JPH03285079A - Formation of alumina film on inorganic substrate of metal, glass, ceramics or the like - Google Patents

Abstract

PURPOSE:To easily form an Al2O3 film excellent in weatherability on an inorg. substrate in the air without using expensive equipment by dipping the inorg. substrate in a sol of the Al compd. obtained by hydrolyzing Al with acid, pulling up the substrate at a specified speed and then heat-treating the substrate. CONSTITUTION:Metallic Al, an Al alkoxide, etc., are hydrolyzed with an org. acid such as acetic acid or an inorg. acid such as hydrochloric acid to form a sol of the Al compd. at pH3-5. The inorg. substrate of metal, glass, ceramics, etc., is dipped in the sol ordinarily for 20-60min, and then pulled up at the speed of 0.5-15.0mm/sec. Since the film formed on the substrate consists of Al(OH)3 or consists essentially of Al(OH)3, the film is heat-treated at >=100 deg.C. Consequently, an Al2O3 film is easily and inexpensively formed on the substrate surface even in the air without using expensive equipment.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for forming an alumina coating on an inorganic substrate such as metal, glass, or ceramics.

[Prior art] There have been attempts to improve the properties of metals, glass, quartz, etc. by forming alumina coatings on the surfaces of these materials, or to modify the surface properties of these materials. being done.

For example, JP-A-49-122498 discloses that an alumina film is formed on the surface of metal or glass by sputtering to impart electrical insulation to the metal or to improve the chemical resistance of the glass. was proposed, and also published in Japanese Unexamined Patent Application Publication No. 1973-
Japanese Patent No. 68169 proposes forming an alumina film on the surface of a quartz container by vacuum evaporation to improve heat resistance.

[Problems to be Solved by the Invention] However, when forming an alumina film by sputtering or vacuum evaporation, expensive sputtering equipment or vacuum evaporation equipment is required, and the coating for film formation is highly sophisticated. In addition to restrictions such as having to perform the process in a vacuum-controlled room, if the alumina coating formed in the vacuum chamber is a highly active coating, it will be susceptible to moisture and moisture in the atmosphere when transferred from the vacuum chamber to the atmosphere. There is a problem that it is deactivated or oxidized and deteriorates due to contact with oxygen.

Therefore, the present invention enables coating to form a film on the surface of an inorganic base material such as metal, glass, or ceramics in the air without requiring expensive equipment. The purpose of the present invention is to provide a method that can easily form an alumina film that is less affected by oxygen and has excellent weather resistance.

[Means for Solving the Problems] The present invention hydrolyzes aluminum with an acid to reduce the pH to 3-3.
After producing a sol of the aluminum compound of No. 5, immersing an inorganic base material such as metal, glass, or ceramics in this sol, and pulling the base material out of the sol at a speed of 0.5 to 15.0 m/sec. The above object is achieved by forming an alumina film on the surface of the base material through heat treatment.

According to the above alumina film formation method, the alumina film is formed by immersing the base material in a sol, pulling it up, and then heat-treating it, which requires expensive equipment like sputtering or vacuum evaporation methods. Also, coating for film formation can be done in the air.
An alumina coating can be easily and inexpensively formed on the surface of a base material. Moreover, since the alumina film formed on the surface of the base material is formed through an oxidation process using heat treatment, it is subject to deterioration due to contact with air, unlike alumina films formed by sputtering or vacuum evaporation. do not have.

According to the present invention, examples of the substrate on which an alumina film can be formed include metals such as stainless steel and iron, and inorganic materials such as glass and ceramics (including quartz).

Metallic aluminum is usually used as the raw material aluminum for producing a sol of an aluminum compound, but aluminum alkoxides such as aluminum isopropoxide and aluminum ethoxide can also be hydrolyzed to produce a sol similar to metallic aluminum. Therefore, it can be used as raw material aluminum in the same way as metal aluminum.

Examples of acids for hydrolyzing the aluminum include organic acids such as acetic acid, formic acid, propionic acid, acetic acid, and Shu M, and inorganic acids such as hydrochloric acid, sulfuric acid, phosphoric acid, and nitric acid. However, when hydrolyzing metal aluminum, an organic acid is used, and when hydrolyzing aluminum alkoxide, an inorganic acid is suitable.

