| Author: | Yang, Yi |
| Title: | Investigation of glassy carbon and pre-carbonized glassy carbon—experiments and applications |
| Advisors: | Ruan, Haihui (ME) |
| Degree: | Ph.D. |
| Year: | 2024 |
| Subject: | Carbon Carbon -- Analysis Hong Kong Polytechnic University -- Dissertations |
| Department: | Department of Mechanical Engineering |
| Pages: | x, 123 pages : color illustrations |
| Language: | English |
| Abstract: | Carbonaceous materials play a crucial role in diverse applications, such as electrochemistry and high-temperature manufacturing. Glassy carbon (GC), a non-graphitized carbon material known for its exceptional hardness and chemical inertness, exhibits ceramic-like properties and serves niche applications. GC is traditionally produced through a powder sintering and pyrolysis method, where the precursor is crushed, compacted into a green body, and then pyrolyzed. However, this process often results in GC products with internal pores and cracks, leading to low yield and high production costs. A more cost-effective alternative is direct pyrolysis of bulk precursors, though early attempts frequently produced cracked GC when thickness exceeded several millimeters, due to limited understanding of carbon structure development. This thesis demonstrates successful production of GC products exceeding 10 mm in thickness from bulk precursors, making direct bulk pyrolysis a viable, low-cost approach with improved yields. The thesis first presents a comprehensive literature review on GC fabrication, covering key research and advancements since the material’s discovery in the 1960s. These studies lay the foundation for developing GC and suggest further exploration of its formation mechanisms and fabrication processes. Building on these insights, GC products were successfully produced by directly pyrolyzing bulk phenol formaldehyde (PF) resin at 1000°C, achieving significant thickness. Further, investigations into the cracking behavior of bulk GC during pyrolysis integrate experimental findings with numerical simulations, revealing critical temperature-dependent mass losses that distinguish pre-carbonized from fully carbonized GC. Notably, pore and crack formation due to gas evolution and pressure buildup begin at around 400 °C, and the subsequent cracking process can be accurately modeled using a phase-field fracture approach. Additionally, our findings reveal a crucial temperature range of 500 – 600 °C where pyrolysis results in the most significant density changes and formation of GC. The study explores the temperature-dependent changes in Young's modulus of GC through impulse excitation techniques (IET), showing that when GC samples are reheated, structural reformation occurs within this range. This causes a decrease in stiffness at heating rates above 3 °C/min, alongside an unexpected restorative effect, where stiffness increases when samples are annealed between 500 and 550 °C. These findings hold important implications for the large-scale, direct formation of glassy carbon from bulk precursors. Finally, the thesis explores pre-carbonized glassy carbon (PGC) produced from bulk PF precursor and its use in infrared glass molding. PGC samples pyrolyzed at 350 °C (PGC-350) exhibited optimal mechanical properties, with compressive and flexural strengths of approximately 370 and 200 MPa, respectively. PGC-350 was then used to mold infrared glass with favorable results across various surface morphologies. The fabrication of PGC-350 molds or structural parts with complex geometries demonstrates excellent manufacturability and specific strength, with potential for further optimization to enhance its industrial applications. In summary, the research presented in this thesis, focusing on the investigation of GC fabrication mechanisms, optimization of fabrication processes, and applications, holds significant implications for the commercialization of GC in the industry. |
| Rights: | All rights reserved |
| Access: | open access |
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