JP3262713B2 - Ceramic coating method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic coating method for forming a ceramic film on a substrate, and more particularly to a ceramic coating method considering heat resistance and corrosion resistance to a high-temperature corrosive atmosphere.

[0002]

BACKGROUND OF THE INVENTION Generally, ceramics are thermally and chemically stable at high temperatures. Therefore, it is a material that may be used in place of a metal material as a material used in a high-temperature environment or a highly corrosive environment. However, due to the limitations on the dimensions that can be manufactured, the difficulty in machining, etc., and the fragility, it is not necessary to use ceramics alone. And heat resistance have been conventionally improved. Methods for coating ceramics on various materials include plasma spraying and C
Although there are methods such as VD and PVD, all of these methods have limitations on the size and shape that can be coated and have problems such as an increase in cost.

Therefore, in recent years, a silica coating of a carbon material by a sol-gel method (Osamu Yamamoto, Journal of the Chemical Society of Japan, No. 9, pp1096)
991099 (1993); hereinafter referred to as the first prior art), the protective properties of alumina coating prepared by sol-gel method on 316 stainless steel (Ying Wang, Materials and Environment, No. 42 pp. 158-165)
(1993); hereinafter, referred to as a second prior art), a titanium nitride coating of graphite material using a sol-gel method (Kanichi Kamiya,
As described in carbon, No. 146, pp. 15-21 (1991); hereinafter, referred to as a third conventional technology), ceramic coating by a sol-gel method has been performed.

The sol-gel method described in the first to third prior arts starts from a solution of an alkoxide or the like, and is obtained by hydrolysis or polymerization of a compound in the solution.
This is a method of obtaining glass or ceramics by heating at several hundred degrees Celsius or hundreds of thousands of degrees Celsius after bonding metal-oxygen-metal-oxygen- or -metal-organic molecule-metal-organic molecule-. It is possible to apply a coating to the substrate.

[0005]

However, the ceramic coating formed by the sol-gel method as described above is a thin film having a thickness of at most about 1 μm, and is a corrosion-resistant coating to be used assuming a certain thickness reduction. It was difficult to use. Further, since the ceramic coating is a dense coating, there is a weak point that cracks and peeling are likely to occur due to thermal shock and thermal stress. Therefore, it is considered that the ceramic coating by the conventional sol-gel method is not optimal for materials used in a high temperature environment or a highly corrosive environment.

An object of the present invention is to provide a ceramic coating method capable of forming a ceramic film having excellent heat resistance and corrosion resistance on a substrate surface even in a high temperature environment or a highly corrosive environment.

[0007]

According to the present invention, there is provided a ceramic coating method for forming a ceramic film on a substrate, comprising adding an oxide ceramic powder to a silicon alkoxide containing an oxide sol. A coating solution is prepared by applying the coating solution to a surface of a graphite substrate, dried, and fired in the air to form a ceramic coating.

In the process of forming a ceramic film according to the present invention having the above-described structure, a silicon alkoxide containing an oxide sol is applied as a coating solution to the surface of a graphite substrate,
It utilizes a sol-gel reaction by firing after drying, and forms a knitted structure of silicon dioxide (hereinafter appropriately referred to as SiO ₂ ) derived from silicon alkoxide and oxide ceramic derived from oxide sol. You.
Then, when such a stitch structure is formed, the oxide ceramic powder added to the coating solution is taken into the stitch. As a result, it is possible to obtain a ceramic film having a thickness of several tens to 200 μm as compared with the conventional sol-gel method in which only a ceramic film having a thickness of at most about 1 μm can be formed. By increasing the thickness of the ceramic coating, a margin for corrosion and thinning of the coating is increased, and the corrosion resistance is improved. In addition, since the ceramic coating formed by adding the oxide ceramic powder to the coating liquid becomes porous, thermal stress and thermal shock inside the coating are easily relieved, cracking and peeling are less likely to occur, and heat resistance is reduced. The performance is improved. However, at the time of firing, silicon alkoxide in the coating solution is converted to SiO ₂ by a sol-gel reaction.
It is necessary to perform the calcination in the atmosphere in order to change to

At the interface between the ceramic coating and the graphite substrate as described above, a chemical bond obtained by a reaction between hydroxyl groups on the graphite surface and SiO ₂ or oxide ceramics having a knitted structure is formed. In addition, the coating adheres due to mechanical bonding obtained as a result of the application liquid penetrating into pores and irregularities in the graphite substrate.

