Advances in Microwave and Radio Frequency Processing Monika Willert-Porada (Ed.) Advances in Microwave and Radio Frequency Processing Report from the 8th International Conference on Microwave and High Frequency Heating held in Bayreuth, Germany, September – 7, 2001 With 469 Figures * P E * * M R * E * A * Professor Dr M Willert-Porada Chair of Materials Processing University of Bayreuth Universitätsstraße 30 D-95447 Bayreuth Germany Library of Congress Control Number: 2005934302 ISBN-10 ISBN-13 3-540-43252-3 Springer-Verlag Berlin Heidelberg New York 978-3-540-43252-4 Springer-Verlag Berlin Heidelberg New York This work is subject to copyright All rights are reserved, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilm or in any other way, and storage in data banks Duplication of this publication or parts thereof is permitted only under the provisions of the German Copyright Law of September 9, 1965, in its current version, and permission for use must always be obtained from Springer-Verlag Violations are liable for prosecution under the German Copyright Law Springer-Verlag is a part of Springer Science+Business Media springer.com © Springer-Verlag Berlin Heidelberg 2006 Printed in the Netherlands The use of general descriptive names, registered names, trademarks, etc in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use Production: SPI Publisher Services Typesetting: SPI Publisher Services Cover Design: E Kirchner, Heidelberg Printed on add free paper SPIN 10850172 30/3100/SPI - Preface Prometheus brought fire to mankind Arthur R von Hippel “Dielectrics and Waves”, 1954 Our contribution? There are only few areas of research and development of a comparable scientific and technological extension as microwave and high frequency processing “Processing” means not only application of radiation of 300 MHz to 300 GHz frequency to synthesis, heating or ionisation of matter but also generation, transmission and detection of microwave and radio frequency radiation Microwave and high frequency sources positioned in the orbit are the foundation of modern satellite telecommunication systems, gyrotron tubes being presently developed in different countries all over the world will most probably be the major devices to open up a new era of energy supply to mankind be means of fusion plasma Although initiated by military purposes during the Second World War (RADAR, Radio Detection and Ranging), microwave and high frequency utilisation has spread over almost every important aspect of normal day life since than, from individual mobile phones and kitchen microwave ovens to industrial food processing, production of composites as sustainable building materials, green chemistry, medical applications and finally infrastructure installations like GPS and Galileo, to name only few examples These different areas of microwave and high frequency radiation application can not be unified within one group of scientists and technologists There are several distinguished communities active e.g., in the area of telecommunication systems, strong microwaves for fusion plasma or plasma based materials processing Research to improve fundamental knowledge leading to new non-military applications of high frequency technology, to support necessary regulations and to provide long term development of commodity and industrial applications as well as to improve the knowledge about these new technologies within the society is less well covered by scientific or professional organizations In order to close this gap and provide a forum for fruitful discussions a group of researchers from academia and industry started to organize Microwave and High Frequency Heating Conferences in 1986, which take place every years in a different European country In 1993 AMPERE, Association for Microwave Power in Europe for Research and Education (www.ampereeeurope.org) was established and the conferences were organized on behalf of AMPERE since than In addition to the regular conference schedule Microwaves in Chemistry meetings were added 1998 and 2000 Conference activities in the field of microwave and RF-applications show a remarkable growth: up to mid-80 of the 20th century IMPI (International Microwave Power Institute, USA) almost exclusively covered the organized activities in the field The widespread availability of kitchen microwave ovens as well as the development of powerful microwave sources within national fusion programmes fa- VI Preface cilitated use of this “cold” radiation for chemical syntheses and materials processing, with often quite unexpected results Therefore professional organizations like e.g., the American Ceramic Society and the Materials Research Society established Microwave Symposia within their regular conferences in the period 1988-1996 Numerous Symposia Proceedings volumes came out of theses conferences (e.g., MRS Proc Vol 124, 189, 269, 347, 430 and Ceram Trans Vol 21, 36, 59, 80), including publications from the 1st and 2nd World Congress on Microwave and Radio Frequency Processing New professional associations enter the scene, like e.g., the Microwave Working Group in the USA, and different Societies in Japan and China The overview and technical papers contained in this book reflect the major areas of activity not only of AMPERE members but also of a representative group of other researchers worldwide The topics were selected from contributions of the 8th International Conference