On the Use of Surfactant Polarity for Grain Boundary Engineering in Electrodeposited Cobalt Coatings and Its Direct Effect on the Coating Corrosion Behavior

Electrodeposition of cobalt coatings on mild steel was carried out by employing surfactants of different polarities (SLS (anionic), CTAB (cationic), and Triton X-100 (non-ionic). Corrosion behavior and micro-texture of the electrodeposited Co coatings were investigated and correlated. From electrochemical impedance spectroscopy (EIS) measurement, the resistance polarization (R_p) value which is a measure of corrosion resistance was determined. The highest R_p value was reported for the CTAB-containing coating followed by the SLS-containing coating and coating without surfactant The lowest R_p value was exhibited by the Triton X-100-containing coating The corrosion parameters (corrosion current density (i_corr) and corrosion potential (E_corr)) acquired from the potentiodynamic polarization analysis agreed with the trend in the R_p values. The coating with CTAB and the pristine coating showed a lower strain and higher crystallite size than the coatings with surfactants SLS and Triton X-100 which showed a higher strain and lower crystallite size. Pristine and Triton X-100-containing coatings showed strong (\(11\overline{2}0\)) texture and the coatings containing SLS and CTAB exhibited both (\(11\overline{2}0\)) and (\(0\overline{1}10\)) textures. As the textures exhibited by all the coatings were high energy, the observed distinct changes in the corrosion rate of the coatings were, therefore, correlated with the grain boundary constitution. A direct correlation was observed. The coating produced using the Triton X-100 showed the lowest corrosion resistance due to the presence of a higher fraction of high-energy high-angle grain boundaries (HAGBs). The CTAB surfactant-containing coating showed the highest corrosion resistance due to the lowest fraction of HAGBs, highest fraction of low-energy special boundaries along [\(0\overline{1}10\)] and [\(11\overline{2}0\)] axis, and highest fraction of CSL boundaries.