As mentioned above, when hydrolyzing metal aluminum,
Organic acids are suitable because they can easily hydrolyze metallic aluminum gently to obtain the desired transparent sol, while inorganic acids such as hydrochloric acid, sulfuric acid, and nitric acid are suitable. However, it is difficult to generate a sol because an oxide film or a corrosion-resistant film is formed on the aluminum surface, and even if a sol can be generated, it is difficult to obtain a transparent sol suitable for forming an alumina film. This is because it is difficult.

In addition, as mentioned above, from the viewpoint of hydrolyzing metallic aluminum under mild conditions to generate a transparent sol (that is, a sol in which the particle size of colloidal particles is smaller than the wavelength of visible light), during hydrolysis, It is preferable to use an organic acid such as acetic acid after diluting it with water to a volume ratio of about 1:40 to 60.

The temperature during hydrolysis is usually 55 to 85°C, preferably 65 to 75°C. In addition, the hydrolysis time is usually 25
~35 hours, but the hydrolysis time can be shortened by adding mercury oxide (Hgo) as a catalyst. When this mercury oxide is added, the mercury oxide reduces the oxidized layer on the aluminum surface, promotes the reaction between aluminum and the organic acid, and shortens the hydrolysis time. However, in order to produce the desired sol, it is preferable to carry out the hydrolysis under as mild conditions as possible, and therefore it is preferable to add the above-mentioned mercury oxide as necessary.

The sol of aluminum compounds produced by hydrolysis of aluminum is thought to be a sol of aluminum hydroxide, but it also contains some sols of compounds of aluminum and the acid used in the hydrolysis, such as aluminum acetate. considered to be a thing.

When forming a film on a base material, it is necessary that the pH of the sol of the aluminum compound is 3 to 5. That is, if the pH of the sol is higher than 5,
The film becomes cloudy and a strong alumina film cannot be obtained even if it is heat-treated, and the pH of the above sol
When the sol is lower than 3, it is difficult to form a sol suitable for film formation, and therefore it is difficult to obtain a film. A particularly preferred pH is around 4.

The concentration of the above-mentioned sol may be any concentration as long as the sol is transparent, but usually the concentration of the sol is 1 to 5% (wt%,
(the same applies hereafter). The upper limit of the concentration at which the sol can maintain transparency and low viscosity cannot be determined unconditionally as it varies depending on various conditions, but since transparency and low viscosity are usually impaired at 8 to 10%, as mentioned above, In the range of 5%, it can remain clear and low viscosity in most cases. The fact that this sol is transparent means that the resulting alumina coating is transparent and has good physical properties (e.g., adhesion to the substrate,
This is thought to be related to the fact that the material has a certain strength (e.g., strength, etc.).

Although the time for which the substrate is immersed in the sol does not have a particularly important effect on film formation, the substrate is usually immersed in the sol for 20 to 60 minutes.

The pulling up of the base material from the sol after immersion in the sol is 0.5
It is necessary to perform this at a speed of ~15.0 km/sec.

Within the above range, the faster the pulling rate, the thicker the film will be on the substrate, and if the pulling rate is slower than 0.5 min/sec, a uniform film will not be formed on the substrate, and if the pulling rate is lower than lt, When the pulling rate reaches Omn/sec, the film thickness almost reaches saturation, and when the pulling rate exceeds 15.0 mn/sec, the structure of the film changes and a strong film cannot be obtained. As mentioned above, the phenomenon that the film thickness increases as the pulling speed increases is thought to be related to the wettability (adhesive force) of the solid-liquid interface.

When pulling up the base material from the sol, it is preferable to pull up the base material perpendicularly to the sol liquid level. Particularly when the substrate is plate-shaped, an appropriate film can be obtained by lifting the substrate perpendicularly to the sol liquid level. However, the method according to the present invention is not limited to substrates having a plate shape, and can be applied to substrates of various shapes.

The above-mentioned immersion of the base material into the sol and lifting of the base material from the sol, that is, coating for film formation, can be performed in air, and this is the process of forming an alumina film using conventional sputtering or vacuum evaporation methods. This is very different from the law. The temperature during this coating is usually 10~
The temperature is 40°C, preferably 15-25°C, and the relative humidity is usually 40-70%, preferably 45-55%.

