Oxide-covered Aluminum Research Articles

Corrosion of Passive Aluminum Anodes in a Chloroaluminate Deep Eutectic Solvent for Secondary Batteries: The Bad, the Good, and the Ugly.

The passivity of aluminum is detrimental to its performance as an anode in batteries. Soaking of native oxide-covered aluminum in a chloroaluminate deep eutectic solvent gradually activates the electrode surface, which is reflected in a continuously decreasing open circuit potential. The underlying processes were studied by analyzing the 3 to 7 nm thick layer of native oxide after increasing periods of soaking with secondary neutral mass spectrometry, X-ray photoelectron spectroscopy, and energy-dispersive spectroscopy in a transmission electron microscope. They consistently show permeation of electrolyte species into the layer associated with gradual swelling. After extended periods of soaking at open circuit potentials, local deposits of a range of foreign metals have been found in scanning electron microscopy images of the electrode surface. The pitting corrosion is caused by trace metal ion impurities present in the electrolyte and results in highly nonuniform current density distribution during discharge/charge cycling of battery cells as shown by local deposits of aluminum. The processes during soaking at open circuit potentials have been monitored by electrochemical impedance spectroscopy and could be analyzed by fitting an equivalent circuit model for pitting corrosion.

A research of the stability of oxide-covered aluminum surface for electrochemiluminescence probe use

A research on the effect of different buffers on the pH range of 6–10 on the thin oxide-covered surface of aluminum cathode has been conducted under the conditions corresponding with those generally used in bioaffinity assays or other determinations made by using aluminum probe based on time-resolved cathodic electrochemiluminoimmuno assay (tr-ECLIA or tr-CECLIA) detection. The experiments have been conducted on impedance and cathodic electrochemiluminescence (CECL) basis using a strong long lifetime having electroluminophore Tb(III)-1 chelate where the ligand 1 is 2,6-bis[N,N-bis(carboxymethyl)aminomethyl]-4-benzoylphenol and Ruthenium(II) tris(2,2′–bipyridine) (Ru(bpy)32+) as the CECL model luminophores. The results point out that the natural oxide layer at the electrode surface does not essentially change as to its thickness but as to its resistance, it can be concluded that the best buffer in these luminophore determinations based on CECL and Al probe use is borate buffer adjusted to pH around 7–8 where the surface of aluminum has its neutral character. In the bioaffinity assays the meaning of the buffer seems to be more difficult to realize due to the complex character of the surface with plenty of different coatings and special handling steps but still with the aforementioned borate buffer the results were noticed to be the most stabile. The tests also pointed out that the character of the pure aluminum surface and the oxide layer above it without any other coatings could be strongly affected by the surrounding solution composition and in that way to the durability of the aluminum probe already during the quite short exposure times. The reported results are useful especially in the field of CECL based on aluminum probe use but could also in a certain extent to be utilized in a large scale of analysis considering the use of aluminum probes.

Hot electron-induced electrochemiluminescence of calcein and calcein-Tb(III) complex at disposable oxide-covered aluminum and polyvinyl butyral-carbon black/metal composite electrodes in aqueous solutions

Hot electron-induced electrochemiluminescence (HECL) of calcein and calcein-Tb(III) complex was generated at oxide-covered aluminum electrode during cathodic pulse polarization. The excitation of calcein as a molecule or as a ligand is based on subsequent one-electron oxidation and reduction steps by oxidizing radicals and solvated electrons. During HECL excitation of calcein-Tb(III) solution a reaction product of the calcein is formed that also enables the photoexcitation of Tb(III) via the formed ligand derivative by ligand-sensitized mechanism. The determination of low concentrations of calcein with aluminum electrodes was complicated by a relatively strong background electroluminescence originating from the Al2O3-layer. Polyvinyl butyral-carbon black composite electrodes coated on brass were fabricated to solve this problem and a fifty-fold lower background emission was obtained for these novel composite electrodes in comparison to that of oxide-covered 99.9% pure aluminum electrodes. The obtained detection limits were 3.2·10−10 M for calcein and 6.4·10−9 M for calcein-Tb(III) at the present composite electrodes. These species could potentially be utilized as electrochemiluminescent labels in bioaffinity assays.

