Particle-mediated anodizing process for white anodized surfaces

Abstract

This provides an improved anodizing method. [Solution] The steps are: providing an anodic oxidation bath mainly composed of oxalic acid but containing t-butoxide; aging the anodic oxidation bath to condense metal alkoxides and produce metal oxide particles and acid esters; heating the bath to 40-80°C; stirring the bath at 200-700 rpm; and immersing the workpiece in the bath at 1-4 A / dm 2 A method for anodizing an aluminum alloy, comprising the steps of: anodizing the workpiece at a constant current density for a period of 1 to 20 minutes or until the bath voltage reaches a threshold of 100 to 200 V; and then anodizing the workpiece at a constant voltage for a period of 20 to 200 minutes to produce an anodized surface with a thickness of 5 to 100 micrometers, wherein the anodized surface includes an optically discontinuous pore structure, the pore structure resulting in a white or nearly white appearance.

Description

[Technical Field]

[0001] This disclosure relates to an improved method for anodizing aluminum or aluminum alloys using an aqueous anodizing bath mainly containing organic acids. More specifically, the present invention relates to a method for anodizing an aluminum substrate under controlled conditions using aqueous solutions of carboxylic acid and boric acid introduced with a particulate medium, the particulate medium being a medium derived from hydrolyzed metal alkoxides, a medium derived from long-chain polymers, or a medium derived from intermetallic compounds or alloying elements eluted from various aluminum substrates, and the method for modifying the anodizing process with this particulate medium to produce a desired anodic coating morphology and a hard, substantially white surface. [Background technology]

[0002] U.S. Patent Application Publication No. 2022 / 0364253 (by Hou et al.), "Method for applying a colored coating to an alloy," describes a method for producing an anodic oxide film structure by anodizing a light metal substrate in an anodic oxidation bath mainly containing phosphoric acid, wherein the anodic oxide film structure exhibits a structurally black or red color when filled with nickel or other metals by plating. The anodic oxidation solution described by Hou et al. generates a regular pore-side-pore structure. When this structure is filled with metal, it exhibits a narrow-band photonic resonator that reflects a single color. Such a surface will not appear white because a white surface inherently requires a broadband reflector.

[0003] International Publication No. 2012 / 119306 (by Nano Institute) describes a method for producing a white aluminum oxide coating by generating a pore structure through anodic oxidation, infiltrating a first chemical substance into this pore structure, and then infiltrating a second chemical substance into this pore structure. When the two chemical substances react within the pore structure, a white compound is produced. A third acidic process modifies the pore structure of the alumina, thereby increasing the opacity of the anodic oxidation layer and enhancing the whiteness of the surface. This method is overly complex for implementation in an industrial environment, and the whiteness of the surface largely depends on a second anodic oxidation step that produces a sufficiently opaque anodic oxidation layer.

[0004] U.S. Patent No. 10,760,175 Specification ("Apple Patent") "Multilayer White Anodic Film" teaches a multi-step method for producing a white anodic film that includes at least two anodic oxidation steps. In the first step, an elastic and dense surface pore structure is generated, and in the second step, an irregular pore structure that provides diffuse reflection is developed, particles such as TiO2 are introduced into the pores, and the pores are sealed. In this process, a surface that appears white is generated by managing reflection in multiple layers, but this process is complex and it is difficult to obtain a whiteness with L exceeding 90 when measured using the CIE Lab * method. This method, similar to the disclosure by Nano Institute, relies on modifying the anodic oxidation pore structure and introducing a secondary material into the anodic oxidized pore structure to color the surface. The multi-step process is complex and difficult to control in an industrial environment.

[0005] Korean Patent No. 102244376 Specification "White Anodic Oxidation Method Using Nanoparticles" teaches a method for forming an anodic structure like the Apple Patent, but a vacuum is used to promote the infiltration of nanomaterials within the anodic oxidation structure. Summary of the Invention Problems to be Solved by the Invention

[0006] This disclosure describes various embodiments and examples relating to the formation of novel anodized coatings on aluminum or aluminum alloys, which exhibit a glossy white, matte white, or opaque white appearance. In particular, one embodiment describes an anodizing process mediated by particles or particulate compounds to produce a white anodized surface. [Means for solving the problem]

[0007] In one embodiment, an aluminum anodizing process is provided to produce a white or substantially white nanocrystalline alumina surface on an aluminum substrate, i. A step of pre-treating the aluminum substrate; ii. Aluminum substrate, as follows: - Buffering material, - One or more particle sources, and - One or more carboxylic acids The steps include immersion in an aqueous anodic oxidation bath containing; iii. Providing an anodized substrate including an anodized surface by anodizing an aluminum substrate according to the specified current and voltage for anodizing; A process including this is provided.

[0008] For example, the specifications for the current and voltage of anodizing include: i. Maintaining a first constant current over the first period; ii. Varying the current to a second constant current over a second period; iii. Perform anodizing with a second constant current until the voltage reaches a threshold, and then switch to constant voltage anodizing; iv. Perform constant voltage anodizing over a third period; It includes.

[0009] In another embodiment, an anodized substrate is provided, comprising an anodized surface, wherein the anodized surface comprises a dense nanocrystalline bottom layer, a nanotube layer substantially filled with nanocrystalline material, and a porous nanotube layer having nanocrystalline walls. In one embodiment, the anodized substrate is an aluminum substrate.

[0010] In one embodiment, a method is provided for forming an anodic oxide surface including a white oxide film, the method comprising: pre-treating an aluminum substrate or an aluminum alloy substrate; anodic oxidizing the substrate in an anodic oxidation bath, wherein the anodic oxidation bath comprises an organic acid electrolyte, the organic acid electrolyte comprising a particle source produced by hydrolysis alkoxide, or another acid activity modifier; the method may further include a step of increasing gloss by polishing the anodic oxide surface; the method may further include a step of increasing the durability of the coating by sealing the anodic oxide surface.

[0011] In one example, the anodic oxide surface produced by this method includes a layered anodic oxide structure, which has a random pore structure and periodic optical discontinuities. A random pore structure is a structure that does not have the regular geometric pore configuration typical of anodized aluminum. The random pore structure can diffusely reflect all visible light frequencies, thereby producing a surface with a white or substantially white surface appearance.

[0012] In one example, the method includes a further step of impregnating an anodized structure having a random pore structure with particles smaller than 40 nm, thereby increasing the diffuse reflectance provided by the anodized surface.

[0013] In a further example, an aluminum alloy substrate or an aluminum substrate may be preformed into an enclosure, equipment housing, device housing, window frame, or other building, commercial, aerospace, or industrial component, wherein, in the application of the component, a white or semi-white anodized surface for aesthetic finishing provides useful aesthetics, improves surface performance, or imparts other functional properties.

[0014] In one example, the particle source and alcohol produced by the hydrolysis of metal alkoxides in an anodic oxidation bath are replaced with a combination of metal oxide nanoparticles with a particle size of approximately 100 nm and alcohol.

[0015] In one example, the particle source and alcohol produced by the hydrolysis of metal alkoxides in the anodic oxidation bath are replaced by metal ions or compounds and alcohol eluted during the anodic oxidation process.

[0016] In one example, the particle source and alcohol produced by the hydrolysis of metal alkoxides in the anodic oxidation bath can be replaced with long-chain organic acids or other long-chain organic molecules.

[0017] While specific embodiments and examples have been described above, it should be understood that further embodiments and examples will become apparent from the detailed description and drawings below. [Brief explanation of the drawing]

[0018] This disclosure will be readily understood by the following detailed description and accompanying drawings, where reference figures indicate corresponding elements.

[0019] [Figure 1] A cross-sectional view of a substrate having a standard anodized surface, which provides a translucent or translucent colored surface, is shown.

[0020] [Figure 2] A cross-sectional view of an optically discontinuous anodized surface, where the structure provides a white appearance, is shown, based on a specific example.

[0021] [Figure 3] A flowchart is shown that defines the process for forming an anode film with a white appearance in a specific example.

[0022] [Figure 4] The graphs of voltage and current during anodizing in a specific example are shown.

[0023] [Figure 5A] SEM surface and cross-sectional images of an anode coating produced by a specific example are shown. [Figure 5B] SEM surface and cross-sectional images of an anode coating produced by a specific example are shown. [Figure 5C] SEM surface and cross-sectional images of an anode coating produced by a specific example are shown. [Figure 5D] SEM surface and cross-sectional images of an anode coating produced by a specific example are shown. [Figure 5E] SEM surface and cross-sectional images of an anode coating produced by a specific example are shown. [Figure 5F] SEM surface and cross-sectional images of an anode coating produced by a specific example are shown. [Figure 5G] SEM surface and cross-sectional images of an anode coating produced by a specific example are shown. [Figure 5H] SEM surface and cross-sectional images of an anode coating produced by a specific example are shown.

[0024] [Figure 6A] The XRD spectrum of a white-appearing anode coating in a specific example is shown. [Figure 6B] The XRD spectrum of a white-appearing anode coating in a specific example is shown. [Figure 6C] The XRD spectrum of a white-appearing anode coating in a specific example is shown.

[0025] [Figure 7]This is a simplified diagram of an anodizing process apparatus showing the orientation of nanoparticles in coating formation.

[0026] [Figure 8] This graph shows the relationship between coating color, coating thickness, and surface pore diameter as a function of anodizing time.

[0027] [Figure 9] This image shows the optical effect generated by the nanoporous zone of a white anode coating. [Modes for carrying out the invention]

[0028] For a more detailed explanation, refer to the representative examples shown in the relevant diagrams.

[0029] In the following explanation, the term "aluminum" is understood to encompass all types of aluminum and wrought aluminum alloys, including pure 1000 series aluminum, high-strength 2000 series aluminum alloys, high-ductility 3000 series aluminum alloys, malleable 5000 series alloys, highly formable 6000 series alloys, and 7000 series aerospace alloys. The term "aluminum" may also include die-cast aluminum alloys such as the A360.0 series, A380.0 series, C443.0 series, and B390.0 series.

