Anodized Specimens Research Articles

Photocatalytic activity and antibacterial efficacy of UVA-treated titanium oxides.

Studies have shown ultraviolet-A (UVA) irradiation of crystalline titanium oxides leads to the production of reactive oxygen species (ROS) via a photocatalytic process. The ROS exhibit antimicrobial properties that may be of benefit in preventing bacterial attachment to implant devices. Recent studies have suggested a potential benefit of mixed anatase and rutile oxides and dopants on the photocatalytic properties of titanium oxides. The goal of this work was to compare the photocatalytic activity of different anodized commercially pure titanium grade 4 (CPTi4) surfaces. CPTi4 specimens were anodized in three mixed-acid electrolytes to create crystalline oxide surfaces that were either primarily anatase, primarily rutile, or a combination of anatase and rutile. Additionally, the primarily anatase and combination oxides incorporated some phosphorous from the phosphoric acid component in the electrolyte. The photocatalytic activity of the anodized specimens was measured using both methylene blue (MB) degradation assay and comparing the attachment of S. aureus under irradiation with UVA light of differing intensities (1 mW/cm2, 8 mW/cm2, and 23 mW/cm2). Primarily rutile oxides exhibited significantly higher levels of MB degradation after exposure to 1 mW/cm2 UVA lights. Primarily rutile specimens also had the largest reduction in bacterial attachment followed by the mixed phase specimens and the primarily anatase specimens at 1 mW/cm2 UVA lights. Phosphorous-doped, mixed phase oxides exhibited an accelerated MB degradation response during exposure to 8 mW/cm2 and 23 mW/cm2 UVA lights. All anodized and unanodized CPTi4 groups revealed similar S. aureus attachment at the two higher UVA intensities. Although MB degradation assay and the bacteria attachment assay both confirmed photocatalytic activity of the oxides formed in this study, the results of the MB degradation assay did not accurately predict the oxides performance against S. aureus.

Post-anodization methods for improved anticorrosion properties: a review

Anodization is a prominent surface treatment for light alloys that has been successfully used in the industry for the last two decades as it provides effective corrosion and wear protection. However, anodic films have porous structures, and the period of corrosion protection is limited by the nature of anodic pores, through which corrosive species may enter and reach the substrate surface. To seal the anodic porous layer, various post-anodization treatments have been developed. The most commonly employed post-treatments are the layered double hydroxide (LDH), sol–gel, hydrothermal, and cerium-based methods. Recent research revealed that after applying these post-treatments to various anodized magnesium alloys, the corrosion resistance of the resulting coatings is sufficiently enhanced because the post-layers seal the pores in the anodic thin films. This article reviews the recent research progress regarding post-anodization coatings formed on anodized magnesium alloys. Furthermore, the corrosion protection performance and microstructural changes of the resulting coatings are elucidated. The LDH method was found to be the most beneficial sealing treatment, as the treated anodized specimens demonstrated excellent corrosion resistance and a significant self-healing effect. In contrast, less satisfactory protection properties were obtained using the sol–gel, hydrothermal, and cerium-based sealing methods.

Oxidation behavior of Ti45Al8.5Nb alloy anodized in NH4F containing solution

Ti45Al8.5Nb was anodized in ethylene glycol and NH4F containing solution to improve the oxidation resistance. Isothermal oxidation test shows that the anodized specimens can provide excellent oxidation resistance and spallation resistance under 1000 °C. During the high temperature oxidation process, a compact and continuous alumina layer would generate on the anodized Ti45Al8.5Nb alloy. This protective alumina layer can efficiently decrease the inward diffusion of oxygen and outward diffusion of the substrate element. The improved oxidation resistance is assigned to the halogen effect caused by the fluorine component generated during the anodization process.

