ABSTRACT
The corrosion inhibition of zinc in 0.1M H2SO4 in the presence of 4-[(4-chlorobenzylidene) amino] benzoic acid (4CBB), 2-[(4-dimethylaminobenzyldene) amino] benzoic acid (2DAB) and 4-[(4-dimethylaminobenzylidene) amino] benzoic acid (4DAB) was studied using gravimetric (weight loss) method at temperatures ranging from 303 K to 343 K. The results showed that inhibition efficiencies of the inhibitors increased as the concentrations increased but decreased with rise in temperature. The efficiencies of 4DAB at the temperatures of study ranged from 38.9% to 36.6% at 5.0g/l concentration. For 4CBB, it ranged from 42.8% to 38.8% at 5.0g/l concentration. The efficiencies of 2DAB were from 38.1% to 35.9%. The efficiencies followed the order: 2DAB˂4DAB˂4CBB. The kinetic data obtained showed that the corrosion process followed first order kinetics. The activation energy, Ea, values obtained for all the inhibited (and uninhibited) solutions were less than 80kJ/mol, indicating that physical adsorption was the predominant mechanism. This was also supported by the fact that free energies of adsorption were less than -40kJ/mol which is required for physisorption. The adsorption data of the inhibitors were fitted to Langmuir, Freundlich and El-Awardy isotherms. Langmuir isotherm gave the best fit to the adsorption data. The calculated free energies of adsorption for 4DAB, 2DAB and 4CBB ranged from -5,122.576J/mol to – 6,390.182J/mol; -5,185.866J/mol to -6,690.542J/mol, and, -4,331.062 J/mol to -6,245.603 J/mol; respectively. The heat of adsorption results, ΔH0ads, showed that the adsorption processes for 4CBB, 2DAB and 4DAB were endothermic.
TABLE
OF CONTENTS
Title Page Title page i
Title Page
i
Declaration
ii
Certification iii
Acknowledgements iv
Table of Contents
v
List of Tables viii
List of Figures x
Abstract xiii
CHAPTER 1
INTRODUCTION
1.1 Background of Study 1
1.2 Statement of Problem 4
1.3 Aim and Objectives of the Study 6
1.3.1 Aim
6
1.3.2
Specific objectives 6
1.4 Scope and
Limitations of the Study
7
1.5 Relevance of the Study
8
CHAPTER 2
LITERATURE REVIEW
2.1 Corrosion
9
2.2 Corrosion Control
10
2.3 Corrosion of Zinc
11
2.4 Inhibitors
13
2.4.1 Inorganic inhibitors
14
2.4.2 Organic inhibitors 15
2.5 Schiff Bases as Corrosion
Inhibitors
16
2.6
Infrared Analysis of Organic Inhibitors 20 2.7 Techniques
for Corrosion Inhibition Analysis 21
2.8 Inhibitor Adsorption and Adsorption Isotherms 25
2.9 Thermodynamic Parameters of Adsorption 29
2.10 Thermodynamics and Kinetics of Corrosion Inhibition 30
2.11 Effects of Inhibitor
Concentration and Temperature on
Corrosion 33
2.12 Dependence of Corrosion Inhibition on Molecular Structure
34
2.13 Quantum Chemical Considerations 36
CHAPTER 3
MATERIALS AND METHODS
3.1 Materials 42
3.2 Materials and Reagents 42
3.2.1 Materials preparation 43
3.3 Infra-Red Measurements 45
3.4 Weight Loss Measurements 45
3.5 Percentage Yield 46
3.6 Kinetic Studies
47
3.7 Adsorption Isotherms and
Thermodynamic Parameters 48
CHAPTER 4
RESULTS AND DISCUSSION
4.1 Yield and Percentage Yield of
the Inhibitors 50
4.2 FT-IR Results 50
4.3 Weight Loss Results 58
4.4 Surface Coverage and Inhibition
Efficiencies 73
4.5 Dependence of Temperature and Concentration on
Inhibition
Efficiency 77
4.6 Corrosion Rate Results 77
4.7 Corrosion and Corrosion
Inhibition Mechanisms 81
4.8 Rate Constants and Half-Lives 82
4.9 Kinetic
Parameters: Half-Life and Rate Constant 113
4.10 Activation Energy and Frequency Factors 114
4.11 Kinetic Parameters:
Activation Energy And
Frequency
Factors 120
4.12 Enthalpy and Entropy of
Activation 121
4.13 Thermodynamic
Parameters: Enthalpies and Entropies of Activation 127
4.14 Adsorption and Thermodynamic
Parameters 128
4.15 Enthalpy and Entropy of
Adsorption 146
4.16 Thermodynamic
