This is the author’s version of a work that was submitted/accepted for pub- lication in the following source: Ong, Teng-Cheong (2018) Research of the suppression effects of cooling rate on crystallization in ZBLAN glass. PhD thesis, Queensland University of Technology. This file was downloaded from: https://eprints.qut.edu.au/116614/ Notice: Changes introduced as a result of publishing processes such as copy-editing and formatting may not be reflected in this document. For a definitive version of this work, please refer to the published source: https://doi.org/10.5204/thesis.eprints.116614 Research of the suppression effects of cooling rate on crystallization in ZBLAN glass Teng-Cheong Ong Bachelor of Engineering (Mechanical) (Hons) Submitted in fulfilment of the requirements for the degree of Doctor of Philosophy School of Chemistry, Physics and Mechanical Engineering Science & Engineering Faculty Queensland University of Technology 2018 Abstract ZBLAN glass is a heavy metal fluoride glass that has great potential in the application of long- haul telecommunication cables. However, during processing in the fibre-drawing temperature region, the material tends to undergo heavy devitrification, resulting in a crystalline fibre that is not usable for such purposes. There are many papers exploring various processing techniques in the aims of creating a test sample that can transmit with the theoretical minimum attenuation loss predicted for ZBLAN. As ZBLAN glass is cooled from its melt, crystallites form throughout the medium, their size and structure dependent on the rate of cooling and degree of undercooling. These crystallites act as scattering centres that degrade a signal that is propagated through the glass. This thesis seeks to explore processing techniques with different cooling rates in order to supress the process of crystallization. Rapidly cooled ZBLAN test samples were analysed with a wide range of spectroscopy, diffraction and imaging techniques including SEM, TEM, XRD and ellipsometry. These techniques were used to characterize the structure of the crystallites in the ZBLAN glass and how they were affected by the various cooling rates. Ultimately, a critical cooling rate was empirically established to be between 900 ⁰C/min and 4000 ⁰C/min for a test volume size of 9.4 x 10-8 m3. This critical cooling rate yielded ZBLAN samples that were fully amorphous and completely free of nano-crystalline inclusions. Using an algorithm that incorporates classical nucleation formulae, a theoretical critical cooling rate was determined to be 1100 ⁰C/min, which is in agreement with the empirical results. Lastly, using Kramers-Kronig relations, the predicted attenuation loss for the fully amorphous ZBLAN test samples is 0.09 dB/Km at a ii wavelength of 1800 nm, which although is not at the theoretical best, is still a marked improvement on the best attenuation loss achieved in ZBLAN glass fibres to date. Recommendations are made for the next critical step for future work of this research, which is to create a fibre with this degree of amorphous “clarity”. Keywords: ZBLAN, fluoride glass, devitrification, crystallization, cooling rate, rapid quenching, amorphous, scanning electron microscopy, transmission electron microscopy, x-ray diffraction, ellipsometry, attenuation loss iii Acknowledgements My PhD Journey has been a very unique one, not unlike other people’s experience in that it was taxing and gruelling at the best of times, but also very unpredictable and turbulent in many ways. However, the overcoming of great tribulations is an excellent teacher of fortitude and determination, where the completion of this thesis was only possible because of the immeasurable amount of help and guidance I received. For those people who helped me in my time of need, I am unbelievably grateful for. Firstly, I would like to thank all of the technicians and staff who helped me with all of my laboratory and analysis work, without them I would have continued to run around like a headless chook. I would like to thank Lauren Butler for dealing with the ever temperamental glove box. The workshops boys in O block, for being ever patient and always meeting all the deadlines, I hope that carton of beers made up for how demanding I was. The Chemstore boys for putting up with my demands and urgent deadlines. Graham Wright for providing me endless support with the electrical side of the project. Leonora Newby, Dr. Peter Hines, Dr. James Riches, Dr. Tony Raftery, Donald McAuley and Rachel Hancock for assisting with the analysis and spectroscopy work. I would like to extend my heartfelt thanks to my fellow PhD students who helped me when they themselves were busy enough with their own work. Thank you Ralf Raud for not just helping me with my lab work, but being a friend whose been there with me for all the ups and down of this roller coaster ride. Thank you Owen for your matlab expertise, but mostly for the good chats, the moral support and the companionship out at the drop tower, we had some fun times out there. I greatly appreciate all of the undergraduate engineers who provided their support to this project, especially when they weren’t being paid or getting credit for the work and just doing it out of the kindness of their own hearts. Special mention goes to Benjamin Forgarty, thank you for the great chats and the endless hours you dedicated to this project, building the rapid electro-thermal processing device (or the REPD, pronounced “repid”) and the portable glove box. You are a man of many great talents and your contribution to this thesis has been monumental to say the least. I would also like to express my deepest appreciation to my family and friends, most of whom did not have a direct contribution to this project, but it is through this personal support network that I was able to spend all of these years focused on this project. Special thanks goes to my mum, who although has iv always questioned some of my decisions in life, has always been an unconditional supporter in all of my endeavours. I would like to extend my gratitude to Dr. Mohammed Saad, senior scientist at THORLABS, for providing me the technical expertise I required, but most importantly for providing the ZBLAN material used in this experiment. The material was magnanimously provided for free, and without it this work would not have been possible. I would like to thank Professor John Bell and Professor Esa Jaatinen, my associate supervisors. John provided me so much support, especially during the very difficult periods of my candidature. Esa, your expertise has been invaluable in this project, you have always been a great source of information and guidance when I needed it most. Last but not least, Professor Ted Steinberg, the Principal Supervisor who inherited me and my project, you were a saviour to me, and so much more than just a supervisor/mentor to me, but a hero and source of motivation for me. Ted played the role of an “adopted surrogate” father, guiding me through the last 200 meters of this marathon run of a candidature with great encouragement and faith. I owe the completion of this thesis solely on your moral support, without you as a Principal Supervisor I wouldn’t have been able to muster the strength to restart this project from scratch and finish on time. v TABLE OF CONTENTS Abstract.................................................................................................................................................. ii Acknowledgements ............................................................................................................................ iv TABLE OF CONTENTS ..................................................................................................................... vi LIST OF TABLES ................................................................................................................................. xi LIST OF FIGURES .............................................................................................................................. xii List of Abbreviations ........................................................................................................................ xix Statement of Original Authorship ................................................................................................... xx CHAPTER 1: Introduction .............................................................................................................. 1 1.1. ZBLAN Glass and its Applications ................................................................................... 1 1.2. Hypothesis ............................................................................................................................ 1 1.3. Research Approach .............................................................................................................. 2 1.4. Project Objective ................................................................................................................... 2 1.5. Limitation of Study .............................................................................................................. 3 1.6. Thesis Chapter Summary .................................................................................................... 4 CHAPTER 2: Background and Literature Review ...................................................................... 6 2.1. Background of ZBLAN Glass ............................................................................................. 6 2.2. Material Properties