Investigation of the Trivalent Chromium Process Conversion Coating as a Sealant for Anodized AA2024-T3

The sealing of an anodic coating on AA2024-T3 with a trivalent chromium process coating (TCP-HF) was investigated. Specimens were anodized in 9.8 wt% H2SO4 at 15 V DC (23 min) producing an oxide coating weight of ca. 1200 mg ft−2 and a thickness of ca. 5 μm. Elemental analysis revealed the sealant forms across the outer oxide layer and within the pores up to a depth at least approaching 1 μm. Anodic and cathodic currents in potentiodynamic polarization curves were suppressed by 5–10× and low frequency impedance (Z0.01 Hz) values were 5× higher for anodized specimens sealed with TCP (∼5 × 106 ohm-cm2), as compared to the unsealed anodized controls. During continuous exposure to 3.5 wt% NaCl, Z0.01 Hz values remained unchanged and greater than 106 ohm-cm2 after 5 days for the TCP-sealed specimen and decreased by 10× for the unsealed anodized control after just three days. A 14-day (336 h) neutral salt-spray exposure produced no significant pitting, discoloration or major coating detachment on anodized specimens sealed with TCP. Overall, the results indicate that the TCP sealant increases the barrier properties of the anodic coating and functions to provide anodic and cathodic corrosion protection.

Characterization of 2017A Anodized Aluminum Alloy by Infrared Thermographic Techniques and SEM Observations During Tensile Testing

The aim of this research is to determine the effect of an electrochemical treatment (anodizing) on the mechanical behavior of 2017A aluminum alloys to improve corrosion. Two surface treatments state, namely, anodized and unanodized were considered. Meanwhile, the tensile and fracture tests for laboratory specimens to failure, yield strength, tensile strength and fracture surface of anodic films at different conditions were investigated. The damage initiation and progression during tensile testing was tracked through the use of complementary non-destructive evaluation by means of technique called infrared thermography. The results showed that the fracture life of anodized specimens was reduced a lot compared to aluminum alloy, which can be attributed to the surface crack sites initiated at the oxide layer. The fracture surface analyses also revealed that the number of crack initiation sites enlarged on the anodizing specimens.

Alkaline Corrosion-Resistant Anodic Aluminum Oxide Formed By Etidronic Acid Anodizing

A newly discovered electrolyte for anodizing aluminum, etidronic acid (CH3C(OH)[PO(OH)2]2), operates at high voltages of more than 200 V, and ordered porous alumina measuring 400-670 nm in cell diameter (interpore distance) can be fabricated via constant voltage anodizing. Because such porous alumina film formed at high voltages possesses a thick barrier layer, etidronic acid anodizing may be useful for corrosion protection of aluminum. Here, we describe the alkaline corrosion-resistant porous alumina formed by high voltage anodizing in an etidronic acid solution, and its hydration behavior in boiling water was investigated. Highly pure aluminum plates (99.999 wt%) were anodized in 0.3 M sulfuric acid, 0.3 M oxalic acid, 0.3 M citric acid, and 0.3 M etidronic acid solutions (293 K) at a constant current density of 30 Am-2 or a constant voltage of 250 V. The anodized specimens were immersed in a 2.5 M NaOH solution (293 K). The nanostructural changes were examined by electrochemical impedance spectroscopy (EIS). The anodized specimens were immersed in boiling water to seal the pores in the porous alumina film. The surface and cross-section of the specimens were characterized by field-emission scanning electron microscopy (FE-SEM) The plateau voltages during anodizing aluminum at a constant current density of 30 Am-2 in sulfuric and etidronic acid solutions exhibited approximately 16 V and 197 V, respectively. As the specimen anodized in sulfuric acid was immersed in a 2.5 M sodium hydroxide solution, H2 gas evolution was observed from the surface at the beginning of immersion, and the amount increased with the immersion time. In contrast, the specimen anodized in etidronic acid did not result in hydrogen gas evolution during immersion until 8 min. Here, the capacitance (Cb ) is inversely proportional to the thickness of the barrier layer. Figure 1 shows the changes in the reciprocal Cb with the immersion time, ti . Complete dissolution of porous alumina formed in etidronic acid takes 15 times longer than dissolution of the alumina formed by sulfuric acid anodizing due to the formation of a thick barrier layer. As the porous alumina formed by etidronic acid anodizing is immersed in boiling water, plate-like hydroxides were formed at the bottom of the pores in the initial immersion stage. The thickness of the hydroxide layer increased with the immersion time, and the nanopores are completely sealed by long-term immersion. Figure 1

Fabrication of Sticky and Slippery Aluminum Alloys Based on Anodic Alumina Nanofibers

