Anodic Oxidation Of Aluminum Research Articles

V-Shaped Heterostructure Nanocavities Array with CM and EM Coupled Enhancement for Ultra-Sensitive SERS Substrate.

The field of semiconductor surface-enhanced Raman scattering (SERS) substrates has experienced significant advancements, leading to a wide range of applications in several fields. However, the quest for new ultra-sensitive semiconductor SERS materials is still of utmost importance. In this regard, an efficient and novel substrate, F4TCNQ/MoS2 heterostructure is introduced, assisted by V-shaped aluminum anodic oxide (AAO) nanocavities with different depths. Utilizing the efficient charge transfer of organic/inorganic semiconducting heterostructure and the photoconfinement capability of the nanocavity structure of the AAO nanotemplate, excellent stability, fast sensing, enhanced Raman, and photodegradation activities are achieved. Due to its unique 3D structure, the optimized F4TCNQ/MoS2/AAO with 1500 nm depth achieves ultra-high sensitivity detection of 9.0×10-16 M for conventional probe molecules. Furthermore, precise detection of water contaminants is observed for the first time with a V-shaped heterostructure due to combined organic/inorganic features that differ significantly from conventional MoS2 structures or other metal/inorganic or inorganic/inorganic semiconductors. This research presents a novel and versatile strategy for SERS and demonstrates its diverse potential performance in practical applications.

Fabrication of a Highly Efficient and Reusable Pd/Al2O3/Al Monolithic Catalyst for the Suzuki‐Miyaura Reaction

AbstractAnodization was employed to treat the aluminum foil surface, leading to in situ the generation of Al2O3, consequently amplifying the specific surface area to aid in the dispersal of palladium nanoparticles. Through the anodic oxidation of aluminum followed by a precipitation‐deposition and calcination process, a highly efficient and reusable Pd/Al2O3/Al monolithic catalyst was synthesized. The effectiveness and reusability of the Pd/Al2O3/Al monolithic catalyst were evaluated in the Suzuki‐Miyaura reaction. The turnover number (TON) and turnover frequency (TOF) of the Pd/Al2O3/Al monolithic catalyst reached 73,880 and 0.86 s−1, respectively. Furthermore, the catalyst could be recovered and reused in reactions regardless of the used substrates.

Electro-Coloring Mechanism of Aluminum Anodic Oxides in Tin-Based Electrolytes

A method for accurately determining the chemical composition of deposits at the bottom of pores during the electrocoloring (e-coloring) of aluminum anodic oxide (AAO) layers in tin-based solutions is developed. The aluminum samples were AC e-colored after DC sulfuric anodization. Free-standing, tin e-colored aluminum oxide film was obtained by selective dissolution of the metallic aluminum from the AAO in copper chloride solution to access the deposit directly at the bottom of the pore. This allowed us to conduct XPS analysis directly on the deposits at pore bottoms without any interference from the base material or insulating barrier layer. The results revealed the presence of a mixture of tin oxide and metal in the deposits, which were richer in oxide content. Furthermore, a cyclic voltammetry experiment mimicking real polarization conditions during AC conditions was optimized and used to gain a deeper understanding of the electrochemical reactions that occur during AC electrocoloring. The comparison of CV results in tin-free and tin-containing electrolytes indicated that the tin deposited during a cathodic cycle is oxidized in the anodic cycle. The formation of tin-based deposits radically changed the CV behavior. The XPS and cyclic voltammetry results consistently show that the deposits formed during e-coloring comprised a mixture of metallic and oxidic tin species richer in oxide content.

Influence of humidity on the tribological performance of graphite reinforced aluminium anodic oxide coating

The effectiveness of graphite as self-lubricating reinforcement in anodic oxide is still unknown despite showing clear dependency towards water to provide lubrication. The objective of this study is to evaluate the tribological behavior of aluminium anodic oxide reinforced graphite coating under different relative humidity conditions. In this study, the oxide coating was reinforced with graphite varied between 0 to 20 gL−1. The graphite distribution, and structure hybridization were first analyzed. The coating with the highest sliding durability at room condition was tested under different relative humidity at 5 and 85 RH%. Overall, graphite reinforcement improved the coating’s hardness and roughness. Tribological wise, coating with 1 gL−1 of graphite reinforcement has the longest durability.