Heterogeneous time-resolved electrochemiluminoimmunoassay of thyroid stimulating hormone with magnetic beads at oxide-covered aluminum electrode

The heterogeneous immunoassay of thyroid stimulating hormone (TSH) was detected by the time-resolved cathodic electrochemiluminescence immunoassay (tr-CECLIA) method using magnetic beads as a mobile support. The magnetic beads coated with sandwich type TSH immunoassay were captured with a magnet for washing and detection processes. The time-resolved cathodic electrochemiluminescence (tr-CECL) signal of Tb(III) chelate label was generated by cathodic pulse polarization in the aluminum working electrode and platinum counter electrode system. The detection method causes injection of high energy electrons into the aqueous solution near the aluminum electrode and creates rigid simultaneous oxidative and reductive conditions that excitate the Tb(III) chelate used as a label luminophore in the heterogeneous sandwich type immunoassay of TSH in the surface of the magnetic beads. The limit of detection of the method was about 50mIUL−1. The precision of it was noticed to be good; the coefficient variation percentage was realized to be lower than 10 %. Unfortunately the limit of detection is not good enough for determination of analyte levels of very low concentrations for instance TSH in body fluids. The possible application areas of the method are in highly sophisticated micro or nano fluidic detection and sensor systems where the aspiration level of the analyte detection limit is not very high and the mobility and manageability and the large surface area of the magnetic beads can be utilized efficiently in separating, washing, moving, coating and detecting processes. In the case of tr-CECLIA the presented method makes possible to use multipurpose working electrodes instead of disposable ones.

Printable Hecl Electrode Materials for Disposable Bioaffinity Assay Cartridges

We have demonstrated earlier that hot electrons can be injected into aqueous electrolyte solution from thin insulating film coated cathodes [1, 2]. Insulating film have typically been fabricated from an insulator material with a band gap of ca. 5 eV or preferably higher, with the Fermi level of the insulator somewhere in the mid band gap region. The hot electrons are emitted to aqueous electrolyte solution by direct field-assisted tunneling at these devices [2, 3]. After injection into the conduction band of water the hot electrons are thermalized and solvated to form hydrated electrons which finally act as reducing mediators in the Hot Electron-induced Electrochemiluminescence (HECL) systems. HECL is utilized mainly in immunoanalysis and in DNA-probe assays in which electrochemiluminescent labels are utilized [ 2 - 5 ]. Best labels are certain aromatic lanthanide chelates which allow sensitive time-resolved HECL detection of the labels [3, 6]. Silicon electrodes or silicon chips on which the working electrode/electrodes and counter electrode have been integrated have been shown to be excellent functional components of disposable assay cartridges [5,7]. Recently, we have been able to develop printable HECL electrode materials that show almost equal performance and are based on conductor particles embedded in polystyrene or in some other organic insulating materials.

Chloride Ion Interactions with Oxide-Covered Aluminum Leading to Pitting Corrosion: A Review

Metals and alloys such as aluminum (Al), stainless steels, and nickel-based alloys exhibit corrosion resistance in a wide range of environments due to the presence of protective, passive oxides. However, in environments that contain aggressive anions such as chloride, Cl−, the passive film becomes unstable and degrades locally causing film breakdown and pitting corrosion. A number of theories describing the initiation of pitting corrosion have been postulated and discussed but to date there is no consensus on the mechanism of breakdown. Since all current mechanisms require Cl− interactions for oxide film breakdown in Cl− containing environments, the question is what is the nature of the interaction of aggressive anions such as Cl− with the passive film, adsorption and/or absorption, leading to pitting? This communication focuses on the interaction of Cl− with the passive oxide film on pure aluminum by reviewing and summarizing the available experimental data concerning Cl− interactions. It should also be noted that the observations for Cl− interactions with Al reviewed and summarized herein might not be applicable to all metals and alloys.