Anodizing aluminum in a pyrophosphoric acid solution (H4P2O7) causes the formation of numerous anodic alumina nanofibers. The nanofiber-covered aluminum surface exhibits superhydrophilicity measuring less than 10° in water contact angle (WCA). In contract, as the alumina surface is modified with a self-assembled monolayer (SAM), the WCA value changes to show superhydrophobicity measuring more than 150°. In the present investigation, the fabrication of highly sticky and slippery aluminum alloys was achieved by optimizing the nanostructure of anodic alumina nanofibers formed on the surface. Commercially available 3004 aluminum alloys (composition: 1.0-1.5 wt% Mn, 0.8-1.3 wt% Mg, small amounts of Cu, Zn, Fe, and Si) were chemically polished in a 2.5 M NaOH solution at 333 K for 5 min, and then were immersed in a 4.0 M HNO3 solution at room temperature for 30 s. The polished specimens were immersed in a pyrophosphoric acid solution (74.0 wt%) at 293 K, and then were anodized at a constant voltage of 75 V for up to 60 min. After anodizing, the specimens were immersed in a 1.5 mM 3,3,4,4,5,5,6,6,7,7,8,8,8,-tridecafluorooctylphosphonic acid (FOPA)/ethanol solution at 313 K for 48 h. The slipping behavior of the water droplet formed on the anodized specimens was examined by advancing and receding contact angle measurements using an optical contact angle meter. As the aluminum alloys were anodized in a pyrophosphoric acid solution, numerous anodic alumina nanofibers with the insoluble intermetallic compounds were formed on the surface. The length of the nanofibers increased with the anodizing time, and many nanofiber-tangled intermetallic particles were exposed to the surface. Figure 1 shows the changes in the advancing contact angle, θ adv, and the receding contact angle, θ rec, on the SAM-modified aluminum surface with anodizing time, t a. The θ adv value increased to approximately 170° by pyrophosphoric acid anodizing, and this superhydrophobicity was maintained upon further anodizing up to 60 min. On the other hand, the θ rec value drastically changed with anodizing time. As a result, the contact angle hysteresis (θ adv - θ rec) was also changed with anodizing time. Therefore, the adhesion interaction between the water droplet and the aluminum surface can easily be controlled by pyrophosphoric acid anodizing. Figure 1

Structural Characterization of Anodic Porous Alumina Formed By Galvanostatic Anodizing in Etidronic Acid

Anodizing aluminum in etidronic acid (1-hydroxyethane-1,1-diphosphonic acid) causes the formation of porous alumina at higher voltage more than 200 V. Highly ordered porous alumina with a large-scale cell can be easily fabricated via two-step constant voltage anodizing in etidronic acid. However, extremely little has been reported on the growth behavior during galvanostatic anodizing in etidronic acid and its structural characterization. In the present investigation, we demonstrate the details of the anodizing behaviors and nanostructures of the porous alumina formed via galvanostatic anodizing in etidronic acid under various operating conditions. High-purity aluminum plates were electrochemically polished, and then were anodized at a constant current density of 0.005-500 Am-2 in 0.03-3 M etidronic acid solutions (273-333 K). After anodizing, the specimens were immersed in a 0.20 M CrO3/0.51 M H3PO4 solution (353 K) to dissolve the porous alumina, and the aluminum dimple array was exposed to the surface. The surface and cross-section of 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. As the electropolished aluminum specimens were anodized galvanostatically under various conditions, the voltage linearly increased, gradually decreased, and then reached plateau value (U p). However, excess current density led to a burning phenomenon and the formation of non-uniform porous alumina. Figure 1 shows the changes in the plateau voltage, U p, and the current density, i a, during anodizing in a 0.3 M etidronic acid solution. The plateau voltage greatly increased with the current density at each temperature, and various porous alumina films were successfully fabricated by anodizing at a wide voltage range measuring 7-218 V. Figure 2 shows the relationship between the cell size, D c and the anodizing voltage, U a. The cell size linearly increased with the anodizing voltage at each solution temperature and current density. A linear proportional constant of 2.5 nmV-1 was obtained, which is similar to the self-ordering condition via constant voltage anodizing. Figure 1

Direct Electrodeposition Li-V-Mn-Ni-O Composite Films on Al Foils Toward Li Ion Battery Cathode Materials

