ABSTRACT
Inhibiting effects of Barteria fistulosa and Spondias mombin leaves extract on the corrosion of low carbon steel and aluminium alloy (AA2024) in 1M HCl and 0.5 M NaCl solution was investigated using gravimetric and electrochemical methods. The results obtained from the weight loss experiment performed at various temperatures (30, 45, and 60 0C) show that inhibition efficiency values decreased with temperature rise but increased as the inhibitor concentrations were increased. However, in all cases, the inhibition efficiency values of the Barteria fistulosa (BF) extracts were found to be greater than those of Spondias mombin (SM). For low carbon steel in 1 M HCl, optimum inhibition efficiency value of 95.27% and 80.32% were respectively obtained for BF and SM at 30 0C while for AA2024 in 1M HCl, an optimum inhibition efficiency value of 69.28 % and 78.06 % were respectively obtained for BF and SM at same temperature. Similarly, for low carbon steel in 0.5 M NaCl, optimum inhibition efficiency value of 78.06 % and 67.25 % were respectively obtained for BF and SM at 30 0C. The values obtained for the standard enthalpy of adsorption were all positive which signifies endothermic adsorption of the inhibitors on the metals’ surface. The values obtained for the standard entropy of adsorption were all negative. Negative value of entropy is associated with decrease in disorderliness and implies that the activation complex encourages association instead of dissociation. For all cases, the difference between the corresponding values of and Ea is approximately 2.64 kJ/mol. More so, results obtained from the isotherm study show that Langmuir isotherm best fitted the adsorption of both leaves extract on low carbon steel in the aggressive media. However, the adsorption of the inhibitors’ extract on AA2024 in the acidic medium best fitted the Freundlich isotherm. The tafel extrapolation plots obtained from the PDP experiments show a decrease in the values of corrosion current density (Icorr) and corrosion potential (Ecorr) as the concentration of the inhibitors (SM and BF) was increased. This implies that the anodic dissolution of mild steel and cathodic reduction of hydrogen ions was inhibited leading to reduction of the corrosive active surface area. The trend of the Nyquist plots obtained from the EIS experiment reveals that the higher the concentration of the inhibitor, the more the increase in radius the semi-circular loops. This confirms that BF and SM are adsorption inhibitors for mild steel and AA2024 in both acidic and saline solutions.
TABLE OF CONTENT
Title
page i
Declaration ii
Certification iii
Dedication iv
Acknowledgement v
Table
of Content vi
List
of Tables xii
List
of Figures xvi
Abstract xxiii
CHAPTER 1: 1
INTRODUCTION 1
1.1
Background to the Study 1
1.2
Statement of Problem 2
1.3
Aim of the Study 4
1.4
Objectives of the Study 4
1.5
Significance of the Study 4
1.6
Scope of the Study 5
CHAPTER 2: LITERATURE REVIEW
2.1 Overview 6
2.2 Consequences of Corrosion 7
2.3 Corrosive Environment 8
2.4 Corrosion Parameters 8
2.4.1 Solution acidity 9
2.4.2 Oxidizing agent 9
2.4.3 Temperature 10
2.4.4 Film deposition 10
2.4.5 Dissolved salt 11
2.4.6 Fluid velocity 11
2.4.7 Impurities 12
2.5 Classification of Corrosion 12
2.5.1 General attack corrosion 12
2.5.2 Localized corrosion 12
2.5.3 Galvanic corrosion 13
2.5.4 Environmental cracking 13
2.5.5 Flow assisted corrosion 14
2.5.6
Intergranular corrosion 14
2.5.7 Fretting corrosion 14