Silicate‐based post‐anodic treatment for lithographic application

AbstractSodium silicate solutions are widely used chemicals for a variety of applications. In particular, they are commonly used in pre‐treatments of aluminium alloys as cleaners and corrosion inhibitors. Another application is found in offset printing, where after graining and anodising, a silicate‐based post‐anodic treatment (PAT) is considered to optimise the aluminium plate characteristics. It is, however, not clear what type of interaction takes place between the oxide‐covered aluminium and the silicate solution. In this work, silicate‐based PAT is studied. Different barrier‐type and porous‐type aluminium oxides are silicate‐treated by dipping in a water‐based sodium silicate solution and the effect of time on the deposition is studied. Particular attention is given to the role of rinsing when the alumina surface is washed in water after the silicate treatment. A good understanding of the role of rinsing allows us to obtain information on the characteristics of the silicate layer which is formed after dipping. The surface modifications induced by the silicate treatment on the aluminium oxides were monitored by means of field emission scanning electron microscopy and infrared spectroscopic ellipsometry. Quantitative measurements on the amount of deposited silicate were taken by X‐ray fluorescence, and relative comparisons between different oxides are shown. Auger electron spectroscopy was used to study the in‐depth composition of the silicate deposition. Experiments show a high affinity of the silicate to the anodic oxide film. A thin nanometric chemisorbed (alumino)silicate layer is present on the surface after rinsing, while the physisorbed part of the layer is washed away. Copyright © 2009 John Wiley & Sons, Ltd.

Electrochemiluminescence Study of Europium (III) Complex with Coumarin3-Carboxylic Acid

The europium (III) complex of coumarin-3-carboxylic acid (C3CA) has been prepared and characterized on the basis of elemental analysis, IR, and emission (photoluminescence and electrochemiluminescence) spectroscopy. The synthesised complex having a formula Eu was photophysically characterized in solution and in the solid state. Electrochemiluminescence, ECL, of the system containing the Eu(III)/C3CA complex was studied using an oxide-covered aluminium electrode. The goal of these studies was to show the possibility of the use of electrochemical excitation of the Eu(III) ion in aqueous solution for emission generation. The generated ECL emission was very weak, and therefore its measurements and spectral analysis were carried out with the use of cut-off filters method. The studies proved a predominate role of the ligand-to-metal energy transfer (LMET) in the generated ECL.

Electrogenerated luminescence of chosen lanthanide complexes at stationary oxide-covered aluminium electrode

The electrochemiluminescence (ECL) of aqueous solutions of Tb3+, Dy3+, and Eu3+ complexes having a variety of ligand groups was studied using an oxide-covered aluminium electrode. The ligand groups, under study, were the aromatic acids (salicylic, phthalic), the chelatic ligands (ethylenediamine dl(o-hydroxy-phenylacetic acid), EDDHA and ethylenediamine tetraacetic acid, EDTA), as well as Schiff bases: 1,10-disalicylidene-4,7-diaza-1,10-decyldiamine and 2-salicylideneamine-2-hydroxymethyl-1,3-propanediol. The results show that the generated emissions were mainly the result of energy transfer from the ligands to the metals. The best ECL properties were observed in the case of the complexes Tb(III)–EDDHA, Dy(III)–EDDHA, and Dy(III)–salicylic acid. In the ternary systems: Schiff base–Tb(III)–Eu(III) energy transfer to the emitting level of the Eu(III) ion was observed.

