Microwave Chemical and Materials Processing (eBook)

Dr. Satoshi Horikoshi, Associate Professor Faculty of Science and Technology, Department of Materials and Life Sciences, Sophia University Satoshi Horikoshi received his PhD degree in 1999, and was subsequently a postdoctoral researcher at the Frontier Research Center for the Global Environment Science (Ministry of Education, Culture, Sports, Science and Technology) until 2006. He joined Sophia University as Assistant Professor in 2006, and then moved to Tokyo University of Science as Associate Professor in 2008, after which he returned to Sophia University as Associate Professor in 2011. Currently he is Vice-President of the Japan Society of Electromagnetic Wave Energy Applications (JEMEA), and is on the Editorial Advisory Board of the Journal of Microwave Power and Electromagnetic Energy and other international journals. His research interests involve new material synthesis, molecular biology, formation of sustainable energy, environmental protection and CO2-fixation using microwave- and/or photo-energy. He has co-authored over 170 scientific publications and has contributed to and edited or co-edited 20 books. Robert F. Schiffmann, Professor President, R.F. Schiffmann Associates, Inc. Bob Schiffmann has been conducting R&D with microwave heating since 1961. He has been an independent consultant since 1971, and, since 1982, has focused exclusively on microwave-heating projects. His work includes applications research in microwave ovens, microwave foods & packaging, industrial microwave systems, medical applications, and more. He has been the president of the International Microwave Power Institute (IMPI) for 16 years; is a Founding Member of AMPERE (the European microwave society); is an Honorary Member of the Microwave Technology Association of the UK, and for five years was a Scientific Lecturer on microwave topics for the Institute of Food Technologists, and is a Certified Food Scientist. He is the first recipient of the Metaxas Microwave Pioneer Award. He has taught numerous international microwave science & technology courses since 1973 and chaired over 20 international microwave conferences. He has 28 US patents, over 50 publications related to microwave science & technology. He has served as an expert & expert witness in 35 microwave-related cases. He is a visiting professor at the Kunming University of Science & Technology in China, and received his MS in Physical & Analytical Chemistry from Purdue University. Nick Serpone Ph.D. F. EurASc. Visiting Professor, PhotoGreen Laboratory, Dip. di Chimica, Universita di Pavia, Italia Nick Serpone is Professor Emeritus (Concordia University, Montreal, Canada) and since 2002 has been a Visiting Professor at the University of Pavia (Italy). He was also a Visiting Professor at the Universities of Bologna and Ferrara (Italy), Ecole Polytechnique Federale de Lausanne (Switzerland), Ecole Centrale de Lyon (France), Tokyo University of Science (Japan), and Guest Lecturer at the University of Milan (Italy). He was program Director at the National Science Foundation (Washington, USA) and consultant to the 3M Company (USA). He has co-edited/co-authored 9 books, contributed 23 chapters to books, and published over 450 articles. His principal interests have focused on the photophysics and photochemistry of metal-oxide semiconductors, environmental remediation, and microwave chemistry. He is a Fellow of the European Academy of Sciences (EurASc) and Head of the Materials Science Division of EurASc. Dr. Jun Fukushima, Assistant professor Chemistry of Molecular Systems, Department of Applied Chemistry, Tohoku University Jun Fukushima received his PhD degree in 2012, and was subsequently an assistant professor at Tohoku University (Dept. of Applied Chemistry). His research interests involve novel solid-state materials synthesis, texture control and diffusion control by microwave processing, and physics of microwave effects. He has co-authored over 50 scientific publications and books.

