ADVANCES IN MOLTEN SALT CHEMISTRY Volume 1

ADVANCES IN MOLTEN SALT CHEMISTRY Volume 1

CONTRIBUTORS TO TIDS VOLUME C.R.Boston Metals and Ceramics Division Oak Ridge National Laboratory Oak Ridge, Tennessee John W. Hastie National Bureau of Standards Washington, D. C. Ronald E. Hester Department of Chemistry University of York York, England Yizhak Marcus Department of Inorganic and Analytical Chemistry The Hebrew University of Jerusalem Jerusalem, Israel D. A. J. Swinkels Senior Research Officer Broken Hill Proprietary Co., Ltd. Central Research Laboratory Shortland, New South Wales, Australia

ADVANCES IN MOLTEN SALT CHEMISTRY Volume 1 Edited by J. BRAUNSTEIN Oak Ridge National Laboratory Oak Ridge, Tennessee GLEB MAMANTOV The University of Tennessee Knoxville, Tennessee and G. P. SMITH Oak Ridge National Laboratory Oak Ridge, Tennessee g:> PLENUM PRESS NEW YORK-LONDON 1971

Library of Congress Catalog Card Number 78-131884 ISBN 978-1-4757-0506-5 ISBN 978-1-4757-0504-1 (ebook) DOI 10.1007/978-1-4757-0504-1 1971 Plenum Press, New York Softcover reprint of the hardcover 1st edition 1971 A Division of plenum Publishing Corporation 227 West 17th Street, New York, N.Y. 10011 United Kingdom edition published by Plenum Press, London A Division of Plenum Publishing Company, Ltd. Davis House (4th Floor), 8 Scrubs Lane, Harlesden, NWI0 6SE, England All rights reserved No part of this publication may be reproduced in any form without written permission from the publisher

ARTICLES PLANNED FOR FUTURE VOLUMES High Temperature Coordination Chemistry of Group VIII K. E. Johnson, University of Saskatchewan at Regina, and J. R. Dickinson, University of Virginia Molten Organic Salts J. E. Lind, Stanford University Optical Interferometry Applied to the Study of Molten Salts A. Lunden and S. E. Gustafsson, Chalmers Institute of Technology, Sweden Gas Solubility in Molten Salts P. E. Field, Virginia Polytechnic Institute Electrode Kinetics of Molten Salts D. Inman and A. D. Graves, Imperial College, London

FOREWORD Molten salts are investigated by very diverse techniques and for differing purposes, and the results are reported in widely scattered journals. There is a need to keep investigators aware of progress in other specialties and to provide students with source and background material. Advances in Molten Salt Chemistry hopes to fill these needs by providing reviews of recent progress presented, insofar as is reasonable, with enough background material and commentary to be comprehensible to a nonspecialist. We prefer a discussion of underlying principles, to the extent that they are known, and we encourage authors to comment critically on the reliability of data, the utility of models, and the cogency of ideas and theories. We take a broad vie~ of the suitability of topics for inclusion in this series. Both fundamental and technological advances have a place here, as do studies on materials related to molten salts (like liquid silicates, very concentrated aqueous solutions, solutions of salts in liquid metals, and solid electrolytes). We intend this series to serve the needs of those who investigate or use molten salts. We welcome suggestions of topics and suitable authors, as well as comments on the strengths and shortcomings of what is published. J. BRAUNSTEIN G. MAMANTOV G. P. SMITH vii

PREFACE Subjects chosen for this volume are among those which have been of interest to molten salt chemists over the years. Structural investigations are discussed in the first chapter, on vibrational spectroscopy of molten salts, and in the last chapter, on mass spectrometry of vapors above molten salts. The second chapter deals with the important area of liquid-liquid extraction including technological applications as well as theoretical aspects. Chapter 3 deals with the haloaluminates, a class of molten salts with a rich chemistry, and Chapter 4, on batteries and fuel cells, covers one of the significant areas of technological application of molten salts. In future volumes we hope to maintain a balance among theoretical, experimental, and applied topics in molten salts and peripheral areas. We thank our many colleagues for their suggestions and cooperation. Special thanks are due Drs. D. M. Moulton and R. A. Strehlow of Oak Ridge National Laboratory for their valuable comments. J. B., G. M., G. P. S. viii

