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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.


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          





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     




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





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






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




5.1 Conclusion                                                                                                152                 

5.2 Recommendations                                                                                    152

            5.3 Contribution to Knowledge                                                                      153     



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








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








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.


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.



1.3.1 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.



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. 


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.



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