Treatment of Adsorption Results 149
4.17 Effects
of Molecular Structure on Inhibition Efficiencies 150
CHAPTER 5
CONCLUSION AND RECOMMENDATIONS
5.1 Conclusion 152
5.2 Recommendations 152
5.3 Contribution to Knowledge 153
References
Appendices
LIST
OF TABLES
2.1: Summary of reviewed schiff bases 18
2.2: IR bands of functional
groups found in the organic inhibitors 20
4.1:
The yield and percentage yield of the inhibitors 50
4.2:
Absorption frequencies of the various functional groups 57
4.3:
Surface coverage and inhibition efficiencies of 4dab 74
4.4:
Surface coverage and inhibition efficiencies of 4cbb 75
4.5:
Surface coverage and inhibition efficiencies of 2dab 76
4.6:
Corrosion rates of 4dab at various concentrations and temperatures 78
4.7:
Corrosion rates of 4cbb at various concentrations and temperatures 79
4.8:
Corrosion rates of 2dab at various concentrations and temperatures 80
4.9:
Rate constants and half-lives of 4dab at 303 k 84
4.10:
Rate constants and half-lives of 4dab at 313 k 86
4.11:
Rate constants and half-lives of 4dab at 323 k 88
4.12: Rate constants and half-lives of 4dab at
333 k 90
4.13: Rate constants and half-lives of 4dab at
343 k 92
4.14: Rate constants and half-lives of 2dab at
303 k 94
4.15: Rate constants and half-lives of 2dab at
313 k 96
4.16: Rate constants and half-lives of 2dab at
323 k 98
4.17: Rate constants and half-lives of 2dab at
333 k 100
4.18: Rate constants and half-lives of 2dab at
343 k 102
4.19:
Rate constants and half-lives of 4cbb at 303 k
104
4.20:
Rate constants and half-lives of 4cbb at 313 k
106
4.21:
Rate constants and half-lives of 4cbb at 323 k 108
4.22:
Rate constants and half-lives of 4cbb at 333 k 110
4.23:
Rate constants and half-lives of 4cbb at 343 k 112
4.24:
Activation energy and frequency factor values for 4dab 116
4.25:
Activation energy and frequency factor values for 2dab 118
4.26:
Activation energy and frequency factor values for 4cbb 120
4.27: Entropies
and enthalpies of activation values for 4cbb 123
4.28: Entropies
and enthalpies of activation values for 2dab 125
4.29: Entropies
and enthalpies of activation values for 4dab 127
4.30:
Free energy and adsorption parameters for 4dab from langmuir plots 129
4.31: Free energy
and adsorption parameters for 2dab from langmuir plots 131
4.32:
Free energy and adsorption parameters for 4cbb from langmuir plots 133
4.33:
Free energy and adsorption parameters for 4dab from freundlich plots 135
4.34: Free energy and adsorption parameters
for 2dab from freundlich plots 137
4.35:
Free energy and adsorption parameters for 4cbb from freundlich plots 139
4.36:
Free energy and adsorption parameters for 4dab from el-awardy plots 141
4.37:
Free energy and adsorption parameters for 2dab from el-awardy plots 143
4.38:
Free energy and adsorption parameters for 4cbb from el-awardy plots 145
4.39: Adsorption Enthalpy and Entropy Values for the
Inhibitors 149
LIST OF FIGURES
PAGE
4.1a: Ft-ir spectrum of 2dab: 4000 cm-1 –
350 cm-1 51
4.1b: Ft-ir
spectrum of 2dab: 1550 cm-1 – 350 cm-1 52
4.2a: Ft-ir spectrum of 4dab: 4000
cm-1 – 350 cm-1
53
4.2b: Ft-ir spectrum of 4dab: 1690
cm-1 – 350 cm-1 54
4.3a: Ft-ir spectrum of 4cbb: 4000
cm-1 – 350 cm-1 55
4.3b: Ft-ir spectrum of 4cbb: 1600
cm-1 – 350 cm-1 56
4.4: Plots of weight loss vs. time
for 4dab at 303 k 59
4.5: Plots of weight loss vs. time
for 4dab at 313 k 60
4.6: Plots of weight loss vs. time
for 4dab at 323 k 61
4.7: Plots of weight loss vs. time
for 4dab at 333 k 62
4.8: Plots of weight loss vs. time
for 4dab at 343 k 63
4.9: Plots of weight loss vs. time for 2dab at 303 k 64
4.10: Plots of weight loss vs. time for 2dab at 313 k 65
4.11: Plots of weight loss vs. time
for 2dab at 323 k 66
4.12: Plots of weight loss vs. time
for 2dab at 333 k. 67
