Mechanistic Study of Cast and 3D-Printed Stainless Steel Electropolishing in Acid Media and Deep Eutectic Solvents
Résumé
The mechanistic analysis of the electropolishing procedure of stainless steel (SS) was revisited using electrochemical impedance spectroscopy. Firstly, the control of the dissolution reaction by diffusion was confirmed with the linear dependence of the limiting current density as a function of the electrode rotation rate using the Levich's law. Nevertheless, varying the viscosity (by changing temperature from 35 °C-70 °C) show a direct relationship between the diffusion coefficient and the kinematic viscosity, irrespective of the cation concentration at the interface, thus suggesting a minor role in the diffusion limiting step. This limitation is therefore provided by the diffusion of an acceptor specie from the electrolyte toward the anode surface. To discriminate the role of water or mineral anion in the so-called acceptor model, a full descriptive model of the electrochemical behavior of interface was devised for analyzing electropolishing results obtained by electrochemical impedance spectroscopy (EIS) for both cast and additive layer manufactoring (ALM) 316L SS in aqueous acid electrolyte and in deep eutectic solvent (DES). It was shown that the model involving an acceptor specie allows to describe with a good accuracy the electrochemical behavior of the different systems at several potentials.