2.5.8 High temperature corrosion 15
2.5.9 De-alloying 15
2.5.10
Biological corrosion 15
2.6 Corrosion Inhibitors 16
2.6.1 Classification of inhibitors 17
2.6.1.1
Anodic inhibitors
17
2.6.1.2
Cathodic inhibitors
18
2.6.1.3 Organic inhibitors 19
2.6.2 Green corrosion inhibitors 21
2.6.2.1
Amino acid as inhibitor 21
2.6.2.2 Plant extract as inhibitor 22
2.6.2.3 Carbohydrates as green corrosion inhibitors 24
2.6.2.4 Exudate gum as green corrosion inhibitor 25
2.7 Methods of monitoring corrosion 26
2.7.1 Weight loss method 26
2.7.2 Electrochemical method
28
2.7.2.1 Electrochemical impedance spectroscopy
28
2.7.2.2 Potentiodynamic polarization 29
2.7.3 X-ray diffraction and x-ray photoelectron
spectroscopy 31
2.7.4 Fourier transform infrared spectroscopy
31
2.7.5 Electrical resistance spectroscopy 32
2.7.6 Thermometric method 32
2.7.7 Scanning electron microscopy 33
CHAPTER 3: MATERIALS AND
METHODS 34
3.1 Materials and Methods 34
3.1.1 Chemical composition of low carbon steel
and aluminium 34
3.1.2 Phytochemical and mineral composition of spondias mombine 35
3.1.3 Phytochemical and mineral composition of barteria fistulosa 36
3.2 Corrodent preparation 37
3.2.1 1 M of hydrochloric acid 37
3.2.2 0.5 M of sodium chloride 37
3.3 Leaves Extraction 38
3.3.1 Barteria
fistulosa extract in 1M HCl 38
3.3.2 Spondias mombine extract in 1M HCl 38
3.3.3 Barteria
fistulosa extract in 0.5 M NaCl 39
3.3.4 Spondias
mombine extract in 0.5 M NaCl 39
3.4 Coupon Preparation 40
3.5 Experimental procedure 40
3.5.1 Weight loss measurement 40
3.5.2 Electrochemical measurements 41
3.5.2.1 Potentiodynamic polarization measurement 41
3.5.2.2 Electrochemical impedance spectroscopy 42
3.5.3 Temperature considerations 43
3.6 Adsorption Isotherm 44
3.6.1 Langmuir isotherm 45
3.6.2 Temkin isotherm 45
3.6.3 Freundlich isotherm 45
CHAPTER 4: RESULTS AND DISCUSSION 47
4.1 Introduction 47
4.2
Gravimetric Measurement 47
4.2.1 Inhibition efficiency and corrosion rate of
low carbon steel in 1M
of HCl in the presence and absence of inhibitor 47
4.2.2 Inhibition efficiency and corrosion rate of
low carbon aluminium
alloy
in 1M of HCl in the presence and absence
of inhibitor 53
4.2.3 Inhibition efficiency and corrosion rate of
low carbon steel in 0.5M
of
NaCl in the presence and absence of inhibitor 58
4.2.4 Inhibition efficiency and corrosion rate of
aa2024 in 0.5M of NaCl
in the
presence and absence of inhibitor 63
4.3 Electrochemical Characterization 68
4.3.1 Electrochemical impedance spectroscopy (EIS) 68
4.3.1.1
EIS of carbon steel in 1M of HCl with and without the inhibitors 68
4.3.1.2
EIS of carbon steel in 3.5% NaCl
environment with and without
the inhibitors 72
4.3.1.3
EIS of aluminium (AA2024) in 1M
HCl environment with and
without the inhibitors 76
4.3.1.4
EIS of aluminium (AA2024) in 3.5%
NaCl environment with
and without the inhibitors 80
4.3.2 Electrochemical potentiodynamic polarization (PDP) 84
4.3.2.1
PDP of carbon steel in 1M of HCl with and without the inhibitors 84
4.3.2.2
PDP of carbon steel in 1M of 3.5%
NaCl with and without the
inhibitors 88
4.3.2.3
PDP of aluminium in 1M of HCl with and
without the inhibitors 92
4.3.2.4
PDP of aluminium in 3.5% NaCl with and without the
inhibitors 96
4.4 Thermodynamic analysis 100
4.4.1 Effects
of temperature variation on the corrosion of low carbon steel
in
1 M HCl environment in the absence and presence of the inhibitors 100
4.4.2 Effects
of temperature variation on the corrosion AA2024 in 1 M
