KR20130095543A

KR20130095543A - Method of a high-field anodization using electrolyte additive

Info

Publication number: KR20130095543A
Application number: KR1020120017067A
Authority: KR
Inventors: 하윤철; 김두헌; 김종욱; 도칠훈; 김민우; 심성주
Original assignee: 한국전기연구원
Priority date: 2012-02-20
Filing date: 2012-02-20
Publication date: 2013-08-28

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-voltage anodic oxidation method using an electrolyte additive, wherein a metal anode and a counter electrode are immersed in an electrolyte of an anodization cell, and a voltage of a predetermined pattern is applied between the metal anode and the counter electrode in the electrolyte solution. In the anodizing method of oxidizing the surface to form a nanostructure on the metal surface, the electrolyte is mixed with charcoal or lignite and water, and the mixture is boiled by applying heat, and then the acidic aqueous solution is added as an additive. The anodic oxidation method is a technical subject matter. Accordingly, by adding a certain amount of an additive to the electrolytic solution, it is possible to suppress the burning that occurs upon application of a high voltage and to manufacture a nanotemplate having an excellent self-alignment even in a high voltage section.

Description

Field of the Invention [0001] The present invention relates to a high-field anodization using an electrolyte additive,

More particularly, the present invention relates to a high-field anodization method using an electrolyte additive, and more particularly, to a method for suppressing burning generated when a high voltage is applied by adding a certain amount of an additive to an electrolyte, The present invention relates to a high-field anodization method using an electrolyte additive capable of producing a nanotemplate.

Anodization has been widely used to prevent corrosion or to color metal surfaces by forming oxide films on metal surfaces as a technique for surface treatment of metals, but recently, nanostructures such as nano dots, nanowires, nanotubes, nanorods, etc. It is widely used as a method of directly forming or manufacturing a mold for forming a nanostructure.

Such metals that can form nanostructures by anodization are known as Al, Ti, Zr, Hf, Ta, Nb, W, etc. Among them, aluminum anodization films are easy to manufacture and use other fluorine ions. Unlike metals, electrolyte handling is relatively safe, and nanoporosity and thickness control are easy, making it widely used in nanotechnology research.

Aluminum is electrochemically polarized in an aqueous solution containing an electrolyte such as sulfuric acid, oxalic acid, or phosphoric acid to form a thick anodic oxide film on the surface, which has pores with regular spacing from a porous layer (JE Houser, et al., Nat Mater. 8, 415-420 (2009)) at the interface between aluminum and aluminum oxide .

It is known that the structure of the porous layer and the boundary layer, that is, the space spacing (D _int ), the pore size, and the boundary layer thickness is generally irrelevant to the type or temperature of the electrolyte and is dominantly determined according to the applied voltage.

The self-alignment of the nanopores is determined by specific voltage and temperature according to the electrolyte. Anodization at the self-aligning condition can produce a nanotemplate in which the nanopores are densely arranged. In particular, the anodic alumina nanotemplate is relatively easy and economical to control the nanopore, and thus is utilized in various fields as nanotemplate technology.

The anodic oxidation of aluminum involves soft anodization (hereinafter referred to as MA) having a film growth rate as low as about several micrometers per hour at a relatively low voltage and hard anodic oxidation with a film growth rate of several tens of micrometers per hour at a relatively high voltage high anodization (HA), as defined in the present invention, is different from hard anodization in the conventional aluminum surface treatment industry. In contrast to hard anodization in the conventional aluminum surface treatment industry, high-feild anodization It can be defined as the specific conditions of anodic oxidation where growth and arrangement occur. Representative soft anodization and high-field anodization, which are self-ordering, one of the important features related to the formation of nanostructures, are known as Table 1.