Nowadays, Lithium-ion secondary batteries (LIBs) are considered as indispensable power sources in our daily life, because they are widely used in various mobile electronic products such as smart phones, portable computers, and recently, extended to electric vehicles (EVs). Commercial LIB comprises LiCoO2 cathode with maximum capacity of 140 mAh g−1. V2O5 has been widely investigated because of its high theoretical capacity of 294 m Ah g−1, low cost and abundant sources on the earth crust. However, problems, such as severe capacity fading and poor rate capability, prevent its use in commercial LIBs. So far, much effort has been done to improve the cycling stability of V2O5 by doping Ag, Cu, Zn, and Mn through sol-gel process, beam evaporation, hydrothermal reaction, etc. In this study, we proposed a novel hybrid electrodeposition to fabricate Li-V-Mn-Ni-O composite films directly on Al foils in ethanol-water bath containing V5+、Ni2+, Mn2+ ions as sulfate or chloride, with and without adding Li+ ions. Before electrodeposition, an electro-etching pretreatment was used to enhance the adhesion between the Al substrate and the electrodeposits. The microstructures, chemical composition, and crystalline structure of the anodized specimens before and after annealed were investigated FE-SEM (EDS), TEM (FIB), XRD, XPS, and GD-OES. Moreover, the cyclic voltammetric behaviors, electrochemical impedance, and charge-discharge performances of various nanostructured composite films on Al foils were investigated as binder-free cathode materials for Li ion secondary batteries.Figs. 1a-b show the representative surface FE-SEM images of as-deposited Li-V-Mn-Ni-O composite films on Al foils. The composite films coated uniformly on electro-etched Al foils irrespectively of the rough surface, composing of nano-flakes (Fig.1a) and nanoparticles (Fig.1b). According to EDS analysis, the compositions of V, Mn, and Ni components except for O were 69 at%–23 at%–8 at% and 45 at%–21 at%–34 at% for the nano-flake and nanoparticle regions respectively. The XPS analysis confirmed that the vanadium existed mainly as mixed V4+ and Mn5+ oxides, manganese as mixed Mn2+ and Mn4+ oxides, and nickel as metallic Ni and Ni2O3 for the composite films before and after heated at different temperatures. Moreover, it was found from GD-OES measurements that Li also included in the V-Mn-Ni-O composite films through a co-deposition process and/or a Li+ insertion/dis-insertion process. Fig. 1c shows the cyclic voltammograms (CVs) of Li-V-Mn-Ni-O composite films after being heated at 723 and 923 K for 2 h, as cathodes with Li-metal as the counter and reference electrodes, in the potential range 2.0–4.5 V vs. Li/Li+, at a slow scan rate of 0.1 mV s-1. Two main anodic peaks (Li-extraction) at around 3 and 4 V are noted for both specimens heated at 723 and 923 K, which can be ascribed to the Li extraction reactions from vanadium oxides and V-Mn-Ni-O compounds. Especially, the current density of 4-V peak increased with heating temperature, indicating the transformation and crystallization of V-Mn-Ni-O compounds from vanadium oxides. Furthermore, the composite films after being heated at different temperatures worked well as binder-free and conductor-free cathode materials for LIBs in galvanostatic charge/discharge tests, and the results will be reported on the meeting. Figure 1

Hybrid Electrodeposition and Characteristics of Ag-Graphene Composite Films on Cu Sheets Toward High-Performance Electric Connectors

