JPH04362182A - Production of ceramic body by sol-gel process - Google Patents

Abstract

PURPOSE:To form an electron microscopically dense film of ceramics such as alumina or zirconia on the surface of a body to be treated such as a metal substrate. CONSTITUTION:When a ceramic film is formed by a sol-gel process on the surface of a body to be treated to produce a ceramic body, a coating film is formed on the surface of the body to be treated with an oxide hydrate sol prepd. by hydrolysis and condensation polymn. of a metal alkoxide and the body with the formed coating film is dried and fired in vacuum to form a ceramic film on the surface of the body to be treated.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a ceramic body by forming a ceramic coating on the surface of a solid material by a sol-gel method.

0002

[Prior Art] Methods for forming ceramic films on the surface of solid materials include plasma spraying, sputter deposition,
Chemical vapor phase synthesis is known as a representative method. However, these methods require complicated and expensive equipment, and because the film is formed in a vacuum device, they are limited by solid angles and cannot be used for members with complex shapes or large areas. However, in the case of plasma spraying, which is often used for surface treatment of structural materials,
There is a problem in that the molten particles are instantaneously fused and an unstable phase is likely to be generated at the bonding interface, resulting in a film with high porosity.

[0003] On the other hand, the method of creating ceramic films via a liquid phase involves a process of dipping the substrate in the liquid phase, pulling it up, drying, and firing, so there is no spatial restriction and it is not possible to create a ceramic film using a large and complicated object. It has the advantage that it can be easily coated. Ceramic coating methods for metal materials that use a liquid phase have been around for a long time, and enamel is a typical example. Enamel is made by fusing glaze at high temperatures to create a glassy coating. On the other hand, the sol-gel method uses a solution to form a ceramic coating at a low temperature and then sintering it to obtain a fine ceramic coating, which is an essentially different manufacturing method from that of enamel. Sol・
The gel method is applied to the synthesis of glass, ferroelectric ceramics, ceramic fibers, and the creation of antireflection films, etc. Its advantages include easy composition adjustment and low-temperature synthesis. , it is easy to obtain an ultrafine grain structure, it can be molded into various shapes, and it can be synthesized in an open system, which is advantageous in terms of equipment.

0004

[Problems to be Solved by the Invention] However, in the formation of ceramic films using the conventional sol-gel method, the adhesion between the substrate and the ceramic film, the suitable method for forming a dense film, etc. are still at the research stage. However, at present, a suitable method for forming ceramic coatings has not been established. A recent example is an adhesion test using a zirconia coating containing yttria added to stainless steel by fixing a jig with resin and performing a tensile test (Jour
nal of American Ceramics
Society, 72 (1989) 1465), and a description of the oxidation behavior of substrates using the sol-gel method as a heat-resistant film coating from observations on the surface of the film (Journal).
al of Materials Science, 2
5 (1990) 1537-1544). However, the structure and oxidation behavior of the coating at the transmission electron microscope level have not been investigated, and the microstructure and properties of ceramic coatings have not been investigated in detail as a method for forming the coating. Therefore, the present invention has been made in view of the above problems, and its purpose is to:
A sol that can form a fine ceramic film with a fine structure at the electron microscope level.
The present invention aims to provide a method for manufacturing a ceramic body using a gel method.

[0005]

Means for Solving the Problems The present invention has the following configuration to achieve the above object. That is, in a method for manufacturing a ceramic body using a sol-gel method, in which a ceramic film is formed on the surface of an object to be treated using a sol-gel method,
A coating film is formed on the surface of the object to be treated using a hydrated oxide sol produced by the hydrolysis and polycondensation reaction of a metal alkoxide, and after drying the object with the coating formed, it is fired in a vacuum. It is characterized by forming a ceramic coating on the surface of the object to be treated. The present invention is also characterized in that an alumina coating is formed using aluminum-iso propoxide as the metal alkoxide, and a zirconia coating is formed using zirconium-tetra-n propoxide as the metal alkoxide. In addition, 5
It is characterized by forming a ceramic coating by performing heat treatment at 00°C or higher.

[0006]

[Summary of the Invention] In the method of the present invention, a coating film is formed on the surface of an object to be treated using a hydrated oxide sol, the object to be treated on which the coating film has been formed is dried, and then fired in a vacuum. It is characterized by closely adhering a ceramic coating to the surface of the object to be treated. In addition,
A hydrated oxide sol obtained by subjecting a metal alkoxide liquid to hydrolysis and polycondensation reaction is used as the coating liquid used to form a coating film on the object to be treated. The metal alkoxide may be of any type as long as it can produce a metal oxide sol through hydrolysis and polycondensation reactions.

