257-263 - AJBAS Journal

Australian Journal of Basic and Applied Sciences, 7(14) December 2013, Pages: 257-263
AENSI Journals
Australian Journal of Basic and Applied Sciences
Journal home page: www.ajbasweb.com
Effect of Vernonia Amygdalina Extract on Corrosion Inhibition of Mild Steel In
Simulated Seawater
1
Debi Gaius Eyu, 2Esah Hamzah, 3Mohammad Ismail, 4Asipita Salawu Abdulrahman, 4Neelam Memon 5Aminu Mohammad
1,2
Faculty of Mechanical Engineering, Universiti Teknologi Malaysia,81310 UTM Johor Bahru. Malaysia
Faculty of Civil Engineering, Universiti Teknologi Malaysia,81310 UTM Johor Bahru. Malaysia
5
Faculty of Science, University Teknologi Malaysia, 81310 UTM Johor Bahru. Malaysia
3,4
ARTICLE INFO
Article history:
Received 22 October 2013
Received in revised form 14
January 2014
Accepted 20 January 2014
Available online 1 February 2014
Keywords:
Corrosion. Inhibition
efficiency. Inhibitor.
Vernonia amygdalina.
Weight loss.
ABSTRACT
The study has investigated the effect of vernonia amygdalina extracts on corrosion
inhibition of mild steel immersed in 3.5wt% NaCl solution by weight loss
measurement. The study was conducted at temperature range within 28 oC to 34.7oC.
The results of the study shown that the plant extracts reduced corrosion rate of mild
steel in 3.5% NaCl and the inhibition mechanism was by physical adsorption, the
adsorbed molecules block the active sites thus prevent the metal from corrosion in the
chloride environment. The inhibition efficiency and degree of surface coverage
determined from the study revealed that the inhibitory actions of the inhibitor increases
with increased dosage and the most suitable inhibitor concentration was found in 6%
v/v with inhibition efficiency of 75%.
© 2013 AENSI Publisher All rights reserved.
To Cite This Article: Debi Gaius Eyu1, Esah Hamzah, Mohammad Ismail, Asipita Salawu Abdulrahman, Aminu Mohammad., Effect of
vernonia amygdalina extract on corrosion inhibition of mild steel in simulated seawater. Aust. J. Basic & Appl. Sci., 7(14): 257-263, 2013
INTRODUCTION
Mild steel are widely used in engineering and industrial applications. However it’s more susceptible to
corrosion. Corrosion is a metallurgical extraction in reverse. This deterioration is due to chemical or
electrochemical reaction of metals with the environment. This natural phenomenon has attracted the attentions
of many scientists and engineers in recent times, to contribute on how to improve the durability of mild steel in
an aggressive environment. The use of corrosion inhibitor is one of the most widely used countermeasures,
because of their simplicity in applications and is relatively less expensive. Corrosion inhibitor is a chemical
substance organic or inorganic which when added (Andrade et al., 2001) in a required amount to corrosive
environment decreases the rate of corrosion. Corrosion inhibitors frequently work as anodic, cathodic or mixed
inhibitors (Pacheco et al., 2011, Xu and Yao, 2008, Liu and Shi, 2009) by adsorbing themselves on the metallic
surface (physical adsorption) by forming a film layer on the surface. Inhibitors reduce corrosion activities by;
(1) Increasing the cathodic and anodic polarization behaviour (2) Decreasing the mobility of ions to the surface
of the metal (3) Raising the electrical resistance of the metallic surface (4) Creating a barrier film on the surface
of the metal (Oguize et al.,2004, Chitounani et al.,2004).For industrial and large scale applications, cost,
availability and environmental friendliness are essential considerations (Ji et al.,2011). Cost of inorganic
inhibitors are relatively low, but many of the effective inhibitors such as chromate, mercride, arsenate are very
toxic (harmful to both human and environment). Plant extracts corrosion inhibitors are cheap, non-toxic and
environmental friendly(Ebenso et al.,2004).These advantages have awaken researchers intensive studies of plant
extracts as organic corrosion inhibitors (Loto and Muhammed, 2005, Okafor, 2007, Davis et al.,2001).In recent
time, due to the search for eco-friendly inhibitors, the use of plant extracts such Carica papaya, Occinum viridis,
Telfairia occidentalis, Vernonia amygdalina, mango juice, Rosmmarius officinalis, and neem leaves as organic
corrosion inhibitors have been reported (Ekanem et al., 2010, Obot et al., 2011, Loganatha et al.,2011, GuzmanLucero et al.,2011, Yurt and Bereket, 2011).The inhibition effects of plant extracts are due to the presence of
tannin, steroids, saponin, alkaloid, glycosides and amino acids (Chauhan and Gunasekaran, 2007).
