Electrochemical Preparation of a Carbon/Cr-O-C Bilayer Film on Stainless Steel in Molten LiCl-KCl-K₂CO₃

Abstract

A carbon film was electrochemically deposited on 304 stainless steel by reduction of carbonate ions in molten LiCl-KCl-K2CO3. A Cr-O-C interlayer was prepared by a joint process of thermal exposure of the steel in air and subsequent electrochemical reactions in molten salt for the enhancement of adhesion between the carbon film and the substrate. The bilayer film was delaminated gradually using electrochemical polarization in an aqueous NaCl solution, and was characterized by XRD, SEM, and XPS. Chromium element aggregates in the oxide scale from the 304 stainless steel substrate during the oxidation process, and transforms to chromium oxycarbide during electro-deoxidation of the oxide scale and diffusion of carbon nucleated from electro-reduction of carbonate ions. The interlayer mainly presents the CrO1.13C0.12 phase, which contains Cr-C and Cr-O bonds confirmed by XPS analysis. The presence of the CrO1.13C0.12 interlayer is an important factor for a continuous and adhesive carbon film on 304 stainless steel.

Electrochemical deposition of tantalum carbide coatings in molten LiCl‐KCl‐K2CO3

“…In this study, TaC coatings have been successfully electro‐deposited on tantalum in molten salt. This process seems to have some similarities to the preparation process for carbon/metal‐O‐C composite films developed in our previous work . However, different deposits were obtained on metallic substrates.…”

“…Figure F shows the XRD pattern of the sample deposited on the tantalum substrate coated with an oxide layer, and the electro‐deoxidation had been performed prior to the carbon deposition. In addition to the diffraction peaks of TaC and Ta, a low bump was observed at approximately 2θ = 26°, which indicate traces of the noncrystalline structure of deposited carbon . Correspondingly, the SEM image in Figure E‐F shows the drastic aggregation of carbon particles above the carbide that creates a bilayer coating.…”

“…The electro‐deoxidation of the Ta substrate used in our work results in a micro‐roughness on the surface due to the removal of oxygen ions, which may accelerate the diffusion of carbon and Ta to each other . Moreover, the electro‐deoxidation treatment also helps carbon nucleation . Figure F shows the XRD pattern of the sample deposited on the tantalum substrate coated with an oxide layer, and the electro‐deoxidation had been performed prior to the carbon deposition.…”

Electrochemical preparation of carbon films with a Mo2C interlayer in LiCl-NaCl-Na2CO3 melts

“…[6][7][8], and an interlayer could also be easily prepared on the substrate by electrochemical reactions, which enhanced the adhesion of the carbon film to the metal substrate [9][10][11][12][13]. Massot et al investigated the electrodeposition of carbon films from carbon ions in molten alkaline fluorides on copper and gold electrodes at a temperature range of 700-800 • C using cyclic voltammetry and chronopoteniometry [6].…”

“…Siambum et al reported the utilization of carbon dioxide for electro-carburisation of mild steel in two different molten salts, Na 2 CO 3 -NaCl and Li 2 CO 3 -K 2 CO 3 , at 800 • C [8]. Song et al conducted a series of experiments in molten LiCl-KCl-K 2 CO 3 to prepare a Ti-O-C gradient on titanium electrode and a carbon/Cr-O-C bilayer film on stainless steel respectively at 500 • C [9][10][11]. Kaplan et al obtained titanium carbide coating on a titanium electrode by cathodic deposition in molten Li 2 CO 3 at 900 • C and the reaction mechanism was investigated in detail [12].…”