The film formed on the surface of the base material as described above is considered to be aluminum hydroxide or a film mainly composed of aluminum hydroxide, so heat treatment is necessary to convert it into an alumina film. be. The heat treatment temperature may be 100° C. or higher, but by performing the heat treatment in a specific temperature range, it is possible to obtain an alumina coating having characteristics depending on the application. For example, 400-60
By heat treatment at 0'C, an activated alumina film is obtained, and by utilizing the change in resistance value due to the adsorption/adhesion phenomenon of water, pyridine, or electron-donating benzene derivatives such as toluene and xylene to the film, It can be used as a water or gas detection sensor. Further, when increasing the heat resistance or corrosion resistance of the base material, it is preferable to perform heat treatment at a high temperature of about 500 to 1,000°C within a range that the base material can withstand. When performing heat treatment at such a high temperature, it is preferable to preheat at a temperature of about 170° C. or lower, for example, to prevent cracks or cracks from forming in the alumina coating.

The thickness of the coating formed on the surface of the base material as described above is
Although it varies depending on the properties of the base material, the concentration and viscosity of the sol, etc., in one coating operation, it is usually 0.1 to 0.2.
It is about μm. Therefore, if a thicker alumina coating is required, coating and heat treatment may be repeated a desired number of times to perform so-called overcoating.

When an alumina film is formed on a metal surface by the method of the present invention, the corrosion resistance of the metal can be improved and electrical insulation properties can also be imparted to the metal. Furthermore, when an alumina coating is formed on a glass surface, by changing the thickness of the coating, the refractive index and reflectance can be arbitrarily adjusted to al1, which can be applied to optical-related applications. Furthermore, the chemical resistance of the glass can also be changed by forming an alumina film on the glass surface.

Furthermore, by forming an alumina film on the surface of ceramics such as quartz, the heat resistance and corrosion resistance of quartz or the like can be improved.

In particular, by heat treatment at 400 to 600°C, an alumina film can be obtained in the state of activated alumina, and water, pyridine, or electron-donating Hensen derivatives such as toluene and xylene can be absorbed and adhered to the alumina film. It can be applied to new applications that cannot be applied to alumina films formed by conventional sputtering or vacuum evaporation methods, such as by making use of the change in resistance caused by the phenomenon and being able to be used as a sensor for water or gas detection. I can do it.

〔Example〕

Next, the present invention will be explained in more detail with reference to Examples.

Example I A stainless steel plate (SUS304 plate) with a thickness of 0.3 m was cut into a rectangular shape with an alumina coating forming part of 2 ci + 3 cm and a protrusion (i.e., a handle-like part) for attachment to a pulling device. This was used as a base material for forming an alumina film, and an alumina film was formed on the surface of this stainless steel plate according to the following specifications.

- Approximately 1c + * of the raw bottom metal aluminum plate (99.99% purity)
The aluminum pieces were cut into corners (weighing about 25 g), and in order to remove the oxidized layer on the surface, the aluminum pieces were immersed in acetic acid and cleaned in an ultrasonic cleaner for about 30 minutes.

After the treatment, the aluminum piece was taken out of the acetic acid and immediately mixed with acetic acid and distilled water at a volume ratio of 1:50, which was kept at 70±5°C.
was added to the mixed solution.

Aluminum was hydrolyzed while stirring this mixed solution at 70±5° C. for about 20 hours.

When the sol concentration at this point was measured, the sol concentration was approximately 0.3%, so 0.05g of mercury oxide (HgO) was added as a catalyst to the mixed solution of acetic acid and distilled water, and 70± Hydrolysis was continued with gentle stirring for an additional 8 hours while maintaining the temperature at 5°C. When the sol concentration was measured again, the sol concentration was 2%, so the hydrolysis was terminated. This sol is separated from impurities and precipitates using a centrifugal separator.
Further, the supernatant was filtered to obtain a transparent sol with a concentration of 2%.

The above-mentioned stainless steel plate prepared as a base material for forming an alumina film on SUNLESS was immersed in Hengan for 1 minute (note that only the part where the alumina film is to be immersed is required; the same applies to the following). After degreasing the mineral oil adhering to the surface of the stainless steel plate, the stainless steel plate was taken out of the heating gun and dried with a hair dryer.

Next, the stainless steel plate was immersed in a 2% aqueous sodium hydroxide solution for 5 minutes to degrease the animal fats and oils adhering to the surface of the stainless steel plate, and then the stainless steel plate was removed from the sodium hydroxide aqueous solution and soaked in running water. After washing, it was washed again with distilled water.

Furthermore, the stainless steel plate was placed in a 10% sulfuric acid aqueous solution for 5 minutes.
After being immersed for a minute to remove the oxidized layer on the surface of the stainless steel plate, the stainless steel plate was taken out of the sulfuric acid aqueous solution, washed with running water, and then washed again with distilled water.

