Metal oxidation kinetics and the transition from thin to thick films

Abstract

We report an investigation of growth kinetics and transition from thin to thick films during metal oxidation. In the thin film limit (<20 nm), Cabrera and Mott's theory is usually adopted by explicitly considering ionic drift through the oxide in response to electric fields, where the growth kinetics follow an inverse logarithmic law log(dl/dt) is proportional to 1/l. It is generally accepted that Wagner's theory, involving self-diffusion, is valid only in the limit of thick film regime (>1 μm) and leads to parabolic growth kinetics dl/dt is proportional to 1/l, where l is the oxide film thickness. Theory presented here unifies the two models and provides a complete description of oxidation including the transition from thin to thick film. The range of validity of Cabrera and Mott's theory and Wagner's theory can be well defined in terms of the Debye-Hückel screening length. The transition from drift-dominated ionic transport for thin film to diffusion-dominated transport for thick film is found to strictly follow the direct logarithmic law log(dl/dt) is proportional to -l that is frequently observed in many experiments.

Influence of Space Charge During the Oxidation of Metal Surfaces

“…(27) at V M = 1 eV [2,7,13] is X D = 10 -6 m, which agrees with the experimental and calculated data reported in the literature [1,13,22]. According to Atkinson's calculations [2], the value of this limiting thickness is equal to X D = 10 -7 m, which corresponds to the intersection point of line E sp with line E ox constructed by the CMT (Fig.…”

“…This thickness corresponds to the Debye screening length L D , which value for semiconductors is L D & 1 lm [16]. The oxide film growth in this thickness interval is accompanied by the transition from drift-dominated ionic transport for thin film to diffusion-dominated transport for thick film and is described by the direct logarithmic law log(dX/dt) µ -X that is frequently observed in many experiments at elevated oxidation temperatures [13,[17][18][19][20][21][22][23][24][25].…”

“…The transition from thin to thick oxide film occurs in the thickness range from X 1 to X D [1,2,13,14], where X D is the critical thickness of the oxide film, above which applies the Wagner's theory, describing the formation of a thick film by parabolic law [15]. This thickness corresponds to the Debye screening length L D , which value for semiconductors is L D & 1 lm [16].…”

Synthesis of magnetic microtubes decorated with nanowires and cells

“…The presence of an electric field, which leads to a voltage gradient, can also contribute to the chemical potential. 18 The oxidation chemical reaction involves a process where a thin oxide layer is formed first on the metal surface, followed by simultaneous outward diffusion of metal ions through the oxide layer and inward diffusion of oxygen from the atmosphere into the core. Metal ions often diffuse outward faster than oxygen diffuses inward, which is consistent with the smaller ionic radius of cations than anions.…”

A comparative review of the aqueous corrosion of glasses, crystalline ceramics, and metals

“…The mechanism of oxide formation and growth includes both ionic and electronic transport through the oxide. 142 Metal cation transport usually dominates over that of anions, 157 whereas electronic transport may be dominated by either electrons or holes. Environmental conditions such as pH and applied potential, as well as material characteristics such as metal orientation, epitaxy, and misfit at the oxide/film interface, oxide structure, oxide composition and ionic defect concentrations, control the interface reactions and ion transport through the oxide and its growth.…”