Electrochemical Waves on Patterned Surfaces:  Propagation through Narrow Gaps and Channels

The dissolution and corrosion of iron and certain types of steel can involve the propagation of electrochemical waves. Low-carbon steel plates covered by nitric acid solutions self-organize pseudo-two-dimensional wave patterns which share many features with reaction−diffusion waves in excitable systems. Here, we investigate the dynamics of these electrodissolution waves in the presence of geometrical constraints. A simple procedure for the preparation of insulating, millimeter-scale obstacles is presented, which allows the controlled, local protection of the metal surface. This method is used in the measurement of the material consumption rate per wave [(850 ± 50) nm/wave or 6−7 g/(m 2 wave)] as well as for the study of front propagation through narrow gaps and long channels. In channels, the wave velocity decreases with decreasing width from 10 to 4 mm/s. Propagation failures occur within the channel if its width is smaller than 0.2−0.4 mm. These results indicate that the obstacles have sink-like boundaries. For the estimation of the critical nucleation size in this system, we prepared short and narrow gaps that induce wave blockage for openings smaller than 0.65 ± 0.1 mm.