Fundamental Insights into the Stabilisation and Chemical Degradation of the Corrosion Product Scales

Carbonate stability plays a crucial role in clarifying the evolution and protection of the naturally formed corrosion scales on the steel surface in the application of geothermal production. In this paper, the stability of the corrosion scales from both micro and atomic level are studied via a combination of electrochemistry, surface analysis and first-principle calculation. The chemical and physical characterisation of various iron–calcium mixed carbonates are experimentally analysed and results are compared with the first-principle calculation. In the presence of Ca2+, the preferential loss of Ca during the dissolution experiments was observed, the interactions within the crystal weaken where Ca2+ co-precipitation, confirmed by a faster degradation rate for Ca0.51Fe0.49CO3 than FeCO3. This work reveals the degradation and protection performance of the naturally formed carbonate layers and provides insights into understanding the corrosion product stability and chemical breakdown of the corrosion scales.