[0007] A coating film is uniformly formed on the object to be treated. It is preferable to adjust the viscosity of the coating liquid by adjusting its acidity before use. If the viscosity of the coating liquid used is too high, cracks will occur in the ceramic coating, so it is necessary to adjust the viscosity. Note that the coating method for the object to be treated may be any method that can uniformly form a coating film, and is not limited to the dipping method. When using the dipping method, the thickness of the coating film can be adjusted by adjusting the pulling speed and the number of times of dipping. Note that the object to be treated on which the ceramic film is to be formed is subjected to pretreatment to clean the surface and form a suitable film before forming the coating film. Since heat treatment is performed when forming the ceramic coating in a later process, heat treatment may be performed in advance depending on the object to be treated.

After forming a coating film on the object to be treated, it is dried and fired in a vacuum. By firing under reduced pressure, discoloration of the surface of the object to be treated can be prevented and a transparent thin film can be coated. This method of firing under reduced pressure is effective in volatilizing components such as alcohol and water in ceramic films such as alumina films, and is effective in making the films denser. The ceramic coating can be suitably fixed to the substrate. In addition, in the conventional sol-gel method, the heat treatment temperature for fixing the ceramic film was considered to be 300 °C to 500 °C if the crystallinity of the film was not a problem, but in the method of the present invention, the heat treatment temperature is 300 °C to 500 °C. By using the above heat treatment temperature, a ceramic coating with good crystallinity can be obtained. In particular, in the case of alumina coating, γ alumina and α are separated by vacuum heat treatment at 1050°C.
It was confirmed that a composite coating made of alumina could be formed. Since the γ→α transformation of alumina occurs slowly, stress caused by the transformation at the bonding interface during firing is alleviated. Furthermore, the properties of the ceramic coating formed by the method of the present invention were observed using electron micrographs, and it was confirmed that a dense ceramic coating was formed.

When the composition of the ceramic film formed on the stainless steel substrate by the method of the present invention was analyzed, it was found that iron, chromium, and nickel were present. This is considered to be due to the elements being diffused from the stainless steel substrate into the ceramic coating and being diffusion bonded. The bonding mechanism when a ceramic film formed by the sol-gel method is heat-treated is that a dehydration condensation reaction occurs between the hydroxyl groups on the surface of the metal substrate and the hydroxyl groups in the coating film, resulting in a metal-oxygen-metal bond mediated by oxygen. However, in the case of the heat treatment method according to the present invention, it is thought that a bonding mechanism involving a diffusion process is used in addition to the dehydration condensation reaction.

0010

EXAMPLES Hereinafter, examples will be described in which a ceramic body is manufactured according to the method of manufacturing a ceramic body by the sol-gel method according to the present invention. (Example 1) An example of forming an alumina film on SUS304 stainless steel using aluminum-iso propoxide will be described. (2) Preparation of liquid used as metal alkoxide It has been confirmed that a coating liquid prepared using aluminum-isopropoxide as a starting material has good wettability for stainless steel and copper. However, if there is too much water, the wettability will deteriorate, so a solution with a fixed mixing ratio as shown in Solution D below was used. Solution A: Isopropyl alcohol solution of aluminum-isopropoxide:
Concentration 0.1M (ISO propyl alcohol solution containing 0.1 mol of aluminum-iso propoxide in 1 liter) Solution B...
・0.01M nitric acid aqueous solution C liquid...B liquid 270m
Solution D: Add isopropyl alcohol to 1 liter to make a total volume of 1 liter Solution D: Solution A and Solution C in a volume ratio of 6:1 to 1:1
solution mixed with

(2) Preparation of coating liquid The metal alkoxide liquid prepared in step (1) above is subjected to the following treatment to prepare a coating liquid. 1) After adjusting the D solution, stir it for about 6 hours or more,
Proceed with hydrolysis reaction and polycondensation reaction. The obtained liquid is referred to as liquid E. 2) Drop a 1N nitric acid aqueous solution into Solution E while stirring to lower the pH and increase the viscosity, and use the resulting solution as Solution F (coating solution). The viscosity of liquid F is
The acidity is adjusted so that the effective viscosity range is between 10 cp and 100 cp. A low viscosity is not a problem, but a high viscosity exceeding 100 cp is not preferable because it may cause cracks in the coating. The pH of the coating liquid is 2.0
A range of 6.5 to 6.5 is preferable. FIG. 1 shows a pH-viscosity diagram of the coating liquid when the volume ratio of the liquid A and liquid B is changed.