[0030] In this description and claims, preformed aluminum substrates or aluminum alloy substrates are not limited to, but include, window frames, extruded window frames, cases for portable personal devices such as watch cases and telephone cases; automotive parts and extruded products, building parts and extruded products; aerospace parts, aerospace extruded products, marine parts, marine extruded products; die-cast or vacuum-cast parts.

[0031] In this description, the term "approximately" as used herein in relation to a referenced numerical indicator means within ±10% of the referenced numerical indicator. For example, the expression "approximately 10 g / L" includes a range of 9 g / L to 11 g / L.

[0032] As used herein, the terms “comprises,” “comprising,” “includes,” and “including” should be interpreted as inclusive, open-ended, and not exclusive. Specifically, as used herein, including in the claims, the terms “comprises,” “comprising,” “includes,” and “including,” and their variations, mean that the specified features, steps, or components are included. These terms should not be interpreted as excluding the existence of other features, steps, or components.

[0033] As used herein, the term “substantially” means largely, often, essentially, or to a significant or remarkable degree.

[0034] In this specification, when the terms “white” and “white shade” are used in reference to surfaces, white means L * >90, a * and b * This means that the range is between -2 and +2.

[0035] As used herein, the term C1-C6 alcohol refers to a linear or branched carbon structure having a monohydric aliphatic alcohol. In one example, a C1-C6 alcohol is obtained from the in-situ hydrolysis of a metal alkoxide added to an anodic oxidation bath. In another example, a combination of metal oxide nanoparticles and any C1-C6 alcohol can be directly added to the anodic oxidation bath.

[0036] The process described herein provides a white, hard anode coating on an aluminum substrate. The anode coating creates a protective surface on a component or part formed from aluminum or an aluminum alloy by providing a relatively dense, thick metal oxide surface. These anode coatings offer considerable hardness, chemical resistance, and optical properties. Therefore, the properties of these anode coatings are desirable.

[0037] Figure 1 shows a schematic diagram of a typical anodic oxidation surface, such as a film 100 formed on an aluminum substrate 101. The film 100 has a plurality of pores 110 with a diameter 102, which can range from approximately 2 nm (formed mainly in a sulfuric acid anodic oxidation bath) to approximately 200 nm (formed mainly in a phosphoric acid anodic oxidation bath). The anodic oxidation surface 100 has a thickness 103, which can range from submicrons to several hundred microns in the case of hard anodizing. The film 100 further includes a barrier layer with a thickness 104. This thickness 104 depends on the anodizing voltage and can range from approximately 2 nm to approximately 200 nm or more. The pore wall thickness 105 and pore diameter 103a can range from approximately 5 nm to approximately 100 nm. In any case, the optical properties of the coating are determined mainly by the substantially transparent anode film 100. The anode coating 100 interferes minimally with incident light, which is often reflected by the substrate below, as shown by rays 106 and 107. The anodic surface refracts rays 106 and 107 and reflects the incident light at a low percentage depending on the angle of incidence, as shown by reflected ray 108 and low-angle incident ray 109. The optical properties of the anodic surface, such as coating 100, give rise to the typical silvery / yellow iridescent appearance of the anodic surface.

[0038] Figure 2 shows a schematic cross-section of an anodized surface 205 on an AL6061 aluminum alloy substrate 201 according to a specific example of this disclosure. The figure also shows exemplary SEM partial images of the morphology of the cross-section of the anodized surface. The interaction between the anodized structure and light can be understood by referring to 200 and associated SEM image fragments 208, 209, and 210 in Figure 2. Here, the anodized surface 200 comprises an aluminum substrate 201 and a surface coating 205. The surface coating 205 comprises several layers 202, 203, and 204. 202 is a dense nanoporous layer substantially in contact with the aluminum substrate 201. 203 is a multiple stack containing several discontinuous nanoporous anodized structures, which are located between and in contact with 202 and 204. 204 is a branched nanoporous layer located furthest out from 201. Each layer can exhibit varying thicknesses depending on the anodizing parameters and the substrate. However, in an example for illustrative purposes (Figure 5), layers 202, 203, and 204 can have nearly equal thicknesses of approximately 10 μm. Referring to Figure 2, the incident light ray 206 can have any angle of incidence without significantly changing its effect and first strikes the surface layer 204. This layer 204 has a random porous structure, and as shown in SEM 208, this porous structure resembles the appearance of frosted glass. As a result, the incident light 206 is scattered, with only a small portion of the light being reflected and scattered 207. The reduced scattered light ray 206 then reaches layer 203, which has a random discontinuous structure. The random discontinuous structure of this layer provides multiple nanotube / alumina interfaces, as shown in SEM 209, and 203 reflects or scatters a considerable proportion of the incident light. The light 206 then enters layer 202. As shown in the SEM210 in Figure 2, layer 202 is the densest layer, providing a further pore / alumina interface, which reflects or scatters substantially all or all of the remaining incident light 206. Therefore, only a small amount of the incident light is reflected from the substrate. The total scattered and reflected light 207 in Figure 2 gives the anodized surface a substantially white appearance. Figure 9 is an image of a sample in which the anodized surface 200 has been electrochemically exfoliated to understand the effect of nanopores on the appearance of the coating.Here, 901 in Figure 9 shows at least the top two layers (compared to layers 203 and 204 in Figure 2) having a white appearance. The remaining coating is sufficiently translucent, and therefore the underlying aluminum substrate (902, compared to substrate 201 and layer 202 in Figure 2) can be observed. The inventors believe that the exfoliated coating is potentially usable in catalytic and photocatalytic applications, nanofiltration devices, and other technologies including porous membranes.

[0039] Figure 3 shows a flowchart of the process for producing a white anodic oxide surface by a specific example of this disclosure. The process is initiated in step 301.

[0040] Step 302 in Figure 3 requires the preparation of an anodic oxidation bath. In certain examples, the anodic oxidation bath contains aqueous solutions of oxalic acid, boric acid, and a carboxylic acid. In one example, oxalic acid is the main acid in the bath, with a concentration of about 10 to about 140 g / L, or about 20 to about 60 g / L, preferably about 25 to 50 g / L, more preferably about 42 g / L. In one example, boric acid acts as a stabilizer in the bath, with a concentration of about 5 to about 20 g / L, about 8 to about 16 g / L, preferably about 10 g / L. In one example, the other carboxylic acid functions as a conductivity enhancer, with a concentration of about 0.1 to about 5 g / L, preferably about 1 g / L. The carboxylic acid can be selected from a wide range of acids, but citric acid is preferred. When anodizing is attempted with this anodic oxidation bath, an anodic oxidation surface is produced, but the depth of anodizing does not increase because the dissolution of alumina occurs at almost the same rate as the formation of alumina.

[0041] In one example, the anodic oxidation bath is modified with a metal alkoxide compound. The metal alkoxide is a source from which metal micro and nanoparticles can be formed. Many metal alkoxides can be used, including titanium butoxide, aluminum butoxide, and zirconium propoxide. The amount of metal alkoxide is not particularly limited, but the required amount of metal alkoxide is sufficient to produce a concentration of nanoscale or microscale particles that give rise to the anodic oxidation process. In one example, the alkoxide of choice is a metal butoxide, preferably titanium butoxide, having a concentration of about 1 to about 80 g / L, or about 10 to about 60 g / L, or about 20 to about 40 g / L, and in a preferred example, the bath contains about 28 g / L of titanium butoxide.

[0042] In one example, a bath can be aged to generate a particle source. The particle source is generated in situ from a dispersion of nanoscale or microscale particles of a metal oxide, produced by the condensation of a metal alkoxide, with an alcohol. The condensation of the metal alkoxide usually occurs spontaneously in the presence of water in the bath. However, the presence of an acid in the bath prevents spontaneous condensation, so the process requires catalysis. In one example, the formation of nanoparticles and butanol is catalyzed by the formation of hydroxide at the cathode during anodic oxidation. In another example, catalysis is achieved by directly adding a hydroxide, such as potassium hydroxide or sodium hydroxide, to the bath.

[0043] For example, the metal alkoxide may be titanium butoxide. Chemical reaction (1) summarizes the metal alkoxide condensation reaction of (exemplary) titanium butoxide in an anodic oxidation bath, which generates metal oxide particles of approximately 80 nm to 3000 nm and liberates butanol. [ka]

[0044] While we do not wish to be bound by any theory, the inventors believe that an alcohol in the presence of one or more metal oxides and one or more organic acids catalyzes the formation of one or more stable esters, which then act as acid activity modifiers to support the formation of a white anodic oxide surface and anodic oxide structure on the substrate. Examples of suitable acid activity modifiers include stable polar esters such as butyl oxalates, butyl citrates, and combinations thereof.

[0045] The source of nanoscale or microscale particles of metal oxide may be any metal oxide produced by the condensation of metal alkoxides. However, titania nanoparticles or microscale particles of titania are preferred. Preferably, the microscale or nanoscale particles of metal oxide have a negative zeta potential. This is so that the particles are attracted to the anode during anodizing, although the zeta potential may be any potential less than -0.2 mV.

[0046] In one example, the anodic oxidation bath further includes a surfactant. The surfactant stabilizes micro- or nanoscale metal oxide particles by adsorption to the particle surface and also has other functions. In principle, any surfactant may be suitable. However, nonionic surfactants, such as Tween® 20 (polyoxyethylene sorbitol ester), and cationic surfactants, such as SDS (sodium dodecyl sulfate), are preferred. The surfactant preferably has a concentration of about 0.1 to about 5 mL / L, more preferably about 1 mL / L.

[0047] In one example, metal alkoxides are condensed through an anodic oxidation process, thereby generating hydroxyl-bonded metal oxide particles.

