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

By

ALADESUYI, Olanrewaju

Presented To

Department of Biological Science

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
10   Introduction      1
111  Corrosion      XX
112  Corrosion Environment  2
113  Principle of Corrosion    2
12    Forms Corrosion 4
121  Uniform Corrosion     5
122  Galvanic or Bimetallic Corrosion 8
123  Pitting corrosion / Crevice corrosion    8
124  Erosion Corrosion 9
125  Filliform Corrosion    10
126  Graphitic Corrosion 11
127  Fretting Corrosion    11
128  Corrosion Inhibitors  12
129  Classification of Inhibitors  13
1210 Natural Corrosion Inhibitors for Metals 17
1211 Carica papaya as a Green Inhibitor  17
1212 Azadirachta indica as a Green Inhibitor   18
1213 Aluminium  18
1214 Applications of Aluminium    18
12 15 Alloy Designation 19
1216 Corrosion behavior of Aluminium and its Alloys  19
1217 Aims and Objective  20

CHAPTER TWO
20   Literature Review    21-29

CHAPTER THREE
30   Materials and Method 30
31   Materials  30
32   Reagent    30
33   Material Preparation  31
331   Preparation of Extract    31
34   Corrosion Inhibition Test 32-34

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

CHAPTER FIVE
50   Conclusion  52
51   Recommendation  52

LIST OF TABLES
Table 10: Green inhibitors for some metals 15
Table 41: Line equation and regression values for graph of volume of
hydrogen gas evolved (Azadirachta indica)          34
Table 42: Line equation and regression values for graph of volume of
hydrogen gas evolved (Carica papaya)            34
Table 43: Correlation coefficient for different adsorption isotherms
(Azadirachta indica)                47
Table 44: Correlation coefficient for different adsorption isotherms
(Carica papaya)                  49

LIST OF FIGURES
Fig 11:   Uniform Corrosion                 5
Fig 12:   Galvanic Corrosion                 7
Fig 13:   Pitting Corrosion                 9
Fig 14:   Crevice Corrosion                 9
Fig 15:   Erosion Corrosion                 10
Fig 16:   Filliform Corrosion                 11
Fig17:   Graphitic Corrosion                11
Fig 18:   Fretting corrosion                 12
Fig 31   Experimental set up for gasometric method          30
Fig41:    Variation of volume of hydrogen (cm3)  evolved with time (min) of Al coupons (Azadirachta indica) extract           34
Fig42:    Variation of volume of hydrogen (cm3)  evolved with time (min) of Al coupons (Carica papaya) extract            36
Fig43:   Percentage inhibition efficiency of varying concentrations of Carica papaya extracts           40
Fig44:   Percentage inhibition efficiency of varying concentrations of Azadirachta indica extracts         41
Fig45:   Corrosion rate of varying concentrations of Azadirachta indica extract        42
Fig46:   Corrosion rate of varying concentrations of Carica papaya extract          42
Fig47:   Temkin isotherm plot for aluminium corrosion in Azadirachta indica  extract              44

Fig48   Freundlich isotherm plot for aluminium corrosion in Azadirachta indica  extract            45
Fig49:   Frumkin adsorption isotherm plot for aluminium in Azadirachta indica extract          45
Fig410:   Langmuir isotherm plot for aluminium in Azadirachta indica extract        46
Fig411   Freundlich isotherm plot for aluminium corrosion in Carica papaya extract             47
Fig412:   Frumkin adsorption isotherm plot for aluminium in Carica papaya  extract           48
Fig413:   Temkin isotherm plot for aluminium corrosion in Carica papaya  extract              48
Fig414:   Langmuir isotherm plot for aluminium in Carica papaya extract            49