T-4061 FABRICATION OF ALUMINUM NITRIDE CRUCIBLES FOR MOLTEN SALT AND PLUTONIUM COMPATIBILITY STUDIES by Jeffrey Allen Phillips ProQuest Number: 10783731 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a com plete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. uest ProQuest 10783731 Published by ProQuest LLC(2018). Copyright of the Dissertation is held by the Author. All rights reserved. This work is protected against unauthorized copying under Title 17, United States C ode Microform Edition © ProQuest LLC. ProQuest LLC. 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106- 1346 T-4061 A thesis submitted to the Faculty and the Board of Trustees of the Colorado School of Mines in partial fulfillment of the requirements for a degree of Master of Science (Materials Science). Golden, Colorado Signed: Approved: Dr. Gerald L. DePoorter Thesis Advisor Golden, Colorado Date . / Dr. William D. Copeland Professor and Coordinator, Materials Science Department ii T-4061 ABSTRACT Aluminum nitride crucibles have been fabricated utilizing an isostatic pressing technigue and subsequent high temperature sintering. These crucibles were pressed from a commercial spray dried powder using calcium carbonate as a sintering additive. The crucibles were exposed at 850°C to various molten chloride salts (e.g., NaCl, KC1, and CaCl2) and evaluated for salt release and corrosion of the ceramic crucible. Data are presented which show the effects of the salt exposure to the aluminum nitride microstructure. Additionally, the predicted high temperature exposure of aluminum nitride to plutonium oxide and plutonium metal in a chloride salt medium, as estimated by a Solgasmix computer modeling program, is detailed. Brief overviews of the direct oxide reduction (DOR) and electrorefining (ER) processes for plutonium processing are discussed. Sintering mechanisms applicable for aluminum nitride processing are also presented. iii T-4061 TABLE OF CONTENTS Page ABSTRACT ............................................. iii TABLE OF CONTENTS ..................................... iv LIST OF FIGURES ....................................... vi LIST OF TABLES ........................................viii ACKNOWLEDGEMENTS ..................................... ix CHAPTER 1: INTRODUCTION ............................. 1 1.1 Scope of Research .......................... 2 1.2 Objective of Research ....................... 4 1.3 Research Conducted ......................... 5 1.4 Thesis Organization ......................... 7 CHAPTER 2: LITERATURE REVIEW ......................... 8 2.1 Direct Oxide Reduction ...................... 8 2.2 Ceramic Materials ........................... 13 2.2.1 Magnesium Oxide ....................... 15 2.2.2 Aluminum Oxide ........................ 16 2.2.3 Zirconium Oxide ....................... 17 2.2.4 Silicon Carbide and Silicon Nitride .... 18 2.2*5 Aluminum Nitride ...................... 19 2.3 Physical Properties of AluminumNitride ...... 20 2.3.1 Thermal Conductivity ................ 2 0 2.3.2 Thermal Coefficient of Expansion ....... 26 2.3.3 Corrosion Resistance ................ 27 2.4 Sintering ................................... 29 2.4.1 Solid State Sintering ................ 33 2.4.2 Liquid Phase Assisted Sintering ........ 35 2.4.3 Sintering of Aluminum Nitride .......... 35 2.4.3.1 Sintering with Yttrium Oxide ........ 37 2.4.3.2 Sintering withCalcium Carbonate ... 41 CHAPTER 3: THERMODYNAMIC CALCULATIONS 4 3 3.1 Solgasmix Computer Modeling 4 3 3.2 Ceramic Materials 4 6 3.2.1 Magnesium Oxide ....................... 47 3.2.2 Aluminum Oxide ........................ 49 3.2.3 Zirconium Oxide ....................... 51 3.2.4 Silicon Carbide ....................... 53 iv T-4061 TABLE OF CONTENTS (continued) Page 3.2.5 Silicon Nitride ....................... 55 3.2.6 Aluminum Nitride ...................... 58 CHAPTER 4: EXPERIMENTAL PROCEDURES ..................... 65 4 .1 Raw Materials ................................ 65 4.2 Isostatic Pressing ........................... 66 4.3 Sintering .................................... 68 4.3.1 Binder Burnout ........................ 69 4.3.2 Sintering ............................. 71 4.4 Analytical Techniques ........................ 72 4.4.1 X-ray Diffraction ..................... 73 4.4.2 Scanning Electron Microscopy .......... 74 4.5 Molten Salt Exposure ......................... 75 4.5.1 DOR Salt Exposure ..................... 75 4.5.2 ER Salt Exposure ...................... 80 CHAPTER 5: DISCUSSION OF RESULTS ...................... 84 5.1 Fabrication Techniques ....................... 84 5.1.1 Isostatic Pressing .................... 85 5.1.2 Sintering ............................. 