High field kinetic processes in anodic oxide films on aluminium. II. Current transients for constant field conditions

1968 ◽  
Vol 46 (4) ◽  
pp. 549-556 ◽  
Author(s):  
M. J. Dignam ◽  
P. J. Ryan
Keyword(s):  
Field Strength ◽  
Oxide Films ◽  
Ionic Current ◽  
Anodic Oxide ◽  
Field Conditions ◽  
Electrolysis Cell ◽  
Constant Field ◽  
Zero Field ◽  
Anodic Oxide Films ◽  
Current Transients

Anodic oxide films were formed on high purity aluminium (99.996%) in a glycol–borate electrolyte. Following aging of the films under zero field conditions either at room temperature or 60 °C the electrodes were returned to the electrolysis cell where the anodic overpotential was increased rapidly until a predetermined value was reached, then maintained constant. The ensuing current transients were recorded and analyzed. As little film growth occurred during these measurements the conditions correspond closely to constant field strength. For sufficiently low field strengths the observed current decreased monotonically with increasing time. No single empirical equation could be found to represent these data, although they appear to be in the nature of charging currents rather than ion currents. For somewhat higher applied fields the current is observed to decrease initially, reach a minimum, and then increase approaching ultimately the steady-state ion current for the applied field strength. These data can be accounted for satisfactorily by only the polarization theory of ionic current transients.

scholarly journals THE THEORY OF FORMATION OF HIGH RESISTANCE ANODIC OXIDE FILMS

1959 ◽  
Vol 37 (1) ◽  
pp. 276-285 ◽  
Author(s):  
L. Young
Keyword(s):  
Field Strength ◽  
Oxide Films ◽  
Anodic Oxide ◽  
The Body ◽  
Oxide Interface ◽  
Oxygen Ions ◽  
Anodic Oxide Films ◽  
Frenkel Defects ◽  
Mobile Ions ◽  
Cation Sites

Various models are considered for the growth of anodic oxide films (metal ions mobile). In general, a transition is expected, as the thickness of the film is increased, from control by the metal/oxide interface (Cabrera and Mott) with very thin films to control by the movement of ions through the body of the film (Verwey), with the concentration of mobile ions taking up the value (p, say) which gives electroneutrality. The field strength only varies with thickness in the transition region of thickness. Dewald's theory is the special case of p zero, which gives a field increasing continuously to infinite thickness. The high field production of Frenkel defects (with the vacant cation sites immobile and the interstitial ions mobile) as postulated by Bean, Fisher, and Vermilyea, and a slight mobility of oxygen ions are two processes which would allow p to vary with the field strength, and which would, therefore, give rise to "overshoot" in the transients in the field strength which occur when the applied current is suddenly changed. However, if the field strength is sufficiently great to produce Frenkel defects it would be expected to be sufficiently great to cause the vacancies to be mobile. This case is considered. Finally, it is noted that in an amorphous oxide it is difficult to maintain a distinction between lattice and interstitial ions, and, in fact, a range of site energies and jump distances would be expected. Some of the observed features (including "overshoot", and Tafel slope anomalies) of the kinetics for tantalum may, therefore, be due simply to the fact that the oxide is amorphous.

High field kinetic processes in anodic oxide films on aluminium. I. Current transients for linearly changing electric field strength

1968 ◽  
Vol 46 (4) ◽  
pp. 535-548 ◽  
Author(s):  
M. J. Dlgnam ◽  
P. J. Ryan
Keyword(s):  
Steady State ◽  
Field Strength ◽  
Electric Field ◽  
Electric Field Strength ◽  
High Field ◽  
Oxide Films ◽  
Anodic Oxide ◽  
Anodic Oxide Films ◽  
Differential Field ◽  
Field Coefficient

Anodic oxide films were formed on high purity aluminium (99.996 %) under steady-state conditions (current and field strength constant) in a glycol–borate electrolyte until the film reached a predetermined thickness at which point the anodic overpotential was changed rapidly and in a linear manner. As little film growth occurred during these linear sweeps, the conditions corresponded to linearly changing field strength. From these data, the transient differential field coefficient, β1, defined by[Formula: see text]where i and E are the ion current density and electric field strength and Es the steady-state formation field strength, was determined β1 was found to vary linearly with Es in the manner [Formula: see text] with [Formula: see text] A recent theory proposed by one of us (M. J. D.) predicts that the parameter [Formula: see text] should have the same value as that deduced from the field dependence of the steady-state differential field coefficient,[Formula: see text]Such agreement was indeed found, two independently determined 'steady-state' values of [Formula: see text] being 3.53 ± 11% and 3.11 ± 14% ÅV−1. A direct comparison of the present results with previous steady-state results gave βs/β1 = μs/μ1 = 3.09. More complex features of the transients were also found to be in accord with the above theory, but could be accounted for almost as well by an earlier theory, the so-called high field Frenkel defect theory.Dielectric constant values determined from the current discontinuity appearing upon application of the linearly increasing field gave K1 = 8.35 ± .1 for transients commencing from steady-state conditions and K1 = 8.85 ± .2 for films formed then 'aged' at E = 0 before measurement. Certain anomalies with regard to the charging current were apparent.

Crystallization in anodic oxide films

1988 ◽  
Vol 28 (1) ◽  
pp. 43-56 ◽  
Author(s):  
J.S.L. Leach ◽  
B.R. Pearson
Keyword(s):  
Oxide Films ◽  
Anodic Oxide ◽  
Anodic Oxide Films

Study of anodic oxide films formed on solid-state sintered SiC-ceramic at high anodic potentials

2021 ◽  
Author(s):  
M. Schneider ◽  
L. Šimůnková ◽  
A. Michaelis ◽  
M. Noeske ◽  
J. Aniol ◽  
...  
Keyword(s):  
Solid State ◽  
Oxide Films ◽  
Anodic Oxide ◽  
Anodic Oxide Films ◽  
Sic Ceramic
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