[0048] The hydroxyl-bonded metal oxide particles may be of any size, but the optimal size is small enough to maintain a suspension state easily in the anodic oxidation bath while being large enough to minimize absorption into the anodic oxidation structure. In one example, the optimal size of the hydroxyl-bonded particles is about 50 nm to about 5 microns. In another example, the hydroxyl-bonded particles are titania particles, with an optimal size of about 500 nm to about 4 microns, or preferably about 2.5 microns. In one example, the hydroxyl-bonded particles have a size of about 3000 nm as measured by dynamic light scattering. In yet another example, the metal particles are zirconia, with an optimal size of 50 nm to 250 nm, preferably about 100 nm.

[0049] In another example, the preparation of the anodic oxidation bath in 302 proceeds without the addition of a metal alkoxide, and this addition of the metal alkoxide is replaced by the addition of a predetermined amount of pre-prepared nano or microscale particles and an alcohol, preferably butanol. The nano or microscale particles added may, in principle, be any nano or microscale particles, but preferably metal oxide nanoparticles, for example, 25 nm nanopowder of anatase-type titanium(IV) oxide from Sigma Aldrich. In one example, the amount of nanopowder added is about 1 to about 20 g / L, preferably about 5 to about 10 g / L. The required alcohol is the amount released by the hydrolysis of the metal alkoxide, and is about 30 to about 100 mL / L, preferably about 65 mL / L. In a more preferred embodiment, the white surface is generated from the anodic oxidation bath using pre-prepared nanoparticles, rather than being generated in situ from micro and nanoparticles generated from the metal alkoxide in the anodic oxidation bath. While we do not wish to be bound by theory, the inventors believe that the in-situ generation of micro and nanoparticles creates incompatibility in particle size and the acid-activated modified esters formed, which affects the resulting surface.

[0050] In yet another example, the preparation of the anodic oxidation bath in 302 proceeds without the addition of metal alkoxides. The metal alkoxides can be replaced with metal oxide powders, such as magnesium oxide powder. Preferably, they can be replaced with magnesium oxide powder from Sigma Aldrich at a concentration of approximately 1 g / L to 2 g / L. Alternatively, they can be replaced with micro or nanoparticles of metal oxides situ generated by dissolution during the anodizing of aluminum alloys in an anodic oxidation bath containing carboxylic acid and boric acid. While we do not wish to be bound by any theory, we believe that certain submicron metal oxides act as acid modifiers by participating in the dissociation of carboxylic acids, similar to the case of stable polar esters.

[0051] In another example, the particle source and alcohol are replaced with succinic acid, long-chain organic acids, or other long-chain organic molecules. A bath prepared using 2-propanol and polyethylene glycol (PEG) produced a white surface, in which case 400 g·mol of PEG was used. -1 The molecular weight is as follows: The alcohol is preferably 2-propanol and has a concentration of about 20 to about 100 mL / L, preferably about 40 to about 60 mL / L. PEG MW 400 has a concentration of preferably about 5 to about 30 mL / L, preferably about 15 mL / L. While we do not wish to be bound by any theory, we believe that the interaction between the long-chain organic molecules of PEG MW400 and the carboxylic acid acts to modify the acid activity, similar to stable polar esters derived from metal alkoxides, thereby enabling the growth of nanostructures that appear white.

[0052] Referring to Figure 3, step 303 of process 300 includes pretreatment of the substrate for preparing it for anodic oxidation. In a particular example, the pretreatment includes removing surface contaminants by soaking the substrate in an alkaline bath. A commercially available alkaline cleaner such as METACLEAN ZX from CMP Ltd in India can be used. Here, the bath is run at about 60°C for about 5 to 30 minutes. After alkaline soaking, an acid etching step can be performed. The acid etching can include a deionized (DI) aqueous solution of 10% by volume sulfuric acid and 5% by volume hydrofluoric acid. In this case, the acid etching step can be performed at a temperature of about 20°C to 30°C for about 3 to 5 minutes, preferably about 4 minutes. Alternatively, any commercially available solution containing ammonium bifluoride as the active chemical can be used. After acid etching, a smut removal step can optionally be performed in a solution of about 50% nitric acid. The smut removal step includes, if necessary, immersing the substrate in the nitric acid solution for about 1 minute.

[0053] In another example, the substrate pretreatment step 303 may include polishing, preferably mechanical polishing or electropolishing. Electropolishing or mechanical polishing reduces surface roughness of the substrate and improves the uniformity of the anodized layer. The electropolishing step may use any of the many well-known electropolishing processes for aluminum substrates. Continuing the electropolishing step provides a mirror or near-mirror surface on the substrate. The mirror or near-mirror surface has a surface roughness Ra of about 0.1 μm to about 0.5 μm, preferably about 0.2 μm or less. A mirror-like substrate may be preferred in certain applications where a reflective surface rather than a matte anodized surface is desired.

[0054] In step 304 of Figure 3, the pre-treated substrate is immersed in a heated and stirred anodic oxidation bath. In a preferred example, the anodic oxidation bath is heated to a temperature of about 20°C to about 90°C, or about 30°C to about 80°C, more preferably about 45°C. By setting the temperature to at least about 35°C, it is ensured that the anodic oxidation process creates a dense nanocrystalline structure and produces a white surface.

[0055] In one example, the anodic oxidation bath is stirred. Many stirring methods are suitable, as long as sufficient stirring is performed to keep the metal nanoparticles in a suspended state. In one example, the bath is magnetically stirred at about 300 rpm to about 800 rpm, or about 400 rpm to about 700 rpm, or preferably about 600 rpm. In another example, stirring of the bath is achieved using an external solution pump. In yet another example, the bath is stirred with low-pressure compressed air. In a preferred example, sufficient stirring is maintained to keep the bath temperature uniform during anodic oxidation while achieving a uniform suspension of the metal micro and nanoparticles.

[0056] In step 305 of Figure 3, a first anodic oxidation current is applied between the substrate (anode) and the cathode. The cathode may be any material that is substantially inert in the bath but has high conductivity. Suitable materials include carbon, titanium, and stainless steel. In a preferred example, the cathode is stainless steel. A suitable cathode will be readily apparent to those skilled in the art.

[0057] In a preferred example, constant-current DC anodizing is performed. Constant-current DC refers to a time-independent constant current (stable current) that does not show changes in intensity over time. Alternatively, pulsed DC anodizing can also be used in this method, which may be beneficial when anodizing certain Al alloys. Pulsed DC refers to a periodic current whose value changes but whose direction does not. In another example, constant-voltage anodizing can be used.

[0058] In step 305 of Figure 3, a first anodic oxidation current density is applied. Preferably, the first anodic oxidation current density is about 0.5 to about 3 A / dm 2, or about 1 to about 2.5 A / dm 2 , or preferably about 2 A / dm 2 It is. In this process, it is preferable to hold the first anodic oxidation current density for about 1 second to about 2 minutes, or about 30 seconds to about 1.5 minutes, preferably about 1 minute.

[0059] In step 306 of FIG. 3, the anodic oxidation current is optionally changed from the first anodic oxidation current density to the second anodic oxidation current density. The second anodic oxidation current density is higher than the first current. Preferably, the second anodic oxidation current density is about 2 A / dm 2 to about 8 A / dm 2 , or about 3 A / dm 2 to about 6 A / dm 2 , or preferably 4 A / dm 2 It is. Preferably, when the second anodic oxidation current is changed from the first anodic oxidation current density to the second anodic oxidation current density, this change is carried out over about 2 minutes to about 4 minutes, optimally about 3 minutes. The nano- or microscale particle content of the substrate and the anodic oxidation bath affects the required second anodic oxidation current density. For example, titania particles require about 4 A / dm 2 to produce the optimal color, while alumina particles require about 6 A / dm 2 to about 8 A / dm 2 It is. In each case, the second anodic oxidation current density preferably has the maximum current density selected to achieve the optimal color and / or the optimal porosity of the anodic oxidation surface.

[0060] In a preferred example, the second anodic oxidation current density is maintained until the voltage reaches a desired anodic oxidation voltage threshold. The anodic oxidation voltage threshold is influenced by the composition of the bath, the type and size of the bath particles, the bath temperature, and the substrate. A preferred anodic oxidation voltage threshold may be about 80V to about 300V, or about 120V to about 250V, or about 140V to about 180V, or preferably about 150V. In an example where the particles of the anodic oxidation bath are titania particles, the particle size is about 3000 nanometers, the composition of the anodic oxidation bath contains about 27 g / L of oxalic acid, about 10 g / L of boric acid, about 1 g / L of citric acid, and about 24 g / L of titanium butoxide; the substrate is 6061-T6 aluminum, and the anodic oxidation voltage threshold is about 150V.

[0061] In another example, a glossy white surface is produced instead of a matte white surface, and the anodizing step (304, 305, 306, 307) is performed on a polished or electropolished substrate. In this example, the first current density and the first period are divided into a small part comprising a first step, a second step, and a third step. The first step of the first current density is approximately 0.5 A / dm 2 ~About 3A / dm 2 Preferably about 2 A / dm 2 Preferably, the first current step period is held for about 5 minutes to about 25 minutes, or preferably about 15 minutes. Preferably, the second step of the first current density is about 2 A / dm 2 ~about 4A / dm 2 Preferably about 3 A / dm 2 Preferably, the second step is held for about 5 minutes to about 25 minutes, preferably about 15 minutes. Preferably, the third step of the first current density is about 3 A / dm 2 ~About 5A / dm 2 Preferably about 3.4 A / dm 2 Preferably, the third step is held for about 5 to about 25 minutes, preferably about 15 minutes. Preferably, the second current density is about 3 to about 6 A / dm 2 Preferably about 4 A / dm 2This period lasts until the voltage reaches the threshold anodizing voltage.

