Corrosion Behavior of Zn-Co Alloy Coating from Acid Sulphate Bath

Optimization of sulphate bath for deposition of a smooth and uniform zn-co alloyover mild steel is discussed in the present work. electrodeposition was done using thiaminehydrochloride(thc) and citric acid (ca) as additives in combination. the bath followedanomalous codeposition with preferential deposition of zn over noble co. the experimentalresults reveal that a bright zn-co alloy having ~1.06 wt. %co was showing peakperformance against corrosion in compliance with other physical properties like reflectance,hardness, thickness and adhesion. the dependency of bath composition, current density,partial current density, ph and temperature on deposit properties like reflectivity, corrosionresistance were discussed. deposition was carried out under different condition of c.d.’s andmolar ratio of [co+2]/[zn+2]. no transition c.d.’s at which codeposition behavior changedfrom anomalous to normal type was observed. cyclic polarization measurement wasperformed to study the nature of corrosion taking place in the corrosion cell. anelectrochemical behavior of zn-co alloy electrodeposition in alkaline solutions was studiedusing cyclic voltammetry technique. the increase in the corrosion resistance of coatingsattributed to the formation of n-type semiconductor film at the interface was confirmed bymott-schottky (m-s) plot with straight line having positive slope. the composition ofdeposits were determined by colorimetric method and confirmed by edx analysis. surfacemorphology of the deposits was examined using scanning electron microscopy (sem). thephase content was examined by xrd analysis at different current densities. a stable acidsulphate bath has been proposed for bright and uniform deposit of zn-co over mild steel anddiscussed