Anodized Specimens Research Articles

Effects of hard anodizing on mechanical and electrochemical characteristics of aluminum alloys under tribocorrosion condition

In this research, the effects of hard anodizing on the mechanical and electrochemical characteristics of aluminum alloys under tribocorrosion conditions was investigated. Compared with dry conditions, friction coefficient of aluminum alloys under tribocorrosion conditions increased, whereas that of hard anodized specimens decreased. This was attributed to corrosive ions in the solution corroding the transfer film of the counter-body and tribofilm of the hard anodized specimen. In potentiodynamic polarization experiments under tribocorrosion conditions, the aluminum alloys exhibited high current density with applied load. However, at potentials above –0.05 V, current density decreased and was reversed. This is believed to be due to the corrosive ions preferentially reacting with the generated wear debris, thereby reducing the oxidation reaction with wear track. However, the current density of the hard anodized specimens increased with load and potential. In addition, the increasing rate in the wear width and depth was significant under tribocorrosion conditions (Width: 42.65 %, Depth: 32.63 %). This is due to the cavitation and fluid impact generated during friction/wear accelerating the cracking and damage of the hard anodizing film with the brittleness and porousity. However, the tribocorrosion resistance of the hard anodized aluminum alloy was improved by more than 97 %.

Exploring the Impact of Potential, Ammonium Fluoride Concentration, and Anodization Time on the Structure, Surface Characteristics, and Corrosion Resistance of Nanotubular Titanium Oxide Coatings on Biomedical Alloy Ti-6Al-4V ELI

The current research delves into assessing the impact of applied potential, ammonium fluoride concentration, and anodization duration on the structural, phase compositional, microhardness, and surface roughness attributes of nanotubular titanium oxide coatings on anodized Ti-6Al-4V ELI. A meticulous experimental design was executed to systematically investigate the varied effects of these factors. Scanning electron microscopy (SEM) unveiled the presence of well-defined titania nanotubes on the surfaces of the anodized specimens. X-ray diffraction (XRD) analysis discerned the composition of the nanotubular oxide layer, revealing the presence of both anatase and a mixture of anatase and rutile phases contingent upon the anodization parameters. Notably, surface microhardness, surface roughness, and corrosion resistance manifested noticeable variations in response to alterations in applied voltage, NH4F concentration, and anodization duration within the designated experimental ranges.

Tribocorrosion Characteristics of Hard Anodized Al Alloys on Hydrogen Valve Application for Fuel Cell Electric Vehicles

In this study, the electrochemical and mechanical characteristics of 6061‐T6 aluminum alloy and hard anodized specimens are investigated after tribocorrosion experiments with rotational speed in dry, distilled water, and sulfuric acid solution. The tribocorrosion experiments indicate that the corrosion potential of aluminum alloys and hard anodized specimens decrease with the initiation of friction/wear. In particular, the increase in the wear track width of an aluminum alloy and the exposure of the base material by completely destroying the anodized layers of the hard anodized specimens dramatically decrease the corrosion potential. Compared to the dry conditions, both the width and depth of damage in the distilled water and sulfuric acid solution increase dramatically. However, damage in the distilled water and sulfuric acid solutions do not present a significant difference. The results are attributed to the fact that the presence of fluid has a greater impact on damage degree in a material than corrosion. In particular, the brittleness and porosity of a hard anodized layer facilitates the impingement and penetration of fluid, making it relatively easy to generate and propagate cracks. These cracks accelerate the degradation and damage to the material by synergistic effects of wear and corrosion.

Electrochemical Noise Analysis Using Experimental Chaos Theory, Power Spectral Density and Hilbert–Huang Transform in Anodized Aluminum Alloys in Tartaric–Phosphoric–Sulfuric Acid Solutions