Soft anodization and high-field anodization conditions where self-alignment occurs division Soft anodic oxidation High-system anodic oxidation Voltage Pore spacing Voltage Pore spacing Electrolyte Sulfuric acid 19 ~ 25V ¹ ⁾ 50 to 65 nm 40 ~ 80 V ⁴ ^{), 5)} 90 to 140 nm Oxalic acid 40V ² ⁾ 100 to 110 nm 110 ~ 150 V ⁶ ^{), 7)} 220 to 300 nm Phosphoric Acid 160 ~ 195V ³ ⁾ 405 to 500 nm - Film growth rate 2 to 6 μm / h 30 to 70 μm / h Current density 2 to 5 mA / cm ² (constant) 30 to 250 mA / cm ² (decrease with time)

1) H. Masuda, et al., J. Electrochem . Soc . 144, L127-L130 (1997).

2) H. Masuda, et al., Science 268, 1466-1468 (1995).

3) H. Masuda, et al.,. Jpn . J. Appl . Phys . 37, L1340-L1342 (1998).

4) S. Chu, et al., Adv . Mater . 17, 2115-2119 (2005).

5) K Schwirn, et al., ACS nano 2, 302-310 (2008).

6) W. Lee, et al., Nat . Mater . 5, 741-747 (2006).

7) W. Lee, et al., European patent application EP 1884578A1, filed Jul. 31, 2006.

Unlike the MA process, the HA process is expected to be able to grow nanotemplates in a short time due to the high current density by applying a high voltage to commercial use. However, in the HA process, alignment occurs only in a voltage range of 110 to 150 V in oxalic acid aqueous solution, and burning of the electrode occurs at a higher voltage.

Li (Y. B. Li, M. J. Zheng, and L. Ma, 'High-speed growth and photoluminescence of porous anodic alumina films with controllable interpore distances over a large range Appl. Phys. Lett. 91, 073109 (2007).)

In order to suppress burning, ethanol was added to aqueous oxalic acid solution and HA experiment was performed at -10 ~ 0 ℃ for 10 minutes to release anodized film in the range of 100 ~ 180V. Due to the temperature rise of the boundary layer was not suppressed, it was not possible to manufacture a nano-template showing excellent alignment. In order to obtain a nanotemplate having a larger pore interval, the MA method in an aqueous solution of phosphoric acid had to be applied. In the MA method, the oxide film Is very slow, about 2 ~ 3 μm / hr.

SUMMARY OF THE INVENTION Accordingly, the present invention has been made in order to solve the problems of the prior art described above, and it is an object of the present invention to provide a method of manufacturing an electrochemical device which can suppress the burning generated when a high voltage is applied by adding a certain amount of an additive to an electrolytic solution, Anodic oxidation method using an electrolyte additive capable of producing an anodic oxidation catalyst.

The present invention for achieving the above object, the metal anode and the counter electrode is immersed in the electrolyte of the anodization cell, a predetermined pattern of voltage is applied between the metal anode and the counter electrode in the electrolyte to oxidize the surface of the metal anode In the anodic oxidation method for forming a nanostructure on the surface, the electrolyte solution is a high-voltage anodic oxidation method using an electrolyte additive in which charcoal or lignite and water are mixed, the mixture is boiled by heating, and the acidic solution extracted therefrom is added as an additive. It is a technical point.

As the metal anode material to be anodized, Al, Ti, Zr, Hf, Ta, Nb, W, and any one of these alloys, it is preferable that the heat treatment, electropolishing or pre-treatment of chemical polishing is performed.

The voltage of the predetermined pattern is preferably applied between the metal anode and the counter electrode by any one of DC, AC, pulse and bias or a combination thereof.

Accordingly, by adding a certain amount of an additive to the electrolytic solution, it is possible to suppress the burning that occurs upon application of a high voltage and to manufacture a nanotemplate having an excellent self-alignment even in a high voltage section.

The present invention according to the above-described constitution makes it possible to suppress the burning which occurs when a high voltage is applied by anodic oxidation in a state where an additive is added to an electrolytic solution in a certain amount of electrolytic solution and also to manufacture a nanotemplate excellent in self- Can be effective.

