High-voltage anodization method and aluminum substrate anodized thereby

Abstract

The present invention relates to a high-voltage anodization method and an aluminum substrate anodized thereby and, more specifically, to a high-voltage anodization method using a phosphoric acid solution as an electrolyte, which enables stable anodization while applying a high voltage without causing a burning phenomenon on the surface of the aluminum substrate, and an aluminum substrate anodized thereby. The high-voltage anodization method according to the present invention improves a voltage ramping process in anodizing using phosphoric acid so that a high voltage of 190 V or higher can be applied while preventing surface burning of the aluminum substrate, thereby enabling stable anodization of the aluminum substrate. In addition, an anodized membrane manufactured using the aluminum substrate produced by the high-voltage anodization method of the present invention can stably form a hexagonal nanostructure having large pores of 150 nm or greater.

Description

High-voltage application anodic oxidation method and aluminum substrate anodicly oxidized by the same

[0001] The present invention relates to a high-voltage applied anodic oxidation method and an aluminum substrate anodicated by the same, and more specifically, to a high-voltage applied anodic oxidation method that uses a phosphoric acid solution as an electrolyte and can stably apply a high voltage while not causing a burning phenomenon on the surface of an aluminum substrate, and an aluminum substrate anodicated by the same.

[0002]

[0003] When aluminum is electrochemically anodic oxidized in an aqueous solution containing an electrolyte such as sulfuric acid, oxalic acid, or phosphoric acid, a thick anodic oxide film is formed on the surface.

[0004] Anodic oxide films exhibit minimal thermal deformation in high-temperature environments and possess electrical insulating properties. Research is underway to utilize these physical and / or electrical characteristics in various fields.

[0005] It is known that the structure of the porous layer and the boundary layer, such as the pore spacing, pore size, and boundary layer thickness, of such anodized films, which have regular spacing pores that grow from the outer surface toward the inner metal, is generally independent of the type or temperature of the electrolyte and is predominantly determined by the applied voltage.

[0006] Well-aligned porous alumina oxide membranes are known to be synthesized under specific anodic oxidation conditions depending on the electrolytic solution, and there are many existing examples of aluminum anodized using sulfuric acid, phosphoric acid, oxalic acid, etc., as the electrolyte.

[0007] In conventional methods, well-aligned anodic oxidation membranes can be fabricated using each electrolyte only under appropriate voltage conditions, but the controllable pore size has been limited. In particular, it was known that using phosphoric acid as the electrolyte and applying a voltage of 190 V or higher was required to fabricate large-pore anodic oxidation membranes with pores larger than 100 nm; however, applying such high voltages causes a burning phenomenon in which the aluminum metal burns during the anodizing process, making it impossible to fabricate large-pore anodic oxidation membranes on a large scale. Consequently, there were limitations in synthesizing anodic alumina membranes with macro-nanoporous pores of 150 nm or larger using anodizing methods based on existing electrolyte solutions.

[0008] Accordingly, while conducting research in consideration of the technical limitations mentioned above, the inventors confirmed that even when anodizing with a voltage of 190V or higher is performed using a phosphoric acid solution as an electrolytic solution to manufacture an aluminum substrate having large pores, if the voltage step-up process is improved, a well-aligned anodic oxidized alumina membrane with large nanopores of 150 nm or more can be stably synthesized without surface burning, and thus completed the present invention.

[0009]

[0010] The present invention aims to provide a high-voltage application anodic oxidation method capable of stably anodic oxidizing large-area aluminum of 10 cm x 10 cm or larger, while having a pore size of 150 nm or larger, by applying a high voltage to solve the problems of the conventional technology described above.

[0011] The present invention also aims to provide an aluminum substrate comprising an anodic oxide layer of 10 cm x 10 cm or larger, which has a pore size of 150 nm or larger and is manufactured by the manufacturing method of the present invention.

[0012]

[0013] The present invention aims to solve the above-mentioned problems.