[0062] In step 307 of Figure 3, the anodizing rectifier can be switched from constant current mode to constant voltage mode, and the anodizing voltage can be maintained at the anodizing voltage threshold for a voltage control period of approximately 10 minutes to approximately 200 minutes, or approximately 50 minutes to approximately 150 minutes, or approximately 80 minutes to approximately 130 minutes, preferably approximately 90 minutes to approximately 120 minutes, and the anodizing voltage can also be maintained until the current drops to less than 10% of the first current density threshold. The threshold is approximately 0.5 A / dm 2 Less than or approximately 0.2 A / dm 2 Less than, preferably about 1 A / dm 2 It is less than.

[0063] In a preferred example, the anodic oxidation current density gradually decreases as a dense, optically discontinuous oxide film is formed that provides a white surface.

[0064] In another example, the rectifier is not switched to constant voltage mode, and the current density is maintained at a second current density for the remainder of the anodizing period. Maintaining a high current density promotes the growth of the anodized surface (film, etc.) and shortens the time required to produce a white anodized surface. The temperature of the anodizing bath is controlled to maintain the maximum anodizing voltage of 405 in Figure 4. Here, lowering the temperature increases the voltage, and vice versa, so to ensure the voltage reaches an optimal point, the temperature is increased if the voltage is too high and decreased if the voltage is too low.

[0065] Referring to Figure 4, a preferred example voltage-current curve 401 is shown, but it should be understood that a white surface can be produced with other voltage-current curves as well. In Figure 4, line 402 shows the applied current density, and line 403 shows the anodizing cell voltage. In this example, at t=0, an excitation voltage 404 is applied to the anodizing cell, and the constant current 402 is approximately 2A / dm 2The anodizing cell voltage 403 was approximately 52V. In this process, a constant current 402 was maintained for approximately 3 minutes while the anodizing cell voltage 403 rose to approximately 60V. Subsequently, the current density 402 was set to approximately 4A / dm² over a period of approximately 3 minutes. 2 The value was changed up to [value]. As the thickness of the anodized film increased, the cell voltage 403 slowly increased. Period 406 is mainly related to the formation of the porous surface 204 in Figure 2. However, the acid in the bath further etches this exposed surface and partially contributes to the structure. At point 405 in Figure 4, the rectifier was switched to constant voltage mode as soon as the cell voltage reached the threshold voltage 405 desired for the growth of the white anodized layer. Subsequently, the current density 402 slowly decreased as the thickness of the anodized film increased until the anodizing was complete, i.e., a total of 2 hours in this case. Periods 407 and 408 reflect the formation of layers 203 and 202, respectively, as also described in Figure 2.

[0066] Figure 7 shows a diagram of the anodizing cell 700. The anodizing cell 700 comprises a bath container 701, a heating device 702, a stirrer 703, a power supply 704, a cathode 705, and a workpiece / anode 706. The anodizing bath further comprises a bath 710 containing an acid and a surfactant, and metal micro or nanoparticles 708 coated with the surfactant.

[0067] While we do not wish to be bound by any theory, the inventors believe that the metal micro or nanoparticles in the bath form a loosely bonded electrophoretic layer 709 on or within the anodic oxidation surface (see Figure 7). This loosely bonded layer 709 significantly delays the diffusion of acid from the anodic oxidation bath 710 to the substrate surface 707, thereby modifying the anodic oxidation process and generating the optically discontinuous nanocrystalline anodic oxidation structure of the present invention.

[0068] In a preferred example, anodizing is carried out in three steps. The first step is the formation of a substantially nanocrystalline layer. Here, the native oxide layer on the aluminum substrate is supported by an initial anodizing voltage of about 50 V, in combination with a film produced by a surfactant and an acid. In certain examples, the surfactant and organic acid (e.g., citric acid) alter the wettability of the surface of the native oxide of aluminum. This reduces the ability of the anodizing bath to dissolve the surface of the native oxide, preventing pitting and promoting coating growth. The acid in the anodizing bath promotes the electrochemical dissolution of the material of the aluminum substrate, as shown in Equation 2, and also promotes the construction of a barrier layer and pore walls, as shown in Equation 3. [ka]

[0069] Equations (2) and (3) represent a standard anodic oxidation process. However, the actual chemical interactions in the substrate are more complex. We have confirmed that in an anodic oxidation bath that does not contain condensed alkoxides, metal micro and nanoparticles, or alcohols, significant depth of anodic oxidation cannot occur. While we do not wish to be bound by any theory, we believe that interactions between carboxylic acids, organic compounds including alcohol-derived compounds, and metal micro and nanoparticles may be necessary to enable the formation of a persistent anodic structure. In other words, without these interactions, formation and dissolution in the anodic structure would occur at equivalent rates. Figure 5B, 507, shows a surface SEM of an aluminum sample anodized in a bath without metal alkoxides. This shows a typical structure associated with excessive acid dissolution of alumina. A pore structure can be seen beneath the thin surface structure. We believe that the adsorption of compounds derived from metal micro and nanoparticles, including alcohols, onto the anodic oxidation surface may cause a delay in the dissolution of the anodic structure.

[0070] The first anodic oxidation step occurred during period 406 in Figure 4, generating a nanoporous outer layer as shown in 502 in Figure 5A and 202 in Figure 2. At the end of period 406 in Figure 4, sufficient metal micro and nanoparticles aggregated on the anodic oxidation surface 201 by electrophoretic transport, influencing the chemical behavior of the anodic oxidation process. In the absence of a source of metal micro and nanoparticles and associated materials, a normal anodic oxidation structure continued to be formed. 508 in Figure 5B shows a cross-sectional SEM of a coating produced from an anodic oxidation bath where particles remained nanoscale, i.e., <100 nm. In this case, the anodic oxidation structure includes porous nanotubes from the substrate to the surface (i.e., layer 202 in Figure 2). At sizes greater than 100 nm, metal micro and nanoparticles can form an adhesive electrophoretic deposition (EPD) layer on the anodic oxidation film, while simultaneously generating a substantially homogeneous porous nanotube structure. For particles larger than 1 micron in size, it was found that a non-adherent layer is formed on the anodic oxidation surface, and this layer suppresses the diffusion of chemical substances into the pores. The inventors found that, when this layer is present, the voltage drop in the anodic oxidation cell is caused by a combination of the voltage drop of the anodic oxidation process as shown in Figure 4, the voltage drop due to the ion diffusion limit within the nanotube, and a voltage drop of up to approximately 100V across the entire particle surface in the case of titania particles with Tween 20 on their surface.

[0071] The second anodic oxidation stage was carried out through periods 407 and 408 in Figure 4, and this second anodic oxidation stage generated layers 503 and 504 in Figure 5A (similarly 203 and 204 in Figure 2). In this case, the interdiffusion of chemical species between the pores and the anodic oxidation bath was limited by the increase in surface particle density. When the anodic oxidation process was inhibited by either the interaction of the nanoparticle material or the interaction of alloying elements derived from the aluminum substrate, the growth of adjacent unoccluded pores initially took precedence, which led to pore branching as shown in 209 and 210 in Figure 2. When a significant number of pores were partially, substantially, or completely covered by metal oxide nanoparticles, these pores underwent pH polarization, changing from strongly acidic near the aluminum substrate to more alkaline towards the anodic oxidation surface. Excess Al 3+ Specifically, aluminum ions that were not immediately incorporated into the anodic oxidation structure (202-204 in Figure 2) at the base of the pores migrated to the alkaline pH region under the influence of an electric field, where they combined with hydroxide ions to form aluminum hydroxide. This aluminum hydroxide adsorbed onto the pore walls, thereby creating nanotube-like intermediate layers substantially filled with nanocrystalline material, as shown in 503 in Figure 5A and 203 and 209 in Figure 2. These structures primarily induce light scattering, which results in the white surface color.

[0072] The growth of intermediate nanostructures 203 / 503 and 204 / 504 (Figures 2 and 5) further suppressed diffusion through the layers, thereby reducing the anodic oxidation current. As the current decreased below a threshold, as shown in 407 to 408 of Figure 4, the final structures of layers 203 / 503 and 204 / 504 were formed. The thickness ratio of the three observed layers, i.e., 502:503:504 in Figure 5A (202, 203, and 204 in Figure 2), was approximately 1:0.4:0.5 to approximately 1:0.8:1.2.

[0073] The elements in the alloy affect surface formation during anodizing from 406 to 408. Insoluble and non-anodic oxidizable alloying elements, such as silicon or silicon-magnesium precipitates, remain in the anode layer as inclusions. The presence of such alloying elements may hinder the growth of the anode film, but may increase the number of light scattering points. Alloying elements such as copper leave pores during anode layer formation, thus promoting the formation of lateral pores. Alloying elements such as magnesium and zinc are oxidized, but less favorably than aluminum, and magnesium or zinc oxides remain in the anode structure.

[0074] In one example, the anodic oxidation surface depends on the maximum anodic oxidation voltage. This maximum anodic oxidation voltage is determined in part by the size of the nanoparticles in the bath. The coating formed at 85V, as shown in 509 in Figure 5C, is associated with small particles 510 ranging from 20 to 100 nm, which are likely oxides and hydroxides of metal nanoparticles, such as titania particles produced by the condensation of t-butoxides. These small particles allow the metal to be incorporated into the growing anode surface 511 as an aluminum-metal compound (Figure 6B) composite (TiAlO2). Larger particles (512 in Figure 5D), ranging from approximately 100 nm to approximately 500 nanometers, can also adsorb onto the anodic oxidation surface as an adhesive electrophoretic layer of titania. The largest particles, >500 nm, were involved only in anode surface formation but were incorporated into the coating. Figure 5E, 513 shows an anodic oxidation surface formed in a bath containing particles of approximately 1700 nm, with a maximum sustained anodic oxidation voltage of approximately 85 V to 100 V, which significantly affected the surface and bulk nanostructure, resulting in a blue / white surface. Figure 5E, 514 shows an SEM of a substantially white anodic oxidation surface prepared at 150 V in a bath containing particles of approximately 3000 nm.

