MICROWAVE PROCESSING OF MATERIALS

COMMITTEE ON MICROWAVE PROCESSING OF MATERIALS: AN EMERGING INDUSTRIAL TECHNOLOGY

NATIONAL MATERIALS ADVISORY BOARD

COMMISSION ON ENGINEERING AND TECHNICAL SYSTEMS

NATIONAL RESEARCH COUNCIL

Publication NMAB-473

National Academy Press
Washington, D.C.
1994



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Microwave Processing of Materials MICROWAVE PROCESSING OF MATERIALS COMMITTEE ON MICROWAVE PROCESSING OF MATERIALS: AN EMERGING INDUSTRIAL TECHNOLOGY NATIONAL MATERIALS ADVISORY BOARD COMMISSION ON ENGINEERING AND TECHNICAL SYSTEMS NATIONAL RESEARCH COUNCIL Publication NMAB-473 National Academy Press Washington, D.C. 1994

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Microwave Processing of Materials NOTICE: The project that is the subject of this report was approved by the Governing Board of the National Research Council, whose members are drawn from the councils of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The members of the committee responsible for the report were chosen for their special competences and with regard for appropriate balance. This report has been reviewed by a group other than the authors according to procedures approved by a Report Review Committee consisting of members of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The National Academy of Sciences is a private, nonprofit, self-perpetuating society of distinguished scholars engaged in scientific and engineering research, dedicated to the furtherance of science and technology and to their use for the general welfare. Upon the authority of the charter granted to it by the Congress in 1863, the Academy has a mandate that requires it to advise the federal government on scientific and technical matters. Dr. Bruce M. Alberts is president of the National Academy of Sciences. The National Academy of Engineering was established in 1964, under the charter of the National Academy of Sciences, as a parallel organization of outstanding engineers. It is autonomous in its administration and in the selection of its members, sharing with the National Academy of Sciences the responsibility for advising the federal government. The National Academy of Engineering also sponsors engineering programs aimed at meeting national needs, encourages education and research, and recognizes the superior achievements of engineers. Dr. Robert M. White is president of the National Academy of Engineering. The Institute of Medicine was established in 1970 by the National Academy of Sciences to secure the services of eminent members of appropriate professions in the examination of policy matters pertaining to the health of the public. The Institute acts under the responsibility given to the National Academy of Sciences by its congressional charter to be an adviser to the federal government and, upon its own initiative, to identify issues of medical care, research, and education. Dr. Kenneth I. Shine is president of the Institute of Medicine. The National Research Council was organized by the National Academy of Sciences in 1916 to associate the broad community of science and technology with the Academy’s purposes of furthering knowledge and advising the federal government. Functioning in accordance with general policies determined by the Academy, the Council has become the principal operating agency of both the National Academy of Sciences and the National Academy of Engineering in providing services to the government, the public, and the scientific and engineering communities. The Council is administered jointly by both Academies and the Institute of Medicine. Dr. Bruce M. Alberts and Dr. Robert M. White are chairman and vice chairman, respectively, of the National Research Council. This study by the National Materials Advisory Board was conducted under Contract No. MDA 972-92-C-0028 with the Department of Defense and the National Aeronautics and Space Administration. Library of Congress Catalog Card Number 94-66560 International Standard Book Number 0-309-05027-8 Available in limited supply from: National Materials Advisory Board 2101 Constitution Avenue, NW HA-262 Washington, D.C. 20418 202-334-3505 Additional copies are available for sale from: National Academy Press 2101 Constitution Avenue, NW Box 285 Washington, D.C. 20055 800-624-6242 or 202-334-3313 (in the Washington Metropolitan Area) B-272 Copyright 1994 by the National Academy of Sciences. All rights reserved. Printed in the United States of America.

