KR20130081367A - Manufacturing methods of nanoporous structure by high temperature anodization of al - Google Patents

Abstract

PURPOSE: A method for manufacturing an ultrafine nanoporous alumina structure is provided to form an alumina structure having nanopores by anodizing aluminum at the temperature more than or equal to 100°C using an organic electrolyte. CONSTITUTION: A method for manufacturing an ultrafine nanoporous alumina structure uses a base metallic material as an anode (200) and platinum as a cathode (300). The base metallic material is aluminum and is immersed in an electrolyte containing metal salt. The method includes a step of anodizing the surface of the base metallic material by applying voltages to the anode and cathode. The electrolyte is an organic electrolyte, and the temperature of the electrolyte is in the range of 120-220°C. The pore sizes of an alumina structure are in the range of 1-30 nm. The metal salt is phosphate. The electrolyte is glycerol or ethylene glycol. The metallic base material undergoes a washing, polishing, and drying operation prior to the anodizing step.

Description

Manufacturing method of nanoporous structure by high temperature anodization of Al}

The present invention relates to a method for producing an ultra-fine nanoporous alumina structure through the electrochemical high temperature anodization of aluminum, more specifically, several to tens of nanometers by anodizing at a high temperature of 100 ℃ or more using an organic electrolyte as an electrolyte. The technical gist of the present invention is a method for producing an ultrafine nanoporous alumina structure through electrochemical high temperature anodization of aluminum to form an alumina structure having metric pores.

Normally, aluminum is present in the form of a compound of silicon, iron and the like in hydroxide form. The bauxite containing 50% or more of aluminum oxide is dissolved in sodium hydroxide to make sodium aluminate solution, and then alumina powder is extracted to produce metal aluminum by electrolysis. The higher the purity of the aluminum sample used, the more suitable it is to make uniform nanoporous alumina.

In general, aluminum has a high chemical affinity for oxygen, forming a thin and dense natural oxide film on the surface, and its oxide is extremely stable to artificially form an acid film on the surface of aluminum, thereby increasing the corrosion resistance and abrasion resistance. It has been widely used in a wide range of applications such as construction, decoration, electrical and communication equipment, optical devices, and mechanical parts.

Recently, studies have been actively made to make anodized alumina (hereinafter referred to as AAO) having uniform pores through anodization using such aluminum metal.

Conventional anodized alumina refers to an alumina / aluminum substrate in which aluminum is anodized to form pores of nanometer size (30-300 nm) regularly arranged on the oxidized aluminum surface. The AAO is used as a template for making one-dimensionally aligned nanostructures such as nanotubes or nanowires, and the AAO template itself is used as a nano mask to exist in the gas phase or liquid phase. Can also be used as a filter to purify.

This aluminum anodization technology has a long history. In 1923, a technique has been reported to obtain a commercial passivation film by anodizing the surface of aluminum for the purpose of preventing corrosion and decoration of aluminum. The structure with nanopores produced during anodic oxidation was used under the commercial name alumite.

Recently, as practical demands and interests on nanostructures have increased, studies on fine multilayer structures, nanowires, nanoparticles, and the like have been actively conducted, and manufacturing these nanostructures by electrochemical anodic oxidation method is economical and fine. It is gaining attention because of the simplicity of control of nanostructures and the possibility of designing free nanostructures for more complex shapes.

AAO can synthesize an alumina oxide film in which anodized aluminum in a strong acid atmosphere forms nanometer-sized pores regularly arranged on the aluminum surface. At this time, the distance between the holes is about tens to hundreds of nanometers, and the size of the holes, the distance between the holes, and the depth of the holes are variously controlled by changing the anodization conditions (anode oxidation voltage, type of acid solution, concentration, temperature, etc.). It is possible.

The diameter of the AAO pores produced by the general method can be controlled by controlling the anodization variable from 30nm to 300nm, the length from 1㎛ to 50㎛. The pore density is 109-1011 cm ^-2 , and is used as a template material for producing high density nanowires.