Aluminum and its alloys find widespread applications across diverse industries such as the automotive, construction, and aeronautics industries. When these alloys come into contact with ambient air, an Al2O3 thin oxide layer is naturally formed, typically measuring 2 to 4 nm and exhibiting remarkable hardness and protective qualities, rendering the alloys corrosion-resistant in specific atmospheric and chemical environments. This study aimed to characterize the electrochemical behaviors of anodized AA2024 and AA7075 alloys within a complex three-component electrolyte composed of tartaric–phosphoric–sulfuric acid (TPSA) solutions. The anodized specimens were subsequently exposed to 3.5 wt.% NaCl solution at room temperature, and their electrochemical performances were meticulously evaluated using an electrochemical noise (EN) analysis in accordance with ASTM G-199, respectively. In the EN, three methods of data analysis were used: the time domain analysis (chaos analysis: application of Lyapunov exponent and dimension correlation), the frequency domain analysis (power spectral density, PSD), and the time–frequency domains analysis (Hilbert–Huang transform, HHT). Scanning electron microscopy (SEM) was used to observe the morphologies of the anodized surfaces. The results indicated that the AA2024-0, AA2024-1, and AA2024-2 alloys and the AA7075-2 and AA7075-3 samples exhibited mixed corrosion according to the Lyapunov constant, with a notable inclination towards localized corrosion when analyzed using the PSD and HHT methods. The surface was not homogenous, and the corrosion process was predominately localized in specific zones.

Effect of anodizing on high cycle fatigue behaviour of cast AlSi8Mg-T6 alloy

The work investigates the effect of anodizing on the high cycle fatigue behaviour of a high-quality cast Aluminium (AlSi8Mg-T6) alloy. Tensile and fatigue tests are carried out on both non-anodized and anodized specimens in order to highlight the differences in tensile and fatigue responses. In addition, roughness measurements, fracture surfaces analyses, metallography, instrumented micro-indentation and scanning electron microscope (SEM) inspections are performed in order to investigate the interplay between the presence of an anodic layer and the fatigue life of anodized specimens.It is demonstrated that, after anodizing, AlSi8Mg-T6 specimens shows a deterioration of the fatigue performance at medium–low stress amplitudes (130 and 110 MPa). In addition, fracture surface analysis reveals that the presence of the anodic layer modifies the fatigue crack initiation and early growth mechanisms. The manuscript paves the way for an accurate fatigue design of anodized, cast AlSix components.

Effect of Anodizing on Very High Cycle Fatigue Properties of Aluminum Alloy A2014-T6 in Laboratory Air and 3 % NaCl Solution

Abstract To examine the effect of oxide layer thickness on fatigue behavior, rotating bending fatigue tests were performed on the aluminum alloy A2014-T6 with oxide layers of 3 different thicknesses in laboratory air and 3 % sodium chloride (NaCl) solution over a wide cycle-life region (104–109 cycles). Tests were also conducted on untreated specimens for comparison. Based on the results of fatigue tests in laboratory air, deterioration of the fatigue strength was observed for anodized specimens having an oxide layer in comparison with untreated specimens. The fatigue strength of anodized specimens decreased with increasing oxide layer thickness. On the other hand, fatigue test results in 3 % NaCl solution showed that anodizing improved fatigue life, which increased with increasing oxide layer thickness. In addition, the thickness of the oxide layer was found to be important from the viewpoint of fracture mechanics.

Oxide Film Formation on Stainless Steel 304L by Anodizing Method with Different Power Sources

In order to generate a nanoporous oxide film, stainless steel 304L is anodized using an alternating current (AC) and direct current (DC) source in an ethylene glycol solution containing ammonium fluoride, NH4F, and water, H2O. This study focuses on the differences between AC and DC anodizing in terms of current density versus time response, thickness, and depth of the oxide film formed on the anodized specimens, surface roughness, and element composition of the specimens because there is limited study on AC anodizing of stainless steel. In 0.5% 0.3M NH4F and 3% H2O in a glycol solution, the AC and DC anodizing is conducted for 30 minutes at voltages ranging from 30 V to 50 V and 21.2 V to 35.4 V, respectively. The current density versus time response revealed that AC anodizing produced more current density than DC anodizing. As for the thickness and depth of the generated oxide films, only the specimens that had been anodized in AC indicated an increase in these films, whereas specimens that had been anodized in DC showed the metal dissolving as the specimens degraded. The surface roughness of AC anodized specimens reduced with increasing anodizing voltage, whereas DC anodized specimens increased with increasing anodizing voltage. The element composition of the anodized specimens revealed that the mass percentage of oxygen, O element is higher for AC anodized specimens compared to DC specimens. This suggests that AC anodizing on stainless steel might offer important advantages and should be further researched.