on Microwave and High Frequency Heating, organised by AMPERE and held in September 2001 in Bayreuth, Germany The papers were referred by major specialists in the respective field The book is intended to provide non-specialists an overview of the State of the Art in the field of microwave and high frequency hardware, measurement and modelling as well as to give the specialists insight into the most advanced R&D topics of microwave and high frequency radiation application in different disciplines Many experts and colleagues contributed to this book I am particularly indebted to (in alphabetical order): J.P Bernard, France; J Binner, UK; J Booske, USA; S Bradshaw, South Africa; A Breccia, Italy; M Brito, Japan; J.M Catalá -Civera, Spain; T Gerdes, Germany; J Gerling, USA; W Jansen, Netherlands; W Van Loock, Belgium; R Metaxas, UK; A Mavretic, USA; T Ohlsson, Sweden; P Püschner, Germany; E de los Reyes, Spain; A Rosin, Germany; G Roussy, France; A Schmidt, Germany; V Semenov, Russia; M Thumm, Germany; N Tran, Australia My deep thanks go to the authors for their patience and effort to collect excellent papers; to colleagues for valuable suggestions and to my co-workers for many hours of work to fit the individual contributions into a book Hopefully this book will facilitate further development of the fascinating field of microwave and high frequency processing, in a synergetic effort of many groups all over the world Monika Willert-Porada, Editor Bayreuth, first half of the first decade of the 21st century Contents PART I: HARDWARE UNDERSTANDING MICROWAVE HEATING SYSTEMS: A PERSPECTIVE ON STATE-OF-THE-ART H C Reader MILLIMETER-WAVE-SOURCES DEVELOPMENT: PRESENT AND FUTURE .15 Manfred Thumm and Lambert Feher 3.5 KW 24 GHZ COMPACT GYROTRON SYSTEM FOR MICROWAVE PROCESSING OF MATERIALS 24 Yu Bykov, G Denisov, A Eremeev, M Glyavin, V Holoptsev, I Plotnikov, V Pavlov DESIGN GUIDELINES FOR APPLICATORS USED IN THE MICROWAVE HEATING OF HIGH LOSSES MATERIALS 31 Juan V Balbastre, E de los Reyes, M C Nuño and P Plaza DESIGN PARAMETERS OF MULTIPLE REACTIVE CHOKES FOR OPEN PORTS IN MICROWAVE HEATING SYSTEMS 39 J M Catalá-Civera, P Soto, V.E Boria, J V Balbastre and E de los Reyes MICROWAVE HIGH-POWER FOUR POST AUTO-MATCHING SYSTEM 48 Pedro Plaza, Antoni J Canós, Felipe L Penaranda-Foix and Elias de los Reyes DESIGN OF AN APPLICATOR FOR PROCESSING OF NANOSCALE ZEOLITE/POLYMER COMPOSITES WITH SUPERPOSED STATIC MAGNETIC FIELD .56 Ralph Schertlen, Stefan Bossmann, Werner Wiesbeck PART II: MEASUREMENT TECHNIQUES AND REGULATIONS MEASUREMENT TECHNIQUES FOR MICROWAVE AND RF PROCESSING 65 Georges Roussy DIELECTRIC CHARACTERISATION OF HIGH LOSS AND LOW LOSS MATERIALS AT 2450 MHZ .77 Andrew Y.J Lee and V Nguyen Tran EUROPEAN REGULATIONS, SAFETY ISSUES IN RF AND MICROWAVE POWER 85 Walter Van Loock VIII Contents FUTURE PROSPERITY OF INDUSTRIAL, SCIENTIFIC AND MEDICAL (ISM) APPLICATIONS OF MICROWAVES 92 David Sánchez-Hernández and José M Catalá-Civera ELECTRIC FIELD MEASUREMENTS FOR COMMERCIALLY-AVAILABLE MOBILE PHONES 103 Antonio Martínez-González, Ángel Fernández-Pascual and David Sánchez-Hernández USE OF THE DIELECTRIC PROPERTIES TO DETECT PROTEIN DENATURATION 107 S A Barringer and C Bircan SANDALWOOD MICROWAVE CHARACTERISATION AND OIL EXTRACTION 119 V Nguyen Tran DIELECTRIC SPECTROSCOPY AND PRINCIPAL COMPONENT ANALYSIS AS A METHOD FOR OIL FRACTION DETERMINATION IN OIL-IN-WATEREMULSIONS WITH VARYING SALT CONTENT 129 M Regier, X Yu, S Ghio, T Danner, H Schubert MICROWAVE NON-DESTRUCTIVE EVALUATION OF MOISTURE CONTENT IN LIQUID COMPOSITES IN A CYLINDRICAL CAVITY AT A SINGLE FREQUENCY 138 J M Catalá-Civera, A J Canós, F Peñaranda-Foix and E de los Reyes MILLIMETER WAVE SPECTROSCOPY OF ALUMINA-ZIRCONIA SYSTEM 149 Saburo Sano, Akihiro Tsuzuki, Kiichi Oda, Toshiyuki Ueno, Yukio Makino and Shoji Miyake A MODIFIED CAVITY PERTURBATION TECHNIQUE FOR MEASUREMENT OF THE DIELECTRIC CONSTANT OF HIGH PERMITTIVITY MATERIALS .155 Sheila Oree PART III: MODELLING FINITE ELEMENTS IN THE SIMULATION OF DIELECTRIC HEATING SYSTEMS 167 G.E Georghiou, R.A Ehlers, A Hallac, H Malan, A.P Papadakis and A.C Metaxas EXAMINATION OF CONTEMPORARY ELECTROMAGNETIC SOFTWARE CAPABLE OF MODELING PROBLEMS OF MICROWAVE HEATING 178 Vadim V Yakovlev A HYBRID APPROACH FOR RESOLVING THE ELECTROMAGNETIC FIELDS INSIDE A WAVEGUIDE LOADED WITH A LOSSY MEDIUM .191 Viktor Vegh, Ian W Turner Contents IX A NOVEL FDTD SYSTEM FOR MICROWAVE HEATING AND THAWING ANALYSIS WITH AUTOMATIC TIME-VARIATION OF ENTHALPYDEPENDENT MEDIA PARAMETERS .199 Malgorzata Celuch-Marcysiak, Wojciech K.Gwarek, Macie Sypniewski SIMULATION OF MICROWAVE SINTERING WITH ADVANCED SINTERING MODELS .210 Hermann Riedel, Jiri Svoboda FINITE ELEMENT MODELLING OF THIN METALLIC FILMS FOR MICROWAVE HEATING 217 R.A Ehlers and A.C Metaxas ANALYSIS OF COUPLED ELECTROMAGNETIC AND THERMAL MODELING OF PRESSURE-AIDED MICROWAVE CURING PROCESSES 226 J M Catalá-Civera, J Monzó-Cabrera, A J Canós, F L Paranda-Foix SELECTIVE HEATING AND MOISTURE LEVELLING IN MICROWAVEASSISTED DRYING OF LAMINAR MATERIALS: AN EXPLICIT MODEL 234 J Monzó-Cabrera, A Díaz-Morcillo, J M Catalá-Civera, E de los Reyes MICROWAVE HEATING OF READY MEALS – FDTD SIMULATION TOOLS FOR IMPROVING THE HEATING UNIFORMITY 243 B Wäppling-Raaholt, P O Risman and T Ohlsson PART IV: FOOD PROCESSING AND ENVIRONMENTAL ENGINEERING APPLICATIONS NOVEL AND TRADITIONAL MICROWAVE APPLICATIONS IN THE FOOD INDUSTRY 259 H Schubert and