Revealing the temperature effects on the corrosion behaviour of 2205 duplex stainless steel from passivation to activation in a CO2-containing geothermal environment

•The passive film at 150 °C is an amorphous-like structure, mainly containing Cr2O3 and Cr(OH)3.•At 300 °C, the nanoscale passive film is replaced by microscale FeCr2O4, CrOOH, and NiFe2O4 layers.•A Ni-rich inner layer was detected in both temperatures of 150 °C and 300 °C via TEM analysis.•pCO2 has no significant effect on the corrosion behaviour of 2205 DSS under the test conditions.•The formation mechanism of the corrosion product scales on 2205 DSS at 300 °C were discussed. The temperatures and pressures influencing the formation mechanism of the passive film and corrosion products, as well as passivation performance of 2205 duplex stainless steel (DSS), were systematically studied via immersion tests, electrochemical measurements, and various advanced surface techniques. The results indicate that the passive film at 150 °C was an amorphous structure, while the corrosion products were comprised of nano-polycrystalline FeCr2O4, CrOOH, and NiFe2O4 at 300 °C. A Ni-rich layer was observed at the inner interface in both temperatures. A thermodynamic assessment was to validate the experimental results and reveal fundamental corrosion mechanisms of 2205 DSS exposed to the geothermal environments.