[0014] i) a step of preparing an aluminum substrate, for providing an aluminum substrate; and

[0015] ii) A high-voltage application anodic oxidation method is provided, wherein the aluminum substrate is immersed in a solution containing phosphoric acid, the temperature of the solution containing phosphoric acid is maintained at -5°C to -2°C, and an anodic oxidation is performed by applying an applied voltage while increasing the voltage from V1 to V4 to form an anodic oxidation layer on the aluminum substrate.

[0016] The high-voltage application anodic oxidation method according to the present invention is characterized by having a different voltage step-up profile to high voltage to solve the problem of burning occurring on the aluminum surface when a high voltage is applied in a phosphoric acid solution, thereby enabling the stable production of an anodic oxidation membrane formation.

[0017] In the high-voltage applied anodic oxidation method according to the present invention, the step of forming an anodic oxidation layer on the aluminum substrate

[0018] A first boosting step for performing an anodic oxidation process by stepwise boosting the applied voltage at a rate of V1s / 1 until it reaches V2 from an initial voltage V1, and then maintaining it for a time t1;

[0019] A second boosting step for performing an anodic oxidation process by stepwise boosting the applied voltage at a rate of V2s / 1 until it reaches V3 from an initial voltage V2, and then maintaining it for a time t2;

[0020] A third boosting step for performing an anodic oxidation process by stepwise boosting the applied voltage at a rate of V3s / 1 until it reaches V4 from an initial voltage V3, and then maintaining it for a time t3; and

[0021] It is characterized by including a first voltage holding step of performing an anodic oxidation process while maintaining an applied voltage V4 for t4 hours.

[0022] In the high-voltage applied anodic oxidation method according to the present invention, the step-up ratio V1s of the first step-up stage, the step-up ratio V2s of the second step-up stage, and the step-up ratio V3s of the third step-up stage satisfy the following relationship.

[0023] V1s ≥ V2s ≥ V3s

[0024] The high-voltage applied anodic oxidation method according to the present invention is characterized by making the step-up rate at low voltage higher than the step-up rate at high voltage, thereby reducing the step-up rate as the voltage increases, so that stable anodic oxidation occurs at high voltage. Specifically, the step-up ratio V1s of the first step-up stage may be 10V to 15V per cycle, the step-up ratio V2s of the second step-up stage may be 5V to 10V per cycle, and the step-up ratio V3s of the third step-up stage may be 1V to 5V per cycle.

[0025] In the high-voltage applied anodic oxidation method according to the present invention, the voltage holding time t1 after the voltage increase of the first voltage increase step and the voltage holding time t2 after the voltage increase of the second voltage increase step satisfy the following relationship.

[0026] t1 ≥ t2 ≥ t3

[0027] The high-voltage applied anodic oxidation method according to the present invention is characterized by making the voltage increase rate at low voltage higher than the voltage increase rate at high voltage, thereby reducing the voltage increase rate as the voltage increases, and accordingly shortening the voltage holding time after voltage increase at high voltage, so that stable anodic oxidation is achieved at high voltage. Specifically, it is preferable that t1 is 30 seconds to 120 seconds, t2 is 20 seconds to 60 seconds, and t3 is 20 seconds to 60 seconds.

[0028] In the high voltage applied anodic oxidation method according to the present invention, V1 is 10V to 20V, V4 is 190V to 200V, and V1 and V4 satisfy the relationship 8≤V2 / V1≤12.

[0029] The high-voltage applied anodic oxidation method according to the present invention is an anodic oxidation method using a phosphoric acid solution as an electrolyte, wherein the final applied voltage V4 is maintained at a high voltage of 190V to 200V, which is known to stably form a honeycomb arrangement in anodizing using phosphoric acid, and the initial applied voltage V1 is maintained at 10V to 20V, and the relationship between V1 and V4 is satisfied as 8≤V2 / V1≤12, so that the anodic oxidation process can be performed stably without burning occurring in the voltage step-up process.