FIG. 1 is a schematic view of an anodizing apparatus for high-system anodization using an electrolyte additive according to the present invention,
FIG. 2 shows current densities with time. FIG. 2 (a) shows the case where the electrolyte additive is not used, FIG. 2 (b) shows the case where the electrolyte additive is used,
3 is a diagram showing a voltage-current-temperature pattern in the case of anodization under a constant voltage, and FIG.
4 is a scanning electron micrograph of a surface of an alumina nanotemplate according to the present invention,
5 is a scanning electron microscope (SEM) photograph showing a cross section of a nanotemplate produced by 200 V high-field anodization using an additive,
6 is a graph showing the relationship between the pore spacing and the voltage in the high-field anodization according to the present invention.

1 is a schematic diagram of an anodizing apparatus for high-system anodization using an electrolyte additive according to the present invention.

Hereinafter, the anodizing apparatus will be briefly described. As shown, the vertical anodizing cell 10 is typically used in the case where a large amount of gas is generated in the electrode, and the metal support 16 connected to the (+) terminal of the power supply means 100 The negative electrode 14 is placed on the upper portion of the electrolytic cell 11 and the negative electrode 13 is connected to the negative terminal of the power supply means 100 through the negative electrode lead 15, And an agitating means 17 such as an impeller for stirring the electrolyte 12 so that the electrolyte 12 does not leak to the outside.

The temperature of each electrode / electrolyte interface may rise due to the oxidation film formation reaction in the anode 13 and the reduction reaction (water electrolysis etc.) in the cathode 14 by the voltage supplied by the power supply means 100 In particular, when the temperature of the anode 13 rises above a certain temperature, the alignment of the pores becomes worse. Therefore, in the high-temperature anodization of aluminum, the temperature should be maintained at 0 ° C. For this, 16, a cooling stand 19 is provided. The cooling base 19 is supplied with a liquid at a low temperature (0 ° C or less) from a circulator serving as a cooling means 220 of the temperature control means 200 to cool the lower portion of the metal support body 16, The heat of the heat exchanger 13 is absorbed. For this purpose, it is preferable to use a copper plate having a high thermal conductivity.

If the heat generated in the anode 13 is excessively large as in the initial stage of high-level anodization, the temperature of the circulator is further lowered for more precise temperature control, And the heating means 230 are provided to maintain the temperature of 0 占 폚 in combination with cooling and heating, the heating means 230 is stopped at the time of occurrence of excessive heat, and rapid cooling is possible.

Also, in order to lower the temperature of the electrolyte solution, cooling water may be supplied to the inside of the cell by using a metal tube instead of the platinum mesh cathode 14 generally used as a counter electrode, or by a method of lowering the temperature of the electrolyte solution 12 by the high- It is also possible. The cooling water is supplied into the tube-shaped counter electrode, and the cooling water is supplied by the electrolyte solution cooling means of the temperature control means.

Therefore, the temperature control means 200 functions to cool the metal support 16 to absorb the heat of the anode 13, and to cool the electrolyte solution by supplying cooling water to the inside of the counter electrode by the electrolyte solution cooling means .

On the other hand, in order to obtain a nanostructure having excellent pore alignment, a two-step anodic oxidation method in which an oxide film generated in the initial oxidation is removed and a voltage is directly applied or an imprint method in which a regular pattern is formed on the surface in advance is applied. Secondary anodization in a high concentration of electrolyte (generally 0.3 mol in the case of oxalic acid) used in the tea anodizing process results in breakage of the nanostructure due to rapid dissolution and dielectric breakdown of the film. This problem can be suppressed by performing secondary anodization in an electrolytic solution diluted to one-hundredth of an electrolyte. In this case, the initial current is also low and continuously decreased, resulting in a case in which a desired growth rate can not be obtained.

In order to solve the above problem, the reaction rate control means 300 adjusts the current value measured by the measuring means 310 so as to be maintained at a specified current value or higher, and the high-concentration electrolyte solution supply means 320 Thereby providing a high concentration of electrolyte. That is, the high-concentration electrolyte supply means 320 is formed to open when a current lower than a preset current value is measured by the user through the measurement means 310, and to close at a high current. By keeping the current value at a certain level, it is possible to prevent the sudden dissolution of the metal by the high electric field or the dielectric breakdown of the oxide film. To this end, the voltage is initially applied at the low concentration electrolyte.