Electrochemiluminescence on Dy(III) and Tb(III)-doped Al/Al 2O 3 surface electrode

The electrochemiluminescence (ECL) of aqueous electrolyte solutions containing EDDHA and an oxide-covered aluminum electrode doped with Dy(III) or Tb(III) during the cathodic pulse-polarisation was investigated. Injection of tunnel-emitted hot electrons from the electrode into complexes of solutions containing S 2 O 8 2 - , induces ECL, as observed in the 5D 4 → 7F J transitions in Tb(III) and 4F 9/2 → 6H 15/2 and 4F 9/2 → 6H 13/2 in Dy(III) ions. Specific electrogenerated luminescence was obtained by producing highly oxidizing and reducing species as: hydrated electrons, hydroxyl and sulfate radicals. These strong red-ox reactants efficiently excite the complexed Tb(III) and Dy(III) ions by ligand → metal energy transfer.

Understanding aluminum behaviour in aqueous alkaline solution using coupled techniques: Part I. Rotating ring-disk study

Rotating disk electrode (RDE) and rotating ring-disk electrode (RRDE) measurements have been undertaken to study the behaviour of pure aluminum electrodes in alkaline media. The measurements did consist of linear sweep voltammetry from anodic to cathodic potentials on 4N, 5N or 5N5-aluminum samples in 4M aqueous potassium hydroxide solution. In the potential range studied (−0.7V versus NHE to −2.5V versus NHE) the aluminum undergoes oxidation/dissolution into aluminates anions at high electrode potential while it yields strong hydrogen evolution at low potentials. Thanks to the RRDE technique, we show that hydrogen starts to evolve from the aluminum electrode even above the open circuit potential. Also, the oxidation state of superficial aluminum varies according to the electrode potential: whereas non-conducting aluminum oxides are present above the open-circuit potential hindering hydrogen evolution reaction (HER), they tend to disappear below the ocp, due to the strong hydrogen evolution, following the probable porous oxide layer blow up induced by the hydrogen bubbles formation. In consequence at very low potential, HER occurs on bare aluminum, HER kinetics being much faster than on oxide-covered aluminum.

Generation of free radicals and electrochemiluminescence from simple aromatic molecules in aqueous solutions

Oxide-covered aluminium electrodes were used to demonstrate that aromatic compounds, such as the simple derivatives of benzene, can be electrochemically excited at cathodically pulse-polarized conductor/insulator/electrolyte (C/I/E) tunnel junction electrodes (e.g. oxide-covered aluminium electrodes). The primary cathodic process at these electrodes was a tunnel emission of hot electrons into an aqueous electrolyte solution. Fluorescence (FL) and electrochemiluminescence (ECL) spectra were compared and the dependence of the electrochemiluminescence on the concentrations of benzene, toluene, phenol, p-cresol and aniline were measured and detailed mechanisms for the present electrochemiluminescence are proposed.

Time-Resolved Detection of Hot Electron-Induced Electrochemiluminescence of Fluorescein in Aqueous Solution

Strong electrogenerated chemiluminescence (ECL) of fluorescein is generated during cathodic pulse polarization of oxide-covered aluminum electrodes and the resulting decay of emission is so sluggish that time-resolved detection of fluorescein is feasible. The present ECL in aqueous solution is based on the tunnel emission of hot electrons into the aqueous electrolyte solution, which probably results in the generation of hydrated electrons and hydroxyl radicals acting as redox mediators. The successive one-electron redox steps with the primary radicals result in fluorescein in its lowest excited singlet state. The method allows the detection of fluorescein (or its derivatives containing usable linking groups to biomolecules) over several orders of magnitude of concentration with detection limits well below nanomolar concentration level. The detection limits can still be lowered, e.g., by addition of azide or bromide ions as coreactants. The results suggest that the derivatives of fluorescein, such as fluorescein isothiocyanate (FITC), can be detected by time-resolved measurements and thus be efficiently used as electrochemiluminescent labels in bioaffinity assays.