[0030] The high-voltage application anodic oxidation method according to the present invention is characterized by further including a second voltage holding step in which the applied voltage is maintained at V3 for t22 hours after performing the second voltage boosting step and the anodic oxidation process is performed. The high-voltage application anodic oxidation method according to the present invention is characterized by further including a step in which the applied voltage is maintained at V3 for t22 hours after performing the second voltage boosting step in the entire voltage boosting process in order to stably apply a high voltage of 190V or higher so that a burning phenomenon does not occur on the aluminum surface. Specifically, t22 is preferably 1 hour to 5 hours.

[0031] In addition, the high voltage applied anodic oxidation method according to the present invention is characterized in that the voltage holding time t22 of the second voltage holding step and the voltage holding time t4 of the first voltage holding step satisfy the following relationship.

[0032] t22 ≤ t4

[0033] In the high-voltage applied anodic oxidation method according to the present invention, the voltage holding time t4 of the first voltage holding step may be determined according to the thickness of the anodic oxidation layer formed on the final anodicated aluminum substrate, and the voltage holding time t22 of the voltage holding step during the voltage boosting process is preferably shorter than the voltage holding time t4 of the final voltage. Specifically, the second voltage holding time t22 is preferably 3 hours or more.

[0034] In the high voltage applied anodic oxidation method according to the present invention, the anodic oxidation process is characterized by being performed in a solution having a phosphoric acid concentration of 0.05 to 2 wt% in a solvent mixed with distilled water and ethanol in a volume ratio of 4:1 to 5:5.

[0035] In the high-voltage applied anodic oxidation method according to the present invention, the current limit in the anodic oxidation process is characterized as being 0.2 to 1 A. The high-voltage applied anodic oxidation method according to the present invention is a constant voltage method that applies a constant voltage, and the voltage and current are controlled by setting a current limit and readjusting the voltage when the applied current exceeds the current limit range. In order to apply high voltage to a large area of ​​10 cm * 10 cm or more, the current limit in the anodic oxidation process according to the present invention is preferably 0.2 to 1 A.

[0036] The present invention also provides an aluminum substrate comprising an anodic oxide layer anodicly oxidized by a high voltage application anodic oxidation method according to the present invention.

[0037] An aluminum substrate comprising an anodic oxide layer according to the present invention is characterized by having a pore size of 150 nm or more and a pore spacing of 400 nm or more.

[0038] The aluminum substrate including the anodic oxide layer according to the present invention is characterized by having a size of 100 mm * 100 mm or larger.

[0039]

[0040] The high-voltage application anodic oxidation method according to the present invention improves the step-up process in anodizing using phosphoric acid, thereby enabling stable anodic oxidation of an aluminum substrate without causing burning on the surface of the aluminum substrate while applying a high voltage of 190V or higher.

[0041] In addition, an anodic oxidation membrane manufactured using an aluminum substrate produced by the high-voltage application anodic oxidation method of the present invention can stably form a hexagonal nanostructure having an atmospheric pore of 150 nm or more.

[0042]

[0043] FIG. 1 shows an aluminum substrate on which a first anodizing process has been performed, manufactured according to an embodiment of the present invention.

[0044] FIG. 2 shows an aluminum substrate that has undergone a second anodizing process manufactured according to an embodiment of the present invention.

[0045] FIG. 3 shows an aluminum substrate that has been processed up to the first anodizing step according to a comparative example of the present invention.

[0046] FIG. 4 shows an aluminum substrate that has been subjected to a second anodizing step according to a comparative example of the present invention.

[0047] Figure 5 shows an anodic oxidation membrane manufactured according to an example of the present invention.

[0048] Figures 6 and 7 show the SEM measurement results of an anodic oxidation membrane manufactured according to an embodiment of the present invention.

[0049] Figure 8 shows the SEM measurement results of an anodic oxidation membrane prepared according to a comparative example of the present invention.

[0050] FIG. 9 shows an aluminum substrate that has been subjected to the second anodizing step in an embodiment of the present invention.

[0051] FIG. 10 shows an anodic oxidation membrane manufactured according to an example of the present invention.

[0052] Figures 11 and 12 show the SEM measurement results of an anodic oxidation membrane manufactured according to an embodiment of the present invention.

