Operando corrosion studies of steel for industrial waste management by ambient pressure XPS

Important results from the project

SSAB´s high strength steels (HSS) used in waste recycling equipment are exposed to corrosive environments. Developing HSS with specific surface oxides increases equipment´s useful lifetime and effectiveness. The aim was to quantify the thickness, composition and stability of the oxide layers formed on HSS grades in different corrosive environments. By applying anodic potentials in-situ with AP-XPS, the evolution of the outer and inner oxide layers could be measured, as well as the composition and continuity, and the thickness was calculated from the spectra using a layer model.

Expected long term effects

The stability and composition of the oxide layer is different for HSS surfaces corroded in a weak acetic acid solution as compared to a salt solution. The surface oxide of HSS in pH 4.5 electrolyte increased in oxide thickness. At increasing corrosion currents, Fe3O4 increased in HX450 whereas Cr2O3 and Cr hydroxide are depleted from the oxide layer in HXHiAce. In the salt solution, both materials increased in oxide thickness, but HXHiAce did not form a continuous layer or replenish Cr. The effect is positive but limited, contributing to waste applications with a longer useful lifetime.

Approach and implementation

Experiments were performed at the HIPPIE beamline, MAX IV in Lund. Samples cut from HX450 and HXHiAce plates were polished to 3 µm roughness, and cleaned by ethanol and acetone. These were mounted in a sample holder with a SCE and a Pt counter electrode, then placed on the manipulator in the vacuum chamber, then set to 18-20 mbar. To run electrochemical reactions, electrodes were dipped in the beaker with electrolyte (CH3COOH resp 0.01M NaCl) and potential was applied by potentiostat connected to the manipulator. After a fixed time electrodes were pulled out and APXPS spectra were measured.