Open Journal of Metal, 2012, 2, 68-73 Published Online September 2012 (
Comparative Study of Corrosion Inhibition Efficiency of
Naturally Occurring Ecofriendly Varieties of Holy Basil
(Tulsi) for Tin in HNO3 Solution
Nutan Kumpawat, Alok Chaturvedi*, Rajesh Kumar Upadhyay
Department of Chemistry, Government College, Ajmer (Rajasthan), India
Email: *
Received June 22, 2012; revised July 21, 2012; accepted August 10, 2012
Weight loss technique has been used to study the corrosion inhibition efficiency of tin in HNO3 solution by using the
leaves and stem extract of different varieties of Holy Basil viz. Ocimum basilicum (EB), Ocimum cannum (EC) and
Ocimum sanctum (ES). The results show that all the varieties under study are good corrosion inhibitors, among which
leaves extract of EB is the most effective. Corrosion inhibition efficiency increases with increasing concentration of in-
hibitor and it also increases with increasing concentration of HNO3 solution. Inhibition efficiency was found maximum
up to 96.19% for tin with 0.6% leaves extract.
Keywords: Acid Solution; Inhibitors; Tin Metal, Weight Loss; Surface Coverage
1. Introduction
Tin and its alloys are found useful for many engineering
applications because of their lightness and strength,
thermal and electrical conductivity, heat and light reflec-
tivity and hygienic and non-toxic qualities. Tin is a reac-
tive metal according to the electrochemical series (Eo =
0.14V), but it is non reactive in moisture due to the
formation of a stable oxide film on its surface. Tin is not
attacked by pure water but dissolves in aqueous acids
with the liberation of hydrogen gas. Acids like hydro-
chloric acid, sulphuric acid etc. are used for drilling op-
eration, pickling and descaling. Many workers [1-4] have
studied corrosion of tin in HNO3 solution.
Holy basil is a very common plant in India. It is anti-
bacterial, anti-fungal and is used as an air purifier and
anti-malarial from ancient times in Indian homes. Pow-
der of its stem and leaves is used as medicine in balanc-
ing blood glucose management, to maintain a healthy
digestive system, to encourage the efficient use of oxy-
gen, to enhance the efficacy of many therapeutic treat-
ments etc.
The importance of the study lies in the fact that natural
plant products are non-polluting, ecofriendly, economic,
less toxic and easily available than synthetic organic
compounds. They are biodegradable and so can be used
without any side adverse effects.
The chemical composition of Ocimum sanctum is highly
complex, containing many vitamins like A and C, calcium,
zinc, iron, chlorophyll along with many other phytonutri-
ents which are present in the extract of Ocimum sanctum.
The major chemical constituents responsible for phys-
ico-chemical action of Ocimum sanctum are volatile oil
(0.1% to 0.9% ), eugenol (60% - 70%), cavacrol (about
3.0%), eugenol methyl ether (20%) and other minor
chemical constituents of Ocimum sanctum are like alka-
loids, glycoside, saponin, tannin, maleic acid, ursolic
acid, citric acid and tartaric acid.
*Corresponding author. Ursolic Acid
opyright © 2012 SciRes. OJMetal
β-bisabolene (13% - 20%), methyl chavicol (3% -
19%), 1-8 cineole (9% - 33%), α-bisabolene (4% - 7%),
α-terpineol (1.7% - 7%), campestrol, cholesterol, stigma
sterol, β-sisterol and methyl ester of common fatty acid
were the main constituents of the oil which are found in
there species.
Generally, the organic compounds containing hetero
atoms like nitrogen, oxygen and sulphur etc. have been
found to be very effective corrosion inhibitors [5-7]. The
efficiency of these compounds depends upon the electron
density of hetero atoms. The inhibition efficiency also
depends upon the number of adsorption active centers in
the molecule, their charge density, molecular size and
mode of adsorption and formation of metallic complexes.
Atoms such as nitrogen, oxygen and sulfur are capable of
forming coordinate covalent bond with metal owing to
their free electron pairs. Compounds with bonds like
aldehydes, ketones, imines also generally exhibit good
inhibitive properties due to interaction of orbital with
metal surface.
In addition to the heterogeneous organic compounds
like Schiff’s bases, Mannic bases etc. which are synthe-
sized in laboratory assist in inhibition, there are also
some naturally occurring substances like Ficus virens[8],
Delonix regia [9], Ocimum sanctum [10], Caparis de-
ciduas [11], Sanaevieria trifascinata[12], Phylanthus
amarus [13], Prosopis julifforar [14], Argemone maxi-
cana [15] etc. have also been evaluated as effective cor-
rosion inhibitors. The present study deals with the study
of three varieties of Holy basil i.e. Ocimum basilicum,
Ocimum sanctum and Ocimum canum which are most
common as corrosion inhibitors of Al in the most corro-
sive medium of HCl solution.
