JP5798900B2 - Method for forming oxide film and oxide film - Google Patents

Description

  The present invention relates to a corrosion resistance treatment for a member made of aluminum or an aluminum alloy, and more specifically, a method of forming an oxide film by anodic oxidation treatment on the surface of a member constituting a vacuum apparatus, and an oxidation formed by this method. It relates to the film.

In a vacuum apparatus using a reactive gas, aluminum and an aluminum alloy (hereinafter, also referred to as “aluminum” or the like) of its constituent members need an anti-corrosion treatment to prevent a reaction with the reactive gas, so that an anodic oxidation treatment is performed. Has been done.
Among them, a porous anodizing treatment is generally performed (see Patent Document 1).
However, since the oxide film formed by this process has a porous structure with a thickness of about several tens of nanometers, the true surface area is large and the surface is a hydrate. There is a problem that there are many. Further, when heated to about 100 ° C., the oxide film is cracked, so that there is a problem that aluminum to be protected is exposed. This problem leads to a problem that magnesium is released under vacuum through cracks in the case of an aluminum alloy containing magnesium with a high vapor pressure.
As another anodizing treatment, there is a barrier type anodizing treatment (see Patent Documents 2 and 3). However, there is a problem that a film pressure of an obtained oxide film is as thin as 1 μm or less, so that it is easily damaged.
Further, as another anodic oxidation treatment, there is a micro arc type anodic oxidation treatment (see Patent Documents 4 to 7). However, since alkali metal such as sodium or potassium is contained in the oxide film, this treatment is performed. When film formation is performed in the vacuum processing apparatus, there is a problem that impurities are mixed into the device.

JP 2001-172895 A JP 2006-322040 A Japanese Patent No. 3568527 Japanese Patent No. 3881461 JP 2008-266701 A JP 2009-107211 A JP 2010-172895 A

  In order to solve the above-mentioned problems, the present invention has been obtained by a method for forming an oxide film containing less gas under vacuum, without cracking due to thermal expansion, being resistant to scratching, and not containing an alkali metal, and this method. An object is to provide an oxide film.

In order to solve the above-mentioned problems, the method for forming an oxide film according to the present invention forms an oxide film by subjecting aluminum or an aluminum alloy to micro-arc type anodic oxidation with spark discharge as described in claim 1. In the method, a solution containing at least one of an ammonium phosphate salt, an ammonium borate salt, and an organic acid ammonium salt, which does not contain an aminocarboxylic acid anion having a stability constant of 9 or more with respect to alkali metal and aluminum , An alkaline solution obtained by adding at least one of ammonia, hydrazine, ethanolamine, and ammonium carbonate is used as an electrolytic solution.
The present invention according to claim 2 is characterized in that, in claim 1, 2-15% by weight of an ammonium phosphate salt, an ammonium borate salt and an organic acid ammonium salt are contained in the solution.
According to a third aspect of the present invention, in the first or second aspect, the current density in the anodic oxidation treatment is 2 A / dm ^{2 to} 8 A / dm ² , and the maximum voltage is 250 V to 650 V.
According to a fourth aspect of the present invention, in the third aspect of the present invention, after reaching the maximum voltage, the anodic oxidation treatment is maintained for at least 15 minutes while maintaining the voltage .

  The form of the oxide film formed by the method of forming an oxide film of the present invention is irregular in lava shape, and the thickness of the oxide film can be formed uniformly and relatively thick as a whole. Even if the coefficient of thermal expansion is significantly different from the target aluminum or aluminum alloy, it is resistant to cracks caused by temperature changes. Moreover, the oxide film to be formed can be made relatively thick and can be resistant to scratches. Furthermore, the formed oxide film may not contain an alkali metal.

(A) Scanning electron microscope image of the surface of Example 1, (b) Scanning electron microscope image of the surface of Comparative Example 1 The graph which shows the voltage change in the process of Example 1 and Comparative Example 3 The graph which shows the voltage change in the process of Example 21 and Comparative Example 5 The graph which shows the change of the voltage in the process of Example 1, and an electric current.

