Preparation Of Tin-Free Steel And The Formation Process Of Cathode

Tin Free Steel (TFS) is a tin-layer plate with plating chromium instead of tin-plating. It has lower cost, excellent performance, and is an ideal product instead of tin-plating and is a solution of lacking of tin resource. The surface of TFS is made up of Cr and hydrous oxide. Using the method of double solutions and steps prepare the mass of dissolved steel under 200mg·m^-2 by changing the technics conditions, such as the kinds of and concentration of the additives , plating technics parameters, the pH of the solution, adding the reverse electro-analysis etc. In this paper, the porosity and corrosion resistance could be analysised and studied with UV-vis Spectrphotometer, CHI604 and Salt Spray Test Box. The morphology of the TFS is studied by SEM and the composition of the film was analyzed by XPS .The thickness of metal Cr and hydrous oxide is tested by XRF.Three additives for KIO₃, H₂SiF₆ and HF are investigated . The influence of the concentration of additives on the thickness of chromium and hydrous oxide and the porosity and corrosion resistance is studied. The porosity is an important target of TFS and the mass of dissolved steel is under 250mg·m-2. Through the discussing and comparing of the three additives, the system of H2SiF6 could be used in big range of concentration and have bright deposition. The product has reached the required target. The image of SEM shows that adding the reverse electrolysis makes the surface homogenous. And the reasonable process parameters of the HF and H₂SiF₆ system are attained through orthogonal test.The composition and structure of the surface of TFS is investigated through XPS. The results show that the main composition of hydrous oxide film is made of Cr₂O₃. and Cr(OH)₃ or CrOOH , the Cr₂O₃ is in the outest layer. After spraying 4 mins,the outer layer (12-16nm) of hydrous oxide film is mainly made of Cr(OH)₃ or CrOOH , the linner layer is chromium.