Chemical stability of porous anodic aluminum oxide in both acidic and alkaline solutions

A porous anodic aluminum oxide (AAO) possessing higher chemical resistance in both acidic and alkaline solutions was fabricated by anodizing Al in an alkaline sodium tetraborate solution. The 5 N Al plates were anodized in five types of major acidic solutions (sulfuric, oxalic, phosphoric, chromic, and etidronic acids) and in alkaline sodium tetraborate solution to form AAOs. The anodized specimens were then immersed in a 0.52 M phosphoric acid solution (pH = 1.3) and a 2.5 M sodium hydroxide solution (pH = 13.8). Subsequently, the electrochemical impedance measurements and morphological characterizations of the AAOs before and after immersion were investigated. The time required for the complete dissolution of the AAOs formed in typical acidic electrolytes, including sulfuric, oxalic, phosphoric, and etidronic acids, increased linearly with the anodizing voltage. The AAO formed in chromic acid exhibited a higher chemical resistance than this linear relationship owing to the formation of high-purity alumina without incorporated anions. Moreover, the AAO formed in sodium tetraborate exhibited the highest chemical resistance in both acidic and alkaline solutions – approximately two times higher than that formed in etidronic and chromic acids. This can be attributed to their higher anodizing ratio and the formation of a high-purity alumina layer.

THE EFFECT OF HEAT TREATMENT AND SURFACE ANODIZATION ON FRICTION AND WEAR COEFFICIENT OF ALUMINIUM 2024 USING PIN ON DISK METHOD

The use of aluminum alloys as a material for engineering components that rub against each other is increasing, so it is important to know the friction characteristics of these aluminum alloys. In this study, Aluminum 2024 was given heat treatment with variation in aging time and anodization. Then, the wear and friction coefficient tests were carried out using a pin tool on the disc. The effect of aging time and surface anodization on wear tests are carried out to determine the amount of wear and the coefficient of friction test is carried out to determine the coefficient of friction of the material when it rubs against a pin made of AISI 52100 Steel. The coefficient of friction test is carried out by adding lubrication as a parameter. The test results showed that the aluminum material given heat treatment had better resistance than that which was not heat treated. This is because the heat treatment creates precipitates that can increase the aluminum's hardness and wear resistance. Whereas for anodized specimens, the alumina layer can act as an abrasive grain when given a high enough friction and load continuously, so the wear testing mode changes from dry sliding wear to three body abrasive wear and decreased wear resistance. From the friction coefficient test results, the aging time affects the hardness of the aluminum alloy, which leads to the value of the coefficient of friction. The harder the sample surface, the smaller the coefficient of friction obtained. Furthermore, applying lubricant to the sample will also decrease the value of the friction coefficient of the sample. Lubricating oil will provide a more significant reduction in friction coefficient than air. Finally, the anodizing surface on the sample will act as a lubricant reservoir when it occurs.

Enhancing the biocompatibility of ZrO2 thin film on Zr-2.5Nb alloy by anodizing treatment using an electrolyte containing biofunctional groups

Surface characteristics of a biomaterial such as morphology, topography, and chemistry influence cell attachment, proliferation, gene expression, and differentiation. Studies have shown that anodizing, one of the most effective electrochemical surface modification methods, could improve cell to implant surface interactions. In this study, the Zr-2.5Nb alloy was anodized in an aqueous electrolyte containing CaF2 and NH4H2PO4. The effect of anodizing treatment on the surface modification of Zr-2.5Nb was also investigated. The biocompatibility of the non-anodized and anodized specimens was evaluated by the MG-63 osteoblastic cells. The results demonstrated that Zr oxide on the anodized Zr-2.5Nb surface consisted of monoclinic and tetragonal structures. Also, the average thickness of the anodic film was measured at about 85 nm, and the electrolyte's fluorine, calcium, and phosphorus ions were incorporated at the top surface of the film. The potentiodynamic polarization and electrochemical impedance spectroscopy tests proved that the anodized specimens exhibit higher corrosion resistance in Ringer's solution than that of the non-anodized specimens. In terms of cell response, MG-63 cells depicted a suitable cell attachment after five days from cell culture as osteoblastic cells showed an excellent proliferation and viability on the anodized specimens. Finally, remarks suggest that anodizing treatment by an electrolyte containing biofunctional groups could enhance the corrosion resistance and cellular performance of the Zr-2.5Nb alloy for biomedical applications.

