Session: 16-01: Poster Presentations

Paper Number: 142134

142134 - Solar-Thermal Photocatalytic Cylindrical Graphite for Thermal Interface Materials 

Abstract: 

Modern computing devices, such as those used in artificial intelligence algorithms, generate high heat fluxes, accelerating performance degradation and failure. This generated heat must be efficiently dissipated to a heat spreader or sink. However, voids 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 scalable manufacturing and high carbon purity. External elemental testing of multiple samples has revealed that the samples produce at least 99.7% carbon; the only measurable trace species are hydrogen and nitrogen. Our preliminary results on consolidated 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. 

In this study, solar-thermal photolytic cylindrical graphite deposition by methane decomposition is used to produce high-quality cylindrical graphite on fibers and carbon nanotube paper 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. Field emission scanning electron microscopy demonstrates the formation of cylindrical graphite on the substrate. Energy dispersive x-ray spectroscopy results identify elemental carbon on pre-treated and processed carbon-based substrates. Raman spectroscopy confirms the formation and quality of graphite on surfaces. A one-dimensional steady-state copper reference bar method is employed to measure thermal resistances. The thermal diffusivity of the cylindrical graphite is measured by a one-dimensional room-temperature modified Angstrom’s method, which 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 thermal interface materials. 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 the 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