Investigation of Anodic Behavior of Nickel in H2SO4 Solutions Using Galvanostatic Polarization Technique. I. Kinetics and Thermodynamic Approach
S. Abd El Wanees, M. Abdallah, Arej S. Al-Gorair, Fahd Tirkistani, Sameer Nooh, R. Assi
Abstract
The electrochemical passivation behavior of Ni in H 2 SO 4 solutions was studied by the galvanostatic anodic polarization method. The data of the polarization curves relied on the polarizing current, I imposed , acid concentration, C, and the temperature, T. The polarized curve elucidated various characteristic regions confirming various oxidation processes. The 1 st region is recognized by a rapid jump in the Ni electrode potential E (zone I), due to the decay of H 2 over-voltage. A large discrete 1 st potential arrest, a , coincides with the formation of Ni + ions, while the 2 nd potential arrest, b , matches the electro-oxidation of Ni + ions to Ni 2+ ions. The second increase in the potential, E (zone II), harmonizes the onset of passivity due to the countenance of Ni 2 O 3 . The duration time, τ , of the two arrests a and b decrease with increasing the I imposed , T, and the acid concentration, C. The thermodynamics activation parameters, E a , Δ H a , and Δ S a for the dissolution and passivation processes are deduced and discussed.