Volume 19 Preprint 48
A new inhibitor cum sealant for Anodized Aluminium surfaces
Keywords: Anodizing, sealing, corrosion inhibition
A new inhibitor cum sealant for anodized aluminium has been used involving 1-cyclopropyl-6-fluoro-4-oxo- 7-piperazin-1-yl-quinoline-3-carboxylic acid [CPFP] drug in 3.5% NaCl. The corrosion resistance of the anodized aluminium surfaces could be improved by this new sealant cum inhibitor. The efficacy of the sealant film was assessed by potentiodynamic polarization and A.C impedance analysis. The calculations of quantum mechanical parameters viz., the localization of frontier molecular orbitalâ€™s, EHOMO, ELUMO, energy gap (Î”E) and dipole moment (Âµ), indicated that this new compound retards the corrosion of Anodized aluminium surfaces through its effective adsorption of Al surfaces.
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A new inhibitor cum sealant for Anodized Aluminium surfaces
School of Mechanical Engineering, VIT University,Vellore-632014,India
A new inhibitor cum
sealant for anodized aluminium has been used involving 1-
cyclopropyl-6-fluoro-4-oxo- 7-piperazin-1-yl-quinoline-3-carboxylic acid [CPFP]
3.5% NaCl. The corrosion resistance of the anodized aluminium surfaces
could be improved by this new sealant cum inhibitor. The efficacy of the sealant film
was assessed by
potentiodynamic polarization and A.C impedance analysis. The
calculations of quantum mechanical parameters
viz., the localization of frontier
molecular orbital’s, EHOMO, ELUMO, energy gap (∆E) and dipole moment (), indicated
that this new compound retards the corrosion of Anodized aluminium surfaces
through its effective adsorption of Al surfaces.
words: Anodizing, sealing, corrosion inhibition
*Corresponding author (firstname.lastname@example.org)
The anodized aluminium is extensively used in the fields of aerospace, automobile,
electronic products, etc. The life of the anodized film is short due to presence micro
pores in the aluminium oxide which pervades the entry of foreign materials ,
is exposed to acidic and hard water media. Organic compounds containing sulphur,
nitrogen and oxygen atoms are capable of reducing metallic corrosion. Several
substituted thiourea and drugs compounds have been investigated as corrosion
for the aluminium and its alloys. All the above studies reveal the one
common observation that thiourea derivatives can be regarded as excellent corrosion
inhibitors for aluminium. However , no systematic approach is available for the
corrosion protection of anodized film using eco friendly sealing agent.The present
paper describes a study of special sealing cum Inhibitor on the corrosion of anodized
aluminium in 3.5% NaCl using potentiodynamic polarization and impedance methods.
The quantum mechanical descriptors substantiate the performance of the CPFP
antibiotics by forming a resilient adherent layer on the metal surface.
and Aluminium remainder, and of size 4 cm2x 2cm were used for anodizing and
1cm2 x 0.02 cm were used for electrochemical studies .
Al 1200 coupons were
mechanically polished and then degreased with tri chloro
ethylene. Then the coupons were subjected to anodizing by following the procedure
as appended below:. Anode: Al 1200 coupons; Cathode: Lead ; electrolyte: 2M Boric
acid + 2M Ammonium tartrate ; Voltage: 15 V ; Time : 12 minutes. Thickness: 35
microns. Colour of the anodized film: Bronze colour.
The sealing of anodized film was carried out by immersing the anodized plates into
CPFP drugs solution of concentrations ranging from 5 to 15x10-4 M mixed with hot
water.The duration of sealing process was 2 minutes.
After sealing, the coupons
were removed , washed , dried and characterized with
electrochemical techniques. Both cathodic and anodic polarisation curves were
recorded in 3.5% NaCl potentiodynamically (10 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(5 cm2) and Hg/Hg2Cl2 /3.5%NaCl were used as auxiliary and
reference electrodes, respectively. Double layer capacitance (Cdl) and charge transfer
resistance values (Rt) were calculated
using AC impedance measurements (EG&G
Princeton Applied research model:7310) as reported elsewhere10. Quantum chemical
calculations were performed
using Gaussian 03 software package. The energy of
highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital
(LUMO) and dipole moment () of the inhibitor Cum Sealant were calculated.
