The Kinetics of the Growth of Oxides

Dignam, M. J.

doi:10.1007/978-1-4757-4825-3_5

Cited by 9 publications

(5 citation statements)

References 89 publications

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“…The oxide lattice may not withstand the large ion or electron fluxes arising at very high fields, or else, high reaction rates of corrosion due to the presence of aggressive chemical species (like chloride or fluoride ions) may locally increase the conductivity, leading to breakdown of the passive film. This may be indicated by several effects such as irregular current peaks, visible sparks, potential fluctuations, increasing electrical noise or even audible noise, depending on the oxide bandgap, and the nature and concentration of ions in solution [30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48].…”

Section: High-field Anodizationmentioning

confidence: 99%

“…Considering the fundamental chemical kinetics theory for electrochemical processes by Butler and Volmer (see details and other considerations in, e.g., [30,33]), the activation energy can be rewritten as…”

Section: Kinetic Modelmentioning

confidence: 99%

“…In general, characterization of the anodic thin films is needed, and diverse experimental techniques have been developed for these purposes: optical, electronic and/or atomic microscopy [50], electrochemical measures controlling voltage, current densities or charges [30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48], electrochemical impedance spectroscopy [53,54], gravimetric measurements with the electrochemical quartz microbalance [55,56], infrared absorption, Raman, laser, UV-vis, UV-vis reflectance, luminescence, acoustic, X-rays, resonance, ellipsometry, and neutron-based spectroscopies [15, 44-47, 50, 57-62], and dynamic characterization based on photoelectrochemical methods [23,63,64].…”

Section: Photocatalysis Based On Metal Oxidesmentioning

confidence: 99%

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High-Field Growth of Semiconducting Anodic Oxide Films on Metal Surfaces for Photocatalytic Application

Vargas

Carvajal

Galavis

et al. 2019

International Journal of Photoenergy

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This work summarizes progresses achieved in the physical chemistry aspects of the growth of anodic oxides under high-field conditions for the synthesis of semiconducting thin solid films and their implementation as photocatalytic materials. We discuss the scope and mechanisms for anodic oxide growth, describing the development of kinetic models and the correlations between theory and kinetic data, leading to fundamental information to characterize the primary processes occurring during the anodization of valve metals under high fields. The main features related to the widely used self-assembly of nanostructures by valve metal anodization are highlighted and briefly discussed. This is followed by general considerations of heterogeneous photocatalysis on these functional materials, considering the kinetics of the heterogeneous catalytic processes involved and the overall photoelectrochemical performance. High control of the characteristics of the materials obtained with the method described, combined with the possibility of electrochemically assisting photocatalysis, allows application of this technology to the treatment of wastewaters, energy conversion, and related fields.

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Section: High-field Anodizationmentioning

confidence: 99%

Section: Kinetic Modelmentioning

confidence: 99%

Section: Photocatalysis Based On Metal Oxidesmentioning

confidence: 99%

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High-Field Growth of Semiconducting Anodic Oxide Films on Metal Surfaces for Photocatalytic Application

Vargas

Carvajal

Galavis

et al. 2019

International Journal of Photoenergy

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“…When a sufficiently large positive voltage is applied to a tantalum electrode immersed in almost any aqueous solution, the resultant electrostatic field E in the oxide causes metal ions to enter the oxide and travel through the pre-existing oxide film to the electrolyte solution where they react to produce more oxide (for reviews see Young 1961a, b;Dell'Oca et al 1971;Dignam 1981;Young 1992). As shown by Davies et al (1962), using xenon markers, oxygen ions (or oxygen bearing ions) also migrate, travelling through the oxide to the metal where more oxide is also produced.…”

Section: Introductionmentioning

confidence: 99%

Anodic oxide films on tantalum: anomalies in steady–state and stepped field ionic conduction and incorporation of electrolyte species

Young

1998

Proc. R. Soc. Lond. A

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The high field ionic transport process by which these films grow has been investigated using a 1M solution of KCl, an electrolyte which has recently been shown not to be incorporated into the films, unlike those previously used. In the steady-state, the current density J ss at a field in the oxide E ss is given by J ss = J 0 exp{−(W 0 − 5qa 1 E ss )/kT }, where log 10 (J 0 /1 mA cm −2 ) = 12.4(5), W 0 = 1.67(7) eV, a 1 = 0.29( 7) nm and q is the proton charge. When the field is rapidly changed to a new value E from its initial steady-state value E ss , the current density J is given by J = J ss exp(5qa 2 (E − E ss )/kT ) where J ss is the initial value and a 2 = 0.12(4) nm. Thus, neither the previously reported curvature of the steady-state log J ss versus E ss line nor the dependence on the initial steady-state field of the slope of the stepped field log J versus E lines were present when this electrolyte was used instead of dilute sulphuric acid. It is concluded that these two effects, which had been considered by some to be fundamental attributes of the ionic conduction process, are due to the incorporation of electrolyte species in the outer part of the oxide, which grows by metal ion movement.

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“…The growth of oxide films was experimentally described to follow the high field model [44], whereby the film grows both by ion migration and diffusion and the dependence of anodization current on the applied electric field is given by Eq. 10:…”

Section: Anodization Of Valve Metalsmentioning

confidence: 99%

Low Voltage Electrowetting-on-Dielectric for Microfluidic Systems

Mibus¹

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Manipulating fluids in micro to nano-liter volumes poses significant challenges, due to the dominance of surface forces with increasingly large surface to volume ratios. Commonly, external pumps or precisely micromachined on-chip pumps were used to generate pressure gradients to induce fluid motion. Alternatively, the wettability of a surface can be manipulated by an applied electric field. This phenomenon, known as electrowetting, consists in the spread of a liquid drop placed on an electrode upon application of a voltage. Electrowetting based devices flourished upon the discovery that an added dielectric layer between the drop and a conductive electrode would tolerate the application of large voltages, allowing for significant contact angle change. Several current commercial devices exploiting this effect include electro-optic displays, electronic paper, and variable focus lenses.Additionally, electrowetting has achieved particular prominence in lab-on-a-chip applications, controlling drop transport across patterned electrode structures.Initially, polymers were utilized as the dielectric layer preventing current flow between the fluid and electrode, while providing a hydrophobic surface to minimize the resistance of drop movement.However, these layers were typically in excess of one micron thickness. As a consequence, these layers required over 100 Volts to achieve appreciable contact angle change. This dissertation aims to reduce the voltage dependence for contact angle change by optimization of a dual layer structure utilizing a dielectric and hydrophobic layer. The dielectric layer uses aluminum and tantalum oxides (15-44 nm thick) formed by electrochemical anodization. The electronic and ionic conduction, breakdown characteristics, and dielectric properties of these films were studied in detail, achieving a comprehensive understanding of the charge transport and failure mechanisms. Three hydrophobic layer were investigated: a commercial fluoropolymer Cytop, and two self-assembled monolayers 3

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The Kinetics of the Growth of Oxides

Cited by 9 publications

References 89 publications

High-Field Growth of Semiconducting Anodic Oxide Films on Metal Surfaces for Photocatalytic Application

High-Field Growth of Semiconducting Anodic Oxide Films on Metal Surfaces for Photocatalytic Application

Anodic oxide films on tantalum: anomalies in steady–state and stepped field ionic conduction and incorporation of electrolyte species

Low Voltage Electrowetting-on-Dielectric for Microfluidic Systems

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