[0075] In another example, the nanoparticle source is zirconium propoxide. Due to the different interaction between the bath and the nanoparticles, the same anodic oxidation results can be obtained even with much smaller particles, typically less than 200 nm in size.

[0076] In step 308 of Figure 3, the aluminum substrate is anodized, thereby forming an anodized substrate having an anodized surface. The anodized substrate is removed from the anodizing bath and rinsed. After rinsing, the surface can be matte or glossy white, depending on the pretreatment of the aluminum substrate. However, the whiteness can be further improved by incorporating additional whitening material into the anodized surface and / or sealing the anodized surface.

[0077] Many surface coloring processes known in the art can be used on this anodized surface to improve or change the surface color. Due to the porosity of the white anodized surface, it is suitable for further coloring by methods such as organic staining of the surface, electrophoretic deposition of metal oxides or other materials, and electrolytic coloring using metal salts.

[0078] One example of improving the whiteness of an anodized surface involves immersing the anodized substrate in a bath suitable for improving whiteness, such a bath containing, for example, an aqueous dispersion of barium sulfate particles. Preferably, the barium sulfate particles are barium sulfate nanopowder. Preferably, the bath suitable for improving whiteness contains barium sulfate nanopowder in a concentration of about 0.01 mol / L to about 0.5 mol / L, or barium sulfate nanopowder in a concentration of about 0.05 mol / L to about 0.3 mol / L, or preferably 0.2 mol / L. Preferably, the barium sulfate nanopowder has an average particle diameter of about 100 nm or less (smaller than the pore diameter of the coating). The presence of equimolar amounts of disodium EDTA is sufficient to stabilize the particles in the suspension. The bath for improving whiteness is stirred to significantly reduce particle aggregation. In this method, a voltage corresponding to an electric field of approximately 1 V / cm to approximately 30 V / cm, or approximately 5 V / cm to approximately 25 V / cm, preferably approximately 20 V / cm, is applied between the substrate and the inert counter electrode. In this method, the voltage polarity is determined according to the surface charge of the particles, which may be influenced by the particle size and the properties of the surfactant. In this method, a constant voltage is applied for approximately 1 minute to approximately 30 minutes, or approximately 5 minutes to approximately 20 minutes, preferably approximately 10 minutes, as a result of the barium sulfate particles being impregnated into the porous surface by electrophoresis. Those skilled in the art will understand the proportional relationship between the applied electric field and the penetration depth of the nanoparticles.

[0079] The inventors confirmed that a white anodic oxide substrate having porous nanomorphology on its anodic oxide surface exhibits hydrophobic properties. This property reduces the effect of aqueous post-treatment. In another example, a dispersion of barium sulfate nanopowder dispersed in a suitable organic solvent mixture within the concentration range specified above was used. In this example, the voltage corresponded to an electric field in the range of approximately 50 V / cm to approximately 200 V / cm, or approximately 60 V / cm to approximately 80 V / cm, preferably approximately 75 V / cm.

[0080] In another example, to change the color from white to pastel, the process includes the step of immersing an anodized substrate in a solution containing an organic dye and an organic solvent. The anodized substrate was immersed for a period of approximately 10 minutes to approximately 20 hours. It was then dried. Drying methods include drying in a stream of compressed air or baking in an oven to remove the solvent and produce a dyed anodized surface. A suitable drying method would be obvious to those skilled in the art. In one example, the color of the dyed anodized surface depends on the density of the dye in the pores within the anodized surface and the depth of dye penetration.

[0081] Step 309 in Figure 3 optionally includes a step of sealing the anode surface. In one example, a polishing step may be performed before the sealing step, which results in a uniformly smooth surface and improves the aesthetic appearance of the surface. For polishing, any commercially available method can be used, depending on the size and shape of the anodized product. Such methods include buffing, burning, tumbling, vibrating, and soda blasting. Polishing the surface before sealing can improve the effectiveness of the sealing process.

[0082] Sealing an anodized surface improves its durability, increases its whiteness, preserves secondary color tones, and enhances its resistance to chemical attack. Anode surface sealing processes are well-known in the art, including boiling water sealing, metal acetate sealing, and polymer sealing, most of which can be successfully applied to anodized surfaces produced by this process.

[0083] A preferred step of sealing an anodized substrate including an anodized surface includes: a step of contacting the anodized substrate with a sealing solution over a contact period to provide a sealed anodized substrate; a step of rinsing the sealed anodized substrate with alcohol; and a step of curing the sealed anodized substrate under curing conditions. Preferably, the anodized substrate is contacted with the sealing solution. Preferably, the sealing solution is a sol gel. Preferably, the sol gel is a silica-siloxane metal oxide sol gel. Preferably, the sol gel is C 1~6 The solution is prepared using an alcohol, preferably a C3 alcohol, more preferably an isopropyl alcohol. Preferably, the step of contacting the anodic oxidation substrate with the sol gel includes electrophoretic deposition. Preferably, the electrophoretic deposition is performed at 30V to 200V, preferably 170V. Preferably, the sol gel penetrates the anodic oxidation substrate over a contact period. The contact period may be 10 to 120 minutes, preferably 30 minutes. Preferably, the step of rinsing the sealed anodic oxidation substrate with alcohol includes an alcohol selected from methanol, ethanol, propanol, isopropanol, and butanol. Preferably, the curing conditions include a temperature of about 50°C, at least 50°C, or below 80°C. Preferably, the curing conditions include a relative humidity of above 80%.

[0084] In a preferred example, the surface was sealed with a hybrid silica and siloxane metal oxide sol gel. For sealing, electrophoretic deposition was used at 30V to 200V, preferably 170V, with a white anodized surface rinsed with ethanol used as the cathode and an inert titanium anode, allowing the sol gel to penetrate the coating for a period of 10 to 120 minutes, preferably 30 minutes; the sealed surface was cured at a temperature above 50°C and a relative humidity above 80% for a period of more than 1 hour. Hybrid silica sol gels were prepared using isopropanol and 0.1-1 M silicon, with a mixture of 70-85% TEOS (tetraethyl orthosilicate), 10-20% OTES (octyltrimethoxysilane), 5% HDTMS (hexadecyltrimethoxysilane), and 10-20% FAS (1H,1H,2H,2H-perfluorooctyltriethoxysilane). The solutions were peptized with 5-15 ml / L hydrochloric acid (37 vol%) or phytic acid (50 vol%).

[0085] In another example, the color and hardness of anodized surfaces can be altered by using siloxane metal oxide sol gels prepared by adding metal alkoxides to hybrid silica sol gels. In one example, 50-100 ml / L of aluminum trisec-butoxide was added to a hybrid silica sol gel, and the solution was peptized with 10-30 ml of hydrochloric acid (37 vol%).

[0086] In another example, an anodic oxidation surface can be sealed with a harmless material, such as a phytic acid solution. A 2.5% by mass PA solution was prepared using Sigma Aldrich phytic acid (PA, 70% by mass in water) and deionized water, and a small amount of Sigma Aldrich triethylamine was added to obtain a sealing solution. Here, the amount of triethylamine is sufficient to adjust the pH of the phytic acid solution to about pH 1.2 to 2.0, preferably about pH 1.5. The phytic acid sealing solution was heated to about 90°C. The anodic oxidation substrate was immersed in the sealing solution for about 15 minutes, thereby creating a deposited film (sealing film) of about 3 to 4 μm on the surface of the anodic oxidation substrate.

[0087] In another example, an anodized surface can be sealed using a commercially available sealant such as Lyndar Clearcoat Aerosol. A Lyndar Clearcoat Aerosol mixture was sprayed onto the anodized surface of an anodized substrate to deposit a transparent sealant approximately 20 μm thick. This transparent sealant was cured for approximately 24 hours. The resulting coating exhibited improved durability and nearly 100 times higher gloss than the prepared coating. The inventors believe this sealing technique is beneficial for white anodized coatings. * We observed that it did not affect the value, while simultaneously imparting a high degree of gloss to the surface.

[0088] In another example, an anodized surface can be sealed using a metal clear coat sealant. In this case, a uniform nanoscale sealant on the anodized surface can be provided using metal deposition techniques such as physical vapor deposition (PVD), chemical vapor deposition (CVD), atomic layer deposition (ALD), and pulsed laser deposition (PLD). In a preferred example, a thin metallic coating was deposited on a white anode surface by PLD. Deposition was carried out on the as-prepared white anodized coating in a low-oxygen environment at approximately 1 J / cm². 2 This can be done with laser fluence.

[0089] The metal oxide layer was thick enough to completely seal the nanoporous structure of the anode coating without altering its aesthetic appearance or tactile behavior. Examples of metal sealants, though not limited to these, include indium tin oxide, vanadium oxide, and zinc oxide.

[0090] The process ends at step 310 in Figure 3. [Examples]

[0091] The following examples illustrate specific operating conditions and exemplify embodiments of the present disclosure. However, these examples should not be considered to limit the scope of the present disclosure. The selected examples specifically illustrate embodiments of anodizing baths and processes for producing a white anodized surface.