Anodic alumina/carbon composite films: extraction and characterization of the carbon-containing component

Alumina/carbon composites are modern nanomaterials used as adsorbents, catalysts, catalyst supports, supercapacitors, and electrode materials for fuel cells. Among other methods, aluminum anodizing is fairly fast and inexpensive for producing anodic alumina/carbon composites with controllable properties. In the present study, the morphology and composition of carbon-enriched anodic alumina films were obtained during aluminum anodic oxidation in formic acid with ammonium heptamolybdate (C content is ca. 5.0 mass%) or oxalic acid (C content 3.4 mass%) additives. The anodic alumina films have a wide blue fluorescence (FL) in the 400–650 nm wavelength range with a maximum at ca. 490 nm. The FL decay is nonexponential and has an average lifetime of 1.54 and 1.59 ns for ammonium heptamolybdate and oxalic acid additives, respectively. As samples obtained in sulfuric acid (i.e. without carbon) do not possess detectable FL in the 400–650 nm wavelength range, it was concluded that carbon-containing inclusions are responsible for the FL properties of the films. The initial samples were dissolved in the hot aqueous HCl solution and then dialyzed to extract the carbon-containing component. It was shown that the solutions contain nanoparticles of amorphous carbon with a 20–25 nm diameter. Carbon nanoparticles also exhibit an excitation-dependent emission behavior at 280–450 nm excitation wavelengths with average lifetimes of 7.25–8.04 ns, depending on the composition of the initial film. Carbon nanoparticle FL is caused by the core of carbon nanoparticles (CNPs) and various emission centers on their surface, such as carbonyl, carboxyl, and hydroxyl groups. As CNPs could be exceptional candidates for detection technologies, the biocompatibility assays were performed with living COS-7 mammalian cells, showing a minimal negative impact on the living cells.

Revisiting the Anodic Stability of Aluminum Current Collectors in High-Voltage Li-Ion Batteries

High-voltage Li-ion batteries are anticipated to play a crucial role in the present transition towards electric vehicles, owing to their high energy density. However, a big challenge is the anodic stability (often referred to as corrosion) of the positive electrodes current collector, aluminum (Al), at potentials > 3.0 V vs. Li+/Li). In this work, we present a systematic study on the corrosion of 12 µm-thick Al foil (©Gränges, Sweden) up to 5.0 V vs. Li+/Li in a series of carbonate electrolytes containing lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl) imide (LiFSI) or lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) salts. The selection of the 12 µm foil was motivated by the need to decrease the mass or volume of the dead weight components (i.e., current collector) to increase the energy density of the battery.The electrochemical behavior was investigated using voltammetric techniques, and the results indicated that the anodic oxidation of the 12 µm Al foil was similar to that of the conventionally used 20 µm-thick Al foil. Notably, the first anodic oxidation scan exhibited a two-step oxidation after 3.5 V vs. Li+/Li, suggesting carbonate solvent oxidation and a liberation of H+ ions attacking the native surface Al2O3 layer followed by oxidation of metallic Al. A passivation was observed on the subsequent scans in 1.0 M LiPF6 solutions due to formation of surface layer of AlF3, as confirmed by X-ray photoelectron spectroscopy (XPS) analyses. [1,2]However, in 1.0 M solutions of the imide salts (i.e., LiFSI or LiTFSI) a continuous anodic oxidation of aluminum was seen between 3.5 and 5.0 V vs. Li+/Li on the first few scans. After this the magnitude of the anodic current decreased significantly. The latter observations can be attributed to formation of soluble Al(TFSI) x or Al(FSI) x complexes [3] and a gradual saturation of the electrolyte. The voltammetric experiments showed that the magnitude of the anodic current increased when increasing the volume of the used imide electrolyte, supporting the saturation hypothesis.Results and analyses regarding the anodic oxidation of Al in a series of carbonate solvents and using different salt concentration, as well as effect of the use of carbon coated Al will also be presented.