[0053]

[0054] The present invention will be explained in more detail below through examples. However, the present invention is not limited by the following examples.

[0055]

[0056] <Example 1>

[0057] <Example 1-1> Pretreatment of an aluminum substrate by electrolytic polishing

[0058] Electropolishing was performed on a 99.999% pure aluminum plate with dimensions of 100mm * 100mm and a thickness of 1mm.

[0059] A titanium mesh coated with platinum was used as the counter electrode of an aluminum plate and immersed in a perchloric acid + ethanol mixed solution (volume ratio 1:3), and electrolytic polishing was performed for 240 seconds at 0°C under constant voltage of 20V and current limit of 41A.

[0060] Afterwards, the aluminum plate was washed in distilled water.

[0061]

[0062] <Example 1-2> Primary Anodic Oxidation

[0063] A primary anodic oxidation was performed using the aluminum substrate electropolished in Example 1-1 above by mixing phosphoric acid to a concentration of 0.05 wt% in a solvent mixed with distilled water and ethanol (volume ratio 4:1).

[0064] Anodizing was performed in a 60L anodizing reactor under constant voltage conditions while maintaining -4℃ to -5℃, using a graphite plate as the counter electrode and a solution of 0.05 wt% phosphoric acid mixed into the solvent of distilled water + ethanol (volume ratio 4:1) as the electrolyte.

[0065] At this time, the voltage boosting profile configuration in the primary anodic oxidation is as follows.

[0066] The following steps 1 through 16 were performed as the first step-up stage.

[0067] Step 1: Applied voltage 10V, current limit 0.5A, hold time 60 seconds,

[0068] In steps 2 through 16, the current was limited to 0.5A, and the voltage was increased by 10V at a time with a holding time of 60 seconds, and the voltage was increased sequentially up to 170V.

[0069] In the second step-up stage, at Step 17, anodic oxidation was performed with a current limit of 0.5A and a boosted voltage of 170V for a holding time of 30 seconds.

[0070] In the second voltage holding step, in Step 18, the applied voltage was increased by 5V to 175V, and anodic oxidation was performed while maintaining the current limit at 0.5A for a holding time of 3 hours.

[0071] In the third step-up, the voltage was increased from 175V to 195V with a current limit of 0.5A, increasing by 1V at a time and maintaining for 6 seconds.

[0072] After being boosted to 195V in the first voltage holding stage, anodic oxidation was performed while maintaining a current limit of 0.5A for 15 hours.

[0073] A photograph of an aluminum substrate that underwent first anodic oxidation while increasing the applied voltage as described above is shown in Figure 1.

[0074]

[0075] <Comparative Example 1>

[0076] The same aluminum substrate, electrolyte solution, and electrode as in Example 1 above were used, but the applied voltage was different as follows to perform the first anodizing.

[0077] With a voltage step-up profile, Step 1 started with an applied voltage of 10V, a current limit of 0.5A, and a holding time of 60 seconds, and continued for 18 steps with a voltage step-up of 10V followed by a holding time of 60 seconds, thereby increasing the voltage to 190V to perform primary anodic oxidation. That is, in Comparative Example 1, unlike in Example 1 above, anodizing was performed by continuously increasing the voltage from 170V without a separate holding time during the process of increasing the voltage to 190V.

[0078] An aluminum substrate subjected to anodic oxidation according to Comparative Example 1 is shown in FIG. 3. As seen in FIG. 3, the aluminum substrate prepared in the present comparative example did not exhibit surface burning up to 170V, but surface burning occurred as the voltage was increased above 170V, and consequently, subsequent etching and secondary anodic oxidation processes could not be performed.

[0079]

[0080] <Examples 1-3> Etching of the primary anodic oxidation membrane

[0081] After washing the aluminum substrate obtained through the above anodic oxidation process with distilled water, the aluminum substrate was immersed in a mixed solution of chromic acid (2 wt%) and phosphoric acid (6 wt%) at a temperature of 70°C for 4 hours to etch and remove the anodic oxidation layer formed by the first anodic oxidation in Examples 1-2, and to form a regular arrangement of seeds on the aluminum substrate.