2. Experimental
The rectangular specimens of tin of dimensions 2.0 cm ×
2.0 cm × 0.014 cm containing a small hole of about 2
mm diameter near the upper edge were cut from a large
sheet of pure tin. The solutions of HNO3 acid were pre-
pared using double distilled water. All chemical used
were of analytical reagent grade. Different inhibitor solu-
tions were prepared in absolute ethanol. The extracts of
leaves and stem of three varieties were obtained by re-
fluxing the dried leaves and stem in a soxhlet using
ethanol as solvent for sufficient time.
Each specimen was suspended with a V-shaped glass
hook made of fine capillary and plunged into a beaker
containing 50 ml of the test solution (HNO3 acid) at
room temperature. After sufficient exposure, the test
specimens were taken out, washed with running water
and dried with hot air dryer. Experiments were repeated
in each case and the mean value of the weight loss was
calculated. The percentage inhibition efficiency was cal-
culated using the following formula [16].
% 100
where Wu and Wi are the weight loss of the metal in
uninhibited acid and in inhibited solution respectively.
The corrosion rate (CR) in mm/y can be calculated by the
following equation [17].
Corrosion rate mmyu
 (2)
where, W is weight loss in mg, A is area of specimen in
cm2, T is time of exposure in hours and d is density of
metal in g/cm3
The degree of surface coverage
by inhibitor can be
calculated as
where Wu and Wi are the weight loss of the metal in
uninhibited acid and in inhibited solution, respectively.
3. Results and Discussion
Weight loss, percentage inhibition efficiency, corrosion
rate and surface coverage in 3.0 M HNO3 solution with
different inhibitors of leaves extract are given in Table 1.
It can be seen from the table that the inhibition efficiency
of the inhibitor increases with increasing concentration of
inhibitor. The maximum inhibition efficiency (96.19%)
was obtained for Ocimum basilicum (EB) at an inhibitor
concentration of 0.6% in 3.0 M HNO3 solution for leaves
extract whereas it was 72.98% in 3.0 M HNO3 solution
with same concentration i.e. 0.6% for stem extract as
shown in Table 2. The results show that there is more
inhibition efficiency of Ocimum basilicum than Ocimum
canum and Ocimum sanctum in HNO3 solution. The
variation of percentage inhibition efficiency (
%) with
inhibitor concentration is depicted graphically in Figure
1 for leaves extract and in Figure 2 for stem extract in
3.0 M HNO3 solution. Variation of percentage inhibition
efficiency (
%) with the concentration of inhibitor indi-
cate that the inhibition efficiency increases with increas-
ing inhibitor concentration. From Table 1 it is clear that
the surface coverage (
) increases with increasing con-
centration of inhibitor.
Adsorption plays an important role in the inhibition of
metallic corrosion by organic inhibitors. Many investi-
gators have used the Langmuir adsorption isotherm to
study inhibitor characteristics [18,19]. Assuming that the
inhibitors adsorbed on the metal surface decrease the
surface area available for cathodic and anodic reaction to
take place. Hoar and Holliday [18] have shown that the
Langmuir isotherm,
log1log log2.303
  (4)
Copyright © 2012 SciRes. OJMetal
Copyright © 2012 SciRes. OJMetal
should give a straight line of unit gradient for the plot of
log 1
versus log C, where A is a temperature
independent constant, C is the bulk concentration of the
inhibitor (percentage) and Q is the heat evolved during
The corresponding plots, shown in Figures 3 and 4 for
3.0 M HNO3 for leaves and stem extract are linear but the
gradients are not equal to unity as would be expected for
Table 1. Weight loss data (W) and percentage inhibition efficiency (
%) for Tin in 3.0 M HNO3 solution with given inhibitor
additions of leaves extract.
Area of specimen = 0.056 cm2
Temperature: 25C0.1 C Exposure time: 7 mins
Inhibition conc. (%) W (mg) I.E. (
%) Surface coverage (
)Corrosion rate (mm/yr)
log 1
Uninhibited 210 3153.60
Ocimum basilicum (EB)
0.1 29 86.19 0.8619 435.50 0.7952
0.2 25 88.09 0.8809 375.43 0.8690
0.4 17 91.09 0.9109 255.29 1.0095
0.6 8 96.19 0.9619 120.14 1.4022
Ocimum cannum (EC)
0.1 33 84.28 0.8428 495.57 0.7292
0.2 28 86.66 0.8666 420.48 0.8126
0.4 23 89.04 0.8904 345.39 0.9097
0.6 16 92.38 0.9238 240.27 1.0836
Ocimum sanctum (ES)
0.1 36 82.85 0.8285 540.62 0.6840
0.2 32 84.76 0.8476 480.55 0.7452
0.4 29 86.19 0.8619 435.50 0.7952
0.6 21 90.00 0.9000 315.36 0.9542
Table 2. Weight loss data (W) and percentage inhibition efficiency (
%) for Tin in 3.0N HNO3 solution with given inhibitor
additions of stem extract.