In particular, the nano pores are arranged regularly can be the ideal template for the electrochemical production of nanowires having anisotropy. When an electric current flows through the aluminum anode in the electrolyte, an initial barrier layer of Al ₂ O ₃ is formed. At this time, if the voltage is sufficient, the boundary layer is locally broken and heat is generated. This heat accelerates more local erosion resulting in a microporous coating and current. At this time, the generated oxygen is combined with Al inside to form a new boundary layer, and the film grows by repeating this process several times. At this time, a regular hexagonal cell is formed, and one nanopore exists at the center thereof, and the diameter of the pore is determined according to the type of electrolyte and the applied voltage.

The aluminum substrate is used as a template for making nanostructures such as nanotubes or nanowires, and the AAO template itself can be used as a nanomask.

Carbon nanotubes, which have high expectations among nanomaterials, are difficult to precisely control the size, length, thickness or density. However, when the carbon nanotubes are synthesized using the AAO template, the thickness and length of the carbon nanotubes can be variously adjusted according to the diameter and arrangement of the AAO holes. It can be applied to nano devices such as emitter tip or AFM tip.

In the case of manufacturing nanowires using an AAO template, nanowires are made by filling various materials in the holes of the AAO template. In addition, it is possible to control the thickness and length of the nanowires by adjusting the size and length of the holes of the AAO. Materials that can produce nanowires using AAO templates are metals, ceramics, and polymers. In the case of metals, nanowires can be effectively synthesized using electroplating. The nanodevices using the nanowires thus manufactured include ultra-high density hard disks, highly integrated memory devices, various electronic devices, and biochip devices.

A method of manufacturing AAO in a well-arranged form includes a two-step anodization process reported by H. Masuda Group in Japan in 1995 (Masuda, H. and Fukuda, K). ., "Ordered Metal Nanohole Arrays Made by a Two-step Replication of Honeycomb Structures of Anidic Alumina," Science, 268, 1466-1468 (1995)).

In the prior art, when the first anodization, an irregular nano structure having a high porosity is formed, and when it is removed from the aluminum surface through chemical etching, regular dimples are formed on the aluminum surface at regular intervals. They serve as the active site of reaction during secondary anodization, resulting in more regular nanoporous structures.

However, the AAO has a problem that it is impossible to produce a diameter of 30 nm or less in a general manner.

In addition, when used as a filter for processing gaseous or liquid materials, synthesis of AAO having smaller pores is required for improved selectivity and efficient separation, and synthesis of high-density ultra-light ultrafine devices is required even when used as a template. As a result, there is a need for a synthetic method in which the hole of the AAO template used as a framework can be manufactured with a very small size.

In addition, a strong acid has been used as an electrolyte to manufacture the existing AAO, but the process of manufacturing the AAO filter to solve the environmental pollution problem itself is a process that causes environmental pollution. The development of a new anodized electrolyte to solve this problem is also urgently needed.

Therefore, the present invention has been made to solve the above problems of the prior art, to form an alumina structure having pores of several to several tens of nanometers in a manner of anodizing at an elevated temperature of 100 ℃ or more using an organic electrolyte as an electrolyte. An object of the present invention is to provide a method for producing an ultrafine nanoporous alumina structure through electrochemical high temperature anodization of aluminum.

In order to achieve the above object, the present invention provides a surface of the metal base material by applying a voltage to the cathode and the anode by using aluminum metal, which is a metal base material, immersed in an electrolyte in which a metal salt is present, and using platinum as a cathode. In the method of producing an ultrafine nanoporous alumina structure through electrochemical high temperature anodization of aluminum to anodize the electrolyte, the electrolyte is an organic electrolyte, and the temperature of the electrolyte is 120 ° C to 220 ° C. Proceeding, a method for producing an ultrafine nanoporous alumina structure through electrochemical high temperature anodic oxidation of aluminum, characterized in that the size of the aperture has a size of 1nm to 30nm.

The metal salt is preferably a phosphate salt.

The phosphate salt is KH ₂ PO ₄ , K ₂ HPO ₄ , K ₃ PO ₄ , K ₂ P ₂ O ₇ It is preferable to become one or more of them.

The electrolyte is preferably glycerol or ethylene glycol.

The metal base material is preferably subjected to a washing step, a polishing step, and a drying step before anodizing.

The washing step is preferably cleaned using ethanol or acetone in an ultrasonic cleaner.

The polishing step is preferably performed by immersing in a solution of alcohol and perchloric acid (perchloric acid).

The drying step is preferably carried out at a temperature of 50 ℃ to 100 ℃.

