Nano structure of the rust formed on chromium bearing steel in concrete after Wet and dry corrosion test

Abstract

Wet and dry corrosion tests using a NaCl solution were performed on Cr bearing steels in concrete. The nano-scale structure and electrochemical behavior of the rust were analyzed by TEM (Transmission Electron Microscopy) and EIS (Electrochemical Impedance Spectroscopy). The carbon steel (SM) had large amount of corrosion and produced cracking in the concrete after corrosion test. On the other hand, the Cr bearing steel showed much less corrosion, and had no concrete cracking. After corrosion test, EIS measurements were performed on the samples to determine rust resistance (R rust) and corrosion resistance (R t) of the different steel types. The R rust and R t of Cr bearing steel were much larger than those of SM after corrosion test. SEM (Scanning Electron Spectroscopy) with EDS (Energy Dispersive Spectroscopy) showed that Cr and Si were enriched in inner rust of the Cr and Si bearing steel. TEM showed that nano-scale complex iron oxides containing Cr and Si were formed in inner rust. It was found that the Cr bearing steel formed nano-scale iron complex oxides containing Cr and Si in inner rust, which increased R rust and R t, and suppressed the corrosion by chloride ions in the concrete.