Abstract
Natural graphite sheet (NGS) is compressible, porous, electrically and thermally conductive material that shows a potential to be used in fuel cells, flow batteries, electronics cooling systems, supercapacitors, adsorption air conditioning, and heat exchangers. We report the results of an extensive material characterization study that focuses on thermal conductivity, thermal diffusivity, electrical conductivity, coefficient of thermal expansion (CTE), compression strain, and emissivity. All the properties are density-dependent and highly anisotropic. Increasing the compression from 100 to 1080 kPa causes the through-plane thermal and electrical conductivities to increase by up to 116% and 263%, respectively. The properties are independent of the sheet thickness. Thermal and electrical contact resistance between stacked NGS is negligible at pressures 100 to 1080 kPa. In the in-plane direction, NGS follows the Wiedemann-Franz law with Lorenz number 6.6 times 10^{-6} W Omega K^{-2}. The in-plane CTE is low and negative (shrinkage with increasing temperature), while the through-plane CTE is high, increases with density, and reaches 33 times 10^{-6} K^{-1}. Microscope images are used to study the structure and relate it to material properties. An easy-to-use graphical summary of the forming process and NGS properties are provided in Appendices A and B.
Highlights
Natural graphite sheet (NGS) is compressible, porous, electrically and thermally conductive material that shows a potential to be used in fuel cells, flow batteries, electronics cooling systems, supercapacitors, adsorption air conditioning, and heat exchangers
Multiple other names are used in the literature to refer to NGS, such as compressed exfoliated natural graphite (CENG), graphite foil, or flexible graphite
We found the emissivity at wavelengths from 2 to 26 μm to decrease with density in the range 0.39 to 0.52
Summary
Natural graphite sheet (NGS) is compressible, porous, electrically and thermally conductive material that shows a potential to be used in fuel cells, flow batteries, electronics cooling systems, supercapacitors, adsorption air conditioning, and heat exchangers. Natural graphite sheet (NGS) is a compressible, porous, electrically and thermally conductive material that has been used primarily to make sealing gaskets because of its ability to conform to rough surfaces, withstand high temperatures, and resist corrosive fluids. It is used—or considered to be used—in numerous applications, including bipolar plates in fuel cells and flow batteries for its electrical conductivity and chemical stability[1,2,3], supercapacitors for its corrosion r esistance[4,5], adsorption cooling systems for its high thermal diffusivity[6], heat spreaders for its high in-plane thermal conductivity[7,8], heat exchangers for its thermal conductivity and corrosion resistance[9], and heat sinks for its thermal conductivity, low weight, and ease of forming into complex s hapes[10,11].
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