Anodic Alumina Films Research Articles

Mechanism of hot water sealing of anodic films formed on aluminum

The mechanism of the hot water sealing of anodic alumina films was studied using electron microscopy and compositional analysis. The films dissolve in boiling water and boehmite precipitates as small flakes due to (100)-oriented growth with 3-nm average thickness and evenly dispersing in the pores and the surface. The quantity and size of flakes increase with increasing sealing time forming a densely intertwined boehmite structure. Eventually, a three-layered structure is formed, which is composed of an outer vertically grown coarse flaky layer, an intermediate dense flaky layer with 2:1 thickness ratio, and a porous layer filled with dense flaky boehmite.

A fluorogenic capped mesoporous aptasensor for gluten detection

Celiac disease is a complex and autoimmune disorder caused by the ingestion of gluten affecting almost 1% of global population. Nowadays an effective treatment does not exist, and the only way to manage the disease is the removal of gluten from the diet. Owing the key role played by gluten, clear and regulated labelling of foodstuff and smart methods for gluten detection are needed to fight frauds on food industry and to avoid the involuntary ingestion of this protein by celiac patients. On that scope, the development of a novel detection system of gluten is here presented. The sensor consists of nanoporous anodic alumina films loaded with a fluorescent dye and capped with an aptamer that recognizes gliadin (gluten’s soluble proteins). In the presence of gliadin, aptamer sequences displace from the surface of anodic alumina resulting in pore opening and dye delivery. The dispositive shows a limit of detection (LOD) of 100 μg kg−1 of gliadin, good selectivity and a detection time of approximately 60 min. Moreover, the sensor is validated in real food samples. This novel probe allows fast gluten detection through a simple signalling process with potential use for food control.

Nano-, helical conducting poly(3-methylthiophene) prepared by one-step electro-deposition using cholesteric liquid crystal and anodic aluminum oxide as dual templates

Due to the importance of nano-, helical conducting polymers in both fundamental studies and applied research, poly(3-methylthiophene) (P3MT) with a nanosized helical structure was synthesized herein by using cholesteric liquid crystal (CLC) and an anodic aluminum oxide (AAO) film as dual templates. The monomer 3-methylthiophene was polymerised and filled into the nanopores of AAO in the CLC medium by a one-step electro-deposition method. Scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), and circular dichroism (CD) analyses proved that the nano-, helical structure of P3MT was successfully obtained by this method. Polarized optical microscopy (POM) revealed that P3MT had the same texture as the CLC, which originated from the template effect of CLC. The electrochemical dual template-assisted approach is easily controlled, highly efficient, and inexpensive for fabricating nano-, helical conducting polymers.

The Role of Hydrated Alumina Layer on the Incorporation of Electrolyte Species in Anodizing of Aluminum

Hydration treatment of aluminum is often used for corrosion protection of aluminum alloys and for the formation of dielectric alumina layer in aluminum electrolytic capacitors. Hydrated alumina layer is usually formed by immersing aluminum with and without a porous anodic alumina layer in hot water. The hydrated alumina layer plays an important role in enhancing the corrosion resistance and forming crystalline γ’-alumina in subsequent barrier-type anodic film growth by anodizing. However, the properties of the hydrated layer are not yet well understood. In this study, we examined the influence of anion incorporation properties into the barrier-type anodic alumina films through the hydrated alumina layer, which was formed in hot water.High purity (99.99%) aluminum plate was used in this study. After electropolishing in a HClO4–ethanol mixed solution below 283 K, a hydrated alumina layer was formed by immersing the electropolished aluminum in hot water (95ºC) for 10 min. The resultant hydrated layer consists of two layers, comprising a flake-like outer porous layer and a relatively dense inner layer. The thickness of the hydrated layer was ~430 nm. Then the aluminum with the hydrated layer was anodized in boric acid and tungstate electrolytes to grow the barrier-type anodic films. When the boric acid electrolyte was used, boron species were incorporated into the outer part of the barrier-type anodic films through the hydrated alumina layer. In contrast, no incorporation of tungsten species into the barrier-type anodic film through the hydrated layer occurred in the tungstate electrolyte. Phosphate anions are known to be incorporated into the 70% of the film thickness in the anodic amorphous alumina film, but in the present study, phosphate anions were not incorporated into the barrier-type anodic films through the hydrated layer. It is likely from the GDOES elemental depth profile analysis suggests that the inner hydrated layer becomes a barrier for the incorporation of tungsten and phosphorus species. Thus, apparently, the inner hydrated alumina layer has cation-selective permeation properties so that anion incorporation is limited. In boric acid electrolyte, the acid dissociation is limited, and non-charged boric acid species can be penetrated through the hydrated layer.

