Research Of Tin Ion Transformation In PSA Tinplating Bath And Corrosion Resistance Of Tin Coatings

The high-speed tin plating solution,which uses phenol sulfonate (PSA) as the main composition, has the excellent performance of friendly environment and high efficiency. In the process of electroplating, the Sn will translate from Sn (II) to Sn (IV) with the continuous electrodeposition. The performance of electrolyte and electroplating coating can be effected by the translation of tin ions.In this thesis, the concentration of tn ions was determined by iodometric method. The measurement methods, which consisted of metallography, scanning electron microscopy, electrochemical experiment, porosity experiments and medium-sized salt spray test, were used to character the surface morphology and the corrosion resistance. From the rsults, it was shown that the content of Sn (IV) was the lowest and the corrosion resistance was the highest when Sn (II) was at 28g/L.When in the static (non-plating) state of PSA tin plating solution, the five facts, which consisted of static placement, mixing placement, plating temperature, blowing air and blowing oxygen, were studied to investigate the transformation of tin ions and the tin slury. From the results, it was shown that the most tin slurry was produced in condition of blowing oxygen. The amount of tin slurry from high to low was plating temperature, blowing air, stirring place and static place in turn.In the state of dynamic (plating) on PSA tin plating solution, two experimental programs were designed. One of the programs was that the initializing concentration of Sn (II) was at 28g/L and no tin slurry existed. From the results, it was shown that the coating had the smooth surface and high corrosion resistance. With the increasing of Sn (IV) in the electroplating solution, the porosity increased, while the corrosion resistance decreased. Another program was that the concentration of Sn (II) kept always at 28g/L(supplying high concentration solution to the system when concentration lower than 20g/L). the results showed that the surface morphology of the coating was related to the Sn (IV) and the tin slury in the solution. The tin slurry, which effected the performance of coating, was also studied. The compositions of the tin slurry were determined by XRD. From the results, it was shown that the compositions of the slurry was the elements of C,O,S and Sn. The main composition of the tin slurry was the SnO₂.