ADSORPTION AND INHIBITIVE EFFECT OF Carica papaya AND Azadirachta indica EXTRACTS ON CORROSION OF ALUMINIUM IN HYDROCHLORIC ACID

The inhibition of aluminium metal from corrosion in 1.85M hydrochloric
acid solutions by crude extract of Azadirachta indica and Carica papaya
leaves was studied using gasometric technique. Aluminium coupons were
immersed in test solutions of uninhibited 1.85 M HCl and those
containing extract concentrations of 10%, 20%, 30%, 40% and 50% (v/v) at
room temperature. The volume of hydrogen gas evolved as a result of the
rate of reaction between aluminium coupons and the acid extracts was
recorded. The inhibition efficiency of the extracts was determined and
the adsorption isotherm of the process was estimated using four
adsorption theories namely; Frumkin, Freundlich, Langmuir and Temkin. It
was observed that the plant extract retarded the acid induced corrosion
of aluminium and the volume of hydrogen gas evolved reduced with
increasing extract concentration. The adsorption studies revealed that
Langmuir isotherm is the best model for the adsorption of Azadirachta
indica (R2 = 0.999) and Carica papaya (R2 = 1) on aluminium surface.
This implied that the adsorption process between Azadirachta indica and
Carica papaya extracts with aluminium metal obeys chemisorption.

TITLE -  -  - .. -  -  -  -  - ..i
ABSTRACT -  -  - . -  -  - ii
DEDICATION -  -  -  -  - .iii
ACKNOWLEDGEMENTS -  - . -  -  - .iv
CERTIFICATION -  -  - . -  -  - v
ABBREVIATION -  -  - . -  -  - vi
TABLE OF CONTENT -  -  -  -
LIST OF TABLES -  -  -  -  - ..
LIST OF PLATES -  -  -  - .


CHAPTER ONE
1.0   Introduction      1
1.1.1  Corrosion      XX
1.1.2  Corrosion Environment  2
1.1.3  Principle of Corrosion    2
1.2    Forms Corrosion 4
1.2.1  Uniform Corrosion     5
1.2.2  Galvanic or Bimetallic Corrosion 8
1.2.3  Pitting corrosion / Crevice corrosion    8
1.2.4  Erosion Corrosion 9
1.2.5  Filliform Corrosion    10
1.2.6  Graphitic Corrosion 11
1.2.7  Fretting Corrosion    11
1.2.8  Corrosion Inhibitors  12
1.2.9  Classification of Inhibitors  13
1.2.10 Natural Corrosion Inhibitors for Metals 17
1.2.11 Carica papaya as a Green Inhibitor  17
1.2.12 Azadirachta indica as a Green Inhibitor   18
1.2.13 Aluminium  18
1.2.14 Applications of Aluminium    18
1.2.15 Alloy Designation 19
1.2.16 Corrosion behavior of Aluminium and its Alloys  19
1.2.17 Aims and Objective  20

CHAPTER TWO
2.0   Literature Review    21-29

CHAPTER THREE
3.0   Materials and Method 30
3.1   Materials  30
3.2   Reagent    30
3.3   Material Preparation  31
3.3.1   Preparation of Extract    31
3.4   Corrosion Inhibition Test 32-34

CHAPTER FOUR
4.0   Results and Discussion    35-38
4.1   Hydrogen Evolution and Corrosion Rate  38-40
4.2   Inhibition efficiency of Azadirachta indica and Carica papaya   41
4.3   Corrosion Rate of Azadirachta indica and Carica papaya Extract on Aluminium 44
4.4   Adsorption Studies 44-51

CHAPTER FIVE
5.0   Conclusion  52
5.1   Recommendation  52

LIST OF TABLES
Table 1.0: Green inhibitors for some metals 15
Table 4.1: Line equation and regression values for graph of volume of
hydrogen gas evolved (Azadirachta indica)          34
Table 4.2: Line equation and regression values for graph of volume of
hydrogen gas evolved (Carica papaya)            34
Table 4.3: Correlation coefficient for different adsorption isotherms
(Azadirachta indica)                47
Table 4.4: Correlation coefficient for different adsorption isotherms
(Carica papaya)                  49

LIST OF FIGURES
Fig. 1.1:   Uniform Corrosion                 5
Fig. 1.2:   Galvanic Corrosion                 7
Fig. 1.3:   Pitting Corrosion                 9
Fig. 1.4:   Crevice Corrosion                 9
Fig. 1.5:   Erosion Corrosion                 10
Fig. 1.6:   Filliform Corrosion                 11
Fig.1.7:   Graphitic Corrosion                11
Fig. 1.8:   Fretting corrosion                 12
Fig. 3.1   Experimental set up for gasometric method          30
Fig.4.1:    Variation of volume of hydrogen (cm3)  evolved with time (min) of Al coupons (Azadirachta indica) extract           34
Fig.4.2:    Variation of volume of hydrogen (cm3)  evolved with time (min) of Al coupons (Carica papaya) extract            36
Fig.4.3:   Percentage inhibition efficiency of varying concentrations of Carica papaya extracts           40
Fig.4.4:   Percentage inhibition efficiency of varying concentrations of Azadirachta indica extracts         41
Fig.4.5:   Corrosion rate of varying concentrations of Azadirachta indica extract        42
Fig.4.6:   Corrosion rate of varying concentrations of Carica papaya extract          42
Fig.4.7:   Temkin isotherm plot for aluminium corrosion in Azadirachta indica  extract              44

Fig.4.8   Freundlich isotherm plot for aluminium corrosion in Azadirachta indica  extract            45
Fig.4.9:   Frumkin adsorption isotherm plot for aluminium in Azadirachta indica extract          45
Fig.4.10:   Langmuir isotherm plot for aluminium in Azadirachta indica extract        46
Fig.4.11   Freundlich isotherm plot for aluminium corrosion in Carica papaya extract             47
Fig.4.12:   Frumkin adsorption isotherm plot for aluminium in Carica papaya  extract           48
Fig.4.13:   Temkin isotherm plot for aluminium corrosion in Carica papaya  extract              48
Fig.4.14:   Langmuir isotherm plot for aluminium in Carica papaya extract            49.