Area of specimen = 0.056 cm2
Temperature: 273 ± 0.1 K Exposure time: 7 min
Inhibitor conc.(%) W (mg) I.E. (
%) Surface coverage (
)Corrosion rate (mm/yr)
log 1
Uninhibited 285 4279.88
Ocimum basilicum (EB)
0.1 114 60.00 0.6000 1711.95 0.1760
0.2 99 65.26 0.6526 1486.69 0.2738
0.4 86 69.82 0.6982 1291.47 0.3642
0.6 77 72.98 0.7298 1156.32 0.4315
Ocimum cannum (EC)
0.1 120 57.89 0.5789 1802.05 0.1382
0.2 108 62.10 0.6210 1621.85 0.2144
0.4 98 65.16 0.6516 1471.68 0.2719
0.6 85 70.17 0.7017 1276.45 0.3714
Ocimum sanctum (ES)
0.1 125 56.14 0.5614 1877.14 0.1072
0.2 112 60.70 0.6070 1681.92 0.1887
0.4 106 62.10 0.6210 1591.81 0.2144
0.6 92 67.71 0.6771 1381.57 0.3215
Figure 1. Variation of inhibition efficiency with concentration of leaves extract for Tin in 3.0 M HNO3.
Figure 2. Variation of inhibition efficiency with concentration of stem extract for Tin in 3.0 M HNO3.
Figure 3. Langmuir adsorption isotherm for Tin in 3.0 M HNO3 with inhibitor concentration for leaves extract.
Copyright © 2012 SciRes. OJMetal
Copyright © 2012 SciRes. OJMetal
Figure 4. Langmuir adsorption isotherm for Tin in 3.0 M HNO3 with inhibitor concentraction for stem extract.
the ideal Langmuir adsorption isotherm equation. This
deviation from unity may be explained on the basis of the
interaction among the adsorbed species on the metal sur-
face. It has been postulated in the derivation of the
Langmuir isotherm equation that the adsorbed molecules
do not interact with one another but this is not true in the
case of organic molecule having polar atoms or groups
which are adsorbed on the anodic and cathodic sites of
the metal surface. Such adsorbed species may interact by
mutual repulsion or attraction. Thus, it is also possible
for inhibitor molecule those are adsorbed on anodic and
cathodic sites to interact with metallic surface as well as
with each other.
[1] A. A. El. Warraky and El. Meleigt, “Electrochemical and
Spectroscopic Investigation of Synergestic Effects in
Corrosion Inhibition of Al Bronze Part 1-in Pure HCl,”
Journal of British Corrosion, Vol. 37, No. 4, 2000, pp.
305- 310.
[2] H. Ashassi-Sorkhabi, B. Shabani, B. Aligholipour and D.
Seifzadeh, “The Effect of Some Schiff Bases on the Cor-
rosion of Aluminum in Hydrochloric Acid Solution,” Ap-
plied Surface Science, Vol. 252, No. 12, 2006, pp. 4039-
4047. doi:10.1016/j.apsusc.2005.02.148
[3] G. Berkt, A. Pinarbasi and C. Orgretir, “Benzimidazole-2-
tione and Benzyoxazole-2-tione Derivatives as Corrosion
Inhibitors for Al in HCl Acid,” Anticorrosion, Methods
and Materials, Vol. 51, No. 4, 2004, pp. 282-293.
[4] A. H. Ali Ahmed, A. H. Ahmed, T. A. Mohamed and B.
H. Mohamed, “Chelates and Corrosion Inhibition of Newly
Synthesized Schiff Bases Derived from o-tolidine,” Tran-
sition Metal Chemistry, Vol. 32, No. 4, 2007, pp. 461-467.
4. Conculsions
A study of three varieties of holy basil viz. Ocimum
basilicum (EB), Ocimum cannum (EC) and Ocimum
sanctum (ES) has shown them to be better corrosion in-
hibitor for Tin metal in HNO3 solution. EB has proved to
be an excellent inhibitor for Tin in HNO3 acid due to the
presence of methyl eugenol terpenoid (75.69%).
[5] A. Mozaleva APoznyok, I. Mozaleval and A. W. Hassel,
“The Voltage—Time Behaviour for Porous Anodizing of
Aluminium in a Fluoride-Containing Oxalic Acid Elec-
trolyte,” Electrochemistry Communications, Vol. 3, No. 6,
2001, pp. 299-305. doi:10.1016/S1388-2481(01)00157-6
Weight loss method has shown that inhibition effi-
ciency of holy basil increases with increasing inhibitor
concentration over the range 0.1% to 0.6% the maximum
inhibition efficiency was found up to 96.19% for tin in
3.0 M HNO3 acid at a concentration of 0.6% for leaves
extract whereas it was 72.98% for stem extract with same
concentration of acid strength. Thus, it was concluded
that leaves extract is a better corrosion inhibitor than
stem extract.
