Characterization of calcareous deposits in artificial seawater by impedance techniques
Résumé
Calcareous deposits were formed on steel under cathodic protection conditions in artificial seawater at various potentials from −0.9 to −1.4 V/SCE. The deposition kinetics was analysed by chronoamperometry measurements and the calcareous layers were characterized by electrochemical and electrohydrodynamical impedance spectroscopies, scanning electron microscopy observations and X-ray diffraction analyses. At 20 °C, the deposits were composed of aragonite CaCO3 when formed at potentials E comprised between −0.9 and −1.1 V/SCE, of brucite Mg(OH)2 and aragonite when formed at −1.2 V/SCE, and only of brucite when formed at potentials E≤−1.3 V/SCE. However, the in situ impedance techniques demonstrated the presence of a Mg(II)-containing porous layer along with the aragonite deposit at E≥−1.1 V/SCE. In seawater enriched with Mg2+, the deposition of aragonite was almost totally inhibited, and the behavior of the film containing Mg(II) could be described.