The Roles of Alloy Elements on Self-Lubrication of Anodic Al2O3/MoS2 Composite Films on Al Alloys

Aluminum alloys have good specific strength, corrosion resistance, and recyclability, so they are attracting attention from the automobile industry as a structural material to replace steel materials. Since aluminum alloys are prone to adhesive wear, resulting in poor tribological performance, it is necessary to improve the wear resistance by appropriate surface modification. It is known that filling some solid lubricants, such as MoS2 or PTFE, inside the anodic porous films is an effective method to improve the wear resistance of aluminum alloys in industry. However, few studies have been conducted on the alloy elements in aluminum alloys containing Si and Cu, especially casting alloys. The intermetallic compounds such as Si and CuAl2 contained in aluminum alloys usually cause defects inside the anodic films, which may affect the wear resistance of the anodic films. In this study, our purpose is to fabricate self-lubricating anodic Al2O3/MoS2 composite films on various aluminum materials by successive anodization and electrodeposition, to investigate the effects of alloy elements in aluminum alloys on the filling of MoS2 and wear resistance.Three kinds of commercial aluminum alloy sheets (A1100: 99.0% Al, A2017: Al-3.85% Cu, A4045: Al-9.85% Si) and an Al-12Si-5Cu casting alloy for automotive engine parts. Anodizing was performed using a sulfuric acid-based solution in constant current mode. After anodizing, anodic electrodeposition was performed in an ammonium tetrathiomolybdate solution, to incorporate molybdenum disulphide (MoS2) into the anodic films. The surface and cross section of the prepared sample were observed by FE-SEM to investigate the influence of intermetallic compounds in aluminum alloy on MoS2 anodic electrodeposition. GD-OES was used to examine the composition depth profiles inside the anodic Al2O3/MoS2 films. XPS was used to investigate the composition and chemical bond state of the formed MoS2. Furthermore, in order to evaluate the influence of the substrate on the wear resistance, the friction coefficient of various samples was measured using a reciprocating wear tester (SRV-4; 20 N, 1.0 mm, 20 Hz). The counterpart material was a high carbon chromium steel ball (100 CR6-DIN) of φ12.7 mm.Fig.1 a-b shows the results of GD-OES measurement of composition depth profiles within the self-lubricating anodic Al2O3/MoS2 composite films formed on (a) pure Al (A1100) and (b) Al-Si-Cu casting alloy. By making only Mo intensity the same measurement condition, it was possible to compare the amount of MoS2 filled inside the anodized films on pure Al and Al-Si-Cu casting alloy. Strong Mo peaks were found on the surface of both pure Al and Al-Si-Cu casting alloy specimens. The, with weak intensity inside the alumina film. Whereas the Mo and 0.1concentrate and Al-Si-Cu casting alloy. In case of pure Al, distribution of Mo mainly accumulates on the surface with only weak intensity inside the alumina film, and the intensity of Mo becomes almost stable toward the inside of the film. Whereas in case of the Al-Si-Cu casting alloy, the intensity Mo is much higher than that of pure Al, with a gradual distribution across the composite films, indicating that more Mo is deposited inside the anodic alumina film. The enhancement of Mo amount is ascribed to the presence of MoS2 in the defects of the anodic alumina film formed by the intermetallic compound (AlCu) contained in the Al-Si-Cu casting alloy, which can also be confirmed by cross-sectional observation by FE-SEM..Fig.1 c shows dynamic friction coefficient vs. number of reciprocating slides of self-lubricating anodic Al2O3/MoS2 composite films. Both the pure Al and the Al-Si-Cu casting alloy maintained a low friction coefficient at the beginning and then showed a sharp rise at a certain point. It is considered that the self-lubricating film was completely worn and reached the base metal at the point where the friction coefficient sharply increased. It can be confirmed that the number of sliding times to reach the base metal is about 26000 times with pure Al and about 36000 times with the Al-Si-Cu casting alloy, and that the Al-Si-Cu casting alloy has a longer coating life. In addition, the friction coefficient of the self-lubricating films decreased from 0.15-0.25 for pure Al to around 0.1for the Al-Si-Cu casting alloy, thus indicating the excellent lubricating effect of MoS2, which can be attributed to the increase of the filling amount of MoS2 inside the anodic film, as shown in the results of GD-OES (Fig.1a-b). Figure 1

