Oxide-covered Aluminum Research Articles

Room temperature phosphorescence emission in fully aqueous medium induced by injection of hot electrons into an electrolyte solution

Tunnel-emitted hot electrons induce the triplet state emission of the ligand of an aromatic Gd(III) chelate while the corresponding Tb(III) chelate shows a metal-centred emission at cathodically pulse–polarised oxide-covered aluminum electrodes in fully aqueous solutions at room temperature.

Determination of the Surface Isoelectric Point of Oxide Films on Metals by Contact Angle Titration

The surface isoelectric point for the native air-formed oxide films on aluminum, chromium, and tantalum has been determined by measurement of contact angles at the hexadecane/aqueous solution interface as a function of pH of the aqueous phase. Application of Young's equation, the Gibbs equation, and surface equilibria conditions for hydroxylated oxide films leads to a mathematical expression which shows that the contact angle goes though a maximum at the isoelectric point of the oxide. The experimentally determined isoelectric point of oxide-covered chromium is 5.2 to 5.3, of oxide-covered aluminum is 9.5, and of oxide-covered tantalum is approximately −0.7. These values for the oxide films are within one to three pH units of the reported isoelectric points for the corresponding bulk oxide powders. The oxide-covered metal surfaces were cleaned by argon plasma treatment prior to measurement of contact angles, in that XPS measurements showed this treatment to be effective in reducing the thickness of the carbon contamination layer. In addition, interfacial tensions were measured at the hexadecane/aqueous solution interface and were observed to have only a slight dependence on the pH of the aqueous phase.

F-Centre luminescence from oxide-covered aluminium cathode induced by two-step reduction of peroxydisulfate anions

S. Kulmala, T. Ala-Kleme, A. Hakanen and K. Haapakka, J. Chem. Soc., Faraday Trans., 1997, 93, 165 DOI: 10.1039/A604025J

Low-Loss EELS Study of Oxide-Covered Aluminum Nanospheres

Note: chercher Reference CIME-ARTICLE-1997-016View record in Web of Science Record created on 2007-02-15, modified on 2017-05-12

Mechanism of electrogenerated luminescence of terbium(III)-“2,6-bis[ N,N-bis(carboxymethyl)aminomethyl]-4-benzoylphenol” chelate at an oxide-covered aluminium electrode

Generation of hydrated electrons at an oxide-covered aluminium electrode during its cathodic pulse-polarization in an aqueous electrolyte may well be the primary step of the electrogenerated luminescence of aromatic Tb(III) chelates. In the presence of appropriate precursors, hydrated electrons produce secondary oxidizing radicals, thus resulting in an energetic electrode/electrolyte interface which initiates the radiative 5D 4 → 7F j transitions of chelated terbium(III); the aromatic moiety of a Tb(III) chelate is excited by its consecutive interactions with hydrated electron and the secondary oxidizing radical followed by an intramolecular transfer of this excitation energy to the 5D 4 level of coordinated terbium(III).

An FT-IR investigation of parabactin adsorbed onto aluminum

A detailed FT-IR study has shown that the catecholate siderophore parabactin isolated from the bacterium Paracoccus denitrificans adsorbs from solution onto the oxide-covered aluminum surface. Comparison of the FT-IR spectra for bulk parabactin and for parabactin adsorbed from solution suggests that the parabactin molecule forms a complex with the aluminum oxide film through the -OH groups present in the aromatic rings in parabactin and that the molecule adsorbs in a horizontal configuration on the oxide-covered aluminum surface.

Modified scratch test for study of the adhesion of ductile coatings

The scratch test is a widely used method for the characterization of the adhesion of hard and brittle coatings. The adhesion is related to the critical normal force, leading to adhesive failure. The present work describes a modified scratch test apparatus and procedure for the determination of the adhesion of soft and ductile coatings. It is based on the simultaneous measurement of the normal and tangential forces. The critical normal force is determined from the observation of a transition in the slope of the curve tangential force vs. normal force. Because the applied forces are smaller by two orders of magnitude than in the case of brittle coatings, a special apparatus had to be built. The modified scratch test is used for the determination of the adhesion of silver films sputter deposited on oxide-covered aluminum substrates. The results show that the critical normal force decreases with increasing thickness of the surface oxide.

Cathodically induced time-resolved lanthanide(III) electroluminescence at stationary aluminium disc electrodes

A time-resolved electroluminometer, which utilizes electrogenerated luminescence (EL) from disposable oxide-covered aluminium electrodes, is described in detail. The cathodic polarization of this disc electrode in aqueous electrolytes induces a faint background EL with peak emission at 570 nm and with a lifetime of 6 μs. This cell can be utilized to excite dysprosium(III), samarium(III) and terbium(III) by electrochemical means to their lowest excited singlet states and, thus, to produce lanthanide(III)-specific emissions. From the lanthanide(III) El systems tested so far, a cathodically induced EL of 2,6-bis[ N, N,bis(carboxymethyl)aminomethyl]-4-benzoylphenol-chelated terbium(III) with a 2.1-ms lifetime is the longest lived and can be efficiently discriminated against the background EL on a time-resolved basis using instrumentally simple time-resolved detection; this time-resolved terbium(III) EL makes possible the determination of terbium(III) even below the picomole level in aqueous solutions.