Recently, silver (Ag) plating for automotive connector has been attracted extensively attention due to the fast progress of HEV/EV system and as a promising candidate material to substitute the costive gold (Au) plating. The Ag plating film possesses the highest conductivity among the metals and excellent corrosion resistance next to Au plating. However, Ag plating suffers a low wear resistance problem because of the soft nature of Ag metal (~80 Hv). Because an oxidation film is difficult to form on silver surface, the corrosion resistance is good. More serious problem of Ag plating is that an adhesion phenomenon often occurs during sliding wear actions as terminal mating materials, because an oxidation film is difficult to form on Ag surface owing to the good corrosion resistance as a noble metal. To solve those problems, many studies focused on fabricate hard Ag plating by adding some alloy elements like Co, Sb, and Se or adding graphite powder into Ag plating films, which improved wear resistance but sacrificed electric conductivity. Here, we propose a new Ag-graphene electro-plating film, with the graphene functioning as solid lubricant and electric component, which may reinforce the wear resistance while without lowering its electric conductivity. The Ag-graphene composite films were fabricated on Cu sheets by a hybrid electrodeposition method, i.e., combining electrodeposition of Ag and electrophoric deposition of graphene nano-flakes, in a non-cyanate plating bath. The graphene nano-flakes were prepared by an electrochemical peeling method from a graphite material. The microstructures, chemical composition, and crystalline structure of the anodized specimens before and after annealed were investigated FE-SEM (EDS), XRD, GD-OES, FT-IR, and Raman spectroscopy. Moreover, the electric resistance meter and wear resistance were also investigated, compared to commercial Ag plating as reference.Figs. 1a and 1b show the surface FE-SEM images of as-electrodeposited pure Ag and Ag-graphene films respectively. It can be seen that, except for the featured Ag nano-particles, some blurry films can be observed on the Ag film in Fig. 1b. The EDS analysis result in Fig.1c demonstrates a strong C peak, indicating the co-deposition of carbon clearly. Moreover, the inclusion of graphene in Ag films were also confirmed by Raman spectra and XRD measurements. The electric resistance of Ag-graphene composite films was equivalent to the commercial Ag films, and the detail results will be reported on the meeting. Figure 1

Electrolytic colouring of anodized aluminium on tin basis

Abstract The aim of the study was to find parameters of electrolytic colouring on tin basis to form uniform black coatings on anodized aluminium. A two steps electrolytic process consisting of aluminium anodization in a sulphuric acid electrolyte and colouring in tin acidic electrolyte was used. Among parameters influencing the colouring process, AC colouring voltage, composition of the counter electrode and agitation of the colouring electrolyte were studied. Spectrocolorimetry was applied to analyse the quality of the colouring. Thickness of the coloured and sealed anodized specimens was also evaluated. Optimal parameters for uniform colouring of anodized specimens were found. Unfortunately, colouring electrolyte on tin basis is susceptible to oxidation which negatively influences the colouring.

Super-hydrophobic stearic acid layer formed on anodized high purified magnesium for improving corrosion resistance of bioabsorbable implants

Abstract Magnesium and its alloys are ideal candidates for bioabsorbable implants. However, they can dissolve too rapidly in the human body for most applications. In this research, high purified magnesium (HP-Mg) was coated with stearic acid (SA) to slow the corrosion rate of magnesium in simulated body fluid at 37 ± 1 °C. HP-Mg was anodized (AC and DC voltages) to form an oxide/hydroxide layer, and then it was immersed in a SA solution. The SA coated layer surface, anodized layer, and the thickness of the oxide/hydroxide layer were investigated with Scanning Electron Microscopy (SEM). Electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP) were used to estimate the corrosion rate of HP-Mg specimens. The results confirm that the hydrophobic coating can decrease the corrosion rate of HP-Mg by more than 1000x. The protectiveness of coated layer for anodized specimens with AC voltage continue for 2 and 3 weeks. For the HP-Mg coated anodized with DC voltage, the coated layer could improve the corrosion resistance for only a few days.

In vitro bioactivity and corrosion resistance enhancement of Ti-6Al-4V by highly ordered TiO2 nanotube arrays

In the present study, the structural features, corrosion behavior, and in vitro bioactivity of TiO2 nanotubular arrays coated on Ti–6Al–4V (Ti64) alloy were investigated. For this reason, Ti64 plates were anodized in an ammonium fluoride electrolyte dissolved in a 90:10 ethylene glycol and water solvent mixture at room temperature under a constant potential of 60 V for 1 h. Subsequently, the anodized specimens were annealed in an argon gas furnace at 500 and 700 °C for 1.5 h with a heating and cooling rate of 5 °C min−1. From XRD analysis and Raman spectroscopy, a highly crystalline anatase phase with tetragonal symmetry was formed from the thermally induced crystallization at 500 °C. Besides, the Ti 2p3/2 and Ti 2p1/2 binding energies showed the presence of the Ti4+ oxidation state. According to the in vitro bioassay, the modified surface proved its outstanding capability in enhancing the bioactivity, where a thick layer of bone-like apatite was formed on the annealed TiO2 nanotube surface. In addition, the corrosion measurements indicated that the corrosion protection efficiency increased remarkably and reached 87% after annealing at 500 °C.