Electrocatalytic Performance of Interconnected Self‐Standing Tin Nanowire Network Produced by AAO Template Method for Electrochemical CO2 Reduction**

AbstractIn this study, we used a specially designed aluminum anodic oxide (AAO) template technique to produce interconnected self‐standing tin nanowire electrocatalysts having a high surface‐to‐volume ratio for CO2 reduction toward formate. These electrodes consisted of interconnected tin nanowires with 150 nm diameter and 7 μm length supported on 70–100 μm thick tin film. As prepared electrodes produced 6 times higher formate than the flat tin sheets, yet Faradaic efficiencies (FE%) were unsatisfactory. The main reason for low FE% is determined as the etching of native oxide on tin nanowires during hot alkali treatment to remove AAO and remnant aluminum. Porous anodic oxidation in 1 M NaOH solution was realized to recover tin oxides on the surface. Anodized tin nanowire electrocatalysts produced higher formate than anodized tin sheets, reaching FEformate% of ~87 at −1 V vs. RHE cathodic reduction potential. Moreover, while anodic oxide on flat tin flaked off the surface in 1 h, these electrodes preserved their integrity and formate production ability even after 12 h.

Experimental Investigation of Tube-in-Tube Nanocomposite Coated Heat Exchanger

In this paper, heat transfer performance is investigated for plain and nanoparticle coated tube-in-tube heat exchangers. Four types of tubes, i.e. bare copper tube, bare aluminium tube, Cu-Al2O3 nanoparticle coated tube and anodized aluminium tubes are used for performing the experimental investigation. The coating thickness of Cu-Al2O3 nanocomposite surface and anodized aluminium tube varies from 10, 25 and 30 micrometres to 15, 20 and 30 micrometres respectively. The surface is found to be hydrophilic in nature as the contact angle changes from 79.82deg to 55.47deg. The prepared surfaces are characterized by FESEM, EDS and FTIR. By adjusting the hot and cold fluids relative mass flow rates, one may calculate not only the overall heat transfer coefficient but also the efficiency of the tube-in-tube heat exchanger. The Cu-Al2O3 nanocomposite coated surface has the highest overall heat transfer coefficient and efficiency, followed by an anodized aluminium surface, bare copper surface and bare aluminium surface. The aluminium anodic oxide (AAO) surface also exhibits an increased heat transfer coefficient, but to a lesser extent than the nanocomposite coating.

Ppb‐Level ethanol gas sensor of porous anodic aluminum oxide at room temperature

AbstractExcessive ethanol in breath can be an indicator of alcoholism and a biomarker of liver disease. Herein, we present a novel porous aluminum anodic oxide (AAO)‐based chemi‐capacitive sensor that can detect ppb‐levels of ethanol gas at room temperature. The oxalic acid‐based porous AAO is an amorphous material contaminated with Al(OH)3 and C2O42− ions (anion‐contamination), which react with adsorbed ethanol gas. The optimal resonance frequency of ethanol was determined to be 500 Hz, and the response to 200 ppm ethanol at this frequency was 1.56%. Especially, the limit of detection of ppb‐level (16.49 ppb) was obtained. The detection range, reliability, and selectivity of the sensor, as well as its surface properties were comprehensively investigated. The proposed sensor is promising for the detection of liver disease as well as for commercial breath ethanol analyzers.

