Uses of scanning electrochemical microscopy for the characterization of thin inhibitor films on reactive metals: the protection of copper surfaces by benzotriazole
Fecha
2010Resumen
Scanning electrochemical microscopy (SECM) was used to study the film formation of
benzotriazole towards corrosion of copper. SECM was operated in the feedback mode
by using ferrocene-methanol as redox mediator, and the sample was left unbiased at all
times to freely attain its open circuit potential in the test environment. Following
exposure to aggressive electrolytes the anticorrosion abilities of the layers were
characterised by image analysis and by an electrochemical method derived from the
experimental approach curves. Changes in the shape of the approach curves were
clearly observed during the inhibitor film formation process. They showed the transition
from an active conducting behaviour towards ferrocinium reoxidation typical of
unprotected copper, to a surface exhibiting insulating characteristics when the metal was
covered by a surface film containing the inhibitor. This supports that SECM is a
practical technique in the investigation of corrosion inhibitor performance. However, a
consistent tendency for the characterization of inhibitor film formation using SECM
measurements in the positive feedback mode for the copper-benzotriazole system was
only found when the experiments were conducted when the inhibitor molecule was not
present in the test solution. That is, inhibitor molecules were found to interact not only
with the copper surface during the monitoring process, but to interact with the SECM
tip as well, this effect being significantly enhanced when chloride ions were present in
the electrolyte. Finally, a procedure to image the chemical activity of copper surfaces
partially covered with the inhibitor film with SECM is proposed