Aluminum In Oxalic Acid Research Articles

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

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

Structural colors of laminated alumina films prepared by ac oxidation in oxalic acid solution

Laminated alumina films were fabricated via the oxidation of aluminum in oxalic acid using alternating current (ac). The color of the prepared samples depended on the anodization conditions. Thus, the structural color of samples was changed without the use of dopants such as dyes. The reflectance band of the film changed according to the color of the sample. The reflectance spectrum showed the highest peak intensity when the concentration of oxalic acid was 0.1 M, and the peak disappeared when the oxalic acid concentration was larger than 0.4 M. The reflectance band of the films tended to shift toward longer wavelengths with the increase in the applied voltage, and the change in color corresponded with the peak positions. The tendency of color change is the same as for the films prepared in sulfuric acid, which was reported recently. The properties of the films prepared in oxalic acid and sulfuric acid are compared and the effects of the electrolytes are discussed.

Controlled Growth of Highly Aligned Cu Nanowires by Pulse Electrodeposition in Nanoporous Alumina.

Metallic nanowire networks are emerging as potential replacements for transparent conducting oxide coatings because of their high conductivity, flexibility and relative transparency. However, a cheap, reliable and controlled manufacturing process is required to exploit this and the surface of the copper nanowire needs to be protected if high conductivity is to be retained. In this study a fabrication method for highly aligned and densely packed copper nanowires with controlled length using pulse-electrodeposition and a nanoporous alumina template has been developed. Nanoporous alumina was obtained by anodisation of pure aluminum in oxalic acid using a two-step anodisation process. In order to provide the conductivity at the bottom of the pores, a dendritic structure at the interface was created through the stepwise voltage reduction method with a voltage reduction rate of 15 V/s followed by mild chemical etching. Highly repeatable near 100% filling of copper is achieved. Copper nanowire length was highly controllable from 100 nm to 2 μm with a fixed diameter of 60 ± 5 nm by monitoring current density during the deposition. Such controlled growth of Cu nanowires could lead towards transparent conducting layer applications but the protection of the material against oxidation remains an issue.

First-Step Anodization of Commercial Aluminium in Oxalic Acid: Role of Anodization Voltage in Tailoring the Structural Features of Porous Alumina Film and Aluminium Substrate

First-Step Anodization of Commercial Aluminium in Oxalic Acid: Role of Anodization Voltage in Tailoring the Structural Features of Porous Alumina Film and Aluminium Substrate

(Invited) Alumina Nanotubes Formed By Anodization of Aluminum Cast Alloy

Anodic porous alumina film, a typical self-ordered nanohole material formed by anodizing aluminum in an appropriate acidic solution, is used as a starting material of nanofabrication of functional devices besides a corrosion resistant surface oxide. In contrast to anodic titania nanotubes, anodic porous alumina is generally compact without spacing between the cell boundary. The tubular shape of anodic titania is suggested to be resulted in enrichment of fluoride between cells which is originated from electrolyte and more soluble than anodic titania. In the case of aluminum, it is reported that enrichment of only sulfate or ethylene glycol from electrolytes produces alumina nanotubes by anodization. In the present paper, the formation mechanisms of alumina nanotubes by anodization of Al cast alloy caused except the electrolyte origin will be discussed. STEM image of vertical cross section prepared by ion-milling of the anodic film, which was formed on 99.99 % pure aluminum in oxalic acid at 160V, indicated close-packed hexagonal cell arrays with small voids of 15-20 nm at the triple cell points. Dark field STEM image clearly revealed a bright particle in the each void suggesting the presence of a heavy metal because of Z-contrast. By EDX point analysis, Cu enriched particles were found in the voids at the triple cell points. Nevertheless, in the case of anodic film formed at the similar condition on AC8A cast alloy including 0.97 % of Cu, tubular cells with the space of approximately 50 nm between cell boundary were formed unlike the case of pure aluminum including 60 ppm of Cu. Numerous branching of pores were also observed. EDX mapping revealed that Si was enriched in the outer layer of the cells and Cu was enriched at the area near the cell boundaries. Therefore, it is deduced that enrichment of Cu at the cell boundaries produces the tubular cells by accelerating oxide dissolution in addition to the electric breakdown accompanied by severe gas evolution that resulted in void formation at the triple cell points.

