Electropolishing of stainless steels in a choline chloride based ionic liquid: an electrochemical study with surface characterisation using SEM and atomic force microscopy

Abstract

We have studied the anodic dissolution (electropolishing) of various stainless steel alloys in an ionic liquid comprising a 2 : 1 stoichiometric mix of ethylene glycol (EG) and choline chloride. We have used a combination of electrochemical and spectroscopic methods together with in situ liquid probe microscopy. We discuss the role and influence of the surface oxide passivation layer, characterized here by X-ray photoelectron spectroscopy (XPS) and linear sweep voltammetry, on the polishing process. We address the question of dealloying during the polish in order to contribute to our understanding of the viability of the ionic liquid as a replacement industrial electropolishing medium; the current commercial process uses a corrosive mixture of phosphoric and sulfuric acids. Also, we present data from ex situ and in situ liquid AFM studies giving both a qualitative and quantitative insight into the nature and scale of morphological changes at the steel surface during the polishing process.

Electrofinishing of metals using eutectic based ionic liquids

“…A new process has been developed for electropolishing stainless steel using a choline chloride/ethylene glycol eutectic. [59][60][61] The operating conditions are similar to the existing acid based solutions and represent simple drop-in replacement technology. Abbott et al 60 have shown that the electropolishing mechanism is fundamentally different in an ionic liquid to an aqueous acid solution.…”

A review on electrochemical properties of choline chloride based eutectic solvent in mineral processing

“…The mechanism of copper nucleation was studied using chronoamperometry and it was shown that progressive nucleation leads to a bright nanostructured deposit. The current efficiency of copper deposition in this system is near 100 % ( Abbott, et al, 2006) Extraction and dissolution using deep eutectic solvents: A voltammetry study was carried out in ethaline based eutectic solvent containing chalcocite (Cu 2 S) and chalcopyrite (CuFeS 2 ). The scan rate was maintained at 10 mV at room temperature.…”

Electropolishing of Re-melted SLM Stainless Steel 316L Parts Using Deep Eutectic Solvents: 3 × 3 Full Factorial Design

“…Abbott and colleagues introduced a new alternative for electropolishing based on a mixture of choline chloride and ethylene glycol, a type III deep eutectic solvent called Ethaline 200 [6]. This approach gave considerable benefits, including high current efficiency, negligible gas evolution at the anode/solution interface and the use of a relatively benign liquid compared to the acid mixture solution normally used [14]. Nowadays, applications of ionic liquids range from fuel desulfurization to organic synthesis, catalysis, electrochemistry and precious metal processing.…”

“…Recently, Abbott and colleagues have introduced the concept of Deep Eutectic Solvents (DES) as a sub-category of ionic liquids [6,13,14,[17][18][19]. The DES is a fluid resulting from the mixing of two or three components which are capable of combining each other, frequently through hydrogen bond interactions.…”