The leaves extracts of vernonia amygdalina was reported to contain tannin and saponnin that contribute to
the inhibitory actions which is by physical adsorption mechanism (Ayeni et al., 2012). Vernonia amygdalina is
an edible plant, its leaves serve as vegetable in some parts of West African countries (Nigeria). It’s commonly
available in most parts of the tropical nations in Africa and Asia, it’s non-toxic and cheap. Vernonia amygdalina
extracts has been reported to have inhibitory effect on mild steel in acidic media (Loto, 1998, Loto, 2003).
However, its effect on mild steel in chloride laden environment has not been unveiled. Hence the aim of the
Corresponding Author: Debi Gaius Eyu, Faculty of Mechanical Engineering, Universiti Teknologi Malaysia,81310 UTM
Johor Bahru
E-mail: [email protected]
258
Debi Gaius Eyu et al, 2013
Australian Journal of Basic and Applied Sciences, 7(14) December 2013, Pages: 257-263
study was to evaluate the effect of vernonia amygdalina extracts on corrosion inhibition of mild steel immersed
in 3.5% NaCl solution. In this study, a varied dosage of vernonia amygdalina extracts was used as inhibitor and
corrosion rate was evaluated by weightloss.
Experimental:
Mild steel plate was used as coupon for the experiment. The steel was analysed by Glow Discharge
Spectrometer (GDS) model Leco 850A and has the following chemical composition as given in Table 2.
Table 2.1: Mild steel sample composition
Element
Iron
Carbon
Maganese
Phosphorus
Sulphur
Silicon
Composition%
99.60
0.032
0.193
0.012
0.014
0.018
The steel plate was characterized with optical microscopy for microstructural examination. A solution of
3.5wt% NaCl was prepared to simulate seawater for the immersion test. Vernonia amygdalina extracts was used
as organic inhibitor for the experiment.
Method:
Preparation of Vernonia Amygdalina Extract:
The leaves were obtained from the plant as shown in Figure 2.1 in the neighbourhood and thoroughly
washed with water to remove unwanted materials and then weighed. The weighed amount (200g) was put in a
bottle container, methanol (100mL) was added and the container was tightly covered to prevent evaporation.
The mixture was left for 48 hours to allow proper removal and concentration of the extracts. Afterward, the
mixture was filtered to obtain a liquid residue containing methanol. The methanol was removed by heating the
resulting solution over a water bath at 760C for 20 minutes in rotary evaporator model Buchi R-200 as shown in
Figure 2.2. The immersion parameters for the 56 days immersion duration is given in Table 2.2.
Fig. 2.1: Vernonia amygdalina plant
Fig. 2.2: Rotary evaporator.
Table 2.2: Immersion parameters for 56 days immersion duration.
Inhibitor
Immersion Time (days)
7
14
28
Without
1
1
1
2%wt VA
1
1
1
4%wt VA
1
1
1
6% wt VA
1
1
1
42
1
1
1
1
56
1
1
1
1
Determination of vernonia amygdalina composition:
The leaves extract was characterized by IR spectroscopic analysis and phytochemical screening
Phytochemical Screening:
The following test was conducted during the phytochemical screening of the plant extract.
Test for alkaloids compounds:
About 50mL of the extract was dissolved in chloroform in a test tube and 2-3 drops of Draggendorff’s and
Mayer’s reagent were added colour precipitation indicates the presence of alkaloids.
XXX et al,2013
Australian Journal of Basic and Applied Sciences, 7(14) December 2013, Pages: x-x
259
Test for saponins compounds:
Froth test: About 0.5 g of the extract was shaken with water in a test tube. Frothing which persisted for 15
min indicates the presence of saponins.
Test for tannins compounds:
Ferric chloride test: A small quantity of the extract was boiled with water and filtered. Two drops of ferric
chloride was added to the filtrate, formation of a blue-black, or green precipitate was taken as evidence for the
presence of tannins.
Infra-ray spectroscopicanalysis:
Alkaloids: these are nitrogen-containing organic compounds. They can be chararcterize with IR spectra
based on the presence of:
C-N bond stretching at 1258.99 cm-1 and N-H bond bending at 1445.84 cm-1.
Saponnins: compose of one or more hydrophillic glycoside moieties combined with a lipophilic triterpene
derivative. They can be chararcterize with IR spectra based on:
C-H bond stretching 2927.24 cm-1. C=C bond stretching 1646.02 cm-1. C-O bond stretching 1159.75 cm-1.
Tannins: polyphenolic compound that binds to and precipitates proteins and various other organic
compounds. They can be chararcterize with IR spectra based on:
C-H aromatic no absorption. C=C aromatic bond no absorption.
