Efficacy Of The Blend Of Extracts From Afzelia Africana, Brachystegia Eurycoma And Momordica Charantia Seeds For Corrosion Inhibition Of Mild Steel In 1m Hcl Solution
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ABSTRACT
The efficacy of blend of Afzelia africana (AA), Brachystegia eurycoma (BE) and Momordica charantia (MC) seed extracts was investigated as a cheap and ecologically friendly alternative mild steel corrosion inhibitor. The experimental aspect of the corrosion inhibition process was carried out in 1.0 M hydrochloric acid at temperatures ranging from 303K to 343K and concentration range of 0.1 to 0.5 g/L using Phytochemical Screening, gravimetric/weight loss, thermometric and hydrogen evolution techniques. The surface characterization was done using scanning electron microscopy (SEM) and Fourier transform infrared spectroscopic (FTIR) techniques. The theoretical aspect was studied using the density functional theory calculations and modeling of the electronic structures of some of the most effective extract constituents, including physisorptive interactions with the mild steel surface. The inhibition efficiency was determined by comparison of the corrosion rates in the absence and presence of the seed extracts. The inhibition efficiency increases gradually in the order: blend > AA > BE > MC with the blend reaching a maximum value of 95.4% within the first 60 minutes of exposure at a concentration of 0.5 g/L and temperature of 303K. The inhibition efficiencies by both the hydrogen evolution and thermometric methods when compared with that obtained by weight loss method, followed the same trend. The adsorption parameters showed that the Freundlich isotherm was the best model for the individual seed extracts and the modified Langmuir adsorption isotherm for the blend. The kinetic study shows that the inhibitory action follows a first order kinetics with the concentration of both the individual seed extracts and their blends. This was further supported by the thermodynamic parameters which reveal that the adsorption of both the individual seed extracts and their blends onto the metal surface was spontaneous, endothermic and followed physical adsorption mechanism. The low values of adsorption equilibrium constant, Kads indicate low interaction between the adsorbed molecules and the metal surfaces which further confirmed that the extracts were physically adsorbed onto the metal surface. FTIR study of the blended seed extracts and the corrosion product of mild steel showed an interaction between the inhibitor and the metal surface. SEM analyses of the corrosion product also confirmed the formation of a protective layer on the surface of the metal. Quantum chemical studies indicated that inhibition was due to adsorption of active molecules leading to formation of a protective layer on surface of mild steel. Quantum chemical parameters such as highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO) energy levels, HOMO–LUMO energy gap and electronic density were virtually identified. Therefore, the inhibition of mild steel corrosion is proposed to occur through synergistic combination of the constituents of the inhibitor, which leads to the formation of inhibitor-metal complex and subsequent protection of the metal from further corrosion attack.
TABLE OF CONTENTS
Cover page i
Title Page ii
Declaration iii
Certification iv
Dedication v
Acknowledgement vi
Table of Contents vii
List of Tables xiii
List of Figures xvi
List of Plates xxiv
Abstract xxv
1.0 Chapter 1: Introduction 1
1.1 Background of Study 1
1.2 Statement of the problem 4
1.3 Aim of the Study 5
1.4 Objectives of the Study 5
1.5 Significance of the Study 6
1.6 Scope of the Study 6
1.7 Justification of the Study 7
2.0 Chapter 2: Literature Review 8