Fabrication of Sticky and Slippery Superhydrophobic Aluminum Surfaces Via Pyrophosphoric Acid Anodizing and SAM Modification

Anodizing aluminum in a concentrated pyrophosphoric acid solution (H4P2O7) leads to the formation of numerous anodic alumina nanofibers measuring less than 10 nm in diameter. As the alumina nanofibers are modified with self-assembled monolayer (SAM), the nanofiber-covered aluminum surface exhibits a superhydrophobic behavior with a water contact angle measuring more than 150°. In the present investigation, we demonstrate the fabrication of slippery and sticky superhydrophobic aluminum surfaces covered by the anodic alumina nanofibers. The effect of the nanostructure of the anodic oxide on the adhesion interaction between the water droplet and the surface was investigated by dynamic contact angle measurements. High-purity aluminum specimens (99.99 wt%, 400 µm thick) were ultrasonically degreased in ethanol for 10 min. The specimens were electropolished in a 78 vol% CH3COOH/22 vol% 70%-HClO4 solution (T = 280 K) at a constant voltage of 28 V for 1 min. The electropolished specimens were immersed in a concentrated pyrophosphoric acid solution (74.0 wt%, T = 293 K), and then were anodized at a constant voltage of 50 V using a PC-connected direct-current power supply. After anodizing, the specimens were immersed in a 0.5 mM 3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluorooctylphosphonic acid (FOPA) / ethanol solution (T = 313 K) for 24 h to form SAM on the anodic alumina nanofibers. The surface nanomorphology of the anodized specimens was examined by field emission scanning electron microscopy (FE-SEM). The water contact angles on the anodized specimens were measured by an optical contact angle meter. The distilled water droplets were formed on the surface using an auto dispenser and a microsyringe with a flow rate of 2 µL/s, and the advancing and receding contact angles were measured by a charge-coupled device (CCD) camera (frame rate: 10 fps). Figure 1 shows the changes in the advancing and receding contact angles with the anodizing time. Here, the anodic oxide was modified with the FOPA-SAM after anodizing. The advancing contact angle rapidly increased to superhydrophobicity more than 160° by the initial stage of anodizing, and the contact angles were maintained at similar values via the long-term anodizing. In contrast, the receding contact angle was drastically changed with the anodizing time: the contact angle rapidly decreased to approximately 0° in the initial stage of anodizing, rapidly increased to 150° in the middle stage, and then gradually decreased to 0° in the final stage. This complicated behavior was due to the nanostructural surface changes via pyrophosphoric acid anodizing. Figure 2 shows the side views of the 20 µL water droplet on the superhydrophobic aluminum specimens fabricated by pyrophosphoric acid anodizing for a) 4 min and b) 20 min and subsequent FOPA-SAM modification. The water droplet was pinned on the surface anodized for 4 min when it was turned upside down (i.e. a sticky surface). Conversely, the droplet easily rolled off with a small sliding angle on the surface anodized for 20 min (i.e. a slippery surface). Figure 1

The Effect of Anodizing Process Parameters on the Fatigue Life of 2024-T-351-Aluminium Alloy

Abstract The effect of an anticorrosive layer on the fatigue life of 2024-T-351-aluminium alloy has been studied in the present investigation. The fatigue tests were conducted on the aluminium alloy with and without anodizing to evaluate the fatigue life. The results indicate that the fatigue life of the anodized specimens is significantly shorter than that of untreated specimens. Further, experiments were conducted to evaluate the effect of the anodizing process parameters on the fatigue life of anodized specimens. These results show that the fatigue life of anodized aluminium alloy can be improved by controlling the anodizing process parameters such as process temperature, voltage, and time of immersion.