In general, the electrolytic solution for micro arc type treatment is composed of sodium phosphate, sodium hydroxide, potassium hydroxide, water glass and the like. Since sodium and potassium are taken into the anodic oxide film formed with such an electrolytic solution, it is not suitable as a surface treatment for constituent members of a vacuum apparatus that performs the treatment in a vacuum atmosphere.
On the other hand, in the present invention, a micro-arc type anodizing process involving spark discharge is performed with an electrolyte containing no aminocarboxylic acid anion having a stability constant of 9 or more for alkali metals and aluminum. .
Specifically, as an electrolytic solution, ammonium phosphate, ammonium borate salt and organic acid ammonium salt (excluding those containing an alkali metal) alone or in a mixture of two or more thereof, ammonia, hydrazine At least one of ethanolamine and ammonium carbonate is added, and an alkaline solution having a pH of 7.5 to 11 is used.
Examples of salts of organic acid ammonium include chain dicarboxylic acids represented by HOOC (CH ₂ ) _n COOH such as malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid and decanedicarboxylic acid. And other dicarboxylic acid salts such as oxalic acid, tartronic acid, fumaric acid, maleic acid, citraconic acid, malic acid and tartaric acid, or rings such as phthalic acid, nitrophthalic acid, tetrahydrophthalic acid and borodisalicylic acid Salts of the formula dicarboxylic acid can be used.

When using an electrolyte that does not contain any additive of ammonia, hydrazine, ethanolamine, and ammonium carbonate, a barrier type anodic oxide film is formed up to the voltage at which dielectric breakdown occurs, and sparking occurs when the voltage is raised above that voltage. Although electric discharge occurs, dielectric breakdown does not concentrate locally, and the dielectric breakdown does not spread over the entire surface of the object to be processed, resulting in spots or unevenness in the oxide film, or growing the oxide film to a thickness of only a few micrometers. Can not be made. In addition, an abnormal fluctuation occurs in the voltage rise curve, and a uniform film cannot be formed. Furthermore, when a voltage of 400 V or higher is applied, there is a problem that the rate of voltage increase is slow and a strong oxide film cannot be formed, or the processing time is long.
Therefore, in the present invention, at least one of ammonia, hydrazine, ethanolamine, and ammonium carbonate is added while adjusting the pH of the electrolytic solution to be 7.5 to 11, and the anodic oxidation treatment is performed. Yes.
As a result, the discharge is dispersed, the voltage disturbance from the start of the anodic oxidation treatment to 1000 seconds is reduced, the stable voltage rise and the voltage at the start of treatment can be stabilized, and during the discharge treatment after 1000 seconds. A stable discharge treatment is possible with a small voltage rise. As a result, it can be formed in a lava-like irregular shape, and the thickness of the oxide film is uniform and relatively thick as a whole (film thickness of about 1 μm to 30 μm, especially 20 μm to 30 μm). Further, the time required to reach the target voltage value is shortened, and the processing time can be shortened.
Moreover, it is preferable to contain 2 to 15 weight% of ammonium phosphate salts, ammonium borate salts, and organic acid ammonium salts in a solution. If the amount is less than 2% by weight, the treatment voltage becomes high. If the amount exceeds 15% by weight, the formed film is uneven and a uniform film cannot be formed.
In addition, when the pH is less than 7.5, the voltage does not increase and the micro-arc oxide film cannot be grown, and the solution exceeding pH 11 is difficult to obtain even when the chemicals used in the present application are mixed. This is because management becomes difficult.

  The member to be formed with the oxide film of the present invention is aluminum or an aluminum alloy, and can be applied to, for example, Al-Si alloy No. 4000 series, No. 1000 to No. 3000, No. 5000 to No. 7000 series aluminum alloys and the like.

After reaching the target voltage value in the course of the anodic oxidation treatment, it is preferable to continue the treatment while maintaining this voltage (constant voltage). This is because, in the case of a through-hole or an intricate structure (for example, a shower plate), the film formation on the details becomes more complete by this constant voltage process. In addition, since the treatment of the constant voltage reduces the current value and provides a repair effect of the oxide film, when applied to a vacuum apparatus constituted by an aluminum alloy member containing magnesium having a high vapor pressure, the treatment under a vacuum atmosphere Spattering of magnesium and the like can be prevented.
The treatment time may be 30 minutes or less when the current value is sufficiently reduced, and is preferably within 15 minutes when the current value is reduced to half or less.

