MOLTEN

SALTS

HANDBOOK

1967 ACADEMIC PRESS

New York • London

CONTENTS

Preface, v

I. PHYSICAL PROPERTIES

I. A. Atomic and Ionic Radii, Melting Points, and Boiling Points of Single Salts and Eutec t ics , 1

Atomic and Ionic (Crystal) Radii, 1 Solid State Interionic Separations, 2 Volumes of Anions, 2 Formula Weights, Melting Points, and Boiling Points for Some Inorganic Compounds, 2 The Effect of Pressure on Melting Points, 30 Melting Points of Some Quaternary Ammonium Salts R4N+X~, 30 Selected Low Melting Binary Eutectics, 31 Additional Low Melting Binary Eutectic Mixtures, 35 Selected Ternary Eutectic Mix­tures, 36 Melting Points and the Law of Corresponding States, 37

I. B. Density, 39

Melt Densities — Single Salts, 39 Density of Some Solid Halide Salts, 45 Percentage Volume Change on Fusion for Some Inorganic Halides, 46 Volume Change of NaCl and KCl on Melting, 46 Volume Changes Due to Melting and Molar Volumes of Some Molten Nitrates, 47 Densities of Cryolite with Additives, 47 Melt Densities - Binary Sys­tems, 48 Melt Densities - Ternary and Quaternary Systems, 51 Literature Values for the Densities of Molten NaCl and KCl, 51

I. C. Viscosi ty , 52

Viscosities of NaNOa and KN03 as Single Salt Melts, 52 Viscosity - Single Salt Melts, 54 Melt Viscosities - Binary Systems, 58 Melt Viscosities - Ternary and Quaternary Mixtures, 62

I. D. Vapor P r e s s u r e , 63

Vapor Pressure Equations for Selected Molten Salts, 63 Vapor Pressures - Additional Studies, 65 Equilibrium Dissociation Pressures of Molten Carbonates, 77 Corre­sponding State Vapor Pressures for Molten Alkali Halides, 78

I. E. Surface Tension, 80

Surface Tensions of Various Compounds as Single Salt Melts, 80 Hole Size in Group IA Chlorides and Nitrates, 84 Hole Size in Group nA and nB Halides, 85 Surface Tensions of Molten Salt Mixtures, 85 Surface Tensions - Additional Studies, 86 Corresponding State Surface Tensions, 87

I. F. Refract ive Index, 89

Refractive Index of Various Molten Salts as a Function of Temperature, 89 Refractive Index of Various Molten Salts, 90 Molar Refractivity of Various Molten Salts, 91 Re­fractive Index — Molten Salt Mixtures, 92

vii

viii Contents

I. G. Cr i t i ca l Data, 93

Critical Temperatures and Percent Dissociation of Several Alkali Halides, 93 Critical Constants of NaCl and KCl, 93 Boiling Points, Entropies of Vaporization, Reduced Temperatures, and Critical Temperatures of Alkali Halides, 94 Saturated Vapor and Liquid Densities of NaCl and KCl above Their Normal Boiling Point, 95

n . THERMODYNAMIC PROPERTIES

II. A. Liquid- Liquid Immiscibi l i ty , 97

Molten Salt Liquid-Liquid Immiscibility, 97

n . B. Metal-Molten Salt Sys tems , 102

Principal Data for Alkali Metal-Alkali Halide (MX-M) Phase Diagrams, 102 Principal Data for Some Alkaline Earth Metal-Halide Systems (MXS-M), 103 Solubility of Some Transition and Post-Transition Metals in Their Molten Halides, 104 Principal Data for Some Rare Earth Metal-I alide Systems, 106 Metal-Metal Chalcogenide Phase Relations, 108 Metal-Molten Salt Equilibria, 109 Metal-Fused Salt Systems - Additional Studies, 112

II. C. Metal Oxide-Molten Salt Sys tems , 116

Metal Oxide-Fused Salt Systems, 116

H. D. Silver Sal ts-Molten Salt Sys tems , 118

Binary Systems with One or More than One Component a Silver Salt, 118 Foreign Cation Classification of Binary Systems with One Component a Silver Salt, 127