Simultaneous Fabrication of Porous Alumina Lines By 3D Printed Multi-Capillary Sf-MDC

IntroductionPorous-type anodic aluminum oxide (porous alumina) films with an ordered nanostructure have attracted much attention in recent years. It is well known that the size and length of the pores are controlled by the anodizing conditions, including the concentration and composition of the used electrolyte.There are demand for formation of porous alumina film at selected area, and are a number of techniques for the formation of porous alumina at the desired size and shape. However, commonly used local anodized techniques present disadvantages in the complex processes involved.One technique that gets around the these problems is the droplet cell techniques. The droplet cell used electrolyte droplet that formed at the tip of capillary tube uses as electrochemical cell. One of the authors reported the application of solution flow type micro-droplet cell with co-axial dual capillary tubes (Sf-MDC) to form porous alumina film at selected area 1, 2, 3, 4. The thickness and width of the oxide film increases with decreasing droplet moving speed, and the growth rate of the oxide film is greatly affected by the specimen temperature. Using this cell makes it possible to form porous alumina lines with layered structure. However previously used Sf-MDC has drawback of slow alumina line fabrication. One technique that gets around this problem is using multi-capillary Sf-MDC. It is difficult to increase number of capillaries using previous making technique for Sf-MDC.3D printer is widely used and recent advancements in 3D printing technology allows us to produce complex structures with great accuracy and minimal production time. Therefor 3D printing technique is apply to make multi-capillary Sf-MDC. The purpose of this experiment is to design and fabricate a novel Sf-MDC using 3D printer and form multi porous alumina lines on the substrate.Fabrication of multi-capillary Sf-MDCA Sf-MDC was designed and photopolymer resin was used for 3D printing the parts. Optimal orientation was chosen to print the parts in order to minimize the number of supports, number of layers, time and volume required for printing. Using optimized printing parameter, multi-capillary Sf-MDC was made. Before using the Sf-MDC for anodizing, the support structure was trimmed and Pt wire was inserted inside the capillaries.ExperimentalSpecimen and electrolyte: High purity Al sheets (99.99 %, 10 × 30 mm, 110 µm in thickness) were used as specimens. The specimens were ultrasonically cleaned with highly purified water for 300 s, followed by ultrasonic cleaning in ethanol for 300 s. Then, the specimens were electropolished in 13.6 kmol m-3 CH3COOH /2.56 kmol m-3 HClO4 at a constant voltage of 28 V for 150 s at 278 K. After the polishing process, specimens were cleaned with highly purified water and acetone.The solutions used as the electrolyte for the anodizing were 0.22 kmol m-3 (COOH)2, 0.22 kmol/m-3 H3PO4, 0.3 kmol/m-3 H2SO4solutions.Anodizing: An electropolished specimen was set on a computer-controlled pulse-XYZ stage, and the specimen temperature during the anodizing was controlled by a Peltier device at 323 K. The cell was filled with electrolyte via a solution pump, then a droplet of electrolyte was formed at the tip of the inner capillary by adjusting the solution flow rate and a vacuum pressure. After the droplet of electrolyte was formed, thereafter, the droplet was put in contact with the specimen surface, and a constant voltage was applied. The moving speed of the specimen was controlled at 2.0 μms-1, and distance was 4 mm for the formation of the oxide film lines.Observation:Specimen surfaces and cross-sections after anodizing were examined by an optical microscope and scanning electron microscope, SEM. The specimens for the cross-sectional observation were prepared by simple curving and breaking. Before the SEM observations, a thin Au layer was sputtered on the specimens.ResultsThree uniformly sized porous alumina lines on the Al specimen can be formed by the Sf-MDC. From SEM observation, formed anodic oxide lines have a porous structure and average pores arrangement and pore diameter is nearly same for each lines.References T. Yamaguchi and M. Sakairi, Journal of The Surface Finishing Society of Japan, 385-390, 65 (2014)M. Sakairi, F. Nishino, and R. Itzinger, Surface and Interface Analysis, 48, 921-925 (2016)T. Matsumoto and M. Sakari, Journal of The Japan Institute of Light Metals, 68, 401-405 (2018).M. Sakairi, E. Han, T. Matsumoto, Journal of The Surface Finishing Society of Japan, 70, 20-24 (2019).T. Murata, Y. Goto, M. Sakairi, K. Fushimi, and T. Kikuchi, ECS Transaction, 33, 57 (2011).

