Electropolishing of NiTi shape memory alloys in methanolic H2SO4

The electropolishing of NiTi shape memory alloys was surveyed electrochemically. Anodic polarization of NiTi up to 8V was performed in various aqueous and methanolic H2SO4 solutions. The passivity could be overcome in methanolic solutions with 0.1moldm-3 < =CH2SO4 < =7moldm-3. The dissolution kinetics was studied in dependence of the polarization potential, the H2SO4-concentration, the water concentration and the temperature. For lower concentrations of sulfuric acids (CH2SO4 < =0.3moldm-3) electropolishing conditions were not observed for potentials up to 8V. The dissolution remained under Ohmic control. In the concentration range from 1 to 7moldm-3 a potential independent limiting current was registered depending linearly on the logarithm of concentration. The best results were obtained with a 3moldm-3 methanolic sulfuric acid at 263K which yielded an electropolishing current of 500Am-2 at a potential of 8V. Surface roughness as well as current efficiency showed an optimum under these conditions.