Passive sampling, definition

The presence of a thin oxide/anodized layer on aluminium alloy surfaces may shift the electrochemical potential (ECP) to more noble values (passive state). In another CRP, ECPs on 1050 (99.5% aluminium) coupons exposed in the same spent fuel storage pool [9.1] were measured. These ECP values (with respect to a saturated calomel electrode) varied in the range 107-382 mV, depending on sample location with respect to the stored spent fuels. Although no definite trend could be observed, all the ECP values were positive, indicating immediate passivation of the coupons upon immersion in the pool water. Detailed ECP measurements on aluminium alloy coupons with surfaces polished by different techniques could help substantiate the observations made in this study. 

---