A new generation of nanosensors based on mesoporous silica nanocapsules with the ability to monitor the onset of metallic corrosion is successfully developed and tested on 304 stainless steel. The core of the nanocapsules contains water insoluble organic molecules that fluoresce during the anodic dissolution of metallic substrates in the corrosion process. The dispersion of the nanosensors in organic coatings applied on metal substrate allows a very sensitive fluorescent detection of the initiation of metal dissolution, close to defects in the substrate. This promising concept offers therefore new perspectives for the development of smart coatings for corrosion sensing.

In recent years Intrinsically Conducting Polymers (ICPs), such as polyaniline and polypyrrole, have become key materials in the search for high-performance coatings for the protection of metals from corrosion. In this work, by means of dedicated model samples, we have found that disconnected ICP particles in composite coatings applied on iron and zinc are capable of inhibiting the oxygen reduction in their vicinity, establishing a region where no or only very slow delamination occurs, i.e. a “protection zone” is created, which relies on the ICP's high potential and its redox activity. The efficiency of this novel protection mechanism may depend on the ICP type, thickness or counter-anion, and is here analyzed by means of Kelvin probe based investigations.

Smart self-healing coatings for corrosion protection safely store active substances which are only released when corrosion occurs. This type of case-sensitive release has to be triggered by parameters that change as a consequence of corrosion. Examples are a change of pH, ionic strength, and electrochemical potential. In most technically relevant applications, a global release of active substances is not possible, i.e. the spreading of the signal which triggers the release of active substances is restricted to a lateral transport through the coating. Hence, the ability of the trigger signal to spread quickly through the coating from the local corroding area is crucial to create highly responsive and effective self-healing coatings. Here we show how the velocity at which the trigger signal spreads laterally along the metal|coating interface can be accelerated and how a penetration of the signal vertically into the coating, i.e. far away from the metal|coating interface, can be achieved.

The scanning Kelvin probe (SKP) is a versatile method for the measurement of the Volta potential difference between a sample and the SKP-tip (Δψ). Based on suitable calibration, this technique is highly suited for the application in corrosion science due to its ability to serve as a very sensitive noncontact and nondestructive method for determining the electrode potential, even at buried interfaces beneath coatings or on surfaces covered by ultrathin electrolyte layers, which are not accessible by standard reference electrodes. However, the potential of the reference (i.e., the SKP-tip) will be influenced by variations of the surrounding atmosphere, resulting in errors of the electrode potential referred to the sample. The objective of this work is to provide a stable SKP-tip which can be used in different or changing atmosphere, e.g., within a wide range of relative humidity (approximately 0-99%-rh) or varying O partial pressure, without showing a change of its potential (note that the work functions measured in non-UHV atmospheres are electrochemical in nature [Hausbrand et al. J. Electrochem. Soc. 2008, 155 (7), C369-C379], and hence in the following we will refer to the potential of the SKP-tip instead of its work function). In that regard, the SKP-tip is in a first approach modified with self-assembled monolayers (SAMs) in order to create a hydrophobic barrier between the metallic surface and the surrounding atmosphere. The changes in potential upon varying relative humidity (ΔE) of different bare metallic substrates are quantified, and it is shown that these potential differences cannot be minimized by SAMs. On the contrary, the ΔE increases for every examined material system modified with SAMs. The major explanation for this observation is the dipole layer at the interface metal|SAM, causing an interfacial adsorption of water molecules even in a preferred orientation of their dipole moments, which leads to a changed work function and consequently to the correlated electrode potential. However, thin paraffin coatings were found to lead to a strongly reduced ΔE, finally validated with novel robust Ag/Ag reference electrodes. It is also shown that nickel as SKP-tip material is seemingly more stable in varying atmospheric conditions compared to widely used Ni/Cr, stainless steel, or gold as SKP-tip material.