Role of Thiamine Hydrochloride and Gelatin on the Electrodeposition of Zinc

Abstract

SUMMARYA search for a non-cyanide zinc plating bath resulted on the development of a zinc acetate bath. To obtain bright zinc deposits, thiamine hydrochloride and gelatin were added. Hull cell studies revealed that in presence of 3 g dm−3 thiamine hydrochloride a bright deposit was obtained at a current density above 2.5 A dm−2. Addition of 3 g dm−3 gelatin produced a bright yellow tinge deposit above 2.5 A dm−2. Voltammetric studies carried out at a glassy carbon electrode in the plating solution revealed that in the pH range of 4.5-5.5, zinc acetate complexes underwent successive reduction to zinc. Acetate ions and pH affected both the dissolution and deposition of zinc. The dissolution of zinc took place with the participation of OH− ions. Gelatin molecules adsorbed on the electrode surface. They favoured both zinc dissolution and deposition and prevented hydrogen evolution in the potential range of interest. Thiamine hydrochloride caused a reduction in zinc dissolution and deposition rates but favoured hydrogen evolution.