[0082]

[0083] <Examples 1-4> Secondary Anodic Oxidation

[0084] After the above first anodic oxidation, the aluminum substrate, on which a seed layer was formed on the aluminum surface by etching to remove the first anodic oxidation layer, was washed with distilled water.

[0085] Subsequently, secondary anodic oxidation was performed in the same solution as in the above example.

[0086] At this time, the voltage step profile configuration used was a voltage step in which, in Step 1, anodizing was performed while maintaining an applied voltage of 10V, a current limit of 0.5A, and a holding time of 60 seconds, and then 18 steps were performed in a manner of increasing the voltage to 10V once and then performing anodizing for a holding time of 60 seconds, thereby sequentially increasing the applied voltage to 190V.

[0087] In Step 19, anodizing was performed with an applied voltage of 190V, a current limit of 0.5A, and a holding time of 30 seconds, and then in Step 20, secondary anodic oxidation was performed by increasing the applied voltage by 5V to 195V and maintaining the current limit of 0.5A for a holding time of 15 hours.

[0088] As such, an aluminum substrate that has undergone a second anodizing step according to an embodiment of the present invention is shown in FIG. 2. As can be seen in FIG. 2, it can be confirmed that the aluminum substrate manufactured in this embodiment has a smooth surface and no burning occurs.

[0089]

[0090] <Comparative Example 2>

[0091] Using the same electrolyte solution and electrode as in Example 1 above, a first anodic oxidation was performed using the same boosting process, and after removing the first anodic oxidation layer by first etching, a second anodic oxidation was performed.

[0092] In the step-up profile, the voltage was increased to 170V by performing a step-up process in 16 steps, starting with an applied voltage of 10V, a current limit of 0.5A, and a holding time of 60 seconds, and then increasing the voltage to 10V and holding for 60 seconds to perform secondary anodic oxidation.

[0093] That is, in Comparative Example 2, unlike in Example 1 above, the second anodic oxidation was performed with the final applied voltage in the second anodic oxidation set to 170V.

[0094] An aluminum substrate subjected to anodic oxidation according to Comparative Example 2 is shown in FIG. 4. As can be seen in FIG. 4, it can be confirmed that no burning occurs on the surface of the aluminum substrate manufactured in the Comparative Example of the present invention in the case of Comparative Example 2, where up to 170V is applied.

[0095]

[0096] <Example 2> Tertiary Anodic Oxidation

[0097] The aluminum substrate that was secondarily anodized in Examples 1-4 above was immersed in an 18M sulfuric acid solution, and a third anodization was performed while applying voltage with the following step-up profile.

[0098] In Step 1, anodizing was performed with an applied voltage of 10V, a current limit of 0.5A, and a holding time of 60 seconds. Then, 18 steps were performed by sequentially increasing the voltage to 190V by increasing the voltage to 10V and performing anodizing for a holding time of 60 seconds.

[0099] In Step 19, anodizing was performed with an applied voltage of 190V, a current limit of 0.5A, and a holding time of 30 seconds, and then in Step 20, a third anodic oxidation was performed with an applied voltage of 195V, a current limit of 0.5A, and a holding time of 1 hour, thereby forming a third anodic oxidation layer, a sulfuric acid anodic oxidation layer, on the lower part of the second anodic oxidation layer formed in Example 1 by the third anodic oxidation.

[0100]

[0101] <Example 3> Separation of the anodic oxidation membrane

[0102] After washing the aluminum substrate obtained in Example 2 above with distilled water, it was immersed in a 6 wt% phosphoric acid solution at 40°C for 5 minutes, and the sulfuric acid anodic oxide layer formed between the aluminum substrate and the second anodic oxide layer in the third anodic oxidation process was removed by etching, thereby separating the aluminum substrate and the second anodic oxide layer.