Results and Discussion:
Potentiodynamic polarization studies
Polarization curves for sealed anodized aluminium in 3.5% NaCl containing different
concentrations of CPFP are given in figure-1. The values of corrosion potential (Ecorr) ,
corrosion current densities (Icorr), anodic tafel slope (βa) ,cathodic tafel slope (βc)
surface coverage(θ) and inhibition efficiency (IE%) calculated using polarization curves
are summarized in table-1.
1 Polarization curves of Al surfaces in 3.5% NaCl
in absence and presence of
different concentrations of sealant
According to the results, corrosion current (Icorr) value decreases with increase in the
concentration of the sealant on Al surfaces . The inhibition efficiency (IE %) and surface
coverage (θ) increases with increase in antibiotic
concentration. The maximum
inhibition efficiency is achieved at 15x10-4 M concentration. Both βa and βc are
reduced, but the values of βc are decreased to a greater extent. This indicates that the
sealing compound behaves as cathodic inhibitor.
1 Potentiodynamic polarization parameters for Anodized Al surfaces immersed
in 3.5% NaCl in absence and presence of different concentrations of sealant.
The Nyquist representations of impedance performance of sealed
in 3.5% NaCl
containing different concentrations of CPFP
are given in
figure 2. A large capacitive circle at higher frequency range is observed at all
concentrations of the sealing compound. The higher frequency capacitive loop is due
to the adsorption of inhibitor molecule .The results are presented in table 2.
Table 3: Electrochemical impedance parameters for sealed anodized aluminium in
3.5% NaCl containing
containing different concentrations of CPFP
Quantum chemical calculations
Quantum chemical calculations were carried out to investigate the adsorption and
inhibition mechanism of the inhibitor. Figure 3 showed the optimized structures of
inhibitor cum sealant. The values of calculated quantum chemical parameters i.e.
EHOMO (highest occupied molecular orbital), ELUMO (lowest unoccupied molecular
orbital), ∆E (energy gap), (dipole moment), σ (softness) etc.
are summarized in
EHOMO is associated with the electron-donating ability of the molecule. Several
researchers have shown that the adsorption of an inhibitor on metal surface can occur
on the basis of donor-acceptor interactions between the π-electrons of heterocyclic
atoms and the vacant d-orbitals of the metal surface atoms
Fig.3a. HOMO of CPFP
A high value of EHOMO indicates a tendency of a molecule to donate electrons to
acceptor molecules with low energy empty molecular orbital. Increasing values of EHOMO
facilitates the adsorption and increases the inhibition efficiency by influencing the
transport process through the adsorbed layer .
Fig.3b. LUMO of CPFP
ELUMO indicates the ability of the molecule to accept the electrons, hence these are
acceptor states. The lower the value of ELUMO, the more probable is that the molecule
can accept electrons and increase the inhibition efficiency.
Table 3: Quantum mechanical parameters for sealants on the corrosion of anodized Al
Regarding ∆E (ELUMO-EHOMO) lower values of energy difference will cause higher
inhibition efficiency because energy to release electron from last occupied orbital will
be low. When dipole moment is concerned higher values of , will favours a strong
interaction of inhibitor molecule with the metal surface .
A new inhibitor cum sealant has been
use of 1-cyclopropyl-6-fluoro-4-oxo- 7-
piperazin-1-yl-quinoline-3-carboxylic acid (CPFP) as sealing compound in 3.5% NaCl
was thoroughly studied using, potentiodynamic polarization and
quantum mechanical studies substantiate the performance of CPFP as excellent
corrosion inhibitor for mild steel in 1M H2SO4.
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