wt% yttria stabilized zirconia (YSZ) raw powder was used. The thermal expansion coefficient of this yttria-stabilized zirconia is 10.9 × 1
0 ^-6 ° C ^-1 . The average particle size of the coarse particles of the raw powder is 50 μm
Medium to large (10 μm to 80 μm)
This is pulverized and sieved to obtain medium-grain (10 μm to 4 μm).
0 μm) and small particles (1 to 10 μm). On the other hand, the separately added yttria fine powder has a specific surface area of 10 m ² / g.
(Average particle size: 0.5 μm), but it is a dry powder, so it is strongly agglomerated.

Here, the difference in the presence or absence of a dispersant was examined for 40% by weight of medium-sized yttria, 40% by weight of small-sized yttria, and 20% by weight of fine-grained yttria. In order to confirm the difference due to the presence or absence of water as a dispersion medium and a dispersant in a ball mill, the slurry slurried under the respective conditions was solidified, dried, and then finely divided into fine particles and fine particles using a mercury intrusion device (porosimeter). The pore volume was measured. At this time, ammonia polycarboxylate was used as a dispersant.

FIG. 1 shows comparative data of pores. As shown in FIG. 1, the properties of the porous body obtained by the presence or absence of a dispersant,
That is, it was confirmed that the average diameter and the pore volume greatly changed. From this, it has been found that in order to reduce the average pore diameter and the pore volume, it is necessary to carry out fine packing of the powder, and for that purpose, the dispersion conditions are important.

[0035] Such a porous body is formed to have a diameter of 20 mm and a thickness of 5 mm.
It was processed into a disk having a diameter of 2 mm, and the gas permeation rate was measured. The gas type was air, and the amount of permeation was measured with a differential pressure applied to both sides. FIG. 2 shows the result of the measurement.

In FIG. 2, the horizontal axis represents the differential pressure, and the vertical axis represents the permeation flow rate. From the results of FIG. 2, it can be seen that when the dispersant was used, 1 / compared to the case where the dispersant was not used.
It was found that the transmission was suppressed to about 20. A good coating material preferably has a small pore diameter and a small pore volume.

Next, the composition of the fine, small, and medium zirconia powders was changed in 10% increments, the coating material was adjusted, and the coating was applied to a graphite substrate (5 cm square). A tape peeling test was performed on the test article that was heat-treated at 1100 ° C. for 2 hours in an argon gas atmosphere. Similarly, by changing the composition of the fine, small, and medium yttria powder in 10% increments, the coating material was adjusted, and the graphite substrate (5c
m square), air-dry and apply at 1100 ° C for 2
A tape peeling test was performed on the test article that was heat-treated in an argon gas atmosphere for a time. FIG. 3 shows a region where the coating does not peel off even when the tape peeling test is performed. In FIG. 3, fine, small, and medium
0, and the height from each base is 10
It is set to 0. Therefore, the sum at each point is 100.

In FIG. 3, the shaded portions are portions that are not peeled off even when a tape peeling test is performed.

Thus, as shown in FIG. 3, medium grains (particle diameter 10 μm to 40 μm) and small grains (particle diameter 1 μm to 10 μm)
m) 8% by weight yttria-stabilized zirconia powder and particle size
The mixing ratio of fine zirconia powder of 0.1 to 1.0 μm (1
(0/20/70 to 30/40/30%), a coating material having a finely packed structure of powder could be obtained. In addition, medium grain (particle size 1
0 μm to 40 μm) and small particles (particle diameter 1 μm to 10 μm) and fine particle yttria powder having a particle diameter of 0.1 to 1.0 μm (10/20/70 to 30/40/3)
0%), a coating material having a finely packed structure of powder could be obtained.

[0040]

As described above, according to the present invention, according to the present invention, the particles in the coating film are formed by combining the coating powders such as fine, small and medium zirconia powders and yttria powders. Is achieved, and the strength and adhesion of the film are improved. In addition, the effect is further enhanced by finely dispersing the fine particles.

[Brief description of the drawings]

FIG. 1 is a characteristic diagram showing the relationship between the presence or absence of a dispersant and the average pore diameter and pore volume.

FIG. 2 is a characteristic diagram showing a relationship between a permeation flow rate and a difference thickness in the presence or absence of a dispersant.

FIG. 3 is a diagram showing the mixing ratio of medium, small, and fine particles and the results of a tape peeling test.

FIG. 4 is a diagram showing a state in which a ceramic coating is formed on the surface of graphite by a thermal spraying method.

[Explanation of symbols]

 11 Pores 12 Graphite 13 Ceramic coating

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Takashi Shige 2-1-1 Shinhama, Arai-machi, Takasago City, Hyogo Prefecture Inside the Takasago Research Laboratory, Mitsubishi Heavy Industries, Ltd. No. 1-1, Mitsubishi Heavy Industries, Ltd. Kobe Shipyard F term (reference) 4J038 HA216 MA14 PC01

Claims (5)

[Claims] 1. A coating material comprising a mixture of a fine powder coating powder and small and medium coating powder obtained by pulverizing coarse particles. 2. The particle size range of the fine-grained coating powder is
0.1 to 1.0 μm, the particle size range of the small-sized coating powder is 1 to 10 μm, and the particle size range of the medium-sized coating powder is 10 to 40 μm, and the mixing ratio of each is 10/2.
0/70 to 30/40/30% by weight. 3. The coating material according to claim 1, wherein the coating powder is zirconia powder or yttria powder. 4. A method for producing a coating material, comprising: dispersing a fine zirconia powder in advance using a dispersant and a dispersion medium; and mixing small and medium zirconia powder. 5. A method for producing a coating material, comprising: dispersing fine yttria powder in advance using a dispersant and a dispersion medium; and mixing small and medium yttria powder.