Fabrication of ordered submicrometer-scale convex lens array via nanoimprint lithography using an anodized aluminum mold

The fabrication of submicrometer-scale ordered convex lens array was demonstrated through nanoimprint lithography using an aluminum dimple array mold fabricated by etidronic acid anodizing and selective oxide dissolution. Highly-pure aluminum plates were anodized in a 0.2M etidronic acid solution at 260V for the formation of ordered porous alumina. The anodized specimens were immersed in a 0.2M CrO3/0.51M H3PO4 solution to dissolve the porous alumina, and an ordered dimple array measuring approximately 670nm in dimple diameter was obtained on the aluminum surface. Phosphonic acid-based self-assembled monolayers (SAMs) were coated on the aluminum dimple array as a release agent for nanoimprint lithography. The shape of the aluminum dimple array mold was transferred to a UV curable photopolymer by nanoimprint lithography. An ordered convex lens array, which corresponded to the negative shape of the dimple array, was successfully obtained by the removal of curable polymer. However, the polymer surface was contaminated with phosphonate molecules due to the multilayered phosphonate films being formed on the aluminum mold. This contamination can be avoided by ultrasonication of the aluminum mold before nanoimprint lithography.

Superhydrophilic and Superhydrophobic Aluminum Alloys Fabricated By Pyrophosphoric Acid Anodizing

Introduction Recently, we demonstrated the fabrication of anodic alumina nanofibers via anodizing in a new electrolyte, pyrophosphoric acid (H4P2O7). Interestingly, the aluminum surface covered by the anodic alumina nanofibers exhibited a superhydrophilic behavior with a contact angle measuring less than 10°. In the present investigation, we described the fabrication of superhydrophilic and superhydrophobic aluminum alloys via pyrophosphoric acid anodizing and subsequent SAM modification. Experimental Two kinds of aluminum specimens (5N aluminum and 3004/1N30/8021 aluminum alloys) were ultrasonically degreased and chemically polished. The specimens were anodized in a concentrated pyrophosphoric acid solution at a constant cell voltage of 25-75 V for 60 min. The anodized specimens were immersed in a 0.5 mM fluorinated phosphoric acid SAM (3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluorooctylphosphonic acid: FOPA)/ethanol solution at 293-323 K for 48 h. anodized specimens were examined by field emission scanning electron microscopy (FE-SEM). The water contact angles were measured by an optical contact angle meter (2 µL in water volume for hydrophilic measurements and 4 µL for hydrophobic measurements). Results Anodizing of aluminum and its alloys in a pyrophosphoric acid solution caused the formation of numerous anodic alumina nanofibers on the aluminum surface. During anodizing of aluminum alloys, many intermetallic compounds were exposed to the surface with anodizing time increase, and the nanofiber-tangled intermetallic particles were formed on the surface. The contact angle decreased with the anodizing time, and the nanofiber-covered aluminum alloys exhibited a superhydrophilic behavior measuring less than 3° in the contact angle (Figure 1, anodizing voltage: Ua = 75 V). As the surface of the nanofiber-covered aluminum alloys was modified with fluorinated phosphoric acid SAMs (solution temperature: Tim = 293-313 K), the contact angle drastically increased with the immersion time and temperature. These aluminum alloys exhibited a superhydrophobic behavior measuring more than 150° (Figure 2). Figure 1. Changes in the water contact angle, θ, with the anodizing time, ta, on the 5N aluminum and 3004 aluminum alloy surfaces after anodizing in a pyrophosphoric acid solution (293 K) at 75 V. Figure 2. Changes in the water contact angle, θ, with the immersion time, tim, on the nanofiber-covered aluminum alloys (3004). The specimens were anodized at 75 V for 10 min, and then were immersed in a 0.5 mM FOPA-SAM/ethanol solution. Figure 1

Fabrication of Superhydrophobic Aluminum Surfaces By Pyrophosphoric Acid Anodizing and SAM Modification