4.13: Plots of weight loss vs. time
for 2dab at 343 k 68
4.14: Plots of weight loss vs. time
for 4cbb at 303 k 69
4.15: Plots of weight loss vs. time
for 4cbb at 313 k 70
4.16: Plots of weight loss vs. time
for 4cbb at 323 k 71
4.17: Plots of weight loss vs. time
for 4cbb at 333 k. 72
4.18: Plots of weight loss vs. time
for 4cbb at 343 k 73
4.19: A graph of –log (weight loss)
vs. time for 4dab at 303 k 83
4.20: A graph of –log (weight loss)
vs. time for 4dab at 313k. 85
4.21: A graph of –log (weight loss)
vs. time for 4dab at 323k 87
4.22: A graph of –log (weight loss) vs. time for 4dab
at 333 k 89
4.23: A graph of –log (weight loss)
vs. time for 4dab at 343 k 91
4.24: A graph of –log (weight loss)
vs. time for 2dab at 303 k 93
4.25: A graph of –log (weight loss)
vs. time for 2dab at 313 k 95
4.26: A graph of –log (weight loss)
vs. time for 2dab at 323 k 97
4.27: A graph of –log (weight loss)
vs. time for 2dab at 333 k 99
4.28: A graph of –log (weight loss)
vs. time for 2dab at 343 k 101
4.29: A graph of –log (weight loss)
vs. time for 4cbb at 303 k 103
4.30: A graph of –log (weight loss)
vs. time for 4cbb at 313 k 105
4.31: A graph of –log (weight loss)
vs. time for 4cbb at 323 k 107
4.32: A
graph of –log (weight loss) vs. time for 4cbb at 333 k 109
4.33: A graph of –log (weight loss)
vs. time for 4cbb at 343 k 111
4.34: An arrhenius plot of InCR vs.
1/T for 4dab 115
4.35: An arrhenius plot of InCR vs.
1/T for 2dab 117
4.36: An arrhenius plot of InCR vs.
1/T for 4cbb 119
4.37:
An
eyring plot of In (CR/T) vs. 1/T for 4cbb 122
4.38: An eyring plot of In (CR/T) vs. 1/T
for 2dab 124
4.39: An eyring plot of In (CR/T) vs. 1/T
for 4dab 126
4.40: Langmuir plots of 4dab at
various temperatures 128
4.41: Langmuir plots of 2dab at
various temperatures 130
4.42: Langmuir plots for 4cbb at
various temperatures 132
4.43: Freundlich isotherm plots for
4dab 134
4.44: Freundlich isotherm plots for
2dab 136
4.45: Freundlich isotherm plots for
4cbb 138
4.46: El-Awardy isotherm plot for
4dab 140
4.47: El-Awardy isotherm plot for
2dab 142
4.48: El-Awardy isotherm plot for
4cbb 144
4.49: A plot of -ΔGadsvs. T for 4dab 146
4.50: A plot of -ΔGadsvs.
T for 2dab 147
4.51: A plot of -ΔGadsvs.
T for 4cbb 148
CHAPTER 1
INTRODUCTION
1.1 BACKGROUND OF STUDY
The economic growth of
any country depends largely on her industrial development. The industries
produce both raw materials and finished goods. In these industries various
kinds of metals are employed in construction of plants, machinery parts and
other installations (Eddy et al., 2014).
Hence metals have an indirect bearing on the social, political and economic
well-being of man. Unfortunately, metals of both industrial and private use do
not continue perpetually in flourishing health. The environments of their
applications, most often, harbour aggressive media such as acids and salts. And
when these metals come in contact with these media, the resultant effect is corrosion
(Eddy et al., 2014).
Corrosion is the deterioration, a reduction
in quality of a material as a consequence of chemical reaction with its
environment. Corrosion as a term could also be used to describe the degradation
of woods, plastic and concretes. But in general it, is used to describe the
degradation of metals (Kazaure et al., 2015).
The problem posed by corrosion has received a considerable degree of attention
due to its safety and economic implications (Mohammed, 2011).
Corrosion can bring about untold damage on
a metal and alloy structure, causing economic consequences by way of repair,
replacement, product losses, safety and environmental pollution (Kazaure et al., 2015). It results in the loss of
many important properties of metals such as malleability, ductility and
conductance (Pasupathy et al., 2015).
