Corrosion of copper in sulphide containing environment: the role and properties of sulphide films: Annual report 2019

OFP-copper samples were exposed to anoxic simulated groundwater with varying amounts of sulphide addition (0-640 mg/L) to study the effect of the presence of sulphides in simulated repository conditions. Copper samples in two states were used: in ground/polished state and pre-oxidised state (7 days, 90 °C in air). The duration of exposure was 4 months in these experiments, to get initial results aiding the selection of experimental parameters for the longer term experiments later. In addition to this, an experiment with the exposure duration of 2 months was conducted. Several characterisation methods were used: visual examination, scanning electron microscopy and energy dispersive X-ray spectroscopy, scanning Kelvin probe force microscopy and high-energy X-ray diffraction. Moreover, electrochemical data was collected throughout the experiment. The results indicate that the addition of sulphide in the simulated groundwater has a distinct effect on copper. The surfaces were affected already at the lowest addition level (3 mg/L), however there was local variance in the surfaces. The electrochemical measurements suggested that the corrosion was the highest with higher sulphide addition (320 mg/L was the highest electrochemically measured sample). Open circuit potentials of the samples were the lower, the higher the addition of sulphide was. Main preliminary conclusion from the synchrotron XRD measurement was that in addition to the copper sulfide compounds formed on the surface, the exposure also induced the structural change of the surface region of copper, which may increase the susceptibility to cracking under mechanical stress. Further measurement and analysis of H and S ingress into the copper are needed to draw a safe conclusion. The water measurements indicated that there may be a reaction between the simulated groundwater with added sulphide and the vessel, and this needs to be considered before the next experiment. As the next steps, the longer term experiments are set up, and the further/more detailed characterisation of the samples continues.