2.1 Corrosion 8
2.2 Corrosion Chemistry 9
2.3 Classification of Corrosion 11
2.3.1 Dry Corrosion 11
2.3.2 Wet Corrosion 11
2.4 Forms of Corrosion 11
2.4.1 Uniform Corrosion 12
2.4.2 Galvanic or Two Metal Corrosion 12
2.4.3 Carbon dioxide Corrosion 13
2.4.3.1 Pitting Corrosion 13
2.4.3.2 Mesa-Type Attack 14
2.4.3.3 Flow-Induced Localized Corrosion 14
2.4.4 Crevice Corrosion 14
2.4.5 Intergranular Corrosion 14
2.4.6 Selective Leaching 15
2.4.7 Erosion Corrosion 15
2.4.8 Stress Corrosion 16
2.5 Factors Affecting Corrosion 16
2.6 The Problem of Corrosion 17
2.7 Corrosion Control 18
2.7.1 Materials selection and design 19
2.7.2 Surface Coatings 19
2.7.3 Modification of the Electrolyte 20
2.7.3.1 Removal of the Aggressive Species 20
2.7.3.2 The Addition of Corrosion Inhibitors 20
2.8 Types of Corrosion Inhibitors 21
2.8.1 Organic Inhibitors 21
2.8.1.1 Synthetic Organic Inhibitors 22
2.8.1.2 Natural Organic Inhibitors 23
2.8.2 Inorganic Inhibitors 24
2.8.2.1 Anodic Inhibitors 24
2.8.2.2 Cathodic Inhibitors 26
2.9 Corrosion Monitoring Techniques 27
2.9.1 Weight loss method 27
2.9.2 Gasometric/Hydrogen Evolution Method 28
2.9.3 Thermometric Method 30
2.10 Plant Description 31
2.10.1 Afzelia Africana (AA) 31
2.10.2 Brachystegia Eurycoma (BE) 32
2.10.3 Momordica Charantia (MC) 33
2.11 Methods Used For Extraction Of Plant Materials 35
2.12 Phyto-Chemical Analysis as a Tool in Corrosion Inhibition 36
2.13 Adsorption Isotherm 38
2.13.1 Langmuir Adsorption Isotherm 40
2.13.2 Temkin Adsorption Isotherm 42
2.13.3 Freundlich Adsorption Isotherm 43
2.13.4 Choice of Appropriate Adsorption Isotherm Model 44
2.14 Determination of Associated Thermodynamic and Kinetic Parameters 44
2.14.1 Thermodynamic Considerations 44
2.14.2 Kinetic Considerations 46
2.14.2.1Effect of Concentration on Reaction Rate 46
2.14.2.2Effect of Temperature on Reaction Rate 48
2.15 Theoretical and Quantum Chemical Studies as a Corrosion Monitoring Techniques 49
2.16 Scanning Electron Microscopy (SEM) 54
2.17 Empirical Review 56
2.17.1 Effects of Concentration on Corrosion Inhibition 56
2.17.2 Effect of Immersion Time on Corrosion Inhibition 61
2.17.3 Effect of Temperature on Corrosion Inhibition 64
2.18 Adsorption Isotherm Studies 68
2.19 Thermodynamics and Kinetic Treatment 71
2.20 Quantum Chemical Studies 76
3.0 Chapter 3: Methodology 79
3.1 Materials and Methods 79
3.1.1 Materials 79
3.2 Experimental Procedure 80
3.2.1 Preparation of Specimen 80
3.2.2 Surface Area and density of specimen 80
3.2.3 Preparation of Blends of Afzelia Africana, Brachystegia Eurycoma and
Momordica Charantia seed extracts 81
3.2.4 Preparation of 1.0M HCl 82
3.3 Phyto-Chemical Analysis 83
3.3.1 Test for Alkaloids 84
3.3.2 Test for Saponins 84
3.3.3 Test for Tannins 84
3.3.4 Test for Phenol 84
3.3.5 Test for Flavonoids 84
3.3.6 Test for Glycosides 84
3.3.7 Test for Steroids 85
3.3.8 Test for carbohydrates 85
3.3.9 Test for Reducing Sugar 85
3.3.10 Test for Proteins 85
3.3.11 Test for Amino acids 86
3.4 Gravimetric Technique 86
3.5 Hydrogen Evolution (Gasometric) Method 88
3.6 Thermometric Method 88
3.7 Adsorption Isotherm Study 89
3. 7.1 Langmuir Adsorption Isotherms 89
3.8 Thermodynamic and Kinetic Studies 90
3.8.1 Standard Gibbs free energy change of Adsorption, ΔG°ads 90
3.8.2 Activation Energy, Ea 90
3.8.3 Rate Constant for the Corrosion Rate, k 91
3.8.4 Half-life, t1/2 91
3.9 Scanning Electron Microscopy (SEM) 91
3.10 Fourier Transform Infrared Spectroscopy (FTIR) 91
3.11 Theoretical and Quantum Chemical Calculations 92
4.0 Chapter 4: Results and Discussion 93
4.1 Elemental Composition of Mild Steel 93
4.2 Phytochemical Screening 94
4.3 Weight Loss Results 97
4.3.1 Effect of Concentration of extracts on Corrosion Rate and Inhibition Efficiency 99