The anodic oxidation is preferably performed two times.

Accordingly, there is an advantage of forming an alumina structure having pores of several to several tens of nanometers in size by anodizing at an elevated temperature of 100 ° C. or higher using an organic electrolyte as an electrolyte.

The present invention by the above configuration, by using an organic electrolyte having an aluminum metal with a neutral phosphate salt anodized at a high temperature to synthesize a three-dimensional aligned structure having a fine aperture, similar to AAO It is possible to synthesize a structure having a one-dimensional pores, and less burden of environmental pollution than the conventional method, there is an effect that can synthesize alumina structure having a few to several tens of nanometer pores that could not be manufactured by the conventional method.

1 is a view showing a schematic configuration of an electrochemical process for forming an ultrafine nanoporous alumina structure through electrochemical high temperature anodization of aluminum according to the present invention;
2 is a graph (a) showing a reaction rate (current density) with time by varying an electrolyte temperature during anodization according to a first embodiment of the present invention, and an electron micrograph (b) of the alumina nanostructure obtained at this time. Is shown,
3 is a graph showing a change in aperture size and distance between apertures of a nanostructure obtained by fixing an electrolyte temperature at 160 ° C. and varying an applied voltage of 10 V to 70 V during anodizing aluminum according to the second embodiment of the present invention (a ) And an electron micrograph (b) showing the appearance change at each applied voltage.
Figure 4 is a correlation between the thickness of the formed film and the pore width when the electrolyte temperature is fixed to 160 ℃, the applied voltage is set to 50V, and the anodic oxidation time is changed during anodizing aluminum according to the third embodiment of the present invention A graph showing a relationship (a) and an electron micrograph (b) showing the appearance change with the anodic oxidation time in detail.
FIG. 5 shows the alumina film obtained by fixing the electrolyte temperature at 160 ° C., the applied voltage at 50 V, and the reaction time at 6 hours when anodizing aluminum according to the fourth embodiment of the present invention, and performing one-step anodization. Figure 2 shows an electron micrograph (a) and an electron micrograph (b) of an alumina film obtained by etching it, removing it from the aluminum surface, and forming an alumina film under the same conditions, followed by two-step anodization.
FIG. 6 is a diagram showing electron micrographs (a) and actual photographs (b) of an alumina membrane film obtained by removing an alumina film obtained after two-step anodization from an aluminum surface according to a fourth embodiment of the present invention.
FIG. 7 illustrates EDX composition analysis results of an alumina membrane obtained through two-step anodization according to a fourth embodiment of the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

The method for producing ultrafine nanoporous alumina structure through electrochemical high temperature anodic oxidation of aluminum according to the present invention is carried out at K salt (KH ₂ PO ₄ , K ₂ HPO ₄ ,) at high temperature (120 ° C. to 220 ° C.), which is a highly efficient anodic oxidation condition. Porous alumina membranes can be obtained using organic electrolytes (glycerol, ethylene glycol) in which K ₃ PO ₄ , K ₂ P ₂ O ₇ ) are present.

The structure is composed of pores of several nanometers to several tens of nanometers, not only has a high specific surface area, but also strongly adheres to a metal base material, so that the structure can be used as a high efficiency, high durability filter and template. This structure can be manufactured by controlling the nanostructure including the diameter, length and film thickness of a film formed according to conditions such as electrolyte condition, applied voltage, anodization temperature and time.

Hereinafter, preferred embodiments of the present invention will be described in detail.

≪ Embodiment 1 >

As shown in FIG. 1, the electrolyte is charged in the water tank 100, and the anode 200 is made of aluminum metal, and the cathode 300 is made of platinum (Pt) metal. Anodization may form an alumina nanostructure on the surface of the metal base material.

Before anodizing, the aluminum (Al) foil is first immersed in ethanol and acetone in an ultrasonic cleaner and washed for 2 minutes. After cleaning, aluminum foil was immersed in a solution of ethanol and 65% perchloric acid in a 1: 4 volume ratio, subjected to electropolishing, washed with distilled water and dried in an oven at 60 ° C. Prepare the specimen.

