JP2000054193A - Formation of ceramic film on aluminum substrate surface - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a ceramic film contg. no alkali metals and having excellent characteristics by executing a spark discharge with an aluminum substrate as an anode in an electrolytic bath contg. colloidal silica and a nitrogen-contg. compd. and substantially contg. no alkali metal ions. SOLUTION: Energizing is executed with an aluminum substrate as an anode in an electrolytic bath contg. about 1 to 200 g/l colloidal silica and about 5 to 500 g/l nitrogen-contg. compd., and in which the concn. of alkali metal ions is controlled to <=100 ppm, preferably to zero, and spark discharge is executed between it and a cathode. As for the colloidal silica, preferably, the silica particle size is controlled to about <=100 nm, particularly to about 1 to 10 nm. Moreover, as the nitrogen-contg. compd., an amine compd. or aliphatic amine in which the atomic number of nitrogen in the molecules is controlled to about 1 to 5, and the carbon number is controlled to 0 to about 10 is preferable. The spark discharge is executed by using an insoluble cathode of stainless or the like at a bath temp. of about 10 to 70 deg.C, a current density of about 0.2 to 10 A/dm2 and under a voltage of about 350 to 600 V, and the ceramic film is formed to about 2 to 200 μm thickness.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for forming a ceramic film on an aluminum substrate surface by anodic spark discharge.

2. Description of the Related Art As a method for forming ceramics on an aluminum substrate, a sintering method, a vapor phase method, and a chemical conversion method are known. Of these, the sintering method is a method of spraying a ceramic raw material powder to be formed on a base material or a method of immersing the base material in a solution in which the powder raw material is dispersed. And then melt-baking in a high-temperature furnace. In contrast, the gas phase method
There are a chemical reaction gas phase method called CVD and a physical evaporation method called PVD. In the former, a ceramic material to be formed is vaporized by heating or the like, and then reacted in a gas phase to form a ceramic film on a substrate. This is to vaporize and physically adhere to the substrate surface to form a ceramic film.

A typical chemical conversion method is an anodic oxidation method. This method utilizes a reaction in which aluminum is electrolytically oxidized in a neutral to acidic solution using an aluminum substrate as an anode, and the aluminum of the substrate becomes aluminum oxide. Apart from these methods, there is known a method of forming a ceramic film on the surface of a substrate by utilizing anodic spark discharge. For example, Japanese Patent Publication No. 58-17
Nos. 278, 59-28636, 59-28637
JP-A-59-28638, JP-A-59-45722, and JP-A-60-12438, etc., constitute an electrolytic cell composed of an alkaline aqueous solution of silicate or various metal oxyacid salts, and are sucked near the anode. A method is disclosed in which an anodic spark discharge is generated between silicate ions and metal oxyacid ions and an anodic metal, thereby forming a ceramic layer on a substrate.

[0003] In recent years, in particular, a film obtained by this method using anodic spark discharge has been found to have features such as excellent gas emission characteristics under ultra-high vacuum, excellent corrosion resistance and flexibility, and further excellent excellent far-infrared radiation. To collect.
However, since ceramic films obtained by the method using anodic spark discharge contain alkali metals such as sodium and potassium, semiconductor manufacturing equipment and the like extremely dislike these metals as contaminants. It was limited and used only in limited places. The above publication discloses a method for forming a film by anodic spark discharge using colloidal silica. Since colloidal silica has a small amount of alkali metal compared to sodium silicate or the like, it is considered that its use can solve the above problem. However, according to this method, a treatment step for forming an underlayer is required. In addition, the operation becomes complicated, and moreover, a problem arises that the underlayer contains an alkali metal.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for forming a ceramic film having excellent properties substantially free of an alkali metal on an aluminum substrate surface by anodic spark discharge.

The present invention has been made based on the finding that the above problem can be efficiently solved by spark discharge using colloidal silica as a ceramic source together with a nitrogen-containing compound such as diethanolamine. is there. That is, the present invention is a method for forming a ceramic film on the surface of an aluminum substrate by spark discharge by applying a current to an aluminum substrate as an anode in an electrolytic bath, wherein the spark discharge occurs in an electrolytic bath containing colloidal silica and a nitrogen-containing compound. The present invention provides a method for forming a ceramic film on the surface of an aluminum substrate, characterized by comprising the steps of:

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION An electrolytic bath contains colloidal silica and a nitrogen-containing compound. Colloidal silica is formed by dispersing amorphous silica particles in water to form a colloid. Typical colloidal silicas include "Snowtex" (trade name of Nissan Chemical Industry Co., Ltd.) and Nippon Chemical Industrial Co., Ltd. (Trade name) "Silica Doll" of Catalysis Chemical Industry Co., Ltd. still,
As the colloidal silica, various types can be used with respect to the particle diameter, pH, concentration, etc. of the silica.
The following are preferred. Examples of the nitrogen-containing compound include amine compounds or aliphatic amines having 1 to 5 (preferably 1 to 3) nitrogen atoms in the molecule and having 0 to 10 (preferably 0 to 7) carbon atoms. . Specifically, ammonia, hydrazine, methylamine, ethylamine, dimethylamine, diethylamine, ethylenediamine, diethylenetriamine, diethylamine, monoethanolamine, diethanolamine, triethanolamine, diethylenetetramine, iminobispropylamine, hexamethylenediamine, tetraethylenepentane Examples thereof include one or a mixture of two or more of amines, preferably ammonia, methylamine, ethylamine, monoethanolamine, diethanolamine, and triethanolamine.

