XII Iberian Meeting of Electrochemistry XVI Meeting of the ...

XII Iberian Meeting of Electrochemistry & XVI Meeting of the Portuguese Electrochemical Society PD 01
In-situ study of corrosion morphology of a duplex stainless
steel in a concentrated LiBr solution and in an impure
phosphoric acid solution by confocal laser scanning
microscopy (C LSM)
R. Leiva-García 1 , M.J. Muñoz-Portero 1 , J. García-Antón 1
1
Univ. Politécnica de Valencia, Ingeniería Electroquímica y Corrosión (IEC), Dep. Ingeniería
Química y Nuclear, Camino de Vera s/n, 46022 Valencia, Spain.
jgarciaa@iqn.upv.es
Corrosion has been mainly studied using large-scale experiments. However, corrosion
mechanisms occur on a smaller scale. Therefore, it can be useful to develop smaller
scale methods and experimental methodologies. In this way, it will be possible to study
reduced surfaces. The aim of this work is the study of the corrosion morphology of a
duplex stainless steel (UNS 1.4462) in a concentrated aqueous LiBr solution (992 g/L)
and in an impure phosphoric acid solution, containing chlorides and sulfates.
The electrochemical techniques used were cyclic potentiodynamic curves and
galvanodynamic curves. Tests were carried out in a minicell developed by this research
group. This cell can be put in the stage of a confocal laser scanning microscope. In this
way, the in-situ observation of the corrosion process at microscopic scale is possible. All
the tests were made at 25 ºC.
The LiBr solution is an aggressive solution that provokes localized corrosion in the
duplex stainless steel. During the potentiodynamic curves, pits appear in the electrode
surface when the pitting potential is reached. These pits grow until affect the entire
electrode surface. When this growth is observed at higher magnifications (200x and
500x), the formation of new small pits is observed in the unaffected area (covered with
the corrosion product) closed to the corrosion front. Then, this corrosion front reaches
the pits and the observed surface ends completely damaged. In the case of the
galvanodynamic curves, a pit appears in the electrode surface when the pitting potential
point is reached and it goes growing in a sequential way with the increase of the current
density.
With regard to the impure phosphoric acid solution, the potentiodynamic and
galvanodynamic tests indicate that corrosion of duplex stainless steel is generalized in
this medium. The images obtained at different magnifications (100x - 500x) show how
the grain boundary of the tested stainless steel goes being revealed with the increase of
the current density. Despite of the presence of impurities, their concentration is not
critical to produce a localized corrosion attack.
Therefore, the developed minicell is useful to study the morphological differences
among different kinds of corrosion attack at microscopic scale.
Acknowledgments: We wish to express our gratitude to MICINN (CTQ2009-07518), to F EDER, to
MAEC (PCI Mediterraneo C/8196/07, C/018046/08, D/023608/09) for their financial support and
to Dr. Asunción Jaime for her translation assistance.
September, 811, 2010. ISEL - Lisbon 83