Imaging by photoelectrochemical techniques of Laves-phases γ-Zr(Fe,Cr)_2 thermally oxidized on Zircaloy-4

摘要

The oxidation of γ-Zr(Fe,Cr)_2 intermetallic particles during the thermal exposition of Zircaloy-4 at 470°C in oxygen was investigated with PhotoElectroChemical techniques (PEC). Via the measurement of bandgap, haematite Fe_2O_3 (2.2 eV), rhomboedric solid solution (Fe_xCr_(1-x))_2O_3 (2.6 eV) and chromia Cr_2O_3 (3.0 eV) phases were identified as components of oxidised particles. Evolution of size, lateral distribution and density of these particles was studied in function of zirconia scale thickness. During the first stage of oxidation, the density of oxidised particles increased with thickness but decreased during a second stage, highlighting in an innovative way the phenomenon of haematite and chromia dissolution in the zirconia matrix. It is concluded that PEC techniques represent a sensitive and powerful way to locally analyse the various semiconductor phases in an oxide scale at the micron scale.