(Invited) Formation Efficiency of Anodic Porous Alumina in Sulfuric Acid Containing Alcohol As Additives

The properties of anodic porous alumina films, which are generally formed by the anodization of aluminum in an acid electrolyte, are well known to be affected by the dimensions of their structure (e.g., pore diameter, pore density, and film thickness). For instance, to increase the hardness of anodic films on aluminum, the anodization is industrially carried out at low-temperature to avoid chemical dissolution of the formed oxide film during anodization. Anodization in an electrolyte containing organic compounds is also one approach for improving the performance of anodic oxide film not only for aluminum but also for other light metals such as titanium and magnesium (1).One such initiative is anodization of aluminum at a relatively high current density or high voltage using a common acidic electrolyte (e.g., sulfuric acid, oxalic acid, or phosphoric acid) with an alcohol added. In such studies, the effects of adding an alcohol are summarized as follows: i) the alcohol functions as an anti-freeze agent in the electrolyte, enabling the anodization temperature to be lowered; ii) the alcohol acts as a cooling agent—specifically, the vaporization of alcohol at the bottom of the pore channels removes the heat generated at the aluminum/oxide interface; and iii) nonuniform growth of the anodic film (i.e., burning) is effectively prevented, even during high-field anodization. However, these effects are observed not only for monohydric alcohols with a boiling point less than 100 °C (e.g., methanol and ethanol) but also for polyhydric alcohols with a boiling point greater than 100 °C (e.g., ethylene glycol and glycerol). Therefore, the effect of alcohol addition cannot be reasonably explained solely on basis of the boiling point of the alcohol used as an additive. Understanding the effects of alcohol addition necessitates a systematic investigation comparing types of alcohols, in addition to further fundamental studies.In this study, monohydric alcohols or polyhydric alcohols were added to the sulfuric-acid-based electrolyte to examine their effects on the anodization behavior of aluminum, the coating ratio, the porosity, the maximum attainable film thickness, and the resulting etching ability. Anodization was conducted in sulfuric acid solutions containing various alcohols with different physical properties under mild anodization conditions with a constant current of 100 A·m−2 at 20 °C (2, 3). The influence of the type and concentration of alcohol on the coulombic efficiency of film formation and the structure of the porous alumina under a constant electric charge was also investigated. In terms of basic research, the potential impact of alcohol addition in electrolytes will be discussed. H. Asoh, K. Asakura, H. Hashimoto, RSC Advances, 10, 9026-9036 (2020).H. Asoh, M. Matsumoto, H. Hashimoto, Surface and Coatings Technology, 378, 124947 (2019).M. Matsumoto, H. Hashimoto, H. Asoh, Journal of The Electrochemical Society, 167, 041504 (2020).

Fabrication of Pt-Nanoparticle-Loaded Mesoporous Alumina Coating through Anodizing of an Al-Pt Alloy

Noble metal nanoparticles, usually dispersed in a mesoporous support, have widespread applications. However, uploading nanoparticles into mesoporous materials and preventing the nanoparticles from aggregation during the fabrication and application processes remain major challenges. Herein, we report a novel, simple and low-cost method for fabrication of Pt-nanoparticle-loaded mesoporous alumina coating through anodizing of an Al-Pt alloy (98.5 at% Al and 1.5 at% Pt) prepared by magnetron sputtering. It was found that the Al-Pt alloy could be effectively anodized at voltages between 2.8 and 4.5 V (SCE), in 0.4 M sulfuric acid solution, at room temperature. The anodizing processes resulted in Pt-nanoparticles of 5∼50 nm dimensions uniformly-dispersed in the porous anodic alumina film. The proposed method can be implemented on a large scale and extended to other alloy systems consisting of a valve metal and different alloying elements with Gibbs free energy of oxide formation less negative than that of the valve metal.