[0103] The manufactured anodic oxidation membrane was separated from the aluminum substrate, and the membrane sample separated from the aluminum substrate was washed with distilled water and dried to produce a membrane as shown in Fig. 5.

[0104]

[0105] <Experimental Example> SEM Photo Measurement

[0106] The anodized membrane prepared in Example 3 above was measured by SEM, and the results are shown in Figures 6 and 7, respectively.

[0107] As shown in FIGS. 6 and 7, an anodic oxidation membrane having through holes with a pore size of 130 nm or more was obtained by an embodiment of the present invention.

[0108] As shown in FIGS. 6 and 7, in Example 1 of the present invention, when anodizing is performed while maintaining the voltage at 170V for a certain period of time during the voltage boosting process and then boosting the final applied voltage to 190V or higher, it can be seen that the manufactured membrane is formed with a pore size of 100 nm or more and pores of 130 nm or more arranged with a high degree of alignment.

[0109] In addition, as seen in the SEM image of Fig. 8, when first and second anodizing are performed with the final applied voltage set to 170V in Comparative Example 2, it can be confirmed that although no burning occurs on the surface, a nanostructure with very low pore alignment is formed.

[0110]

[0111] <Example 4>

[0112] <Example 4-1> Pretreatment by Electrolytic Polishing

[0113] To perform anodic oxidation on a large area, a 99.999% pure aluminum plate with dimensions of 220 mm * 240 mm and a thickness of 6 mm was prepared, and electrolytic polishing was performed.

[0114] A platinum-coated titanium mesh was used as the counter electrode of an aluminum plate and immersed in a perchloric acid + ethanol mixed solution (volume ratio 1:3), and electrolytic polishing was performed for 600 seconds at 0°C under constant voltage of 20V and current limit of 80A.

[0115] Afterwards, the aluminum plate was washed in distilled water.

[0116]

[0117] <Example 4-2> Primary Anodic Oxidation

[0118] A primary anodic oxidation was performed using an aluminum substrate electropolished in the above example by mixing phosphoric acid to a solvent mixed with distilled water and ethanol (volume ratio 4:1 to 5:5) to a concentration of 0.5 wt%.

[0119] Anodic oxidation was performed in a 300L PVC tank using a solution of 0.5 wt% phosphoric acid mixed into the solvent of distilled water + ethanol (volume ratio 4:1) as the electrolyte, and a graphite plate as the counter electrode while maintaining -4℃ to -5℃ under constant voltage conditions.

[0120] At this time, the voltage boosting profile configuration in the primary anodic oxidation is as follows.

[0121] Step 1: Perform anodizing at an applied voltage of 10V, a current limit of 1A, and a holding time of 60 seconds, and

[0122] In steps 2 through 16, the current was limited to 1A, and the voltage was increased by 10V at a time and maintained for 60 seconds, and then the voltage was increased to 170V by performing anodizing while increasing the voltage.

[0123] In Step 17, the voltage was increased to 170V with a current limit of 1A and a holding time of 30 seconds, and in Step 18, the applied voltage was increased by 5V to 175V with a current limit of 1A and a holding time of 3 hours.

[0124] Afterwards, the voltage was maintained at a current limit of 1A for 6 seconds, and then increased from 175V to 195V by increasing the voltage by 1V at a time.

[0125] After being boosted to 195V, primary anodic oxidation was performed for 15 hours while maintaining a final applied voltage of 195V and a current limit of 1A.

[0126] A photograph of an aluminum substrate after the first anodic oxidation is shown in Fig. 8. As can be seen in Fig. 8, it can be confirmed that the surface of the anodicated aluminum substrate manufactured according to the embodiment of the present invention is smooth and no burning phenomenon occurs, even though the size is 220 mm * 240 mm.

[0127]

[0128] <Example 4-3> Etching of the primary anodic oxidation membrane

[0129] After washing the aluminum substrate sample obtained through the above first anodic oxidation process with distilled water, the sample was immersed for 4 hours in a mixed solution of chromic acid (1.8 wt%) and phosphoric acid (6 wt%) while maintaining the temperature at 70°C to remove the first anodic oxidation layer formed by the first anodic oxidation by etching, and a regular arrangement of seeds was formed on the surface of the aluminum substrate.

