Investigation of the Inhibition Effect of Basic Oxygen Furnace Slag on the Corrosion of Galvanized Steel

Master thesis (2015)

Authors

Contributors

J.M.C. Mol (mentor)
Department
Materials Science & Engineering (Mechanical, Maritime and Materials Engineering) (TU Delft)
Copyright: © 2015 Van Dam, J.P.B.
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Published Date

27-08-2015

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Faculty

Mechanical, Maritime and Materials Engineering

Department

Materials Science & Engineering

Abstract

Basic oxygen furnace (BOF) slag is a by-product of the steel conversion process in a basic oxygen furnace. A previous study at Tata Steel in Ijmuiden has discovered the inhibition effect of BOF-slag on the corrosion of cold rolled- and hot-dip galvanized steel. This inhibition effect and its mechanism was studied in this work and its was attempted to incorporate BOF-slag as a corrosion inhibitor pigment in an organic coating. Its inhibition capacity was first assessed on bare galvannealed and hot-dip galvanized (Zn-Mg-Al) steel and its performance was benchmarked against commercially available corrosion inhibitors. The inhibition effect of BOF-slag on the corrosion of both substrates in a 0.1M NaCl aqueous solution was confirmed by linear sweep voltammetry and it proved to have the highest inhibition efficiency of all tested corrosion inhibitors. The inhibition mechanism was further studied by electrochemical impedance spectroscopy (EIS),ICP-MS, SEM-EDS and XPS. The results showed the slag solution consisted of colloidal silicates, which upon anodic dissolution of zinc react with the zinc cations and precipitate on the surface. A protective gel-like network film is deposited on the surface, hereby suppressing both the anodic and cathodic current and reducing the corrosion current density by almost two decades. A pigment was retrieved from the slag particles and was successfully incorporated into an organic waterborne coating and applied to both substrates. The corrosion resistance and barrier properties were evaluated by EIS and salt spray tests (SST). The results show the slag particles had a negative effect on the mechanical and barrier properties of the coating and caused severe damaging of the coating as a result of minor deformation. The particles showed no tendency to restore some of the corrosion resistance of the coating after damaging. Chemical analysis showed the pigment was retrieved from Ladle furnace slag instead of BOF-slag. This explained inability of the pigment to restore the barrier properties of the coating or to inhibit the corrosion of the underlying substrate.