Corrosion Preventive Materials and Corrosion Testing S.K. Dhawan CSIR-National Physical Laboratory New Delhi, India Hema Bhandari Chemistry Department Maitreyi College, University of Delhi New Delhi, India Gazala Ruhi Chemistry Department Maitreyi College, University of Delhi New Delhi, India Brij Mohan Singh Bisht National Test House, Ministry of Consumer Affairs Ghaziabad, Uttar Pradesh, India Pradeep Sambyal CSIR - National Physical Laboratory New Delhi, India p, p, A SCIENCE PUBLISHERS BOOK A SCIENCE PUBLISHERS BOOK Cover credit: Cover illustrations reproduced by kind courtesy of the authors. CRC Press Taylor & Francis Group 6000 Broken Sound Parkway NW, Suite 300 Boca Raton, FL 33487-2742 © 2020 by Taylor & Francis Group, LLC CRC Press is an imprint of Taylor & Francis Group, an Informa business No claim to original U.S. Government works Version Date: 20200106 International Standard Book Number-13: 978-1-138-11875-1 (Hardback) Th is book contains information obtained from authentic and highly regarded sources. Reasonable eff orts have been made to publish reliable data and information, but the author and publisher cannot assume responsibility for the validity of all materials or the consequences of their use. Th e authors and publishers have attempted to trace the copyright holders of all material reproduced in this publication and apologize to copyright holders if permission to publish in this form has not been obtained. If any copyright material has not been acknowledged please write and let us know so we may rectify in any future reprint. 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Trademark Notice: Product or corporate names may be trademarks or registered trademarks, and are used only for identifi cation and explanation without intent to infringe. Visit the Taylor & Francis Web site at http://www.taylorandfrancis.com and the CRC Press Web site at http://www.crcpress.com Preface The design and production of “Corrosion Preventive Materials and Corrosion Testing” is entirely different from other handbooks dealing with the same subject. While other corrosion handbooks have been generally the state-of-the-art information on corrosion engineering by a principal author, this book is a result of collective efforts of many authors who have a clear understanding on corrosion and its implementation in different areas. Although four author’s names appear on its cover, this handbook is indeed the result of the cumulative efforts of many generations of scientists and engineers and their understanding and preventing the effects of corrosion, one of the most constant foes of human endeavors. The design and construction of this handbook are made for the new millennium with latest information processing techniques presently available. This book deals with prominent topics, for example, how conducting polymer-based composite coatings have addressed and tackled corrosion problems. The conducting polymer systems, selected as supportive examples, have been chosen for the performance of coatings in the marine environment. The conducting polymer-based paints/ coatings have found an immense application in its fight against corrosion. These coatings overcome the drawbacks of conventional anti-corrosive coatings, and offer following advantages like its self- healing ability (it helps in passivating the regions of scratch, pores, etc.), are environmental friendly and based on green technology (free from heavy metal ions and hazardous chromates), have a long service life, are economically feasible and also have additional anti-static properties. This book is aimed at practicing engineers, providing a comprehensive guide and a reference source for solving corrosion problems by new generation coatings based on conducting polymers. During the past decades, progress in the development of materials capable of resisting corrosion has been significant. There have been substantial developments