Preface 5
Contents 7
About the Authors 14
1 Microwave as a Heat Source 17
Abstract 17
1.1 Applications of Microwaves 17
1.2 Some Applications of Microwave Heating 20
1.3 Fields of Microwave Chemistry and Materials Processing 20
1.4 Overview of Microwave Chemistry 23
1.5 Overview of Microwave Usage in Materials Processing 26
1.6 Overview of Microwave Usages in Other Sciences 28
1.7 Coffee Break 1: Raytheon Corporation 29
References 31
2 The Nature of Heat 34
Abstract 34
2.1 What is Heat? 34
2.2 Historical Aspects of Heat 34
2.3 Heat Versus Temperature 37
2.4 Thermodynamics 41
2.5 Heat Transfer 42
2.6 Coffee Break 2: Background on the Relationship Between Microwaves and Foods 43
References 46
3 Electromagnetic Fields and Electromagnetic Waves 48
Abstract 48
3.1 The Nature of Electromagnetic Fields and Electromagnetic Waves 48
3.2 History of Electromagnetic Waves 49
3.3 The Nature of Microwaves 52
3.4 Maxwell’s Equations 54
3.5 Microwaves as Electromagnetic Waves 56
3.5.1 History of the Name “Microwave” 56
3.5.2 Differences in the Features of Communication by Light and Microwaves 56
3.5.3 Responses of Substances to Electromagnetic Waves 57
3.6 Coffee Break 3: Frequencies Used for Food Heating 58
References 60
4 Microwave Heating 61
Abstract 61
4.1 Types of Microwave Heating 61
4.1.1 Overview of Microwave Heating 61
4.1.2 Microwave Heating of Substrates in Solutions 63
4.1.3 Microwave Heating of a Solid Substance 64
4.1.4 Difference(s) Between Microwave Heating and Conventional Heating 66
4.1.5 Features of Microwave Heating Relative to Other Heating Methods 67
4.2 Direct Heating of Materials 67
4.2.1 Internal Heating and External Heating 67
4.2.2 Precise Temperature Measurement by Using Microwave Internal Heating 70
4.2.3 Applications of Internal Heating 70
4.3 Selective Heating 72
4.3.1 Fundamental Selective Heating 72
4.3.2 Application of Microwave Selective Heating 73
4.4 Hotspots or Local Heating 75
4.4.1 What Is a Hotspot? 75
4.4.2 Hotspot Formation in Catalyzed Reactions—Background 75
4.4.3 Mechanism(s) of Formation of Hotspots 80
4.4.4 Control of the Occurrence of Hotspots 82
4.5 Hotspots in Microwave Sintering 84
4.5.1 Background for Hotspots in Solid Processing 84
4.5.2 Principles and Control of Occurrence of Hotspots in Samples 86
4.5.3 Principles and Control of Hotspots and Electromagnetic Waves 87
4.6 Superheating of Liquids 88
4.6.1 What Is Superheating? 88
4.6.2 Mechanistic Stages of Superheating 90
4.6.3 Applications of Superheating to Chemical Reactions 92
4.7 Coffee Break 4: What Is a Microwave Oven? 94
References 97
5 Physics of Microwave Heating 100
Abstract 100
5.1 Dielectric Properties 100
5.2 Permeability 107
5.3 Measurement of Electric and Magnetic Permeabilities 108
5.3.1 The Transmission/Reflection Line Method 109
5.3.2 The Open-Ended Coaxial Probe Method 109
5.3.3 The Free-Space Method 111
5.3.4 The Resonant Method 112
5.4 Adjustment of the Impedance 113
5.4.1 What Is Meant by Impedance in the Present Context? 113
5.4.2 Impedance in Equipment and Sample 114
5.5 Microwave Heating Mechanism 115
5.5.1 Phenomena of Dipole Rotation on Application of Microwaves 115