M Regie MICROWAVE DRYING: PROCESS ENGINEERING ASPECTS 271 SM Bradshaw QUALITY OF MICROWAVE HEATED MULTICOMPONENT PREPARED FOODS 282 Suvi Ryynänen SENSORY EVALUATION OF DRIED BANANAS OBTAINED FROM AIR DEHYDRATION ASSISTED BY MICROWAVES .289 Sousa, W.A.; Pitombo, R.N.M.; Da Silva, M.A.A.P.; Marsaioli, Jr., A MICROWAVE METHOD FOR INCREASING THE PERMEABILITY OF WOOD AND ITS APPLICATIONS 303 G Torgovnikov and P Vinden X Contents SELECTIVE HEATING OF DIFFERENT GRAIN PARTS OF WHEAT BY MICROWAVE ENERGY 312 E Pallai-Varsányi; M.Neményi; A.J.Kovács; E.Szijjártó MICROWAVE IN SITU REMEDIATION OF SOILS POLLUTED BY VOLATILE HYDROCARBONS 321 D.Acierno, A.A.Barba, M.d'Amore ,V.Fiumara, I.M.Pinto, A.Scaglione BIO-DIELECTRIC SOIL DECONTAMINATION 329 J.P.M Janssen-Mommen, W.J.L Jansen WASTE TREATMENT UNDER MICROWAVE IRRADIATION .341 A Corradi, L Lusvarghi, M R Rivasi, C Siligardi, P Veronesi, G Marucci, M Annibali, G Ragazzo ENVIRONMENTAL ASPECTS OF MICROWAVE HEATING IN POLYELECTROLYTE SYNTHESIS 349 E Mateescu, G Craciun, D Martin, D Ighigeanu, M Radoiu, I Calinescu and H Iovu PART V: MICROWAVE APPLICATIONS IN CHEMISTRY ROLE OF MICROWAVE RADIATION ON RADIOPHARMACEUTICALS PREPARATIONS 359 Enrico Gattavecchia, Elida Ferri, Biagio Esposito, Alberto Breccia FAST SYNTHESIS OF BIODIESEL FROM TRIGLYCERIDES IN PRESENCE OF MICROWAVES 370 C Mazzocchia, A Kaddouri, G Modica, R Nannicini ALTERATION OF ESTERIFICATION KINETICS UNDER MICROWAVE IRRADIATION 377 L A Jermolovicius, B Schneiderman and J T Senise MULTISTEP MICROWAVE-ASSISTED SOLVENT-FREE ORGANIC REACTIONS: SYNTHESIS OF 1,6-DISUBSTITUTED-4-OXO-1,4-DIHYDROPYRIDINE-3-CARBOXYLIC ACID BENZYL ESTERS 386 Mauro Panunzio, Maria Antonietta Lentini, Eileen Campana, Giorgio Martelli, Paola Vicennati RECENT APPLICATIONS OF MICROWAVE POWER FOR APPLIED ORGANIC CHEMISTRY 390 Bernd Ondruschka and Matthias Nüchter LIQUID PHASE CATALYTIC HYDRODECHLORINATION OF CHLOROBENZENE UNDER MICROWAVE IRRADIATION 398 Marilena T Radoiu, Ioan Calinescu, Diana I Martin, Rodica Calinescu Contents XI CONVENTIONAL AND NEW SOLVENT SYSTEMS FOR MICROWAVE CHEMISTRY 405 Jens Hoffmann, Antje Tied, Matthias Nüchter and Bernd Ondruschka PART VI: INDUSTRIAL MICROWAVE APPLICATIONS STATE OF THE ART OF MICROWAVE APPLICATIONS IN THE FOOD INDUSTRY IN THE USA .417 Robert F Schiffmann MICROWAVE VACUUM DRYING IN THE FOOD PROCESSING INDUSTRY 426 G Ahrens, H Kriszio, G Langer DEVELOPMENT OF AN INDUSTRIAL SOLID PHASE POLYMERIZATION PROCESS USING FIFTY-OHM RADIO FREQUENCY TECHNOLOGY 436 Joseph W Cresko, L Myles Phipps, Anton Mavretic RF WORLD TOUR 445 Jean-Paul Bernard PART VII: FUNDAMENTALS OF MICROWAVE APPLICATION TO MATERIALS PROCESSING HOW THE COUPLING OF MICROWAVE AND RF ENERGY IN MATERIALS CAN AFFECT SOLID STATE CHARGE AND MASS TRANSPORT AND RESULT IN UNIQUE PROCESSING EFFECTS 461 John H Booske and Reid F Cooper ENHANCED MASS AND CHARGE TRANSFER IN SOLIDS EXPOSED TO MICROWAVE FIELDS 472 V.E Semenov, K.I Rybakov THERMAL RUNAWAY AND HOT SPOTS UNDER CONTROLLED MICROWAVE HEATING 482 V.E Semenov, N.A Zharova DENSIFICATION AND DIFFUSION PROCESSES IN THE BA,SR-TITANATE SYSTEM UNDER MICROWAVE SINTERING 491 O.I Getman, V.V Panichkina, V.V Skorokhod, E.A Shevchenko, V.V Holoptsev OBSERVATION OF THE MICROWAVE EFFECT ON THE DIFFUSION BEHAVIOR IN 28 GHZ MILLIMETER-WAVE SINTERED ALUMINA 498 Toshiyuki UENO, Yukio MAKINO and Shoji MIYAKE, Saburo SANO DILATOMETER MEASUREMENTS IN A MM-WAVE OVEN .506 G Link, S Rhee, M Thumm 658 Schubert rounding precursor solution The observed heating rates are about 1K/sec for the system with Vulcan Carbon Black and about K/sec for Sigrafil® fibres The overheating effect is accompanied by arcing between the fibers, which can be observed during the process Therefore, the thermal decomposition of the Ptprecursor could start preferably at the overheated carbon fibers, which leads to a real catalyst rich coating (Fig 8) Fig SEM: Site-selective catalyst deposition on carbon support with microwave heating: Pt / TiO2-coated Sigrafil® fibre For the employment as fuel cell catalyst material a site-selective deposition improves the electrical contact of the catalyst in the MEA and therefore the catalyst utilization A schematic description is shown in Figure Fig Scheme of a MEA with site-selective deposited Pt on Sigrafil fibres (left) and of commercial E-TEK catalyst material (right) Only Pt particles on a conducting support material can be utilized for the fuel cell reactions Therefore the site selective deposition is assumed to improve catalyst utilization and electrical percolation in the MEA For practical purposes, a coating thickness of - µm as on the Sigrafil fibres is to high Therefore support materials with a higher surface area should be used in order to decrease the coating thickness As already described, in the system Pt(acac)2 / Ti(BuO)4 / Paraffin not only nanosized Platinum, but also an x-ray-amorphous titania is synthesized, which decreases the catalyst activity The ratio of Pt : Ti depends on the heating method and the carbon support during the synthesis: The ratio can be increased from about Microwave Assisted Synthesis of Catalyst Materials for PEM Fuel Cells 659 40% up to 60% Pt by CMP on Vulcan carbon black A further purification of the Platinum, and therefore a higher catalyst activity can be reached by an additional 'washing' step with 2n H2SO4 The Pt particle size slightly increases up to 2.8 nm, which is still acceptable Catalyst activity and fuel