in the area of protective coatings. This book should prove to be a key information source concerning numerous facets of corrosion damage, from detection and monitoring to its prevention and control. The book is divided into six main chapters and is followed by a short chapter on the future directions of this area accompanied by supporting materials. Each chapter is relatively independent and can be consulted without having to go through the previous chapters. The first chapter contains fundamental principles governing aqueous corrosion and covers the main environments causing corrosion such as atmospheric, natural waters, seawater environments, inspection, monitoring and testing. This section also provides elements for understanding protective coatings, corrosion inhibitors, cathodic protection and anodic protection. The second chapter gives an overview of conducting polymers that are considered as futuristic electronic materials with promising properties. It has attracted the attention of many material scientists because of its boundless applications in corrosion protection and other areas like energy storage, EMI shielding, sensors, batteries, anti-static, supercapacitors, organic solar cells, light emitting diodes, field emission transitions, electrochromic devices, etc., that can be attributed to its tailorable electrical conductivity, ease of synthesis, low processing cost, corrosion resistant, lightweight and good environmental stability. The third chapter covers the development of conducting copolymer composites, to be used as the corrosion protection with hydrophobic properties, greater durability and high wear resistance that is iv Corrosion Preventive Materials and Corrosion Testing expected to encourage a major revolution in the world of corrosion. It describes the development of highly resilient, inexpensive and environment friendly hydrophobic epoxy coating based on conducting copolymer composite. SiO particles were incorporated in conducting copolymer based on aniline 2 and pentafluoro aniline. The synthesized poly(aniline-co-pentafluoro aniline)/SiO composites were 2 formulated with epoxy resin. Different physico-mechanical properties as well as anti-corrosion performance of epoxy formulated copolymer-silica composites coatings is demonstrated by using mild steel substrate in 3.5 wt.% NaCl medium. The fourth chapter is devoted to epoxy coating modified with conductive copolymer nanocomposites based on poly(AN-co-PFA)-zirconia, which is an excellent corrosion resistant material under the harsh marine environment. This may also disclose a new opportunity in various technological applications for marine engineering materials, which requires very high salt resistance ability. The fifth chapter discusses the chemistry of polypyrrole and mentions different synthesis routes of the polypyrrole composites. Various polypyrrole based composites, containing fillers like SiO, 2 TiO, clay, ZnO, AlO, MWCNTs, grapheme, etc., and their designing as corrosion resistant coatings 2 2 3 over ferrous and non-ferrous substrates are presented in this chapter. The corrosion characterization of the polypyrrole-based composite coatings is the core content of the chapter. An interesting section of this chapter is on the self-healing property shown by the polypyrrole/SiO composite coatings 2 and presents the FESEM images of the artificial defect on the coated surfaces and their self-healing tendency with the passage of time. The present chapter concludes that the polypyrrole-based composite coatings offer advanced corrosion protection to the metal surfaces. Next, how biopolymer conducting polymer hybrid coatings can effectively control corrosion forms the basis of the sixth chapter. Elaborate discussions on two different composite coating systems, namely: chitosan/polypyrrole/SiO and Polypyrrole/gum acacia are presented in this chapter. In 2 order to develop highly durable and efficient