Surface Microstructure and Performance of Anodized TZ30 Alloy in SBF Solution

Anodization is performed on the Ti-30Zr-5Al-3V (TZ30) alloy to improve its surface performance. X-ray diffractometer (XRD), scanning electron microscopy (SEM), and Olympus microscope are used to determine the phase constitution, morphology, and thickness of the anodization film (AOF). Tribological tests and electrochemical corrosion experiments are carried out to measure, respectively, the wear behavior and corrosion resistance of AOFs in simulated body fluid (SBF) solution. The microstructure characteristic of the AOF anodized at low voltage (20 V) is composed of compact and loose regions. As the applied voltage increases to 60 V, the compact regions transform progressively into loose regions, and then grow into nanotube regions. Besides, an increase in thickness of the AOF from 8.6 ± 4.61 μm to 20.7 ± 2.18 μm, and a gradual increase in surface microhardness from 364.6 ± 14.4 HV to 818.4 ± 19.3 HV, are also exhibited as the applied voltage increases from 20 V to 60 V. Specimens anodized at 40 V and 60 V have a low friction coefficient (~0.15) and wear rate (~2.2 mg/N/m) in the SBF solution. The enhanced wearability originates from the high hardness and various wear mechanisms. Potentiodynamic polarization curves suggest that the corrosion resistance in the SBF solution of all anodized specimens is greatly improved, thanks to the protection from the anodized TiO2 film.

Optimization of delamination resistance of vacuum infused glass laminate aluminum reinforced epoxy (GLARE) using various surface preparation techniques

GLARE (glass-reinforced fibre–metal laminate ) is aluminum based material of fiber metal laminate (henceforth FML) that is often fabricated by expensive autoclave procedure. In this study, the process of Injected Molding or (also known as VARTM was employed as a cost-effective alternative to produce GLARE. Several aluminum surface preparation procedures are applied to improve the interlaminar shear strength. A T3 temper 2024 aluminum alloy with 1*1 plain fabricated glass fabrics were used to make GLARE composites. GLARE consists of two aluminum sheet as external layer and glass fabric as internal layers. Four sets of aluminum sheets were prepared, one unanodized and three other anodized. Three different anodizing procedures (constant voltage mode, increasing voltage mode and decreasing voltage mode) have been adopted in this research. Two types of curing treatments were applied on VARTM fabricated specimens. According to ASTM D1876 T-peel test standard, the sets of prepared specimens have been tested to examine the adhesive bonding strength and fracture toughness of mode-I. The obtained results which include force-displacement curves, peak loads and fracture toughness were showed that a significant improvement for anodized specimens with all voltage modes. The first curing treatment offered better results than second curing treatment. The best improvement was obtained from anodized specimen with decreasing voltage mode cured by the first treatment which reaches to six times the results obtained from unanodized specimen. The delamination behavior for this specimen was verified numerically.

Influence of Anodization on the Fatigue and Corrosion-Fatigue Behaviors of the AZ31B Magnesium Alloy

The aim of the present work was to investigate the effect of anodization on the fatigue and corrosion-fatigue behavior of the AZ31B magnesium alloy. Samples were anodized in constant current density mode at 20 mA cm−2 for 5 min at room temperature, in an environmentally friendly electrolyte consisting of a mixture of sodium hydroxide and sodium silicate. Fatigue tests were conducted in air and in phosphate buffer solution (PBS) at room temperature in the tension-tension mode, at a frequency of 5 Hz and stress ratio of 0.1. S-N curves were obtained for polished and anodized samples. Fracture surface morphology was examined by optical stereo-microscopy and scanning electron microscopy. Results indicated that the fatigue limit was reduced approximately 60% at 106 cycles for the anodized specimens, either for the fatigue tests conducted in air or PBS solution. Anodization had a remarkable effect on the fatigue behavior of the AZ31B alloy. The effect of the corrosive environment, in turn, was not significant.