4.3.2 Effect of Immersion Time on Corrosion Inhibition 104
4.3.3 Effect of Temperature on Corrosion Rate and Inhibition Efficiency 106
4.4 Gasometric Results 111
4.5 Thermometric Results 116
4.6 Adsorption Mechanism 118
4.7 Thermodynamic and Kinetic parameters for the corrosion inhibition of both the
individual seed extracts and their Blends 128
4.7.1 Standard Gibbs free energy of adsorption, ΔG°ads 129
4.7.2 Activation Energy (Ea) for the Corrosion Process 130
4.7.3 Activation Parameters for the Corrosion Process 132
4.7.4 Rate of Reaction and Rate Constant of the Reaction 134
4.7.5 Half Life 147
4.8 Surface Studies by Scanning Electron Microscopy 149
4.9 Fourier transform infrared spectroscopy (FTIR) analysis 151
4.10 Theoretical and Quantum Chemical Studies 155
4.10.1 Mulliken charge distribution of Glucose, Arginine, Flavonol and Leucine 163
5.0 Chapter 5: Conclusion and Recommendations 166
5.1 Conclusion 166 5.2 Recommendations 168
References 169
Appendixes 183
LIST OF TABLES
3.1 List of Materials Used for the Experiments 79
3.2 List of Equipment for the Experiments 80
4.1 Elemental composition of mild steel employed in the study 93
4.2 Phytochemical Constituent of blends of AA, BE and MC extract 94
4.3 Hydrogen evolution data for mild steel corrosion in 1 M HCl solution in the absence and presence of the blended seed extract 111
4.4 Thermometric data for mild steel in 1.0 M HCl solution in the absence and presence of blended seed extract (AA, BE and MC) 116
4.5 Isotherm parameters for the adsorption of ethanolic extract of Afzelia africana seed
on the surface of mild steel in HCl 118
4.6 Isotherm parameters for the adsorption of ethanolic extract of Brachystegia eurycoma
seed on the surface of mild steel in HCl 120
4.7 Isotherm parameters for the adsorption of ethanolic extract of Momordica charantia
seed on the surface of mild steel in HCl 122
4.8 Isotherm parameters for the adsorption of ethanolic extracts of the blends of Afzelia africana, Brachystegia eurycoma and Momordica charantia seeds on the surface of
mild steel in HCl 124
4.9 Calculated values of thermodynamic and kinetic parameters for mild steel corrosion in
1 M HCl in the absence and presence of Afzelia africana seed extract as inhibitor 128
4.10 Calculated values of thermodynamic and kinetic parameters for mild steel corrosion in
1 M HCl in the absence and presence of Brachystegia eurycoma seed extract as
inhibitor 128
4.11 Calculated values of thermodynamic and kinetic parameters for mild steel corrosion in
1 M HCl in the absence and presence of Momordica charantia seed extract as
inhibitor 128
4.12 Calculated values of thermodynamic and kinetic parameters for mild steel corrosion in
1 M HCl in the absence and presence of blended seed extracts as inhibitor 129
4.13 Calculated values of the rate constant for mild steel corrosion in 1 M HCl in the absence
and presence of Afzelia africana seed extract 141
4.14 Calculated values of the rate constant for mild steel corrosion in 1 M HCl in the absence
and presence of Brachystegia eurycoma seed extract 141
4.15 Calculated values of the rate constant for mild steel corrosion in 1 M HCl in the absence
and presence of Momordica charantia seed extract 142
4.16 Calculated values of the rate constant for mild steel corrosion in 1 M HCl
in the absence and presence of blended seed extracts 143
4.16 Calculated values of the half life for mild steel corrosion in 1 M HCl in the absence
and presence of Afzelia africana seed extract 147
4.17 Calculated values of the half life for mild steel corrosion in 1 M HCl in the absence
and presence of Brachystegia eurycoma seed extract 147
4.18 Calculated values of the half life for mild steel corrosion in 1 M HCl in the absence
and presence of Momordica charantia seed extract 148