Hot electron-induced time-resolved electrogenerated chemiluminescence of a europium(III) label in fully aqueous solutions

Time-resolved electrogenerated chemiluminescence of multidentate phenolic Eu(III) chelates were studied in aqueous solution. 2,6-bis[ N, N-bis(carboxymethyl)-aminomethyl]-4-benzoylphenol forms a photoluminescent and electrochemiluminescent Eu(III) chelate, whereas 2,6-bis[ N, N-bis(carboxymethyl)-aminomethyl]-4-methyl phenol-chelated Eu(III) turned out to be not luminescent at all. The importance of the redox properties of both the ground and the excited states of the ligands and the central ion is shown. The former chelate shows relatively weak ECL at an oxide-covered aluminum electrode but the ECL intensity can be strongly enhanced by the addition of peroxodisulfate ions. In the presence of 1 mM peroxodisulfate ions the ECL lifetime of this chelate is 0.94 ms, thus easily allowing time-resolved detection of the chelate. This chelate can be conjugated to antibodies by thioureido linkage and used as an electrochemiluminescent label in immunoassays as a marker which displays long-lived luminescence in the red end of the optical spectrum. The present ECL is mainly based on the ligand sensitized redox excitation of the chelate by analogous pathways to those known from the studies of aromatic Tb(III) chelates but the energy transfer from the emission centers of the aluminum oxide film can also have minor contribution to the excitation of the label.

Hot electron-induced electrochemiluminescence of fluorescein in aqueous solution

Strong electrogenerated chemiluminescence (ECL) of fluorescein is generated in aqueous solution during cathodic pulse polarization of oxide-covered aluminum electrodes. The present method is based on the injection of hot electrons into the aqueous electrolyte solution, which probably results in the generation of hydrated electrons as reducing mediators. The successive one-electron redox reactions result in fluorescein in its lowest excited singlet state, i.e., the emission spectrum is similar to the corresponding fluorescence emission spectrum. This ECL can be enhanced by added coreactants, e.g., by peroxodisulfate, peroxodiphosphate, hydrogen peroxide and azide ions. The method can detect fluorescein over several orders of magnitude of concentration with detection limit below nanomolar concentration level in the presence of azide ions. The results suggest that the derivatives of fluorescein, such as fluorescein isothiocyanate, can be used as electrochemiluminescent labels in aqueous solution in bioaffinity assays carried out on the surface of thin aluminum oxide film-coated aluminum electrodes. This cathodic ECL is mainly based on the one-electron oxidation of fluorescein by the cathodically produced oxidizing radicals followed by reduction of the formed semioxidized fluorescein by hot or hydrated electrons back to the original oxidation state which finally emits light.

Competitive immunoassay by hot electron-induced electrochemiluminescence detection and using a semiautomatic electrochemiluminometer

A homogeneous immunoassay of T4 was developed using a semiautomatic electrochemiluminometer modified from a commercially available fluorometer. In addition, from the same analyte panel an immunometric immunoassay of TSH at similar disposable oxide-covered aluminum rake electrodes was studied using this instrument both on homogeneous and heterogeneous basis. Detection was based on hot electron-induced cathodic electrochemiluminescence utilizing a commercially available Tb(III) chelate label. The assays were reasonably sensitive and comparison was made with other older methods. Thus, it is possible to develop both non-competitive and competitive immunoassays based on detection of hot electron-induced ECL of the labels.

Direct current-induced electrogenerated chemiluminescence of hydrated and chelated Tb(III) at aluminum cathodes

Cathodic DC polarization of oxide-covered aluminum produces electrogenerated chemiluminescence from hydrated and chelated Tb(III) ions in aqueous electrolyte solutions. At the moment of cathodic voltage onset, a strong cathodic flash is observed, which is attributed to a tunnel emission of hot electrons into the aqueous electrolyte solution and the successive chemical reactions with the luminophores. However, within a few milliseconds the insulating oxide film is damaged and finally dissolved due to (i) indiffusion of protons or alkali metal ions into the thin oxide film, (ii) subsequent hydrogen evolution at the aluminum/oxide interface and (iii) alkalization of the electrode surface induced by hydrogen evolution reaction. When the alkalization of the electrode surface has proceeded sufficiently, chemiluminescence is generated with increasing intensity. Aluminum metal, short-lived Al(II), Al(I) or atomic hydrogen and its conjugated base form, hydrated electron, can act as highly reducing species in addition to the less energetic heterogeneously transferred electrons from the aluminum electrode. Tb(III) added as a hydrated ion in the solution probably luminesces in the form of Tb(OH) 3 or Tb(OH) 4 − by direct redox reactions of the central ion whereas multidentate aromatic ligand chelated Tb(III) probably luminesces by ligand sensitized chemiluminescence mechanism in which ligand is first excited by one-electron redox reactions, which is followed by intramolecular energy transfer to the central ion which finally emits light.