cell performance of the synthesized catalyst materials The catalyst activity has been measured with chemisorption of the supported catalyst In spite of the small particle size, no catalytic activity could be found for the CMP-derived platinum on Vulcan XC-72R A MEA made of this material reached the desired open-circuit voltage of 0.95 V, but only poor power performance could be achieved As described above, the surface area of the catalyst is coated with a mixture of amorphous titania and organic residue After the 'washing' operation with 2n H2SO4, which partially removed the titania and residue, the measured active metal surface area still is low (| m²/g Pt) Therefore future work should focus on improvement of the catalyst activity, in order to reach and exceed the catalyst activity of commercial catalyst materials (| 50 m²/g Pt) Discussion For Pt(acac)2 -Al(OR)3 mixtures, Bönnemann found a stabilizing effect of the platinum particle size due to a partial exchange of ligands of the propylate and acetylacetone groups between the precursors [2], before the decomposition starts In our system a reduction of the decomposition temperature of about 40°C was detected, as compared to a system without Ti(BuO)4 In addition to that, NMR results show the presence of two different acetylaceton-groups in the slurry after the synthesis Therefore, an exchange of ligands in Pt(acac)2 -Ti(OBu)4 seems probable, but further examinations still have to be done In order to promote the Pt-deposition at 4-phase contact sites, microwave heating of the carbon support is applied Carbon particles in poor electrical contact to each other will convert the high frequency electromagnetic radiation into arcs Pt deposition at these sites would be preferred, yielding the desirable 4-phase contacts and improving the performance of an electrically conductive network The microwave assisted synthesis of nanosized platinum is possible in the presence of the support material; the achieved average particle size of the Pt is reduced as compared to the commercial catalyst material E-TEK Vulcan Pt (20 wt%) by a factor of 660 Schubert Conclusion Platinum with nm particle size can be synthesized from the Pt(acac)2 / Ti(BuO)4 Paraffin mixtures by thermal decomposition of the precursor solution The synthesis also can be carried out in the presence of carbon support material, yielding Pt with a primary particle size of 2.5 nm Microwave enhanced synthesis doesn't change the Pt-particle size significantly as compared to a conventionally heated process However, evidence is given that a local overheating of the carbon particles with microwaves allows a site-selective deposition of platinum as coating on the carbon support At present, Titania from the precursor decomposition decreases the catalyst activity Acid leaching is used for removal of the oxide, without grain growth of the platinum particles Acknowledgment Financial support of DFG, Wi-856-13-1 is gratefully acknowledged References [1] T.R Ralph et al., Low Cost Electrodes for Proton Exchange Membrane Fuel Cells, Performance in Single Cells and Ballard Stacks, Journal of the Electrochemical Society, Vol 144, No 11, 1997, p 3845 - 3857 [2] H Bönnemann et al., Nanoscale Colloidal Metals and Alloys Stabilized by Solvents and Surfactants - Preparation and Use as Catalyst Precursors, Journal of Organometallic Chemistry 520, 1996, p 143 - 162 [3] A Fischer, J Jindra, H Wendt, Porosity and catalyst utilization of thin layer cathodes in air operated PEM-fuel cells, Journal of Applied Electrochemistry, Vol 28, 1998, p 277 - 282 [4] E.J Taylor, E.B Anderson, N.R.K Vilambi, Preparation of High-Platinum-Utilization Gas Diffusion Electrodes for Proton-Exchange-Membrane Fuel Cells, Electrochemical Society Letters, Vol 139, 1992, p L45 - L46 [5] Ch Gerk C-W Schmidt, A Niesenhaus, and M Willert-Porada, Microwave Interaction with Emulsions and its Application to the Synthesis of Nanostructured Powders and Composites, Ceram Trans Vol 80, 387-392 [1997] [6] T Schubert, M Willert-Porada, Synthesis of n-TiO2 for Photovoltaic Applications by Colloidal Microwave Processing, Ceram Trans Vol 111, Microwaves: Theory and Application in Materials Processing V, Ed D.E Clark, J Binner, D.A Lewis, The Amer Ceram Soc., Ohio, 2001, p 419 - 425 [7] T Schubert, PhD-Thesis, University Bayreuth, in preparation Excitation of Sodium in Powderlike Silicates by Microwave Heating M Hasznos-Nezdei1, E Pallai-Varsányi1, L P Szabó2 and S Szabó2 University Kaposvár Research Institute of Chemical and Process Engineering, Veszprém, H-8201 Veszprém P.O.Box 125, Hungary, University of Veszprém, H-8201 Veszprém, P.O.Box 158, Hungary Abstract Based on previous research work, authors investigated the effect of microwave treatment with respect to changes in microstructure of zeolite Na-4A Depending on the generated heat, dehydration of the zeolite is observed It was found, that from a given specific energy threshold a sudden temperature rise, above 1200 1300°C occurs, leading to excitation of sodium ions and causing microstructure transformation Detailed information about the role of the water content, e.g., free water, adsorbed-, and structural water and of the sodium content on the evolution of temperature runaway and microstructure transformation is presented Introduction Energy absorption in zeolites is a complex process According to Wittington >1@, it can be strongly affected by the presence of