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Microwave Processing of Materials DEDICATION This report is dedicated to the memory of Joe Pentecost. Joe served as a member of the National Materials Advisory Board from 1988 until his death in 1992. This study was initiated by his efforts, and he was to have been a member of the study committee. We miss him as a person, always gracious and optimistic; as a technical leader with a vision of the future; and as a worker who always did more than his fair share. Our lives take their meaning from their interlacing with other lives, and when one life is ended those into which it was woven are also carried into darkness. Neither you nor 1, but only the hand of time, slow-moving, yet sure and steady, can lift that blanket of blackness. Adlai Stevenson

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Microwave Processing of Materials COMMITTEE ON MICROWAVE PROCESSING OF MATERIALS: AN EMERGING INDUSTRIAL TECHNOLOGY DALE F. STEIN Chairman, Michigan Technological University, Houghton RICHARD H. EDGAR, Amana Refrigeration, Inc., Amana, Iowa MAGDY F. ISKANDER, University of Utah, Salt Lake City, Utah D. LYNN JOHNSON, Northwestern University, Evanston, Illinois SYLVIA M. JOHNSON, SRI International, Menlo Park, California CHESTER G. LOB, Varian Associates, Inc., Palo Alto, California JANE M. SHAW, IBM-T.J. Watson Research Center, Yorktown Heights, New York WILLARD H. SUTTON, United Technologies Research Center, East Hartford, Connecticut PING K. TIEN, AT&T Bell Laboratories, Holmdel, New Jersey Government Liaison Representatives WILLIAM COBLENZ, Advanced Research Projects Agency, Arlington, Virginia ALAN DRAGOO, Department of Energy, Washington, D.C. SUNIL DUTTA, National Aeronautics and Space Administration, Cleveland, Ohio CHARLES LEE, Air Force Office of Scientific Research, Bolling Air Force Base, Washington, D.C. WILLIAM MESSICK, Naval Surface Warfare Center, Silver Spring, Maryland JOHN W. WALKIEWICZ, U.S. Bureau of Mines, Reno, Nevada WALTER ZUKAS, Army Materials Technology Laboratory, Watertown, Massachusetts National Materials Advisory Board Staff THOMAS E. MUNNS, Senior Program Officer AIDA C. NEEL, Senior Project Assistant

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Microwave Processing of Materials ACKNOWLEDGMENTS The committee is most grateful to the many individuals who took the time to make very informative and useful presentations to the committee. Speakers at the August 12, 1992 meeting included: Dr. Mark Janney, Oak Ridge National Laboratory, processing of ceramics and decontamination of concrete Dr. Joel Katz, Los Alamos National Laboratory, processing of ceramics and hazardous waste processing Dr. Jes Asmussen, Michigan Sate University, electrical engineering considerations related to microwave processing Dr. Martin Hawley, Michigan State University, application of microwave processing to polymers and polymer composites Dr. Raymond Decker, University Science Partners, utilizing microwaves in the former Soviet Union and the application of microwave processing to a number of problems Dr. Leonard Dauerman, New Jersey Institute of Technology, using microwaves to treat hazardous waste Mr. Edward Daniels, Argonne National Laboratory, dissociation of hydrogen sulfide, using microwave energy Speakers at the December 14, 1992 meeting included: Dr. Ed Neas, The Rubbright Group, use of microwave heating in chemistry, with a special emphasis on analytical laboratory applications Mr. Hal Kimrey, Oak Ridge National Laboratory, process scaling, technology transfer, and temperature measurement techniques used at the Oak Ridge National Laboratory Special thanks to Arthur C. Lind of McDonnell Douglas Research Laboratories who provided valuable information on microwave processing of polymeric composites. Government liaison representatives briefed the committee on the programs and needs of their respective agencies: Mr. John Walkiewicz, Bureau of Mines' Reno Research Center, the use of microwaves for drying, comminution, and fragmentation

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Microwave Processing of Materials Dr. Alan Dragoo, Department of Energy Basic Sciences Office, microwave programs at Oak Ridge and Los Alamos National Laboratory Dr. Walter Zukas, Army Materials Laboratory, microwave processing of polymers, ceramics, and thick section polymeric composites Dr. William Messick, Office of Naval Technology, Materials processing needs of the Navy Dr. Sunil Dutta, National Aeronautics and Space Administration, Lewis Research Center, needs in ceramics, ceramic composites and composites Dr. William Coblenz, Advanced Research Project Agency, Defense Science Office, microwave processing of structural ceramics, CVD of ceramics and diamond, and curing of conducting polymer adhesives and polymeric composites The committee is grateful for their contribution to defining the scope of the study and their active participation in the work of the committee. The Chair thanks the members of the committee for their efforts. Many made in-depth presentations on special topics, and all contributed to the writing and rewriting of the report. Through it all they remained congenial, hard working, and committed to a balanced and objective report. A Chair could not ask for a better group of people. Special thanks go to Aida Neel, who made the many arrangements necessary for productive and pleasant meetings, and Tom Munns, the National Materials Advisory Board program officer; whose dedication, good humor, and steady prodding kept the report on schedule.