Development and certification of chromic acid-free anodizing process for aircraft grade aluminium alloys

Chromic acid (Cr 6+ ) anodization process is widely used for the corrosion protection of aircraft aluminium alloys. Hexavalent chromium being toxic in nature need to be phased out by eco-friendly alternatives. In the present study modified tartaric-sulphuric acid (TSA) process has been developed followed by sealing in permanganate based bath to obtain 4 to 6 µm thick anodic oxide layer on 2024-T3, 6061-T6 and 7075-T6 aluminium alloys. The process was carried out using a pilot scale anodizing plant. The anodized specimens were characterized for visual observation, thickness, adhesion, electrical breakdown voltage, corrosion resistance and tensile behaviour. All the tests were carried out as per MIL-A-8625F specifications. The specimens were also subjected for about 800 hrs to real time corrosion testing, 200 metres away from sea shore at Mandapam Camp, Rameshwaram, India. The performance of the permanganate sealed TSA anodized aluminium alloys are comparable with that of the conventional chromic acid anodized coatings. This chromic acid-free anodization process has been qualified to airworthiness regulating standards by Indian military certification authorities. Efforts are in progress to commercialize this technology for use on aero platforms.

(Invited) Advanced Coating with Self-Healing Property By Healing Agent in Pore of Porous Film Formed on Al Alloy

Al and Al alloys are used for many purposes, e.g. automobiles, heat exchanger, electronics, because of their good properties such as lightness, high heat conductivity, good processability, hardness, and so on. However, corrosion protection of these materials are not so high, corrosion of Al, such as pitting corrosion and atmospheric corrosion, will occur during operation. From this, some kinds of surface treatments are needed for improvement of corrosion protection of Al used for long-term. A polymeric coating is one of popular technique to improve the corrosion protection of substrate metal. However, corrosion protection of substrate covered by polymeric coating will easily lose by mechanical damage of the coating, leading to exposure of substrate metal to surroundings and to the local corrosion of substrate under damaged area of coating.From above, new surface treatment techniques for Al substrate to keep high corrosion protection, even the surface was damaged, are developed in our research group. This is a coating, with self-healing property by dispersion of micro-capsules containing the healing agent of coating. When the coating is damaged, the healing agent flow out to the damaged area of coating and react with water vapor to form the self-healing structure and this can be covered to the damaged area of coating. However, the procedure of synthesis of micro-capsule containing healing agent is too complex and yield of this is too low to synthesize the capsules with low cost.From above, we start to develop the new type of self-healing coating. This coating can be formed on Al alloy anodized. As you know by anodic oxidation of Al alloy, electrochemically in some kind of acidic solution, porous type of anodic oxide film can be formed on Al alloy, which have many small pores arranged regularity. Pores of porous film are used as a container of healing agent of coating. Firstly, the pores in porous film formed on Al alloy were filled by healing agent. And then, this sample was covered by polyurethane coating. If this coating was damaged, mechanically, healing agent contained in pores of porous film, flow out to the damaged area and reaction with water to form polyurea as a self-healing structure and cover to the exposed Al substrate. In this study, healing property of this type of self-healing coating is investigated by observation of the surface of specimen with scratchin.#1050 Al alloy (size : 20 mm × 20 mm × 1.5 mmt) were electro-polished in CH3COOH / HClO4solution. And then anodic oxide films were formed on pretreated specimens by anodizing in (COOH)2 solution with a constant current density of 200 Am-2 for 1 hr. The anodized specimens immersed in IPDI for 100 min with ultrasonic bath, in order to promote that IPDI soln. to penetrate to pores of the porous film. After wiping the surface of the specimen by soft tissue, then a mixed solution of ethylene glycol and prepolymer of polyurethane coating was purged to specimen surface and leave for 24 h to form the polyurethane coating on anodized Al alloy surface. The prepolymer was synthesized by using the mixture of TDI, glycerol and cyclohexanone. Mixture was agitated under 600 rpm of stirring rate for 24 h. In order to remove the water dissolved in this mixture, the first 1 h of agitation, the mixture was bubbled by passing pure N2 gas. During the agitation, TDI reacts with glycerol to form the precursor of polyurethane.After specimen damaged by scratching with 7 N of load and ageing, corrosion protection of damaged Al alloy specimens with polyurethane coating were evaluated by immersion tests. The coated specimens were immersed to CuSO4 / KCl solution kept at room temperature for 1 day. After the immersion tests, to remove the coating, the specimens were immersed to the coating remover solution. And then, specimens were immersed to H3PO4 / K2CrO4 solution. Surfaces after immersion tests and removing of surface layer were observed by scanning electron microscopy (SEM).From the SEM observation for damaged specimen covered with porous film and normal coating, as shown in Fig. 1-a, sharp and deep scar can be seen at the canter of image of specimen surface. The scar can be seen on the image of damaged specimen with self-healing coating on anodized specimen, however, unique structure also can be observed at the bottom of scar, shown in Fig .1-b. This structure may be formed by the reaction between water in air and IPDI contained in the pore of porous film on Al alloy, thus, this coating has a self-healing property. Figure 1

