Space Charge Effects on the Growth of Anodic Oxide Films on Zirconium Metal

Abstract

The kinetics of growth of anodic oxide films in different electrolytic solutions, and in a range 1–32 mA cm−2 of current density has been investigated. By interferometric measurements an increase in the electrical field strength has been measured with increasing film thickness at all current densities and in all solutions. This finding has been attributed to the existence of a mobile ionic space charge. A test of this hypothesis has been made by fitting the 1/COX vs. VE curves on the basis of Fromhold's theory. Nonlinear Tafel plots have been obtained in sulfuric acid and in carbonate solutions while a straight line behavior was observed in sulfamic acid solutions. Lower dielectric constant values also have been measured for films formed in the former two solutions which are known to give incorporation of anions in ZrO2 films. No incorporation of anions seems to occur when anodization process is performed in sulfamic acid solutions. Some discrepancies between experimental results and the existing theory have been pointed out.

Impedance spectroscopy study of anodic growth of thick zirconium oxide films in H2SO4, Na2SO4 and NaOH solutions

“…Although it is generally assumed that the dielectric constant of zirconia is close to 20 [4,20], values up to 38.3 can be found in the literature [21,22]. This parameter is described as depending upon the electrolyte used since some anions can be inserted in thick zirconium oxide layers [4,23,24]. High calculated dielectric constants can be due to an overestimation of the film thickness measured from the charge exchanged (e.g.…”

“…Correlation between the EIS data and the film thickness was made by means of Equation (4). For a given solution and sweep rate, v b , the dielectric constant e was estimated by fitting C f calculated from EIS data and several d assessed by SEM layer observation.…”

“…Thick oxide films can be obtained by sputtering, pulsed laser deposition, chemical vapor deposition and atomic layer epitaxy [3] and also by wet methods such as anodisation. This latter technique is based on the anodic electrochemical oxidation of the metal [4,5]. In the case of dielectric oxide films formed by anodisation, a high electric field must be maintained in the layer in order to control the growth kinetics.…”

“…Metallic zirconium is oxidized in Zr 4+ at the metal/oxide interface where it reacts with O 2) supplied by migration. The transport number of Zr 4+ is almost zero [4,5]. The film growth reactions are thus:…”

Comparative study and imaging by PhotoElectroChemical techniques of oxide films thermally grown on zirconium and Zircaloy-4

“…In these studies, ZrO 2 was mainly prepared by anodic oxidation, very seldom by thermal oxidation. The growth kinetics [10][11][12][13][14], electrical, optical and structural properties of films [14][15][16][17][18][19][20][21] were described in detail. Based on PEC experiments, the authors have assessed n-type semiconducting behaviour for thin anodic oxides and thicker thermal oxides [15,16,22], but they diverged on the value of band-gap energy of oxides.…”