KR100730776B1 - Method for producing ceramic coating on the surface of aluminium alloys using microplasma - Google Patents

Abstract

A microplasma technology for forming a coating layer without containing an alkali metal, and a microplasma technology for removing a porous external coating layer or minimizing thickness of the porous external coating layer are provided. A method for forming a protection film on an aluminium alloy using microplasma process comprises applying an alternating current of an alternating component and a cathode component into an aqueous alkali solution of 30 to 50 deg.C at 60 Hz to form a ceramic coating layer on the aluminum surface using microplasma formed on an aluminum surface, wherein the aqueous alkali solution is 0.0136 to 0.136 M of a quarternary organic aqueous ammonium solution, and comprises a principal component of tetraethyl ammonium hydroxide, (C2H5)4NOH, as a quarternary organic aqueous ammonium-based solution, or a principal component of tetrabutyl ammonium hydroxide, [CH3(CH2)3]NOH, as the quarternary organic aqueous ammonium-based solution.

Description

TECHNICAL FOR PRODUCING CERAMIC COATING ON THE SURFACE OF ALUMINIUM ALLOYS USING MICROPLASMA}

The present invention relates to a microplasma electrolytic process for improving the wear, heat, corrosion and insulation properties of aluminum and aluminum alloy surfaces, and more particularly to a method of forming a thick ceramic coating layer on an aluminum alloy. The invention is particularly applicable to metal surfaces that are exposed to harsh conditions such as corrosion, high temperatures, wear and the like.

Aluminum and its alloys are very useful materials for manufacturing machines and their parts because of their low density and relatively low cost compared to other alloys than iron. However, aluminum and its alloys are relatively weak to wear and wear. In addition, in the absence of a protective coating, it is relatively well corroded under the chemical composition, and in severe cases, may react with moisture. Many protective film forming techniques have been developed to solve this problem. One such type is a microplasma electrolytic coating technique which applies a current in which alternating current and alternating current are applied to the metal to induce a microplasma discharge between the metal and the electrolyte, and thereby relies on an electrochemical reaction.

Conventionally, it was possible to form a ceramic coating layer having excellent properties using a microplasma coating method, but a critical problem is that, firstly, there is a disadvantage that the concentration of alkali metal in the coating layer is high. This is because there is a second disadvantage in that a porous, coarse outer layer grows at the same time as the high-density functional coating layer.

On the other hand, the inner wall of the dry etching chamber used in the semiconductor manufacturing process or the devices inside the chamber are mainly coated by anodizing, but are frequently recoated due to the limitation of mechanical properties of the coating layer formed by the conventional anodizing. There is a problem that must be done. Therefore, although the microplasma technique was applied to the inner wall of the dry etching chamber or the surface of the devices in the chamber, the ceramic coating layer by the conventional microplasma technique was basically formed in the electrolyte solution containing the alkali metal. It is difficult to apply the conventional microplasma technology because the Na and K components may come out of the coating layer and contaminate the semiconductor when an alkali metal component such as K exists in several atomic percent and the semiconductor etching chamber is in a vacuum state. In addition, the coating layer formed by the microplasma technique should be used after removing the porous coating layer, which occupies 30-40% of the total thickness of the coating layer.

Accordingly, the technical problems to be solved through the present invention are to provide a micro plasma technology for forming a coating layer containing no alkali metal and a micro plasma technology for removing the porous outer coating layer or minimizing its thickness.

This object can be achieved by forming a microplasma on a metal surface in an alkaline electrolyte at 30-50 ° C. using an alternating current and a cathode current of 60 Hz.

Specifically, the present invention is characterized by forming a ceramic coating layer on the aluminum surface by using a microplasma formed on the aluminum surface by applying a cross current of the alternating current component and the cathode component at 60 Hz in an aqueous alkali solution at 30-50 ° C. Provided is a method of forming a protective film of an aluminum alloy using a microplasma method.

The alkali aqueous solution is a 0.0136-0.136M quaternary organic ammonium aqueous solution, and the main component is a 4-membered organic ammonium aqueous solution, 4-ethyl ammonium hydroxide ((C ₂ H ₅ ) ₄ NOH) or a quaternary organic ammonium aqueous solution. 4-butyl ammonium hydroxide ([CH ₃ (CH ₂ ) ₃ ] NOH) is used. The aqueous alkali solution includes a powder or gel dispersed as a mobile component, and a powder of 5 micron silicon dioxide (SiO ₂ ) of 0.0167-0.167M is used as a powder, and a gel of water silicate of 0.003-0.006 is used as a gel. Na ₂ O · 3SiO ₂ ), and in some cases, 0.0004 M of 25 mass% aqueous ammonium hydroxide solution may be included as a buffer component.

In the present invention, the current ratio (I _AC / I _CC ) of the alternating current (AC) component to the cathodic current (CC) component is in the range of 1.3 to 2.5, and the time ratio τ _AC / τ _CC is 3. It is desirable to keep it in the range of -4.

In the present invention, the alkaline electrolyte is prepared by adding particles or gel dispersed in an alkali salt. Tetraethyl ammonium hydroxide was used as the main component, and 0.0156-0.156M of 20 wt% tetrabutyl ammonium hydroxide solution was added. The pH of this solution has an appropriate range of 8.5-13.5. If the pH is less than 8.5 or higher than 13.5, the aluminum alloy surface is etched.

The 5 micron-sized silicon dioxide dispersed particles added in an amount of 0.0167-0.167M are hydrated in an alkaline atmosphere to further promote the formation of a passivation film on the aluminum alloy surface. If the silicon dioxide content is less than 0.0167M, the formation of the passivation film is not promoted. If the silicon dioxide content is more than 0.167M, the proportion of the porous outer layer is increased.