Anodizing is one of the most important surface finishing techniques for aluminum and its alloys in various industrial applications. Recently, we reported a novel anodic aluminum oxide formed via anodizing in a new electrolyte, pyrophosphoric acid solution (H4P2O7). Pyrophosphoric acid anodizing leads to the formation of numerous alumina nanofibers measuring less than 10 nm in diameter on the aluminum substrate. In the present investigation, we report the fabrication of a superhydrophobic aluminum surface modified by anodic alumina nanofibers and self-assembled monolayers (SAMs). High-purity aluminum specimens (4N, 400 µm thick) were ultrasonically degreased and electropolished. The specimens were immersed in a concentrated pyrophosphoric acid solution (74.0 wt%, T = 273–293 K), and then were anodized at a constant voltage of 10 to 75 V to form anodic alumina nanofibers. After anodizing, the specimens were immersed in 5 mM n-alkylphosphonic acid / ethanol solutions (Ti= 293–313 K) for up to 48 h to form SAMs on the anodic alumina nanofibers. Seven types of n-alkylphosphonic acid with different chain lengths were used for SAM-modifications. The surface nanomorphology of the anodized specimens was examined by field emission scanning electron microscopy (FE-SEM). The water contact angles on the specimens were measured by an optical contact angle meter. Distilled water droplets (2–3 µL volume) were placed on the specimens, and the contact angles of the droplets were measured by a charge-coupled device (CCD) camera. Figure 1 shows the appearances of water droplets on the a) electropolished aluminum surface and b) nanofiber-covered aluminum surface after TDPA-SAM modifications (Ti = 313 K, ti= 24 h). The contact angle greatly increased from approximately 110° to 160° by pyrophosphoric acid anodizing. Because the pyramidal alumina bundles were formed on the aluminum specimen by pyrophosphoric acid anodizing (Figure 2), the water droplet was supported by the top of the pyramidal alumina bundles with TDPA-SAMs, and a large amount of air was trapped in the spaces between the alumina bundles. As the aluminum specimens were anodized at the low temperature of 273 K, the contact angle increased with anodizing time, and the aluminum surface exhibited a superhydrophobic behavior after anodizing for 4 h. However, the contact angle gradually decreased after that time, and the superhydrophobic angles above 150° no longer appeared after the excess anodizing process. High-aspect-ratio anodic alumina nanofibers then bent under their own weight, and the aluminum surface was completely covered by the long alumina nanofibers. The contact angle decreases by long-term anodizing at low temperature because of the loss of the air trapping space caused by the excess growth of the alumina nanofibers. Figure 1

Influence of tunable diameter on the electrochemical behavior and antibacterial activity of titania nanotube arrays for biomedical applications

The conventional bone implants based on titanium metals requires long time treatment process. Since the osteoporosis become a common chronic disease, rapid osseointegration of bone implants will help to shorten the period of treatment and enhance the comfort of patients. The fabrication of nanostructured bone implants resembles like native bone promotes rapid osseointegration. Here we studied the influence of tunable diameter of titanium nanotube arrays for bio implant applications. A facile electrochemical anodization process was performed to fabricate array of nanotube structures on Ti surface using the mixture of glycerol and ammonium fluoride electrolyte containing water. The diameter of the nanotubes was controlled by varying water content and studied their surface morphology, corrosion behavior and antibacterial activity. The morphological studies revealed an increase in nanotube diameter and reduction in length with increasing addition of water. X-ray diffraction analysis showed that the intensity of anatase peak increases with the addition of water. Wettability measurements revealed that the formed titania nanotubes were hydrophilic in nature. The study examined the adhesion of Staphylococcus aureus on substrate and anodized specimens by bacterial viability test and the results showed that the anodized specimens showed higher percentage of inhibition compared to substrate. The decrease in icorr value observed for TNTA specimens obtained from the potentiodynamic polarization studies was attributed to the variation in tube diameter and intertubular spaces with varying water content. The results of electrochemical impedance spectroscopy studies in Hanks' solution also have endorsed the structural changes occurred in the nanotube morphology by the variation of water content influenced the electrochemical properties.

Development of a Chromium-Free Post-Anodizing Treatment Based on 2-Mercaptobenzothiazole for Corrosion Protection of AA2024T3

The anticorrosion performance provided by new anodizing and sealing methods for the AA2024T3 aluminum alloy is discussed in this work. Two anti-corrosion post-anodizing treatments based on immersion in an ethanol solution containing 2-mercapto-benzo-thiazole (2-MBT) were applied. Both treatments consisted of the immersion of the anodized specimens in 2-MBT ethanol solution, but the second was followed by hydrothermal sealing in water. Electrochemical Impedance Spectroscopy (EIS) and an immersion test show that both treatments exhibited improved corrosion resistance compared with anodized AA2024-T3 that was only hot water sealed. Considering that these novel anti-corrosion methods appear to provide enhanced, long-term and stable corrosion resistance to the AA2024T3 aluminum alloy, the use of 2-mercaptobenzothiazole (2-MBT) is proposed as a promising inhibitor in sealing treatments.