Invariant hydrodynamic patterns formation: fast rotating disk electrode under dissolution conditions

摘要

During the dissolution of stainless steel in a highly concentrated iron(III) chloride (3.5 M) solution, patterns in the micrometer range can be observed on the surface of the rotating disk. These patterns are formed by convection vortices in the direction of hydrodynamic flow. At fast rotational speeds (2000-6000 rpm), the etched patterns are spiral in shape. By digitizing the observed patterns, the mathematical equation for the spirals can be determined and a description obtained for their invariant logarithmic shape, with an aspect ratio of 1/2~(1/2) for the radial and tangential velocity. A comparison with classical hydrodynamic equations for the rotating disk electrode and the analysis of previous investigations of patterns formed on slowly rotating disk electrodes provides an explanation for chemically induced invariant hydrodynamic pattern formation.