Weight Loss Measurement:
The size of the coupon used for the immersion test was 50x25x1.5mm. Twenty specimens were used, the
four set of five coupons were abraded with emery papers from 220 to 1200 grits ,were washed doubly with
deionized water, degreased with acetone and air dried at room temperature. The specimens were weighed in
setra electronic digital weighing balance and each weight recorded prior to immersion. Five coupons suspended
by inextensible thread were immersed in a non-conductive container of 3.5% NaCl solution of 2725 ml (20
ml/cm2).Four immersion containers were used, three with vernonia amygdalina extracts (organic inhibitors) in
the proportion of 2% v/v, 4% v/v and 6%v/v, and the controlled experiment was without inhibitor. The weight
loss of each coupon was determined after 7 days, 14 days, 28 days, 42 days and 56 days. After each immersion
period the specimens were carefully removed from the ponding solution, cleaned, thoroughly washed with
distilled water, acetone, dried and then weighed in order to determine the weight loss, rate of corrosion,
inhibition efficiency and degree of surface covering. The experiment was conducted at temperature range within
28oC-34.7oC.
Determination of Corrosion Rate (mmpy), degree of surface coverage and inhibition efficiency (%):
The weight loss was calculated by finding the variation between initial and final weight of each coupons
after each immersion period as shown in equation (1).
W = Wi –Wf
Wi = initial weight, Wf = final weight
Corrosion Penetration Rate ( mm/yr) =
(1)
87600W/ ρAt
(2)
W is the weight loss (mg) after exposure time t (h), ρ is density of metal (g/cm³) and A is the area of the
specimen (cm²) and t, time of exposure in hours.
The standard expression for measurement of corrosion rate in millimetre per year (mm/y) in equation (2)
above was used to determine the corrosion rate as given in ASTM G 1-03.
The degree of surface coverage, Da at each concentration of inhibitor was determined thus;
Da =
(3)
Where 1 and 2 are the weight loss in coupon without and with inhibitor respectively.
The inhibition efficiency (IE %) was evaluated as given in the equation below:
IE % = (1Where R and Ro are the corrosion rates with and without inhibitor respectively.
(4)
XXX et al,2013
Australian Journal of Basic and Applied Sciences, 7(14) December 2013, Pages: x-x
260
RESULTS AND DISCUSSION
Phytochemical screening: The results of the phytochemical screened plant extract are given in Table 3.1.
Table 3.1: Phytochemical results
Phytochemicals Tested
Alkaloids
Saponins
Tannins
Remark
Positive
Positive
Positive
The phytochemical screening reveals that vernonia amygdalina contains alkaloid, saponin and tannin as
shown in Table 3.1.
Infra-Ray spectroscopy
The infra-ray analysis of the extract shows that vernonia amygdalina contains –N-H group compounds
(band range of between 3456 and 1620) as reported by Chennappan and Mathur [23].
72.4
71
801.15
721.59637.52
70
69
897.16
68
67
66
1443.09
65
1714.06
64
1377.28
1258.99
1159.75
1646.02
63
2857.14
%T
62
2868.13
61
60
1075.78
59
1043.18
2927.24
58
57
56
55
3401.22
54
53
52.0
4000.0
3600
3200
2800
2400
2000
1800
cm-1
1600
1400
1200
1000
800
600
450.0
Fig. 3.1:Infra Ray analysis results of vernonia amygdalina extract.
Corrosion evaluation of test specimens after immersion time:
Corrosion evaluation was carried by visual inspections, weight loss measurement, corrosion rate, inhibition
efficiency and degrees of surface coverage as explained as follows:
Visual inspection:
From the visual inspection,as shown in Fig.3.2, it is evident that the sample without corrosion inhibitor
corrodes uniformly and the thickness of the corrosion products (rust) increased with immersion time. However,
the presence of inhibitors in the immersion solution reduced the formation of rust which implies that the
specimens’ surfaces were modified due to adhesive layer formation. Although, the presence of cracks were
observed on coupons with 2%v/v inhibitor within the immersion time (Ayeni et al., 2012).
a
b
c
d
e
f
g
h
Fig. 3.2: Immersed samples in 3.5% NaCl solution for 56 days exposure time.
