STUDY OF PASSIVE OXIDE FILMS ON METALS USING INFRARED SPECTROSCOPY (original) (raw)
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Oxidizing valve metals: effect of electronic properties of the oxide films
Russian Journal of Electrochemistry, 2000
Photocurrents emerging during the formation of anodic oxide films (AOF) on such valve metals as W, Ti, Zr, Nb, Ta are measured during an increase (direct run) and a decrease (reverse run of voltammetric curves) in the anodic potential. Capacitances of AOF formed at certain potentials are measured at potentials below the AOF formation potential. Effect of semiconductor properties on the AOF growth is considered through the formation of a Schottky barrier at the oxide/electrolyte interface. Calculated thicknesses of AOF and the depleted layer are compared. The donor-concentration drop in AOF with the distance from the metal/oxide interface is a condition for the growth of thick semiconductor oxide films. The measured potential dependence of the semiconductor-film capacitance is used to plot the donor concentration drop as a function of the distance from the Nb2O5/Nb interface in the oxide layer on a niobium electrode.
Characterization of the anodic growth and dissolution of oxide films on valve metals
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Chemical dissolution processes coupled to anodic oxide growth taking place by a ''high-field" conduction mechanism, are considered. The equation for the steady-state current density obtained during potentiodynamic polarization measurements is derived and the effect of the oxide dissolution rate on the overall potentiodynamic behaviour by applying repetitive scans with either fixed or increasing anodic switching potentials is discussed. The procedure for obtaining the current dissolution as well as the parameters that characterize the highfield growth is discussed.
FEATURES OF THE FORMATION OF THE OXIDE LAYER DURING THE ANODE VIBRATION
Transstellar Journals, 2020
The vibration effect of the ozonated liquid in the interelectrode gap on the oxide layer growth has been established. The formation stages of the strengthening coating are determined in accordance with the dynamics of changes in the current strength and anode oscillation frequency. The ultrathin surface layer is investigated.
Kinetics of anodic oxide-film growth on titanium—I. Acid media
Electrochimica Acta, 1971
Studies on the kinetics of anodic oxidation of Ti are made in H,SO,, HNOI, HCl and H90, solutions of varying concentration. Charging curves are measured at constant cd. Formation rates, and reciprocal capacitance data are reported as functions of the polarizing cd. The exponential relation between ion cd and electric field is also applicable in acid solutions. Values are recorded for the electrolytic parameters A and 23. Potential/log (cd) relations are constructed at constant time of polarization, and at constant Q, where Q is the charge passed. While the slope is a function of cd in the first set, linear relations are obtained at constant Q. These allow the calculation of estimates of the pre-immersion oxide thickness. Measurements at high cds indicate breakdown potentials of about 100 V. R6sum&Etude des cinetiques de l'oxydation anodique du Ti dans des solutions de H,SO,, HNOI, HCI et H,PO, & diverses concentrations. Les courbes de charge sont Ctablies a densite de courant constante. Les vitesses de formation et les valeurs de l'inverse de la capacitance sont rapport&es, en tant que fonctions de la densite du courant de polarisation. La relation exponentieile entre densite de courant ionique et champ electrique est aussi applicable aux solutions acides.
A COMPARATIVE STUDY OF ANODIC OXIDE FILMS ON TITANIUM, NIOBIUM AND TANTALUM
Anodic oxide films were formed on titanium, niobium and tantalum, mostly up to about 40 volts, using three electrolytes of quite different composition and a particular electrical program intended to prevent uncontrolled transient phenomena. The existence of several different anodic oxides was observed for each metal, depending upon the electrolyte used. The growth of the oxides occurs at the oxide/electrolyte interface by a mechanism of cation migration through a stationary oxygen sub-lattice. At this interface, a transition region similar to an electrochemical double layer appeared to behave as a dielectric layer added to the anodic oxide layer during anodization. Data were compared concerning the differential thickness, the specific capacitance, the dielectric constant and the apparent electronic charge on the anions electrodeposited into the oxides. From the latter it was deduced that water is the main oxidizing agent and that protons are incorporated into the anodic oxides as well as some sulfuric anions when certain electrolytes are used.
Electrochimica Acta, 2001
The semiconducting properties of passive films formed on AISI type 304 stainless steel in borate buffer solution were studied by capacitance (Mott-Schottky approach) and photocurrent measurements. The oxide films formed on 304 stainless steel in air in the temperature range between 50 and 450°C have also been studied. The results obtained show that, in all cases the electronic structure of the films is comparable to that of a p -n heterojunction in which the space charges developed at the metal-film and film-electrolyte interfaces have also to be considered. This is in accordance with the analytical results showing that the oxide films are in all cases composed of an inner region rich in chromium oxide and an outer region rich in iron oxide. When the temperature of the film formation changes the thickness of the films and the doping densities also change but the model to explain the semiconducting properties of the very thin passive films and the relatively thick well-crystallized thermally grown films is basically the same. To confirm the existence of the heterojunction measurements on thermally grown films before and after the cathodic reduction were also carried out.