Formation Mechanism of Alumina Nanotubes By Anodization of Aluminum Alloy

Anodic porous alumina film, a typical self-ordered nanohole material formed by anodizing aluminum in an appropriate acidic solution, is used as a starting material of nanofabrication of functional devices besides a corrosion resistant surface oxide. In contrast to anodic titania nanotubes, anodic porous alumina is generally compact without spacing between the cell boundary. The tubular shape of anodic titania is resulted in enrichment of fluoride between cells which is originated form electrolyte and more soluble than anodic titania. In the case of aluminum, it is reported that enrichment of only sulfate or ethylene glycol originated form electrolytes produces alumina nanotubes by anodization. In the present paper, the formation mechanism of anodic alumina nanotubes will be discussed. STEM image of vertical cross section prepared by ion-milling of the anodic film, which was formed on 99.99 % pure aluminum in oxalic acid at 160V, indicated close-packed hexagonal cell arrays with small voids of 15-20 nm at the triple cell points. Dark field STEM image clearly revealed a bright particle in the each void suggesting the presence of a heavy metal because of Z-contrast. By EDX point analysis, Cu enriched particles were found in the voids at the triple points. Nevertheless, in the case of anodic film formed at the similar condition on AC8A cast alloy including 0.97 % of Cu, tubular cells with the space of approximately 50 nm between cell boundary were formed unlike the case of pure aluminum including 60 ppm of Cu. Numerous branching of pores were also observed. EDX mapping revealed that Si was enriched in the outer layer of the cells and Cu was enriched at the area near cell boundaries. Therefore, it is deduced that enrichment of Cu at the cell boundaries produces the tubular cells by accelerating oxide dissolution similar to the cases of enrichment of sulfate and ethylene glycol.

Downscaled anodic oxidation process for aluminium in oxalic acid

The increasing multi-functionality of parts and assemblies in several fields of engineering demands, amongst others, highly functionalised surfaces. For the different applications, on the one hand, there is a need to scale up surface modification processes originating in the nano- and micro-scale. On the other hand, conventional macro-scale surface refinement methods offer a huge potential for application in the said nano- and micro-scale. The anodic oxidation process, which is established especially for aluminium and its alloys, allows the formation of oxide ceramic layers on the surface. The build-up of an oxide ceramic coating comes along with altered chemical, tribological and electrical surface properties. As a basis for further investigations regarding the use of the anodic oxidation process for micro-scale-manufacturing, the scale effects of oxalic acid anodising on commercially pure aluminium as well as on the AlZn5.5MgCu alloy are addressed in the present work. The focus is on the amount of oxide formed during a potentiostatic process in relation to the exchanged amount of charge. Further, the hardness of the coating as an integral measure to assess the porous oxide structure is approached by nano-indentation technique.

Effect of processing parameters on pore opening and mechanism of voltage pulse detachment of nanoporous anodic alumina

The free-standing through-hole porous alumina membranes (PAMs) were fabricated by two-step self-organized anodization of aluminum in oxalic acid followed by the subsequent voltage pulse detachment performed in an environmental-friendly solution based on HClO4 and C2H5OH. The effects of oxalic acid concentration used for anodic oxide synthesis and the chemical composition of the barrier oxide layer on the effective detachment of PAMs were studied. On the other hand, the voltage detachment conditions such as applied voltage, number of pulses, and temperature of electrolyte were tested as parameters which might affect the detachment of PAMs and their bottom side morphology. It was found that the voltage detachment process is affected by applied detachment voltage while the bottom surface morphology of detached PAMs is influenced by oxalic acid concentration used for anodization, the chemical composition of the barrier oxide layer, and the time gap between anodization and detachment (storage period). Furthermore, it was revealed that number of applied pulses and electrolyte temperature maintained during the detachment have a little effect on the morphology of PAM films. The most feasible and detailed mechanism of the voltage pulse detachment, considering the individual stages of the process, was proposed. At the beginning, the mechanism was related to an electric field assisted dissolution of oxide enhanced by its chemical dissolution induced by Joule's heating. These processes occur at the pore bottoms upon application of the voltage pulse and results in pore widening and thinning of the barrier layer. Then, after the electrical breakdown of the barrier layer, the intensive electropolishing of aluminum at the metal/oxide interface takes place.