As the oxide ceramic powder, for example, alumina (hereinafter, appropriately referred to as Al ₂ O ₃ ) or oxide of yttrium (hereinafter, appropriately referred to as yttria or Y ₂ O ₃ ) is used. As the material sol, for example, alumina sol (hereinafter, appropriately referred to as Al ₂ O ₃ sol) is used, and as the silicon alkoxide, for example, tetramethoxysilane (Si (OCH ₃ ) ₄ ) is used.
The most preferred composition of the coating solution is tetramethoxysilane
The solution containing 30 wt% of alumina sol and 50 wt% of alumina powder in a solution containing 14 wt% of ethanol and 14 wt% of ethanol. In particular, if the addition amount of the oxide ceramic powder is increased beyond the above, the viscosity of the coating liquid increases, and the coating liquid becomes unsuitable for application. Cannot be obtained. It is also possible to use oxide ceramic powder other than the above, oxide sol other than the above, and silicon alkoxide other than the above.

The particle diameter of the oxide ceramic powder is preferably 10 to 44 μm. This is because the addition of the oxide ceramic powder having the above-mentioned particle diameter makes the ceramic coating porous, and it is easy to reduce thermal stress and thermal shock inside the coating, thereby improving heat resistance. When the particle size is smaller than the above and is about several μm or less, the ceramic film becomes dense, so that thermal stress and thermal shock cannot be relaxed inside the film and the heat resistance is reduced, for example, about 1 hour in a vacuum at 1000 ° C. The coating cracks when heated. Conversely, when the particle size is larger than the above, it becomes difficult for the oxide ceramic powder to be taken into the stitch structure as described above,
Handling as powder becomes difficult.

When firing in the atmosphere, 400
It is preferable to fire at a temperature of up to 450 ° C., at which time the adhesion of the ceramic film is maximized. At a temperature higher than the above, the graphite base material reacts with oxygen in the large air, and the thickness reduction and weight reduction of graphite become remarkable. Further, if the temperature is lower than the above, sintering becomes insufficient, and a ceramic film having desired properties cannot be obtained.

Preferably, the graphite substrate is immersed in the coating solution to apply the coating solution to the surface of the graphite substrate. As described above, when the coating liquid is applied to the surface of the graphite base, it is easy to immerse the graphite base in the coating liquid, use a brush, or spray the coating liquid onto the graphite base by spraying. Is preferred. In addition, when the viscosity of the coating liquid is large, the use of a brush tends to cause unevenness, so that the method of dipping or spraying is more preferable.

Before applying the coating liquid, preferably, the surface of the graphite base material is roughened in advance by a roughening means. As a result, the mechanical bonding force at the interface between the graphite substrate and the ceramic film increases, and the chemical bonding force increases by increasing the effective surface area of the substrate.
Therefore, it is possible to increase the adhesion of the ceramic film.

Further, in the above description, the coating liquid is applied to the surface of the graphite substrate, but the same coating liquid may be applied to the surface of a metal substrate or another ceramic substrate, and the same firing may be performed. Good.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of a ceramic coating method according to the present invention will be described with reference to FIGS.

FIG. 1 schematically shows the formation and adhesion mechanism of a ceramic film by the ceramic coating method of the present embodiment, and FIG. 2 shows a flowchart of the operation. First, as shown in step S1 of FIG. 2, tetramethoxysilane, ethanol, Al ₂ O ₃ sol (particle diameter 50 μm)
m), Al ₂ O ₃ ceramic powder (particle size: 10-44 μm)
m) is 6 wt%, 14 wt%, 30 wt%, 5
The mixture was mixed and adjusted to be 0 wt% to prepare a coating solution. Note that another alcohol may be used instead of ethanol.

