JPH0313593A - Formation of ceramic coating film on surface of aluminum substrate - Google Patents

Abstract

PURPOSE:To form a high quality ceramic coating film on the surface of an Al substrate by carrying out spark discharge with the substrate as the anode in an electrolytic bath contg. silicate to form a coating film and by further carrying out spark discharge in an electrolytic bath contg. colloidal silica. CONSTITUTION:Spark discharge is carried out with an Al substrate as the anode in an electrolytic bath contg. silicate to form a coating film on the surface of the substrate. The silicate may be sodium silicate, the concn. is regulated to about >=10g/l and the coating film is preferably formed in about >=0.5mum thickness. Spark discharge is then carried out with the substrate as the anode in a second electrolytic bath contg. colloidal silica. The concn. of the colloidal silica in the bath is about 10-500g/l and the pref. thickness of the resulting film is about 2-200mum. A ceramic coating film having superior insulating property, smoothness and hardness is formed on the surface of the Al substrate.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for forming a ceramic film on the surface of an aluminum substrate by anodic spark discharge.

[Conventional technology]

Sintering methods, vapor phase methods, and chemical conversion methods are known as methods for forming ceramics on aluminum substrates.

The sintering method is a method in which raw powder of the ceramic to be formed is applied to a base material by spraying or dipping, and then melted and baked in a high-temperature furnace.

Gas phase methods include chemical reaction gas phase method called CVD and PV
There is a physical evaporation method called D. In the former method, after vaporizing the raw material of the ceramic to be formed by heating,
The latter method involves reacting in a gas phase to form a film on a substrate, while the latter method involves vaporizing the ceramic to be formed and physically adhering it to the surface.

A typical chemical conversion method is an anodic oxidation method. This method utilizes a reaction in which aluminum in the base material becomes aluminum oxide by electrolytically oxidizing the base material in a neutral to acidic solution using the base material as an anode.

Furthermore, methods using anodic spark discharge are known. For example, Special Publications No. 58-17278, No. 59-28636, No. 59-28637, No. 59-28638, No. 5
No. 9-45722 and No. 60-12438, etc., disclose that an electrolytic cell is composed of an alkaline aqueous solution of silicate or various metal oxyacids, and silicate ions, metal oxyacid ions, and the like are attracted near the anode. discloses a method of forming a ceramic layer by generating an anode spark discharge between the anode metal and the anode metal.

Particularly in recent years, films obtained by this method using anodic spark discharge have attracted attention because of their excellent outgassing properties in ultra-high vacuum, corrosion resistance, and flexibility, as well as excellent far-infrared radiation. It looks like this.

However, there is a problem in that the film obtained by the anodic spark discharge is inferior in insulation properties, etc., compared to other methods. It is also desired to increase smoothness and hardness.

[Problem to be solved by the invention]

An object of the present invention is to provide a method for forming a film having excellent properties in terms of insulation, smoothness, and hardness on the surface of an aluminum substrate by anodic spark discharge.

[Means for solving the problem] The ceramic film described in the official gazette in the conventional technology column contains several percent of alkali metals such as sodium and potassium, as expected from the silicate used. It is presumed that these alkali metals have an adverse effect on performance such as hardness and dielectric breakdown voltage. Furthermore, in semiconductor manufacturing equipment, these alkali metals are prohibited because they have an adverse effect. In contrast, in colloidal silica, the amount of alkali metal is several tenths of that of sodium silicate, etc., and we thought that performance could be improved by using these to form a spark-scattering film. .

Incidentally, although there is also a statement in the publication in the prior art section that it is possible to form a film with colloidal silica, it is not possible to form a film sufficient to achieve the object of the present invention only by anodic electrolysis using a colloidal silica solution.

However, as a result of study, the present invention has shown that if a spark discharge is first performed using an electrolytic bath containing silicate, and then a spark discharge is performed using an electrolytic bath containing colloidal silica,
This was done based on the assumption that the above three issues could be achieved efficiently.

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 electricity to an aluminum substrate as an anode in an electrolytic bath, the method comprising: a first electrolytic bath containing a silicate; Provided is a method for forming a ceramic film on the surface of an aluminum substrate, characterized in that the film is formed by spark discharge in a second electrolytic bath containing colloidal silica, and then spark discharge is performed in a second electrolytic bath containing colloidal silica.