II. E. Phase -Ru le Studies, 129

Phase Characteristics of Binary Salt Mixtures, 129 Binary Salt Systems - Additional Phase-Rule Studies, 131 Phase Relations - Ternary Salt Systems, 141 Compounds in the Binary Phase Diagrams of the Monovalent Chlorides with Multivalent Chlorides, 149 Phase-Rule Studies - Quaternary Systems, 175

n . F. Solubility, 176

Henry's Law Constant for Noble Gases, 176 Solubility of Argon in Molten Sodium Nitrate at 369°C, 177 Oxygen and Carbon Dioxide Solubilities in Molten Carbonates, 177 Sol­ubility of Water in Molten Salts, 178 Solubility of HF in ZrF4 -NaF Molten Mixtures, 179 Solubility of Various Solutes in (Li,K)NOs Eutectic at 160°C, 179 Solubility of Metal Oxides in Fused Salts, 180 Solubility of Metals - Effect of Added Halides, 181 Solu­bility of Aluminum in Fused Salts, 181 Solubilities in Molten Salts - Additional Studies, 182

II. G. T h e r m a l Data, 184

Heats and Entropies of Fusion and Volume Changes upon Melting of the Halides and Ni­trates of Group I and IIA Elements, 184 Heats of Fusion-Selected Salts, 185 Heats of Fusion - Recent Studies, 191 Heats of Fusion - Selected Eutectic Mixtures, 192 Entropies of Phase Transition and Fusion, 192 Heat of Mixing — Binary Mixtures of Fused Salts, 194 Heat of Mixing Data for Silver Chloride-Alkali Chloride and Silver Bromide-Alkali Bromide Systems, 195 Heat of Mixing Data for Binary Alkali Halide Systems, 195 Heats of Mixing of Halides, Perrhenates, and Perchlorates, with Nitrates, and Heats of Solution, 196 Heats of Mixing - Additional Studies, 197 Heat Conductance of Molten Salts, 198 Temperature Dependence of the Thermal Conductivity of Molten

Contents ix

NaOH, 199 Thermal Conductivity of Pure Molten Nitrates and Nitrites, 199 Thermal Conductivity of Molten Nitrate Mixtures, 199 Heat Capacity of Selected Molten Salts, 200 Increase of Molar Heat Capacity on Melting, 201 Heat Capacity - Additional Studies, 201 Heats of Formation, 204 Heats of Sublimation and Vaporization of Alkali Halides at Their Melting Points, 205 Partial Molar Heats of Solution, 205

n . H. Cryoscopy and Related Thermodynamic Studies, 212

Cryoscopic Constants - Selected Salts, 212 Results of Some Cryoscopic Studies of Molten Salt Systems, 214 Cryoscopy-Recent Studies, 215 Cryoscopy - Additional Studies, 220 Association Constants of Ionic Species in Fused Salt Solvents, 226 Association Constants - Additional Studies, 228 Thermodynamic Properties Calculated from emf Data, 229 Thermodynamic Data from emf Studies, 230 emf of Galvanic Jacobi-Daniell Cells, 232 Activity Data from emf Studies, 235 emf Cells - Additional Studies, 237 Activity Data for PbCl2 in Molten Mixtures from Vapor Pressure Measurements (1003 ± 5° K), 246 Thermodynamic Properties - Additional Studies, 246

II. I. Expansivity, Compress ib i l i ty , Ul t rasonic , and High P r e s s u r e Studies, 248

Molar Volumes and Coefficients of Expansion of NaCl and KCl, 248 Molar Volumes and Expansivities of Molten Halides, 248 Expansivities of Fused Salts at T = T e (°K), 249 Velocity of Sound in Molten Salts, 251 Adiabatic and Isothermal Compressibilities for Group I Molten Salts, 252 Isothermal and Adiabatic Compressibility of Group n Molten Halides, 253 Free Volume for Molten Nitrates and Nitrites, 254 Relation of Free Volume to Hole Volume and Heat of Activation of Viscous Flow of Some Group HB Halides, 255 Rao's Constant for Various Molten Salts and Organic Liquids, 255 Values of 7?3 /?7g for Molten Salts, Associated and Nonassociated Liquids, 256 Difference in Ac­tivation Energies for Shear and Structural Viscosity, 256 Values of Parameters for Equations Relating to Shear and Structural Viscosity in Molten Salts, 257 Viscosity, Density, and Absorption Data for Several Molten Salts, 257 Viscosity and Absorption Data, 258 Compressibility of Certain Molten Silicates and Borates, 259 Density and Expansivity of Liquid Silicates, 261