HCl environment in the absence and presence of
the inhibitors 114
4.4.3 Effects
of temperature variation on the corrosion of low carbon steel in
0.5
M NaCl environment in the absence and presence of the inhibitors 128
4.5 Adsorption Isotherm Results 142
4.5.1
Temperature effect on the adsorption of barteria
fistulosa and spondias
mombin on low carbon
steel in 1 M HCl 142
4.5.2 Temperature effect on the adsorption of barteria fistulosa and spondias mombin on low carbon steel in
0.5 M NaCl 151
4.5.3 Temperature
effect on the adsorption of barteria
fistulosa and spondias mombin on
AA2024 in 1 M HCl 160
Chapter
5: Conclusion and Recommendation 169
5.1 Conclusion 169
5.1.1 Gravimetric method 169
5.1.2 Potentiodynamic polarization technique (PDP) 170
5.1.3 Electrochemical impedance spectroscopy (EIS) 170
5.1.4 Thermodynamic and adsorption isotherm studies 171
5.2 Recommendation 172
REFERENCES 171
LIST OF TABLES
2.1:
Some Anchoring (Functional) Groups in Organic Inhibitors 20
3.1: Elemental Composition of low Carbon steel 34
3.2: Elemental Composition of AA2024 34
4.1:
Electrochemical Impedance Parameters for low carbon Steel in 1 M
HCl in the Absence and Presence of SM and BF 71
4.2: Electrochemical Impedance
Parameters for low carbon Steel in 3.5%
NaCl solution in the
Absence and Presence of SM and BF 75
4.3: Electrochemical
impedance Parameters for AA2024 in 1 M
HCl in the Absence and Presence of SM
and BF 79
4.4: Electrochemical
impedance Parameters for AA2024 in 3.5%
NaCl in the
Absence and Presence of SM and BF 83
4.5: Potentiodynamic Polarization
Parameters for low carbon Steel in 1 M
HCl in the Absence and Presence of SM and BF 87
4.6: Potentiodynamic Polarization
Parameters for low carbon Steel in
3.5% NaCl in the
Absence and Presence of SM and BF 91
4.7: Potentiodynamic Polarization
Parameters for Aluminium in 1 M
HCl in the Absence and Presence of SM and BF 95
4.8: Potentiodynamic Polarization
Parameters for Aluminium (AA2024)
in 3.5% NaCl in the
Absence and Presence of SM and BF 99
4.9:
Calculated values of corrosion
parameters obtained from weight loss experiments involving low carbon steel
immersed in 1 M HCl containing various concentrations of Barteria fistulosa at temperature of 300, 450,
and 600 101
4.10: Calculated values of corrosion parameters
obtained from weight loss experiments involving low carbon steel immersed in 1
M HCl containing various concentrations of Spondias
mombin at temperature of 300, 450, and 600. 102
4.11:
Calculated values of activation energy (Ea) and the Arrhenius
constant (A) for LCS in 1 M HCl in the absence and
presence of various concentration of BF leaves extract 108
4.12:
Calculated values of activation energy (Ea) and the Arrhenius
constant (A) for
LCS in 1 M HCl in the absence and presence of various concentration of SM leaves extract 109
4.13: Transition state parameters for the
adsorption of BF extract on low carbon steel surface immersed in 1 M HCl 112
4.14: Transition state parameters for the
adsorption of SM extract on low carbon steel surface immersed in 1 M HCl 113
4.15 : Calculated values of corrosion
parameters obtained from weight loss experiments involving AA2024 immersed in 1
M HCl containing various concentrations of Barteria
fistulosa at temperature of 300, 450, and 600 115
4.16: Calculated values of corrosion
parameters obtained from weight loss experiments involving AA2024 immersed in 1 M HCl
containing various concentrations of Spondias
mombin at temperature of 300, 450, and 600 116
