Volume 18 Preprint 63
Quantum mechanical and corrosion studies of electrochemically oxidized aluminium surfaces
S. Karthikeyan, P.A. Jeeva
Keywords: oxidation, anodizing, corrosion resistance, quantum, electrochemical
The quantum mechanical descriptors such as the localization of frontier molecular orbitalâ€™s, EHOMO, ELUMO, energy gap (Î”E) and dipole moment (Âµ), were used to substantiate the impressive formation of non-toxic chemical film comprises of Clarithromycin (CMN) drug on electrochemically oxidized Aluminum and the corrosion resistance of the metal surfaces were found to be improved. The performance of the corrosion resistant barrier films was evaluated through potentiodynamic polarization and A.C impedance analysis.
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Quantum mechanical and corrosion studies of
electrochemically oxidized aluminium surfaces
S. Karthikeyan*, P.A. Jeeva
School of Mechanical and Building Sciences, VIT University, Vellore-632014, India
quantum mechanical descriptors
such as the localization of frontier molecular
orbital’s, EHOMO, ELUMO, energy gap (ΔE) and dipole moment (µ), were used to substantiate
the impressive formation of non-toxic chemical film comprises of Clarithromycin (CMN)
on electrochemically oxidized Aluminum and the corrosion resistance of the metal
surfaces were found to be improved. The performance of the
corrosion resistant barrier
films was evaluated through potentiodynamic polarization and A.C impedance analysis.
Key words: oxidation, anodizing, corrosion resistance, quantum, electrochemical
The electrochemically oxidized or anodized aluminium is widely used in the fields of
aerospace, automobile, electronic products, etc. However, the so formed oxidized film of Al
is less durable due to the presence of porosity which allows the environmental substances
to interact on the surface.
It was found that Sulphur, nitrogen and oxygen
organic molecules are proficiently
reducing metallic corrosion. Several substituted
thiourea and drugs compounds have been reported as corrosion inhibitors [1-5] for the
aluminium and its alloys. All the above studies bring one common observation that thiourea
derivatives can be regarded as excellent corrosion inhibitors for aluminium in acidic and
alkaline media. However, no methodical approach is existing for the corrosion protection of
anodized film using unified drugs a sprayed chemical agent. The present paper designates
a study of non-toxic spraying agent based on
and Clarithromycin (CMN)
proprietary aromatic poly hydroxy gel
drugs on corrosion inhibition of electrochemically oxidized
aluminium surfaces in 1M NaOH using potentiodynamic polarization and impedance
methods. The quantum mechanical parameters validate the performance of the non-toxic
spraying agent through the formation of a strong adherent layer on the metal surface.
Aluminium specimens of compositions, Cu = 0.15%, Mg = 0.5%, Mn = 0.1%, Si = O.5%,
Zn = 0.5%, and Aluminium
remainder, and of size 10 cm2x 10cm
were used for
electrochemical oxidization of Al panels. For potentiodynamic polarization and AC
impedance measurements both electrochemically oxidized and un oxidized Al specimens of
size 0.5cm2 x 0.01 cm were used.
Electrochemical Oxidation of Aluminium
The aluminium specimens of the above composition was mechanically polished and then
degreased with trichloro ethylene. Then the panels were subjected to electrochemical
oxidation using the plating formulation which consisted of : Anode: Al panels; Cathode:
Lead; electrolyte: 1M NaOH; current:
600 mA cm-2; Time : 5 minutes. Thickness: 50
Exactly (0.5 wt%) of proprietary aromatic poly hydroxy gel and (0.8% wt , 1.0 % Wt and
1.2% Wt) Clarithromycin (CMN) drug
proprietary surfactant solution
were dissolved in 32% isopropyl alochol + 1 ml of
were mixed well. The mixture was
diluted to 500ml and
ready to spray on electrochemically oxidized aluminum surfaces. The spraying is carried
out using spray guns or it can be poured directly on the anodized aluminium surfaces After
spraying, the plates were removed, washed with DI water, dried and then characterized
using electrochemical methods. Both cathodic and anodic polarisation curves were recorded
in 1M NaOH potentiodynamically (1 mv s-1) using corrosion measurement system BAS
Model : 100A, computerised electrochemical analyser (made in West Lafayette, Indiana) and
PL-10 digital plotter (DMP-40 series, Houston Instruments Division). A platinum foil (4 cm2)
and Hg/Hg2O /1M NaOH were used as auxiliary and reference electrodes, respectively.