m . ELECTROCHEMICAL PROPERTIES

m . A. Reference E lec t rodes and emf S e r i e s , 265

Reference Electrodes, 265 Gaseous and Redox Electrodes, 267 Various Metals Used as Electrode Systems in Fused Salts, 269 Reference Electrodes - Additional Studies, 272 Ep° in Pure Metal Fluorides at High Temperatures Compared with Ej° in Aqueous Solutions at 25° C, 275 Ep° in Pure Metal Chlorides at High Temperatures Compared with Ei* in Aqueous Solutions at 25° C, 276 Ep° in Pure Metal Bromides at High Temperatures Com­pared with Ej° in Aqueous Solutions at 25° C, 278 Ep° in Pure Metal Iodides at High Tem­peratures Compared with Ei° in Aqueous Solutions at 25° C, 279 Standard Potentials in Bromides and Iodides Compared with Chlorides at 700°C, 280 emf Series in Alkali Chlor­ide Solvents Compared with Ep°, 281 emf Series in Fused MgCl2-NaCl-KCl Solvent at 475° C, 282 emf Series in Various Fused Salt Electrolytes, 283 emf Series - Additional Studies, 285

HI. B. E lec t r i ca l Conductance, 287

Equivalent Conductance - Single Salt Melts, 287 Specific Conductance of Single Salt Melts, 290 Temperature Dependence of Specific Conductivity of Molten Sulfides, 300 Specific Conductivity of Cryolites, 300 Specific Conductance of Molten KCl, 301 Trans­port Parameters of Liquid BeF2 , Typical Halides, and Network Oxides, 301 Electrical Conductance of Low Melting Acid Sulfates, 302 Effect of Additives on Electrical Con­ductance of LiClOj , 302 Effect of p-Xylene on Conductance, Density, and Viscosity of (n-Amyl)4NCNS, 303 Effect of Inert Gas Solubility and Pressure on Electrical Conduc-

Contents

tance of NaNOs , 304 Effect of H20 on Conductance, Density, and Viscosity of NaOH-KOH, 304 Effect of Additives on Electrical Conductance of Cryolite, 305 Degree of "Ionic Dissociation" in Molten Compounds, 305 Conductance Parameters for KN03 + Ba(N03)2 Melts at 350°C, 306 Melt Conductance - Binary Systems, 307 Melt Con­ductance - Ternary and Quaternary Mixtures, 311 Electrical Conductance - Metal-Molten Salt Systems, 312 Molar Conductance A m of Na and K in Infinitely Dilute Solu­tion in Their Molten Halides at 900° C, 315 Electrical Conductivity of Metal-Molten Salt Systems — Additional Studies, 315

III. C. Polarography, Chronopotent iometry, and Double Layer Capacity Studies, 318

Polarographie Data for Fused Salts, 318 Solid Electrodes for Molten Salt Voltammetry, 325 Polarography-Additional Studies, 329 Chronopotentiometric Data for Metal Ions in KCl-LiCl at 450° C, 333 Chronopotentiometry - Diffusion Coefficients for Ag+ in Molten KN03-NaNOs , 333 Diffusion Data from Chronopotentiometric Studies, 334 Chronopotentiometry - Formation Constants for Halide Complexes of Cd(II) in Molten NaNOs-KN03 at 263°C, 335 Chronopotentiometry - Additional Studies, 335 Double Layer Capacities in Molten Salts, 337 Comparison of the Potentials of Zero Charge and the Corresponding Standard Electrode Potentials, 338 Exchange Currents and Kinetic Parameters in Molten Salt Electrode Processes, 340 Exchange Currents and Double Layer Capacitance — Additional Studies, 341

