ABSTRACT
Corrosion processes results to numerous failures and eventual losses in industries. These failures imposed by corrosion effects can be reduced through the use of inhibitors. The aqueous extracts of Aloe Vera gel was investigated as a novel corrosion inhibitor for mild steel in both acid and alkaline media using gravimetric method. Corrosion rate, inhibition efficiency, degree of surface coverage, adsorption mechanism, free energy and thermodynamic parameters were determined through the performance of the corrosion inhibition efficiency obtain in both media. The adsorption on mild steel surface agrees with the Langmuir adsorption isotherm model, the negative Gibbs G and equilibrium constant K values indicated the spontaneity, physisorption, stability of the adsorption and the exothermic nature on mild steel, suggesting that Aloe vera gel is a common inhibitor for corrosion for Hydrochloric Acid (HCl) and Sodium Hydroxide (NaOH) media and can be used as a replacement to toxic and non-bio gradable inhibitors.
TABLE OF CONTENTS
Cover page
Pages
Title
Page
i
Declaration
ii
Certification
iii
Dedication
iv
Acknowledgement v
Table
of contents vi
List
of Tables x
List of Figure xi
Abstract vii
CHAPTER 1
1.0 INTRODUCTION 1
1.1
Inhibition 2
1.2 Aim
and Objective 3
1.3
Statement of Problem 3
1.4 The
Present Research 3
1.5
Significance of Study 4
CHAPTER
2
2.0 REVIEW
OF RELATED LITERATURE 5
2.1
Adsorption 6
2.2
Adsorption Isotherm 7
2.3
Classification of Corrosion 8
2.3.1 Dry corrosion 8
2.3.2 Wet corrosion 8
2.4
Forms of Corrosion 8
2.4.1 Uniform corrosion 9
2.4.2 Galvanic or two metals corrosion 10
2.4.3 Pitting corrosion
11
2.4.4 Crevice corrosion 11
2.4.5 Intergranular corrosion 12
2.4.6 Selective leaching 13
2.4.7 Erosion corrosion 14
2.4.8 Stress corrosion 15
2.5 The
Problem of Corrosion 15
2.6
Corrosion Inhibitors 17
2.6.1 Types of Corrosion 17
2.6.1.1 Organic Inhibitor 18
2.6.1.2 Inorganic Inhibitor 18
2.6.1.3 Green Corrosion Inhibitor 18
2.7 Classification of Corrosion Inhibitors 19
2.7.1 Passivators 19
2.7.2 Pickling inhibitors 20
2.7.3 Vapour phase inhibitors 20
2.8 Plants Extract from Aloe Vera Gel 20
2.9
Review of Related Past Work 23
2.9.1 The leaves extract of different
plants 23
CHAPTER
3
3.0
METHODOLOGY 26
3.1
Materials 26
3.2
Experimental Procedure 26
3.3 Preparation of Aloe Vera Gel 26
3.4 Gravimetric Method 27
3.5 Thermodynamics of Corrosion 27
3.5.1 Film attractive power 28
3.5.2
Corrosion rate 28
3.5.3 Percentage inhibitor efficiency 29
3.5.4 Degree of surface coverage 29
3.5.5
Free energy of adsorption 30
3.5.6
Enthalpy and entropy of adsorption 27
3.5.7
Artificial neural network (ANN) 31
3.5.8
Multiple regression (MR) 31
CHAPTER 4
4.0
RESULTS AND DISCUSSION 32
4.1
Thermodynamics Principle 32
4.2 Adsorption Isotherm Model 32
4.3 Effect of Concentration on the
Corrosion of Mild Steel 33
4.4 Effect of Exposure Time on the Corrosion of Mild Steel 33
4.5 Effect of Inhibitor Concentration on
the Corrosion of Mild Steel 34
4.6 Prediction of Corrosion Rate of Mild
Steel Multiple regression and
Artificial Neural
Network 34
CHAPTER 5
5.1 Conclusion 44
5.2 Recommendation 45
Reference 46
Appendix 67
LIST OF TABLE
2. 1 Phytochemical
components of Aloe Vera gel 22
3.1 Weight loss (mg) parameters of mild steel
samples in 0.5M of HCl
without additives. 44
3.2 Weight loss (mg)
parameters of mild steel samples in 0.5M of NaOH
without additives. 45
3.3 Weight loss (mg)
parameters of mild steel samples in 0.5M of HCl
containing 5ml of Aloe vera gel. 46
3.4 Weight loss (mg)
