Electrochemical behaviors of different gradesof pure aluminum in alkaline solution

Effects of impurity (Fe, Si, Cu), temperature and Na2SnO3 on anodic behaviors of various grades of pure aluminum namely Al-1(99.999%),Al-2(99.99%),Al-3(99.82%) and Al-4(99.5%) in 4mol/L KOH solution have been examined by studying corrosion rate, polarization, open circuit potential (OCP, or E-ocp), discharge performance and transfer resistance values (R-t) of EIS. The results indicate that aluminum has higher activation and more severe corrosion with the temperature increase. When impurities (Fe, Si, Cu) content increases, aluminum has higher corrosion and achieving stationary open current potential (OCP) needs longer time. However, A1-3 has lower polarization and higher current density(400mA/cm(2),at 1.224V) than others at 50 degrees C. Meanwhile, for A1-3, the stationary OCP is about 120 mV more negative at 50 degrees C than at 25 degrees C. In order to achieve the stationary OCPs and avoid the appearance of tin oxidation peak, 20min is suitable soaking time for Al in 5mmol/LNa2SnO3 +4mol/LKOH solution. The optimal electrochemical behaviors of Al including corrosion-resistance, activation, OCP and shorter delay time of electrode potential, have been achieved by adding 5mmol/L SnO32+ into 4mol/LKOH solution.