Environmentally Friendly Zr-Based Conversion Nanocoatings for Corrosion Inhibition of Metal Surfaces Evaluated by Multimodal X-ray Analysis

Chemical conversion coating as an effective corrosion inhibition has wide range of applications in industries and is of great expectation to be environmentally friendly and cost-effective. Zirconium-based (Zr-based) conversion coating using hexafluorozirconic acid with copper (Cu) additive on low carbon steel which improves anticorrosion and adhesion properties was studied using synchrotron X-ray and electron-based techniques. To understand the elemental evolution during coating formation process, in situ synchrotron X-ray fluorescence (XRF) microscopy has been applied to observe Zr, Cu, iron (Fe), and zinc (Zn) concentration evolution. By quantifying the density, average size, and size distribution of the cluster as a function of time and temperature, the growth mechanism of the coating can be concluded as a reaction-controlled mechanism. X-ray absorption near edge structure and X-ray photoelectron spectroscopy (XPS) were used to characterize the composition of the Cu-rich clusters embedded in the coating which was determined to be mainly Cu₂O, Cu, and CuF₂; the cluster composition varies from the surface to the internal region as determined by the depth-profiling of XPS. Our study shed light on the chemical and morphological evolution in environmentally friendly surface conversation coating and demonstrated new methodology in studying the coating formation via in situ synchrotron XRF.