Hence, corrosion studies have become important due to the increasing awareness
to conserve the world’s metal resources (Muthu and Ganesan, 2015). The current
study focuses on the corrosion of zinc in an acid medium using newly
synthesized Schiff bases.
Zinc is a very important non-ferrous metal
which finds applications in construction, metal processing and metallurgical industries.
It is used as a roofing material and sacrificial coating for more superior
metals such as iron or steel.
Mankind’s use of the metal dates back to
about 1000 years B.C, and it constitutes some of the earliest alloy systems
known to man. In biblical times, zinc ores were used for making brass and 87%
zinc alloy was found in prehistoric ruins in Transylvania (Xiaoge, 1996). The
applications of zinc are broad, ranging from galvanizing to die castings to
electronics. It is a preferred anode material in high energy density batteries
(examples, Ni/Zn, Ag/Zn, Zn, air), so that its electrochemistry, especially in
alkaline media has been extensively explored. Since zinc is considered to be an
excellent battery anode, it has been mostly applied as a sacrificial anode for
the protection of ships and pipelines from corrosion. The widespread use of
zinc is due largely to its electrochemical properties which include well-placed
position in the galvanic series for protecting iron and steel in natural
aqueous environment. (Xiaoge, 1996).
The appearance of zinc at the lower
regions of electrochemical series is the result of its high negative standard
electrode potential. Hence zinc is a very active metal whose corrosion is relatively
rapid in aggressive media. In the light of this and its vast importance, there
is need for the use of inhibitors to combat, among other metals, the corrosion
of zinc.
The use of corrosion inhibitors is one of many
methods available for securing metal against corrosion (Pasupathy, 2015).
Inhibitors are substances which when added in small quantities to the aqueous
corrosive environment, decreases the rate of corrosion of the metal. They
inhibit corrosion by either acting as barrier by forming an adsorbed layer or retarding
the cathodic and/or anodic process (Muthu and Ganesan, 2015). Inhibitors are of vital importance in production industries
as they are used in reducing metallic waste and in minimizing the risk of the
material failure. If unchecked, both of these factors can lead to sudden shutdown
of an industrial process, which in turn leads to added costs (Roberge, 1999).
The inhibitory potential of organic
compounds on metallic species is normally related to the adsorption interaction
between the inhibitors and the metal surface (Pruthviraj et al., 2015). The planarity and lone pairs of electron present on
N, O and S atoms are important structural features that control the adsorption
of these molecules on to the surface of the metal (Pruthviraj et al., 2015). It is reported by many
researchers that the inhibition effects depend mainly on some physiochemical
and electronic properties of the organic inhibitor which in turn is related to
its functional groups, orientation, and electron density of donor atoms and orbital
character of the donor electrons (Abdallah, 2002). The corrosion studies of
zinc in acid medium have been carried out using organic inhibitors such as
natural product extracts (James and Akaranta, 2011; Odiongenyi et al., 2015) and Schiff bases (Kumar et al., 2014; Pruthviraj, 2016).
Schiff bases are organic compounds that
have general formula, R-C=N-R-; where R and R- are aryl, alkyl or heterocyclic
groups. Schiff bases are formed by the condensation reactions of a primary
amine and a ketone or aldehyde, and are potential corrosion inhibitors. The
greatest advantage offered by Schiff base compounds is that they are easily
synthesized from relatively cheap materials. Due to the presence of the imine
group (-C=N-) and electronegative nitrogen, sulphur and or oxygen atoms in the
molecule, Schiff bases have been reported to be effective inhibitors
(Pruthviraj et al., 2015).
The Schiff bases used in this study are 4-[(4-dimethylaminobenzylidene)
amino] benzoic acid (4DAB), 2-[(4-dimethylaminobenzyldene) amino] benzoic acid
(2DAB), and 4-[(4-chlorobenzylidene) amino] benzoic acid, (4CBB). 4DAB has a relative
molecular mass of 268.31 g/mol; same as 2DAB. 4DAB and 2DAB have melting points
of 250 0C and 248 0C respectively. 4CBB has a relative
molecular mass of 259.69 g/mol and a melting point of 260 0C. The inhibition
efficiencies of these compounds vary with their surface coverage which is
dependent on their structural and electronic properties.
1.2 STATEMENT OF PROBLEM
Metallic materials are vastly applied in
industries. With recent advances in technology, more expensive metals are being
added to the industrial set-up. The results of corrosion on these materials are
many and varied, being more serious than the simple loss of a mass of metal.