The same passivation effect can be obtained by adding 0.003-0.006M of liquid glass (sodium silicate), which is particularly important for silicon-containing aluminum alloys with high surface etch rates. If the addition amount of water glass is 0.003M or less, no passivation layer is formed, and if it is more than 0.006M, sodium remains in the coating layer.

Adding 0.0004M of 25 wt% sodium hydroxide as the buffering component helps to maintain a constant pH and improves the uniformity of the coating layer.

The applied current mode used to obtain a uniform coating layer maintains a current ratio (I _AC / I _CC ) of alternating current (AC) component and cathodic current (CC) component of 60 Hz at 1.3-2.5, The time ratios τ _AC / τ _CC are maintained at 3-4, respectively.

Example

A reactor made of stainless steel having a volume of 1 liter was used for the microplasma process. The reactor simultaneously serves as a counter electrode. A bubbler is installed at the bottom of the reactor for effective cooling and circulation of the solution. The reactor is further equipped with a cooling device to maintain the inside of the reactor at a temperature of 30 ° C. Aluminum 2024 alloy material is immersed in the solution and used as the anode electrode.

The microplasma process is performed by cross-applying an alternating current component and a cathode component current of 60 Hz and lasts for 30 minutes. At this time, the application time ratio (τ _AC / τ _CC ) of the AC component and the cathode component current was 3. At the end of the process, turn off the power, remove the specimen from the electrode, wash with distilled water, dry with warm air and measure the thickness. The ceramic coating layer produced under these conditions consisted of only a functional coating layer, or very thin, even if a porous outer coating layer was formed in addition to the functional coating layer. In addition, even though the Na-containing liquid glass (Liquid glass) in the electrolyte solution, it was found that the Na component inside the coating layer is very small at 0.18 atomic% or less at 0.006M or less.

Table 1 changes the parameters of the microplasma process using electrolyte solutions having various aluminum alloys, different anode current densities, and various chemical compositions, according to various embodiments of the present invention.

TABLE 1

number Aluminum alloy material Electrolyte Component (M) Current application condition Thickness (㎛) Coating layer structure K concentration (atomic%) One A2024 (Et) ₄ NOH (0.0136) SiO ₂ (-) Liquid glass (-) NH ₄ OH (-) J (AC) = 12 (A / dm ² ) T = 30 ℃ t = 30min I _AC / I _CC = 2.5 30 Functional coating layer - 2 A2024 (Et) ₄ NOH (0.034) SiO ₂ (0.0167) Liquid glass (0.006) NH ₄ OH (0.0004) J (AC) = 33 (A / dm ² ) T = 50 ° C t = 20min I _AC / I _CC = 1.45 70 Functional coating layer + porous coating layer 0.11 or less 3 A2024 (Et) ₄ NOH (0.1360) SiO ₂ (0.167) Liquid glass (0.006) NH ₄ OH (-) J (AC) = 33 (A / dm ² ) T = 45 ℃ t = 55min I _AC / I _CC = 1.45 205 Functional coating layer + porous coating layer 0.18 or less 4 A2024 (Bu) ₄ NOH (0.1020) SiO ₂ (0.167) Liquid glass (0.003) NH ₄ OH (-) J (AC) = 12 (A / dm ² ) T = 40 ℃ t = 55min I _AC / IC _C = 1.33 70 Functional coating layer + porous coating layer 0.03 or less 5) A7075 (Et) ₄ NOH (0.034) SiO ₂ (0.025) Liquid glass (0.006) NH ₄ OH (0.0004) J (AC) = 19 (A / dm ² ) T = 50 ℃ t = 50min I _AC / I _CC = 1.45 95 Functional coating layer + porous coating layer 0.05 or less

According to the present invention, it is possible to form a ceramic coating layer on the surface of an aluminum alloy in which alkali metals such as Na or K are not present in the coating layer and almost no porous layer is present in the coating layer using the microplasma technique. The ceramic coating layer obtained through this technique can be applied to the inner surface of the semiconductor etching chamber or the surface of the device embedded in the chamber, and various other applications are expected.

Claims (5)

A ceramic coating layer is formed on the aluminum surface by using a microplasma formed on the aluminum surface by applying a cross current of an alternating current component and a cathode component at 60 Hz in an alkali aqueous solution at 30-50 ° C., The alkali aqueous solution is a 0.0136-0.136M quaternary organic ammonium aqueous solution, and the main component is a 4-membered organic ammonium aqueous solution, 4-ethyl ammonium hydroxide ((C ₂ H ₅ ) ₄ NOH) or a quaternary organic ammonium aqueous solution. And 4-butyl ammonium hydroxide (tetrabutil ammonium hydroxide, [CH ₃ (CH ₂ ) ₃ ] NOH). delete The method of claim 1, wherein the aqueous alkali solution comprises a powder or a gel dispersed as a mobile component, the powder is used as a 5 micron silicon dioxide (SiO ₂ ) powder of 0.0167-0.167M, the gel is 0.003-0.006 The water film (sodium silicate, Na ₂ O · 3 SiO ₂ ) of the protective film forming method of the aluminum alloy using a microplasma method characterized in that it comprises. The method of claim 1, wherein the aqueous alkali solution comprises 0.0004M of 25% by mass aqueous ammonium hydroxide solution as a buffer component. The method according to claim 1, wherein the current ratio (I _AC / I _CC ) of the alternating current (AC) component to the cathodic current (CC) component is in the range of 1.3 to 2.5, and the time ratio τ _AC / τ _CC is The protective film formation method of the aluminum alloy using the microplasma method characterized by maintaining in the range of 3-4.