Optical properties of multicolor, hierarchical nanocomposite films based on anodized aluminum oxide

Abstract With three distinct layers, multicolor, hierarchical nanocomposite films based on anodized aluminum oxide (AAO) were fabricated on the 6063 aluminum alloy surface by anodizing and alternating current electrodeposition. The impact of the electrolysis time on the nanostructures and optical properties of the as-grown film was investigated. It was found that with the extension of electrolysis time, the sample color could be varied from gray, yellow, red, blue, to green, realizing almost full-spectrum colors of the AAO-based films in the visible light range. The nanostructure characterizations and the UV–Vis reflectance spectroscopy of the AAO-based films showed that the thickness of the bottom one (i.e., layer 3) of the three layers was dictated by the electrolysis time over the range of 55–145 s, corresponding to the thickness from 135 to 264 nm. Additionally, the optical pathway of the AAO-based film with hierarchical composite nanostructures was analyzed. An increase in the layer 3 thickness would cause a shift in the peak wavelength in the corresponding reflectance spectra, conforming to the Bragg-Snell formula. The colors of AAO films were speculated to originate from constructive interference between the light reflected from the layer 1-layer 2 interface and the light reflected from the layer 3-aluminum alloy substrate interface.

Volcano-like hierarchical superhydrophobic surface synthesized via facile one-step secondary anodic oxidation

Superhydrophobic surface has been extensively applied in the field of self-cleaning and corrosion prevention, and the common preparation route of the superhydrophobic surface involves the construction of rough structure and modification with low-surface-energy regents in multistep process. Herein, a facile one-step method was proposed to fabricate the superhydrophobic surface with the simultaneous construction and modification of hierarchical microstructure and surface, the volcano-like anodic aluminium oxide (AAO) -based superhydrophobic surfaces with controllable roughness were synthesized via secondary anodic oxidation (SAO) process of AAO film in an organic–inorganic sol–gel system. During the SAO process, the perfluorooctyl triethoxysilane, which covalently bonded onto the surface, resulted in the inhomogeneous distribution of surface free energy and heterogeneous generation of volcano-like structure. The hydrophobic ability was enhanced by the rough hierarchical micro-/nanostructure with low surface energy, and the TiO2/PFOTS-AAO-15 exhibited the optimal water repellence with a WCA of ~154°, self-cleaning performance and anticorrosion property in corrosive medium. This convenient method is anticipated to unlock various superhydrophobic surfaces on different substrates in the practical fields of self-cleaning and anticorrosion.

In vitro Biocompatibility Evaluation of Anodic Alumina Substrates with Electrochemically Embedded Silver

Anodic aluminum oxide films modified by silver incorporation (Al-O-Ag) under specific electrodeposition conditions were produced and their biocompatibility was analyzed by in vitro assays using mammalian cell lines. The results obtained demonstrate that Al-O-Ag substrates are well tolerated by human dermal fibroblasts. The alumina pads doped with silver for short time-period (30 seconds) showed the highest biocompatibility among all modified metal substrates and in comparison with three dental alloys.

Fabrication of an artificial ionic gate inspired by mercury-resistant bacteria for simple and sensitive detection of mercury ion

Bioremediation of mercury pollution by mercury-resistant bacteria requires the key steps of mercury ions (Hg2+) capture and transportation. Inspired by the functions of mercury transporters in mercury-resistant bacteria, we have fabricated an artificial ionic gate, which may further behave as an Hg2+ biosensor. The gate is constructed by using the asymmetrically modified porous anodic alumina (PAA) film capable of forming Hg2+-activated complexes to control ionic current, while the gate works due to the changes between graphene oxide (GO) and different DNA structures. Specifically, single strand poly(T)n DNA on PAA film may transform into duplex structure through T-Hg2+-T coordination chemistry when Hg2+ exists. Compared with the ring by ring delivery via S-Hg intermediates in bacteria, this artificial gate may show better flexibility for Hg2+ transport, because the poly(T)n-Hg2+ complex can be wrapped in a chain structure with controllable DNA length. Furthermore, with the advantages of simple structure, convenient operation and good practicality, the constructed artificial Hg2+-activated ionic gate has been developed as a biosensor for sensitive detection of Hg2+, with the limit of detection (LOD) down to 0.07 fM. The fabricated ionic gate may be used for building an instrument that can absorb and detect Hg2+ from wastewater in the future.