[0130]

[0131] <Example 4-4> Secondary Anodic Oxidation

[0132] The aluminum substrate sample with the above-mentioned regular seeds formed was washed in distilled water.

[0133] Afterwards, secondary anodic oxidation was performed while varying the applied voltage in the step-up process below.

[0134] The boost profile configuration used is

[0135] Step 1: Anodizing was performed with an applied voltage of 10V, a current limit of 1A, and a holding time of 60 seconds, and then anodizing was performed with a voltage increase of 10V once and a holding time of 60 seconds. This method was performed 18 times to increase the applied voltage to 190V.

[0136] In Step 19, anodizing was performed with an applied voltage of 190V, a current limit of 1A, and a holding time of 30 seconds, and then in Step 20, anodizing was performed with the applied voltage increased by 5V to 195V and a current limit of 1A for a holding time of 15 hours.

[0137] As such, an aluminum substrate that has undergone secondary anodic oxidation according to an embodiment of the present invention is shown in FIG. 9. As can be seen in FIG. 9, it can be confirmed that the aluminum substrate that has undergone secondary anodic oxidation manufactured in this embodiment has a smooth surface and no burning occurs.

[0138]

[0139] <Examples 4-5> Tertiary Anodic Oxidation

[0140] The aluminum substrate that was secondarily anodized in Example 4-4 above was immersed in an 18M sulfuric acid solution, and third anodization was performed while applying voltage with the following step-up profile.

[0141] In Step 1, anodizing was performed with an applied voltage of 10V, a current limit of 0.5A, and a holding time of 60 seconds. Then, 18 steps were performed by sequentially increasing the voltage to 190V by increasing the voltage to 10V and performing anodizing for a holding time of 60 seconds.

[0142] In Step 19, anodizing was performed with an applied voltage of 190V, a current limit of 0.5A, and a holding time of 30 seconds, and in Step 20, anodizing was performed with an applied voltage of 190V, a current limit of 0.5A, and a holding time of 30 seconds, and in Step 21, a third anodic oxidation was performed by increasing the applied voltage to 195V by 5V, with a current limit of 0.5A and a holding time of 1 hour, thereby forming a sulfuric acid anodic oxidation layer, which is a third anodic oxidation layer, on the lower part of the second anodic oxidation layer formed in Example 4-1 by the third anodic oxidation.

[0143]

[0144] <Example 4-6> Separation of Anodic Oxidation Membrane

[0145] After washing the aluminum substrate obtained in Examples 4-5 above with distilled water, it was immersed in a 6 wt% phosphoric acid solution at 40°C for 5 minutes to remove the sulfuric acid anodic oxidation layer formed between the aluminum substrate and the second anodic oxidation layer in the third anodic oxidation process by etching, thereby separating the aluminum substrate and the second anodic oxidation layer.

[0146] The manufactured anodic oxidation membrane was separated from the aluminum substrate, and the membrane sample separated from the aluminum substrate was washed with distilled water and dried to produce a membrane as shown in Fig. 10.

[0147]

[0148] <Example 4-7> Pore expansion of an anodic oxidation membrane

[0149] The anodic oxidation membrane separated from the aluminum substrate obtained in Examples 4-6 above was immersed in a 6 wt% phosphoric acid solution at 30°C to expand the pores of the generated anodic oxidation membrane.

[0150]

[0151] <Experimental Example> SEM Photo Measurement

[0152] The pore-expanded anodic oxidized membranes prepared in Examples 4-7 above were measured using SEM, and the results are shown in Figures 11 and 12, respectively.

[0153] As shown in FIGS. 11 and 12, an anodic oxidation membrane was obtained by an embodiment of the present invention having a high degree of pore alignment and through holes with a pore size expanded to 300 nm or more.

