Structure, hydrophobicity, corrosion, and tribological performance of saccharin-modulated cobalt electrodeposits

Abstract

The electrodeposition of cobalt coatings is widely utilized in various industrial applications. Saccharin is commonly added as an organic additive to modify deposition quality, but its influence on coating properties is not yet fully understood. This study examines how saccharin adsorption affects cobalt electrodeposition process and its role in altering the chemical, structural, electrochemical, tribological, and wetting characteristics of cobalt coatings. Linear sweep voltammetry showed saccharin blocks active sites, increasing overpotential and altering deposition. The morphological transition from pyramidal structures to a smooth surface was accompanied by a crystallographic shift from the (1120) to the (0002) orientation, with crystallite size decreasing by approximately 78 % at 0.6 g L- 1 saccharin. Atomic force microscopy and contact angle measurements showed that roughness decreased while hydrophobicity increased up to 0.3 g L- 1, where the highest contact angle of 130 +/- 2 degrees was recorded. At 0.6 g L- 1, surface roughness notably decreased, resulting in a lower hydrophobicity and a mirror-like surface. Corrosion analysis demonstrated improved corrosion resistance with increasing saccharin content, with the corrosion current density decreasing from 10.5 to 0.1 mu A cm- 2 at 0.6 g L- 1 due to lower roughness and incorporation of organic saccharin-derived species. Hardness increased from 326 HV (without saccharin) to 544 HV at 0.6 g L- 1, leading to a 75 % reduction in abrasive wear. However, higher saccharin concentrations resulted in increased crystallite size, reduced corrosion resistance, lower hardness, and higher wear, indicating a limit to saccharin's beneficial effects. These findings provide insights into role of saccharin in controlling the deposition mechanism and cobalt coating's performance.