① Pretreatment of Substrate In this example, SUS304 steel was used as the object to be treated. After mechanically polishing this SUS304 steel substrate, it was washed with pure water and an organic solvent such as alcohol or acetone, and dried. SUS304 steel is heat-treated at 950°C or higher in the post-process, so in order to prevent peeling due to grain growth on the sample surface, heat treatment is performed at 1050°C to 1100°C in advance.
The sample was heat-treated and used.

[0013] ■ Coating work The coating liquid prepared by the above ■ SUS3
A coating film was formed by dipping a substrate of 04 steel and pulling it up. In the example, the pulling speed was 1 to 2 m.
m/sec. 50-10 in one coating
A film thickness of about 0 nm was obtained.

[0014] After drying the coated substrate by the method of (1) drying and baking in a vacuum at room temperature,
Dry in air at 100°C to 120°C for 1 hour. After drying, in vacuum (~1 x 10-4 Torr) for 5
It was fired at a temperature of 00°C to 1100°C. This made it possible to form an alumina coating on the surface of the stainless steel substrate.

FIGS. 2 and 3 show that SU
The results of a scratch test performed using a diamond indenter on an alumina film formed on an S304 steel substrate are shown. The example shown in FIG. 2 shows the test results for a sample formed under the firing conditions of 500° C. for 2 hours, and shows an electron micrograph after scratch marks were formed. The right half of the figure shows scratch marks. It can be seen that the alumina coating has peeled off near the scratch marks. The example shown in FIG. 3 shows an electron micrograph of a sample formed under sintering conditions of 700° C. for 2 hours. The right half of the figure is the scratch mark. In this example, the alumina coating was only deformed together with the substrate, and no peeling of the coating was observed. It was confirmed that the alumina film was well fixed in this way when the firing temperature was 700°C or higher.

FIGS. 4 to 7 show the results of testing the properties of alumina coatings formed on SUS304 steel substrates according to the above method under vacuum firing conditions (1×10 −4 Torr) at 900° C. for 2 hours. FIG. 4 is a scanning electron micrograph of a substrate on which an alumina coating is formed, with the upper half of the figure showing the alumina coating and the lower half showing the substrate without the alumina coating. FIG. 5 shows another example in which an alumina film is formed. In this example, since the alumina film was formed as a thin film, the roughness of the passive film on the substrate was reflected in the roughness of the thin film surface. FIG. 6 shows a transmission electron micrograph of the alumina coating. The upper half of the figure (bright field image) is an image of the alumina coating, and the lower half of the figure is an image of the substrate. The lower right image in the figure is an electron diffraction pattern. From the electron beam diffraction pattern, it was confirmed that the alumina film formed on the substrate surface was a γ alumina film. FIG. 7 is a dark field transmission electron micrograph of the γ alumina film in the same part as FIG. 6. What appears to be shining white in the figure are individual crystals of gamma alumina. Since this is a dark-field transmission electron micrograph, only the crystals that diffract the specific electron beam that passes through the objective aperture appear to glow white.

[0017] Next, the results of an oxidation test in the atmosphere performed by the following method on a stainless steel substrate on which an alumina film was formed by the above method will be explained. Samples of stainless steel substrates on which alumina coatings were formed were coated 10 times using a coating solution in which the above-mentioned solutions A and C were mixed at a ratio of 6:1 as solution D. Created by firing. As a comparative example, a sample was used in which the same stainless steel substrate was subjected to the same heat treatment and surface treatment. FIGS. 8 and 9 are electron micrographs of the samples of the above examples and comparative examples after being heated in the air at 700° C. for 2 hours. FIG. 8 shows a sample with an alumina coating formed thereon, and FIG. 9 shows a sample of a comparative example. FIGS. 10 and 11 are electron micrographs after heating at 600° C. for 2 hours in the air. FIG. 10 shows the results for a sample on which an alumina film was formed, and FIG. 11 shows the results for a comparative sample. These electron micrographs show that no peeling of the alumina film was observed in the sample with the alumina film formed, and that in the comparative example without the alumina film, roughness was noticeable due to oxidation of the passive film on the surface of the stainless steel substrate. On the other hand, it can be seen that the sample with the alumina film formed is much smoother than the passive film. In addition, as a result of oxidation experiments, the average weight increase due to oxidation on stainless steel substrates without an alumina coating was 58 μg/cm2, while on the one with an alumina coating, it was 35 μg/cm2.
cm2, and was confirmed to be effective in preventing oxidation despite being a thin film.