Effect of anodizing temperature and organic acid addition on the structure and corrosion resistance of anodic aluminum oxide films

Anodic aluminum oxide films, industrially produced by anodizing aluminum alloys under the galvanostatic mode at a relatively low temperature of 20°C (electrolyte bath temperature), present the reliable anticorrosive effect for numerous applications. For fabricating anodic aluminum oxide films with the promising corrosion resistance as well as high growth rate in a wide temperature range, the effect of anodizing temperatures on the structure and growth mechanism of anodic aluminum oxide films was investigated. As the temperature increases up to 30°C, the stress-driven breakdown of porous-type anodic aluminum oxide layers induced by their thinner pore walls was estimated. This phenomenon is interpreted by an increase of electronic current and thus a strong scour effect of O2 bubbles on the porous-type anodic aluminum oxide layers. Moreover, with the addition of composite organic acid into the sulfuric acid-based electrolyte solution, the anions (C6H5O73−,C4H4O62−) that incorporated into the anodic oxide contribute to lowering the electronic current and thus suppressing the formation of oxygen bubbles, resulting in a thicker barrier-type anodic aluminum oxide layer. This is assumed to be responsible for the enhanced corrosion resistance of anodic aluminum oxide films prepared at 30°C with 50 g/L organic acid addition.

Evaluation of the electrochemical corrosion behavior of anodic aluminum oxide produced by the two-step anodization process

Purpose This study aims to investigate the effect of different pore diameter and pore length on corrosion properties of anodic aluminum oxide (AAO) film. Design/methodology/approach AAO layer was produced by two-step anodization aluminum in oxalic acid. The surface morphology was investigated using field emission scanning electron microscopy. The pore diameters were ranging from 25 ± 5 to 65 ± 5 nm and the pore length ranging from 5 to 17 µm. The corrosion properties of the AAO films was analyzed by potentiodynamic polarization and electrochemical impedance spectroscopy tests. Corrosion properties and morphology of the anodic films depending on anodization times and pore expansion times were evaluated. Findings All highlights of this work can be summarized with the following specified below: more treatment with the protective barrier layer of the solution as the pore diameter increases depends on the morphology of the nanotube structured AAO layer. The excellent corrosion resistance renders AAO films without pore expansion very promising. The oxide layer thickness does not affect the corrosion resistance. The better corrosion resistance of AAO films at low pore length can be ascribed to the barrier layer thickness and the more homogeneous structure. The presence of defects for the higher pore length decreases its corrosion resistance. Originality/value The AAO films were fabricated by a two-step anodization method in oxalic acid. The anodization times and pore expansion times affect the corrosion performance. The AAO film without pore expansion has good corrosion resistance. The corrosion resistance decreases as the pore length increases.

The effect of the current pulse amplitude on the nanopore structures of 3D-AAO films

The microstructure of porous anodic aluminum oxide (AAO) has a crucial influence on its properties. In this paper, three-dimensional AAO (3D-AAO) film with mallet-shaped nanopores structure and 185–187 nm pore diameters was prepared by periodic pulse anodizing of high-purity aluminum foil in phosphoric acid using asymmetric sawtooth current waves. Highly ordered 3D-AAO membranes with periodically modulated nanostructure were achieved, and the nanopores were changed from mallet shape to Y-branched channels with a length of 249–742 nm by adjusting the amplitude of the asymmetric sawtooth current wave. The effect of current amplitude on the nanostructure of 3D-AAOs was analyzed by combining the scanning electron micrograph (SEM) of the samples and the V-T images during the anodization process. The results show that the anodization time of the high-potential anodization stage and the low-potential anodization stage in each cycle can be adjusted by changing the amplitude of the asymmetric sawtooth current wave, to realize the regulation of the 3D-AAO nanostructure. These 3D-AAO film with structural modulation may be used as templates for the fabrication of novel nanowires or nanotubes with excellent electromagnetic properties.

The aluminum current collector with honeycomb-like surface and thick Al2O3 film increased durability and enhanced safety for lithium-ion batteries

Durability and safety are main factors contributing to the market requirement of lithium-ion batteries (LIBs) in practical applications. The improvement of current collector has been proven as an effective approach to enhance comprehensive performance of LIBs. To achieve a sufficient electrical contact between the current collector and active materials, honeycomb-like surface of aluminum current collector is etched by direct current in sulfuric acid and phosphoric acid mixed solution. At the same time, a dense anodic aluminum oxide film is formed on the surface of aluminum current collector, which can protect LIBs from corrosion and thermal runaway. Experimental results show that the adhesion between the active material and aluminum current collector was improved by 23% after anodization. The corrosion resistance of alumina foil was promoted significantly in ethyl methyl carbonate and ethylene carbonate electrolyte with LiPF6. The corrosion current peak reduces to 0.022 mA/cm2 from 0.267 mA/cm2 after surface treatment. The capacity retention rate of the LiCoO2 electrode with an oxidation-treated aluminum current collector is 6.3% higher than with untreated aluminum foil at 5C after 500 cycles. What’s more, the nail penetration demonstrates that the aluminum current collector we prepared can reduce the temperature of the full batteries surface when the nail pierced, which improved the safety performance of LIBs.

