Effect of Calotropis Gigantea on Corrosion Inhibition of Mild Steel in Acidic Medium

EFFECT OF CALOTROPIS GIGANTEA ON CORROSION INHIBITION OF MILD STEEL IN ACIDIC MEDIUM A DISSERTATION SUBMITTED FOR THE PARTIAL FULFILLMEN OF THE REQUIREMENTS FOR THE MASTERS OF SCIENCE DEGREE IN CHEMISTRY SUBMITTED BY: Bishnu Bahadur Dawadi Exam Roll No.: 422/072 (T.U. Regd. No.: 5-2-240-679-2011) SUBMITTED TO: CENTRAL DEPARTMENT OF CHEMISTRY, INSTITUTE OF SCIENCE AND TECHNOLOGY, TRIBHUVAN UNIVERSITY, KIRTIPUR, KATHMANDU,NEPAL June, 2019 i BOARD OF EXAMINER AND CERTIFICATE OF APPROVAL This dissertation work entitled- “Effect of Calotropis gigantea on corrosion inhibition of mild steel in acid medium” submitted by Mr. Bishnu Bahadur Dawadi (Roll No. 422/072, T.U. Regd. No. 5-2-240-679-2011) has been accepted as a partial fulfillment of the requirements for the Degree of Master of Science in Chemistry. ………………………………. Supervisor Prof. Dr. Amar Prasad Yadav Central Department of Chemistry Tribhuvan University, Kathmandu, Nepal …………………………………….. …………………. Internal examiner External examiner Prof. Dr. Vinay Kumar Jha Assoc. Prof. Dr. Surendra Kumar Gautam Central Department of Chemistry Department of Chemistry Tribhuvan University, Kirtipur Tri-Chandra Campus Kathmandu, Nepal Tribhuvan University Kathmandu, Nepal …………………………………….. Prof. Dr. Ram Chandra Basnyat Head of the Department Central Department of Chemistry Tribhuvan University, Kirtipur Kathmandu, Nepal Date: June 26, 2019 i RECOMMENDATION LETTER This dissertation work entitled- “Effect of Calotropis gigantea on corrosion inhibition of mild steel in acid medium” submitted by Mr.Bishnu Bahadur Dawadi (Roll No. 422/072, T.U. Regd. No. 5-2-240-679-2011) for the Degree of Master of Science in Chemistry of Tribhuvan University was carried out under my supervision in the academic year 2017-2019. During the research period, Mr. Bishnu had performed the dissertation work sincerely and satisfactorily. ………………………. Supervisor Prof. Dr. Amar Prasad Yadav Central Department of Chemistry Tribhuvan University, Kirtipur Kathmandu, Nepal Date: June 26, 2019 ii DECLARATION I, Bishnu Bahadur Dawadi, hereby declare that the present dissertation work is done originally and has not been submitted elsewhere for any degree. Any literature, data or works done by others and cited in this dissertation has been given due acknowledgements and listed in the reference section. …………………………….. Bishnu Bahadur Dawadi Central Department of Chemistry Tribhuvan University, Kirtipur Kathmandu, Nepal Date: June 26, 2019 iii DEDICATED TO My Father Man Bahadur Dawadi & Mother Saraswoti Dawadi iv ACKNOWLEDGEMENTS I express my sincere gratitude to my respected supervisor Prof. Dr. Amar Prasad Yadav of Central Department of Chemistry, Tribhuvan University, Kirtipur, Kathmandu for their valuable guidance, support and suggestion throughout this dissertation work. I owe my deep gratitude to Professor Dr. Ram Chandra Basnyat, Head of Central Department of Chemistry, T.U., Kirtipur for providing me necessary research facilities to carry out this dissertation work. Besides, I would like to thank Assoc. Prof. Nabin Karki Asst. Prof. Dipak Kumar Gupta and Asst. Prof. Sanjaya Singh for their insightful comments, encouragement and consistent help and support. I would always be grateful towards both of them for inlighting me the first glance of research. Further, I am indebted to Associate Prof. Dr. Deepak Raj Pant from Central Department of Botany, Tribhuvan University for this help. I would like to acknowledge to my senior; Shyam Prasad Shrestha, Basu Dev Poudel, Roshan Lama and Colleagues, Amrit Ojha, Ritu Thakur, Sumnath Khanal and other friends of Central Department of Chemistry for their help to carry out this dissertation work. Last but not the least, I would like to thank my family: my parents Mr. Man Bahadur Dawadi and Mrs. Saraswoti Dawadi, Sister Shanta Dawadi and brother Krishna Dawadi for supporting me throughout writing this thesis and my life in general. Bishnu Bahadur Dawadi v LIST OF ABBREVIATIONS IUPAC International Union of Pure and Applied Chemistry GNP Gross National Product GDP Gross Domestic Product VCI Volatile Corrosion inhibitors Cdl Double layer Capacitance Ecorr Corrosion Potential Cls Corrosion Inhibitors Icorr Corrosion Current Density CR Corrosion Rate IE Inhibitor Efficiency ppm Parts Per Million OCP Open Circuit Potential 휃 Degree of Surface Coverage SCE Saturated Calomel Electrode FTIR Fourier Transform Infrared vi ABSTRACT The inhibition effect of Calotropis gigantea extract on corrosion of mild steel in 1M H2SO4 was investigated using weight loss measurement along with electrochemical techniques viz. open circuit potential and potentiodynamic polarization. Weight loss technique was employed to study various concentration effect of extract along with effects of temperature and time while electrochemical techniques were performed to evaluate both concentration and dipped and non dipped effect of test solution. Inhibition efficiency of as high as 89.23 % for dipped sample and 75.42% percent for non