85 5.2 DOR Salt Exposure ............................ 91 5.2.1 Calcium Chloride Salt ................. 94 5.2.2 Calcium Metal/Calcium Chloride Salt .... 102 5.2.3 Evaluation of Corrosion ............... 108 5.3 ER Salt Exposure ............................ 115 5.3.1 Sodium-Potassium ChlorideSalt ......... 115 5.3.2 Evaluation of Corrosion ............... 119 CHAPTER 6: CONCLUSION ................................. 121 6.1 Enumerated Conclusions ...................... 121 6.2 Recommendations for Further Study ........... 124 BIBLIOGRAPHY 12 6 APPENDICES ............................................ 135 Appendix A: Solgasmix Data Files ................. 136 Appendix B: JC-PDS X-ray Cards ................... 148 Appendix C: X-ray Diffraction Data ............... 175 v T-4 061 LIST OF FIGURES Figure Description Page 2.1 DOR vessel ................................... 9 2.2 Wetting of a liquid on a solid ............... 14 2.3 Wurtzite crystal structure ................... 21 2.4 Depiction of neck formation due to diffusion of matter to the contact region ............. 34 2.5 Yttria-Alumina phase diagram ................. 38 2.6 Parallel/Series thermal conductivity models... 40 2.7 Calcia-Alumina phase diagram ................. 42 3.1 Gibbs free energy vs. temperature of silicon nitride and plutonium nitride ............... 57 3.2 Gibbs free energy vs. temperature of aluminum nitride and plutonium nitride ............... 60 4.1 Green aluminum nitride crucible dimensions ... 67 4.2 TGA results in nitrogen and air of spray dried aluminum nitride powder ..................... 7 0 4.3 Sybron furnace setup for DOR salt exposure ... 78 4.4 Photograph of ER salt test furnace ........... 82 5.1 Photograph of sintered aluminum nitride crucible .................................... 86 5.2 XRD pattern of aluminum nitride powder ....... 88 5.3 XRD pattern of spray dried aluminum nitride powder ...................................... 89 5.4 XRD pattern from sintered aluminum nitride ... 90 5.5 SEM micrographs of sintered aluminum nitride at 500X and 2,000X .......................... 92 5.6 SEM micrographs of sintered aluminum nitride at 5,000X and 10,000X ....................... 93 5.7 Photographs of crucible/salt cross section ... 95 5.8 SEM micrographs of calcium chloride salt exposed aluminum nitride at 33X ............. 96 5.9 SEM micrographs of calcium chloride salt exposed aluminum nitride at 500X ............ 97 5.10 XRD pattern of virgin calcium chloride salt .. 100 5.11 XRD pattern of molten calcium chloride salt .. 101 5.12 XRD pattern of molten calcium metal/calcium chloride salt ............................... 103 5.13 SEM micrographs of calcium metal/calcium chloride exposed aluminum nitride at 3 3X .... 105 vi T-4061 LIST OP FIGURES (continued) Figure Description Page 5.14 SEM micrographs of calcium metal/calcium chloride exposed aluminum nitride at 500X and 5,000X .................................. 106 5.15 SEM micrographs of calcium metal/calcium chloride exposed aluminum nitride at 500X and 5,000X .................................. 107 5.16 XRD pattern of calcium chloride exposed aluminum nitride ............................ Ill 5.17 XRD pattern of calcium chloride exposed aluminum nitride ............................ 112 5.18 SEM micrographs of sodium-potassium chloride exposed aluminum nitride at 500X and 5,000X .................................. 116 5.19 SEM micrographs of sodium-potassium chloride exposed aluminum nitride at 500X and 5,000X .................................. 117 vii T-4061 LIST OF TABLES Table Description Page 2.1 Physical properties of common ceramic materials 2 6 3.1 Thermodynamic modeling of DOR process in a magnesium oxide crucible .................... 48 3.2 Thermodynamic modeling of DOR process in an aluminum oxide crucible ..................... 50 3.3 Thermodynamic modeling of DOR process in a zirconium oxide crucible .................... 52 3.4 Thermodynamic modeling of DOR process in a silicon carbide crucible .................... 54 3.5 Thermodynamic modeling of DOR process in a silicon nitride crucible .................... 56 3.6 Thermodynamic modeling of DOR process in an aluminum nitride crucible ................... 59 3.7 Thermodynamic modeling #1 of ER process in an aluminum nitride crucible ................... 62 3.8 Thermodynamic modeling #2 of ER process in an aluminum nitride crucible ................... 64 4.1 Dow Chemical spray dried aluminum nitride powder formulation .......................... 65 5.1 EDX results from calcium chloride salt exposed aluminum nitride crucible ........... 98 5.2 EDX results from calcium metal/calcium chloride salt exposed aluminum