Next, as shown in step S2 of FIG.
The surface of the graphite substrate to be coated was blasted at a pressure of ² kg / cm ² for several seconds using Al ₂ O ₃ ceramic powder having a particle size of 250 μm to roughen the surface. As a graphite substrate (test piece), a graphite plate having a size of 50 mm square and a thickness of 0.5 mm was used. Next, in step S3, the coating liquid adjusted as in step S1 was applied to the surface of the graphite substrate. The coating method at this time is shown in FIG.

As shown in FIG. 3, the graphite base 1 is attached to a moving mechanism 3 for moving the graphite base 1 in a vertical direction, and the graphite base 1 is immersed in a coating solution 4 contained in a container 2. The immersion time is about several seconds, and the coating liquid 4 is applied to the surface of the graphite substrate 1 by quickly pulling it up. According to this method, a large substrate having a size of about several meters can be easily and quickly coated with a uniform film thickness. Further, when the viscosity of the coating liquid 4 is large and it is difficult to apply the coating liquid 4, it is also possible to increase the ratio of alcohol to about 20% to reduce the viscosity. Further, the shadowed portion cannot be coated by plasma spraying or the like, but according to this method, even a substrate having a complicated shape can be easily coated by utilizing the fluidity of the coating solution.

Next, in step S4, the graphite substrate coated with the coating solution as described above is washed at room temperature (in air) for about 15 minutes.
After drying for an hour, it was further dried at 50 ° C. for 0.5 hour. In the meantime, hydrolysis and polycondensation occur in the coating solution, and hydrogen gas (H ₂ ), oxygen gas (O ₂ ), alkyl hydroxide (R′O
H), etc., and the coating liquid gradually changes from a sol to a gel. FIG. 1 shows tetramethoxysilane and Al ₂ O ₃
FIG. 1 shows a structural diagram of the sol. The structural diagram of tetramethoxysilane shown in FIG. 1 shows a structure in which a hydroxyl group (OH ⁻ ) is added by hydrolysis. In FIG. 1, R,
R ', R "represents an alkyl group _{(C n H 2n + 1)} .

Further, in step S5, at 450 ° C.
For 1 hour. As a result, the hydrogen gas (H ₂ ), the hydrocarbon (C _n H _m ) and the like fly off, and a ceramic film is formed on the surface of the graphite substrate. The state of the coating at this time is as schematically shown in FIG. 1, and a stitch structure of SiO ₂ derived from tetramethoxysilane and Al ₂ O ₃ derived from the Al ₂ O ₃ sol is formed, and The Al ₂ O ₃ ceramic powder added to the coating solution is taken into the stitch structure. The thickness of the ceramic film formed as described above is about 100 to 200 μm, and a ceramic film thicker than the conventional sol-gel method can be obtained.

[0022] In the interface between the ceramic coating and the graphite substrate as described above, the hydroxyl group of the graphite surface - obtained by reaction between SiO ₂ and Al ₂ O ₃ became like a stitch structure ^(OH) The coating adheres due to the chemical bonding and the mechanical bonding obtained as a result of the permeation of the coating liquid into the pores and irregularities in the graphite substrate.

In order to evaluate the heat resistance of the ceramic coating, the graphite plate (hereinafter, referred to as a test piece as appropriate) was heated at 1000 ° C. for 1 hour in a vacuum. As a result, no cracking or peeling was observed in the coating. It was found that the composition maintained a healthy state and had good heat resistance.

On the other hand, to evaluate the corrosion resistance of the ceramic film, a graphite plate (test piece) coated in the same manner as above was immersed in a uranium iron alloy at 1000 ° C. in a vacuum for 400 hours. As a result of observing the appearance and cross-section of the graphite plate taken out after immersion, the coating did not show any cracks or peeling, and did not penetrate into the coating of the uranium iron alloy. It was found to have corrosion resistance.

As described above, by increasing the thickness of the ceramic film, the margin for corrosion and thinning of the film is increased, and the corrosion resistance is improved. In addition, since the ceramic coating formed by adding the oxide ceramic powder to the coating liquid becomes porous, thermal stress and thermal shock inside the coating are easily relieved, cracking and peeling are less likely to occur, and heat resistance is reduced. The performance is improved.

