1. Introduction
Interaction of metallic alloy with aggressive ions
(Cl-, SO42-,
NO3-) and O2 through
the coating defects; establishes the corrosion products, diminishing the
lifetime of steel or copper components and durability of assets. This
corrosion is of inevitable in definite to the aerospace, automotive,
structural engineering, oil and gas (energy)
industries.1-3 In order to avert the financial
drainage and to combat the coating deterioration, the application of
protective coatings is one of the proficient methods. Most extant
literature reported that Ni-W coatings were considered as ennobling
alternate to chromium based (hexavalent) coatings. The governing factors
those demerits the hard chrome is: low propulsion power of chromium
(hexavalent) ions and its toxicity in the electrolyte bath, high
consumption of electricity, low cathodic current density, and crucially
a high chance of failure and in execution due to its residual tensile
stress and cracks.4,5 Its superlative properties made
it to applicable in many technological applications like faucets,
springs, magnetic heads and relays6 and in particular
as an electrode for H2electrocatalysis.7 The traditional macroscopic scale
experimental evaluations (Tafel slope, A.C. Electrochemical impedance
spectroscopy, Weight loss measurements. etc) have paved a way in
revealing the electrochemical behavior and kinetics of corrosion process
occurring at the juncture of metal or alloy/corrosive solution.
Nevertheless, the above mentioned techniques have left some caveats,
which are to be dealt with. Researchers of corrosion science crave for
in knowing the (i) potential correlation between the intrinsic
electronic properties and inhibition mechanism, (ii) nature of reactive
groups that aids in the organic adsorptions onto the surface of
metals/alloys, and (iii) orientation of additive molecule over the alloy
surface, which dictates the surface binding
propensity.8 To an answer of above all, sophisticated
and efficient computational simulations (DFT, MC, MD,RDF, Fukui indices
etc) came into light to be dealt with the structure-reactivity
relationship of additive/inhibitor9,10 in revealing
the mechanism and the key role of each atoms or functional groups of the
additive for electrodeposition11,12 and predominantly
to corroborate single point corrosion experimental
data.13,14 The accurate and precise information
(molecular properties) like polarizability, excitation energies,
electron donating ability, etc throws up a light in encoding the design
of typical additive15,16 and intervene in exact
synthesis strategy of additive molecule, cutting down the time and cost
associated with exhaustive experimentations.17Furthermore, greenness and novelty of the said computational techniques
aids in avoiding the consumption or release of reductant malicious
substances into the ecosystem, contrasting empirical
pathways.18
On the continuation of our previous work,19 herein we
have theoretically investigated the corrosion behaviors of salen-type
ligand (OPD and PPD) which comprising of ortho- and
para-phenylenediamine tethered hydroxy naphthalene, respectively on Ni-W
alloys in H2SO4 medium. The unique
features of these OPD and PPD containing ample electron-rich aromatic
centers (13 π-electrons) along with two nitrogen and oxygen atoms and
their delocalization could improve the metal-inhibitor interactions via
coordination bonding. In addition, by introducing isomeric spacers on
salen-type ligands that prominently affects the numerous factors, such
as electron-donating ability, nature of bonding, hardness/softness, rate
of adsorption, molecular orientations, the distance between two layers
(Ni-W and ligand), etc., and thus undeniably challenging to determine
those issues from experimentally. Keep in mind, we have systematically
examined the aforementioned issues with the aid of DFT, MC, MD, and RDF
and thus compared with experimental results.