3 Stainless steel The stainless steel plate pretreated as in (1) above was placed in a dryer and dried in air at 110°C for 1 hour.

The stainless steel plate dried as described in ② above is attached to the lifting device perpendicular to the sol liquid level in the container, and immersed in the sol at a rate of 11 cm/see to remove the stainless steel plate. After immersing the steel plate in the sol for 30 minutes, the stainless steel plate was immersed in the sol for 11++ a/s with the plate perpendicular to the sol liquid level.
It was pulled up from the sol at a speed of ec. The atmosphere during this coating was air, temperature 21±1℃, relative humidity 45℃.
The temperature was ±5°C.

The coated stainless steel plate as described in (1) above was placed in a dryer and heat treated in air at 170°C for 30 minutes to fix the alumina coating on the surface of the stainless steel plate.

The thickness of the alumina film formed on the surface of the stainless steel plate as described above was measured using an electron beam microanalyzer (EPM).
The thickness of the alumina coating was measured by the surface distribution of the α signal on the aluminum cross section of the coating according to A), and the thickness of the alumina coating was 0.
The thickness was 15 μm, and when the thickness variation was examined using the same method for each of the three samples, it was found to be 0.15 ± 0.05.
The thickness was within the pm range, and the thickness was almost uniform.

In addition, when the adhesion of the alumina coating formed as described above to the stainless steel plate was examined using the base grain method, the number of base grains that did not peel off and remained on the stainless steel plate was 100/1.
100, indicating sufficient adhesion. The adhesion test method is as follows.

11iIL or alumina coating, 11 vertical and 11 horizontal grooves reaching the substrate (stainless steel plate in this example) are made at intervals of 1 square width to form 100 base marks, and 100 base marks are formed. This is measured by pressing the cellophane tape on the substrate and then rapidly peeling it off.The alumina film does not peel off from the substrate and determines the number of base lines that remain on the substrate. The denominator of the evaluation value is the number of base grains that were tested, and the numerator is the number of base grains that remained on the substrate without the alumina coating peeling off.

Example 2 A quartz plate with a thickness of 2 mm was used as a base material, and an alumina coating was formed on the surface of this quartz plate according to the following specifications. Note that the alumina film forming portion of the quartz plate has a rectangular shape of 2 cm x 3 cm as in Example 1.

Similar to Example 1, metal aluminum was hydrolyzed to obtain a transparent sol with a concentration of 2%.

In the same manner as in Example 1, the quartz plate was immersed in a benzene and sulfuric acid aqueous solution to degrease fats and oils adhering to the surface of the quartz plate, and to remove the oxidized layer and rust on the surface of the quartz plate.

Breath-Quartz Plate East Dry Shoes As in Example 1, they were dried in air at 110"C for 1 hour.

[Phase] -": Convex Hijin Otohisa As in Example 1, the quartz plate was placed perpendicular to the sol liquid level, and the quartz plate was placed in the sol at a dipping rate of 2 g/see and a dipping time of 30 minutes. was immersed in the sol and pulled out of the sol at a pulling speed of 2 w/sec to perform coating. The atmosphere during coating was air, temperature 20±1"C1 relative humidity 45±5°C.

〇-Treatment Similar to Example 1, heat treatment was performed at 170° C. for 30 minutes to fix an alumina film on the surface of the quartz plate.

The thickness of the alumina coating formed on the surface of the quartz plate as described above was measured using the same method as in Example 1.
The thickness of the alumina coating was 0.15 μm, and when the thickness variation was examined using the same method as in Example 1, it was within the range of 0.15 to 0.05 μm, and the thickness was almost uniform. It had

In addition, when the adhesion of the alumina film formed as described above to the quartz plate was examined using the base grain method in the same manner as in Example 1, the number of base grains that did not peel off and remained on the quartz plate was 100/1.
100, indicating sufficient adhesion.

Example 3 A stainless steel plate similar to that in Example 1 was used as a base material for forming an alumina film, and this stainless steel plate was pretreated in the same manner as in Example 1, and then immersed in a transparent sol with a concentration of 2% as in Example 1. After coating and heat treatment, the coating and heat treatment were further repeated 8 times, so-called 9 times of overcoating, to form an alumina film on the surface of the stainless steel plate.

The coating conditions, atmosphere during coating, and heat treatment conditions each time (1st to 9th time) are as follows.

