Stress corrosion cracking investigation of copper in groundwater with ammonium under potential polarisation

The objective of this work was to study the stress corrosion susceptibility of copper in simulated ground water conditions in the presence of ammonium. The experiments were performed with potential controlled samples in order to simulate the existence of oxygen or other oxidising agents and their effects in the final repository. Potentials were selected so that the lowest potential was in the range where monovalent copper is stabile, the second potential being close to the Cu+/Cu2+ equilibrium, the third and fourth potentials being in the stability range of divalent copper. The experimental work consisted of mechanical material testing (slow strain rate tests) and ex situ fracture surface analysis of the samples. Also additional electrochemical tests were included in the study. The obtained results indicate that the SCC susceptibility on copper is the highest in the 0.1 M NH3 solution, where SCC was observed at the three highest potentials. And of these three potentials, the one close to Cu+/Cu2+ equilibrium showed rather strong SCC. Otherwise, no clear indications of SCC were observed in other solutions. Instead, general corrosion occurs especially at the highest potentials. (orig.)