Investigating the infrared spectral radiative properties of self-ordered anodic aluminum oxide for passive radiative heat dissipation

Nanoporous self-ordered anodic aluminum oxide (AAO) film has shown great promise for applications in passive radiative heat dissipation due to its high infrared thermal emissivity and its good economic efficiency for mass production. However, the passive radiative cooling mechanism of AAO is not yet fully understood. In this study, the finite-difference time-domain (FDTD) method is adopted to theoretically investigate how the structure of AAO, pore diameter, interpore distance, porosity, and thickness included, impact its infrared spectral emissivity for radiative cooling. The results demonstrate that the infrared spectral emissivity of AAO film is mainly influenced by the porosity and the film thickness. There exists an optimal porosity for a certain film thickness to obtain the maximum infrared emissivity. When the difficulty in practical fabrication of thick AAO film is considered, the ideal AAO film thickness locates between 50 and 100 μm. The results reported in this study can be exploited to guide the design and development of high-emissivity passive radiative cooling materials.

Pore structure control of anodized alumina film and sorption properties of water vapor on CaCl2-aluminum composites

Recently, increasing research attention has been given to the development of an absorber to enhance the coefficient of performance (COP) and the capacity of an adsorption heat pump by improving the sorbent in the sorption chamber or reactor. This study introduces the preparation method for an efficient adsorbent with a high thermal conductivity. Three types of host matrix aluminum composite sorbents were prepared through anodizing and pore widening treatment (PWT). This created an aluminum oxide film that was 92 μm thick with a mean pore diameter of 76 nm on an aluminum plate. To improve the sorption ability, the anodized aluminum was impregnated with calcium chloride. The sorption isotherm of the aluminum composite demonstrated its ability to uptake 7.5 mol-H2O/mol-CaCl2 water at a relative pressure of 0.33 at 30 °C. A numerical method was used to predict water sorption and temperature distribution in the aluminum composite layer via a heat and mass transfer model. The specific cooling power (SCP) was used to indicate the cooling performance of a sorption heat pump that employed the aluminum composite as laminate sorbent fins by varying the spacing between each fin.

Aluminum ASA 6061 Anodizing Process by Chromic Acid Using Box–Wilson Central Composite Design: Optimization and Corrosion Tendency

The behavior of anodic porous alumina film formed on an aluminum surface by anodizing in chromic acid solutions was optimized using Box–Wilson experimental design. The film thickness was correlated as a function of temperature, acid concentration, applied voltage, and time. A mathematical model was suggested and optimized. Results of coating thickness indicate that both temperature and time play an important role in the anodizing process. The interaction effect of variables on the film thickness is less pronounced compared with the effect of the main variables. Optimum film thickness obtained during the anodizing process was 10.43 µm at the optimum value of temperature (45 °C) and time (68 min). The polarization measurement of anodized aluminum ASA 6061 in chromic acid shows a high corrosion resistance in the presence of coating. The results confirmed by using surface morphology investigations.

A set of empirical equations describing the observed colours of metal-anodic aluminium oxide-Al nanostructures.

Structural colours have received a lot of attention regarding the reproduction of the vivid colours found in nature. In this study, metal–anodic aluminium oxide (AAO)–Al nanostructures were deposited using a two-step anodization and sputtering process to produce self-ordered anodic aluminium oxide films and a metal layer (8 nm Cr and 25, 17.5 and 10 nm of Au), respectively. AAO films of different thickness were anodized and the Yxy values (Y is the luminance value, and x and y are the chromaticity values) were obtained via reflectance measurements. An empirical model based on the thickness and porosity of the nanostructures was determined, which describes a gamut of colours. The proposed mathematical model can be applied in different fields, such as wavelength absorbers, RGB (red, green, blue) display devices, as well as chemical or optical sensors.