4.19 Calculated values of the half life for mild steel corrosion in 1 M HCl in the absence
and presence of blended seed extracts 148
4.21 IR Absorption of Afzelia africana seed extract 151
4.22 IR Absorption of Brachystegia eurycoma seed extract 151
4.23 IR Absorption of Momordica charantia seed extract 151
4.24 Quantum chemical parameters for most important components of the ethanol extract
of Blend of AA, BE and MC 155
4.25 Mulliken Charge Distribution on Flavonol, Leucine, Arginine and Glucose 165
LIST OF FIGURES
2.1 Anodic Inorganic Inhibitors Effect and their Mechanism of Action 25
2.2 Mechanism of Actuation of the Cathodic Inhibitors 26
2.3 Gasometric assembly for measurement of hydrogen gas evolved 29
2.4 Extraction method used for preparation of plant extracts 36
2.5 Schematic representation of an adsorption isotherm 39
4.1 Structures of the Phytochemicals Present in the blended seed extracts 95
4.2 Variation of weight loss with time for mild steel coupons in 1 M HCl solutions
containing Afzelia africana at 303K 97
4.3 Variation of weight loss with immersion time for mild steel coupons in 1 M HCl
solutions containing Brachystegia eurycoma at 303K 97
4.4 Variation of weight loss with immersion time for mild steel coupons in 1 M HCl
solutions containing Momordica charantia at 303K. 97
4.5 Variation of weight loss with immersion time for mild steel coupons in 1 M HCl
solution containing the Blend at 303K 98
4.6 Variation of corrosion rate with concentration of Afzelia africana extract for mild steel coupons in 1 M HCl solution at different time intervals at 303 K 99
4.7 Variation of corrosion rate with concentration of Brachystegia eurycoma extract for
mild steel coupons in 1 M HCl solution at different time intervals at 303 K 99
4.8 Variation of corrosion rate with concentration of Momordica charantia extract for mild
steel coupons in 1 M HCl solution at different time intervals at 303 K 100
4.9 Variation of corrosion rate with the concentration of Blend extract for mild steel coupons in 1 M HCl solution at different time intervals at 303 K 100
4.10 Comparisons of corrosion rate of the individual extract with the blend at 60 min
at 303 K 101
4.11 Variation of inhibition efficiency with concentration of Afzelia africana extract
for mild steel coupons in 1 M HCl solution at different time intervals at 303 K 101
4.12 Variation of inhibition efficiency with concentration of Brachystegia eurycoma extract for mild steel in 1 M HCl solution at different time intervals at 303 K 102
4.13 Variation of inhibition efficiency with concentration of Momordica charantia
extract for mild steel in 1 M HCl solution at different time intervals at 303 K 102
4.14 Variation of inhibition efficiency with extract concentration of the blend for mild steel coupons in 1 M HCl solution at different time intervals at 303 K 103
4.15 Comparisons of inhibition efficiencies of the individual extracts with the blend
at 60 min at 303 K 103
4.16 Variation of corrosion rate with different concentrations of Afzelia africana extract
showing the effect of temperature on the corrosion inhibition process 106
4.17 Variation of corrosion rate with different concentrations of Brachystegia eurycoma
extract showing the effect of temperature on the corrosion inhibition process 106
4.18 Variation of corrosion rate with different concentrations of Momordica charantia
extract showing the effect of temperature on the corrosion inhibition process 107
4.19 Variation of corrosion rate with different concentrations of the blend showing the effect
of temperature on the corrosion inhibition process 107
4.20 Variation of inhibition efficiency with different concentrations of Afzelia africana
extract showing the effect of temperature on the corrosion inhibition process 108