Galvanic Corrosion Behavior between Aluminum and Iron in Chloride Solutions at Near-Neutral pH and Corrosion Prevention By Anodizing

The joints between steels and aluminum alloys are expected to be used as multi-material structures due to their low cost, high stiffness, and high corrosion resistance. When aluminum alloys are connected to steels, galvanic corrosion is expected to occur because the corrosion potentials of aluminum alloys are lower than those of iron and steels. In the case of the galvanic corrosion in chloride solutions at near-neutral pH, the anodic reaction on aluminum alloys are oxide film formation and/or pitting. For pure Al and aluminum alloys, the generation of localized corrosion is evaluated by the critical potential for localized corrosion, such as pitting potential. In this study, the electrode potential under galvanic coupling and pitting potential were compared. Surface modification is effective methods for improvement on corrosion resistance of aluminum alloys. However, there is little research related to the galvanic corrosion between steels and aluminum alloys. In this research, the galvanic corrosion behavior of pure aluminum coupled to pure iron in chloride containing near-neutral pH solutions and the effect of anodizing on galvanic corrosion were investigated.Pure iron and pure aluminum were prepared as specimens in this research. The specimen surface of aluminum was polished down to 0.25 µm with a diamond paste. The iron surface was also polished down to 1 µm with a diamond paste. Diluted synthetic seawater (200 mg/L Cl-, pH 8.2) was used as the electrolyte for electrochemical measurements. The electrode area was ca. 10 mm2. Ag/AgCl (3.33 M KCl) was used as the reference electrode. Galvanic currents and electrode potentials were measured. The distance between iron and aluminum electrodes was kept at 10 mm. A zero resistance ammeter was used to measure the galvanic currents. The electrode potential of pure aluminum was also measured. Additionally, anodizing in sulfuric acid was conducted to pure aluminum in various voltages and times. Galvanic current measurements were carried out between these anodized specimens and pure iron to evaluate the effect of anodizing on galvanic corrosion prevention.The galvanic currents and electrode potentials of pure aluminum coupled to pure iron were measured. The galvanic currents were anodic currents. The oscillations of galvanic currents and electrode potentials were generated during the measurements. Filiform corrosion was observed on pure aluminum after the measurements. The generation of filiform corrosion was caused by higher electrode potentials of pure aluminum coupled to pure iron compared with the initiate potential for filiform corrosion.The time variation of galvanic currents and electrode potentials of anodized aluminum coupled to pure iron were also measured in the diluted synthetic seawater (pH 8.2). Pure aluminum specimens were anodized at 4, 8 and 16 V at 18 s. The oscillations were observed in the galvanic currents of anodized aluminum (4 and 8V); however, no oscillation was measured on the specimen anodized at 16 V. After the measurements, pitting was observed on anodized aluminum (4 and 8V). However, no pitting was observed on the specimen anodized at 16 V. The thickness of anodic oxide film was measured. It was confirmed that the thickness of the oxide film increased with anodizing voltage. Consequently, it was indicated that the galvanic corrosion resistance of pure aluminum for galvanic corrosion was enhanced by the increase of the thickness of the oxide film.