[0092] In each example, the result is determined by the degree of whiteness of the process. Color measurement is often performed using CIE 1976 L * a * b * A color space standard was used, and this was also used in this disclosure to measure the color of the anodized surface. The measuring instruments used were an NR10QC colorimeter and a GC268 reflectometer. Measuring light colors and white (white tones) with a CIE L value of 85 or higher is prone to significant errors, especially for surfaces whose coloration is determined by their structure, and the measured values ​​can change depending on the angle of incidence of light. Therefore, to improve accuracy, the measured values ​​were compared with Resene Paints color samples. Example 1 - Effects of Bath Composition

[0093] To deepen our understanding of the theoretical foundations of the anodic oxidation process, various anodic oxidation bath compositions and formulation approaches were tested. The anodic oxidation bath composition included 25 g / L oxalic acid, 10 g / L boric acid, 1 g / L citric acid, and 1 ml / L Tween 20 surfactant. In all experiments, the anodic oxidation bath was stirred at 70°C using a magnetic stirrer at 300 rpm, maintained with a hot plate stirrer, and a water bath was used. In experiments containing butoxide, the butoxide concentration was 47 mL / L. In all cases, the pH of the anodic oxidation bath was in the range of 2 to 2.4 pH units. Table 1 shows a list of bath additives and processes. [Table 1]

[0094] Each substrate sample consisted of a 2 x 3 cm 6061-T6 aluminum coupon with a 2 mm insulated 4000 series aluminum welding wire attached for connection. The wire was pressed into a 1.8 mm hole drilled in the upper center of the aluminum substrate sample. The aluminum substrates were pre-treated with Activax alkaline soaking at 60°C for 8 minutes, followed by smut removal with 50% nitric acid for 1 minute.

[0095] Referring to the anodic oxidation bath 1.1 in Table 1, the results showed that the organic acid mixture alone was insufficient to generate a sufficient anodic oxide layer. The maximum voltage achieved was approximately 30V, and the resulting anode structure appeared to have an incomplete and collapsed anodic morphology (see 518 in Figure 5H). The inventors also revealed that substrates lacking a sufficient native oxide layer could not even achieve an initial voltage of 30V. This suggests that the initial barrier layer is not constructed by the anodic oxidation bath alone, and that anodizing of the native oxide layer is necessary for aluminum substrates.

[0096] Referring to anodic oxidation bath 1.2 in Table 1, the aging bath containing a combination of 25 g / L oxalic acid, 10 g / L boric acid, 1 g / L citric acid, 1 ml / L Tween 20 surfactant, and hydrolyzed t-butoxide produces L * The results showed that a "white" coating with a value of ≥90 was produced. The maximum voltage reached was 150V. The resulting anodic oxide surface appeared to have non-uniform nanoscale pores of 50–100 nm on its surface (506 in Figure 5A). From the cross-sectional image (501 in Figure 5A), it was found that approximately 38 mm of the coating showed the generation of three stages of morphology. While we do not wish to be bound by theory, we believe that this is a factor that scatters and diffuses incident light, thereby providing an anodic oxide substrate containing an anodic oxide surface with a substantially white appearance. We have revealed that a combination of particles derived from hydrolyzed t-butoxide, esters, and butanol with organic acids may be a factor that contributes to the white coloration of the anode coating.

[0097] Referring to 1.3 in Table 1, this investigates the effect of butanol on the formation of the anodic oxide structure on the anodic oxide surface. Butanol was released by the condensation of butoxides in the bath (Equation 1 above). The results of this experiment suggest that butanol alone did not increase the voltage, making it impossible to form a significant anodic oxide layer. However, the presence of butanol modified the anodic oxide surface and its structure, because the surface color changed. Figures 519, 510, and 511 in Figure 5C show the pore structure of the anodic oxide surface when formed in anodic oxide bath 1.3. The pores of approximately 30 nm are characteristic of this anodic oxide bath and anodic oxide voltage.

[0098] In experiments using bath 1.4, the addition of 25 nm TiO2 powder facilitated the formation of a colored anodic oxide film. This was demonstrated by both the voltage increase and the appearance of the anodic oxide surface. Therefore, it became clear that the presence of nanoparticles and butanol-derived compounds in the anodic oxidation bath is important for the anodic oxidation process.

[0099] Further experiments not included in Table 1 also revealed that TiO2 nanoparticles without butanol are insufficient for generating anodized surfaces. Figure 5F, 515 is an illustrative image showing the surface morphology of aluminum anodized in an anodizing bath containing TiO2 nanoparticles but without butanol. The coating appears discontinuous and has exposed grain boundaries. High-magnification image 516 shows that the composition of this anodizing bath resulted in a poor anodic structure of the anodized surface with collapsed nanotubes.

[0100] In the experiment using bath 1.5 in Table 1, particles were filtered from the anodic oxidation bath of Experiment 1.2. The remaining liquid component was sufficient to generate a relatively thick anodic oxidation structure, as the anodic oxidation voltage reached 150V. However, this anodic oxidation bath did not support the formation of a white anodic oxidation surface. The anodic oxidation current decreased to zero over a period of approximately 20 minutes, resulting in a gray surface with a translucent nanoporous surface (517 in Figure 5G).

[0101] Orthogonal experiments demonstrated that a white anode surface is produced by varying the acid concentration of the anodic oxidation bath across a wide range of conditions. Table 2 shows various anodic oxidation bath formulations along with the color of the resulting anodic oxidation surface. [Table 2]

[0102] Table 2 shows the results of anodizing using standard anodizing voltage-current profiles unless otherwise specified. In each experiment, a new bath was first prepared using the chemical substance of interest. In the experiment, a pre-treated aluminum substrate coupon (same as above) measuring 5 cm × 3 cm was first anodized to a voltage of 150 V. In this process, the bath was thoroughly aged to produce a suspension of titania particles of approximately 3 microns and the associated butanol-derived ester.

[0103] In this process, initially 2A / dm 2 The material is anodized with a constant current of 4 A / dm² for 1 minute, and then the current density is increased to 4 A / dm² over a period of 3 minutes. 2 The voltage was increased linearly until it reached 150V. Next, when the voltage reached 150V, the DC supply was switched to a constant voltage, and the anodizing process continued for a total of 120 minutes.

[0104] In each experiment, the bath temperature was maintained at approximately 60°C to 80°C.

[0105] The data showed that a surface with very high whiteness was produced at oxalic acid concentrations of approximately 28 g / L, boric acid concentrations of approximately 5 g / L, and butoxide concentrations of approximately 24 g / L. The oxalic acid concentration appeared to be the most important factor.

[0106] The ratio of oxalic acid to boric acid also appears to be important at low oxalic acid concentrations. A ratio of approximately 3:1 was found to produce a surface with very high whiteness. When the ratio was less than 2:1, the rate of initial anodic oxidation increased, and the process reached its peak anodic oxidation voltage in a short time. When the concentrations of oxalic acid and boric acid were approximately 1:1, the bath yielded 4 A / dm³. 2 It was not maintained.

[0107] The amount of butoxide did not appear to affect the surface brightness, but in small amounts, it seemed to improve the purity of the color. Example 2 - Generation of t-butoxide particles

[0108] Table 3 shows the morphology of a series of metal butoxide particles, along with the color of the resulting anodic oxidation surface. 47 g / L of titanium butoxide was used in anodic oxidation baths 3.2, 3.2, and 3.4. Butoxide was not present in anodic oxidation bath 3.1. [Table 3]

[0109] The sample pretreatment and preparation followed the procedure of Example 1 described above.

[0110] The bath temperature used was 60°C, and magnetic stirring was performed at 600 rpm.

[0111] In Experiment 3.1 in Table 3, the sample was anodized in a bath that did not contain t-butoxide. The bath remained transparent, and the anodic oxidation structure was insufficient to produce surface coloration.

[0112] In Experiment 3.2, 47 g / L of titanium t-butoxide from Sigma Aldrich was added to the bath. In this experiment, the current density was controlled to delay the condensation reaction of the butoxide and to investigate the structures of various anodic oxide surfaces generated at different particle generation stages. The surfaces were formed from an anodic oxide bath containing substantially transparent butoxide, i.e., from a bath containing newly formed particles smaller than 100 nm. The results suggest that the particle generation state in the anodic oxide bath is important in the formation of white anodic oxide surfaces. Normally, t-butoxide added to a high-temperature acidic solution completes condensation immediately, but in this experiment, it appears that the condensation reaction can proceed initially, while the particles are stabilized at the nanoscale in the anodic oxide bath. The generated surfaces were relatively thick and exhibited a translucent purple color (Figure 5E, 513).

[0113] The results of Experiment 3.3 showed that although the formation on the anode surface is supported by partially formed oxide particles, the voltage rise is still limited by the structure of the oxide particles because free material exchange is possible between the anodic oxidation bath and the pore structure. The structure of the generated surface is similar to that of a coating obtained from an anodic oxidation bath containing fully formed particles, but some TiO2 deposits bound to the anode surface by electrophoresis (510 in Figure C), resulting in a blue / white surface.

[0114] Experiment 3.4 shows that a white anodic oxidation surface was generated on the aluminum substrate by a fully formed anodic oxidation bath containing particles approximately 3000 nm in size. Experiment 4 used voltage changes under current control, followed by current changes under voltage control. In this process, 2 A / dm 2 This is applied using the first current for 3 minutes, and then 3A / dm 2 A second current was applied for 3 minutes. This current was then changed to a third current of 4 A / dm 2 The voltage was increased and maintained at this value until it reached 150V. At this stage, the process was switched to a constant voltage control phase, and 150V was supplied for 120 minutes. The resulting anodized surface was white, L * The value was 91.3. The approximately 35 mm coating exhibited heterogeneous nanoporous morphology, as observed in 514 in Figure 5E. The results also showed that larger particles, 3037 nm in size, significantly influenced the surface and bulk nanostructure without being incorporated into the anodic oxidation surface, thereby generating a white surface. Example 3 - Formation of anodized surface

[0115] Degreased 3 x 5 cm Al6061-T6 samples were immersed in a pre-prepared white anodic oxidation bath formulated according to Table 2 above. These aluminum substrates were anodized for various periods ranging from 5 minutes to 2 hours, and then removed from the anodic oxidation bath and rinsed with deionized water.

[0116] After color measurement using a colorimeter, cross-sections were prepared for SEM analysis.

[0117] SEM analysis was used to examine the formation of pores and surface features along with the thickness of the coating. [Table 4]

[0118] Figure 8, section 801, shows the color change of the sample over time during anodizing, using data from Table 4. Table 4 also shows the morphological changes of anodizing that are related to the whiteness of the surface.