Next, in order to evaluate the proportion of the added Al ₂ O ₃ ceramic powder, to prepare a coating liquid having different proportions of Al ₂ O ₃ ceramic powder in the range of 46～60Wt% added to the coating solution, above A test piece was prepared in the same manner as described above, and a heat resistance test of heating at 1000 ° C. for 1 hour in a vacuum was performed. As a result, in the test piece in which the addition amount of the Al ₂ O ₃ ceramic powder was 50 wt%, it was confirmed that the test piece had a sound state without cracking or peeling, and had good heat resistance. Do you get it. When the addition amount of the Al ₂ O ₃ ceramic powder is increased above the above, for example, to 60 wt%, the viscosity of the coating liquid becomes large, and it becomes unsuitable for coating. On the other hand, if it is less than the above, the amount of powder taken into the stitch structure is reduced, and a ceramic film having desired characteristics cannot be obtained. Therefore, it is appropriate to add about 50 wt% of the Al ₂ O ₃ ceramic powder.

Next, Al ₂ O ₃ to assess the particle size of the ceramic powder, Al ₂ O ₃ when the ceramic powder of a particle size as small as 2 [mu] m, and in the case of 10～44Myuemu 2
Various types of coating liquids were prepared, test pieces were prepared in the same manner as described above, and a heat resistance test of heating at 1000 ° C. for 1 hour in vacuum was performed. As a result, when the particle size of the Al ₂ O ₃ ceramic powder to be added is as small as 2 μm,
After firing at 50 ° C., the coating cracked. In addition, a part of the coating was also peeled off by an adhesion evaluation test in which the pressure-sensitive adhesive tape was applied and then peeled off. When the particle size is small as described above, the coating is easily cracked or peeled off, and the ceramic coating becomes dense, so that thermal stress or thermal shock cannot be reduced inside the coating, and the heat resistance is reduced.

On the other hand, when the particle size of the ceramic powder to be added is 10 to 44 μm, which is larger than the above, no cracking or peeling occurs, and a heat resistance test of heating at 1000 ° C. for 1 hour in a vacuum is conducted. Also, the coating showed no cracking or peeling, and showed good heat resistance. This is 10-44
It is considered that the addition of the Al ₂ O ₃ ceramic powder having a thickness of μm made the ceramic coating porous and improved the heat resistance. Conversely, if the particle size is larger than the above, the oxide ceramic powder is less likely to be taken into the above-described stitch structure, and handling as a powder becomes difficult.

Next, in order to evaluate the sintering temperature, test specimens coated with the coating solution and dried in
Firing at various temperatures in the range of 600 ° C. for 1 hour. As a result of measuring the adhesion of the ceramic film of those test pieces,
As shown in FIG. 4, the adhesion of the ceramic film fired at 400 to 450 ° C. was the largest. However, FIG.
The relative value is shown with the adhesion of the fired product being set to 1.
From the above, it turned out that 400-450 degreeC is suitable as a baking temperature. On the other hand, at the temperatures above the above, the graphite substrate reacts with oxygen in the large air, and it is considered that the thinning and weight loss of the graphite become remarkable, and the calcination becomes insufficient at the above-mentioned temperatures, It is considered that a ceramic film having desired properties cannot be obtained.

Next, in order to evaluate the surface roughening of the graphite base material, test pieces were prepared by the same method as described above using graphite base materials with and without blasting. The adhesion of the ceramic coating was measured. as a result,
As shown in FIG. 5, the case with blast showed a higher adhesive force than the case without blast. However, FIG.
Indicates a relative value when the adhesion force when blasting is performed is 1. The increase in adhesion when blasting occurs is due to the increase in the mechanical bonding force at the interface between the graphite substrate and the ceramic coating due to the roughening, and the chemical bonding due to the increase in the effective surface area of the substrate. This is because the power increases.
Thus, the surface roughening by blasting is effective in the present embodiment. For roughening, sandpaper may be used instead of blasting.

