Space-Charge and Concentration-Gradient Effects on Anodic Oxide Film Formation

Fromhold, A. T.; Krüger, J.

doi:10.1149/1.2403545

Cited by 26 publications

(23 citation statements)

References 7 publications

(17 reference statements)

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“…31 For a 64 nm thick oxide ͑160 monolayers ϫ 0.4 nm lattice parameter͒ growing under a range of current densities, the space-charge region was approximately 15% of the overall thickness of the oxide, i.e., 9.6 nm thick. 30 If specific anions such as fluoride were not present in the electrolyte, the dissolution of the oxide would be greatly reduced ͑and nanopores would not form͒. As such, 10 nm is a reasonable value of the width of the space-charge region for the conditions of anodization considered in the present study.…”

Section: Estimation Of Spacing Of Nanopores and Nanotubesmentioning

confidence: 86%

Initiation of Organized Nanopore/Nanotube Arrays in Titanium Oxide

Bhargava

Nguyen

Devine

2009

J. Electrochem. Soc.

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In a series of two papers, a mechanism is proposed to describe the initiation of organized arrays of nanopores and nanotubes formed via anodization of titanium. Part I describes the mechanism of initiation, based on the instability of the planar oxide/ electrolyte interface, and develops a criterion for the initiation of nanopores, while the present paper uses this planar interface instability criterion to calculate the size/spacing of nanopores. To facilitate the calculation, the destabilized interface is modeled by a series of sine waves, representing surface perturbations. Because the growth rates of the sine waves are a function of their wavelengths, the spacing of the ultimate array of nanopores and nanotubes is related to the wavelength of the fastest-growing perturbation. The proposed mechanism explains the transition from disorganized to organized and the influence of voltage on pore spacing and size.Nanoporous and nanotubular oxides of valve metals exhibit extremely high surface areas as well as electronic and electrochemical properties that strongly suggest applications in batteries, fuel cells, solar cells, and chemical sensors. [1][2][3] The size and spacing of nanopores and nanotubes are important parameters which govern the properties of the oxide nanostructures and, in our view, are established by the process of pore nucleation. The first of our two papers presented a mechanism of initiation of the nanopores in titanium oxide as well as equations expressing the criterion for pore initiation. In the present work, an expression is developed for the spacing of nanopore nuclei. The results provide estimates of pore spacing/size that are consistent with experimentally measured values of titanium oxide. In addition, the analysis explains three key experimental observations: ͑i͒ the simultaneous and homogeneous initiation of nanopores, ͑ii͒ the transition from disorganized to organized arrays of pores, and ͑iii͒ the increase in pore spacing/size with applied voltage. In the present study, scanning electron microscopic inspection of anodized titanium as a function of time of anodization confirms these three observations. ExperimentalProcedure.-Anodization of Ti foils ͑0.125 mm, 99.6% ϩ purity, Goodfellow͒ was performed in a two-electrode cell, where Pt served as the counter electrode. Before anodization, the foils were sonicated in acetone and deionized ͑DI͒ water and then dried in a N 2 stream. Each foil sample was then immersed in an ethylene glycol solution containing 0.5 wt % NH 4 F and anodized at a constant potential of 20 V with a dc power supply. Different anodization times ͑30 s, 15 min, and 1 h͒ were applied to different foil samples. After the anodization step, the samples were again sonicated in DI water for 10 s and dried with N 2 before characterization. An FEI Strata 235 dual-beam scanning electron microscope was used to examine the morphology of the pores/tubes that formed on the surface of the foils.Results.-The influence of time of anodization on the appearance of the anodized surface of ...

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Section: Estimation Of Spacing Of Nanopores and Nanotubesmentioning

confidence: 86%

Initiation of Organized Nanopore/Nanotube Arrays in Titanium Oxide

Bhargava

Nguyen

Devine

2009

J. Electrochem. Soc.

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“…The gradual decrease in current that precedes breakdown I suggests, however, that the rate of growth may be lowered by the accumulation of space-charge as the film thickens (11,(16)(17)(18), and a more detailed analysis of the growth law will be given elsewhere (19).…”

Section: Resultsmentioning

confidence: 99%

Instability of Anodic Oxide Films on Titanium

Peter

1982

J. Electrochem. Soc.

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ConclusionThe polyhedral boron halide anions B,jX92-(X --C1, Br, I) and B,0Cllo 2-can be oxidized electrochemically in two successive reversible one-electron processes (2). The initial oxidation products are stable and persistent in solution although the neutral species BpX9 and B,0Cllo react with CH~CN. The simple B10Cll02-electrochemistry provides an interesting contrast to the coupling of the parent boron hydride ions under similar conditions. Acknowledgment ABSTRACT Linear sweep voltammetry, photocurrent spectroscopy, impedance and reflectance measurements have been used to study the growth and stability of anodic oxide films on titanium in H2SO4 and H3PO4. Films were grown typically to a formation voltage of 40V (-100 rim) and had a density close to that of anatase, 3.9 g cm -3. Two regimes of oxide film instability have been identified. The first occurs during growth and is manifested by a reduction in growth current efficiency preceded by unusual photocurrent and impedance behavior. The second, which occurs when the field is reduced, appears as a sharp current spike accompanied by film thickening and sudden changes in the impedance and photocurrent conversion efficiency. A link between the two phenomena is established and the dependence on growth rate and formation voltage discussed. A model based on the formation of a damaged surface layer covering a fresh barrier layer is presented.

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“…(12)-(15), (16a) and (16b) are simultaneously satisfied. The creation of electric fields in diffusion in ionic solids is found in oxidation of metals [16][17][18] and is believed to be responsible for non-parabolic oxidation kinetics during Zircaloy oxidation in air [19]. Electric-field effects in the oxide film are probably the origin of the initial ''cubic" rate law during Zircaloy oxidation in PWR water.…”

Section: Discussionmentioning

confidence: 99%

Point-defects in irradiated UO2

Olander

2010

Journal of Nuclear Materials

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Space-Charge and Concentration-Gradient Effects on Anodic Oxide Film Formation

Cited by 26 publications

References 7 publications

Initiation of Organized Nanopore/Nanotube Arrays in Titanium Oxide

Initiation of Organized Nanopore/Nanotube Arrays in Titanium Oxide

Instability of Anodic Oxide Films on Titanium

Point-defects in irradiated UO2

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