Rectification by Anodic Oxide Films on Zirconium

Abstract

The electrical conduction characteristics of anodic oxide films on zirconium were studied using evaporated metal and aqueous electrolyte contacts. All the films tested showed electrolytic rectification. In the dry systems rectification was not observed, but asymmetry in conduction was pronounced in the case of films grown in the nitric acid solution. Capacitance measurements under an applied d‐c bias provided no positive evidence for the presence of a p‐n junction either in the bulk oxide or at the oxide‐electrolyte boundary. The conduction characteristics were influenced by the anodizing electrolyte used: (i) the relatively flaw‐free films grown in KOH gave nonohmic but nearly symmetrical I–V curves; (ii) a porous and hydrated oxide film, essentially monoclinic zirconia, grown in HNO3 resulted in asymmetric conduction; and (iii) phosphate ion incorporation in oxides grown in a solution containing phosphoric acid led to space charge limited current flow characteristics.

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

“…It is meaningful to observe that the curvature in the log tial capacitance of ZrO2 electrodes was frequency dependent in the range 10 Hz-30 kHz (21); and (ii) a nearly constant C value, slightly increasing in the negative electrode potentials range, was measured by decreasing UE from +3.0 to --1.4V vs. MSE when a large drop in the measured capacitance was observed. Such a behavior can be attributed to the electrical behavior as insulators of the ZrO2 anodic films (22) analogously to the reported findings on HfOs anodic films (23). A very small hysteresis in the C vs. UE plots was recorded in the reversal scans of the potential sweeps in accordance with the observed time-dependence of the ZrO2 films/electrolyte interface capacitance.…”

“…(26), Eq. [21]- [22]) x* = apace-charge screening parameter; Eo = surface charge electric fiel l; E* = kT/zea; Vc~ = electrode potential v~lues estimated by using Eq. [4] and [5] at the second minimum of the interference curces; and Ve~p = experimentally measured cell voltage in the interference curves corrected for the ohmic drop.…”