4.17:
Calculated values of activation energy (Ea) and the Arrhenius
constant (A) for AA2024 in 1 M HCl in the absence and
presence of various concentration of BF leaves extract 122
4.18:
Calculated values of activation energy (Ea) and the Arrhenius
constant (A) for AA2024 in 1 M HCl in the absence and
presence of various concentration of SM leaves extract 123
4.19: Transition state parameters for the
adsorption of BF extract on AA2024 surface immersed in 1 M HCl 126
4.20: Transition state parameters for the
adsorption of SM extract on AA2024
surface immersed in 1 M HCl 127
4.21:
Calculated values of corrosion parameters obtained from weight loss experiments
involving low carbon steel immersed in 0.5M NaCl containing various
concentrations of Barteria fistulosa at
temperature of 300, 450, and 600 129
4.22: Calculated values of corrosion
parameters obtained from weight loss experiments involving low carbon steel
immersed in 0.5M NaCl containing various concentrations of Spondias mombin at temperature of 300, 450,
and 600 130
4.23:
Calculated values of activation energy (Ea) and the Arrhenius
constant (A) for LCS in 0.5 M NaCl in the absence and
presence of various concentration of BF leaves extract 136
4.24:
Calculated values of activation energy (Ea) and the Arrhenius
constant (A) for LCS in 0.5 M NaCl in the absence and
presence of various concentration of SM leaves extract 137
4.25:
Transition state parameters for the adsorption of BF extract on low carbon
steel surface immersed in 0.5 M NaCl 140
4.26:
Transition state parameters for the adsorption of SM extract on low carbon
steel surface immersed in 0.5 M NaCl 141
4.27:
Adsorption isotherm parameter of BF
leaves extract on low carbon steel in 1 M HCl environment after 4 hours of
exposure 143
4.28: Adsorption isotherm parameter of SM leaves extract on low carbon steel in
1 M HCl environment after 4 hours of exposure 144
4.29: Adsorption isotherm parameter of BF leaves extract on LCS in 0.5 M NaCl
environment after 4 hours of exposure 152
4.30: Adsorption isotherm parameter of SM leaves extract on LCS in 0.5 M NaCl
environment after 4 hours of exposure 153
4.31: Adsorption isotherm parameter of BF leaves extract on AA2024 in 1 M HCl
environment after 4 hours of exposure 161
4.32:
Adsorption isotherm parameter of SM
leaves extract on AA2024 in 1 M HCl environment after 4 hours of exposure 162
LIST
OF FIGURES
2.1:
Schematic diagram of EIS circuit 28
2.2: Nyquist plot with impedance vector 29
2.3: Potentiodynamic polarization curves 30
3.1: Spondias
mombine plant 35
3.2: Barteria fistulosa plant 36
4.1: Corrosion rate of low carbon steel in 1M HCl
containing various concentrations of BF 49
4.2: Corrosion rate of low carbon steel in 1M HCl
containing various concentrations of SM 50
4.3: Inhibition efficiency of various
concentrations BF on low carbon steel in 1M HCl 51
4.4: Inhibition efficiency of various
concentrations SM on low carbon steel in 1M HCl 52
4.5: Corrosion rate of AA2024 in 1M HCl containing
various concentrations of
BF 54
4.6: Corrosion rate of AA2024 in 1M HCl containing various Concentration of SM 55
4.7: Inhibition efficiency of various
concentrations of BF on AA2024 in 1M HCl 56
4.8:
Inhibition efficiency of various
concentrations of SM on AA2024 in 1M HCl 57
4.9: Corrosion rate of low carbon steel in 0.5M
NaCl containing various concentrations of BF 59
4.10:
Corrosion rate of low carbon steel in 0.5M NaCl containing various concentrations of SM 60
4.11:
Inhibition efficiency of various concentrations of BF on carbon steel in 0.5M NaCl 61
4.12:
Inhibition efficiency of various concentrations of SM on carbon steel in 0.5M NaCl 62
4.13:
Corrosion rate of AA2024 in 0.5M NaCl containing various concentrations of BF 64
4.14:
Corrosion rate of AA2024 in 0.5M NaCl containing various
concentrations of SM 65
4.15:
Inhibition efficiency of various concentrations of BF on AA2024 in 0.5M NaCl 66
4.16:
Inhibition efficiency of various concentrations of SM on AA2024 in 0.5M NaCl 67
4.17: Nyquist plot of low
carbon steel in 1 M HCl
environment in the absence and presence of SM 69
4.18: Nyquist plot of low
carbon steel in 1 M HCl
environment in the absence and presence of BF 70
4.19: Nyquist plot of low
carbon steel in 3.5% NaCl environment in the absence and presence of SM 73
4.20: Nyquist plot of low
carbon steel in 3.5% NaCl environment in the absence and presence of BF 74
4.21: Nyquist plot of AA2024 in 1 M HCl environment
in the absence and presence of SM 77
4.22: Nyquist plot of AA2024 in 1 M HCl environment
in the absence and presence of BF 78
4.23: Nyquist plot of AA2024 in 3.5% NaCl environment in the absence and presence of SM 81
4.24: Nyquist plot of AA2024 in 3.5% NaCl environment in the absence and presence of BF 82
4.25: Potentiodynamic polarization plot of low
carbon steel in
1 M HCl environment in the absence and presence of SM. 85
4.26: Potentiodynamic polarization plot of low
carbon steel in
1 M HCl environment in the absence and presence of BF 86
4.27: Potentiodynamic polarization plots
of low carbon steel in
3.5% NaCl environment in the absence and presence of SM. 89
4.28: Potentiodynamic polarization plots of low
carbon steel in
3.5% NaCl
environment in the absence and presence of BF. 90
4.29: Potentiodynamic polarization plot of
AA2022 in 1 M HCl
environment in the absence and presence of SM. 93
4.30: Potentiodynamic polarization plot of AA2022 in 1 M
HCl
environment in the absence and presence of BF. 94
4.31:
Potentiodynamic
polarization plot of AA2024 in 3.5% NaCl
environment in the absence and presence of SM. 97
4.32:
Potentiodynamic
polarization plots of AA2024 in 3.5% NaCl
environment in the absence and presence of BF. 98
4.33: Plot of inhibition efficiency against
concentration for LCS
immersed in 1M HCl containing various concentration of
Barteria Fistulosa 103
4.34: Plot of inhibition efficiency against
concentration for LCS
immersed in 1M HCl containing various concentration of
Spondias mombin 104
4.35:
Arrhenius plot for the corrosion of low carbon steel in 1 M
HCl containing various concentrations of BF 106
4.36:
Arrhenius plot for the corrosio of LCS in 1 M HCl containing various
concentrations of SM 107
4.37: Transition state plot for the corrosion of LCS in solution of 1 M
HCl containing various concentrations of BF 110
4.38: Transition state plot for the corrosion of LCS in solution of 1 M
HCl
containing various concentrations of
SM 111
4.39:
Plot of inhibition efficiency against concentration for AA2024
immersed in 1M HCl containing various concentration of BF 117
4.40: Plot of inhibition efficiency against
concentration for AA2024
immersed in 1M HCl containing various concentration of SM 118
4.41:
Arrhenius plot for the corrosion of AA2024 in 1 M HCl containing various concentrations of BF 120
4.42:
Arrhenius plot for the corrosion of AA2024 in 1 M HCl containing various concentrations of SM 121
4.43: Transition state plot for the corrosion of AA2024 in solution of 1
