Corrosion Inhibition of Aluminum in Acidic Medium by Bamboo Leaves Extract

ABSTRACT 

The inhibitive effects of bamboo leaves extracts (BLE) on the corrosion of aluminum in 1M HCl were studied using weight loss, adsorption, thermodynamics and kinetic studies. The phytochemical constituents of the BLE were tannins, polyphenols, flavonols, terpenoids, sterols and alkaloids. BLE was noted to contain more of the polyphenols and terpenoids which were largely responsible for the inhibitive action of the extracts. Results obtained from the experiments carried out at 303K and 333K revealed that, the corrosion rate decreased as the concentration of BLE increased. The inhibition efficiency increased as the concentration of BLE increased at 333K. As the temperature increased from 303K to 333K, the corrosion rate increased significantly. The adsorption parameters showed that the adsorption of the BLE conformed perfectly to the Langmuir, Temkin and Freundlich adsorption isotherms, with the Langmuir isotherm being the best model with R2 = 0.992. The negative values of Gibbs free energy indicated that the reaction was spontaneous and the mechanism of adsorption was electrostatic (physical) adsorption mechanism since the negative values of ΔG°ads were lower than -20 kJ/mol. The values of activation energy, Ea, being lower than 80 kJ/mol, also confirmed a physical adsorption mechanism. The values of heat of adsorption being lower than 40 kJ/mol, also confirmed that the adsorption mechanism was physisorption. The positive values of heat of adsorption, Qads indicated that the reaction was endothermic. The small values of adsorption equilibrium constant, Kads indicated low interaction between the adsorbed molecules and the metal surfaces and thus the extracts were physically adsorbed on the metal surfaces. The reaction showed a first order kinetics, since the plots of log Wf vs Time were linear for all the concentrations of the extracts. The increase in half-life as the concentration of the extract increased indicated more protection of the metals by the BLE.

TABLE OF CONTENTS

COVER PAGE - - - - - - - - - i

CERTIFICATION - - - - - - - - - ii

DEDICATION - - - - - - - - - iii

ACKNOWLEDGEMENT - - - - - - - - iv

ABSTRACT - - - - - - - - - - v

TABLE OF CONTENT - - - - - - - - vi

LIST OF FIGURES - - - - - - - - - xii

LIST OF TABLES - - - - - - - - - xiii

LIST OF APPENDICES - - - - - - - - xiv

ABBREVIATIONS - - - - - - - - - xv

CHAPTER ONE

Introduction

1.1 Background of the Study - - - - - - - - 1

1.2 Statement of the Problem - - - - - - - - 3

1.3 Justification of the Study - - - - - - - - 3

1.4 Aims and Objectives - - - - - - - - - 4

CHAPTER TWO

Literature Review

2.1 Conceptual Review - - - - - - - - - 5

2.1.1 Corrosion Inhibitors - - - - - - - - - 5

2.1.2 Classification of Inhibitors - - - - - - - - 5

2.1.3 Inorganic Inhibitors - - - - - - - - - 6

2.1.3.1 Anodic Inhibitors - - - - - - - - - 6

2.1.3.1 Cathodic inhibitors - - - - - - - - - 7

2.1.4 Organic Inhibitors - - - - - - - - - 9

2.1.5 Industrial Application of Corrosion Inhibitors - - - - - 13

2.1.6 Hydrochloric Acid - - - - - - - - - 14

2.1.7 Bamboo Leaves - - - - - - - - - 16

2.1.8 Langmuir Adsorption Isotherm - - - - - - - 18

2.1.9 Temkin Adsorption Isotherm - - - - - - - - 18

2.1.10 Freundlich Adsorption Isotherm - - - - - - - 19

2.2 Empirical Review - - - - - - - - - 19

2.2.1 Effect of Concentration on Corrosion Inhibition - - - - - 19

2.2.2 Effect of Immersion Time on Corrosion Inhibition - - - - - 22

2.2.3 Effect of Temperature on Corrosion Inhibition - - - - - 23

2.2.4 Adsorption Isotherm Studies - - - - - - - - 25

2.2.5 Thermodynamic and Kinetic Treatment - - - - - - 27

CHAPTER THREE

Methodology

3.1 Materials and Methods - - - - - - - - 30

3.1.1 Materials - - - - - - - - - - 30

3.1.2 Preparation of Test Coupon - - - - - - - - 31

3.1.3 Preparation of 1.0M HCl - - - - - - - - 31

3.1.4 Preparation of Leaves Samples - - - - - - - 32

3.1.5 Extraction - - - - - - - - - - 32

3.2 Phytochemical Screening - - - - - - - - 32

3.2.1 Test for Tannins - - - - - - - - - 32

3.2.2 Test for Polyphenols - - - - - - - - - 33

3.2.3 Test for Flavonols - - - - - - - - - 33

3.2.4 Test for Terpenoids - - - - - - - - - 33

3.2.5 Test for Sterols - - - - - - - - - 34

3.2.6 Test for Alkaloids - - - - - - - - - 34

3.3 Gravimetric Techniques - - - - - - - - 34

3.4 Corrosion Data - - - - - - - - - 35

3.4.1 Corrosion Rate - - - - - - - - - 35

3.4.2 Inhibition Efficiency - - - - - - - - - 36

3.4.3 Surface Coverage - - - - - - - - - 36

3.5 Adsorption Isotherm Studies - - - - - - - - 36

3.5.1 Langmuir Adsorption Isotherm - - - - - - - 36

3.5.2 Temkin Adsorption Isotherm - - - - - - - - 37

3.5.3 Freundlich Adsorption Isotherm - - - - - - - 37

3.6 Thermodynamics and Kinetic Studies - - - - - - 38

3.6.1 Standard Gibbs free energy change of Adsorption - - - - - 38

3.6.2 Activation Energy - - - - - - - - - 38

3.6.3 Heat of Adsorption - - - - - - - - - 39

3.6.4 Rate Constant - - - - - - - - - - 39

3.6.5 Half-life - - - - - - - - - - 40

CHAPTER FOUR

Results and Discussion

4.1 Phytochemical Screening - - - - - - - - 41

4.2 Gravimetric Results - - - - - - - - - 44

4.3 Effect of Concentration on Corrosion Inhibition - - - - - 46

4.4 Effect of Immersion Time on Corrosion inhibition - - - - - 49

4.5 Effect of Temperature on Corrosion Inhibition - - - - - 50

4.6 Adsorption Isotherm Studies - - - - - - - - 51

4.6.1 Langmuir Adsorption Isotherm - - - - - - - 57

4.6.2 Temkin Adsorption Isotherm - - - - - - - - 57

4.6.3 Freundlich Adsorption Isotherm - - - - - - - 57

4.7 Thermodynamics and Kinetic Studies - - - - - - 58

4.7.1 Standard Gibbs free energy change of Adsorption - - - - - 61

4.7.2 Activation Energy - - - - - - - - - 61

4.7.3 Heat of Adsorption - - - - - - - - - 61

4.7.4 Rate of the Reaction and Rate Constant of the Reaction - - - - 61

4.7.5 Half-life - - - - - - - - - - 62

4.8 Findings from the study - - - - - - - - 62

4.8.1 Factors responsible for the inhibitive action of BLE - - - - - 62

4.8.2 Effect of BLE concentration on the boiling point of the stock acid solutions - 63

4.9 Contribution To knowledge - - - - - - - - 64

CHAPTER FIVE

Conclusions and Recommendations

5.1 Conclusions - - - - - - - - - - 65

5.2 Recommendations - - - - - - - - - 65

References - 67

Appendices - 80