Nanostructure of Anodic Porous Alumina Fabricated By Galvanostatic Anodizing in Etidronic Acid

Galvanostatic and potentiostatic anodizing processes of aluminum leads to the formation of large-scale porous alumina. It is previously reported that self-ordered porous alumina measuring above 500 nm in cell diameter can be fabricated via two-step anodizing in etidronic acid at higher voltage more than 200 V. On the other hand, extremely little has been reported on the growth behavior and their nanostructure during galvanostatic anodizing in etidronic acid. Herein, we investigate the nanostructural characterization of the porous alumina film formed via galvanostatic anodizing in etidronic acid under various operating conditions. Electropolished aluminum specimens were anodized at a constant current density of 0.005-500 Am-2 in 0.03-3 M etidronic acid solutions at 273-333 K. After anodizing, the porous alumina film was dissolved in a 0.20 M CrO3/0.51 M H3PO4 solution at 353 K, and the aluminum dimple array, which corresponded to the bottom shape of porous alumina, was exposed to the surface. The anodized specimens were examined by field-emission scanning electron microscopy (FE-SEM). The cell size (interpore distance) of the porous alumina was calculated using image analysis software. Typical voltage-time curves for the formation of anodic porous alumina were obtained during galvanostatic anodizing in etidronic acid: The voltage linearly increased, gradually decreased, and then reached plateau value. However, excess current density caused oxide burning with unstable oscillation in the voltage-time curve, and non-uniform porous alumina was formed on the aluminum surface. The plateau voltage greatly increased with the current density at each operating temperature, and various porous alumina films with different nanostructures were successfully fabricated by anodizing at a wide voltage range measuring 7-218 V. Figure 1 shows the changes in the average, maximum, and minimum cell sizes with the anodizing voltage under various operating conditions. The cell sizes are directly proportional to the anodizing voltage with proportionality constants of 2.5 (average), 3.5 (maximum), and 0.7 (minimum), respectively. Figure 1

Adhesive Property of Aluminum Oxide Formed By High Temperature Anodizing

Aluminum and its alloys have been widely used various situations because of their light weight, specific strength, heat conductivity. Surface treatment can impart corrosion protection, hardness, coating film adhesion and others to aluminum. Anodizing is one of the most important surface finishing processes of aluminum. In recent years, technology to use multimaterials has been attracting attention to achieve the production of energy-efficient automobiles. In such activities, adhesive bonding is increasingly used in automobile manufacturing. However, the reliability and strength of the joint surface is very important to use adhesive bonding for vehicle such as car, aircraft and motorcycle. Herein, we demonstrate the fabrication of high adhesive aluminum surface via high temperature anodizing process. High-purity aluminum specimens (99.99 wt%, 300 µm thick) were ultrasonically degreased in acetone for 10 min. These specimens were immersed in a oxalic acid solution (0.3 M), and then were anodized at a constant current density using a direct-current power supply. After anodizing, the specimens were quickly removed from the electrolyte solution and then washed with distilled water. The surface nanomorphology of the anodized specimens was examined by field emission scanning electron microscopy (FE-SEM). The adhesion property of anodized specimen was measured by tape peel test using 90 degree peel test machine. Figure 1 shows the surface appearance of the specimens covered with a) typical anodic oxide formed by low-temperature anodizing and b) anodic oxide formed by high-temperature anodizing. Anodic oxide formed by high-temperature anodizing had an irregular shape numerous pores due to the chemical dissolution of anodic oxide. These photographs were taken after tape peel test. On the typical anodic oxide, the tape was easily peeled off and no adhesive remained on the surface. On the other hand, the tape adhesive remained on the irregular anodic oxide covered surface fabricated by high temperature anodizing and the strong tape peel strength was measured. High-temperature anodizing causes the intense chemical dissolution. Thus, the anodic oxide which had wide-pore outer layer and intricate inner layer was formed on the aluminum surface by high-temperature anodizing. Adhesive layer of tape might be able to penetrate such anodic oxide. Therefore, the strong peel strength by the anchoring effect was measured on the surface. Although the adhesive mechanism has not been clear in detail, this surface treatment technique has a potential for the fabrication of composite material which is consist of aluminum and another material． Figure 1

Fabrication and Electrochemical Performance of TiO2-TiN/Sn-SnO2 Composite Films for High Capacity and High Conductivity Lib Anodes