4.21 Variation of inhibition efficiency with different concentrations of Brachystegia
eurycoma extract showing the effect of temperature on the corrosion inhibition process 108
4.22 Variation of inhibition efficiency with different concentrations of Brachystegia eurycoma extract showing the effect of temperature on the corrosion inhibition process 108
4.23 Variation of inhibition efficiency with different concentrations of the blend
showing the effect of temperature on the corrosion inhibition process 109
4.24 Variation of volume of H2 gas evolved with time for mild steel corrosion in
1.0 M HCl in the absence and presence of the blended seed extract at 303 K 111
4.25 Variation of volume of H2 gas evolved with time for mild steel corrosion in
1.0 M HCl in the absence and presence of the blended seed extract at 313 K 112
4.26 Variation of volume of H2 gas evolved with time for mild steel corrosion in 1.0 M HCl
in the absence and presence of the blended seed extract at 323 K 112
4.27 Variation of volume of H2 gas evolved with time for mild steel corrosion in 1.0 M HCl
in the absence and presence of the blended seed extract at 333 K 113
4.28 Variation of volume of H2 gas evolved with time for mild steel corrosion in1.0 M HCl
in the absence and presence of the blended seed extract at 343 K 113
4.29 Variation of inhibition efficiency with the concentration of the blended seed extracts
for mild steel corrosion in 1.0 M HCl solution at different temperatures 114
4.30 Variation of temperature with time in 1.0 M HCl for mild steel corrosion in the absence
and presence of the blended seed extracts 116
4.31 Plot of RN against Log of inhibitor concentration 117
4.32 The Langmuir isotherm for the adsorption of Afzelia africana extract on mild steel
surface in 1.0 M HCl 118
4.33 The Freundlich isotherm for the adsorption of Afzelia africana extract on mild steel
surface in 1.0 M HCl 119
4.34 The Temkin isotherm for the adsorption of Afzelia africana extract on mild steel surface in 1.0 M HCl 119
4.35 The Langmuir isotherm for the adsorption of Brachystegia eurycoma extract on mild
steel surface in 1.0 M HCl 120
4.36 The Freundlich isotherm for the adsorption of Brachystegia eurycoma extracts on mild
steel surface in 1.0 M HCl 121
4.37 The Temkin isotherm for the adsorption of Brachystegia eurycoma extracts on mild
steel surface in 1.0 M HCl 121
4.38 The Langmuir isotherm for the adsorption of Momordica charantia extract on
mild steel surface in 1.0 M HCl 122
4.39 The Freundlich isotherm for the adsorption of Momordica charantia extract on
mild steel surface in 1.0 M HCl 123
4.40 The Temkin isotherm for the adsorption of Momordica charantia extract on
mild steel surface in 1.0 M HCl 123
4.41 The Langmuir isotherm for the adsorption of the blended seed extracts on mild steel
surface in 1.0 M HCl 124
4.42 The Freundlich isotherm for the adsorption of the blended seed extracts on mild steel
surface in 1.0 M HCl 125
4.43 The Temkin isotherm for the adsorption of the blended seed extracts on mild steel
surface in 1.0 M HCl 125
4.44 Plot of log CR against 1/T for mild steel in 1 M HCl solution in the absence and presence of various concentrations of Afzelia africana extract 130
4.45 Plot of log CR against 1/T for mild steel in 1 M HCl solution in the absence and presence of various concentrations of Brachystegia eurycoma extract 130
4.46 Plot of log CR against 1/T for mild steel in 1 M HCl solution in the absence and presence of various concentrations of Momordica charantia extract 131
4.47 Plot of log CR against 1/T for mild steel in 1 M HCl solution in the absence and presence of various concentrations of blended seed extracts 131
4.48 Plot of log CR/T against 1/T for mild steel in 1 M HCl solution in the absence and