III. D. E lec t romigra t ion : T ranspo r t Numbers and Diffusion, 342

Movement of Inorganic Ions in Fused Anhydrous LiCl-KCl Eutectic at 450° C, 342 Move­ment of Metal Ions in Fused Salts, 342 Movement of Cd(n) and Pb(II) in Fused Salts When Employed as Different Salts, 343 Electrophoresis - Additional Studies, 343 Transport Numbers - Single Salt Melts, 344 Comparison of Cation Transference Num­bers Calculated with Those Measured Relative to Porous Plugs, 346 Transport Num­bers - Mixed Fused Salts, 347 Transport Numbers - Additional Studies, 349 Self-Diffusion Coefficients, 349 Tracer Diffusion of Na22 in Molten NaN03, 350 Tracer Dif­fusion in Molten Carbonates, 351 Interdlffusion Coefficients-Dilute Binary Systems, 351 Diffusion-Additional Studies, 352 Interionic Friction Coefficients for Some Single Salt Melts, 353 Transport Properties at Various Temperatures for Molten Nitrates, 355

III. E. Die lec t r ic and The rmoe lec t r i c P r o p e r t i e s , 356

Dielectric Constants of Molten Salts, 356 Thermoelectric Properties, 357 Thermo­electric Properties - Additional Studies, 357

IV. SPECTROSCOPY AND STRUCTURE

IV. A. Vibrat ional Spectroscopy, 359

Vibrational Spectra of Molten Nitrates, 359 Assignments and Calculated Frequencies for In-Plane Vibrations of Molten Nitrates in C2V Symmetry, 360 Urey-Bradley Force Constants of Coordinated Nitrate Ions in Nitrate Melts, 360 Vibrational Spectra of Molten Hydroxides, Chlorates, Perchlorates, Sulfates, and Bisulfates, 361 Vibrational Spectra of Molten Halides, 362 Characteristic Vibrational Bands in Molten Halides, 362 Raman Spectra of Gallium Dichloride and Dibromide, 363 Raman Spectra of Molten and Aqueous Thiocyanates, 363 Vibrational Spectra of Molten Nitrate Mixtures, 364 Vi­brational Spectroscopy — Additional Studies, 364

IV. B. Visible and U. V. Spectroscopy, 366

U.V. and Visible Absorption Spectra Studies, 366 Coordination Numbers and Config­urations of 3d Metal Ions in Molten Chlorides, 368 Correlation of Results with Elec-

Contents xi

trostatic and Crystal Field Stabilization Energies, 369 Colors Produced by Transition Metal Ions in Molten Salts, 370 Frequencies of Absorption Maxima E(2) for Alkali Ni­trates , 371 Spectra of Ni2 + and Co2+ in Molten Sulfates, 371 Spectra of Pr*+ and Pd2* in Molten LiCl-KCl, 372 Calculated Parameters for Ni2+ in Various Media, 372

IV. C. Nuclear Magnetic and Elec t ron Pa ramagne t i c Resonance Spectroscopy, 373

NMR Chemical Shift on Fusion of Thallium Salts, 373 Chemical Shift in Solid and Molten Thallium Salts, 373 Chemical Shift of 20ST1 + in Solutions of RbCl and AgCl, 374 NMR Spectroscopy — Additional Studies, 374 Electron Spin Resonance Spectroscopy, 374 Magnetic Susceptibility of Some Molten Metals, Molten Salts, and Their Solutions, 375 Magnetic Susceptibility— Additional Studies, 375

IV. D. X-Ray and Neutron Diffraction, 376

Structural Parameters from the First Peaks of Alkali Halide Radial Distributions, 376 Cation-Cation or Anion-Anion Distances and Coordination in Molten and Crystalline Alkali Halides, 377 X-Ray and Neutron Diffraction- Additional Studies, 378

IV. E. Fused Salt E lec t ro ly tes , 380

Current Viewpoints, 380

V. PRACTICAL FEATURES

V. A. Melt P r epa ra t i on and Purif icat ion, 383

Principles of Electrolyte Purification, 383 Electrolyte Purification- Recent Studies, 385 Crystal Growth from Melts, 387

V. B. Containment and Corros ion , 388

Containment of Fused Salts, 388 Containment of Molten Metals, 392 Containment of Molten Oxides, 395 Molten Salt Corrosion Data, 397 Corrosion Processes in Melts, 403