Journal of the Brazilian Chemical Society, 2002
Estudaram-se as propriedades semicondutoras de filmes passivos formados em aço inoxidável AISI 304 e em ligas de base Ni (Alloy 600) em soluções tampão de borato. Os filmes foram estudados por medidas de capacidade (Mott-Schottky) e de fotocorrente. Estudaram-se também filmes formados em aço inoxidável AISI 304 por oxidação ao ar, à temperatura de 350ºC. Os resultados mostram que a estrutura electrónica dos filmes é comparável à de uma heterojunção do tipo p-n, onde as cargas de espaço desenvolvidas nas interfaces filme-metal e filme-electrólito devem ser consideradas. O estudo electroquímico está de acordo com os resultados analíticos que demonstram que os filmes de óxido são, em todos os casos, compostos por uma região interna rica em óxido de crómio e por uma região externa rica em óxido de ferro. The semiconducting properties of passive films formed on AISI 304 stainless steel and Alloy 600 in borate buffer solution were studied by capacitance (Mott-Schottky approach) and photocurrent measurements. Oxide films formed on 304 stainless steel in air at 350 ºC have also been studied. The results obtained show that, in all cases the electronic structure of the films is comparable to that of a pn heterojunction in which the space charges developed at the metal-film and film-electrolyte interfaces have also to be considered. This is in accordance with analytical results showing that the oxide films are in all cases composed of an inner region rich in chromium oxide and an outer region rich in iron oxide.
Thin Solid Films, 2007
The main goal of this work is to show the interesting contribution of reflectance infrared spectroscopy to determine the composition of oxide films on metal surfaces. Illustration is reported on oxidation of α 2 -TiAl (Ti75-Al25 at.%) and γ-TiAl (Ti50-Al50 at.%) alloys, carried out at 650°C under laboratory atmosphere. Reflectance infrared spectra were recorded on an FTIR 710 Nicolet spectrophotometer, equipped with a Nicolet IR plan microscope. The knowledge of the infrared optical constants makes it possible to predict the infrared reflection spectra of different thin layers. As there is a lack of data in literature, theoretical calculations have been made in order to study experimental spectra. To illustrate these computations the first band observed for a thin film (200 nm) of Al 2 O 3 is the higher longitudinal optical (LO) mode, the position of which is 920 cm − 1 for α-Al 2 O 3 , 930 cm − 1 for γ-Al 2 O 3 or a broad band at 980 cm − 1 for amorphous Al 2 O 3 . In the case of TiO 2 /alloy system, the LO mode moves from 830 cm − 1 for rutile TiO 2 to 880 cm − 1 for anatase TiO 2 . A peak fit program was applied to the spectra in order to extract each oxide contribution. The position of the fitted single absorption bands makes it possible to identify the different oxides. The oxide grown on α 2 -TiAl phase, consists of α-Al 2 O 3 and rutile TiO 2 (24 h to 500 h of oxidation treatment), γ-Al 2 O 3 and rutile TiO 2 for 1000 h of oxidation treatment. Chemical maps reveal heterogeneous distribution of the oxides in the layer. A detailed surface characterization showed that the surface was principally covered with α-Al 2 O 3 and locally with an Al 2 O 3 /TiO 2 mixture. In the case of γ-TiAl oxidation, the oxide film consists of α-Al 2 O 3 , γ-Al 2 O 3 and rutile TiO 2 mixture. FTIR spectroscopy provides important information about amorphous, poor or well crystallized materials when X-ray diffraction is only convenient for crystallized phases.
Journal of applied electrochemistry, 2007
The growth kinetics and properties of potentiodynamically formed thin oxide films on Al were investigated in 0.05 M citric acid solutions of different pH (5, 6 and 7) by means of potentiodynamic polarization and a.c. electrochemical impedance spectroscopy (EIS) measurements. Al showed passive behaviour within the pH range that was examined. The potentiodynamic growth of the oxide film on Al takes place due to ionic conductivity under the influence of the high electric field. Characteristic kinetic oxide film growth parameters such as the high-field growth exponential law constants (A and B), ionic conductivity through the oxide film, field strength and half barrier width have been calculated. Impedance measurements were used to determine the parameters related to the characteristic sizes and properties of oxide film. The capacitive response of the impedance spectrum was related to the thickness and dielectric properties of the barrier oxide film. The oxide film resistance values were very high, indicating that the oxide films formed under potentiodynamic conditions are highly uniform in thickness and very resistant. The anodic behaviour of Al in the citric solutions under potentiodynamic conditions were characterized by the rapid growth of the oxide film which diminished the influence of relaxation processes on the growth kinetics and structural characteristics of the aluminium/anodic oxide film/electrolyte system.