Anodic oxidation was proceeded using the above-described anodizing apparatus, and an aluminum substrate (Goodfellow) having a diameter of 15 mm, a thickness of 0.5 mm and a purity of 99.999% was attached to the anode (13) in order to produce an anodized alumina nanotemplate. And used without heat treatment.

First, perchloric acid (60%, Aldrich) and ethanol (ethanol, 99%, Aldrich) were washed with acetone in an ultrasonic washing machine to remove impurities on the surface of the aluminum substrate, Was electropolished by applying 23 V to the mixed solution for 2 minutes.

In order to control the temperature of the boundary layer more precisely, an aluminum substrate 13 is provided on a metal support 16 for cooling and a stainless steel (SUS) mesh is used for a cathode 14.

The electrolytic solution 12 containing the additive, which is the core of the present invention, was filled in the electrolytic bath 11. The electrolytic solution was added with an additive based on an aqueous solution of 0.3M oxalic acid.

The additive is prepared by mixing charcoal or lignite with water to form a mixture, and heating the mixture under high temperature and high pressure at a temperature of 100 ° C or higher and a pressure of 10 atm or higher. The acidic aqueous solution is extracted from the heated mixture and used as an additive.

The additive includes various kinds of trace components such as organic acid, phenol, carbonyl compound, and alcohol.

The addition amount of the additive is added in a ratio of 10 parts by weight of the additive to 90 parts by weight of the oxalic acid aqueous solution.

After charging the electrolytic solution 12 containing the additive into the electrolytic bath 11, the voltage was increased to 160 V, 180 V, and 200 V at 0.5 V / s, and maintained for 1 hour, .

At this time, the temperature of the electrode was set to be maintained at 1 캜 using the temperature control means 200.

In order to effectively remove the boundary layer between the aluminum layer and the alumina layer after the anodic oxidation, a mixture of perchloric acid (60%, Aldrich) and ethanol (ethanol, 99%, Aldrich) in a volume ratio of 1: To remove the alumina film from aluminum.

After the removal of the remaining boundary layer, the pores were expanded by maintaining at 40 ° C for 10 minutes in a solution of phosphoric acid (5 wt.%, Juisei) for pore expansion of the alumina surface.

The surface and cross-sectional structures of the alumina nanotemplate were analyzed by scanning electron microscopy (FESEM, Hitachi S-4800, 10 kV).

In order to observe the current change when no electrolyte additives were used and 10 parts by weight of additives were injected, the voltage was maintained at 160 V after scanning the voltage at 0.5 V / s up to 160 V in 0.3 M oxalic acid. 1 is shown.

FIG. 2 (a) shows that the current density increased to 2500 mW / cm 2 when the electrolyte additive was not used, resulting in the burning of the electrode as shown in the specimen image. However, in the electrode using the additive of FIG. It can be seen that burning of the specimen does not occur because it is maintained in the range of ㎃ / cm 2.

Using the effects of these additives, high-voltage anodization experiments of 160V, 180V and 200V were performed to examine the self-alignment when applying a voltage of 150 V or more in an oxalic acid solution.

3 (a) is a voltage-current-temperature pattern in the case of anodizing at 140 V without using an additive, and FIG. 3 3 (b) is a pattern at 160 V using an additive, FIG. 3 (c) is a pattern at 180 V using an additive, and FIG. 3 (d) is a pattern at 200 V using an additive.

FIG. 3 (a) shows a typical four-stage high-level anodization.

However, patterns of 160V, 180V, and 200V show current peaks indicating another step at around 150 V, in which the additive suppresses abrupt current rise, but the higher the final voltage, the higher the current and the higher the temperature of the electrode.

However, once the constant voltage condition is reached, the current decreases exponentially and the temperature of the electrode gradually decreases and the oxide film grows steadily.

It is also possible to predict that the anodic oxidation will be possible even at a voltage of 200 V or higher, since the peak of this current is made at 165-170 V and the current pattern after reaching the constant voltage is almost similar.

This pattern is thought to be because current is determined by the diffusion rate of the electrolyte into the pores when the anion of the electrolyte is consumed when the nano pores are formed and the anion concentration in the pores rapidly decreases.

