Leaching in active protective coatings observed in-situ by nano-CT using synchrotron radiation

Active protective coatings have been used and studied for decades. It is well known that the coating composition and microstructure determine the leaching behavior of the corrosion inhibiting species from the coating matrix. However, the leaching process on the microscale is a complex phenomenon important details of which remain obscured till today. Non-destructive spatial observation of the leaching process by nano-computed tomography using synchrotron radiation can contribute to a deeper understanding. Here, we report on the first truly in-situ 3D observation of microscale leaching. 3D images were generated while individual inhibitor particles dissolve from the coating matrix due to exposure to flowing water. The development and growth of pores and pore clusters was observed with a sequence of 3D images as a function of time demonstrating that leaching progresses by successive dissolution of inter-connected soluble particles. • First ever in-situ 3D observation of microstructural changes due to leaching. • 3D image sequence, obtained non-destructively, allows to track gradual changes in space and time. • Pores are observed to appear, merge, and form networks. • Measurements reveal pore network bottlenecks of widths 1-2 μ m. • Results strongly support the hypothesis that pore networks are the dominant way of ion transport.