ISSN 1070-4272, Russian Journal of Applied Chemistry, 2016, Vol. 89, No. 3, pp. 505−516. © Pleiades Publishing, Ltd., 2016.
The text was submitted by the authors in English.
Experimental and Theoretical Study of Some N-Pyridinium Salt
Derivatives as Corrosion Inhibitors for Mild-Steel
in Acidic Media
Mehdi Salih Shihab* and Atheer Fadhil Mahmood
Department of Chemistry, College of Science, Alnahrain University, Baghdad, Iraq
Received February 27, 2016
Abstract—N-pyridinium salt derivatives (1–5) were prepared and investigated as corrosion inhibitors for mild
steel in 1 M H
solution at 30°C for 24 h. The corrosion inhibiting action was studied using weight loss
measurements. The results demonstrated that the corrosion rate decreases, inhibition efﬁ ciencies increase, and
surface coverage degree increases with increasing inhibitor concentration. Inhibition efﬁ ciencies for prepared
N-pyridinium salt derivatives have highest inhibiting efﬁ ciency for even low concentration. The values of ∆G°
showed physisorption effect for all prepared compounds. Molecular modeling systems were achieved for suggested
inhibitors 1–5. Theoretical calculations could be used as a useful tool to obtain information for explaining the
mechanism and nature of interaction between the metal surface and the organic molecule as a corrosion inhibitor.
Corrosion of materials keeps getting more signiﬁ -
cance in the wide ﬁ elds of technology. Corrosion in-
hibition researches work hard for ﬁ nding variant and
efﬁ cient ways to protect the metals against corrosion.
Mechanistic basis of corrosion inhibitors depends on the
speciﬁ c interaction between certain atoms of the inhibi-
tors with the corroded sites on the metal surface
the atoms as nitrogen, oxygen, sulfur serve mainly in
this interaction for donating their free electron pairs
[1, 2]. Schiff bases found interest applications as corro-
sion inhibitors for carbon steels [3, 4], and other metals
[5, 6]. Literature revealed that alkyl quaternary ammo-
nium compounds are important as inhibiting additives
in acidic media to reduce the corrosion process of iron
and steel [7, 8].
Methods of theoretical chemistry such as quantum
chemical calculations were used to illustrate the mecha-
nism of corrosion inhibition [9, 10]. Theoretical calcu-
lation could be a useful tool on ﬁ nding the relationship
between the corrosion inhibition efﬁ ciency and a num-
ber of quantum parameters, which are determined by the
demanding a molecular modeling of effective corrosion
In the study the inhibition of mild steel corrosion in
1 M H
in the presence of the prepared N-pyridinium
salt derivatives was evaluated at 30°C and different con-
centrations of inhibitor using the weight loss method.
The results of measurements showed excellent inhibi-
tion efﬁ ciency of the corrosion inhibitors. The relation-
ship between high efﬁ ciencies and molecular structure
of the corrosion inhibitors were studied using quantum
chemical calculations at PM3 level.
Materials. The sheet of mild steel was of the follow-
ing composition percentages: 0.002% P, 0.288% Mn,
0.03% C, 0.0154% S, 0.0199% Cr, 0.002% Mo, 0.065%
Cu, 0.0005% V, and the remainder iron). The mild steel
sheet was mechanically press-cut into disc shapes with
a diameter of 2.5 cm and thickness of 0.05 cm. These
disc shapes were polished with emery papers ranging
from 500 to 1500 grades to get a highly smooth surface.
However, surface treatments of the mild steel involved
degreasing in absolute ethanol and drying in acetone.