Glycerol solution containing 10wt% K ₂ HPO ₄ as an electrolyte for anodic oxidation is heated to a temperature of 120 ℃ ~ 220 ℃. The prepared specimen was immersed in a heated electrolyte, and a voltage of 50 V was applied and then anodized for 6 hours.

In the first embodiment of the present invention, the temperature of the glycerol was 120 ° C, 140 ° C, 160 ° C, 180 ° C anodic oxidation was carried out, respectively, Figure 2 at different times the electrolyte temperature at the time of anodic oxidation A graph showing a reaction rate (current density) according to the present invention and an electron micrograph (b) of the alumina nanostructure obtained at this time.

As shown in FIG. 2, in the case of 120 ° C. and 140 ° C., when the temperature of the anodizing electrolyte is low, the current is relatively low at an applied voltage of 50 V, and the formed alumina film also has a thin porous film having a level of about 200 nm.

In contrast, when the temperature of the electrolyte is 160 ° C. and 180 ° C., the nanoporous alumina structure having a high current density and a thickness of about 5 μm or more can be obtained.

Particularly, in the case of 160 ° C., a structure in which one-dimensional pores having a pore diameter of about 20 nm is evenly obtained can be obtained, and in the case of 180 ° C., a 5 nm to 30 nm pore generates a three-dimensional porous structure. It was. In particular, it was confirmed that the pore size was small and the most stable nanoporous alumina structure was obtained near the electrolyte temperature of 160 ° C.

When the temperature of the electrolyte did not reach 120 ° C, anodization hardly occurred even when the applied voltage was increased, and when the temperature of the electrolyte exceeded 220 ° C, the temperature of the solution was so high that the anodized film melted by chemical etching. It was confirmed.

≪ Embodiment 2 >

In the second embodiment of the present invention, the specimen and the electrolyte were prepared in the same manner as in the first embodiment, and the anodization was performed by varying the applied voltage during the anodic oxidation. The results are shown in FIG.

Figure 3 is a graph (a) showing a change in aperture size and distance between apertures of a nanostructure obtained by fixing the electrolyte temperature at 160 ° C and varying the applied voltage from 10V to 70V when anodizing aluminum according to the present invention, and each applied voltage. Is a diagram showing an electron micrograph (b) showing the change in appearance at.

In FIG. 3, the pore size and pore size of the alumina film obtained by anodic oxidation for 6 hours were fixed at 160 ^° C and applied voltage was 10V, 30V, 40V, 50V, 60V, 70V. A graph showing the change of the center-to-center distance (Interpore distance) and a picture showing in detail the pore structure of the alumina film obtained at each voltage.

At an applied voltage of 10 V, a dense, thin (about 100 nm thick) alumina film without pores can be obtained, and as the applied voltage increases, the pore size and the interpore distance increase. It was confirmed that the pore size was suitable between about 30 V and 60 and the most stable nanoporous alumina structure was obtained.

Third Embodiment

In the third embodiment of the present invention, a specimen and an electrolyte were prepared in the same manner as in the first embodiment, and anodization was performed by varying the anodic oxidation time during anodization, and the results are shown in FIG. 4.

4 is a graph showing the correlation between the thickness of the formed film and the pore width when the anodic oxidation of the aluminum according to the present invention is fixed at an electrolyte temperature of 160 ° C. and an applied voltage of 50 V, and the anodic oxidation time is different. (b) shows an electron micrograph to show the change in appearance with a) and the anodic oxidation time in detail.

4, the thickness and pore size of the alumina film obtained by fixing the temperature and voltage of the anodizing electrolyte at 160 ° C. and 50 V, respectively, and varying the anodizing time to 1 hour, 6 hours, 15 hours, and 18 hours. Graph showing the change in width and detail of the alumina film obtained during anodization for 15 hours (b, c, d in FIG. 4 (b) and 18 hours (e, f, g in FIG. 4 (b)). It is a photograph.

As shown in FIG. 4, the resulting alumina film increases the thickness of the alumina film and the pore diameter of the upper portion as the anodic oxidation time increases, but the pore diameter of the lower portion is less than 10 nm shows no significant difference. In particular, when the anodic oxidation time is increased, it is possible to obtain an alumina film having a uniform pore thickness of at least 15 μm.

That is, it was confirmed that the nanoporous alumina structure having a desired pore size (Channel width) can be obtained by maintaining the anodization time for 1 hour or more.

