Ref.: MmeCo14-004
Apresentador: Ricardo Manuel Souto
Autores (Instituição): Souto, R.M.(Universidad de La Laguna); Pérez, J.I.(Universidad de La Laguna);
Resumo:
The performance of metallic components is often limited by the loss of their properties due to environmentally induced degradation. Advanced research in corrosion science mainly aims for a better understanding of the surface chemical processes involved in the micrometre and submicrometre range, thus promoting the efficient and durable application of metallic materials to new societal expectations. To better control corrosion and its effects, researchers must integrate emerging advances in many areas of science and technology to understand mechanistic effects and relate them to underlying structures, compositions, and dynamics.
It has long been known that corrosion processes start at micrometre or nanometre scales, although until recently no suitable techniques were available to study reactions at such scales. Additionally, surface chemical heterogeneity is frequently observed for many metallic materials, particularly when dealing with alloys or joined (i.e., galvanically coupled) metals, but this can also occur with individual metallic materials that were once mistakenly considered stable and uniform in their passive state, examples of which are stainless steels and prosthetic-quality titanium . The issue of surface inhomogeneity is even more relevant when corrosion protection methods involve the chemical modification of surfaces. Progress in corrosion research will therefore depend on the availability of experimental techniques capable of probing materials with higher spatial resolution and shorter time scales that can provide new or additional evidence of reaction mechanisms, preferably in situ, or even in operation. In this context, the use of scanning electrochemical microscopy (SECM) in corrosion science has been shown to be a powerful technique.
However, the application of SECM to the study of corrosion reactions has been significantly slower than that for other electrochemical applications, partly because in its early stages SECM was mainly an amperometric and potentiostatic technique. Although attractive advantages were recognised in regard to performing local quantitative electrochemical experiments, the possibility of using all the electrochemical techniques on both the probe and the substrate, and the possibility of coupling in situ electrochemical measurements with other techniques, their application to corrosion systems was limited by the requirement of a redox process at the tip for imaging (i.e., feedback mode). In fact, the addition of a redox mediator to the solution for its faradaic conversion at the tip would inevitably generate a Nernst potential at the metal surface under investigation, which may significantly alter the spontaneous mixed potential state of the corrosive system, and thus produce changes in the mechanism of the process under investigation. Advances have resulted from the adaptation of other operating modes, as reviewed in this contribution.