2: J-column 4-color production Dipping speed: 2111I/SeC Dipping time: 30 minutes Pulling speed: 2wl/Sec Note: The thickness of the alumina film formed on the surface of the stainless copper plate as described above was measured in the same manner as in Example 1 at 170°C for 130 minutes, and the thickness of the alumina film was 1°35 μm.

In addition, when the variation in thickness was investigated using the same method as in Example 1, it was found to be within the range of 1.35 ± 0.5 μm.
It had a fairly uniform thickness.

Furthermore, when the adhesion of the alumina coating formed as described above to the stainless steel plate was examined using the same base grain method as in Example 1, the number of base grains that did not peel off and remained on the stainless steel plate was 100/100. , and had sufficient adhesion.

Example 4 The alumina coating formed on the surface of the stainless steel plate in Example 3 was further heat-treated at 300'C in air for 1 hour.

When the thickness and variation in thickness of the alumina coating after heat treatment were examined in the same manner as in Example 3, there was no change in either thickness or variation.

In addition, the adhesion of the alumina coating to the stainless steel plate after heat treatment was examined using the substrate method as in Example 1.
The number of base grains that remained on the stainless steel plate without peeling was 100.
/100, indicating sufficient adhesion.

Example 5 The alumina film heat-treated at 300° C. for 1 hour in Example 4 was further heat-treated at 500° C. for 1 hour in air.

When the thickness and variation in thickness of the alumina coating after heat treatment were examined in the same manner as in Example 3, there was no change in either thickness or variation.

In addition, the adhesion of the alumina coating to the stainless steel plate after heat treatment was examined using the substrate method as in Example 1.
The number of base grains that remained on the stainless steel plate without peeling was 100.
/100, indicating sufficient adhesion.

Example 6 A glass plate (Pyrex glass) with a thickness of 2 fi was used as a base material, and this glass plate was pretreated and dried in the same manner as in the case of the quartz plate in Example 2, and then coated in the same manner as in Example 2.
Heat treatment was performed to form an alumina film on the surface of the glass plate. The sol used was also the same as in Example 2.

When the alumina coating 11 formed on the surface of the glass plate as described above was measured using the same method as in Example 1, the thickness of the alumina coating was 0.15 μm. When examined by the same method as in Example 1, it was found that the thickness was within the range of 0.15±0.05 μm and had a nearly uniform thickness.

In addition, when the adhesion of the alumina covering 119 formed as described above to the glass plate was examined using the base grain method in the same manner as in Example 1, the number of base grains that remained on the glass plate due to peeling and flaws was 100/1. 100, indicating sufficient adhesion.

〔Effect of the invention〕

As explained above, according to the present invention, an alumina film can be easily formed on the surface of an inorganic base material such as metal, glass, or ceramics. An alumina film is formed on the surface of the substrate by immersing it, pulling it up, and then heat-treating it, so there is no need for expensive equipment such as sputtering equipment or vacuum evaporation equipment, and coating can be performed in the air. Therefore, the alumina coating can be formed easily and at low cost.

Moreover, since the alumina film formed according to the present invention is formed through an oxidation process using heat treatment,
Unlike alumina films formed by sputtering or vacuum evaporation, there is no deterioration due to contact with air.

Furthermore, according to the present invention, a thin alumina film with a thickness of about 0.1 to 0.2 μm can be formed, and if a thicker alumina film is required, by repeating coating and heat treatment, A thick alumina coating can be obtained. Furthermore, the obtained alumina coating has a substantially uniform thickness and good adhesion to the substrate.

Claims (4)

[Claims] (1) Hydrolyze aluminum with acid to generate a sol of an aluminum compound with a pH of 3 to 5, immerse an inorganic base material such as metal or glass, or ceramics in this sol, and then A method for forming an alumina film on an inorganic base material such as metal, glass, or ceramics, which comprises pulling it out of a sol at a speed of 15.0 mm/sec and then heat-treating it to form an alumina film on the surface of the base material. . (2) The metal, glass, ceramic, etc. according to claim 1, wherein the acid for hydrolyzing aluminum is acetic acid, and when hydrolyzing aluminum, acetic acid is diluted with water at a volume ratio of 1:40 to 60. A method for forming an alumina film on an inorganic base material. (3) The method for forming an alumina film on an inorganic substrate such as metal, glass, or ceramics according to claim 1 or 2, wherein the substrate is pulled up perpendicularly to the sol liquid level. (4) The method for forming an alumina film on an inorganic substrate such as metal, glass, or ceramics according to claim 1, 2 or 3, wherein the heat treatment is carried out at 400 to 600°C.