[Examples 1 to 30]
As electrolytic solution A, diammonium adipate, ammonium tetraborate, or triammonium phosphate was used, and as electrolytic solution B, hydrazine, triethanolamine, ammonia, monoethanolamine, or ammonium carbonate was used. An electrolytic solution prepared by mixing the electrolytic solution A and the electrolytic solution B shown in FIG.
A 30 mm × 40 mm × 2 mm plate sample of aluminum alloy A6061 was immersed in the electrolyte prepared as Examples 1-30. The sample side was a positive electrode, and a carbon electrode was attached to the negative electrode of the counter electrode. While maintaining a constant current density of 4 A / dm ² , anodization with spark discharge is performed to a maximum voltage of 410 V to 450 V, and after the voltage reaches the set maximum voltage, the anodization is performed for 30 minutes while maintaining the maximum voltage. went.
Table 1 shows the pH of the electrolyte when anodizing was performed under the conditions of Examples 1 to 30, the thickness of the oxide film grown by anodizing, and the amount of gas released.
In addition, the amount of gas released indicates the amount of gas released per unit area during the temperature rising from room temperature to 300 ° C. by the temperature programmed desorption method.

For comparison with Examples, Comparative Examples 1 to 6 shown in Table 2 below were prepared. In addition, the comparative consideration with respect to an Example is demonstrated concretely after Table 2.

[Comparative Example 1]
15 wt. % Sulfuric acid was prepared. A 30 mm × 40 mm × 2 mm plate sample of aluminum alloy A6061 was immersed in the electrolyte. The sample side was a positive electrode, and a carbon electrode was attached to the negative electrode of the counter electrode. Anodization was performed at a constant current density of 2 A / dm ² to form a porous anodic oxide film having a thickness of 15 μm. The voltage at the end of processing was 20V. When the gas release amount was compared with the examples, all of Examples 1 to 30 were about 1/10 or less of the gas release amount of Comparative Example 1.

FIG. 1A shows a scanning electron microscope image of the surface of Example 1, and FIG. 1B shows a scanning electron microscope image of the surface of Comparative Example 1 as a representative surface form of the embodiment of the present application.
In Example 1, the surface is in the form of lava and is in the form of an oxide film in which pores existed in some places, but Comparative Example 1 was in the form of a general porous type anodic oxidation treatment.

[Comparative Example 2]
A mixed solution of 3 g / L-trisodium phosphate, 3 g / L potassium hydroxide, and 3 g / L-sodium metasilicate was prepared as the electrolytic solution. A 30 mm × 40 mm × 2 mm plate of aluminum alloy A6061 was immersed in an electrolytic solution, and an anodic oxidation treatment with spark discharge was performed in the same manner as in the example to form an oxide film on the sample surface.
FIG. 1C shows a scanning electron microscope image of the surface of Comparative Example 2. The film form was the same as in Example 1.
Table 3 below shows the results of analyzing the constituent components of the oxide films of Example 1 and Comparative Example 2 using an electron beam μ analyzer (EPMA). In Comparative Example 2, a relatively large amount of sodium and potassium, which are anions of the electrolytic solution, were detected in the oxide film. On the other hand, in Example 1, since sodium and potassium were not included in the electrolytic solution, neither sodium nor potassium was present in the formed oxide film.
From these results, sodium and potassium are the most disliked impurities during film formation and etching in the manufacturing process of semiconductors and flat panels, but the members subjected to the corrosion resistance treatment by the method of the present invention are sodium and potassium. It was found that it can be used for manufacturing processes of semiconductors, flat panels and the like.