The first electrolytic bath contains silicate. That is, a solution containing a silicate is used, and the silicate has the general formula M20.nsioz (M represents an alkali metal,
n is a positive number from 0.5 to 20), such as sodium silicate, potassium silicate, lithium silicate, etc. The concentration of silicate is 10g/j! or more, preferably 50 to 300
g/l.

In the first stage of electrolysis, an insoluble electrode such as stainless steel, iron, or nickel is used as the anode, and an aluminum substrate is used as the anode to perform spark discharge. The electrolysis time, that is, the discharge time including the time before spark discharge is preferably 1 minute or more, preferably 2 to 5 minutes. More preferably, the first stage electrolysis forms a film having a thickness of 0.5 μm or more, preferably 1 to 10 μm. In other words, if such a film is formed, a ceramic film made of colloidal silica can be efficiently formed in the second spark discharge performed next.

The temperature of the electrolytic solution may be any temperature at which the dissolved salt does not change, but preferably 5 to 60°C.

The current density is preferably 0.2 A/dv" to IOA/dm2, and the voltage is 150 V or more. The preferred current density range is 0.5 to 3 A/dm'. In other words, if the current density is low, This is because it takes a long time to start spark discharge, which is impractical, and if the temperature is too high, the film will become rough, making it unsuitable.

As for the aluminum substrate of the present invention, cleaning, etching, etc. are not particularly necessary as long as it is a numerically clean aluminum plate. However, in order to improve the uniformity and smoothness of the film, cleaning, etching, etc. is good.

The waveform of the rectifier for spark discharge may be arbitrary, such as three-phase full wave, sawtooth wave, pulse wave, etc., but since it shortens the spark discharge start time and makes the film uniform,
Sawtooth waves and pulse waves are preferred.

The second electrolytic bath contains colloidal silica.

Colloidal silica is made up of amorphous silica particles dispersed in water to form a colloid, and a typical example of colloidal silica is the product name "Snowtex" manufactured by Yasan Kagaku Kogyo ■. In addition, silica particle size, pH, 8
Various degrees can be used. However, if the particle size is 30 μm or more, precipitation will occur in spots, so particles of 30 μm or less are preferable.

The concentration of the electrolyte is 10 to 50 as colloidal silica.
0g/J! (1 to 200 g/l in terms of silicic anhydride)
), preferably 2.5 to 10 in terms of silicic anhydride
0 g/l is good. This is because when the concentration is high, jelly-like precipitation occurs and no ceramic film is formed, and when the concentration is low, the deposition rate becomes slow and is not practical.

An insoluble electrode made of stainless steel, iron, nickel, or the like is used as the cathode, and the aluminum substrate is used as the anode to perform spark discharge. The current density during electrolysis is 0.2 to IOA/dm"
It can be carried out at 0.5 to 3 A/d.
m" is good. If the current density is low, the deposition will not be smooth,
If it is too high, the underlying film tends to be destroyed or the deposited film tends to become rough. Further, the voltage during electrolysis is preferably 450V or higher. The electrolysis time can be any time required to obtain the required film thickness, but usually when the film thickness is 2 to 200μ
It is better to set it so that it is m. Furthermore, considering the functionality of the film and the practicality of the electrolysis time, the most preferable range is 5~
It is 40 μm.

The waveform of the rectifier used may be any one such as three-phase full wave, sawtooth wave, pulse wave, etc., but in order to obtain a more uniform film, 7'25 wave or pulse wave (rectangular waveform) is recommended. good.

[Effects of the Invention] According to the present invention, the concentration of caustic alkali on the surface of the obtained film can be reduced to several tenths of that of the conventional method, and the hardness, dielectric breakdown voltage, smoothness, etc. Improved. Moreover,
Since the flexibility and far-infrared radiation characteristics are not inferior to those of conventional methods, the method of the present invention makes it possible to form a film on an aluminum substrate that has features not found in conventional ceramic films.

Therefore, according to the present invention, for example, by applying a ceramic coating to an aluminum wire, a ceramic-coated electric wire that can be used in high vacuum can be obtained, and by forming a coating on a thin aluminum plate, the high thermal conductivity of aluminum can be utilized. In addition, a flexible substrate for electronic circuits can be obtained. Furthermore, conventionally,
It has come to be used in semiconductor manufacturing equipment, etc., which used to be difficult to use because it contains alkali metals.

Next, the present invention will be explained with reference to examples.