Instrumentally simple flow detector for the determination of traces of electroluminescent compounds in aqueous solutions

A flow detector based on the observation of the cathodic electroluminescence at an oxide-covered aluminium electrode is described. The detector responds only to electroluminescent compounds in aqueous eluents, and additional selectivity can be achieved by making use of optical filters for wavelength discrimination. The optimum detection conditions were determined by using the cathodic electroluminescence induced by a polynuclear aromatic hydrocarbon in micellar solutions as the model electroluminescence. This instrumentally simple detector can be used to determine electroluminescent compounds in a wide concentration range with good precision. For instance, its detection limit, dynamic range and precision (i.e., relative standard deviation for 20 successive measurements of 1 × 10 −7 M samples) for the determination of micelle-encapsulated 9,10-diphenylanthracene were found to be 1 × 10 −8 M, four orders of magnitude and 7%, respectively.

Specific determination of trace copper(II) by cathodic electroluminescence

Copper (II) stimulates cathodic electroluminescence at the oxide-covered aluminum electrode in the presence of hydrogen peroxide and 2,2′-bipyridine in 0.1 M sodium acetate. The detection limit is 5 × 10 −9 M; no other metal ions interfered. The mechanism of the reactions is discussed.

Fluorophor-enhanced cathodic electroluminescence at an oxide-covered aluminum electrode

Symmetric double-step potential (i.e., positive and negative potential) pulses with intermittent zero potential pulses at the oxide-covered aluminum electrode generates anodic and cathodic electroluminescence in an aqueous environment in the presence of potassium peroxodisulfate. Organic fluorescent compounds generate changes in the cathodic electroluminescence but not in the anodic emission: intensity is greatly enhanced and the spectrum of a fluorophor-enhanced electroluminescence becomes similar to the fluorescence spectrum of the fluorophor. The mechanism of the fluorophor-enhanced peroxodisulfate-induced cathodic electroluminescence is discussed. It is demonstrated by means of salicylic acid as the model fluorophor that this electroluminescence can be exploited to determine trace organic fluorescent compounds.

Feasibility of low-voltage cathodic electroluminescence at oxide-covered aluminum electrodes for trace metal determinations in aqueous solutions

Metal-catalyzed electroluminescence is generated at an oxide-covered aluminum electrode during the reduction of oxygen, potassium peroxodisulfate, and especially hydrogen peroxide in aqueous solutions. The feasibility of this electroluminescence for the determination of copper (5 × 10 −9 M) and thallium (> 10 −10 M) is demonstrated.

Surface plasmon scattering on flat surfaces at grazing incidence

This paper reports a study of surface plasmon excitation on the flat, oxide-covered aluminum surface, using high energy electrons which pass the surface at a finite, and sometimes large, impact parameter. The scattering probability dependence on impact parameter agrees qualitatively with classical, quasi-static calculations, which assume that the materials are characterized by homogeneous dielectric constants. A broad intensity maximum near 16 eV is identified as a surface plasmon made possible by the frequency dependence of the aluminum oxide dielectric constant.

ChemInform Abstract: THE CHEMICAL NATURE OF ALUMINUM CORROSION. V. ENERGY TRANSFER IN ALUMINUM DISSOLUTION

AbstractDer Energietransfer während der Auflösung von A1 wird durch eine Potentialfläche dargestellt.

Electron energy loss spectroscopy of A {111} oriented aluminum single crystal

Recently, the electron energy loss spectroscopy (ELS) and secondary electron spectroscopy (SES) of the interaction of oxygen with polycrystalline aluminum were reported for primary energies in the range 30 ⩽ E p ⩽ 250 eV. Two new transitions were resolved in the ELS spectra (one at 4 eV for clean aluminum and the other at 12 eV for oxide-covered aluminum) for low primary energies ( E p ~ 30 eV). In this paper we report on experiments utilizing a {111} oriented single crystal of aluminum that confirm the existence of these loss peaks for low primary energies and show that the 4 eV peak position for pure aluminum depends on the primary beam energy. This suggests that this low energy loss peak is due to direct nonvertical inter- and intraband transitions which differs from the previous assignment.

Electron energy loss spectroscopy of a {111} oriented aluminum single crystal

Recently, the electron energy loss spectroscopy (ELS) and secondary electron spectroscopy (SES) of the interaction of oxygen with polycrystalline aluminum were reported for primary energies in the range 30 ⩽ E p ⩽ 250 eV. Two new transitions were resolved in the ELS spectra (one at 4 eV for clean aluminum and the other at 12 eV for oxide-covered aluminum) for low primary energies ( E p ≈ 30 eV). In this paper we report on experiments utilizing a {111} oriented single crystal of aluminum that confirm the existence of these loss peaks for low primary energies and show that the 4 eV peak position for pure aluminum depends on the primary beam energy. This suggests that this low energy loss peak is due to direct nonvertical inter- and intraband transitions which differs from the previous assignment.

Characteristic emission of negatively charged particles during tensile deformation of oxide-covered aluminum alloys

Electrons, positive and negative ions as well as photons are known to be emitted from oxide- covered pure polycrystalline Al, Ni, and Ti during tensile deformation. It has been shown that the propagation of cracks in the oxide is uniquely associated with this so-called tribo-stimulated exoemission phenomenon. In this paper we report recent results of tribo-stimulated emission of negatively charged particles from bare and Al-clad aluminum alloys. The investigated samples were anodically oxidized under various conditions such as to produce oxide layers of different thickness as well as chemical and mechanical properties. Of particular interest in this connection are certain porous oxides which facilitate adhesive bonding. The characteristic exoemission curve (emission rate versus strain of the Al substrate) is obtained by measuring the number of emitted negative particles as a function of strain ϵ during tensile deformation of the sample with a constant strain rate dϵ/d t. The features of the curves obtained from different oxides are compared. Initial evidence is presented indicating that the exoemission curve is unique for a given oxide- metal alloy system and has potential as a monitor of certain characteristics of the oxide layer.