CONTENTS Chapter 1 VIBRATIONAL SPECTROSCOPY OF MOLTEN SALTS R. E. HESTER 1. Principles of Infrared and Raman Spectroscopy. 1.1. Introduction.... 1.2. Molecular vibrations 1.3. Normal modes... 1.4. Infrared and Raman spectra: Selection rules....... 2. Experimental Techniques.................. 2.1 Spectrometer Modifications for Molten Salt Work... 2.2. Transmission, Reflectance, and Emission Infrared Methods 2.3. Arc Lamps, Discharge Lamps, and Lasers as Raman Light Sources 2.4. Sample Cells.. 3. Results....... 3.1. Monatomic Ions. 3.2. Polyatomic Ions 3.3. Covalent Melts. 4. Theoretical Problems References 1 2 4 7 11 11 13 16 17 27 27 35 52 52 57 Chapter 2 LIQUID EXTRACTION FROM MOLTEN SALTS Y. MARCUS 1. Introduction......... 1.1 The Scope of the Survey. 1.2. Experimental Techniques. 63 63 67 ix

x Contents 2. Thermodynamics of the Distribution 2.1. Activities in Molten Salt Systems.... 2.2. Activities from Distribution Measurements 2.3. Thermodynamic Functions of Transfer.. 3. Immiscible Molten Salts.......... 3.1. Thermodynamics of Immiscible Molten Salts 3.2. Criteria for Immiscible Salt Systems. 3.3. Survey of Systems with Miscibility Gaps 4. The Kinetics of the Distribution..... 4.1. Diffusion Controlled Rates...... 4.2. Rates Controlled by Boundary Crossing 4.3. Rates Controlled by Slow Chemical Reactions 71 71 72 74 76 76 79 82 90 90 90 91 5. Survey of Selected Distribution Systems..... 93 5.1. Distribution of Solutes between Molten and Liquid Bismuth 93 5.2. Distribution of Solutes between Molten Borates and Molten Halides... 99 5.3. Distribution of Solutes between Molten and Aromatic Solvents 104 5.4. Extraction from Molten Salts with Long-Chain Amine Salts III 5.5. Miscellaneous Systems Recently Studied 116 6. Concluding Remarks References............... 120 121 Chapter 3 MOLTEN SALT CHEMISTRY OF THE HALOALUMINATES C. R. BOSTON 1. Introduction............... 129 2. The Aluminum Halides......... 130 2.1. Physical and Thermodynamic Properties 130 2.2. Structure....... 133 2.3. Solvent Properties... 135 2.4. Electrical Conductivity. 135 2.5. Subvalent Species... 135 3. Physical Properties of Salt Mixtures Containing Aluminum Halides 136 4. Phase Studies and Thermodynamic Properties of Salt Mixtures Containing Aluminum Halides.......... 139 4.1. Phase Studies................ 139 4.2. Alkali Metal Halide-Aluminum Halide Mixtures 140

Contents xi 5. Spectroscopy and Structure 5.1. Raman Spectroscopy 5.2. Crystal Structures... 6. Solvent Properties..... 6.1. Acid-Base Systems and Solubilities 6.2. Stabilization of Subvalent Species. 6.3. Spectroscopy.......... 6.4. Electrochemical Studies of Solutes 6.5. Immiscible Liquid Studies 141 141 143 144 144 145 146 147 148 7. Electrochemistry....... 149 7.1. Conductivity...... 149 7.2. Decomposition Potentials, Electrolysis and Other Electrochemical Studies 152 8. Technological Applications.. 9. Melt Preparation and Handling Acknowledgments References 152 154 155 155 Chapter 4 MOLTEN SALT BATTERIES AND FUEL CELLS D. A. J. SWINKELS 1. Introduction. 1.1. Scope 1.2. Advantages of Molten Salt Electrolytes. 1.3. Disadvantages of Molten Salt Electrolytes 2. General Discussion 2.1. Cell emf's 2.2. Electrode Polarization 2.3. Energy and Power Limits 2.4. Self Discharge. 3. Specific Battery Systems 3.1. Concentration Cells 3.2. Thermal Batteries. 3.3. Lithium-Chlorine Cells 3.4. Sodium-Sulfur Cell 165 165 166 167 168 168 170 173 175 181 181 188 191 200

xii Contents 4. Fuel Cells 4.1. Carbonate Fuel Cell. 4.2. Solid Oxide Fuel Cell 5. Other Systems References 203 203 210 215 218 Chapter 5 THERMODYNAMIC STUDIES, BY MASS SPECTROMETRY, OF MOLTEN. MIXED HALIDE SYSTEMS J. W. HASTIE 1. Introduction.. 225 2. Experimental Techniques.................. 226 2.1. Use of Total Vaporization Isotherms for Mass Spectrometric Determination of the Partial Pressures and Relative Ionization Cross Sections of Molecules. 228 3. Results for Binary Systems.... 232 3.1. Group IA-IA Halide Systems 232 3.2. Group la-ii Halide Systems. 234 3.3. Group la-iii Halide Systems 237 3.4. Group la-iva Halide Systems 238 3.5. Group la-transition Metal Halide Systems 240 3.6. Group la-rare Earth Halide Systems. 244 3.7. Group la-actinide Halide Systems. 245 4. Reciprocal and Similar Systems 245 5. Miscellaneous Mixed Halide Reactions 247 6. Structures and Unifying Concepts 247 References 254 Author Index Formula Index Subject Index 259 271 279