M
HCl containing various concentrations
of BF 124
4.44: Transition state plot for the corrosion of AA2024 in solution of 1
M
HCl containing various concentrations
of BF 125
4.45: Plot of inhibition efficiency against
concentration for LCS immersed in
0.5 M
NaCl containing various concentration of BF 131
4.46: Plot of inhibition efficiency against
concentration for LCS
immersed in 0.5 M NaCl containing various
concentration of SM 132
4.47:
Arrhenius plot for the corrosion of low carbon steel in
0.5
M NaCl containing various concentrations
of BF 134
4.48:
Arrhenius plot for the corrosion of low carbon steel in 0.5 M
NaCl containing various concentrations of SM 135
4.49:
Transition state plot for the corrosion of LCS in solution of 0.5 M
NaCl containing various
concentrations of BF 138
4.50: Transition state plot for the corrosion of LCS in solution of 0.5
M
NaCl containing various
concentrations of SM 139
4.51: Langmuir adsorption isotherms for the adsorption
of BF leaves
extract on LCS in 1 M HCl environment 145
4.52: Langmuir adsorption isotherms for the adsorption
of SM leaves
extract on
LCS in 1 M HCl environment 146
4.53: Temkin adsorption isotherms for the adsorption
of BF leaves
extract on LCS in 1 M HCl environment 147
4.54: Temkin adsorption isotherms for the adsorption
of SM leaves
extract on LCS in 1 M HCl environment 148
4.55: Freundlich adsorption isotherms for the
adsorption of BF leaves
extract on LCS in 1 M HCl environment 149
4.56: Freundlich adsorption isotherms for the
adsorption of SM leaves
extract on LCS in 1 M HCl environment 150
4.57: Langmuir adsorption isotherms for the adsorption
of BF leaves
extract on LCS in 0.5 M NaCl
environment 154
4.58: Langmuir
adsorption isotherms for the adsorption of SM leaves
extract on LCS in 0.5 M NaCl
environment 155
4.59: Temkin
adsorption isotherms for the adsorption of BF
leaves
extract
on LCS in 0.5 M NaCl environment 156
4.60: Temkin
adsorption isotherms for the adsorption of SM leaves
extract on LCS in 0.5 M NaCl
environment 157
4.61:
Freundlich adsorption isotherms for the adsorption of BF leaves
extract on LCS in 0.5 M NaCl
environment 158
4.62:
Freundlich adsorption isotherms for the adsorption of SM leaves
extract on LCS in 0.5 M NaCl
environment 159
4.63: Langmuir
adsorption isotherms for the adsorption of BF
leaves
extract on AA2024 in 1 M HCl
environment 163
4.64: Langmuir
adsorption isotherms for the adsorption of SM leaves
extract on AA2024 in 1 M HCl
environment 164
4.65: Temkin adsorption isotherms for the adsorption
of BF leaves
extract on AA2024 in 1 M HCl
environment 165
4.66: Temkin
adsorption isotherms for the adsorption of SM
leaves
extract on AA2024 in 1 M HCl
environment 166
4.67: Freundlich
adsorption isotherms for the adsorption of BF leaves
extract on AA2024 in 1 M HCl
environment 167
4.68: Freundlich
adsorption isotherms for the adsorption of SM
leaves
extract
on AA2024 in 1 M HCl environment 168
CHAPTER
1
INTRODUCTION
1.1
BACKGROUND
TO THE STUDY
Corrosion is the degradation of a material usually
metal(s) as a result of chemical or electrochemical reaction with its
surrounding environment (Winston and Uhlig, 2008; Roberge, 2000). Corrosion is a surface electrochemical phenomenon common to all base
metals in aqueous or humid environments whereby metal ions are developed at a
cathodic site and the electrons associated with this dissolution are accepted
at an anodic site (Toshiaki et al.,
2018; Buchanan and Stansbury, 2012).