[0119] Examples 4.2–4.4 demonstrate that the surface color of anodized surfaces is determined by a combination of surface structure and thickness. When the total surface thickness was less than 20 microns, the interaction between incident light and the pore / alumina interface appeared insufficient, making it impossible to reflect a significant proportion of the incident light. However, as the surface thickness increased, the number of interactions increased, and the coating became whiter as observed.

[0120] It was observed that thinner samples appeared to have a more bluish tint. This is thought to be a characteristic of the nanopore size (sample number 1). However, as the coating thickened, the color became more greenish, and b * The degree of negativity decreases, a * An increase in the degree of negativity was observed. The change in color was thought to be due to an increase in the pore diameter of the coating surface caused by the dissolution of alumina by the acid. Example 4 - Glossy surface

[0121] The sample pretreatment and preparation were carried out according to the procedure described in Example 1 above.

[0122] In the electropolishing step, any of the many well-known electropolishing processes for aluminum substrates can be used. Here, the composition of the electropolishing bath contained 800 ml / L phosphoric acid, 30 ml / L hydrofluoric acid, 70 ml / L sulfuric acid, and 100 ml / L glycerin. The temperature of the electropolishing bath was maintained at 80°C. A constant DC voltage of 12V was applied for 2-3 minutes, followed by rinsing with deionized water. This process produced a mirror finish on the aluminum alloy surface with an Ra of approximately 0.1.

[0123] The electropolished samples were anodized using burn-in bath 2.5 as shown in Table 2 of Example 1. The constant current density for anodizing was 2 A / dm². 2 This is applied for 8 minutes, and then 3A / dm 2 Increase the voltage to 3.5 A / dm² and apply for 5 minutes, then apply for the third time at 3.5 A / dm². 2 The voltage was increased and applied for another 5 minutes. Then, when the voltage reached 150V during the final constant current period, constant voltage anodizing was performed at 150V, and the anodizing was continued for a total of 75 minutes.

[0124] The resulting surface is substantially white, and its color is L * a * b * The values ​​were measured at 87.3, -2.77, and -1.63, and the surface gloss at 85° was measured at 88.5 GU (gloss units). Example 5 - Preparation of a colored surface

[0125] An anodized white sample was prepared using the bath and process 1.2 of Example 1 described above.

[0126] The anodized samples were completely dried by baking them in a temperature-controlled oven at 120°C for 2 hours.

[0127] The dried sample was suspended for 20 hours in a 0.01 g / L methylene blue solution prepared by dissolving it in deionized water or ethanol.

[0128] The sample was removed from the methylene blue solution and dried with compressed air.

[0129] The color of the samples was measured using a colorimeter, and the results are reported in Table 5.

[0130] Due to methylene blue in water, L * As indicated by the low value, the surface reflectivity was reduced. Furthermore, methylene blue in water produces a baby blue surface. However, in the case of methylene blue in alcohol, a much bluer surface is produced.

[0131] The inventors believe that the surface is only partially wetted, limiting the penetration of water into the pores, whereas alcohol penetrates the pores easily. Figure 9, 903, shows the wetting behavior of a white anodic oxidation sample using deionized water. The water contact angle of the droplet is approximately 40°. [Table 5] Example 6 - Sealing of the white anode surface with a clear coat

[0132] A white anodic oxidation substrate was prepared using the anodic oxidation bath and process 1.2 detailed in Example 1 above. The surface of the anodic oxidation substrate was approximately 92.16 L * The value was shown.

[0133] The surface of the anodic oxidation substrate was sealed with a commercially available clear coat sealant such as Lyndar Clearcoat Aerosol. When the clear coat sealant is applied, the surface initially becomes slightly translucent, L * The value decreased significantly. This is because the solvent in the sealant enters the anodic oxidation pores, altering the optical properties of the surface.

[0134] A clear coat was sprayed onto the anodized surface and cured for approximately 2 hours. As the solvent evaporated from the sealant, the surface whiteness recovered to a value consistent with the whiteness before the sealant was applied, and the measured L * The value was 92.1. The sealant was fully cured after 24 hours.

[0135] The sealed anodized surface was white and exhibited higher gloss than the unsealed anodized surface, due to the properties of the sealant. The unsealed surface showed a gloss of approximately 1.3 GU (gloss units) at 85°, but after sealing, the GU increased to 90.1. Example 7 - Siloxane alumina sealing of a white anode surface

[0136] A white anodic oxidation substrate was prepared using the anodic oxidation bath and process 1.2 detailed in Example 1 above. The color of the prepared white surface was measured by optical colorimetric measurement and was found to be approximately 92.75 L. * It had a value.

[0137] Approximately 400 mL of siloxane alumina sol gel was prepared. A mixture of 21 mL of TEOS (tetraethyl orthosilicate) and 2 mL of HDTMS (hexadecyltrimethoxysilane) in 360 mL of isopropanol was vigorously stirred, and then 25 mL of aluminum trisec-butoxide was added using a syringe, followed by peptization of the sol by dropwise addition of 12 mL of hydrochloric acid (37 vol%). The suspension changed from a turbid state to a clear state after stirring for 5–10 minutes, thereby providing a suitable seal for the anodic oxidation surface. However, superior results were obtained by stirring for a longer period (e.g., 4 hours or more) to substantially complete the hydrolysis and condensation reactions.

[0138] The white anodic-oxidized surface was rinsed with ethanol to prepare it for electrophoretic deposition.

[0139] Siloxane alumina sol gel was impregnated into the anodic oxide surface by electrophoretic deposition for approximately 30 minutes. By performing the deposition at 170V, DC using a white anodic oxide surface as the cathode and a parallel titanium anode, a sealed anodic oxide surface was obtained.

[0140] The sealed anodized substrate having an anodized surface was first air-dried for 30 minutes, and then cured at approximately 50°C for 1 hour in a humidity-controlled environment with an RH exceeding 80%.

[0141] By color measurement of the sealed anodized surface, L * The value showed a slight increase of approximately 0.5 units, reaching 93.23.

[0142] After heat treatment at 200°C for 4 hours following sealing, the hardness of the sealed anodized surface is 206 HV. 0.1 The value increased to a level exceeding [a certain value]. While we do not wish to be bound by theory, the inventors believe that α-alumina in the anodic oxidation pore walls catalyzes the conversion of amorphous alumina in the sol / gel to a more robust boehmite form.

[0143] The sealed anodized surface remained white and exhibited superhydrophobic properties with a contact angle exceeding 150° (904 in Figure 9), and the silica alumina sealant provided excellent chemical resistance and abrasion resistance. Example 8 - Replacement of organic particle source

[0144] A nearly white anodic oxide surface was generated on an aluminum substrate using a bath in which the alkoxide component was replaced with high molecular weight polyethylene glycol.

[0145] A 50mm x 30mm x 1.2mm Al 7075 substrate was pre-treated and prepared according to the procedure of Example 1 described above.

[0146] A white anodic oxidation bath was prepared containing 42.5 g / L oxalic acid, 10 g / L boric acid, 1 g / L citric acid, 42 mL / L 2-propanol, and 15 mL / L PEG MW 400.

[0147] A pure organic bath required a bath temperature of 30±4℃. This bath was stirred by magnetic agitation at 600 rpm.

[0148] 4A / dm 2Constant current anodizing was performed using a stainless steel cathode for approximately 60 minutes until the anodizing voltage reached 150V. The rectifier was switched to constant voltage mode for the remainder of the anodizing period. The final current density was 2A / dm². 2 The sample was anodized for a further 120 minutes until it reached the desired result. The anodized sample was removed from the bath, rinsed, and dried with compressed air.

[0149] Color measurements were performed using a Shenzen ThreeNH Technology 3nh ASTM D1500 colorimeter. The surface had L values ​​of 88.65, -3.66, and 0.22, respectively. * a * b * The measured values ​​were obtained. This indicates that a white surface was produced by a bath that did not contain particles. Example 9 - Organic bath containing particles

[0150] A white surface could be produced using an organic bath containing a small amount of alkoxide.

[0151] A 50mm x 30mm x 3mm Al 7075-based aluminum substrate was pre-treated and prepared according to the procedure of Example 1 described above.

[0152] Organic baths containing particles were prepared using both long-chain organic particles and small amounts of metal alkoxides. These baths contained 42.5 g / L of oxalic acid, 10 g / L of boric acid, 1 g / L of citric acid, 42 mL / L of 2-propanol, 15 mL / L of PEG MW 400, and 10 mL / L of zirconium propoxide.

[0153] 4A / dm 2 Constant current anodizing was performed using a stainless steel cathode for approximately 30 minutes until the anodizing voltage reached 150V. The rectifier was switched to constant voltage mode for the remainder of the anodizing period. The final current density was 2A / dm 2The sample was anodized for a further 120 minutes until it reached the desired result. The anodized substrate was removed from the bath, rinsed, and dried with compressed air.

[0154] Color measurements were performed using a Shenzen ThreeNH Technology 3nh ASTM D1500 colorimeter. All surfaces were L * The measured value exceeded 91, demonstrating that a white surface can be produced by a bath containing small amounts of alkoxide and long-chain organic substances.

[0155] As shown in the results and detailed above, one of the advantages of the above method is that it provides a single-step anodizing process that can directly generate substantially random anodized surface structures by using a bath containing one or more organic acids, including hydrolyzed metal alkoxides. The anodized surface structures themselves are not secondary materials and reflect a wide bandwidth of visible frequencies. * When measured with a scale, the brightness (L * ) exceeds 91, and the color component (a * , b * A surface is produced in which the value is less than 2, i.e., a substantially white surface.

[0156] Where references to external sources, including patent specifications and other documents, are made herein primarily intended to provide context for discussing the features of the present invention. Unless otherwise specified, references to such sources should not be construed in any jurisdiction as an admission that such sources constitute prior art or part of common sense in the art.