conducting copolymer based anti-corrosion material, a significant effort has been presented in this book. Finally, what is the future scope and how self-healing coatings can be designed using conducting polymer coatings form the basis of the seventh chapter. An appendix appears at the end of the book which explains all the terminologies used in the chapters. In this book, an attempt is made to present data on highly durable, self-healing and hydrophobic conducting copolymers based nanocomposites and evaluation of such copolymers nanocomposites for the use of corrosion protection of iron in a corrosive environment. S.K. Dhawan Hema Bhandari Gazala Ruhi Brij Mohan Singh Bisht Pradeep Sambyal Acknowledgments The book Corrosion Preventive Materials and Corrosion Testing is an outcome of the extensive research carried out by my students Dr. Hema Bhandari, Dr. Gazala Ruhi, Dr. Brij Mohan Singh Bisht and Dr. Pradeep Sambyal along with my other students whose contribution can never be forgotten. In fact, Ms. Ridham Dhawan is the researcher, whose contribution in designing some of the chapters have been very fruitful and her input has been a part and parcel of many sections of this book. Our acknowledgments also go to the staff working in the conducting polymer group, who are the key figures in designing the pilot plant, powder coating units and preparation of samples. As mentioned in the Preface, this book attempts to summarize the present state of our knowledge of the corrosion phenomena and their impact on our societies. Many of the opinions expressed in the book have come either from our work with corrosion team at NPL or more often from our study of the work of other corrosion engineers and scientists. Of the first kind, we are particularly indebted to Mr. Brijesh Sharma, who is a pioneer in setting up lab reactors and other experiments that were carried out by us in the laboratory. We are also thankful to various science and engineering pillars responsible for the present state of our knowledge in the field of corrosion. Our utmost gratitude goes to Dr. D.K. Aswal, Director of National Physical Laboratory, for his pragmatic vision of the quantification of corrosion damage. Heartfelt thanks to National Test House team as well, where our samples were tested in the Salt Spray Chamber under corrosive conditions. Contents Preface iii Acknowledgments v 1. Introduction to Corrosion 1 1.1 What is corrosion? 1 1.2 Problems due to corrosion 2 1.3 Classification of corrosion 4 1.3.1 Pitting corrosion 4 1.3.2 Crevice corrosion 5 1.3.3 Galvanic corrosion 6 1.3.4 Erosion corrosion 7 1.3.5 Intergranular corrosion 7 1.3.6 Cracking corrosion 8 1.3.7 Stress corrosion cracking 8 1.3.8 Fatigue corrosion 9 1.4 Electrochemistry of corrosion 10 1.4.1 Thermodynamics aspects of corrosion process (Pourbaix diagram) 14 1.4.2 Kinetic aspects of the corrosion process 15 1.4.2.1 Polarization methods of determination of corrosion rate 15 1.4.2.2 Electrochemical Impedance Spectroscopy (EIS) 17 1.5 Metal corrosion and passive film 20 1.6 Tests for corrosion protection 22 1.6.1 Surface studies 22 1.6.2 Salt spray test 23 1.6.3 Weight loss method 24 1.7 Methods of corrosion protection 24 1.7.1 Materials selection 25 1.7.2 Cathodic and anodic protection 25 1.7.3 Corrosion inhibitor 27 1.7.4 Corrosion resistant coating 31 1.7.5 Paints 31 1.7.6 Metallic coatings 33 1.7.7 Inorganic coatings 35 1.7.8 Conversion coatings 36 1.7.9 Organic coatings 36 1.7.10 Mechanism of protection 36 1.7.11 Barrier protection 37 1.7.12 Ennobling mechanism 37 1.7.13 Self-healing mechanism 37 viii Corrosion Preventive Materials and Corrosion Testing 1.8 Testing methods of coatings 37 1.8.1 Mechanical testing of coating 38 1.8.1.1 Standard test methods for measuring adhesion by tape test 38 1.8.1.2 Knife test 39 1.8.1.3 Tape test 40 1.8.1.4 Cross-cut adhesion test 41 1.8.1.5 Pull-Off test 41 1.8.1.6 Mandrel bend test 41 1.8.1.7 Taber