[0006] The concentration of the electrolytic solution is selected from colloidal silica, 1
To 200 g / L (in terms of silicic anhydride), more preferably 10 g in terms of silicic anhydride.
１００100 g / L. When the concentration is high, gel-like precipitation occurs and the ceramic film is not formed. On the other hand, when the concentration is low, the deposition rate is low, which is not practical. The concentration of the nitrogen-containing compound is preferably from 5 to 500 g / L, and more preferably from 10 to 200 g / L. When the concentration is high, the time required for spark discharge is extended or the deposition rate is slow. Also, when the concentration decreases,
The appearance of the ceramic film is mottled, making it impractical. The pH of the electrolyte is not particularly limited, but preferably,
8-12 is good. It is essential that the electrolytic bath used in the present invention contains colloidal silica and a nitrogen-containing compound as described above, and the balance can be water, but ammonium carbonate, nonionic surfactant, aldehyde, etc. Optional additives may be included. In addition, as such optional additives, those that do not substantially contain an alkali metal are preferable. Further, the concentration of the alkali metal ion in the electrolytic bath is preferably 100 ppm or less, and particularly preferably, it does not contain any alkali metal ion.

In the present invention, the substrate on which the ceramic film is formed by the anodic spark discharge is an aluminum substrate. For this, aluminum itself, an aluminum alloy or aluminum die casting can be used. The aluminum base may have a two-dimensional shape such as a flat plate or a wire, or a three-dimensional three-dimensional shape. In the present invention, it is preferable to use an aluminum substrate which has been previously degreased, alkali-etched, acid-activated and washed by a conventional method. At this time, it is preferable to sufficiently wash the alkaline bath so as not to bring the alkali metal into the electrolytic bath. When performing anode spark discharge, that is, the bath temperature during electrolysis is preferably from 10 to 70C, more preferably from 20 to 50C. A spark discharge is performed using an insoluble electrode such as stainless steel, iron, or nickel as the cathode, and using the aluminum substrate as the anode. The area ratio between the anode and the cathode is preferably as large as possible.

The current density during electrolysis is 0.2 to 10 A / dm ²
And more preferably 0.5 to 3 A / dm.
² If the current density is low, smooth deposition does not occur. If the current density is too high, the underlying film tends to be destroyed or the deposited film tends to be rough. If the voltage at the time of electrolysis is 200 V or more, a film is formed. However, in order to obtain a practical film, the voltage is preferably 350 to 600 V. The electrolysis time can be any time for obtaining the required film thickness, but it is usually preferable that the film thickness be 2 to 200 μm. The most preferable range in consideration of the functionality of the film and the practicality of the electrolysis time is 5 to 40 μm. The waveform of the current used for the electrolysis may be an arbitrary one such as a three-phase full wave, a sawtooth wave, and a pulse wave. In order to obtain a more uniform film, a sawtooth wave and a pulse wave (short waveform) are preferable. . Usually, the stirring of the electrolytic solution is not required, but it is preferable to perform the stirring.

[0009]

According to the present invention, the caustic alkali concentration on the surface of the obtained film is so low that it cannot be detected by the energy dispersive X-ray elemental analysis, and the hardness, dielectric breakdown voltage, smoothness, etc. of the conventional film are low. I was able to get almost the same. According to the method of the present invention, it is possible to form a film having features not found in a conventional ceramic film on an aluminum substrate. Therefore, according to the present invention, for example, if a ceramic film is applied to an aluminum wire, a ceramic-coated electric wire that can be used in a high vacuum is obtained, and when a film is formed on a thin aluminum plate, the high thermal conductivity of aluminum is utilized. Thus, a flexible substrate for an electronic circuit is obtained. Further, the present invention can be used for a semiconductor manufacturing apparatus which has conventionally been difficult to use because it contains an alkali metal.
Next, the present invention will be described with reference to examples.

[0010]

EXAMPLE 1 An aluminum plate was degreased, alkali-etched, acid-activated and washed, and then used as an anode. A stainless steel plate was used as a cathode, and 50 g of colloidal silica (Snowtex XS).
/ L (in terms of silicic anhydride, the same applies hereinafter), an electrolytic bath consisting of an aqueous solution containing 28% ammonia water at 20 g / L and the balance being water, stirring with a stirrer, 1 A / dm ² at 25 ° C., and a sawtooth wave for 10 minutes. Discharge was performed to form an 8 μm ceramic film. The electrolysis voltage at that time was 250 to 400V. The properties of the ceramic film were measured by the following methods. Thickness eddy current thickness gauge, permascope E110B type (FISC
her). Alkali metal concentration energy dispersive X-ray element analyzer (HORIBA EMAX-2
770).

