Stochastic and deterministic behaviours of 316 stainless steel pitting corrosion in phosphate-borate buffer containing sodium chloride

Abstract The pitting corrosion of 316 stainless steel (SS) in phosphate-borate buffer (pH 8.00) containing 0.5 M NaCl at 25°C is studied through current transients run under a constant potential step, potentiodynamic runs and scanning electron microscopy. According to the potential and time windows different laws for pitting kinetics are observed. For small number of pits, the kinetics of pit growth is governed by a stochastic law whereas for a large number of pits a deterministic law which corresponds to an instantaneous nucleation and growth is obeyed. At the initial stages two different rate constants for pit nucleation are obtained. This fact correlates with two well distinguishable types of pits observed through SEM observations. Results are discussed through a model involving the penetration of chloride ions through the passive film and the existence of at least two types of sites at the metal surface which in turn become centers of pit nucleation. Pit stability is directly related to the Cr(III) content in the passive layer which can be shifted by changing the applied potential with respect to that of the Cr2O3/CrO2−4 redox couple.

[1]  T. Shibata,et al.  Stochastic Theory of Pitting Corrosion , 1977 .

[2]  A. Arvia,et al.  Kinetics of passivation and pitting corrosion of polycrystalline copper in borate buffer solutions containing sodium chloride , 1985 .

[3]  G. Okamoto,et al.  THE INHIBITIVE ACTION OF BOUND WATER IN THE PASSIVE FILM OF STAINLESS STEEL AGAINST CHLORIDE CORROSION , 1980 .

[4]  G. Okamoto.  Passive film of 18-8 stainless steel structure and its function , 1973 .

[5]  U. Bertocci,et al.  An Examination of Current Fluctuations during Pit Initiation in Fe‐Cr Alloys , 1984 .

[6]  Norio Sato,et al.  Stochastic Process of Chloride Pit Generation in Passive Stainless Steel , 1976 .

[7]  T. Okada,et al.  Halide Nuclei Theory of Pit Initiation in Passive Metals , 1984 .

[8]  R. Davidson,et al.  Analysis of Passive Films on Stainless Steel by Cyclic Voltammetry and Auger Spectroscopy , 1985 .

[9]  G. Staikov,et al.  Monolayer formation by instantaneous two-dimensional nucleation in the case of electrolytic crystal growth , 1983 .

[10]  I. Olefjord,et al.  Surface Composition of Stainless Steels during Anodic Dissolution and Passivation Studied by ESCA , 1985 .

[11]  David E. Williams,et al.  Stochastic Models of Pitting Corrosion of Stainless Steels I . Modeling of the Initiation and Growth of Pits at Constant Potential , 1985 .

[12]  A. Arvia,et al.  The pitting of mild steel in phosphate-borate solutions in the presence of sodium sulphate , 1985 .

[13]  M. Y. Abyaneh,et al.  The electrocrystallisation of nickel , 1981 .

[14]  A. Arvia,et al.  The influence of temperature and the role of chromium in the passive layer in relation to pitting corrosion of 316 stainless steel in NaCl solution , 1986 .

[15]  A. Arvia,et al.  The kinetics and mechanism of the localized corrosion of mild steel in neutral phosphate-borate buffer containing sodium fluoride , 1985 .

[16]  O. J. Murphy,et al.  Chloride Ion Penetration of Passive Films on Iron , 1983 .