Origin of nanopore alumina film photoluminescence: three kinds of defect centers

Nanopore alumina films (PAF) are fabricated by two-step anodic oxidation of aluminum in oxalic acid. The field emission scanning electron microscope measurement reveals the surface microstructure of PAF, and the defect formation mechanism in PAF is analyzed. The energy dispersive X ray spectroscopy and the Fourier transform infrared spectroscopy results indicate that oxalic ions are incorporated into the PAF in the synthesis process and further heating up to 500 ℃ does not cause oxalic ions to completely decompose. The photoluminescence (PL) spectra of PAF can be divided into three bands by Gaussion fitting method. The measurement results and the defects in PAF show that the PL originate from optical transitions of two kinds of different oxygen-deficient defect centers (F and F+) and oxalic impurities related defect center, PL centered at 402, 433 and 475 nm, respectively. We put forward for the first time that F centers play a leading role. The PL characteristics of the PAF prepared in oxalic acids with different concentrations suggest that three kinds of the luminescent center positions do not change with the increase of the oxalic acid concentration, but their relative intensities change with the increase of the oxalic acid concentration, i.e., F and F+ decrease, oxalic impurities related defects increase, and these will cause the PL peak position to be red-shifted. Finally, we put forward that the oxalic impurities in PAF can be changed by controlling the concentration of oxalic acid. The present experiments and results will be beneficial to the understanding of light-emitting mechanism in PAF, meanwhile, in this paper we propose a new train of thought for PAF preparation application.

Ultra-small nanopores obtained by self-organized anodization of aluminum in oxalic acid at low voltages

A simple method of fabrication of anodic aluminum oxide at low voltages (from 5 to 15V) in 0.3M oxalic acid is presented. To overcome the issues concerning the anode's burning, a high velocity stirring was applied. It allowed to achieve nanopores with ultra-small diameters (even 12nm), interpore distance (even 31nm) and tremendously high pore densities (up to 980 pores per 1µm2) with simultaneous high porosity (up to 38%). Moreover, the presented approach (no modifier added to the electrolyte) resulted in the AAO with relatively well arranged ultra-small nanopores.

Self-Ordered Nanoporous Alumina Templates Formed by Anodization of Aluminum in Oxalic Acid

Anodic aluminum oxide (AAO) membranes with highly ordered nanopores serve as ideal templates for the formation of various nanostructured materials. The procedure of the template preparation is based on a two-step self-organized anodization of aluminum. In the current study, AAO templates were fabricated in 0.3 M oxalic acid under the anodizing potential range of 30–60 V at an electrolyte temperature of ~5°C. The AAO templates were analyzed using scanning electron microscopy, x-ray diffraction, Fourier-transform infrared spectroscopy, and differential thermal analysis. The as obtained layers are amorphous; the mean pore size is between 40 nm and 75 nm and increases with the increase of the anodization potential. Well-defined pores across the whole aluminum template, a pore density of ~1010 pores/cm2, and a tendency to form a porous structure with hexagonal symmetry were observed.

Effect of anodizing voltage on the sorption of water molecules on porous alumina

The amount of water adsorbed on different centers on the surface of oxalic acid alumina films is a function of the anodizing voltage. It is decreased with increasing the anodizing voltage from 20 up to 50V, came up to maximum value at 20–30V and slightly increased at voltages above 50V. Water adsorption by oxide films formed at voltages below 50V can be due to the negative surface charge that is present on the alumina surface. The negative surface charge disappears in the films formed at voltages higher than 50V, and thus, the water is adsorbed on aluminum ions in a tetrahedral and octahedral environment. The correlation between anodizing conditions of aluminum in oxalic acid and the structure and composition of anodic alumina was established by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM), thermogravimetric and differential thermal analyses (TG/DTA).

Quantitative characterization of acid concentration and temperature dependent self-ordering conditions of anodic porous alumina

Acid concentration and temperature dependent self-ordering conditions of anodic porous alumina formed by anodization of aluminum in oxalic acid are quantitatively characterized by a new technique involving the distribution of the angular orientation of the triangles formed by neighboring pore centers, in order to detect the self-ordering domains in each porous pattern. This technique is found to be more sensitive in quantifying ordering of the patterns than the radial distribution function and angle distribution function. Using this technique, the optimal acid concentration which can result in the best self-ordering of the porous alumina under a given temperature is established. The optimal acid concentration is found to be approximately linearly increasing with temperature. The oxide growth rate increases approximately exponentially with acid concentration and also with temperature. The results suggest that anodization conducted at relatively higher temperatures at the corresponding optimal acid concentrations can enable fast production of self-ordered anodic porous alumina for industrial applications.

Ultrasound-assisted anodization of aluminum in oxalic acid

Porous anodic alumina is an important nanoscale template for fabrication of various nanostructures. We report a new ultrasound-assisted anodization process in oxalic acid. Under the continuous irradiation of ultrasound, the one-step-anodized sample has a smooth and clean surface, and two-step-anodization brings ordered porous anodic alumina with higher growth rate of 52 μm/h. The ultrasound applied during the anodization can clean the surface and enhance the nanopore growth since it can accelerate the oxide dissolving on the electrolyte/oxide interface. The ultrasound-assisted anodization may be utilized for other anodizations.