Cathodic electrogenerated chemiluminescence of Ru(bpy) 32+ chelate at oxide-coated heavily doped silicon electrodes

High amplitude cathodic pulse polarization of ultra thin oxide film-coated heavily doped silicon electrodes induces tunnel emission of hot electrons into aqueous electrolyte solution, which probably results in the generation of hydrated electrons in the vicinity of the electrode surface. The method allows the detection of tris (2,2′-bipyridine) ruthenium(II) chelate at subnanomolar concentration level. This paper shows that both n- and p-type heavily doped silicon electrodes can be used, illustrates the effect of oxide film thickness upon the silicon electrode on the intensity of ECL of tris (2,2′-bipyridine) ruthenium(II) and discusses the basic features of tris (2,2′-bipyridine) ruthenium(II) chelate-specific ECL at these electrodes. Thin oxide film-coated silicon electrodes provide a lower blank emission and a higher ECL intensity of the present ruthenium chelate than oxide-covered aluminium electrodes. This suggests that thin oxide film-coated silicon is a very promising working electrode material, especially in microanalytical systems made fully or partly of silicon.

Chromate Inhibition of Filiform Corrosion on Organic Coated AA2024-T3 Studied Using the Scanning Kelvin Probe

The influence of in-coating strontium chromate pigment dispersions on the kinetics and mechanism of HCl-induced filiform corrosion (FFC) affecting polyvinyl butyral coated AA2024 T3 aluminum alloy is studied using a scanning Kelvin probe. FFC initiation and propagation are detected by imaging time-dependent changes in local free corrosion potential distribution patterns. Area rates of coating delamination fall from to zero as the volume fraction is increased from zero to 0.06. Increasing over the same range produces minimal change in filament-head values but depresses filament tail and intact coating values by up to 0.3 V. It is proposed that filament tail depression results from increased polarization of cathodic reduction reactions at sites of high pH, where insoluble is the predominant reduction product. It is further proposed that intact coating depression results from reversible, nonfaradaic adsorption of at the oxide-covered aluminum surface. Both effects are implicated in FFC inhibition, as is pH buffering by which acts in conjunction with adsorption to forestall anodic attack at the coating-substrate interface. © 2004 The Electrochemical Society. All rights reserved.

Lewis Acid/Lewis Base Effects in Corrosion and Polymer Adhesion at Aluminum Surfaces

Lewis acid/Lewis base (electron acceptor/electron donor) interactions are important in the breakdown of oxide films on aluminum by chloride ions and in the adhesion of organic polymers onto oxide-covered aluminum surfaces. This paper considers the pitting of aluminum by (a Lewis base) in terms of the acid-base nature of the oxide film. Topics addressed are the adsorption of on oxide films on aluminum, the effect of pH on the pitting potential of aluminum, and the pitting potential of various pure metals or surface-modified aluminum. Lewis acid/Lewis base interactions are also important in the adhesion of polymers to oxide-covered metal surfaces, as shown by experimental adhesion tests. The adhesion strength of a basic polymer poly(methyl methacrylate) was greatest on the most acidic oxide films. The adhesion strength of an acidic polymer (a commercially available pressure-sensitive adhesive) was the greatest on the most basic oxide films. © 2003 The Electrochemical Society. All rights reserved.