FIG. 4 is a scanning electron micrograph of the surface of an alumina nanotemplate according to the present invention. FIG. 3 (a) shows a case of 140 V without using an additive, and FIG. 3 3 (d) are photographs of each of the high voltage anodizing conditions of 160 V, 180 V and 200 V using the additives.

That is, a scanning electron microscope photograph of the surface of the bottom portion of the bottom portion after keeping the voltage for 1 hour by removing the boundary layer by the pulse separation method and the chemical pore expansion, In the case of FIG.

Also, it can be visually recognized that nanostructures having excellent uniformity and alignment of pores are formed in each case.

5 is a scanning electron micrograph showing a cross section of a nanotemplate produced by 200 V high-field anodization using an additive.

5 (a) is an enlarged photograph of the center and a bottom portion of a cross section, and in FIG. 5 (a), a thickness Is about 60 탆, which is about 30 times faster than anodic oxidation in an aqueous phosphoric acid solution at the same voltage.

In FIGS. 5 (b) and 5 (c), the channel of the nano pores is in the form of a perfect wire. When necessary, the nanowire is filled with the nanowire by a method such as electrolytic plating or sol- Gt; nanotemplates < / RTI >

FIG. 6 is a graph showing the relationship between the pore spacing and the voltage in high-field anodization according to the present invention. FIG. 6 (a) shows the relationship between the pore spacing and the voltage in the high- And FIG. 6 (b) shows the result of anodic oxidation in an aqueous phosphoric acid solution based on 195 V of phosphoric acid, which is one of well-known self-alignment conditions as a comparative example, in relation to the pore interval and the voltage.

6 (b) typically shows convergence to 2.5 nm / V, which is the slope of the soft anodization. Similarly, in FIG. 6 (a) resulting from the present invention, the slope agrees with 2.2 nm / V, Which corresponds to the slope in the 110 to 150 V interval.

Also, a nanotemplate having a pore interval of 440 nm at a voltage of 200 V can be produced.

As described above, the nanotemplate with a pore gap of up to 440 nm can be produced only by the addition of an additive for suppressing burning, and it can be inferred that a nanotemplate having a desired pore interval can be produced even if the voltage is increased.

As described above, in order to enable anodic oxidation of aluminum higher than 150 V, which is known as the limit of high-field anodization, additives for suppressing burning were introduced. Anodic aluminum oxide nanotemplate Were confirmed by electrochemical experiment and spectroscopic analysis. It was confirmed that the ratio of the pore interval to the voltage was maintained at 2.2 nm / V even in the voltage range of 150 V or more. It was also found that the oxide film was formed about 30 times faster in the first hour than the conventional anodic oxidation based on the aqueous phosphoric acid solution.

10: anodizing cell 11: electrolytic cell
12: electrolyte 13: anode
14: cathode 15: negative lead wire
16: metal support 17: stirring means
18: O-ring 19: Cooling zone
100: power supply means 200: temperature control means
210: temperature sensor 220: cooling means
230: heating means 300: reaction rate adjusting means
310: measuring means 320: high concentration electrolyte supply means

Claims

In the anodizing method, a metal anode and a counter electrode are immersed in an electrolyte of an anodizing cell, and a voltage of a predetermined pattern is applied between the metal anode and the counter electrode in an electrolyte to oxidize the surface of the metal anode to form nanostructures on the metal surface. In
The electrolytic solution is a high-potential anodic oxidation method using an electrolyte additive, characterized in that the charcoal or lignite and water is mixed, the mixture is boiled by applying heat, and then the acidic aqueous solution is extracted as an additive.

According to claim 1, The metal anode material to be anodized, Al, Ti, Zr, Hf, Ta, Nb, W and any one of these alloys, characterized in that the heat treatment, electropolishing or chemical polishing pretreatment is made High anodic oxidation method using an electrolyte additive.

The method of claim 1, wherein the voltage of the predetermined pattern is applied between the metal anode and the counter electrode by using any one of DC, AC, pulse, and bias, or a combination thereof. .