Semiconducting properties of passive films and corrosion layers on weathering steel

Effect of Rare Earth Ce on Microstructure and Properties of Q370qENHY Bridge Steel

To enhance the mechanical characteristics and corrosion resistance of bridge steel, three distinct groups of test steels with varying Ce contents were formulated. The objective was to investigate the influence of rare earth Ce on the microstructure, impact performance, and corrosion resistance of bridge steel. The addition of rare earth elements improves both the impact performance and the corrosion resistance of bridge steels. The present research systematically examines the impact of cerium (Ce) incorporation on the structural and impact performance of bridge construction steels, with particular emphasis on elucidating the fundamental mechanisms governing these modifications. This investigation establishes a comprehensive theoretical framework that facilitates the advancement of next-generation rare earth-enhanced high-performance steel alloys specifically designed for bridge engineering applications. The investigation reveals that rare-earth elements exert a significant influence on microstructural refinement, leading to the diminution of grain size. Additionally, these elements catalyze the modification of inclusion morphology in the test steel, transitioning from an irregular form to a spherical one, with a concomitant decrease in inclusion size. The tested steel with a rare earth mass fraction of 0.0025 wt.% has the best impact performance and the lowest corrosion rate. The impact performance improved by 7.37% compared with the experimental steel without the addition of rare earth elements. The incorporation of rare earth elements has been observed to promote the accumulation of Cu in the rust layer, which contributes to the improved stability of the layer. Concurrently, it has been noted that, for equivalent periods of corrosion exposure, there is a positive correlation between the arc radius of bulk resistance and the incremental levels of rare earth Ce.

Semiconducting Behaviour and Corrosion Resistance of Passive Film on Corrosion-Resistant Steel Rebars

Chloride-induced corrosion of steel rebars is one of the major causes of the premature failures of reinforced concrete structures served in different environments. This paper investigates the semiconducting behaviour and corrosion resistance of the passive film formed on the corrosion-resistant rebars exposed to simulated concrete pore solutions with different pH values and chloride concentrations. The electronic properties of the passive film were studied using potentiodynamic measurements and capacitance measurements (Mott-Schottky analysis). The results indicate that, firstly, the passive film of corrosion-resistant steel rebar shows n-type semiconducting behaviour with shallow and deep donor states in the band gap during passivation, and the deep donor energy level of corrosion-resistant steel rebar passive film is not sensitive to the decreasing pH value; secondly, under the same conditions, the passive film of corrosion-resistant rebars has a larger negative flat-band potential and thicker space charge layer than hot-ribbed rebars; thirdly, n-type semi-conductivity at a higher potential disappears once the chloride concentration at the rebar surface attains the chloride threshold value; and finally, a reverse charge layer forms on the surface of CR rebar at 0.50 V potential.