The Corrosion Behavior of Nickel 270 in Phosphate-Containing Solutions

Abstract

The corrosion behavior of Ni 270 in 1M H 3 PO4, NaH2 PO4 , Na2 HPO4 , and Na3 PO4 solutions, in the 25 to 100 C temperature range, was studied. Potentiokinetic and potentiostatic polarization curves were drawn in the four solutions. Anodic kinetics of Ni 270 increased with increasing temperature and increasing acidity of the solution.Corrosion potentials in 1 M H 3 PO4 and 1 M NaH 2 PO4 solutions were in the active corrosion range at all tested temperatures. Active to passive transition took place by successive steps at 25 and 50 C in both solutions. The first retardation in the anodic kinetics of Ni 270 seemed to be related to NiO formation and the second one to Ni 304 formation. At 75 and 100 C only one active peak was observed. Peak potential values were close to Ni/Ni 3 04 redox potentials for the 1M H 3 PO4 solution and to Ni/NiO redox potentials for the 1M NaH 2 PO4 solution.Passivation potential values for both solutions in the 25 to 100 C range were close to the corresponding Ni/Ni203 redox potentials.Potentiostatic polarization curves of Ni 270 in 1M Na 2 HPO4 solution showed that corrosion potentials were in the passive range at 25, 50, and 75 C. An active peak was obtained at 100 C, followed by a passive region. The corrosion potential of Ni 270 in the 1M Na 3 PO4 solution was in the passive zone in the 25 to 100 C temperature range.Film growth mechanism of the oxide film in the passive range was estimated from current density decay curves at constant potential. The initial state of anodic film growth follows a logarithmic or an inverse logarithmic law for most of the testing conditions. Film thickness values were also estimated in 1 M H 3 PO4 and 1 M NaH 2 PO4 solutions at 25 and 50 C.

Spectroelectrochemical Studies of Nickel Oxidation in Aerated Phosphate Solutions

“…One of the possible reasons for the popularity of a phosphate buffer to study Ni oxidation could be that one can achieve a wide range of pH conditions without substantially changing the nature of anions in solution. The oxidation of Ni in phosphate solutions at this pH (5.4) has not been studied by either ellipsometry or conventional electrochemical techniques. − ,,, Previous studies of time dependence of film growth in phosphate have largely been under deaerated conditions. ,, Film formation under open-circuit conditions in aerated phosphate at pH 4.5 and 9.1 has been reported earlier . It will be demonstrated in this work that the exact sequence of potentials to which the electrode has been subjected has a bearing on growth modes of the surface oxide/hydroxide.…”

“…The electrochemical oxidation of Ni has been a topic of study for many years. − Many electrochemical methods have been combined with various techniques, including ellipsometry, ,,,,− , ultrahigh vacuum surface analytical methods, ,,,,,, UV−visible reflectance spectroscopy, ,− , X-ray absorption spectroscopy, surface-enhanced Raman spectroscopy, , scanning tunneling microscopy, , and quartz crystal microbalance methods, to obtain information about both the active dissolution of Ni and passive film composition. According to the literature, − …”