Steel and aluminum alloys due to their physical
properties (weldability, formability, toughness, and high temperature
resistance) have wide range of industrial application(s) in; oil and gas,
automotive and aerospace industries.
Aluminum alloy (AA2024) like other 2000 series
contains copper as its major alloying element. The high strength, fatigue
resistance, and workability features of AA2024 makes it suitable for use in
aerospace industry to manufacture some special parts such as wing structure,
gears and shafts, as well as the fuselage. However, this aluminum alloy has poor
corrosion resistance property and is therefore susceptible to attacks when
exposed to corrosive environment.
Low carbon steel, also known as mild steel contains
approximately 0.05 - 0.15 carbon and has a density of approximately
7.85 g/cm3.
Due to its properties such as ductility, malleability
and weldability, mild steel has wide range of use. Mild steel is the most
common form of steel because its price is relatively low while it provides
material properties that are acceptable for many industrial applications such
as construction of bridges, automobile and aircraft body, pipes, chains, bolts
and shafts. Mild steel is also
economical for use in the manufacture of heat resistant materials such as heat
exchanger. However, the life span of the mild steel in contact with acidic or
alkaline medium depends on the protection or inhibition techniques adopted in
such environment.
Corrosion of metallic materials due to exposure to corrosive
environment has been investigated by researchers (Ogwo et al., 2017; Adama and Onyeachu, 2023; Ulaeto et al., 2012; Ejikeme et al.,
2015; Ekanem et al., 2010; Satapathy et al., 2009; Ebenso and Oguzie, 2005)
using organic or inorganic inhibitors. Organic compounds capable of serving as
inhibitors must have active adsorption centers and should also possess
hetero-atoms such as oxygen, sulphur, phosphorous, chlorine, bromine, iodine
and nitrogen (Brycki et al., 2017). The
inhibitive effect of plants extracts can be attributed to the presence of
organic species such carbohydrates, tannins, alkaloids and nitrogen bases,
amino acids and proteins (Proenca et al.,
2022; Magu and Ugi, 2017).
There are a number
of means of controlling corrosion. The choice or means of corrosion control
depends on economics, safety requirements, and a number of technical
considerations. Aside the use of organic inhibitors, other corrosion control
means are; use of protective paints or protective metal, control of aqueous
solution pH values toward slightly alkaline, and application of electric
potential to equipment.
1.2
STATEMENT
OF PROBLEM
Corrosion is a major concern in aerospace industry as
well as in industries where aggressive chemical solutions are used for
processes such as ore production, oil well acidizing, chemical cleaning and
acid pickling of steel.
The significant limitation of mild steel and aluminum
alloy is that it loses its corrosion resistance property when exposed to
alkaline or acidic environment.
Huge losses of natural
resources and finances are sustained annually all over the globe as a result of
corrosion. In aviation industry, some airplane body
parts made of aluminum alloy are susceptible to corrosion when exposed to
acidic rain, moisture or air. Undetected
corrosion often leads to failure of the airplane’s wing propeller, cylinder
fins and crankshaft.
In the petroleum and gas industries, more than
half of the registered oil spills due to undetected cracks in steel pipelines
are caused by corrosion (Obike et al., 2020). More
so, failure of oil exploration equipment such as drilling rig can be attributed
to corrosion due to exposure to high temperature acidic environment.
However,
corrosion processes can be controlled or inhibited by employing organic or
inorganic inhibitors. Inorganic substances suitable as metal corrosion
inhibitor must easily oxidize the metal to form an impervious layer which prevents
direct ions-metal interaction and hence retard the rate of metal dissolution in
the medium (Nnanna et al., 2014).