[0011] The varnish coating test method Test methods dielectric strength of a solid electrically insulating material breakdown voltage JISC2110, breakdown voltmeter B-51
It was measured with a model 10AF (manufactured by Face Co., Ltd.). Smoothness The surface condition was observed visually and by a scanning electron microscope, and judged according to the following criteria. ○… Good △… Slightly good ×… Poor

Example 2 Sparks were prepared in the same manner as in Example 1 except that the aqueous solution of the electrolytic bath of Example 1 was changed from Snowtex XS to 100 g / L of Snowtex N and from 28% ammonia water to 40 g / L of monoethanolamine. Discharged. Example 3 Spark discharge was carried out in the same manner as in Example 1 except that the aqueous solution of the electrolytic bath of Example 1 was changed from Snowtex XS to cataloid S-20L 80 g / L and from 28% aqueous ammonia to methylamine 20 g / L.

Example 4 The aqueous solution of the electrolytic bath of Example 1 was prepared by adding 10 g / L of colloidal silica (Silica Doll 20B) and 5% of 28% aqueous ammonia.
Spark discharge was performed in the same manner as in Example 1 except that g / L and the spark discharge time were changed to 60 minutes. Example 5 Spark discharge was carried out in the same manner as in Example 1 except that the electrolytic bath of Example 1 was changed from Snowtex XS to Snowtex N 20 g / L and the bath temperature was set to 50 ° C.

Example 6 Except that the spark discharge time of Example 1 was changed to 20 minutes.
Spark discharge was performed in the same manner as in Example 1. Comparative Example 1 A stainless steel plate was prepared by using an aluminum plate pretreated in the same manner as in Example 1 as an anode at 25 ° C., 1 A / dm ² for 10 minutes with an aqueous solution containing 50 g / L of silicate K ₂ O.nSiO _2. Spark discharge occurred as a cathode.

Comparative Example 2 From the ammonia in the electrolytic bath of Example 1, K ₂ O.nSiO _{2 was used.}
The discharge was changed to 10 g / L, and spark discharge was performed at 25 ° C., 1 A / dm ² for 10 minutes using the aluminum plate pretreated as in Example 1 as an anode and a stainless steel plate as a cathode.
The properties of the ceramic films obtained in Examples 2 to 6 and Comparative Examples 1 and 2 were measured in the same manner as in Example 1. Table 1 shows the conditions of the electrolytic bath and Table 2 shows the properties of the coating.
Shown in

[0016]

Table 1 (Electrolytic bath conditions) Bath composition and concentration Bath temperature Treatment time Example 1 Snowtex XS 50g / l Ammonia 20g / l 25 ° C 10 minutes 2 Snowtex N 100g / l Monoethano 40g / l 25 ° C 10 minutes Luamine 3 Cataloid S-20L 80g / l Methyl Amine 20g / l 25 ° C 10min 4 Silica Doll 20B 10g / l Ammonia 20g / l 25 ° C 60min 5 Snowtex N 20g / l Ammonia 10g / l 50 ° C 10min 6 Snowtex XS 50g / l Ammonia 20g / l 25 ℃ 20 minutes Comparative Example 1 K ₂ O ・ nSiO ₂ 50g / l −−−−−−−−−− 25 ° C 10 minutes 2 Snowtex XS 53g / l K ₂ O ・ nSiO ₂ 10g / l 25 ° C 10 minutes And the amount of colloidal silica is a value calculated as silicic anhydride.

[0017]

Table 2 (Characteristics of the obtained film) Alkali Breakdown film thickness (μm) Metal concentration (%) Voltage (V) Smoothness Example 18 Not detected 280 ○ 26 Not detected 290 ○ 36 Not detected 260 ○ 47 Not detected 270 ○ 5 4 Not detected 240 ○ 6 15 Not detected 280 ○ Comparative Example 1 89% * 240 △ 212 1% 250 △ * Calculated as potassium metal.

As is evident from the results in Table 2, according to the method of the present invention (Examples 1 to 6), no alkali metal was contained in the obtained coating, and the dielectric breakdown voltage was lower than that of Comparative Example 1.
And 2, but more excellent in smoothness than these. In addition, “not detected” for the alkali metal concentration is determined by an energy dispersive X-ray elemental analyzer (HORIBA
Limit (1 pp)
From m), it is considered that the content of the alkali metal in the ceramic film is 1 ppm or less.

Claims (1)

[Claims] 1. A method for forming a ceramic film on a surface of an aluminum substrate by means of spark discharge by applying a current to an aluminum substrate as an anode in an electrolytic bath and performing spark discharge in an electrolytic bath containing colloidal silica and a nitrogen-containing compound. A method for forming a ceramic film on a surface of an aluminum substrate, characterized by comprising: