Steel rebars with oxide scale, which is usually rich of defects, are widely used in industry. On the surface of the oxide scale, it is difficult to prepare a conversion film with desirable corrosion resistance because of the acidity of conventional conversion solutions. In this work, a sol–gel solution (pH = 11) was employed to retard the diffusion of cerium ions avoiding the formation of cerium salt precipitates at room temperature. After treatments, the diffusion of cerium ions would be accelerated and a protective conversion film would form to repair natural defects on oxide scale of steel rebars at a higher temperature. This strategy can not only avoid the peeling of the oxide scale by the acid solution, but also prevent a large amount of non-uniform precipitation of the film-forming Ce 3+ ions. The conversion film@oxide scale was characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), electrochemical impedance spectroscopy (EIS), potentiodynamic polarization curve (PPC) etc. It is found that the corrosion resistance of the prepared film@oxide scale was enhanced greatly when the concentration of added cerium ion (III) was 0.5 M, with pH adjusted to 11. After 30 days of immersion, R ct of surface treated rebar is more 180 times that of blank sample. The excellent corrosion resistance is closely related to the double-layer structure of the prepared sol-gel film, especially an about 2 nm inner layer of cerium oxide.
Song Yufeng,Zhang Yi,Shen Siyi,Pan Chenyu,Yan Dongming,Wang Zhiguang,Wang Su,Ruan Shaoqin
This study aims to explore the effects of different Ca(OH) 2 contents on the mechanical performance and corrosion behaviors of steel in Calcium sulfoaluminate (CSA) cement, where compressive strength, corrosion potentials of reinforcements, corrosion current density, pH of pore solution as well as mortar resistivity of CSA/Ca(OH) 2 mortar were researched, and the corrosion behaviors were further interpreted by the clarification of hydration phases through microstructural analyses. The initial results highlighted the positive effects of using adequate Ca(OH) 2 (~ 6%) in CSA mortar in terms of strength, yet its excessive addition could delay the subsequent hydration reaction of CSA. Meanwhile, with an increased quantity of Ca(OH) 2 , the amount of some hydration phases, such as Al(OH) 3 reduced, resulting from their reaction with Ca(OH) 2 . Finally, the corrosion current density increased with the reduced mortar resistivity when the reinforcement in CSA/Ca(OH) 2 system was corroded, and their relationship was also provided in this study.
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