(Example 2) Zirconium-tetra-n
An example will be described in which a zirconia coating is formed on SUS304 stainless steel using propoxide. (2) Working liquid A: A 0.1M n-propyl alcohol solution of zirconium-tetra-n-propoxide was used. ■ Coating method After creating the above liquid A, immediately immerse the SUS304 steel substrate and coat it by pulling it up, or add pure water to liquid A at a volume ratio of 2:1 to proceed with the hydrolysis reaction (B (liquid), the SUS304 steel substrate is immediately immersed and coated by pulling up. Note that if coating is not performed immediately after adjusting the coating liquid, cracks will occur in the coating. Therefore, coating must be performed immediately after preparing the solution. Also, A
Nitric acid is added dropwise to both the solution and B solution to adjust the viscosity of the coating solution to 2 to 9 cp and the pH to 2 to 6. (2) Drying and firing The coated sample is dried at room temperature to 120°C, and then fired in a vacuum furnace at 500°C or higher to form a zirconia coating.

The properties of the zirconia coating were observed using a transmission electron microscope on the samples on which the zirconia coating was formed by the above method. FIG. 12 is a scanning electron micrograph of a zirconia film formed under heat treatment conditions of 900° C. for 2 hours. Figure 13 similarly shows the temperature at 900 °C and 2
These are transmission electron micrographs and electron beam diffraction images of a zirconia film formed under different heat treatment conditions. As a result of observation of scanning electron micrographs, it was confirmed that the zirconia film was uniformly formed over the entire substrate surface. Furthermore, from the observation results of transmission electron micrographs and electron beam diffraction images, it was confirmed that the zirconia film was a monoclinic zirconia film composed of submicron-sized fine particles.

In the above embodiment, a stainless steel substrate was used as the object to be processed, but various objects can be used as the object to be processed. Examples of its use include the formation of insulating and corrosion-resistant coatings for various electrodes or substrate metal materials (stainless steel, copper, aluminum, etc.), structural metal materials (steel, aluminum, titanium, and other alloys), ceramic materials ( For example, corrosion-resistant coatings may be formed using materials such as silicon nitride, silicon carbide, aluminum nitride, glass, etc.), and carbon fiber materials. Sol・
As mentioned above, the gel method for forming ceramic coatings has the advantage of being able to be formed into various forms such as fibers, films, and bulk shapes, and can be easily applied to objects with complex shapes. This is a method that can be expected to be developed in various fields as a synthetic method.

[0021]

[Effects of the Invention] As described above, according to the method of manufacturing a ceramic body using the sol-gel method according to the present invention, it is possible to effectively form a dense ceramic coating on the level of an electron microscope. A film with excellent adhesion can be formed. Further, since heat treatment in a vacuum is easy, manufacturing can be easily performed, and other remarkable effects are achieved.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between pH and viscosity of a coating liquid.

FIG. 2 is an electron micrograph showing the particle structure of an alumina coating after a scratch test.

FIG. 3 is an electron micrograph showing the particle structure of alumina coatings subjected to different firing conditions after a scratch test.

FIG. 4 is an electron micrograph showing the particle structure of an alumina film formed on a substrate.

FIG. 5 is an electron micrograph showing the particle structure of a thin alumina coating formed on a substrate.

FIG. 6 is a transmission electron micrograph (bright field image) showing the particle structure of the γ alumina coating formed on the substrate.

FIG. 7 is a transmission electron micrograph (dark field image) showing the particle structure of the γ alumina coating formed on the substrate.

FIG. 8 is an electron micrograph showing the particle structure of an alumina coating after an oxidation test.

FIG. 9 is an electron micrograph showing the metal structure of a stainless steel substrate after an oxidation test.

FIG. 10 is an electron micrograph showing the particle structure of an alumina coating after an oxidation test.

FIG. 11 is an electron micrograph showing the metal structure of a stainless steel substrate after an oxidation test.

FIG. 12 is an electron micrograph showing the particle structure of a zirconia coating.

FIG. 13 is an electron micrograph showing the grain structure of a zirconia coating.

Claims (4)

[Claims] [Claim 1] A method for manufacturing a ceramic body by a sol-gel method in which a ceramic film is formed on the surface of an object to be treated using a hydrated oxide sol produced by hydrolysis and polycondensation reaction of a metal alkoxide. to form a coating film on the surface of the object to be treated,
A method for producing a ceramic body using a sol-gel method, which comprises drying the object on which the coating has been formed, and then firing it in a vacuum to form a ceramic film on the surface of the object. 2. The method of manufacturing a ceramic body by the sol-gel method according to claim 1, wherein the alumina film is formed using aluminum-iso propoxide as the metal alkoxide. 3. The method for producing a ceramic body by the sol-gel method according to claim 1, wherein the zirconia coating is formed using zirconium-tetra-n propoxide as the metal alkoxide. 4. The method of manufacturing a ceramic body by the sol-gel method according to claim 1, 2 or 3, wherein the ceramic film is formed by heat treatment at 500° C. or higher in vacuum.