parameters of mild steel samples in 0.5M of HCl
containing 5ml of Aloe vera gel.(cont’) 47
3.5 Weight loss (mg)
parameters of mild steel samples in 0.5M of NaOH
containing 5ml of Aloe vera gel. 48
3.6 Weight loss (mg)
parameters of mild steel samples in 0.5M of NaOH
containing 5ml of Aloe vera gel.(cont’) 49
3.7 Weight loss (mg)
parameters of mild steel samples in 0.5M of HCl
containing 10ml of Aloe vera gel. 50
3.8 Weight loss (mg)
parameters of mild steel samples in 0.5M of HCl
containing 10ml of Aloe vera gel.(cont’) 51
3.9 Weight loss (mg)
parameters of mild steel samples in 0.5M of NaOH
containing 10ml of Aloe vera gel. 52
3.10 Weight loss (mg)
parameters of mild steel samples in 0.5M of HCl
containing 10ml of Aloe vera gel.(cont’) 53
3.11 Weight loss (mg)
parameters of mild steel samples in 0.5M of HCl
containing 20ml of Aloe vera gel. 54
3.12 Weight loss (mg)
parameters of mild steel samples in 0.5M of HCl
containing 20ml of Aloe vera gel. (cont’) 55
3.13 Weight loss (mg)
parameters of mild steel samples in 0.5M of NaOH
containing 20ml of Aloe vera gel. 56
3.14 Weight loss (mg)
parameters of mild steel samples in 0.5M of NaOH
containing 5ml of Aloe vera gel.(cont’) 57
LIST OF FIGURES
2.1 Uniform Corrosion of
metal sheet. 9
2.2
Galvanic Corrosion of a pipe. 10
2.3 Pitting Corrosion of inside and outside of
a pipe. 11
2.4 Crevice Corrosion of on the surface of a
flange. 12
2.5 Intergranular Corrosion
of a copper pipe. 13
2.6 Selective Leaching
Corrosion on the surface of a metal. 13
2.7 Erosion Corrosion along
the elbow of a metal pipe. 14
2.8 Stress Corrosion of
metal. 15
4.1 Variation of Weight
Loss (mg) with Exposure Time (hrs) for
Mild Steel in 0.5M HCl containing different concentration of
the
inhibitors extract. 35
4.2 Variation of Weight
Loss (mg) with Exposure Time (hrs) for Mild
Steel in 0.5M NaOH containing different concentration of the
inhibitors extract. 36
4.3 Variation of
Corrosion Rate (mmpy) with Exposure Time (hrs) for
Mild Steel in 0.5M HCl containing different concentration of the
inhibitors extract. 37
4.4 Variation of
Corrosion Rate (mmpy) with Exposure Time (hrs) for Mild
Steel in 0.5M NaOh containing different concentration of the
inhibitors extract. 38
4.5 Variation of
Corrosion Rate (mmpy) with Concentration of inhibitor
(ml) for Mild Steel in 0.5M HCl containing different
concentration
of the inhibitors extract. 39
4.6 Variation of
Corrosion Rate (mmpy) with Concentration of inhibitor
(ml) for Mild Steel in 0.5M NaOH containing different concentration
of the inhibitors extract. 40
4.7 Inhibition Efficiency
(%) with Exposure Time (hrs) for Mild Steel
in 0.5M HCl containing different concentration of the inhibitors
extract. 41
4.8 Langmiur Adsorption Isotherm of Aloe vera
on Mild Steel. 42
CHAPTER 1
1.0 INTRODUCTION
Corrosion is the deterioration of materials by
chemical interaction with their environment. It
cuts short the lifetime of steel products such as bridges and automobiles. The
cost of corrosion is huge and reducing corrosion is one of the most important problem
in engineering. Corrosion is all around us and can
affect our lives in many ways, because metals are widely used in our world. Corrosion-related
failures in industries is often catastrophic.
Failures caused by corrosion could and do lead to a direct failure of a
component which could affect the entire system and can not only be very
expensive in terms of down-time to repair or replace equipment, but can also be
costly in loss of productivity, human life and health as to the environment
(Corrosion Control Solutions, 2013).