Recently, anodic nanoporous TiO2 films have gained widespread attention as promising anode candidates for Li ion batteries to replace traditional C-based anodes. TiO2 delivers very small volume expansion (<4%) and works at a relatively high working voltage (1.7 V vs. Li/Li+) during Li+ insertion/extraction. This eliminates the influence from the solid electrolyte interface (SEI) layer and avoid the risk of lithium electrodeposition during charge/discharge process, thus further ensuring the cycling stability and safety of batteries. However, the development of TiO2 materials as LIB anodes is limited by its poor electric conductivity and low theoretical capacity. Therefore, we propose a new approach to fill Sn-based materials, which possess around 3 times theoretic capacity higher that the C-based anode, into the nanoporous anodic TiO2 films. Since the TiO2 nanostructure can alleviate the volume expansion of Sn-based materials, the synergistic effect of Sn with high capacity and TiO2 with large surface area is expected.In this study, we first formed nanoporous TiO2-TiN composite films on Ti foils by a smart anodization in NO3 –-based solutions. The inclusion of conductive TiN component in TiO2 matrix film improves the electronic conductivity effectively, which enables the successive electrodeposition on anodic TiO2 film. Then, the nanoporous TiO2-TiN composite films were used as matrix films to deposit Sn and/or SnO2 nanoparticles by a cathodic electrodeposition in acidic baths containing different Sn ions. The electric conductivity and nanostructures were tailored through anodizing process to perform successive electrodeposition. The microstructures, chemical composition, and crystalline structure of the anodized specimens before and after annealed were investigated FE-SEM (EDS), TEM (FIB), and XPS. Moreover, the cyclic voltammetric behaviors, impedance spectra, and charge-discharge performances of various composite films on Ti foils were investigated as binder-free anode materials for Li ion secondary batteries.Fig.1a-b shows the FE-SEM images of surface and cross section of TiO2-TiN composite films. An ordered nanoporous structure is obtained, with parallel pores of 50-100 nm in diameter and around 3-μm thickness after anodization for 90 min. Fig.1c shows the surface morphology of a TiO2-TiN/Sn composite film by electrodeposition in a Sn2+-based solution for 25 min. A granular Sn-based film with particle size of 100-300 nm in diameter formed on the anodic TiO2-TiN film. This indicates that the prolonged electrodeposition led to the filling of Sn not only inside but also on the anodic TiO2-TiN film. XPS analysis revealed that Sn deposits existed in metallic Sn and Sn oxides as SnO and/or SnO2. Moreover, it is confirmed by TEM observation that the nanocrystalline Sn-SnO2 deposits filled in the porous TiO2-TiN film. It is normally that the particles emerging on the film surface are larger than the pores of TiO2-TiN film.Fig.1d demonstrates the cycling performance and coulombic efficiency of TiO2-TiN/Sn-SnO2 and TiO2-TiN composite films on Ti sheets at 30 mA cm-2 for the first cycle and then 80 mA cm-2. The initial capacity of TiO2-TiN/Sn-SnO2 is 2100 μA h cm-2, which is around 5 times larger than the TiO2-TiN matrix film of 396 μA h cm-2. After 40 cycles, the capacity of the composite film remains 1153 μA h cm-2 and 4.6 times higher than the film without Sn electrodeposition. Since the nanoporous structure of TiO2-TiN can alleviate the volume expansion of Sn-based particles inside, the capacity deterioration can be mainly ascribed to the Sn-based particles overflowed on the surface, which may fall off or crush during charge/discharge process by the large volume expansion. Moreover, it was found from the EIS measurement that the internal electrical resistance of the TiO2-TiN composite film decreased considerably after the electrodeposition of the Sn-based materials, in proportional to the deposition time. Therefore, electrodeposition of Sn-based material in porous TiO2-TiN films is an effective approach to enhance the capacity and to improve the conductivity of the electrode material. Nevertheless, optimizing the conditions of anodization Ti base materials and Sn-based electrodeposition are necessary and will be an issue in the future study. Figure 1

Unusual surfaces with structural gradients: Investigation of potential gradients on bipolar electrodes during bipolar anodization of aluminum

The electrical potential gradients on aluminum bipolar electrodes (BPEs) subjected to bipolar anodization in an alternating current (AC) electric field were investigated by performing scanning electron microscopy, dyeing the anodized specimens, and measuring the resistance in the alumina films after re-anodizing the samples. The thickness and morphology of each alumina film varied, which reflected the unique potential distributions on the BPEs in the AC electric field. The electrical resistance was symmetrical and increased linearly from the centers of the BPEs to their extremities. This synthetic approach should lead to the development of various functional materials using bipolar electrochemistry.