Study on Thermal Effect of Aluminum-Air Battery

The heat released from an aluminum-air battery has a great effect on its performance and operating life during the discharge process. A theoretical model was proposed to evaluate the resulting thermal effect, and the generated heat was divided into the following sources: anodic aluminum oxidation reaction, cathodic oxygen reduction reaction, heat production against the battery internal resistance, and hydrogen-evolution reaction. Quantitative analysis was conducted on each part, showing that all heat production sources increased with discharge current density. It should be noted that the heat caused by hydrogen evolution accounted for the most, up to 90%. Furthermore, the regulation strategy for inhibiting hydrogen evolution was developed by addition of hybrid additives to the electrolyte, and the hydrogen-evolution rate was greatly reduced by more than 50% as was the generated heat. This research has important guidance for the thermal effect analysis of aluminum-air batteries, together with control of the thermal management process by inhibiting hydrogen evolution, thus promoting their practical application.

Electrodeposition and magnetic properties of Co x Dy1−x nanotube arrays

Well-ordered Co x Dy1−x nanotubes are electrodeposited into self-made anodic aluminum oxidation templates under different potentials. The composition of Co x Dy1−x alloy nanotubes can be tuned by deposition potentials. The deposited Co x Dy1−x alloy nanotubes are amorphous, however, there appears a diffraction peak corresponding to Co7Dy2 in the sample annealed at 600 °C. The easy magnetization direction is always along the longitudinal axis of arrays for all samples. Dysprosium alloying significantly increases the coercivity of Co x Dy1−x nanotubes in comparison with Co nanotubes. By using the hybrid Monte Carlo micromagnetic method, the exchange stiffness constant of Co7Dy2 nanotubes can be conveniently estimated to be 8.0 × 10−11 J m−1.

Tuning the sensing responses towards room-temperature hypersensitive methanol gas sensor using exfoliated graphene-enhanced ZnO quantum dot nanostructures

A suitable and non-invasive methanol sensor workable in ambient temperature conditions with a high response has gained wide interest to prevent detrimental consequences for industrial workers from its low-level intoxication. In this work, we present a tunable and highly responsive ppb-level methanol gas sensor device working at room temperature via a bottom-up synthetic approach using exfoliated graphene sheet (EGs) and ZnO quantum dots (QDs) on an aluminum anodic oxide (AAO) template. It is verified that EGs-supported AAO with a vertical electrode configuration enabled high and fast-responsive methanol sensing. Moreover, the hydroxyl and carboxyl groups of the high surface area EGs and ZnO QDs with a 3.37 eV bandgap efficiently absorbing UV light led to 56 times high response due to the enhanced polarization on the sensor surface compared to non-UV-radiated EGs/AAO at 800 ppb of methanol. The optimal resonance frequency of methanol is determined to be 100 kHz, which could detect methanol with high response of 2.65% at 100 ppm. The limit of detection (LOD) concentration is obtained at 2 ppb level. This study demonstrates the potential of UV-assisted ZnO, EGs, and AAO-based capacitance sensor material for rapidly detecting hazardous gaseous light organic molecules at ambient conditions, and the overall approach can be easily expanded to a novel non-invasive monitoring strategy for light and hazardous volatile organic exposures.

Nanoengineered nanochannels for thermally ionic nanofluidic energy harvesting

This work demonstrates thermal-to-electric energy conversion based on ionic nanofluidic transport in nanochannels inducted by a temperature gradient. Two types of highly periodic and high aspect ratio nanochannels have been fabricated in a silicon (Si) substrate and in an aluminium oxide (Al2O3) membrane. Silicon nanochannels with diameter of 100 nm and height of 300 μm have been produced by metal-assisted chemical etching process (MACE), while nanochannels with the dimensions of the 10 nm and 3 μm respectively, were fabricated in a Al2O3 membrane by the anodic aluminum oxidation (AAO) process. Moreover, a novel approach of thermally nanofluidic energy harvesting was proposed and conducted. The performance of the thermally ionic nanofluidic energy harvesting system in cases with and without nanochannels has been evaluated and compared. The advantage of the presence nanochannels on energy conversion has been confirmed. The electrolyte concentration dependence on the output power has been determined. Also, the effect of nanochannel materials, including alumina and silicon materials, on the power density has been verified. The ionic Seebeck coefficient was enhanced by 7.3 times when the nanochannels were present. The silicon substrate with nanochannels demonstrated the highest performance for energy harvesting. Its power density reaches approximately 1.47 mW/m2, which was 13.3 times larger than the case without nanochannels. This investigation may open new opportunities for the future thermoelectric generators based on ionic transport in nanochannels.