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Microwave Processing of Materials ABSTRACT The use of microwaves in industrial materials processing can provide a versatile tool to process many types of materials under a wide range of conditions. Microwave processing is complex and multidisciplinary in nature and involves a wide range of electromagnetic equipment design and materials variables, many of which change significantly with temperature. A high degree of technical and other (e.g., economic) knowledge is required in determining how, when, and where to use microwaves most effectively, and when not to use them. The committee conducted an assessment of the potential of microwave technology for industrial applications. This assessment included a review of microwave technology, equipment, processing methods, and applications. Barriers to industrial applications and gaps in understanding of microwave processing technology were identified, as were promising applications and development opportunities that take advantage of unique performance characteristics of microwaves.

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Microwave Processing of Materials PREFACE The microwave processing of materials is a relatively new technology that provides new approaches to improve the physical properties of materials; provides alternatives for processing materials that are hard to process; reduces the environmental impact of materials processing; provides economic advantages through the saving of energy, space, and time; and provides an opportunity to produce new materials and microstructures that cannot be achieved by other methods. Microwave processing is an unusual technology. It is widely used (more than 60 million home units are used to cook food) in an environment in which the user understands little of the technology. Yet, the difficulty in applying the technique in industrial processing has often lead to frustration of technically competent materials processors. Some of the mystery of microwave processing is associated with this dichotomy. If it is so easy to "nuke" a meal, it must certainly be as easy to sinter a ceramic or cross-link a polymer. The apparent ease in using microwaves in food processing is a tribute to the equipment manufacturers for their success in making a "user friendly" oven, but these ovens also have the advantage of having a molecule widely distributed in the food, the water molecule, that easily "couples" to microwaves. In materials processing coupling of microwave energy must be to atoms or atomic groups other than water, at much greater technical complexity. The purpose of this report is to: Introduce the reader to the use of microwaves for processing materials. The basic interactions will be described, along with the basic equipment required to process materials. Examples of successful applications will be presented, as will an evaluation of the conditions or parameters needed for the successful application of microwaves to the processing of materials. Provide an assessment of the state-of-the-art of microwave processing as an industrial technology. Identify gaps, limitations, or weaknesses in the understanding of the use of microwaves in materials processing, and suggest research and development to address these issues. The committee approached its responsibility to evaluate the potential of microwave processing of materials in a critical and objective way. To some the report may seem overly cautious and to others it may seem overly critical. It is very clear that the microwave processing of materials has had some major advantages and major successes. But it is equally clear that potential users should take the time to become knowledgeable about microwaves and their interaction with materials before embarking on a program of using microwaves to process

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Microwave Processing of Materials materials. It is the committee's hope that this report will promote the successful application of microwave processing to real-world problems. DALE F. STEIN CHAIR

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Microwave Processing of Materials CONTENTS     EXECUTIVE SUMMARY   1 1   INTRODUCTION   5     Perspective,   6     Materials Interaction,   7     Other Considerations,   8 2   MICROWAVE FUNDAMENTALS   9     Microwave Generators,   10     Candidate Generators,   12     Wave Propagation,   18     Waveguide Modes,   22     Interactions Between Microwaves and Materials,   27 3   MICROWAVE SYSTEM INTEGRATION   39     Microwave Applicators,   39     Microwave Safety Standards,   46     Temperature Measurements,   49     Computer Modeling and Computer Simulation,   59 4   APPLICATION CRITERIA   67     Unique Performance Characteristics,   67     Economics of Microwave Processing,   71 5   MICROWAVE APPLICATIONS   79     Introduction,   79     Ceramics/Ceramic Matrix Composites,   80     Polymers and Polymer Matrix Composites,   98     Microwave Plasma Processing of Materials,   105     Minerals Processing,   107     Microwave Chemistry,   108     Waste Processing and Recycling,   112     Summary,   115

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Microwave Processing of Materials 6   CONCLUSIONS AND RECOMMENDATIONS   117     Applications Development,   118     Process Modeling and Simulation,   118     System Design and Integration,   119     Nonthermal Microwave Effects,   120     REFERENCES   121     APPENDIX   149