An evaluation of the thickness and emittance of aluminum oxide films formed in low-temperature water

Abstract

The emittance of aluminum components exposed to low-temperature aqueous solutions were required for thermal analysis of a Loss of Cooling Accident for the Savannah River Site production reactors. Experimental data for the thickness and emittance of oxide films formed under these conditions were collected and reviewed. Correlations were developed for the oxide film thickness and corresponding total hemispherical emittance. Film thickness and emittance were also measured for the specific conditions of interest in order to verify the predictions based on the literature data. After one year of exposure in 30°C reactor moderator, the aluminum oxide film thickness is predicted to be 6.4 μm ± 10%; this value is relatively insensitive to exposure time. Some phenomena which would tend to yield thicker oxide films in the reactor environment relative to those obtained under experimental conditions were neglected, and the predicted film thickness values are therefore conservative (e.g. thinner). Dehydration of the film at elevated temperatures would result in a film thickness of 6.0 μm + 11%. The total hemispherical emittance for this film thickness (6 μm) can be expressed as ϵ h ( T) = 0.887(1.492–2.886 × 10 −3 T + 3.047 × 10 −6 T 2−1.18 × 10 −9 T 3), where T is temperature in K. This expression gives a total hemispherical emittance of 0.45 at 600°C. The one-sigma standard deviation for the total hemispherical emittance expression given above is 11%.