metal ions, first of all by Na+ Both, ionic conduction and dipole rotation of water molecules can take place, but the entire process and the changes in the crystal structure are not yet completely understood In previous research work changes in microstructure of 4A zeolites resulting from microwave heat treatment were investigated Because of its well known structure, ion exchange and catalytic properties, zeolite Na-4A can be preferably used to investigate changes in crystal structure and in certain properties In accordance with earlier publications, it was found that the temperature rise occurring upon microwave heating of zeolites is caused by the rotation movement of water molecules Depending on the generated heat, dehydration proceeds >2@ From a given specific microwave energy threshold, around 7Wh/g, a sudden temperature rise takes place Above 1200 - 1300°C, in the emission spectrum recorded by Fiber Optic Spectrometer the Na-doublet line appears, typical for excitation of sodium-ions >3@ The reason of this „temperature runaway” could be the mobility 662 Hasznos-Nezdei of dipole molecules and metal ions, which upon the presence of an external microwave field migrate into large cavities, forming supercages >4, 5@ In this case the dimension of channels and cages of the crystal lattice can also play an important role The purpose of the present investigations was to obtain more information about the microstructure transformation in zeolite Na-4A taking place upon different microwave treatment conditions in order to clear up the role of water content bound in the crystal lattice with different forces: free water, adsorbed water, structural water Furthermore, the effect of sodium content and of structural and micromorphological properties of the zeolite with respect to temperature runaway causing sodium excitation and microstructure transformation was of particular interest Experiments As starting material zeolite Na-4A (6 Na2O 6Al2O3 12 SiO2 27 H20) powder from a commercial source was employed Table Composition of all materials used for microwave heat treatmentsa Code Material cryst amorWater Sodium Degree of alline phous content content ion exchange (% m/m) (% m/m) (%) Z-0 + 21.4 14.78 Z450 + 7.5 14.78 Z600 + 2.8-3.0 14.78 + + 14.78 Z800 Z1000 + + 14.78 Z*-1 + 6-7 14.63 1.0 Z*-2 + 6-7 12.68 14.2 Z*-3 + 6-7 11.0 25.7 LS-0 + 0-0.2 25.3 10 WGl+ 20-22 20.2 11 Nam + 55-57 16.2 S-0 a sample 1: Zeolite Na-4A (6Na2O•6Al2O3•12SiO2•27H2O); samples - 5: zeolite Na-4A samples heated conventionally at 450°C - 600°C - 800°C - 1000°C successively; sample 8: the sodium content was modified by ion exchange process; sample 9: layered silicate (SKS-6 Hoechst, G-Na2>Si,Al@2O5 ); sample 10: hydrated water glass powder (SiO2/Na2O=2); sample 11: sodium-metasilicate (Na2O•SiO2•9H2O) The zeolite is dried or conventionally heat treated prior to further experiments under different conditions, as described in the footnote of Table Throughout the paper the symbol Z is used, with indication of the conventional pre-treatment temperature as lower symbol, e.g Z800 if the zeolite was heated to 800°C For microwave heated samples the symbol ZM is used, for samples modified in Sodium-ion content by ion exchange (Na+ is exchanged by H+) the symbol Z* is used Excitation of Sodium in Powderlike Silicates by Microwave Heating 663 The following materials were employed as model compounds: G-Na2[Si,Al]2O5, SKS-6 from Hoechst, a layered silicate Throughout the paper the symbol LS-0 is used Hydrated water glass powder with a sodium content according to a SiO2:Na2O-ratio of 1:2 Throughout the paper the symbol WG-0 is used Sodium-metasilicate, Na2O SiO2•9 H2O, abbreviated as NamS-0 A summary of the properties of the materials investigated within the presented work is shown in Table The microwave heat treatments were carried out in a domestic microwave oven (Philips M734), operating at a frequency of 2.45 GHz with a minmum power of 50 W and a maximum power of 750 W Using a supplementary microwave power control unit the average output power could be varied in 12 steps, by applying a duty cycle equivalent to 70 W-steps The following series of experiments were carried out The dehydration process was followed by measurement of the sample weight changes Classical heat treatment using an electric furnace were performed with zeolite Na-4A to investigate dehydration and microstructure transformations in the temperature range between 450°C and 1000°C (see Footnote Table 1) During the microwave experiments carried out to investigate the dehydration process, the microwave power output was kept constant at 350 W, whereas the length of the heating treatment was subsequently extended, until a maximum temperature of 650 - 700°C was reached (results in Table 2) At this temperature, in the vicinity of the sample emission of yellow light from excitation of sodium was detected In further microwave heat treatments carried out to investigate the microstructure transformation, the microwave power output was kept constant at 700 W until the maximum temperature of 650 - 700°C is reached (results in Table 3) At this temperature the characteristic emission of yellow light from excitation of sodium is visible The heating process was than continued for 14, 35, 60, 300, and 600 s, whereas the temperature of the treated samples increased from about 900°C up to 1300 - 1400°C Under such conditions, an exponential temperature increase