5.5.2 Relationship of Microwave Heating Behavior with the Materials’ Physical Properties 117
5.5.3 Conduction Loss Heating (Eddy Current Loss and Joule Loss) 117
5.5.4 Dielectric Heating and Magnetic Loss Heating—An Introduction 118
5.5.5 Dielectric Heating—Energy Loss in a Microwave Field 120
5.5.6 Magnetic Loss 123
5.6 Penetration Depth and Skin Depth 124
5.6.1 What Are They? 124
5.6.2 Penetration Depth 125
5.6.3 Penetration Depths of 915-MHz, 2.45-GHz, and 5.80-GHz Microwaves 128
5.6.4 Skin Depth 129
5.7 Frequency Effect 130
5.7.1 Is It Possible to Use Various Frequencies? 130
5.7.2 Historical Overview of Microwave Frequency Effects in Chemical Reactions and Sintering 131
5.7.3 Microwave Chemical Equipment for 0.915, 2.45, and 5.80 GHz Frequencies 132
5.7.4 Frequency Effects for the Common Solvents 133
5.7.5 Rates of Temperature Increase of Common Solvents 137
5.8 Frequency Effects in Organic Synthesis 137
5.8.1 Application to a Diels–Alder Reaction 137
5.8.2 Synthesis of a Room-Temperature Ionic Liquid (RTIL) 140
5.8.3 Synthesis of Gemini Surfactants Under 915-MHz Microwave Irradiation 142
5.8.4 Frequency Effects in Nanoparticle Synthesis 144
5.8.5 Summary Remarks on the Frequency Effect 146
5.9 Electromagnetic and Thermodynamics Simulations 147
5.10 Transmission Modes 148
5.11 Coffee Break 5: Using the Microwave Oven 152
References 154
6 Engineering of Microwave Heating 157
Abstract 157
6.1 Components in Microwave Heating Equipment 157
6.2 Microwave Generators 160
6.2.1 Vacuum Tubes as Microwave Sources 160
6.2.2 Magnetron Generation of Microwaves 161
6.2.3 Klystron and TWT Generators 163
6.2.4 Semiconductor Generation of Microwaves 164
6.3 Waveguides, Isolators, Power Monitors, Tuners, Iris, and Short Plungers 169
6.3.1 Waveguides 169
6.3.2 Coaxial Cables 172
6.3.3 Isolators 173
6.3.4 Power Monitors 173
6.3.5 The Tuner 174
6.3.6 Iris and Short Plungers 175
6.4 Single-Mode Versus Multimode Applicators 176
6.4.1 What Is an Applicator? 176
6.4.2 Single-Mode Applicator 178
6.4.3 Multimode Applicator 179
6.5 Temperature Measurements 181
6.5.1 Thermometers 181
6.5.2 Temperature Measurement in a Solution Sample 181
6.5.3 Temperature Measurements in Solid Samples 182
6.6 Prevention of Microwave Leakages 184
6.6.1 Choke Trap 184
6.6.2 Prevention of Microwave Leakages at the Sample Observation Window 186
6.7 Visualization of Microwaves 188
6.8 Coffee Break 6: Browning and Crisping in a Microwave Oven 190
References 193
7 Microwave Chemistry in Liquid Media 195
Abstract 195
7.1 Effective Microwave Heating in Chemistry 195
7.2 Reactors 196
7.3 Heat Insulators 198
7.3.1 Differences in Heat Insulation for Classical Chemistry and Microwave Chemistry 198
7.3.2 Heat Insulators 199
7.3.3 Dewar-like Double-Walled Insulated Reactor 201
7.4 Effects of Samples in a Microwave-Assisted Process 207
7.5 Temperature Control by Cooling 213
7.6 Microwave Chemical Synthesis Equipment and Its Development 218
7.7 Coffee Break 7: Microwaves and Steam—a Unique Hybrid Cooking System 221
References 223
8 Microwave Materials Processing in Solid Media 225
Abstract 225
8.1 Effective Microwave Heating in Materials Processing 225
8.2 Useful Aspects in Carrying Out Uniform Heating 226
