In-situ Investigation of Metal Corrosion and Corrosion-Resistant Coatings by Micro-Beam X-ray Spectroscopy and Electron Microscopy

K. Chen-Wiegart, M. Ge, G. Williams, E. Nazaretsky, Y. Chu, J. Thieme, K. Kisslinger, E.A. Stach, H. Jiang, K. Foster, D. Vonk, KW. Chou, S. Petrash
Henkel Corporation,
United States

Keywords: corrosion, surface, metals, steel, in-situ, synchrotron, X-ray spectroscopy, X-ray fluorescence, electron microscopy

Summary:

The development of advanced materials and processes require equally advanced characterization methods that are non-destructive, have good spatial, chemical and temporal resolution, as well as capable of performing measurements under complex operating conditions. We conducted an in-situ investigation of a metal corrosion process and of the deposition of nano-scale anti-corrosion treatment with synchrotron radiation micro-beam X-ray Absorption Spectroscopy (XAS) and X-ray Fluorescence (XRF) spectro-microscopy, using a micro-fabricated liquid cell. The oxidation resistance of an untreated steel was compared to steel treated with a phosphate-free anti-corrosion conversion coating. XANES spectra, taken in-situ at the Fe K-absorption edge of the untreated steel, showed a gradual conversion of Fe(0) to Fe(III) within 30-60 min of exposure to a corrosive medium. XANES spectra taken of the treated steel showed however very little change upon exposure, with only a slight reduction in the X-ray peak intensity at the edge, indicating good resistance to corrosion. The kinetics of chemical conversion process was monitored using in-situ XRF micro-spectroscopy. The local structure and morphology of the conversion coating were characterized using X-ray micro-beam XAS and electron microscopy. EXAFS spectra at the Fe K-edge and electron microscopy images of the treated steel samples revealed the local structure and surface morphology that were different compared to the untreated steel surface. The combination of an in-situ setup with the chemical and spatial resolution of micro-beam X-ray Spectroscopy and Electron Microscopy enables detailed studies of corrosion, surface treatments designed to prevent it, and wide range of other electrochemical processes.