V. C. Chromatographic Analys is , 406

Chromatographic Behavior of Inorganic Ions in Molten LiCl-KCl Eutectic at 450° C under Various Conditions, 406 Chromatography on Various Supports with Different Eluants (160° C), 407 Comparison between Adsorption, Oxide Solubility, and Ionic Potentials, 409 Electromigration in Fused Salts, 409 Chromatography - Additional Studies, 410

V. D. E lec t ro lys i s , 411

Metal Formation, 411 Electroplating from Fused Salts, 430 Electrolysis — Additional Studies, 431 Inorganic Compound Formation by Fused Salt Electrolysis, 433 Alloy Formation by Fused Salt Electrolysis, 435 Isotope Enrichment - Single Salts, Binary Mixtures, 440 Polarization Potentials — Fused Salt Electrolysis, 442 Decomposition Potentials in Fused Salt Electrolysis, 447 Decomposition Potential Studies, 450 Elec­trode Discharge Potentials of Anions (700°C), 456

V. E. Chemical P r o c e s s e s , 457

Chemical Synthesis with Molten Salts as Reaction Media, 457 Acid-Base Concepts in Molten Salts, 459 Molten Salts as Reaction Media — Additional Studies, 461

x i i Contents

V. F. Fuel Cel ls , Ba t t e r i e s , Nuclear Technology, 464

Fuel Cells, 464 Molten Salts in Voltaic Cells, 465 Vapor Pressure Data of Some Molten Fluoride Systems Used in Nuclear Reactor Fuels, 468 Thermochemical Data for Some Molten Fluoride Systems Used in Nuclear Reactor Fuels, 471 Density and Viscosity Data of Some Molten Fluoride Systems Used in Nuclear Reactor Fuels, 481 Thermal Conductivity and Equilibrium Data for Some Molten Fluoride Systems Used in Nuclear Reactor Fuel, 490 Effect of Temperature on Corrosion and Corrosion Reac­tions of Some Molten Fluoride Systems Used in Nuclear Reactor Fuels, 491 Radiation Stability of Some Molten Fluoride Systems Used in Nuclear Reactor Fuels, 496 Some Molten Fluoride Systems Used in Nuclear Reactor Fuels - Additional Studies, 496

VI. EXPERIMENTAL TECHNIQUES

VI. A. I l lus t ra t ions of Exper imenta l Assembl i e s , 499

Conductance Cells, 499 d.c. Conductance Cell and Transformer Circuit for Electrode Cells, 500 Cell for Potentiometrie Measurements and Electrode Assemblies, 501 Electrodes for Polarography, 502 U.V. Spectroscopy Assembly, 503 Molten Salt In­frared Cells, 503 Molten Salt Raman Cells, 504 Molten Salt NMR Assemblies, 505 Transport Number Electrolysis Cells, 506 Electromlgratlon (Electrophoresus) Assembly, 507 Viscometers, 507 Heat of Mixing and Heating Fusion Calorimeters, 508 Cryo-scopic Assemblies, 509 Density and Surface Tension Assemblies, 510 Ultrasonic Velocity Assembly, 511 Refractive Index Apparatus, 511 Molten Salt Chromatography Apparatus, 512 Reaction Vessel for Chemical Synthesis Using Melts as Reaction Media, 512

VI. B. Experimental Techniques - Annotated Bibliography, 513

Additional References and Data Sources, 513 Preparation and Purification of Melts, 515 Container Materials, 515 Furnace and Temperature, 516 Electrochemical Techniques, 516 Electrolysis, 516 Conductance, 517 Potentiometry, 518 Polarography, 520 Chronopotentiometry, 521 Electrode Polarization Methods, 521 Visible and Ultraviolet Spectroscopy, 522 Infrared and Raman Spectra, 523 NMR and ESR Spectra, 524 X-Ray and Neutron Diffraction, 525 Electrical Transport, 525 Diffusion, 526 Vis­cosity, 527 Calorimetry, 528 Phase Equilibria, 528 Cryoscopy, 530 Thermo­electric Properties, 531 Surface Tension, 532 Density and Compressibility, 532 Refractive Index, 532 Magnetic Susceptibility, 533 Adsorption and Chromatography, 533 Chemical Reactions, 533

CHEMICAL FORMULA INDEX, 535