According to the present embodiment as described above, Al ₂
O ₃ sol-containing tetramethoxysilane with particle size of 10-4
A coating liquid is prepared by adding 4 μm of Al ₂ O ₃ ceramic powder, applied to the surface of a graphite substrate, dried, and dried in air.
Since firing is performed at a temperature of 00 to 450 ° C., the Al ₂ O ₃ ceramic powder is taken into the stitch structure of SiO ₂ derived from tetramethoxysilane and Al ₂ O ₃ derived from the Al ₂ O ₃ sol. In addition, the thickness of the ceramic film can be increased to about 100 to 200 μm as compared with the related art. As a result, a margin for corrosion and thinning of the coating is increased to improve corrosion resistance to, for example, uranium, and the ceramic coating is made porous so that cracks and peeling are less likely to occur, thereby improving heat resistance.

Since the surface of the graphite substrate is roughened beforehand by blasting or the like before the application of the coating solution, the mechanical bonding force at the interface between the graphite substrate and the ceramic film increases, and As the effective surface area increases, the chemical bonding force increases, and therefore, the adhesion of the ceramic film can be increased.

Next, the second and third embodiments of the ceramic coating method according to the present invention will be described with reference to FIGS. FIG. 6 shows a second embodiment in which a coating liquid is applied to a graphite substrate by means of a brush, and FIG. 7 shows a third embodiment in which a coating liquid is applied to a graphite substrate by spraying.

In the second embodiment shown in FIG. 6, a coating liquid is applied to a graphite substrate by a brush 7 attached to the tip of a coating robot 6. Here, in order to obtain a uniform film and to improve the efficiency of the coating operation, a rotation mechanism 8 for rotating the graphite substrate 1 is provided. The hood 5 is provided to prevent the application liquid from scattering. According to the present embodiment, the coating liquid can be easily applied, and can be applied only to a target portion, so that it is effective for partial repair or re-application of the coating.

In the third embodiment shown in FIG. 7, a compressor 9 and a spray 10 are provided in place of the brush in the second embodiment, and the coating liquid 4 is sprayed from the spray 10 to the graphite base 1. Apply. Here, the hood 5 is also provided, but in the case of the present embodiment in which the coating liquid 4 is jetted, the hood 5 functions effectively to prevent the coating liquid 4 from scattering. The spray 10 can be driven by a painting robot. According to this embodiment, the application liquid can be easily applied, and it is effective for mechanization and automation of the application operation.

In the case where the viscosity of the coating solution is large, the use of a brush as in the second embodiment tends to cause unevenness. Therefore, the immersion or spray method as in the first or third embodiment is more preferable. It is suitable.

Next, a fourth embodiment of the ceramic coating method according to the present invention will be described with reference to FIG.

In the present embodiment, the oxide ceramic powder to be added to the coating liquid is not Al ₂ O ₃ ceramic powder but Y ₂ O ₃ ceramic powder. The particle size of the Y ₂ O ₃ ceramic powder was set to 10 to 44 μm, which is the same as the Al ₂ O ₃ ceramic powder in the first embodiment, and a test piece was prepared in the same manner as in the first embodiment. Then, the test piece was subjected to a heat resistance test of heating at 1000 ° C. for 1 hour in a vacuum and a corrosion resistance test of being dipped in a uranium iron alloy at 1000 ° C. for 400 hours in a vacuum. As a result, the ceramic coating did not show any cracking or peeling, and did not penetrate into the coating of the uranium iron alloy, maintaining a healthy state and having good heat resistance and corrosion resistance. Do you get it. This is because the addition of Y ₂ O ₃ ceramic powder, which has chemically high corrosion resistance to uranium, further increased the corrosion resistance of the coating.
And Al ₂ O ₃ ceramic powder coating by the addition of Y ₂ O ₃ ceramic powder of 10~44μm like the case of adding it is believed that due to the heat resistance becomes porous is improved.

According to the present embodiment as described above, the first
The same effect as that of the embodiment can be obtained. Further, by adding Y ₂ O ₃ ceramic powder, high corrosion resistance to uranium can be obtained.