Breakdown of various kinds and the need for expensive replacement may occur
despite the fact that the amount of metal is not quite small. Even the
application of corrosion inhibitors requires financial commitment; although to
a lesser degree.
The danger posed by corrosion goes beyond
financial loss. Structural failure and breakdown of bridges and crude oil
pipeline pose mortal danger to man when these structures are left to the
degrading effect of corrosion.
The efficiency of moving parts of machines
is drastically reduced by corrosion when corrosion products are allowed to
accumulate in them. The efficiency of industrial machinery is also adversely
affected by reduction in metal thickness, which leads to loss of mechanical
strength.
The value of goods is reduced due to
deterioration of their packaging. Contamination could also result if corrosion
is not checkmated. Corrosion products in a machine could also contaminate and
quench an industrial reaction process; or add to the products an erratic
quality undesirable to the manufacturers.
Corrosion leads to perforation of metallic
container whose content could be subject to leakage. Such container as petrol
tanker could prove to be a moving danger if the metallic materials are not kept
from corrosion. Also, several roofing sheets in Africa always have need to be
replaced after some years as raindrops leak through them from corrosion.
1.3 AIM AND OBJECTIVES OF THE STUDY
1.3.1
Aim
The aim of this study is to investigate
the inhibitory properties of the novel Schiff bases, 4DAB, 2DAB and 4CBB on the
corrosion of zinc in 0.1M H2SO4.
1.3.2
Specific objectives
The specific objectives include:
1.
To propose appropriate
corrosion and corrosion inhibition mechanisms of the inhibitors.
2.
To determine how
functional group substitution and positional isomerism affected their
inhibitory properties.
3.
To determine the
inhibitory properties such as percentage inhibition efficiency, corrosion rate
and surface coverage of 4DAB, 2DAB and 4CBB.
4.
To determine the kinetic
and thermodynamic parameters of inhibition such as enthalpy, entropy, Gibb’s
Free energy of adsorption, heat of adsorption, activation energy, rate
constant, Arrhenius constant and half-life of reaction.
5.
To propose a theoretical
description as to how the physicochemical properties of these points of
attachment influenced their relative inhibition efficiencies.
6.
To give a theoretical
explanation of how these parameters affected experimental results.
1.4
SCOPE AND LIMITATIONS OF THE STUDY
Corrosion is such a problem of enormous
concern that huge amount of money is spent by both public and private sectors
to replace metal parts damaged by corrosion. Hence this development has
consigned to us the need to look for means of preventing the corrosion problem,
or at least, reducing it to the barest minimum.
Considering this therefore, this study is
limited in scope to the application of 4DAB, 2DAB and 4CBB as corrosion
inhibitors on zinc in 0.1M H2SO4 at 303 K, 313 K, 323 K,
333 K, and 343 K, by gravimetric method.
According to researchers, the imine,
-C=N-, functionality of Schiff bases and the presence of aromatic systems play
prominent roles in the corrosion inhibition properties of Schiff bases. Hence,
the inhibitors as used in this study were chosen because they have several
properties in common, varying only by functional group substitution and as
positional isomers. The choice of these compounds was largely informed by the
fact that they are easily synthesized from cheap organic compounds which are
readily available in chemical stores. Zinc was chosen for its widespread use in
Sub-Saharan Africa, mostly as roofing sheets and coatings for steel alloys.
Although the study as carried out in this
present case is limited to Zinc and the three inhibitors mentioned above, the
results thereof could find application on other metals and/or alloys under similar
conditions. Since most metals in tropical Africa are mostly subject to
identical conditions of use, the corrosion problem they face might yet be
similar.
1.5 RELEVANCE OF THE STUDY
It is known that the protection of metals
and alloys from corrosion is of vital importance in the industrial and private sectors,
and saves monumental cost in replacing metals damaged thereby. This study therefore provides grounds for the
evaluation of 4DAB, 2DAB and 4CBB as novel Schiff bases and as alternatives to
most expensive inhibitors used in combating the problem of zinc corrosion.
The inhibition properties of 4DAB, 2DAB
and 4CBB as determined in this thesis could find a wide range of employment
advantageous in construction industries, metal production, oil and gas industries,
as well as food processing and storage industries.
Click “DOWNLOAD NOW” below to get the complete Projects
FOR QUICK HELP CHAT WITH US NOW!
+(234) 0814 780 1594
Login To Comment