[0157] The present invention and its embodiments are described in detail. However, the scope of the present invention is not limited to any specific example of any process, manufacture, apparatus, means, method and / or step described in the specification. Various modifications, substitutions, and variations can be made to the disclosed materials without departing from the spirit and / or essential features of the present invention. Accordingly, those skilled in the art will readily understand that later modifications, substitutions, and / or variations that perform substantially the same function or achieve substantially the same results as the examples described herein can be utilized according to the relevant examples of the present invention. Accordingly, the following claims shall encompass modifications, substitutions, and variations of the features, components, kits, means, and / or methods disclosed herein.

Claims

1. An aluminum anodizing process for producing a white or substantially white anodic oxide surface on an aluminum substrate, i. A step of pre-treating the aluminum substrate; ii. The aluminum substrate is as follows: - Buffering agent, - One or more particle sources, and - One or more carboxylic acids The steps include: immersing in an aqueous anodic oxidation bath containing; iii. Providing an anodized substrate including an anodized surface by anodizing the aluminum substrate according to the specified current and voltage for anodizing; A process that includes this.

2. The process according to claim 1, wherein the aluminum substrate includes pure aluminum or an aluminum alloy preformed into a member.

3. The process according to claim 1 or 2, wherein the pretreatment step includes an alkaline degreasing step.

4. The process according to claim 3, wherein the pretreatment of the aluminum substrate includes an acid pickling step.

5. The process according to any one of claims 1 to 4, wherein the pretreatment step is an electropolishing step.

6. C １～６ The process according to any one of claims 1 to 5, comprising the step of adding alcohol.

7. Said C １～６ The process according to claim 6, wherein the alcohol is selected from methanol, ethanol, propanol, and butanol.

8. The process according to any one of claims 1 to 5, wherein the one or more particle sources are selected from one or more metal oxide particles, one or more hydrolyzable metal alkoxides, one or more low molecular weight polymers, one or more long-chain organic substances, succinic acid, and combinations thereof.

9. The process according to claim 8, wherein the hydrolyzable metal alkoxide particles are selected from titanium butoxide, titanium isopropoxide, aluminum trisec-butoxide, zirconium butoxide, and combinations thereof.

10. The process according to claim 8 or 9, wherein the one or more hydrolyzable metal alkoxides are present in the aqueous anodic oxidation bath at a concentration of about 10 g / L to about 70 g / L.

11. Said C １～６ The step of adding alcohol is carried out by hydrolysis of a hydrolyzable metal alkoxide particle source, and by the hydrolysis, one or more metal oxide particles and the C １～６ The process according to any one of claims 6 to 10, wherein alcohol is produced.

12. The process according to claim 11, wherein the hydrolysis is performed in situ during the anodic oxidation step.

13. The process according to any one of claims 8, 11, or 12, wherein the metal oxide particles are microparticles or nanoparticles.

14. The process according to any one of claims 1 to 13, wherein the one or more carboxylic acids are selected from oxalic acid, citric acid, and combinations thereof.

15. The process according to claim 14, wherein the oxalic acid concentration is approximately 10 g / L to approximately 70 g / L.

16. The process according to claim 14 or 15, wherein the citric acid concentration is approximately 1 g / L to approximately 10 g / L.

17. The process according to any one of claims 1 to 16, wherein the buffering agent is boric acid.

18. The process according to claim 17, wherein the boric acid concentration of the boric acid buffer is approximately 5 g / L to approximately 20 g / L.

19. The process according to any one of claims 1 to 18, wherein the aqueous anodic oxidation bath further comprises a surfactant.

20. The process according to claim 19, wherein the surfactant is selected from nonionic surfactants and cationic surfactants.

21. The process according to claim 20, wherein the nonionic surfactant has a concentration of about 1 g / L to about 5 g / L.

22. The process according to claim 20 or 21, wherein the nonionic surfactant is Tween® 20.

23. Said C １～６ The process according to any one of claims 6 to 22, wherein the alcohol is present at a concentration of about 30 mL / L to about 100 mL / L.

24. Said C １～６ The process according to any one of claims 6 to 23, wherein the alcohol is substantially evaporated from the bath and / or converted to an oxalate or oxalic acid ester.

25. The process according to any one of claims 8 to 24, wherein the metal oxide nanoparticles are added to the anodic oxidation bath.

26. The process according to claim 25, wherein the metal oxide nanoparticles are present in the aqueous anodic oxidation bath at a concentration of about 1 g / L to about 10 g / L.

27. The process according to claims 1 to 26, wherein the one or more particle sources include a low molecular weight polymer.

28. The process according to claim 27, wherein the low molecular weight polymer comprises polyethylene glycol 400.

29. The process according to any one of claims 1 to 26, wherein the one or more particle sources include a combination of succinic acid and a metal oxide powder.

30. The process according to claim 29, wherein the metal oxide powder is magnesium oxide powder.

31. The specified current and voltage for the anodizing process are as follows: i. A first anodic oxidation step comprising applying a first current density over a first period of time; ii. A second anodic oxidation step is provided by changing the first current density to a second current density and voltage over a second period, wherein the second current density is higher than the first current density; iii. Perform the anodizing in the second anodizing stage until the voltage reaches the anodizing voltage threshold; iv. Switching the second current density to a voltage control stage, wherein the voltage control stage includes a constant anodizing voltage and an anodizing current density, and is performed over a voltage control period; The process according to any one of claims 1 to 30, including the process described in any one of claims 1 to 30.

32. The first current density is approximately 0.5 A / dm ２ ~About 3A / dm ２ The process according to claim 31.

33. The first period mentioned above is - Approximately 2 seconds to approximately 1.5 minutes; - Approximately 15 minutes to approximately 75 minutes The process according to claim 31 or 32.

34. The second current density is from about 2 A / dm ２ to about 8 A / dm ２ The process according to any one of claims 31 to 33.

35. The second current density is approximately 4 A / dm ２ The process according to any one of claims 31 to 34.

36. The process according to any one of claims 31 to 35, wherein the second period is approximately 5 to approximately 25 minutes.

37. The process according to any one of claims 31 to 36, wherein the second period is maintained for approximately 15 minutes.

38. The process according to any one of claims 31 to 37, wherein the anodizing voltage threshold is approximately 80V to approximately 300V.

39. The process according to any one of claims 31 to 38, wherein the voltage control stage is maintained at a constant anodic oxidation voltage and anodic oxidation current for a voltage control period of about 10 minutes to about 120 minutes.

40. The process according to any one of claims 31 to 39, wherein the voltage control step is maintained until the anodic oxidation current decreases to a value 10% below the first current density.

41. The process according to claim 31, wherein the first current density comprises a first step, a second step, and a third step.

42. The first step of the first current density is approximately 0.5 to approximately 3 A / dm ２ Preferably about 2 A / dm ２ The process according to claim 41, comprising the current density.

43. The process according to claim 41 or 42, wherein the first step of the first current density is maintained for about 5 minutes to about 25 minutes, preferably about 15 minutes.

44. The second step of the first current density is approximately 2 A / dm ２ ~About 4A / dm ２ Preferably about 3 A / dm ２ The process according to any one of claims 41 to 43.

45. The process according to any one of claims 41 to 44, wherein the second step of the first current density is maintained for about 5 minutes to about 25 minutes, preferably about 15 minutes.

46. The third step of the first current density is approximately 3 A / dm ２ ~About 5A / dm ２ Preferably about 3.4 A / dm ２ The process according to claims 41 to 45.

47. The process according to any one of claims 41 to 46, wherein the third step of the first current density is maintained for about 5 minutes to about 25 minutes, preferably about 15 minutes.

48. The second anodic oxidation step is approximately 3 A / dm ２ ~About 6A / dm ２ Preferably about 4 A / dm ２ The process according to any one of claims 41 to 47, having a second current density.

49. The process according to any one of claims 30 to 48, wherein the first anodizing step, the second anodizing step, and the voltage control step each provide a crystalline layer on the anodized surface, and each crystalline layer has a different crystalline morphology.

50. The process according to claim 49, wherein the crystalline layer is a nanocrystalline layer.

51. i) The first anodic oxidation step provides a substantially branched, random outermost layer of nanoporous material, the outermost layer having nanocrystalline walls and located furthest from the substrate; ii) The second anodic oxidation step provides an intermediate layer of nanotubes substantially filled with nanocrystalline material; iii) The voltage control step provides a nanocrystalline bottom layer, the bottom layer being in substantial contact with the substrate and being denser than the outermost layer and the intermediate layer; The process according to any one of claims 31 to 50, wherein the substantially nanocrystalline nanotube layer is located between the substantially branched random nanoporous layer having nanocrystalline walls and the nanocrystalline bottom layer which is denser than the outermost layer and the intermediate layer, and is substantially in contact with the nanoporous layer and the bottom layer.

52. The process according to any one of claims 1 to 51, further comprising the step of staining the anodic surface of the anodic oxidation substrate.

53. The process according to any one of claims 1 to 52, wherein the process includes a further step of sealing the anodic oxidized surface of the anodic oxidized substrate.

54. The process according to any one of claims 1 to 53, wherein a dense nanoporous element is produced by separating and processing the anodic oxide surface from the aluminum substrate.

55. An anodized surface constructed on an aluminum substrate, wherein the anodized surface is i) The outermost layer is a substantially branched random nanoporous outermost layer, the outermost layer having nanocrystalline walls and located furthest from the substrate; ii) A nanotube intermediate layer substantially filled with nanocrystalline material; iii) A bottom layer made of nanocrystalline material, wherein the bottom layer is in substantial contact with the substrate and is denser than the outermost layer and the intermediate layer; Includes, The nanotube layer, substantially filled with nanocrystalline material, is located between a substantially branched random nanoporous layer having nanocrystalline walls and a nanocrystalline bottom layer which is denser than the outermost layer and the intermediate layer, and is substantially in contact with the nanoporous layer and the bottom layer, on an anodized surface.

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