[0154]

[0155] The high-voltage application anodic oxidation method according to the present invention improves the step-up process in anodizing using phosphoric acid, so that an aluminum substrate can be stably anodic oxidized without causing burning on the surface of the aluminum substrate even while applying a high voltage of 190V or more, thereby enabling the industrial production of an anodic oxidation membrane having a nanostructure of large pores.

[0156]

[0157] CROSS-REFERENCE TO RELATED APPLICATION

[0158] This patent application claims priority pursuant to Section 119(a) of the U.S. Patent Act (35 USC §119(a)) to Korean Patent Application No. 10-2024-0164810 filed on November 19, 2024, the entire contents of which are incorporated by reference into this patent application. Additionally, this patent application claims priority in countries other than the United States for the same reasons as above, and the entire contents of which are incorporated by reference into this patent application.

Claims

1. i) a step of preparing an aluminum substrate, wherein an aluminum substrate is prepared; and ii) after immersing the aluminum substrate in a solution containing phosphoric acid, maintaining the temperature of the solution containing phosphoric acid at -5°C to -2°C and applying an applied voltage while increasing it from V1 to V4 to perform anodic oxidation and form an anodic oxidation layer on the aluminum substrate. High voltage applied anodic oxidation method.

2. In Paragraph 1, The step of forming an anodic oxide layer on the aluminum substrate above A first boosting step for performing an anodic oxidation process by stepwise boosting the applied voltage at a rate of V1s / 1 until it reaches V2 from an initial voltage V1, and then maintaining it for a time t1; A second boosting step for performing an anodic oxidation process by stepwise boosting the applied voltage at a rate of V2s / 1 until it reaches V3 from an initial voltage V2, and then maintaining it for a time t2; A third boosting step for performing an anodic oxidation process by stepwise boosting the applied voltage at a rate of V3s / 1 until it reaches V4 from an initial voltage V3, and then maintaining it for a time t3; and A first voltage holding step of performing an anodic oxidation process while maintaining an applied voltage V4 for a time t4; High voltage applied anodic oxidation method.

3. In Paragraph 2, The step-up ratio V1s of the first step-up stage, the step-up ratio V2s of the second step-up stage, and the step-up ratio V3s of the third step-up stage satisfy the following relationship. High voltage applied anodic oxidation method. V1s ≥ V2s ≥ V3s 4. In Paragraph 2, Voltage holding time t1 after boosting in the first boosting step above, Voltage holding time t2 after boosting in the above second boosting stage, The voltage holding time t3 after the step-up of the above third step-up stage satisfies the following relationship. High voltage applied anodic oxidation method. t1 ≥ t2 ≥ t3 5. In Paragraph 1, The above V1 is 10V to 20V, and The above V4 is 190V to 200V, and The above V1 and V4 satisfy the relationship 8≤V2 / V1≤12 High voltage applied anodic oxidation method.

6. In Paragraph 1, The method further includes a second voltage holding step of performing an anodic oxidation process while maintaining the applied voltage at V3 for t22 hours after performing the second voltage boosting step. High voltage applied anodic oxidation method.

7. In Paragraph 6, The voltage holding time t22 of the second voltage holding step and the voltage holding time t4 of the first voltage holding step satisfy the following relationship. t22 ≤ t4 High voltage applied anodic oxidation method.

8. In Paragraph 1, The above anodic oxidation process is performed in a solution having a phosphoric acid concentration of 0.05 to 2 wt% in a solvent mixed with distilled water and ethanol in a volume ratio of 4:1 to 5:

5. High voltage applied anodic oxidation method.

9. In Paragraph 1, In the above anodic oxidation process, the current limit is 0.2 to 1 A. High voltage applied anodic oxidation method.

10. An aluminum substrate comprising an anodic oxide layer prepared by the anodic oxidation method of claims 1 to 10.

11. In Paragraph 10, The above aluminum substrate comprises pores having a pore size of 150 nm or more and an inter-pore distance of 400 nm or more. aluminum substrate 12. In Paragraph 10, The above aluminum substrate is an aluminum substrate with a size of 100 mm * 100 mm or larger.

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