기공성 알루미나 산화 피막을 이용한 나노 금속화합물의 제조

Porous film can be utilized as template for fabrication of nano-structured materials. Porous anodic alumina layer as template was prepared by anodization of aluminum in oxalic acid, and the pore diameter and barrier-type alumina layer can be controlled for proper anodizing parameter by widening process in solution. The nanodot and Ni nanowire was fabricated using anodic alumina template and their characteristics were investigated using SEM and TEM with EDS. Especially the growth mechanism of nanodot in alumina membrane compared with thinning of the alumina barrier layer during anodization was also investigated.

Anodic Oxidation of Aluminium in Oxalic Acid by Cyclic Voltammetry

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Structural features of self-organized nanopore arrays formed by anodization of aluminum in oxalic acid at relatively high temperatures

Anodic aluminum oxide (AAO) membranes with a highly ordered nanopore arrangement typically serve as ideal templates for the formation of various nanostructured materials. A typical procedure of the template preparation is based on a two-step self-organized anodization of aluminum carried out at the temperature of about 1–3 °C. In the current study, AAO templates were fabricated in 0.3 M oxalic acid under the anodizing potential range of 30–65 V at a relatively high electrolyte temperature ranging from 20 to 30 °C. Due to a high rate of porous oxide growth, about 5–10-fold higher than in low-temperature anodizing, the process of the template fabrication can be shorten significantly. Similarly to the low-temperature anodization, the best hexagonal pore arrangement is observed for samples anodized at 40 V. With a prolonged duration of the first anodizing step the order degree of triangular nanoporous lattice, observed after the second anodization, improves considerably. The effects of the anodizing potential and the process duration on the structural features of porous anodic alumina such as: pore diameter ( D p), interpore distance ( D c), porosity ( P), pore density ( n) and anodizing ratio ( B U) were investigated in details at various temperatures. The obtained results were compared with theoretical predictions and data reported in the literature.

Blue luminescence in porous anodic alumina films

We have investigated the luminescence property of anodic alumina membranes (AAM) with orderednanopore arrays prepared by electrochemically anodizing aluminium in oxalic acid, sulfuricacid and phosphoric acid solutions. The photoluminescence (PL) intensity of AAM prepared inC2H2O4 is much higher than that of AAMs prepared inH2SO4 and H3PO4. The PL spectra obtained show that there are two optical centres for the AAMs prepared inH2SO4 andH3PO4, of which the firstoriginates from the F+ centres, and the second is associated with the F centres. It is found that the oxalic impuritiesincorporated in the AAMs should have important influences on the optical properties of AAM preparedin C2H2O4. The blue emission band in the AAM prepared inC2H2O4 originates fromthe coactions of the F+ centres, the F centre and the luminescent centres transformed from oxalic impurities.

THERMODYNAMIC PARAMETERS OF INHIBITION OF ALUMINUM DISSOLUTION IN OXALIC ACID SOLUTIONS USING SOME ORGANIC COMPOUNDS

Corrosion of aluminum in oxalic acid has been done by using wt-loss technique and polarization technique in presence of different concentrations of different organic derivatives of (5-Acetyl, 3-Cyano, 6-Methyl, 2-Thiopyridone, …) such as (…, 4-p Anisyl [A1]), (…,4-p Bromo phenyl [A2]), (…, 4-p Tolyl, [A3]), (…,4-p Nitro phenyl [A4]) and (…,4-p Chloro phenyl [A5]) at different temperatures. It is noticed from the observed thermodynamic parameters derived from wt-loss measurements that ∆H for the adsorption of A1, A2, A3 and A5 resulted in a negative value (exothermic), the adsorption typed is chemical adsorption, whereas A4 acquired physical adsorption and accelerated the dissolution of aluminum. This behavior is also observed at high temperatures for A5 compound. From the polarization method studied the dissolution of aluminum in oxalic acid is decreasing as the concentration of the acid increased due to the formation of oxide passive layer (Al2O3. 3H2O), the application of Evans diagram showed that the used compounds A1, A2, A3 and A5 can act as anodic inhibitors.

Alumina nanotubes and nanowires from Al-based porous alumina membranes

Using ultrasonic vibrations, we have successfully fabricated alumina nanotubes and nanowires from Al-based porous alumina membranes, which are the products of bulk aluminium in oxalic acid via electrochemical etching. Fine configurations and structures of the alumina nanotubes and nanowires are clearly revealed following a series of atomic force microscope and transmission electron microscope observations. Their formation mechanisms are analyzed in detail by comparing different growth characteristics of Al-based alumina membranes with Si-based alumina membranes. Based on our experimental results, we have also pointed out that when using porous alumina templates to fabricate nanostructured materials, it is necessary to carefully distinguish the obtained products from the alumina nanotubes and nanowires.