A Thesis Entitled Autohydration of Nanosized Cubic Zirconium Tungstate by Nathan A. Banek Submitted to the Graduate Faculty as partial fulfillment of the requirements for the Master of Science in Chemistry ___________________________________ Dr. Cora Lind, Committee Chair ___________________________________ Dr. Jared Anderson, Committee Member ___________________________________ Dr. Jon Kirchhoff, Committee Member ___________________________________ Dr. Patricia Komuniecki Dean of College of Graduate Studies The University of Toledo August 2011 An Abstract of Autohydration of Nanosized Cubic Zirconium Tungstate by Nathan A. Banek Submitted in partial fulfillment of the requirements for The Master of Science in Chemistry The University of Toledo August 2011 In recent years, negative thermal expansion (NTE) materials have become of increasing interest. These materials contract upon heating, and have potential for achieving better control of thermal expansion in composite materials. By using an NTE compound as a filler material into these composites, it is possible to offset the positive thermal expansion of other components in the composite. As a result, these NTE materials can find use in a wide range of applications such as optics, polymers, electronics, tooth fillings and any other area where exact positioning of parts over a wide range of temperatures is crucial. One of the most popular NTE materials is cubic ZrW2O8. Thermodynamically stable zirconium tungstate was first synthesized in the 1950’s through traditional solid state methods. It was only recent that the metastable phases could be achieved through low temperature methods, that involves conversion of a precursor material ZrW2O7(OH)2·2H2O to cubic ZrW2O8. Through hydrothermal synthesis, previous work on ZrW2O7(OH)2·2H2O showed exceptional particle and morphology control with use of iii alcohols/HCl, which is desirable for optimal composite integration. It was recently discovered that ZrW2O8 particles obtained through this synthesis route had reduced stability in atmosphere. The instability was linked to autohydration that changed the properties of the material resulting in weak positive thermal expansion. Interestingly, nanosized ZrW2O8 obtained hydrothermally in perchlorate/NaCl with the absence of alcohols show very limited autohydration; however this is a non-preferred synthesis route due to high agglomeration levels. Reported autohydration on mixed ZrMoxWx-1O8 solid solutions by Sleight et al. provided a logical defect driven explanation for the cubic ZrW2O8 nanoparticles. Detailed investigation was performed on cubic ZrW2O8 hydrothermally obtained by the alcohol/HCl synthesis pathway. An understanding of what is causing autohydration was discovered through the used of powder X-ray diffraction, scanning transmission electron microscopy, thermogravimetric analysis and Brunauer-Emmett- Teller surface analysis. iv Acknowledgements It has been a great journey to arrive at this point in my life and I could not have done it by myself. I would like to recognize those who have provided significant help along the way. I would like to thank my parents and my family for their continued support throughout my life; it would have been very hard to succeed without them. I would like to thank my advisor Dr. Cora Lind for her continued support and advice on this project. Dr. Lind has taught me a significant amount of details that I am very grateful for. I would like to thank my committee members, Dr. Jon Kirchhoff and Dr. Jared Anderson for their advice and support. I would like to thank my labmates, past and present, for their support and friendship. Many thanks to Pannee Burckel for her assistance with X-ray diffraction and electron microscopy experiments; Stacy Gates for various instrumentation help; Dr. Wendell Griffith and Tamam Baiz for providing excellent advice when I needed it; and Pam Samples and Charlene Hanson for their administrative help. I would also like to thank the University of Toledo for providing me with the opportunity to further my education. This material is based upon work supported by the National Science Foundation under Grant No. 0840474 and Grant No. 0545517. v Contents Abstract .............................................................................................................................. iii Acknowledgements ............................................................................................................. v Contents ............................................................................................................................. vi List of Tables ................................................................................................................... viii List of Figures ..................................................................................................................... x 1. Introduction ................................................................................................................. 1 1.1 Thermal Expansion ............................................................................................. 1 1.2 Negative Thermal Expansion Materials .............................................................. 2 1.2.1. Scandium Tungstate Family ....................................................................... 3 1.2.2. Zirconium Vanadate Family ....................................................................... 4 1.2.3 ZrW2O8 Family ........................................................................................... 4 1.3. Nanoparticles ...................................................................................................... 6 1.4. ZrW2O8 Composites............................................................................................ 7 1.5. Hydration of ZrW2O8 .......................................................................................... 8 1.6. Project Goals ....................................................................................................... 9 2. Characterization ........................................................................................................ 10 2.1. Powder X-ray Diffraction ................................................................................. 10 2.1.1. Diffraction Experiments............................................................................ 11 2.1.2 Crystallite Size Estimates ......................................................................... 12 2.2. Electron Microscopy ......................................................................................... 13 2.2.1 Field Emission Scanning Electron Microscopy ........................................ 14 2.2.2 Scanning Transmission Electron Microscopy .......................................... 15 2.3. Thermogravimetric analysis.............................................................................. 15 2.4. Brunauer-Emmett-Teller Surface Analysis ....................................................... 16 3. Synthetic Variables in the Preparation of ZrW2O7(OH)2·2H2O ............................... 17 3.1. Introduction ....................................................................................................... 17 3.2. Zirconium Tungstate Synthesis......................................................................... 18 3.2.1 Hydrothermal Synthesis ............................................................................ 18 3.2.2 Micron-sized ZrW2O8 Particles ................................................................ 18 3.2.3 Nanosized ZrW2O8 Particles ..................................................................... 19 vi 3.3. General Synthesis Protocols ............................................................................. 19 3.4. Results and Discussion ..................................................................................... 25 3.4.1 Effect of Temperature ............................................................................... 25 3.4.2 Effect of Reaction Time ............................................................................ 29 3.4.3 Effect of Acid Concentration .................................................................... 33 3.4.4 Influence of Solvent Type on ZrW2O7(OH)2·2H2O Morphology ............. 38 3.4.5. Effect of Solvent Concentration................................................................ 44 3.5. Conclusions ....................................................................................................... 46 4. Autohydration of Cubic ZrW2O8 .............................................................................. 49 4.1. Introduction ....................................................................................................... 49 4.2. Experimental ..................................................................................................... 51 4.2.1 Preparation of Cubic ZrW2O8 from Nanosized ZrW2O7(OH)2·2H2O ..... 51 4.2.2. Study of Autohydration Kinetics .............................................................. 51 4.3. Results and Discussion ..................................................................................... 53 4.3.1 Effect of Temperature ............................................................................... 54 4.3.2 Effect of Heating Time ............................................................................. 61 4.3.3 Effect of Acid Concentration .................................................................... 63 4.3.4 Effect of Solvent Concentration...............................................................