(a,b) Samples immersed in 3.5% NaCl solution with vernonia amygdalina inhibitor for 56 days exposure
time ( surface before cleaning and after cleaning)
(c,d) Samples immersed in 3.5% NaCl solution with sodium nitrite inhibitor for 56days exposure time(
surface before cleaning and after cleaning)
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Australian Journal of Basic and Applied Sciences, 7(14) December 2013, Pages: x-x
(e,f) Samples immersed in 3.5% NaCl solution with calcium nitrite inhibitor for 56 days exposure time
(surface before cleaning and after cleaning)
(g,h) Samples immersed in 3.5% NaCl solution without inhibitor for 56 days exposure time
(surface before cleaning and after cleaning)
Weight loss measurement after exposure time:
Figure 3.3 shows the weight loss as a function of immersion time for coupons immersed in 3.5% NaCl
solution for 56 days exposure duration. From the chart, it is obvious that weight loss increases with immersion
time. For the coupon without inhibitor, the weight loss increased dramatically from 0.016 gram in the first week
to 0.289g at the end of the exposure time. Similarly, weight loss for samples with 2% inhibitor show a slight
increase from 0.011 to 0.056g for the first 28 days and then increased significantly to 0.149g at the end of the
immersion duration due to chloride ion attack on the unprotected metal surface. However, for coupons with 4%
and 6% inhibitor, weight loss increased gradually in the first four weeks and declined progressively 0.075 and
0.072g respectively at the end of the test. This reduction in weight loss is due to physical adsorption of inhibitor
molecules on the metal creating a barrier film on the surface of the metal (Oguize et al., 2004, Chetouani et al.,
2004).
Fig. 3.3: Weight loss versus immersion time for mild carbon steel immersed in 3.5% NaCl solution for 56 days
exposure time.
Corrosion rate in mm/yr:
Figure 3.4 shows the corrosion rate versus time, from the figure it is evident that carbon steel corrodes
uniformly in 3.5% NaCl solution without inhibitor within the first fourteen days due to aggressive chloride ions
attack. However, corrosion tends to decrease afterward; this is due to corrosion products (rust) which tends to
shield the metal surface from the corrosive environment. The presence of oxygen forms ferrous oxide
precipitates from the solution which subsequently oxidizes to ferric salt (corrosion product) popularly known as
rust (Fontana and Greene, 1982).Corrosion rates decreased significantly with increased in concentration
dosages. However, coupons in solution with 2%v/v inhibitor shows slight increase in corrosion rate in the first
28 days of immersion and increased significantly till the end of the immersion period. This is as a result of
breaking down of protective layer initially formed on the metal surface (Ayeni et al., 2012. The rate of corrosion
decreased from 0.027mm/yr to 0.023 and 0.022 at the end of the immersion period for 4%v/v and 6%v/v
respectively. The presences of tannins,alkaloids and saponnins in vernonia amygdalina acts as a barrier on the
metal surface, thus preventing the diffusion of ions from or to the surface of the corrodent thereby blocking the
anodic or cathodic site which consequently reduces corrosion rates (Loto, 2003)].The inhibition mechanism is
by physical adsorption due to the presence of heteroatoms in alkaloid with functional group –N-H. This finding
is in conformity with the report of Abdulrahman (Adulrahman, 2012).
Fig. 3.4: Corrosion rate as function of immersion time of mild steel immersed in 3.5% NaCl solution for 56
days exposure time.
262
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Australian Journal of Basic and Applied Sciences, 7(14) December 2013, Pages: x-x
Inhibition efficiency:
The inhibition efficiency versus immersion time chart as shown in Figure 3.5, clearly revealed that
efficiency of vernonia amygdalina increases with dosage, the inhibition efficiency at the end of the study is as
follow; 75 %, 74% and 48.4% with 6%, 4% and 2% dosage of the inhibitor respectively. However, 6%v/v gave
the maximum efficiency with insignificant difference of 1.4% in comparison with the efficiency of 4% vernonia
amygdalina at the end of the immersion time. This results shows that the inhibition efficiency does not improve
further beyond required dosage.
Fig. 3.5: Inhibition efficiency versus immersion time of mild steel immersed in 3.5% NaCl solution for 56 days
exposure time.
Degree of surface coverage:
From the chart in Figure 3.5, it is evident that more protective surfaces for coupons in solution with 4% and
6% inhibitor concentrations at the end of the exposure time. Thus higher degree of stable surface coverage
promotes inhibition efficiency
.
Fig. 3.5: Degree of surface coverage versus immersion time of mild steel immersed in 3.5% NaCl solution for
56 days exposure time.
Conclusions:
The following conclusions can be drawn from the study:
The order of inhibition efficiency was found to be 75%, 74% and 48% for 6%, 4% and 2% inhibitor
concentrations respectively at the end of the immersion test. The average corrosion rate at the end of the
immersion time is as follow; without inhibitor is 0.09 mm/yr, 2% inhibitor is 0.04mm/yr, 4% inhibitor is 0.03
mm/yr, 6% inhibitor is 0.03 mm/yr. Vernonia amygdalina inhibition mechanism is by physical adsorption.
ACKNOWLEDGEMENTS
The authors express their thanks to the members of staff and laboratory technicians in the department of
chemistry, Civil and Materials engineering in Universiti Teknologi Malaysia for their patience and moral
support during the studies.
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