In the above, the embodiment in which the coating liquid is applied to the surface of the graphite base material has been described. However, the same coating liquid is applied to the surface of a metal base material or another ceramic base material, and the same firing is performed. In this case as well, the corrosion resistance and heat resistance of the ceramic film can be similarly improved.

Also, oxide ceramic powders other than the Al ₂ O ₃ ceramic powder and Y ₂ O ₃ ceramic powder used above, oxide sols other than Al ₂ O ₃ sol, Can be used.

[0042]

According to the present invention, an oxide ceramic powder is added to a silicon alkoxide containing an oxide sol to form a coating solution, which is applied to the surface of a substrate, and dried and fired. The powder is taken into the stitch structure of the ceramic, and a thicker ceramic coating can be obtained than in the conventional sol-gel method. Thereby, the corrosion resistance and heat resistance of the ceramic film can be improved.

Since the surface of the base material is roughened before the application of the coating solution, the mechanical and chemical bonding forces of the ceramic film can be increased, and the adhesion can be increased.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a ceramic coating method according to a first embodiment of the present invention, and is a diagram schematically illustrating a formation and adhesion mechanism of a ceramic film.

FIG. 2 is a flowchart showing an embodiment of the ceramic coating method of FIG. 1;

FIG. 3 is a diagram showing a method of applying a coating liquid to the surface of a graphite substrate by immersing the graphite substrate in the coating liquid.

FIG. 4 is a diagram showing the effect of the firing temperature on the adhesion of a ceramic film.

FIG. 5 is a diagram showing the effect of roughening by blasting on the adhesion of a ceramic film.

FIG. 6 is a view illustrating a ceramic coating method according to a second embodiment of the present invention, and is a view illustrating a method of applying a coating liquid to a graphite substrate by using a brush.

FIG. 7 is a view illustrating a ceramic coating method according to a third embodiment of the present invention, and is a view illustrating a method of spraying a coating liquid onto a graphite base material by spraying to apply the coating liquid.

FIG. 8 is a view for explaining a ceramic coating method according to a fourth embodiment of the present invention, in which the formation and adhesion of a ceramic film when the oxide ceramic powder added to the coating liquid is Y ₂ O ₃ ceramic powder; It is a figure which shows a mechanism typically.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Graphite base material 2 Container 3 Moving mechanism 4 Coating liquid 5 Hood 6 Painting robot 7 Brush 8 Rotation mechanism 9 Compressor 10 Spray

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Ikugo Domori 3-1-1, Sachimachi, Hitachi-shi, Ibaraki Pref. Hitachi, Ltd. Hitachi Plant (72) Inventor Kazunari Uchida 3-chome, Sachimachi, Hitachi, Ibaraki No. 2 Hitachi Nuclear Engineering Co., Ltd. (72) Inventor Eriko Suzuki 3-2-2 Komachi, Hitachi City, Ibaraki Pref. Hitachi Nuclear Engineering Co., Ltd. Examiner Yoshifumi Saeki (56) References JP Sho 62 JP-A-32157 (JP, A) JP-A-3-45583 (JP, A) JP-A-3-190984 (JP, A) JP-A-5-302173 (JP, A) JP-A-5-247657 (JP, A) (58) Field surveyed (Int.Cl. ⁷ , DB name) B05D 7/24 B05D 3/02

Claims (3)

(57) [Claims] 1. A ceramic coating method for forming a ceramic coating on a graphite substrate, comprising the steps of: providing a silicon alkoxide containing an oxide sol having a powder particle size of 10 to 44 μm;
A coating liquid is prepared by adding yttrium oxide powder, and the coating liquid is subjected to a blast treatment in advance to obtain a surface coating.
Is applied to the surface of a roughened graphite substrate, dried, and
A ceramic coating film by baking at a temperature of 400 to 450 ° C. 2. The ceramic coating method according to claim 1, wherein the oxide sol is an alumina sol. 3. The method according to claim 1, wherein said silicon alkoxide is tetramethoxysilane.