[Comparative Examples 3 to 5]
As shown in Table 2, an electrolytic solution in which each electrolyte was dissolved alone was prepared. A 30 mm × 40 mm × 2 mm plate sample of aluminum alloy A6061 was immersed in the electrolyte. The sample side was a positive electrode, and a carbon electrode was attached to the negative electrode of the counter electrode. Anodization with spark discharge was performed under the same conditions at the same current density as in the example.
When the electrolyte of diammonium adipate alone in Comparative Example 3 was used, the maximum voltage could be increased up to 450V, but the dielectric breakdown became unstable, and within 1000 seconds from the start of treatment as shown in FIG. The voltage rise curve fluctuated on the way (specifically, after 400 seconds to 700 seconds) (a voltage drop exceeding 20 V occurred). This phenomenon appeared prominently irregularly and every time the number of treatments was increased. Further, it was found that the location of the dielectric breakdown of the sample was local, and uniform and stable treatment could not be performed with an electrolyte solution of diammonium adipate alone. On the other hand, the voltage increase curve of Example 1 had less fluctuation than that of Comparative Example 3, and was stable even after repeated processing.
When the electrolytic solution of ammonium tetraborate alone in Comparative Example 4 was used, the maximum voltage could be increased up to 450 V, and the voltage increase curve was stable. However, when the number of treatments was repeated, the dielectric breakdown became unstable, and the voltage rising curve fluctuated in the middle like the diammonium adipate single electrolyte. It was found that there was a problem with the life of the liquid. The voltage curve in the case of Example 15 showed a stable increase in voltage as in Example 1 of FIG.
FIG. 3 shows a voltage increase curve when the electrolytic solution of triammonium phosphate alone in Comparative Example 5 is used. In Comparative Example 5, the increase in voltage was slower than that of other electrolytes, and a voltage drop exceeding 20 V occurred within 1000 seconds from the start of treatment. When the voltage finally increased to 410V, a current suddenly stopped flowing, and as a result, a voltage suddenly increased (an increase of 60 V or more per second). Furthermore, the current began to flow again and the voltage suddenly dropped. It was a treatment that was significantly less stable. From the voltage curve of Example 21, it was found that the voltage increased stably and stable treatment was possible.

[Comparative Example 6]
20 wt. % -Diammonium adipate, 10 vol. An electrolytic solution in which% -triethanolamine was mixed was prepared. A 30 mm × 40 mm × 2 mm plate sample of aluminum alloy A6061 was immersed in the electrolyte. The sample side was a positive electrode, and a carbon electrode was attached to the negative electrode of the counter electrode. While maintaining a constant current density of 4A / dm ^2, subjected to anode oxidation process with a spark discharge to around the maximum voltage 400V, after reaching a voltage to the maximum voltage set, the anodized at a constant voltage while maintaining a maximum voltage It went for 30 minutes. The reason why the maximum voltage is set to 400 V is that the dielectric breakdown becomes unstable, the voltage fluctuates, and the voltage cannot be further increased. The location where the dielectric breakdown occurred was also local, and when the film-formed sample was visually observed, the shape was uneven and uniform and stable treatment could not be performed. This is considered due to the high concentration of diammonium adipate.

In the treatments of Examples 1 to 30, after reaching the maximum voltage, the anodic oxidation treatment was maintained for 30 minutes while maintaining the voltage.
As a reference, FIG. 4 shows a graph of the relationship between the current and voltage in the process of Example 1.
FIG. 4 shows an example in which the constant voltage process is continued for 30 minutes. From this graph, it can be seen that the current value is halved in about 15 minutes from the start of the constant voltage process. I understood that.

Claims (4)

In a method for forming an oxide film by subjecting aluminum or an aluminum alloy to micro arc type anodizing treatment with spark discharge, an aminocarboxylate anion having a stability constant of 9 or more with respect to alkali metal and aluminum is not contained, and phosphorus An alkaline solution prepared by adding at least one of ammonia, hydrazine, ethanolamine and ammonium carbonate to a solution containing at least one of acid ammonium salt, ammonium borate salt and organic acid ammonium salt A method for forming an oxide film, characterized by being used as an electrolytic solution.   The method for forming an oxide film according to claim 1, wherein the solution contains 2 to 15% by weight of ammonium phosphate, ammonium borate and organic acid ammonium salt. 3. The method for forming an oxide film according to claim 1, wherein a current density in the anodic oxidation treatment is 2 A / dm ^{2 to} 8 A / dm ² , and a maximum voltage is 250 V to 650 V. 4.   4. The method of forming an oxide film according to claim 3, wherein after the maximum voltage is reached, the anodic oxidation treatment is maintained for at least 15 minutes while maintaining the voltage.