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The Effect of Composition on the Structure Symmetry and Stability of Tunnel-Structured Hollandite Ceramics for Nuclear Waste Immobilization" (2018)

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The Effect of Composition on the Structure Symmetry and Stability of Tunnel-Structured Hollandite Ceramics for Nuclear Waste Immobilization Clemson University TigerPrints All Dissertations Dissertations 12-2018 The ffecE t of Composition on the Structure Symmetry and Stability of Tunnel-Structured Hollandite Ceramics for Nuclear Waste Immobilization Robert L. Grote Clemson University, [email protected] Follow this and additional works at: https://tigerprints.clemson.edu/all_dissertations Recommended Citation Grote, Robert L., "The Effect of Composition on the Structure Symmetry and Stability of Tunnel-Structured Hollandite Ceramics for Nuclear Waste Immobilization" (2018). All Dissertations. 2248. https://tigerprints.clemson.edu/all_dissertations/2248 This Dissertation is brought to you for free and open access by the Dissertations at TigerPrints. It has been accepted for inclusion in All Dissertations by an authorized administrator of TigerPrints. For more information, please contact [email protected]. THE EFFECT OF COMPOSITION ON THE STRUCTURE SYMMETRY AND STABILITY OF TUNNEL-STRUCTURED HOLLANDITE CERAMICS FOR NUCLEAR WASTE IMMOBILIZATION A Dissertation Presented to the Graduate School of Clemson University In Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy Materials Science and Engineering by Robert Lansing Grote December 2018 Accepted by: Dr. Kyle Brinkman, Committee Chair Dr. Rajendra Bordia Dr. Fei Peng Dr. Lindsay Shuller-Nickles ABSTRACT The ceramic phase hollandite is a component material for some multi-phase ceramic waste forms and has been a prominent ceramic waste form for the immobilization of cesium and strontium radionuclides. The immobilization of cesium is difficult due to its large size and water solubility. This dissertation is focused on understanding the fundamental structure of hollandite and the effect cesium doping has on the properties of hollandite in order to develop a more effective and efficient waste form for cesium immobilization. The topics cover the structure and stability, thermodynamic properties and phase formation, irradiation resistance, and leaching resistance of hollandite. A brief history, the current status, and advantages and shortcomings of hollandite as a waste form are given in the introduction and background chapter. In chapter 2, the effect of elemental doping on the hollandite structure, symmetry, and stability are described, and methods to improve these properties are presented. Different B-site dopants were tested to probe the monoclinic/tetragonal symmetry boundary of hollandite. Additionally, cesium doping into barium-zinc-titanium hollandite was performed to develop a better understanding of how divalent cations affect the stability of hollandite and how cesium doping and occupancy can be controlled to increase the stability of hollandite. In chapter 3, the thermal properties were studied and calorimetry was performed. The melting, thermal stability, and cesium loss behaviors were measured and found to be ii dependent on the cesium content. Calorimetry data was collected for a series of cesium-doped hollandite. The drop solution enthalpy was measured and the formation enthalpy was calculated. Zinc hollandite formation was more favorable and energetic stability increased as the cesium content increased. In chapter 4, the radiation stability of hollandite was measured over a full range of cesium doping. The onset of amorphization did not vary with cesium content; however, the dose required for full amorphization doubled with full cesium substitution. Amorphization was also measured at an elevated temperature, and the critical amorphization temperature of hollandite was measured between 200 °C and 300 °C. A defect mechanism was proposed, and the amorphization model for hollandite was determined. In chapter 5, elemental leaching dependence on cesium content was studied. The amorphization mechanism and effect of irradiation on leaching rate were discussed. The leaching rate decreased with increasing cesium content. Leaching experiments were also performed on irradiation samples. Cesium leaching was found to increase after irradiation with the high cesium content intermediate compositions exhibited the lowest cesium losses. In summary, the stability of zinc hollandite was measured and found to be primarily dependent on cesium content with some occupancy effect. Cesium doping increased the stability of the tetragonal symmetry, reduced cesium loss during processing and leaching, stabilized hollandite formation, increased radiation tolerance, and reduced iii elemental leaching. Thus, high cesium content hollandite has improved the waste form properties. iv DEDICATION This dissertation is dedicated to my wife Kelsey Grote, my children, and my family for their incredible support. Your sacrifices have made this journey possible. v ACKNOWLEDGMENTS Foremost, I would like to convey my great appreciation to my advisor Kyle Brinkman for his support, guidance, and patience during my graduate study. He has been an excellent guide and mentor who had provided valuable advice on my research and writings. A special thanks to Professor Lindsay Shuller-Nickles, who has been helpful with research and a joy to work with. I also give my sincere thanks to my committee members, Professor Rajendra Bordia and Professor Fei Peng for their advice and agreeing to serve on my committee. I am grateful for their time, effort, and suggestions. I want to thank my group mates and collaborators, Dr. Ming Tang, Dr. Jake Amoroso, Dr. Yun Xu, Dr. Yuqing Meng, Dr. Tao Hong, Dr. Ye Lin, Dr. Siwei Wang, Devin Harkins, Changlong Li, Jun Gao, Mingyang Zhao, and George Wetzel. Finally, I want to thank my beloved wife, Kelsey Grote. I am incredibly grateful and exceptionally blessed to have a woman like her at my side. Her support and encouragement have been essential through this experience. vi TABLE OF CONTENTS Page TITLE PAGE ................................................................................................................... i ABSTRACT ..................................................................................................................... ii DEDICATION ................................................................................................................. v ACKNOWLEDGMENTS .............................................................................................. vi LIST OF TABLES .......................................................................................................... ix LIST OF FIGURES ........................................................................................................ xi CHAPTER I. INTRODUCTION ......................................................................................... 1 1.1 Scientific Objective ............................................................................ 2 1.2 Background ........................................................................................ 2 1.3 Experimental Procedure ................................................................... 27 II. STRUCTURE AND STABILITY ............................................................... 34 2.1 Introduction ...................................................................................... 34 2.2 Experimental Procedure ................................................................... 35 2.3 Results and Discussion .................................................................... 36 III. CESIUM LOSS, MELTING POINT AND FORMATION ENTHALPY .. 56 3.1 Introduction ...................................................................................... 56 3.2 Experimental Procedure ................................................................... 57 3.3 Discussion ........................................................................................ 58 IV. IRRADIATION ........................................................................................... 74 4.1 Introduction ...................................................................................... 74 4.2 Experimental Procedure ................................................................... 75 4.3 Discussion ........................................................................................ 77 vii Table of Contents (Continued) Page V. LEACHING ................................................................................................. 94 5.1 Introduction ...................................................................................... 94 5.2 Experimental Procedure ................................................................... 95 5.3 Discussion ........................................................................................ 97 VI. CONCLUSIONS........................................................................................ 105 REFERENCES ............................................................................................................ 107 viii LIST OF TABLES Table Page 1.1 Target wt% concentrations for simulated waste stream. The phase which partitions each element is given by: hollandite (H), pyrochlore (Py), perovskite (Py), and zirconolite (Zr) 20 ........................ 5 1.2 Reported melting points for different M2+/3+ doped hollandite from Aubin 23, Carter 49, and Costa 48 ............................................................. 16 2.1 B-site dopant series of Cr,Sn, Zn,Zr, In,Ti, and Ga,Ti hollandite with primary and secondary phases. Most of these compositions did not form hollandite even though the tolerance factor, tH, was close to one ..................................................................................... 38 2.2
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