Corrosion is
a constant and continuous problem, often very difficult to eliminate
completely, (Rani and Basu, 2012). Most metals corrode on contact with the
following: water, moisture in the air, acids, bases, salts, aggressive metal
polishes, and other solid and liquid chemicals.
In practice
corrosion can never be stopped but can be reduced to a reasonable level. Due to
problem from corrosion that are confronting industries, several methods of
corrosion control and prevention have been put in place. These include: cathodic
protection, lubrication, anodic protection, alloying, coating, inhibition etc.
The choice and application of these methods are based on their efficiency,
economic factors and the nature of the corrosive environment (Njoku, 1998). Many
attempts have been made to predict analytical corrosion behaviors. Multiple Regression
(MLR) and Artificial Neural Network were used in attempt to predict the corrosion
rates with the aid of the SPSS software.
1.1 INHIBITION
Inhibition
is one of the most practical method for protection against corrosion in
corrosive environments. Inhibitors are
substances that directly or indirectly coat a film on a metal surface to protect
it from its environment. Metals are suppressed by the action of adsorptive
inhibitors which may prevent the adsorption of the aggressive ions, and by the
formation of a more resistant film on the metallic surface (El Maghraby, 2009).
Corrosion
inhibition is of great practical importance, being extensively employed in
curtailing wastage of engineering materials and minimizing corrosion control
costs, in oil extraction and processing industries, heavy industrial
manufacturing, water treatment facility, water-containing hydraulic fluids,
engine coolants, ferrous metal cleaners, automatic transmission fluids,
automotive component manufacture, cutting fluids etc. to minimize localized
corrosions and failures (Loto et al.,
2012).
The use of
natural products otherwise tagged, green corrosion inhibitors has been
advocated because of the cost, toxic nature and environmentally unfriendliness
of some of the inorganic and organic corrosion inhibitors. Moreover, they are readily
available, cheap and a renewable source of materials. Steels are used in many
engineering applications and are subjected to acidic environment. Thus it becomes imperative to investigate the
corrosion behavior of mild steels in acid solution as well as their response to
inhibition in such media (Njoku, 1998). Inhibitors had great acceptance in the
industries due to excellent anti-corrosive proprieties. Thus environmentally
friendly inhibitors like the organic inhibitors in the form of Aloe Vera gel is
my best option in doing the comparative studies of this work.
1.2 AIM AND OBJECTIVES
The
aim of the work is to generate experimental data towards the control of
corrosion using Aloe Vera gel extract inhibitor on Mild steel.
1.3 SPECIFIC OBJECTIVES OF THE STUDY
The
objectives of the research are:
i.
Evaluating the effects of Aloe
Vera gel extract on the corrosion of mild steel in 0.5 M HCl and 0.5 M NaOH
through Weight loss measurement.
ii.
Determining metal-inhibitor
interaction mechanism using adsorption isotherm; Langmuir isotherms.
iii.
Determining the inhibition mode of
the inhibitors using the kinetic parameters.
iv.
To carry out ANN modelling of the
corrosion data emanating from the Weight loss experiments.
v.
To carry out ANOVA (MLR) modelling
of the corrosion data emanating from the Weight loss experiments.
1.4 STATEMENT OF PROBLEM
Most
of the corrosion inhibitors used in the processing industry are synthetic in
nature, hence not environmentally friendly. Human health hazards like lung cancer
are known to have arisen as a result of long time exposure to inorganic
inhibitors such as chromates, phosphates, etc.
Many
research efforts have shown that gaps exist in the modelling of experimental
corrosion data. Among such gaps is the fact that there appears to be no
Artificial modelling of experimental data, thereby encouraging constant
recourse to experimentation.
1.5 SIGNIFICANCE OF STUDY
i. The development of an alternative
corrosion inhibitors that is effective and environmentally friendly when
compare to chromates which are toxic and carcinogenic in nature (Loto et al., 2012).
ii.
Most of the corrosion inhibitors
are not just only synthetic and hazardous in nature but very expensive.
Therefore, it is desirable to source for cheaper and environmentally safe
inhibitors (Paul et al., 2012).
iii.
Due to the availability of these
plants and the simplicity in processing them into inhibitors, they are
preferred to synthetic chemicals.
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