A study of the evolution of rust on weathering steel submitted to the Qinghai salt lake atmospheric corrosion

Abstract

The corrosion evolution of weathering steel in Qinghai salt lake atmospheres as a function of exposure duration (up to 30 months) was investigated by corrosion weight gain, XRD, SEM, EDX and electrochemical techniques. The results indicated that the corrosion kinetics was closely related to the characteristics of the rust layer including composition, structure and electrochemical properties. The weight loss monotonically increased as exposure time prolonged with the fluctuations of average corrosion rate. The rust composition was mainly changed from γ-FeOOH and β-FeOOH (6 months), via β-FeOOH and magnetite (18 months), to magnesioferrite and iowaite (30 months). Correspondingly, the rust structure altered from loose and porous (6 months), via relative dense and adherent (18 months), to incompact and discontinuous again (30 months). The result of electrochemical measurements showed that rust resistance was very small, indicating that the rust layer had a poor barrier function which cannot prohibit the corrosion of steel effectively. The presence of iowaite (Mg4Fe(OH)8OCl·4H2O), which could attract Cl ions due to its special structure, was detrimental to the corrosion resistance of the rust layer and responsible for the poor weatherability of weathering steel.