〔Example〕

Example 1 After cleaning an aluminum plate by degreasing, alkali etching, and acid activation, it was used as an anode, a stainless steel plate was used as a cathode, and a first electrolytic bath consisting of an aqueous solution containing 2200 g/l of KtO·n5io was prepared. at 25°C, IA
/d+n'', spark spraying was carried out for 1 minute to form a 2 μm rg- ceramic film on the aluminum plate. The aluminum plate was taken out from the electrolytic bath, washed with water, and then spark discharged in the second electrolytic bath shown below.

Using the aluminum plate as an anode and a stainless steel plate as a cathode, colloidal silica (Snowtex XS) 25
A ceramic film of 15 μm was formed by spark discharge at −25° C. for 10 minutes at IA/dm in a grade 2 electrolytic bath consisting of an aqueous solution containing 0 g/l (pHIO).

The properties of this film are shown in Table 1, and compared to Comparative Example 1, it exhibited superior properties in hardness, dielectric breakdown voltage, and smoothness.

Example 2 The aqueous solution of the second electrolytic bath of Example 1 was mixed with 500 g/j of colloidal silica (Snowtex N)! (pH about 10
) Spark discharge was performed in the same manner as in Example 1 except that the spark discharge was performed in the same manner as in Example 1.

The properties of the obtained film are shown in Table 1, and it was found to be excellent in hardness, dielectric breakdown voltage, and smoothness.

Example 3 The aqueous solution of the second electrolytic bath of Example 1 was mixed with colloidal silica (
Snowtex 40) 125g/j! (pH about 10
) Spark discharge was carried out in the same manner as in Example 1 except that the

The properties of the obtained film are shown in Table 1, and it was found to be excellent in hardness, dielectric breakdown voltage, and smoothness.

Example 4 The aqueous solution of the second electrolytic bath of Example 1 was mixed with colloidal silica (Snowtex O) at 250 g/j! (p)
Spark discharge was carried out in the same manner as in Example 1 except that the method was changed to I4).

The properties of the obtained film are shown in Table 1, and it was found to be excellent in hardness, dielectric breakdown voltage, and smoothness.

Example 5 Spark discharge was performed in the same manner as in Example 1 except that the liquid temperature of the second electrolytic bath was 50°C.

The properties of the obtained film are shown in Table 1, and it was found to be excellent in hardness, dielectric breakdown voltage, and smoothness.

Comparative Example 1 Na1OHn similar to that used in the first electrolytic bath of Example 1
By an aqueous solution containing 200 g/1 of 5io*
Spark discharge was performed at 25° C. and IA/dm2 for 10 minutes using an aluminum plate pretreated in the same manner as in Example 1 as an anode and a stainless steel plate as a cathode.

Comparative Example 2 Spark discharge was performed using only the second electrolytic bath without using the electrolytic bath of Example 1.

The properties of the obtained film are shown in Table 1, but it was not practical because it was on granules. Therefore, hardness, dielectric breakdown voltage, etc. could not be measured.

In Table 1, film thickness, hardness, dielectric breakdown voltage, and smoothness were determined by the following methods.

Membrane eddy current thickness gauge, permascope EIIOB type/Fi
schar m).

After drying the hardness test plate at 110℃ for 1 hour and leaving it to cool, a lead cap with a sharpened tip and a sharp edge was strongly pressed against the coating surface at an angle of 45℃ and at an even speed ( 3cs/sec)
I played vJ. The test was repeated 5 times, and the hardness of the lead lid was shown if it did not break 4 times or more.

Dielectric breakdown voltage was measured using a breakdown voltmeter model B"-5110AF (manufactured by @Faith) according to the Fes coating film test method of JIS C2110 Test method for dielectric strength of solid electrical insulating materials.

Smoothness The surface condition was observed visually and using a scanning electron microscope, and evaluated based on the following criteria.

◎・・・Very good O...good △・・・Slightly good X...Bad hand Continued Supplementary Positive book 1.Display of the incident 1999 patent No. 149061 3. Person who makes corrections Relationship with the incident

Claims (1)

[Claims] A method of forming a ceramic film on the surface of the aluminum substrate by spark discharge by applying current to the aluminum substrate as an anode in an electrolytic bath, the method comprising: forming a ceramic film on the surface of the aluminum substrate by spark discharge in a first electrolytic bath containing a silicate; A method for forming a ceramic film on the surface of an aluminum substrate, the method comprising performing spark discharge in a second electrolytic bath containing colloidal silica.