Session: 17-01-01: Research Posters

Paper Number: 150245

150245 - Solar-Thermal Photocatalytic Cylindrical Graphite for Thermal Interface Materials 

Modern computing devices for artificial intelligence algorithms and high-performance computing generate high heat fluxes, accelerating performance degradation and even failure. This generated heat must be efficiently dissipated through a heat spreader or to a heat sink. However, gaps between mating surfaces hinder heat conduction and create bottlenecks at interfaces that, in turn, can produce hotspots that deteriorate device performance. Many types of thermal interface materials have been developed to enhance heat flow between contacting surfaces and have been widely studied, including carbon-based materials such as carbon nanotubes. This study utilizes a unique form of cylindrical graphite as a highly conductive and flexible thermal interface material.

Graphene and graphite have been widely studied because of their exceptional mechanical and thermal properties. 'Flake graphite' is the most valuable and desired shape for the rapidly growing and coupled electric vehicle and Li-ion battery markets. Here, we report a simulated solar process that produces a synthetic turbostratic graphite in cylindrically curved form, i.e., cylindrical graphite. The solar-thermal synthesis process involves a photolytic methane pyrolysis variant that offers sustainable and scalable manufacturing with high carbon purity. External elemental testing of multiple samples has revealed that the samples produce at least 99.7% carbon; hydrogen is the only measurable trace species. Our preliminary results on coalesced cylindrical graphite fiber groups suggest that the effective thermal conductivity is above 100 W/mK, even without extensive process refinement to improve crystallinity. Moreover, cylindrical graphite fibers offer high bending flexibility and the ability to coalesce covalently. Importantly and in contrast to the predominant processing of electronics and electronics packaging materials, the synthesis approach reported here offers minimal environmentally degrading impacts and is essentially an emissions-free green manufacturing process. 

This study uses solar-thermal photolytic cylindrical graphite deposition by methane decomposition to produce high-quality cylindrical graphite on carbon fiber veils that can be used as a thermal interface material. Cylindrical graphite exhibits high thermal conductivity due to the high purity and crystallinity of the deposited material. Scanning electron microscopy results demonstrate the formation of cylindrical graphite on the carbon fiber veil. X-ray diffraction results identify the crystallographic structure of deposited material. Raman spectroscopy confirms the formation and quality of graphite on surfaces. A one-dimensional steady-state copper reference bar method measures thermal resistances and effective cross-plane thermal conductivities. The thermal diffusivity of the cylindrical graphite is estimated by a one-dimensional room-temperature modified Angstrom’s method in Cartesian coordinates that can then be used to derive the effective thermal conductivity. The overall performance of this insertable thermal interface material is competitive with state-of-the-art alternatives. This study provides foundational results on the fabrication, chemical, and thermal characterization of solar-thermal cylindrical graphite thermal interface materials.

Presenting Author: Min Jong Kil University of California, Los Angeles

Presenting Author Biography: Min Jong Kil received a B.S. degree in the Manufacturing Systems and Design Engineering department from Seoul National University of Science and Technology, Seoul, Republic of Korea and Northumbria University, Newcastle, UK, in 2020, the M.S. degree in Mechanical Engineering from the University of California, Los Angeles (UCLA), CA, USA, in 2021. He is currently pursuing a Ph.D. degree in Mechanical Engineering from UCLA, CA, USA and joined Nanoscale Transport Research Group (NTRG). In NTRG, his current research focus is the solar-thermal graphite synthesis of the heat spreader and thermal interface materials for electronics cooling.

Authors:

Min Jong Kil University of California, Los Angeles
Timothy Fisher University of California, Los Angeles