The Study of Ni Corrosion in Dependence of Time

The aim of the present study is to investigate Ni corrosion behavior in solutions containing 0.25 M citrates at various pHs as a function of the immersion time. The corrosion tests consisted of electrochemical impedance spectroscopy (EIS), and chronopotentiometric and chronocoulometric measurements. The registration of the electrochemical data was started after pre-treatment of Ni electrode at potentials ranged – 0.7 V to – 0.5 V (NHE) during 300 s. Parameters of the corrosion process were determined upon the analysis of obtained impedance spectra that were interpreted in frame of equivalent circuit containing constant phase element is connected parallel to transfer resistance (related to corrosion resistance), then all these elements in series are connected to the solution resistance. The open circuit potentials (OCP) of Ni are settling within 1000 s and changes of OCP are obtained from – 0.7 V to ( – 0.1 ÷ 0.1) V. The values of the transfer resistance also depend on time: in acidic media almost constant values are settled within 500 s, whereas in alkaline media the steady and relatively fast increasing of corrosion resistance is observed. That might be explained by the developing passivity of the surface. The thickness of passive films were evaluated as about 100 – 300 layers of NiO or Ni(OH)2 formed on the surface in the alkaline media