Electrochemical dissolution of cast iron in NaNO3 electrolyte

Abstract

The electrochemical dissolution of three cast iron types in NaNO3 electrolyte was investigated by cyclic voltammetry, chronoamperometry, and numerical simulations. The measurements were performed with commercially available materials with different iron matrix compositions and graphite particle shapes: lamellar graphite particles in a ferritic/perlitic matrix, spheroidal graphite particles in a ferritic matrix, and spheroidal graphite particles in a ferritic/perlitic matrix. With regard to electrochemical machining (ECM) applications, the measurements were performed in different kinds of flow cells which realize the high electrolyte flow of an ECM experiment. It could be shown that the electrochemical dissolution was especially influenced by the microstructure of the cast iron and the pH of the electrolyte. Electrochemical measurements as well as numerical simulations show that the graphite geometry and the matrix structure are responsible for inhomogeneities of the electric field in the outer sample surface region which were formed during the dissolution process. The resulting shape of the electric field is responsible for different dissolution mechanisms. The kinetics of the dissolution reaction was influenced in the same manner. Finally, it was found that an alkaline electrolyte pH impedes the dissolution process, whereas no significant difference can be observed between acidic and neutral electrolytes.