Fundamental Aspects of Corrosion Films in Corrosion Science PDF
Preview Fundamental Aspects of Corrosion Films in Corrosion Science
Fundamental Aspects of Corrosion Films in Corrosion Science Fundamental Aspects of Corrosion Films in Corrosion Science Bruce D. Craig Metallurgical Consultants, Inc. Houston, Texas Springer Science+ Business Media, LLC Library of Congress Cataloging-In-Publication Data Cra1g, Bruce D. Fundamental aspects of corros1on f1l•s 1n corros1on sc1ence I Bruce D. Cra1g. p. em. Includes b1bl1ograph1ca1 references and 1ndex. ISBN 978-1-4899-2559-6 ISBN 978-1-4899-2557-2 (eBook) DOI 10.1007/978-1-4899-2557-2 1. Corros1on and ant1-corros1ves. I. T1tle. TA418.74.C73 1990 620.1'1223--dc20 90-48814 CIP ISBN 978-1-4899-2559-6 © 1991 Springer Science+ Business Media New York Originally published by Plenum Press, New York in 1991 Softcover reprint of the hardcover 1st edition 1991 All rights reserved No part of this book may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, microfilming, recording, or otherwise, without written permission from the Publisher This book is dedicated to my sons, Jason and Nathan. Preface The purpose of this book is to stimulate thinking among corrosion scientists and engineers to examine corrosion mechanisms and corro sion control from another perspective. While the presence of corro sion films in electrochemical corrosion has been recognized for over a century, the contribution of these films to all facets of corrosion has not been explored to a significant degree. Rather the role of films in certain mechanisms (i.e., stress corrosion cracking) has been empha sized, yet almost ignored for other corrosion mechanisms. This is viewed by the author as solely attributable to the lack of investigation into, and an understanding of, the contribution of films to these mech anisms or forms of attack. The lack of emphasis and study of corrosion films and their contribution to all forms of corrosion attack are probably the result of current university instruction that utilizes two popular corrosion texts (Uhlig and Fontana and Greene) for teaching. These texts provide an excellent understanding at the undergraduate level of corrosion funda mentals; however, the major implicit premise in these texts is that bulk properties of an alloy or metal control the corrosion resistance in a particular environment. For many applications and for a simple under standing of corrosion mechanics, this approach is sufficient. Yet, research on corrosion films indicate these films often have an entirely different composition than the bulk metal (ratio of alloying elements). Moreover, the film may be protective in certain environments and nonprotective in others. Furthermore, once a film is established, vii viii Preface transport through the film and reactions at the metal/film and film/ environment interfaces are in many cases rate controlling as well as mechanistically controlling. Therefore, since most metallic systems rapidly form some type of film when exposed to an environment, the environment/film/metal system becomes more important in evaluat ing alloy-environment behavior than just corrosion behavior of the bulk alloy. This book is not intended to be a theoretical text on oxide films, since this has been dealt with elsewhere; instead it is meant to comple ment the more basic texts on corrosion, allowing the student/scientist to extend this basic knowledge of corrosion fundamentals to an appre ciation of the role of films in corrosion. As such it completely emphas izes films, and no attempt has been made to address other factors that at times may be of equal or greater importance. It is further hoped that corrosion scientists, engineers, and students will gain a new perspec tive on the importance of corrosion films in corrosion science and include this insight in further work. The obvious role of corrosion films in the future will be complete control of corrosion by manipulation of the film. In other words, it is hoped that future research will provide sufficient insight into all as pects of corrosion films so that the surface layers of a metal can be alloyed to grow the necessary film to create protection and provide a self-healing system when the film is damaged in service. While this eventual goal is certainly many years in the future, current research suggests that such goals are generally achievable. Thus, engineer ing the bulk or surface alloy content of a metal to produce a pro tective film for a specific service environment is the future emphasis of corrosion films, and it is the purpose of this book to be a guidepost to this goal. The book is divided into seven chapters. Chapters 1 and 2, review thermodynamics and kinetics, with emphasis on corrosion films. Chapter 3 represents the main thrust of the book and is intended to provide the reader with a fundamental understanding of films and how they affect corrosion mechanisms. This chapter is an introduction to transport in films and some of the important models currently used to describe films. As with Chapters 1 and 2, there are other texts that are more theoretically detailed and should be consulted if a deeper knowl- Preface ix edge of this topic is desired. Chapters 4-7 specifically address the roles of films in the areas of corrosion inhibition, pitting, environ mental cracking, and erosion-corrosion. While films contribute to essentially every form of corrosion, these certain forms of corrosion were chosen because of their impor tance to corrosion research. Acknowledgments It is extremely difficult to write a book on a subject of this magnitude without failing to acknowledge the considerable contribution of the many researchers in this field. Therefore, I express gratitude to all those people referenced in this book and especially to those not men tioned that have advanced the science of corrosion. I would personally like to thank Professor David L. Olson of the Colorado School of Mines: first, for his enthusiasm in teaching the subject of this book, which inspired my interest, and second, as a friend who has championed my cause from the beginning of my career. No one can ask for a better example of a teacher. Furthermore, I would like to acknowledge Professors William Mueller and William Copeland for their support in achieving my academic goals. Without their early assistance this book would not have been possible. Appre ciation is also extended to Dr. Donald T. Klodt, who stepped in to assist after my first technical paper was rejected and, thereafter, en couraged me to continue publishing. Finally, I thank two important women for their support and assis tance in the substantial effort of this book: my secretary, Dannia Lou Stovall, and my wife, Dolly. xi Contents 1. Thermodynamics of Corrosion . . . . . . . . . . . . . . . . . . . . . . . 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Charged Surfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Electrochemical Reactions. . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 High-Temperature Aspects . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 2. Kinetics of Corrosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 Polarization. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 Passivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 High-Temperature Oxidation. . . . . . . . . . . . . . . . . . . . . . . . . . 42 References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 3. Properties of Corrosive Films........................ 47 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 7 Interface Reactions.................................. 48 Interphase Development.............................. 51 Defects in Crystalline Solids. . . . . . . . . . . . . . . . . . . . . . . . . . 5,3 Duplex and Multiphase Corrosion Films . . . . . . . . . . . . . . . . 70 Deviation of Films from Semiconductor Behavior. . . . . . . . . 73 Discontinuous and Polycrystalline Films................ 75 Breakaway Oxidation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78 xiii
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