Fourth Embodiment

In the fourth embodiment of the present invention, a specimen and an electrolyte were prepared in the same manner as in the first embodiment, and anodized twice, and the results are shown in FIG. 5.

FIG. 5 shows the alumina film obtained by fixing the electrolyte temperature at 160 ° C., the applied voltage at 50 V, and the reaction time at 6 hours during the anodic oxidation of aluminum according to the fourth embodiment of the present invention. Figure 2 shows an electron micrograph (a) and an electron micrograph (b) of an alumina film obtained by etching it, erasing it from an aluminum surface, and forming an alumina film under the same conditions, followed by two-step anodization.

Here, during the etching of the first alumina film, the specimen was immersed in a mixed solution of H ₃ PO ₄ (6 wt.%) And H ₂ CrO ₄ (1.8 wt.%) And removed by etching at 70 ° C. for 45 minutes.

In FIG. 5, an alumina coating having a uniform pore diameter self-aligned more and more one-dimensionally was obtained through anodization in a two-step process.

6 is an electron micrograph (a) and an actual photograph (b) of an alumina membrane film obtained by removing an alumina film obtained after two-step anodization from an aluminum surface according to a fourth embodiment of the present invention.

Chemical etching was used to remove the alumina film from the aluminum surface, and the specimen was immersed in a mixture of H ₃ PO ₄ (6 wt.%) And H ₂ CrO ₄ (1.8 wt.%) And etched through aluminum at 70 ° C. for 45 minutes. The film was removed from the aluminum surface.

As shown in Fig. 6, the alumina film pierced from the surface can be seen that it is a membrane structure in which both sides having a thickness of about 8 mu m having a uniform pore of about 20 nm are transparent. It can be used as a template or as a highly selective metal oxide filter.

FIG. 7 illustrates EDX composition analysis results of an alumina membrane obtained through two-step anodization according to a fourth embodiment of the present invention.

The ratio of quantitated Al / O is 1.58 / 3.00 and it can be confirmed that this is a typical Al ₂ O ₃ (alumina) composition.

As described above, by controlling the temperature of the electrolyte for the anodic oxidation or the like, an alumina film having a pore size ranging from several to several tens of nanometers can be formed.

100: tank 200: anode
300: cathode

Claims (9)

Electrochemical high temperature anodic oxidation of aluminum to anodize the surface of the metal base material by applying a voltage to the cathode and the anode by using aluminum metal, which is a metal base material, immersed in an electrolyte having a metal salt, and using platinum as a cathode. In the manufacturing method of the ultra-fine nanoporous alumina structure through,
The electrolyte is an organic electrolyte is used, the temperature of the electrolyte is anodized oxidation in the temperature range of 120 ℃ to 220 ℃, the size of the electrochemical high temperature anode of aluminum, characterized in that the size of 1nm to 30nm size Method for producing ultra-fine nanoporous alumina structure through oxidation. The method of claim 1, wherein the metal salt is a phosphate salt. The method of manufacturing ultrafine nanoporous alumina structures through electrochemical high temperature anodization of aluminum. The method of claim 2, wherein the phosphate salt is KH ₂ PO ₄ , K ₂ HPO ₄ , K ₃ PO ₄ , K ₂ P ₂ O ₇ Method for producing an ultra-fine nanoporous alumina structure through the electrochemical high temperature anodic oxidation of aluminum, characterized in that at least one of. The method according to any one of claims 1 to 3, wherein the electrolyte is glycerol or ethylene glycol, wherein the ultrafine nanoporous alumina structure is obtained through electrochemical high temperature anodic oxidation of aluminum. According to any one of claims 1 to 3, wherein the metal base material is subjected to a cleaning step, a polishing step, and a drying step before anodizing the ultra-fine nano through the electrochemical high temperature anodization of aluminum Method for producing a porous alumina structure. 6. The method of claim 5, wherein the cleaning step is performed by using an ethanol or acetone in an ultrasonic cleaner. 6. The method of claim 6, wherein the polishing step is performed by immersing in a mixture of alcohol and perchloric acid. 7. The method of claim 7, wherein the drying step is performed at a temperature of 50 ° C. to 100 ° C. 9. 5. The method of claim 4, wherein the anodic oxidation is performed twice. 6.

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