Characterization of calcareous deposits in artificial seawater by impedance techniques

• Published in: Electrochimica acta Vol. 48; no. 12; pp. 1645 - 1654
• Main Authors: Barchiche, Ch, Deslouis, C., Festy, D., Gil, O., Refait, Ph, Touzain, S., Tribollet, B.
• Format: Journal Article
• Language: English
• Published: Elsevier 01.05.2003
• Subjects: Chemical Sciences; Calcareous deposits; Steel; Impedances; Seawater; Porous layer
• ISSN: 0013-4686
• DOI: 10.1016/S0013-4686(03)00075-6

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.