Over the years, inorganic inhibitors such as; chromate (Bastos et al.,
2006) and phosphate (Jing-Zhang et al.,
2019) compounds were employed to check corrosion process. The high toxicity of
these inorganic inhibitors gave rise to environmental and health related
issues. As a result, strict international laws were imposed (Dariva et al., 2013). The ban on some inorganic
compounds as inhibitors led to search for environmentally benign alternatives
such as green (organic) inhibitors. These green inhibitors are plant extracts
which have the qualities of being biodegradable, eco-friendly, low toxicity,
cost effective and readily available (Sethuraman and Raja, 2008). Organic
inhibitors can be adsorbed on the metal surface either through physical
adsorption which is due to electrostatic attraction between the inhibitor and
the metal surface or chemical adsorption, a process that involves charge
sharing or transfer between the inhibitor molecules and the metal surface
(Sastri, 1998; Fragoza-Mar et al.,
2012; Nnanna et al., 2015).
1.3
AIM
OF THE STUDY
The
aim of this research work is to investigate the corrosion inhibitory effects of
Barteria fistulosa (Oje) and Spondias mombine (Ichikara) leaves extract
on the corrosion of low carbon steel (LCS) and aluminum alloy (AA2024) in 1 M
acidic (HCl) and 0.5 M saline (NaCl) solutions at various temperatures.
1.4
OBJECTIVES
OF THE STUDY
In order to achieve the aim of this study, the objectives of the
study shall include the following,
i.
To determine the corrosion
behavior of AA2024 and low carbon steel in 1 M HCl and 0.5 M NaCl media without inhibitors
ii.
To determine the corrosion
processes of the metals in the presence of the inhibitors
iii.
To investigate the corrosion
inhibitive properties of the extracts on the metals
iv.
To determine the effect of
variations of temperature and its inhibition efficiencies
v.
To analyse the kinetic and
thermodynamic processes and the adsorption characteristics of the extracts
vi.
To investigate the corrosive behaviour of
the metals exposed to the acidic and alkaline media in the presence and absence
of the inhibitor using electrochemical measurements.
1.5 SIGNIFICANCE OF THE STUDY
This study emphasizes on
the importance of using plant extracts as corrosion inhibitors which are benign
and ecologically accepted. The plant product used must be non-toxic,
inexpensive and readily available. Inhibitors have wide application such as
cleaning of airplanes and industrial equipment. HCL is widely used in various
industries for processes which include; acid pickling of metals, de-scaling and
acidizing of oil wells (Ejikeme et al.,
2014). Inhibitors are usually employed in these processes to control corrosion
rate of metals in industries. However, most corrosion inhibitors are toxic and
have resulted in health related issues. This research is designed to
investigate the corrosion inhibition capability of Barteria fistulosa and Spondias mombine leaves extract as a
corrosion inhibitor which is non-toxic, readily available and environmentally
friendly. There has been no existing investigation on the use of Barteria fistulosa leaves extract as
corrosion inhibitor to the best of my knowledge. The leaves plant extracts of Spondias mombin has been investigated as corrosion
inhibitor of low carbon steel in acidic
medium by some researchers (Obi-Egbedi et al., 2012; Adama
and Onyeachu, 2023; Magu et al.,
2017). However, these works were mostly limited to the inhibitory performance
of Spondias mombin on mild steel in
acidic medium. This observation encouraged the further investigation of the
inhibitory effect Spondias mombin leaves extract on mild steel in both acidic
(HCl) and saline (NaCl) media. More so, the inhibitory effect Spondias mombin leaves extract could possibly be influenced by
the choice of metal or alloy used. Therefore, corrosion inhibition of aluminium
alloy (AA2024) in 1 M HCl and 0.5 M NaCl containing various concentrations of Spondias mombin leaves extract was also
investigated.
1.6
SCOPE
OF THE STUDY
This work focuses on
investigating corrosion inhibitory effect of Barteria fistulosa and Spondias
mombine leaves extract on low carbon steel and AA2024 when exposed to
acidic (HCl) and alkaline (NaCl) chemical solution environments using weight
loss and electrochemical methods.
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