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Develop and Characterization of Transparent Glass Matrix Composites DEVELOPMENT AND CHARACTERIZATION OF TRANSPARENT GLASS MATRIX COMPOSITES Bo Pang A thesis submitted in fulfilment of the requirements of the degree of Doctor of Philosophy Imperial College London Department of Materials LONDON, 2011 Preface This thesis describes research carried out by the author in the Department of Materials of Imperial College during the period from January 2008 to January 2010, under the supervision of Dr. David McPhail and Prof. Aldo R. Boccaccini. No part of this work has been accepted or is being currently submitted for any other qualification in this college or elsewhere. Some of the results presented in this thesis have been published and presented in various journals and conferences. Journal publications B. Pang, D. McPhail, D.D. Jayaseelan, and A.R. Boccaccini, Development and Characterization of Transparent Glass Matrix Composites. Advances in Science and Technology, 2011. 71: p. 102-107. B. Pang, D. McPhail and A.R. Boccaccini, Glass Matrix Composites for Transparent Security Measures. Materials World, February 2011: p.20-22. Conference contributions Development and characterisation of transparent glass matrix composite. B. Pang, D. McPhail and A.R. Boccaccini. Oral presentation at the Annual Meeting of Society of Glass Technology, Murray Edwards College, Cambridge, UK. 6-10 September 2010. Development and characterisation of transparent glass matrix composite. B. Pang, D. McPhail and A.R. Boccaccini. Oral presentation at CIMTEC 2010 - 12th International Ceramics Congress, Montecatini Terme, Italy. 6-11 June 2010. 1 Abstract Glass matrix composites based on NextelTM alumina fibre reinforced borosilicate glass have been fabricated to improve their mechanical property and fracture toughness. In this work, a novel processing technique, which is called “sandwich” hot-pressing, has been used. It consists of arranging the reinforcing fibres in two directions with a periodic interspacing between glass slides, and submitting the material to a heat-treatment for consolidation into highly dense and transparent composites, which were proved by XRD analysis and SEM observations. These composites’ mechanical, optical and microstructural properties were studied and compared to those of the unidirectional fibre reinforced borosilicate glass composite and unreinforced glass matrix produced under the same conditions. Furthermore, a hybrid sol-gel technique has been employed for coating the fibres with a smooth and crack free ZrO2 interfacial layer to provide a weak bonding at the fibre/matrix interface to promote fibre pull-out during fracture. ZrO2 coated and uncoated fibre-reinforced borosilicate glass matrix composites were fabricated, with different sizes of optical windows including 4x4, 5x5 and 6x6 cm2. Moreover, a geometry based equation was derived to evaluate the expected light transmittance of the composites. These multi-directional fibre reinforced glass matrix composites retained at least 50% of the light transmittance and higher flexural strength compared with the unreinforced glass matrix. The highest measured flexural strength value of these composites was 56 ± 7 MPa. The composites reinforced by ZrO2 coated fibres had higher flexural strength (approx. 36%) and lower standard deviation (approx. 47%) compared with those reinforced by uncoated fibres. The introduction of a ZrO2 interfacial layer was to improve the mechanical properties and to retain the composites’ integrity, which was proved by the observations of fibre pull-out and crack deflection upon failure during mechanical tests. To investigate the microstructure of the interfacial layer in the composite, SEM, FIB-SIMS and TEM were employed. The present composites show potential for applications in architecture and special machinery requiring strong transparent windows. 2 Acknowledgements I would like to acknowledge my supervisors Prof. Aldo R. Boccaccini and Dr David McPhail, for their invaluable support and guidance, for all the encouragement and opportunities provided. I am also grateful to all my colleagues, who dedicated their time to help and provide valuable input towards the research work carried out, especially Dr. D. Desimone Silva and Dr. D. Doni Jayaseelan. Dr. Ivo Dlouhy (Institute of Physics of Materials, Bmo, Czech Republic) and Dr. Dietmar Koch (University of Bremen, Germany) are kindly acknowledged for their excellent collaboration, as well as Dr. John Travers and Prof. Roy Taylor from the Photonics group at the Physics Department of Imperial College, where part of this research work was carried out. Finally, I would like to thank my dearest friends Mikey Meng, Bai Cui, Jianye Wang Tayyab, Fatima and Pipa, whose friendship has been the best part of being at Imperial College. Lilai Zhang, Lulu Ye, Kan Chang, Cong Wan, Jianfeng Wang and Suqi Shen, who make London feel like home. I will send my deepest gratitude to my family who have always believed in me and taught me to be independent. Despite the distance, you are a constant inspiration, my example of dedication and hard-work. To Zhuo Peng, my best friend and love, you are also my example of hard-work and integrity. Thank you for your unconditional support and accompanying with me all the time. This accomplishment is also yours. 3 Contents Preface .............................................................................................................................. 1 Abstract ............................................................................................................................. 2 Acknowledgements .......................................................................................................... 3 Contents ............................................................................................................................ 4 List of Tables .................................................................................................................... 8 List of Figures ................................................................................................................. 10 1 Introduction .............................................................................................................. 18 2 Literature Review ..................................................................................................... 21 2.1 Introduction to ceramic matrix composites ........................................................ 21 2.2 Glass matrix composites .................................................................................. 22 2.2.1 Optomechanical composites ................................................................... 24 2.3 Reinforcements ................................................................................................ 28 2.4 Matrices ........................................................................................................... 30 2.4.1 Matrix requirements ................................................................................ 30 2.4.2 Glass matrices ........................................................................................ 31 2.4.3 Glass-ceramic matrices .......................................................................... 33 2.4.4 General properties of glasses ................................................................. 34 2.4.5 Glass sintering ........................................................................................ 37 2.4.6 Stress relief and annealing ..................................................................... 38 2.5 Composite fabrication techniques..................................................................... 39 2.6 Fibre coatings................................................................................................... 42 2.7 Mechanical properties of brittle matrix composites ........................................... 43 2.7.1 Typical energy dissipating phenomena at the interface ........................... 45 2.7.2 Mechanical properties of GMCs reinforced by oxide fibres ..................... 49 4 2.8 Conclusions ..................................................................................................... 53 3 Aims and objectives ................................................................................................. 54 4 Fibres characterisation and results ........................................................................ 57 4.1 Introduction ...................................................................................................... 57 4.2 NextelTM fibre: general description .................................................................... 57 4.3 Fibre characterisation: experimental methods .................................................. 61 4.3.1 Heat-cleaning process and thermal treatment of fibres ........................... 61 4.3.2 Fibre physical properties......................................................................... 61 4.3.3 Thermal analysis .................................................................................... 62 4.3.4 Microstructural analysis .......................................................................... 63 4.3.5 Mechanical properties ............................................................................ 63 4.4 Results and discussion ..................................................................................... 66 4.4.1 Fibre physical properties......................................................................... 66 4.4.2 Thermal analysis ...................................................................................
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