abrasion resistance test 43 1.8.1.8 Scratch resistance test 44 1.9 New aged smart surface coating 44 1.9.1 Conducting polymer-based coatings 47 1.9.2 Polyaniline and its derivatives 48 1.9.3 Polypyrrole and its derivatives 52 1.10 Conclusion 55 References 56 2. Conducting Polymers 61 2.1 Conducting polymers 61 2.2 Structure of conducting polymers 62 2.3 Methods of doping 63 2.3.1 Chemical doping by charge transfer 64 2.3.2 Electrochemical doping 64 2.3.3 Mechanism of conductivity 65 2.3.4 Polymers with degenerate ground states 65 2.3.5 Polymers with non-degenerate ground states 65 2.4 Poly(3,4-ethylene dioxythiophene) (PEDOT) 70 2.4.1 Synthesis of PEDOT/PSS 71 2.4.2 Mechanism of EDOT to PEDOT/PSS polymerization 71 2.4.2.1 Synthesis of PEDOT in DBSA medium 71 2.4.2.2 Synthesis of PEDOT/MWCNT composites 72 2.4.2.3 PEDOT as corrosion inhibitor 74 2.5 Polyaniline 74 2.5.1 Synthetic routes to polyaniline 76 2.5.2 Chemical oxidative polymerization 76 2.5.3 Mechanism of oxidative polymerization of aniline 77 2.5.4 Electrochemical polymerization of aniline 79 2.5.5 Corrosion protection by conducting polymers 84 2.6 Polypyrrole 90 2.6.1 Polypyrrole as corrosion inhibitor 93 References 94 3. Poly(Aniline-co-Pentafluoroaniline)/SiO Composite Based Anticorrosive Coating 101 2 3.1 Introduction 101 3.2 Mechanism of oxidative polymerization of aniline 102 3.2.1 Preparation of Poly(AN-co-PFA)/SiO composites 107 2 3.2.2 Preparation of Poly(aniline-co-phenetidine)/SiO composites 107 2 3.2.3 Preparation of Poly(aniline-co-o-toluidine) Flyash composites 109 3.3 Development of epoxy formulated copolymer composites coating on mild steel 109 3.4 Characterization of epoxy formulated copolymer composite coated substrate 111 3.4.1 FTIR spectroscopy 111 3.4.2 Thermogravimetric analysis (TGA) 112 Contents ix 3.4.3 Micro-structural analysis 114 3.4.4 Surface wettability test 117 3.4.5 Physico-mechanical testing of coating 118 3.4.6 Corrosion studies of the coated mild steel substrate 120 3.4.6.1 Salt spray test 120 3.4.6.2 Electrochemical studies of the coating 122 3.4.6.2.1 Open Circuit Potential (OCP) versus time 122 3.4.6.2.2 Tafel extrapolation measurement 124 3.4.6.2.3 Electrochemical Impedance Spectroscopy (EIS) 129 3.5 Mechanism of corrosion protection of mild steel coated with polyaniline based 133 copolymer composites 3.6 Conclusion 135 References 136 4. Poly(Aniline-co-Pentafluoroaniline)/ZrO Nanocomposite Based Anticorrosive 141 2 Coating 4.1 Introduction 141 4.2 Synthesis of zirconia (ZrO) nanoparticles 144 2 4.3 Preparation of poly(An-co-PFA)/ZrO nanocomposites 145 2 4.4 Development of epoxy formulated poly(An-co-PFA)/ZrO nanocomposites coating 147 2 on mild steel 4.5 Characterization of copolymer nanocomposite and epoxy modified copolymer 147 nanocomposite coated substrate 4.5.1 Fourier Transform Infrared Spectroscopy (FTIR) 147 4.5.2 X-ray diffraction analysis 148 4.5.3 Thermogravimetric analysis (TGA) 149 4.5.4 Morphological analysis 150 4.5.5 Wettability test (contact angle measurement) 151 4.6 Physico-mechanical properties 154 4.6.1 Cross-cut tape test 154 4.6.2 Taber abrasion and scratch resistance test 154 4.6.3 Mandrel bend test 156 4.7 Corrosion protection performance of the coating 156 4.7.1 Salt spray test 156 4.7.2 Electrochemical studies of the coating 159 4.7.2.1 Open Circuit Potential (OCP) versus time measurement 159 4.7.2.2 Tafel extrapolation measurement 161 4.7.2.3 Electrochemical Impedance Spectroscopy (EIS) 164 4.8 Role of poly(An-co-PFA)/zirconia nanocomposites on metal protection 168 4.9 Conclusions 169 References 170 5. Polypyrrole-Based Composite Coatings 174 5.1 Introduction 174 5.2 Polypyrrole composites and their synthesis routes 177 5.3 Compositional, thermal and micro-structural studies of the PPy-based composites 182 5.3.1 FTIR spectroscopy 182 5.3.2 X-Ray diffraction studies 183 5.3.3 Thermogravimetric analysis (TGA) 185 5.3.4 Micro-structural studies 187