dipped sample were achieved for green extract of Calotropis gigantea for 1000 ppm concentration from Tafel plot. The open circuit potential measurement showed that methanolic extract of Calotropis gigantea as mixed type of inhibitor forming a protective layer on the surface of mild steel by the process of adsorption. The inhibition effect of the plant extract could be accelerated by the presence of functional group such as Carbonyl, Nitro, Hydroxyl along with heteroatom and multiple bonds containing compounds as suggested by FTIR results, which is adsorbed on the surface of mild steel. Keywords: Corrosion, FTIR, Green Inhibitors, Inhibitors, Mild steel, Polarization, Potentiodynamic, Weight Loss Measurements, vii TABLE OF CONTENTS Board of Examiners and Certificate of approval i Recommendation Letter ii Declaration iii Dedication iv Acknowledgements v List of Abbreviations vi Abstract vii Contents viii List of figures xi List of tables xii CHAPTER-1: INTRODUCTION 1-31 1.1 Introduction of Corrosion 1 1.2 Importance of Corrosion study 2 1.3 Corrosion Control 4 1.3.1 Selection of right material of construction 4 1.3.2 Surface coating 4 1.3.3 Design 5 1.3.4 Electrical protection 6 1.4 Inhibitors 7 1.4.1 Anodic Inhibitors 7 1.4.2 Cathodic Inhibitor 9 1.4.3 Mixed Inhibitors 10 1.4.4 Volatile Corrosion Inhibitors (VCI) 10 1.5 Natural products as green Inhibitors 10 1.5.1 Use of green inhibitors 12 1.5.2 Mechanism of corrosion inhibitor 12 1.6 Calotropis gigantea as Green Inhibitor 13 viii 1.7 Adsorption of Inhibitors 14 1.8 Corrosion Monitoring 16 1.8.1 Importance of corrosion monitoring and others engineering system 16 1.8.2 Types of corrosion monitoring techniques 16 1.9 Mild steel 20 1.10 Literature Review 22 1.11 Objectives of the Study 1.11.1 General Objectives 27 1.11.2 Specific Objectives 27 CHAPTER-2: MATERIALS AND METHODS 28-32 2.1 Preparation of plane extract and its solution 2.1.1 Selection, specimen collection and plant identification 28 2.1.2 Preparation of power of plant specimen 28 2.1.3 Preparation of Concentrated Methanol Extract 29 2.1.4 Preparation of solution 29 2.2 Phytochemical screening test. 29 2.3 Preparation of Mild Steel Sample 30 2.4 Electrochemical Measurements 30 2.4.1 Open Circuit potential Measurement 30 2.4.2 Potentiodynamic Polarization 31 2.5 Weight Loss Measurements 32 ix CHAPTER-3: RESULTS AND DISCUSSION 33-48 3.1 Variation of open circuit potential with time 33 3.2 Polarization of mild steel in 1M H2So4 and inhibitor solution 37 3.3 Effect of Concentration of Calotropis gigantea extract 39 3.4 Effects of concentration on inhibition Efficiency 40 3.5 Variation of weight Loss with time of immersion 41 3.6 Variation on inhibition Efficiency with time of immersion 42 3.7 Variation of inhibition Efficiency with concentration of Calotropis gigantea extract by weight loss method 46 3.8 Variation of inhibition Efficiency of Calotropis gigantea extract with temperature 46 3.9 FTIR Spectroscopic Analysis 47 CONCLUSIONS 49 REFERENCES 51 APPENDIX A1-A3 x LIST OF FIGURES Fig. 1.1 : Classification of inhibitors 9 Fig. 1.2 : Calotropis gigantea plant 13 Fig.1.3 : Adsorption of negatively charged inhibitor 15 Fig. 1.4 (a) : Positively charged inhibitor molecules 15 Fig.1.4 (b) : Synergistic adsorption of positively charged inhibitor 15 Fig.1.5 : Tafel plot 20 Fig. 2.1 : Google map showing the study site 28 Fig.2.2 : Experimental set up for potentiodynamic polarization 31 Fig. 3.1(a) : Variation of OCP with immersion of as dipped sample 34 Fig. 3.1(b) : Variation of OCP with 1 hr dipped sample 35 Fig. 3.1(c) : Variation of OCP with 24 hr dipped sample 36 Fig. 3.2 : Polarization behavior of mild steel in 1M H2SO4 37 Fig. 3.3 (a) : Effects of concentration with as dipped sample 38 Fig. 3.3 (b) : Effects of concentration with 1 hr dipped sample 38 Fig. 3.3(c) : Effects of concentration with 24 hr dipped sample 39 Fig. 3.4 : Variation of inhibition efficiency with concentration 40 Fig. 3.5 : Variation of weight loss with time for immersion 42 Fig. 3.6 : Variation of inhibition efficiency with time for 43 immersion Fig. 3.7 : Variation of corrosion rate with time for immersion 43 Fig. 3.7(a) : Variation of corrosion rate with concentration 43 Fig. 3.8 : Variation of inhibition efficiency with temperature 45 Fig.3.9 : FTIR spectrum of 1000 ppm extracts solution 47 xi LIST OF TABLES Table No.1 : Inhibition efficiency for the as dipped sample A-1 Table No.2 : Inhibition efficiency for 1 hour dipped sample A-1 Table No.3 : Table for the 24 hours dipped sample A-1 Table No.4 : Table for the weight loss and surface coverage A-2 Table No.5 : Variation of concentration with inhibition efficiency A-2 Table No.6 : Variation of temperature with inhibition efficiency A-2 Table No.7 : Table for the FTIR Spectrum A-3 xii CHAPTER ONE: INTRODUCTION 1.1 Introduction of Corrosion In general gradual deterioration, damage and failure of structures of surfaces of metallic materials as the result of interaction of metal with corrosive environments is called corrosion.

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