An important factor in determining the breakdown of the barrier layer of the passive film on carbon steel in halide-containing solutions is the anion size. In this study, the influence of the size of aggressive anions on the passivity breakdown of UNS K02700 grade carbon steel exposed to saturated Ca(OH)2 solutions with the addition of different halides was investigated by using the potentiodynamic polarization (PDP) experiments. The PDP results were interpreted by using a mechanistic description based on the Point Defect Model (PDM). The experimental results revealed a linear dependence of the critical breakdown potential (Ec) on the logarithm of the activity of the breakdown-inducing halide (F-, Cl-, Br-, and I-), as predicted by the PDM. Furthermore, the PDM successfully accounted for the order with which the halides induce passivity breakdown, F- < Cl- > Br- > I-, in terms of competitive Gibbs free energy of anion dehydration and expansion of surface oxygen vacancies, into which the halide must absorb as the initial event in the breakdown process.
|Title of host publication||NACE - International Corrosion Conference Series|
|Number of pages||8|
|State||Published - 16 Apr 2018|
|Event||2018 - CORROSION: Conference & Expo - Phoenix Convention Center, Phoenix|
Duration: 15 Apr 2018 → 19 Apr 2018
|Conference||2018 - CORROSION|
|Period||2018-04-15 → 2018-04-19|