8.2.1 Heat Transfer 226
8.2.2 Conduction 227
8.2.3 Convection 227
8.2.4 Radiation 228
8.2.5 Heat Insulation 228
8.2.6 Isothermal Adiabatic Wall 229
8.3 Purity of Samples 230
8.4 Microwave Heating of Solid Samples 230
8.4.1 Heating Efficiency of Materials 230
8.4.2 Dielectric Heating 231
8.4.3 Magnetic Field Heating 232
8.4.4 Joule Heating 233
8.5 Heating of Materials Usually Unsuitable for Microwave Heating 234
8.6 Hybrid Microwave Heating with Susceptors 236
8.7 Question: Can Microwaves Heat Metals? 242
8.8 Microwave Sintering Equipment 243
8.9 Coffee Break 8: Microwave Food Processing Industry 247
References 250
9 Microwave-Assisted Chemistry 254
Abstract 254
9.1 Microwave-Assisted Organic Synthesis 254
9.1.1 Heat Sources in Organic Synthesis 254
9.1.2 Overview of Microwave-Assisted Organic Syntheses 255
9.1.3 Microwave-Assisted Organic Synthesis (MAOS) in Green Chemistry 259
9.1.4 Solvent-Free Microwave-Assisted Organic Syntheses 262
9.1.5 Water Solvent System 263
9.1.6 Labeling by an Isotope Element 266
9.1.7 Removal of Dissolved Oxygen 266
9.1.8 Scaling Up of Microwave-Assisted Organic Syntheses (MAOS) 268
9.2 Microwave-Assisted Polymerization 271
9.2.1 Overview of Microwave-Assisted Polymer Syntheses 271
9.2.2 The Advantage of Microwaves in Macromolecular Syntheses 273
9.2.3 Scale-Up of Polymer Syntheses 273
9.3 Enzymatic Reactions 276
9.3.1 Situation of Microwave Heating in Biomaterials 276
9.3.2 Microwave Effect in Enzymatic Reactions 278
9.3.3 Some Relevant Issues Regarding the Equipment Used in Enzymatic Reactions 284
9.3.4 Summary of Data in Microwave-Assisted Enzymatic Reactions 287
9.4 Catalysts 287
9.4.1 History of Microwave-Assisted Reactions 287
9.4.2 Advantages of the Microwave-Assisted Heterogeneous Catalytic Method 293
9.4.3 Gaseous Reactions with Solid Catalysts 297
9.4.4 Applications Directed Toward Hydrogen Storage 302
9.4.5 Microwave-/Photo-Driven Catalytic Treatment of Wastewaters 305
9.4.6 Synthesis of Metal Catalysts on Carbonaceous Material Supports 308
9.4.7 Catalyst Synthesis Using Features of Microwave Heating 312
9.5 Coffee Break 9: Future of Microwave Processing of Foods 314
References 316
10 Materials Processing by Microwave Heating 331
Abstract 331
10.1 Processing of Solid-State Materials 331
10.1.1 Sintering and Drying of Ceramics 331
10.1.2 Ceramics with Structural Features, Heated by Microwave Sintering 334
10.1.3 Metallic Substrates 340
10.1.4 Why Microwave Sintering? 343
10.1.5 Drying of Monolithic Refractory Substrates 343
10.1.6 Drying of Transparent Conductive Films and Nano-Inks 349
10.1.7 Features of Microwaves in Syntheses 350
10.1.8 Control of Magnetic Properties of Spinel Oxide by Microwave Magnetic Field Irradiation 353
10.1.9 Minerals Processing 354
10.2 Microwave Processing in the Liquid State 359
10.2.1 Syntheses in Liquid Media 359
10.2.2 Nanoparticle Synthesis in Liquid Media 362
10.2.3 Specific Microwave Synthesis 367
10.2.4 Nanoparticle Syntheses in Continuous-Flow Reactors 371
10.2.5 Compendium of Microwave-Assisted Nanoparticle Syntheses 374
10.3 Coffee Break 10: Future Developments in Microwave Ovens 375
References 383
Appendix A 392