is observed In order to provide experimental knowledge about the relationship between microstructure of a sodium containing silicate and the suszeptibility of such a material to undergo a thermal runaway upon microwave heating, model materials containing water and sodium as part of a completely different structure as compared to the zeolite, were investigated Furthermore, the sodium content of the zeolite Na-4A starting material was reduced by ion-exchange with H+, in order to study the influence of the sodium-ion content in the zeolite itself on the microwave heating behaviour The phase composition and the crystallinity of heat treated samples was studied using powder-XRD The patterns were analysed using the intensities and the interplanar spacing value, d, of the characteristic 002 reflection of zeolite Na-A, 664 Hasznos-Nezdei which is the most intensive peak A summary of the XRD-results is shown in Figure Results The results of microwave treatment of the zeolite samples at 350 W and 700 W incident microwave power for a different period of time are shown in Table and Table 3, respectively Moisture content is shown in Table 2, structural changes detected by X-ray diffraction in Table Table Microwave treatment of zeolite Na-4A samples at 350 W incident power Sample code Z-0 ZM-1 ZM-2 ZM-3 ZM-4 ZM-5 ZM-6 ZM-7 ZM-8 Treatment time (s) 60 120 180 240 300 360 420 450 Microwave treatment conditions and measured data Temperature Moisture content Observation of sample (°C) (% m/m) 21.4 141 20.4 182 15.4 270 11.0 305 7.8 371 4.8 472 3.4 490 2.0 670 0.4 excitation Table Structural changes of microwave treated zeolite Na-4A samples at 700 W incident power Sample code Z-0 ZMe ZM-1 ZM-2 ZM-3 ZM-4 ZM-5 Mw-treatment period (s) 120 134 (120+14) 155 (120+35 180 (120+60) 420 (120+300) 720 (120+600) 200 8780 7293 6304 5520 3505 3648 Peak intensity (cps) at planes 220 222 7293 7225 5975 5242 5300 4597 4872 4147 2921 2483 2916 2460 ZMe: sample treated by microwave until beginning of sodium excitation Concerning the dehydration process it can be concluded, that the „free” water content of zeolite Na-4A (between 22 - 15%) can be removed in the temperature range of 180 - 200°C at 700 W, during about 60 s, or at 350 W and treatment period of 120 s The water content of 15 - 3% (adsorptive bound water) is removed in the temperature range of 200°C - 470°C at 700 W during 120 s, or at 350 W during 350 - 400 s The structural bound water molecules (between 3% - 0%) Excitation of Sodium in Powderlike Silicates by Microwave Heating 665 could be removed totally only at temperatures close to the temperature of sodium ion excitation, that is between 500 - 1300°C Table Heat treatment of silicates Sample Sample code material 10 11 Z-0 Z450 Z600 Z800 Z1000 Z*-1 Z*-2 Z*-3 LS-0 WGl-0 NamS-0 Microwave treatment conditions and measured data Moisture content Treatment Temperature of Sodium ex(%) before mw- time (s) sample (°C) citation treatment 21.4 120 690 + 7.5 95 600 + 2.8-3.0 130 580 + 360 85-90 360 75-80 6-7 140 780 + 6-7 115 586 + 6-7 360 260 0.2 600 108 20-22 600 138 55-57 720+720 195-102 - XRD-patterns of the microwave treated zeolite samples (see Table 3), relating to the microstructure transformation are presented in Figure The XRD patterns from the front to the back refer to the original zeolite (zeolite Na-4A), furthermore to ZM-1 ZM-5 (microwave treated zeolite Na-4A samples) Fig XRD patterns of microwave treated zeolites In the patterns of the microwave treated series, increasing peaks of one or more new phases appear besides the decreasing zeolite peaks Based on the XRD measurement it could be stated, that the zeolite dehydrated due to the microwave energy absorption for a certain treatment period, transforms into „low carnegieite” The unit cell of low carnegieite is primitive orthorhombic, it contains six-membered rings built by alternating Si and Al tetrahedral and Na 666 Hasznos-Nezdei ions This framework is very similar to the zeolite Na-A structure It could be due to this similar structure, that carnegieite appears to grow at the expense of the zeolite, when the temperature is raised Some unidentified reflections are also present in the pattern, suggesting the existence of a third phase, but this phase could not be identified because of the very low intensities and excessive peak overlap During classical heat treatment the zeolite structure changes gradually As the temperature rises, amorphous or strongly disordered states can be found between the subsequent crystalline phases The original zeolite Na-4A is transformed into the stable nepheline structure at about 800°C Discussion Before coming to discussion of results obtained by evaluation of experiments on the model compounds, attention should be drawn to the most important structural characteristics of the A-type synthetic zeolites (Si4+/Al3+=1) A-type zeolites present unit cell structure which comprise E-cages linked in an octahedral form via double four-membered rings, as shown in Figure Due to this structural feature, formation of large cavities (D-cages) of 11.4 A° free diameter, separated in a cubic arrangement by 4.2 A° diameter windows which are formed by 8-membered oxygen rings (8MR) is possible The structure is completed by the E-cages of 4.4 A° free diameter formed by 6-membered oxygen rings (6MR) In the dehydrated form of the zeolite three cation sites have been investigated >6@: Site I, in case of zeolite Na-4A: Na (I) is the most preferable site where the ion stays close to the 6MR windows, that is close to the E-cages of 4.4 A° free diameter) Site II, with Na (II) ) close to the 8MR, that is close to the large D-cages of 11.4A°free diameter Site III., Na(III), near to the four membered oxygen ring (4MR) In the hydrated A-type zeolite Site I and Site II have coordinates slightly different, compared to those of the dry materials The Site III can not always be defined in the hydrated form, due to the low affinity of cations for this site The unit cell contains three 8MR, twelve 4MR, and eight 6MR The cation distribution among the three site groups is determined mainly by the number of the counterions (Li+, Na+, Ag+, K+, Ca2+, and Zn2+) per unit cell Excitation of Sodium in Powderlike Silicates by Microwave Heating 667 Fig Unit cell of the zeolite 4A The ordered occupancy of the three site groups, mainly of the Site I and Site II affects to a large extent the physicochemical properties of zeolites >7@ Based on the crystal analysis it was presumed that inside the small E-cages there are water molecules, while in the large D-cages probably 20 water molecules are bound with adsorptive forces Taking into account these results it can be supposed that an important part - about 60 - 75% - of the whole water content of zeolite Na-4A is bound in the large D-cages Upon microwave energy absorption the water molecules bound in large cages can move nearly free like in liquid state This water mobility in large cages could result in sudden temperature increase promoting the evolution of the so called „temperature runaway” The results of microwave treatments proved that the water content of zeoliteNa-4A, here mainly the part of water content bound with adsorptive forces in the supercages, is a necessary but not a sufficient prerequisite to cause temperature runaway, leading finally to the visible light emission due to „sodium excitation” Upon microwave treatment of samples - 6, which have a nearly constant sodium ion content of 14.78% - 14.68% visible light emission due to sodium excitation happens only in cases when the water content is in the range of 22% - 3%, much larger then that of structural bound water content After decreasing the sodium content by ion-exchange process, sodium excitation happens only at microwave treatment of samples and (degree of ion-exchange was 1.0 and 14.2%) but if decreasing the sodium content by 25.7% (sample 8), temperature runaway causing sodium excitation is not observed at all, although the water content of 6-8 samples was sufficiently high These results proved that not only the free dipole rotation of water molecules in large cages, but also the ion conduction (Na+ content) has a decisive effect on the appearance of thermal runaway To investigate the effect of the sodium content, on the basis of the structural formula and of the number of the 4, 6, and 8-memberd rings in the unit cell, the sodium content for ions located at different cation sites was calculated For the different sites quite remarkable values are obtained: Sodium content at Site I.: 66 - 67% 668 Hasznos-Nezdei Site II.: 25% Site III.: 8% Taking into account the results of microwave treatments carried out with samples 6,7, and it can be assumed, that the influence of sodium ions located at Site II close to the large D-cage - could be important for the temperature increase responsible for microstructure transformation Experiments performed with samples - 11 demonstrate the following: In case of layered silicate, sample 9, sodium excitation is missing because of the very low water content In case of water glass powder, sample 10, no sodium excitation is observed due to the disordered, amorphous microstructure of the material Conclusions From experimental results evidence is given that during microwave treatment of zeolite Na-4A performed under suitable conditions the whole water content, inclusive of the structural bound water, can be removed at high temperatures, which are close to the temperature at which sodium ion excitation occurs, indicated by visible light emission Additional experiments proved that upon microwave heating causing sodium excitation, the zeolite Na-4A is gradually transformed into low carnegieite Such high temperatures, however, can be obtained only in crystalline silicates having definite water-, and sodium contents, and suitable porous structure with large cages Acknowledgement Financial support from the Hungarian National Scientific Research Fund (OTKA T026224) is gratefully acknowledged References >1@ Wittington B.J and Milestone N.B.: The microwave heating of zeolites, Zeolites 12 (1992) pp.815 >2@ Pallai-Varsányi E., Hasznos-Nezdei M et al: Dehydration and crystal-structure transformation of synthetic zeolites by microwave and classical heat treatment, Proceedings of The First European Congress on Chemical Engineering (Florence, Italy, May 4-7, 1997.) pp 1551-1553 >3@ Hasznos-Nezdei M Nagy J.B., Pallai-Varsányi E et al: Effect of Microwave Treatment on Low Silica Zeolites, Proceedings of The First European Congress on Chemical Engineering (Florence, Italy, May 4-7, 1997.) pp 1555-1558 Excitation of Sodium in Powderlike Silicates by Microwave Heating 669 >4@ Roussy G Zoulalian A et al: How Microwaves Dehydrate Zeolites, J Phys Chem., 1984, 88, pp.5702-5708 >5@ Pallai-Varsányi E., Hasznos-Nezdei M et al: Investigation of Temperature Runaway in Microwave