Double layer capacitance (Cdl) and charge transfer resistance values (Rt) were carried out
using AC impedance measurements (EG&G Princeton Applied research model:7310.
Quantum calculations were carried using Gaussian 03 software package. The energy of
highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO)
and dipole moment (µ) of the sealing compounds were measured
with the above given
computer code package.
Results and Discussion
Table 1 gives values of corrosion kinetic factors
such as Tafel slopes ( ba
corrosion current (Icorr) and corrosion potential (Ecorr) and percentage of corrosion resistance
electrochemically oxidized aluminum in 1M NaOH after application of non-toxic corrosion
resistant spray coating agent. It is established that enhancing the thickness of corrosion
protection agent improves the values of both anodic and cathodic Tafel slopes to equal
extent. After spraying with various concentration of non-toxic spraying agent, the
inhibition of corrosion of electrochemically oxidized aluminium in 1M NaOH
follow mixed type of reaction [6-8]. Ecorr
was found to
shifted to positive directions in the
presence of various concentrations of spraying compound. This can be attributed to the
formation of strappingly adherent protective on the metal surface. The coating thickness
varied from 10 µm, 30 µm and 55 µm at various concentrations of spray coatings. Icorr
values were reduced to greater extent in 1M NaOH due to the block of micro pores of
coatings and also the strong coverage of protective films by Clarithromycin (CMN) drugs on
the oxidized surfaces of Al.
Table 2 showed that the corrosion protection of electrochemically oxidized aluminium in
1M NaOH solution before
and after the application of Clarithromycin (CMN)
unified coatings by electrochemical impedance spectroscopy . The values of the charge
transfer resistance (Rt ) is found to increase with the increasing thickness of anodized film
double layer capacitance (Cdl) are fetched
down to a great extent . This can
be attributed to increasing the adsorption of the spray coatings
on the micro pores of
anodized film with an increase in thickness of protective films [9-11].
Quantum Mechanical Studies
Quantum mechanical calculations were performed to investigate the adsorption and
inhibition mechanism of the applied spray coatngs comprise of Clarithromycin (CMN) drugs
unifed compounds. Figure 1 shows the structure of Clarithromycin. The values of calculated
quantum chemical parameters i.e. EHOMO (highest occupied molecular orbital), ELUMO (lowest
unoccupied molecular orbital), ∆E (energy gap), µ (dipole moment) etc. are summarized in
table-3. EHOMO is related to the electron-releasing capacity of the molecule. In the present
investigation, the adsorption of a CMN on electrochemically oxidized surface of Al acquired
on the basis of donor-acceptor interactions between the π-electrons of heterocyclic ring
and carbonyl group of CMN. The gap between HOMO–LUMO energy levels of molecules was
another important factor that desires to be considered. Higher the value of E of an
inhibitor, higher is the inhibition efficiency of that inhibitor. It has been reported that, large
values of the dipole moment will enhance corrosion inhibition.
A special spray non-toxic coating
process for electrochemically oxidized aluminum parts
has been formulated and the corrosion resistance of the coatings with and without the
application of coatings has been systematically evaluated through electrochemical
techniques. The quantum mechanical studies confirmed the mere adsorption of the
Clarithromycin (CMN) drugs on the Al anodized surfaces.
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Table 1: Potentiodynamic polarization of electrochemically oxidized
(V vs SCE)
Clarithromycin (CMN) spraying agent (thickness in µm)
Table 2: Impedance data for electrochemically oxidized aluminium. Medium: 1M NaOH
1N NaOH solution
spraying (Rt) Ohm.cm2
Table 3: Quantum mechanical parameters for sealants on the corrosion of anodized Al
Figure 1. Structure of Clarithromycin
Figure 2. Highest molecular orbital of Clarithromycin molecules
Figure 3. Lowest unoccupied molecular orbital of Clarithromycin molecules