[6] E. E. Ebenso, P. C. Okafor and U. G. Eppe, “Studies on
the Inhibition of Al Corrosion by 2-Acetylphenothiazine
in Chloroacetic Acids,” Anticorrosion, Methods and Ma-
terials, Vol. 50, No. 6, 2003, pp. 414-421.
[7] C. Blanc, S. Gastaud and G. Mankowski, “Mechanistic
Studies of the Corrosion of 2024 Aluminum Alloy in Ni-
trate Solutions,” Journal of the Electrochemical Society,
Vol. 150, No. 8, 2003, pp. B396-B404.
[8] T. Sethi, A. Chaturvedi, R. K. Upadhyay and S. P. Mathur,
“Inhibition Effect of Nitrogen Containing Ligands on
Corrosion of Aluminium in Acid Media with and without
KCl,” Polish Journal of Chemistry, Vol. 82, No. 3, 2008,
5. Acknowledgements
One of the authors (Nutan Kumpawat) is grateful to
R.G.N. fellowship from U.G.C. govt. of India as J.R.F.
[9] O. K. Abiola, N. C. Okafor, E. E.Ebenso and N. M.
Nwinuka, “Ecofriendly Corrosion Inhibitors: The Inhibitive
Action of Delonix Regia Extract for the Corrosion of Alu-
minium in Acidic Media,” Anticorrosion, Methods and
Materials, Vol. 54, No. 4, 2007, pp. 219-224.
[10] N. Kumpawat., A. Chaturvedi and R. K. Upadhyay, “A
Comparative Study of Corrosion Inhibition Efficiency of
Stem And Leaves Extract of Ocimum sanctum (Holy Basil)
for Mild Steel in HCl Solution,” Protection of Metals and
Physical Chemistry of Surfaces, Vol. 46, No. 2, 2010, pp.
[11] P. Arora, S. Kumar, M. K. Sharma and S. P. Mathur,
“Corrosion Inhibition of Aluminium by Capparis decide-
uas in Acidic Media,” Journal of Chemistry, Vol. 4, No. 4,
2007, pp. 450-456. doi:10.1155/2007/487820
[12] E. E. Oguzei, “Corrosion Inhibition of Aluminium in
Acidic and Alkaline Media by Sansevieria trifasciata
Extract,” Corrosion Science, Vol. 49, No. 3, 2007, pp.
1527-1539. doi:10.1016/j.corsci.2006.08.009
[13] P. C. Okafor, M. E. Ikpi, I. E. Uwah, E. E. Ebenso, J.
Elcpe and S. A. Umoren, “Inhibitory Action of Phyllanthus
amarus extract on the Corrosion of Mild Steel in Acid
Media,” Corrosion Science, Vol. 50, No. 8, 2008, pp.
[14] N. Kumpawat, A. Chaturvedi and R. K. Upadhyay,
“Study on Corrosion Inhibition Efficiency of Stem Alka-
loid Extract of Different Varieties of Holy Basil on Alu-
minium in HCl Solution,” Journal of the Korean Chemi-
cal Society, Vol. 56, No. 4, 2012, pp. 1-5.
[15] P. Sharma, R. K. Upadhyay, A. Chaturvedi and R. Parashar,
“Study of Corrosion Inhibition Efficiency of Naturally
Occurring Argenmone mexicana on Al in HCl Solution,”
Journal of Technical and Research in Chemistry, Vol. 5,
No. 1, 2008, pp. 21-27.
[16] J. D. Talati and D. K.Gandhi, “N Heterocylic Compounds
as Corrosion Inhibitor for Aluminium Copper Alloy in
Hydrochloric Acid,” Corrosion Science, Vol. 23, No. 12,
1983, pp. 1315-1332.
[17] D. A. Jones, “Principles and Prevention of Corrosion,”
2nd Edition, Prentice-Hall, London, 1996.
[18] T. P. Hoar and R. D. Holliday, “The Inhibition by Quino-
lines and Thioureas of the Acid Dissolution of Mild
Steel,” Journal of Applied Chemistry, Vol. 3, No. 11,
1953, pp. 502-513.
[19] J. R. Meakins, “Alkyl Quaternary Ammonium Compound
as Inhibitors of the Acid Corrosion of Steel,” Journal of
Applied Chemistry, Vol. 13, No. 8, 1963, pp. 339-345.
Copyright © 2012 SciRes. OJMetal