The investigation of the reversibility of the "green" rare earth carboxylate corrosion inhibitor La(4-OHcin)3 on mild steel through an experimental and multi-scale computational approach

Samenvatting

The rare earth carboxylate (REC) corrosion inhibitor La(4-OHcin)3 has proven to be an
excellent green and sustainable replacement for the C

6+ based inhibitors. However, despite
being studied for decades, a comprehensive understanding of the underlying chemistry and

physics is not yet well established. Furthermore, the irreversibility of inhibition is an es-
sential property for it be suitable in active protective coatings but is yet to be addressed

for La(4-OHcin)3. In this thesis, an experimental approach comprised of electrochemical
and surface analysis measurements was used to examine the active protective properties

(inhibition and reversibility) of 0.7mM La(4-OHcin)3 on mild steel in a 0.01M NaCl aque-
ous solution. We discovered for the first time that the nature of inhibition is reversible.

Besides, the desorption was observed to occur on specific areas of the mild steel surface re-
sulting in rapid metal dissolution on those regions. To acquire a deeper understanding and

bridge the knowledge gap on the mechanism(s) of La(4-OHcin)3 inhibition and reversibility
at a molecular level, we have developed an advanced multiscale computational approach.
The use of such a multiscale framework allows for the investigation of all the possible bulk
and electrochemical interfacial interactions and, as a consequence helps to elucidate the
La(4-OHcin)3 inhibition and reversibility mechanism(s). Density functional theory (DFT)
simulations shed light on the chemistry of the adsorption mechanism, inhibition efficiency

and complex stability of 4-hydroxy cinnamate and 4-hydroxy phenyl propionate. More-
over, a new route was suggested via the DFT approach to systematically screen optimal

carboxylates for REC inhibitors. On the other hand, various physicochemical properties
of the La(4-OHcin)3 inhibition system on a molecular level have been investigated through
a preliminary bulk and electrochemical interface atomistic model simulated via molecular

dynamics. The simulation results show a good agreement with previous experimental find-
ings, which verified the proposed approach. A remarkable finding was that the inhibitor

in the model displayed the same reversible nature as observed during our experimental
approach.

Datum prijs	4 jun 2020
Originele taal	English
Prijsuitreikende instantie	Vrije Universiteit Brussel