3.2.1 Monte Carlo simulations
It is of imperative in quantifying the various energetic outputs, to
know the preferential adsorption and orientation of the adopted
additives on the alloy surface.45 The energy values
(in term of different contributions) during the random MC configuration
search are shown in Figure 3 . From this figure 3, the total
average energy reached the equilibrium at after 3000000 MC suggesting
that additives reached the low energy stable arrangement. The
interaction of the OPD & PPD onto the Ni-W surface gives a mean to
evaluate the required energies for this adsorption. The quantitative
adsorption energy (Eads) is calculated by using equation
2:25,27,46,47
\begin{equation}
E_{\text{adsorption}}=E_{\text{Ni}-W\left(110\right)\text{CPQ}\ \text{orMPQ}\text{\ \ \ }}-\left({\text{Ni}-W}_{\left(110\right)}+E_{\text{OPD}\ \text{or}\text{\ \ }\text{PPD}}\right)\text{\ \ \ .\ \ .\ \ .\ \ \ }\text{Equation}\ 2\nonumber \\
\end{equation}where\(\text{Ni}-W\left(110\right)\text{OPD}\ \text{or}\ \text{PPD}\)is the total energy of the simulated corrosion system,
ENi-W, and EOPD or PPD is the total
energy of the Ni-W(110) surface and free inhibitor.
The most stable or the low energy adsorption sites of organic additives
(OPD & PPD) in the vicinity of Ni-W alloy surface and corresponding
adsorption energetic outputs (Eads) obtained via a huge number of
randomly configurations from Monte Carlo calculations were figured out
in Figure 4. It is of significant in knowing the adsorption energy
(Eads) which denotes to the sum of deformation energy
and rigid adsorption energy of additive components.48Additionally, Eads corresponds to the release of energy,
while the organic additives (OPD&PPD) relaxed on the surface of alloy.
The Max.adsorption energy distribution was found to be −121.25 kcal/mol
and −195.55 kcal/mol for OPD & PPD additive molecules respectively. A
noticeable larger negative value of Eads = −195.55
kcal/mol (PPD) infers that the adsorbed organic layer on the alloy
surface is spontaneous and more stable,49 then the
earlier molecular layer (OPD). Moreover, this higher negative value
(Eads = −195.55 kcal/mol) evidence the fact that mere
amount of energy is required for the PPD molecule for adsorption onto
the Ni-W alloy surface45 intensifying the surface
coverage area, thus providing a durable shield against corrosive
suppressing agents.50