THERMODYNAMICS OF ADSORPTION OF BRIGHTENERS ON POLARIZED NICKEL FROM WATTS BATH SOLUTION

The adsorption of coumarin, nitrocoumarin, and p-toluene sulfonamide o n nickel from Watts bath solution has been studied using a polarizatio n technique. The exchange current densities (i(o)) with and without ad ditives were evaluated using a Tafel relation. The addition agents inh ibited the deposition process. Surface coverages calculated from the i (o) values were fit into the Langmuir adsorption isotherm. Thermodynam ic parameters (DELTAG(a)o, DELTAH(a)o, and DELTAS(a)o) for the adsorpt ion of the addition agents have been evaluated using the Bockris-Swink les adsorption isotherm. The values of DELTAG(a)o are negative indicat ing the strong interaction and reactive inhibition of the deposition p rocess by these additives. The electrodeposition interaction is discus sed from the viewpoint of the adsorption of the additive molecules on the metal solution interface.