External control of anodic dissolution mechanism of 100Cr6 in nitrate/chloride mixed electrolytes

Andreas Lesch,Chris Burger,Günther Wittstock ,Benjamin D Walther ,Jurgen Hackenberg

doi:10.5599/jese.2011.0004

Abstract

The anodic dissolution of 100Cr6 steel in neutral electrolytes containing sodium chloride and sodium nitrate was investigated potentiodynamically and galvanodynamically with a rotating disc electrode at room temperature. The total concentration of the mixed electrolyte was 3 mol L-1 with variation of chloride/nitrate mole ratios. The potentiodynamic linear sweep voltammograms (LSVs) in mixed electrolytes are similar to the LSVs in pure chloride electrolyte at lower current densities and switch to behaviour observed in pure nitrate electrolytes at higher current densities. Provided that both anions are present, it seems that the dissolution reactions at the steel anode are determined by the interface layer only. The effect of these layers on surface quality and current efficiency was also investigated in a flow channel applying galvanostatic pulses. An evidence for different dissolution mechanisms can be seen with an important influence of duty cycle and flow conditions. This allows external control of the desired dissolution mechanism in mixed electrolytes.

Highlights

Electrochemical machining (ECM) is often applied to deburring and shaping components made of e.g. iron and steels in aqueous inorganic salt electrolytes[1,2]
According to the reported results from Mao et al [18] we describe in this paper more detailed insights and process conditions under which the dissolution mechanism of soft annealed steel in chloride/nitrate mixed electrolytes can be externally controlled, i.e. switched between two mechanisms
In NaCl electrolyte a limiting current is reached because the concentration of reaction products increases to saturation

Summary

Introduction

Electrochemical machining (ECM) is often applied to deburring and shaping components made of e.g. iron and steels in aqueous inorganic salt electrolytes[1,2]. At lower current densities which occur at potentials below 1.6 V at the resting electrode, the dissolution mechanism must be dominated by the chloride anions and the LSV is very similar to the curve in pure chloride solution. With respect to the proposed mechanistic model, increasing θ leads to higher current densities at which the change of dominating mechanism occurs due to the transport of chloride anions from the bulk of the electrolyte through the diffusion layer to the steel surface.

Results

Conclusion