presence of various concentrations of Afzelia africana extract 132
4.49 Plot of log CR/T against 1/T for mild steel in 1 M HCl solution in the absence and
presence of various concentrations of Brachystegia eurycoma extract 132
4.50 Plot of log CR/T against 1/T for mild steel in 1 M HCl solution in the absence and
presence of various concentrations of Momordica charantia extract 133
4.51 Plot of log CR/T against 1/T for mild steel in 1 M HCl solution in the absence and
presence of various concentrations of blended seed extracts 133
4.52 Plot of Log Wf vs Time for mild steel in 1 M HCl solution in the absence and
presence of various concentrations of Afzelia africana extracts at 303 K 134
4.53 Plot of Log Wf vs Time for mild steel in 1 M HCl solution in the absence and
presence of various concentrations of Afzelia africana extracts at 313 K 134
4.54 Plot of Log Wf vs Time for mild steel in 1 M HCl solution in the absence and
presence of various concentrations of Afzelia africana extracts at 323 K 135
4.55 Plot of Log Wf vs Time for mild steel in 1 M HCl solution in the absence and presence
of various concentrations of Afzelia africana extracts at 333 K 135
4.56 Plot of Log Wf vs Time for mild steel in 1 M HCl solution in the absence and presence
of various concentrations of Afzelia africana extracts at 343 K 135
4.57 Plot of Log Wf vs Time for mild steel in 1 M HCl solution in the absence and presence
of various concentrations of Brachystegia eurycoma extracts at 303 K 136
4.58 Plot of Log Wf vs Time for mild steel in 1 M HCl solution in the absence and presence
of various concentrations of Brachystegia eurycoma extracts at 313 K 136
4.59 Plot of Log Wf vs Time for mild steel in 1 M HCl solution in the absence and presence
of various concentrations of Brachystegia eurycoma extracts at 323 K 136
4.60 Plot of Log Wf vs Time for mild steel in 1 M HCl solution in the absence and presence
of various concentrations of Brachystegia eurycoma extracts at 333 K 137
4.61 Plot of Log Wf vs Time for mild steel in 1 M HCl solution in the absence and presence
of various concentrations of Brachystegia eurycoma extracts at 303 K 137
4.62 Plot of Log Wf vs Time for mild steel in 1 M HCl solution in the absence and presence
of various concentrations of Momordica charantia extracts at 303 K 137
4.63 Plot of Log Wf vs Time for mild steel in 1 M HCl solution in the absence and presence
of various concentrations of Momordica charantia extracts at 313 K 138
4.64 Plot of Log Wf vs Time for mild steel in 1 M HCl solution in the absence and presence
of various concentrations of Momordica charantia extracts at 323 K 138
4.65 Plot of Log Wf vs Time for mild steel in 1 M HCl solution in the absence and presence
of various concentrations of Momordica charantia extracts at 333 K 138
4.66 Plot of Log Wf vs Time for mild steel in 1 M HCl solution in the absence and presence
of various concentrations of Momordica charantia extracts at 343 K 139
4.67 Plot of Log Wf vs Time for mild steel in 1 M HCl solution in the absence and presence
of various concentrations of blended seed extracts at 303 K 139
4.68 Plot of Log Wf vs Time for mild steel in 1 M HCl solution in the absence and presence
of various concentrations of blended seed extracts at 313 K 139
4.69 Plot of Log Wf vs Time for mild steel in 1 M HCl solution in the absence and presence
of various concentrations of blended seed extracts at 323 K 140
4.70 Plot of Log Wf vs Time for mild steel in 1 M HCl solution in the absence and presence
of various concentrations of blended seed extracts at 333 K 140
4.71 Plot of Log Wf vs Time for mild steel in 1 M HCl solution in the absence and presence
of various concentrations of blended seed extracts at 343 K 140
