DIRECT MEASUREMENT OF THE THICKNESS AND OPTICAL-PROPERTIES OF ZIRCONIA CORROSION FILMS

By varying the angle of incidence during the measurement of interference fringes on oxide films from Zircaloy and Zr-2.5% Nb alloy specimens, oxidised in a number of environments, it has been shown that the largest source of the variation in fringe spacing with wavelength arises from changes in the phase shifts upon reflection and not from variation in the refractive index. The refractive index of the films measured was relatively constant for wavelengths from 2-10 mum, and only changed significantly when affected by the ZrO2 absorption bands. Numerical values for the refractive index lie in the range 2.0-2.2 and appear to vary with alloy, batch and oxidising environment. The extent of these variations will appear as more specimens covering these sources of variability are studied. No evidence for unexpectedly large pore volumes was found, but the difficulty in correlating a spot technique with the weight gain data, that give averages over the whole surface, prevents any accurate determination of the relation between weight gain and oxide thickness by this technique.