Selected Mathematical Optimization Methods for Solving Problems of Engineering Practice

Engineering optimization is the subject of interest for many scientific research teams on a global scale; it is a part of today’s mathematical modelling and control of processes and systems. The attention in this article is focused on optimization modelling of technological processes of surface treatment. To date, a multitude of articles are devoted to the applications of mathematical optimization methods to control technological processes, but the situation is different for surface treatment processes, especially for anodizing. We perceive their lack more, so this state has stimulated our interest, and the article contributes to filling the gap in scientific research in this area. The article deals with the application of non-linear programming (NLP) methods to optimise the process of anodic oxidation of aluminium using MATLAB toolboxes. The implementation of optimization methods is illustrated by solving a specific problem from engineering practice. The novelty of this article lies in the selection of effective approaches to the statement of optimal process conditions for anodizing. To solve this complex problem, a solving strategy based on the design of experiments approach (for five factors), exploratory data analysis, confirmatory analysis, and optimization modelling is proposed. The original results have been obtained through the experiment (performed by using the DOE approach), statistical analysis, and optimization procedure. The main contribution of this study is the developed mathematical-statistical computational (MSC) model predicting the thickness of the resulting aluminium anodic oxide layer (AOL). Based on the MSC model, the main goal has been achieved—the statement of optimal values of factors acting during the anodizing process to achieve the thickness of the protective layer required by clients, namely, for 5, 7, 10, and 15 [μm].

The long-term degradation behavior of the durable superhydrophobic coating on Al matrix

The corrosion of aluminum and its alloys triggered by the aggressive environment seriously affects the service life and causes great economic loss. Superhydrophobic surface have been applied to deal with this problem, but their natural vulnerability cannot resist the intense external damage. Herein, a durable superhydrophobic coating is fabricated by combining the electrochemical growth of TiO2 nanoparticles in the aluminum anodic oxide (AAO) coating with modification of octadecyl trimethoxysilane (OTS), and its long-term corrosion behaviors are investigated through the comparative analysis during the static immersion test. The superhydrophobic AAO-TiO2@OTS coating exhibits the optimal hydrophobicity and corrosion resistance among all samples after being soaked in 3.5 wt% NaCl solution for 28 days, and the synergistic effects of OTS network, AAO layer and TiO2 nanoparticles endow the coating with the durable corrosion resistance. Thus, the integration of low-surface-energy modifier and hard porous frame is beneficial to improve the durability of superhydrophobic coating, and it is anticipated to propose a potential guidance for corrosion protection of metal and its alloys during the long-term service process.

Electrochemical Anodic Oxidation of Aluminum in the Presence of a Diamond Blend Obtained by Detonation of Tetryl

Electrochemical Anodic Oxidation of Aluminum in the Presence of a Diamond Blend Obtained by Detonation of Tetryl

Nanoporous nickel thin film anode optimization for low-temperature solid oxide fuel cells

Thin film solid oxide fuel cells (TF–SOFCs) having anode–substrate nanostructure that was optimized for the low-temperature operation were fabricated. Nickel thin film anodes with four different anode thicknesses were deposited on anodic aluminum oxide templates, nanoporous substrates having two different pore sizes, by the sputtering method. Subsequently, a yttria-stabilized zirconia (YSZ) electrolyte and platinum cathode were deposited on them, which completed the entire fuel cell structure. The anode nanostructure of fuel cells in six combinations was analyzed by the cross-sectional view, surface microscopy method, and three-dimensional morphology observation. Those investigations enabled the anode nanostructure to be identified, such as the anode porosity and the roughness of the interface between anodes and electrolytes. Then, the six TF–SOFCs were electrochemically characterized in a 500 °C operating environment. The maximum power densities were obtained through the i–V–P curves, and the highest performance of 294.1 mW/cm2 was measured in the cell having a combination of 200 nm–sized porous aluminum anodic oxide (AAO) and 1200 nm–thick Ni anode. This showed up to 20.1% improvement over the other cells. EIS analysis showed that the optimized ohmic and faradaic resistance originated from each part of the unique TF–SOFC structure.