4.72 Plot of Wf vs Time for mild steel in 1M HCl solution in the absence and presence of
various concentrations of Afzelia africana extracts at 303K 144
4.73 Plot of 1/Wf vs Time for mild steel in 1M HCl solution in the absence and presence
of various concentrations of Afzelia africana extracts at 303K 144
4.74 Plot of Wf vs Time for mild steel in 1M HCl solution in the absence and presence of
various concentrations of Brachystegia eurycoma extracts at 303K 144
4.75 Plot of Wf vs Time for mild steel in 1M HCl solution in the absence and presence of
various concentrations of Brachystegia eurycoma extracts at 303K 145
4.76 Plot of Wf vs Time for mild steel in 1M HCl solution in the absence andpresence of
various concentrations of Momordica charantia extracts at 303K 145
4.77 Plot of Wf vs Time for mild steel in 1M HCl solution in the absence and presence of
various concentrations of Momordica charantia extracts at 303K 145
4.78 Plot of Wf vs Time for mild steel in 1M HCl solution in the absence and presence of
various concentrations of blended seed extracts at 303K 146
4.79 Plot of 1/Wf vs Time for mild steel in 1M HCl solution in the absence and presence
of various concentrations of blended seed extracts at 303K 146
4.80 SEM micrograph of mild steel immersed in hydrochloric acid without inhibitor at
200μm magnification 149
4.81 SEM micrograph of mild steel immersed in hydrochloric acid in the presence of
ethanol extract of Blend of AA, BE and MC at 200μm magnification 149
4.82 FTIR spectra of the ethanol extract of Blend of AA, BE and MC 152
4.83 FTIR spectra of the corrosion product of mild steel in the presence of the blended extracts
in 1 M HCl acid 152
4.84 Optimized Structure of Glucose Leucine, Arginine and Flavonol 156
4.85 HOMO and LUMO orbitals of Leucine 157
4.86 HOMO and LUMO orbitals of Flavonol 157
4.87 HOMO and LUMO orbitals of Glucose 157
4.88 HOMO and LUMO orbitals of Arginine 158
4.89 ESP Optimized mapped density of (a) Leucine, (b) Flavonol and (c) Glucose
(d) Arginine 162
LIST OF PLATES
2.1 Afzelia africana (Akparata) seeds 32
2.2 Brachystegia eurycoma (Achi) seeds 33
2.3 Brachystegia eurycoma (Achi) processed seeds and fruits 33
2.4 Unripe Momordica charantia fruits and leaves 34
2.5 Ripe Momordica charantia fruits and Seeds 35
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APA
OZOEMENA, & PETER, C. (2023). Efficacy Of The Blend Of Extracts From Afzelia Africana, Brachystegia Eurycoma And Momordica Charantia Seeds For Corrosion Inhibition Of Mild Steel In 1m Hcl Solution . Michael Okpara University of Agriculture. Retrieved June 8, 2026, from http://repository.mouau.edu.ng/works/efficacy-of-the-blend-of-extracts-from-afzelia-africana-brachystegia-eurycoma-and-momordica-charantia-seeds-for-corrosion-inhibition-of-mild-steel-in-1m-hcl-solution-7-2
MLA
OZOEMENA, and CHIMEZIE PETER. "Efficacy Of The Blend Of Extracts From Afzelia Africana, Brachystegia Eurycoma And Momordica Charantia Seeds For Corrosion Inhibition Of Mild Steel In 1m Hcl Solution ." Michael Okpara University of Agriculture, 15 Aug. 2023, http://repository.mouau.edu.ng/works/efficacy-of-the-blend-of-extracts-from-afzelia-africana-brachystegia-eurycoma-and-momordica-charantia-seeds-for-corrosion-inhibition-of-mild-steel-in-1m-hcl-solution-7-2. Accessed June 8, 2026.
Chicago
OZOEMENA, and CHIMEZIE PETER. "Efficacy Of The Blend Of Extracts From Afzelia Africana, Brachystegia Eurycoma And Momordica Charantia Seeds For Corrosion Inhibition Of Mild Steel In 1m Hcl Solution ." Michael Okpara University of Agriculture (2023). Accessed June 8, 2026. http://repository.mouau.edu.ng/works/efficacy-of-the-blend-of-extracts-from-afzelia-africana-brachystegia-eurycoma-and-momordica-charantia-seeds-for-corrosion-inhibition-of-mild-steel-in-1m-hcl-solution-7-2