Heated Synthetic Zeolites, Proceeding of the Conference Microwave and High Frequency Heating 1997 (San Martino Conference Hall, Fermo, 9-13 September 1997), pp 461-464 >6@ Kalogeras J.M and Vassilikou-Dova A.: Molecular Mobility in Microporous Architectures: Conductivity and Dielectric Relaxation Phenomena in Natural and Synthetic Zeolites, Cryst Res Technol 31 (1996) pp.693-726 >7@ Breck D.W et al: Crystalline zeolites I The properties of a new synthetic zeolite, Type A., J Amer Chem Soc 78 (1956), pp.5972 RF and Microwave Rapid Magnetic Induction Heating of Silicon Wafers Keith Thompson1, John Booske1, Yogesh Gianchandani1, Reid Cooper2 Department of Electrical Engineering, University of Wisconsin, Madison 53706 USA Department of Materials Science and Engineering, University of Wisconsin, Madison 53706 USA Introduction It is well established that microwaves can heat ceramics for processing applications, but considerably less attention has been given to the use of high frequency radiation for the processing of silicon wafers There are many aspects of semiconductor processing that require heating, including dopant or ohmic contact interdiffusion, implantation damage annealing, and wafer bonding Conventionally, the wafers are heated in furnaces or halogen lamp Rapid Thermal Processing (RTP) chambers An alternative, electromagnetic induction heating (EMIH), uses radio (RF) and microwave radiation to rapidly (125°C/s) and volumetrically heat silicon wafers to temperatures in excess of 1000°C In contrast to conventional (heat lamp) RTP, which heats through surface absorption, EMIH has the advantage of heating throughout the material The presence of insulating layers, most notably thick oxides (several hundred nanometers) on the surface of the wafer, not inhibit rapid heating since the wave transmits through the insulator and directly into the silicon Conventional RTP, due to its dependence on surface absorption, may have trouble rapidly heating through this insulating layer Furthermore, the volumetric nature of the heating makes it attractive for low thermal budget microelectromechanical systems (MEMS) applications [1] which may require rapid heating well below the wafer surface Because of this, EMIH has found applications in ultra shallow junction formation [2], direct silicon bonding for MEMS applications [1], and direct silicon bonding for silicon on insulator technology [1] Background A basic mathematical description of EMIH lies in Ampere’s and Faraday’s laws An oscillating magnetic flux, transverse to the wafer surface, is associated with 674 Thompson induced current flow in the silicon wafer A fraction of this magnetic flux is reduced through destructive interference with an opposing flux re-induced by the current flowing in the wafer The remainder of the field energy is either dissipated in the wafer through ohmic collisions between electrons and the lattice or transmitted through the wafer The energy dissipation is the source of the wafer heating while the field‘s transmission and reflection represent lost energy A selfconsistent solution of Ampere’s and Faraday’s laws, discussed in detail in previous publications [1, 2] provides the following equation for steady state power absorption Pabs S a t w3 G V H o2 t w G Watts G Z o P n , pV m An illustration of this equation of absorbed power is provided in Fig for both 13.56 MHz and 2.45 GHz At low conductivity, the skin depth is large and power absorbtion is low as the wave mainly transmits through the silicon Absorption peaks as the skin depth approaches the thickness of the wafer, whereus at smaller skin depth the net incident magnetic flux is reduced as the surface currents re-induce an opposing magnetic flux Fig Coupling power into (semi)conductive materials Left: illustrative power absorption as a function of conductivity at 2.45 GHz (top curve) and 13.56 MHz (lower curve) into a wafer of mm thickness Right: skin depth as a function of conductivity Several issues are apparent from this equation First, the well known skin depth term plays a prominent role Plotted in Figure for various frequencies of interest, skin depth characterizes the volumetric nature of the heating A large skin depth corresponds to uniform heating through the 1-dimensional thickness of the wafer while a small skin depth results in power deposition within a thin surface layer Fig (left part) illustrates the impact that skin depth has on heating efficiency Poorly conducting materials have a large skin depth; therefore the power absorption is inefficient as a large fraction of the field energy transmits through the wafer As conductivity increases, the skin depth shrinks and a greater fraction of the power is absorbed by the wafer As the skin depth becomes on the order of the wafer thickness the re-induced flux reduces the net incident flux because most ... 25-30 30 25-30 roomtemp roomtemp roomtemp roomtemp PM, 68 kg roomtemp roomtemp cryo.mag cryo.mag cryo.mag TE02 TE02 15 38.7 40 PM, 600 kg tapered B Comparison of Different Millimeter-Wave Sources... declares: ? ?in my opinion the best applicator is the simplest applicator and the best overall system is a hybrid system that uses the minimum amount of microwave energy and the maximum amount of... Lambert Feher and Manfred Thumm BASIC RESEARCH AND INDUSTRIAL PRODUCTION USING THE SPARK PLASMA SYSTEM (SPS) .745 Mamoru Omori COMBINED PROCESSES: LASER ASSISTED MICROWAVE PROCESSING