Formation of Alumina Nanotubes and Jet Effect during High‐Voltage Local Anodization of Aluminum

Using an improved heat sink from the barrier layer, the voltage of anodic electrochemical oxidation of aluminum in sulfuric electrolytes is successfully increased from the conventional limit of about 40 to 200 V. This is done by localization of the anodized regions within the windows in the niobium thin film masks with the diameters of 0.3 μm to 2.5 mm. High‐voltage anodization in water solutions of sulfuric acid is observed to be accompanied by a reproducible formation of densely packed alumina nanotubes and intense gas propulsion from the pores of the forming alumina. The latter is proposed and experimentally confirmed for use as an efficient driving agent in micro‐ and nanoengines. Test samples are accelerated to the velocities up to 1 cm s−1, demonstrating a thrust‐to‐weight ratio of about 1000.

Coupling of cathodic aluminum dissolution and anodic oxidation process for simultaneous removal of phosphate and ammonia in wastewaters

Removal of excessive nutrients (N and P) is one of the most concerned issues for wastewater treatment. This study presents a paired electrolytic system consisting of Al cathode and RuO2/Ti anode for the simultaneous removal of phosphate and ammonia in wastewaters. The comparative study on the dissolving behaviors of Al cathode and Al anode showed that Al cathode could achieve a continuous and stable dissolution of aluminum, thereby forming flocs and small amounts of water soluble aluminum species for decontamination. The electrogenerated OH– in the vicinity of cathode raised the local alkalinity and caused the chemical dissolution of aluminum. According to the experiment of non-electrolytic dissolution of aluminum in alkaline solution, the local pH resulting in the cathodic dissolution of Al was estimated. The paired electrolytic system showed the capability to simultaneously remove ammonia and phosphate in simulated wastewater, and the pH neutralizing effect in association with the formation of Al species could promote the electrochemical oxidation of ammonia. When the paired electrolytic system was applied to the treatment of landfill leachate, 96.9% of ammonia nitrogen, 87.4% of total phosphorous and 89.9% of COD could be eliminated after three hours of electrolysis at 80 mA/cm2. The results shown in study reveal that the dissolution process of Al cathode enables a convenient control on the dissolving-out amounts of aluminum via regulating the applied current density, and the paired electrolytic system can be developed as an energy-efficient electrochemical wastewater treating method.

Low-Cost Nanostructured Coating of Anodic Aluminium Oxide Synthesized in Sulphuric Acid as Electrolyte

The anodic oxidation of aluminium is an electrochemical technique that allows obtaining nanostructures with easily adjustable morphology depending on the synthesis variables, for its application in medicine, engineering, biotechnology, electronics, etc. In this work, low-cost aluminium oxide nanostructured films were synthesized and morphologically characterized using two anodization steps in sulphuric acid, varying the concentration and temperature of the electrolyte and anodization voltage. The order of the porous matrix, pore diameter, interpore distance, pore density, thickness, and porosity were measured and statistically analyzed. The results showed that under the proposed conditions it is possible to synthesize low-cost nanoporous aluminium oxide films, with a short-range ordering, being the best ordering conditions 10 °C and 0.3 M sulphuric acid at 20 V and 5 °C and 2 M sulphuric acid at 15 V. Furthermore, it was determined that the pore diameter and the interpore distance vary proportionally with the voltage, that the pore density decreases with the voltage and increases with the concentration of the electrolyte, and that the thickness of the oxide film increases with electrolyte concentration, temperature, and anodization voltage.