Graphene thermal conductivity
Thermal transport in graphene is a thriving area of research, thanks to graphene's extraordinary heat conductivity properties and its potential for use in thermal management applications.
The measured thermal conductivity of graphene is in the range 3000 - 5000 W/mK at room temperature, an exceptional figure compared with the thermal conductivity of pyrolytic graphite of approximately 2000 W⋅m−1⋅K−1 at room temperature. There are, however, other researches that estimate that this number is exaggerated, and that the in-plane thermal conductivity of graphene at room temperature is about 2000–4000 W⋅m−1⋅K−1 for freely suspended samples. This number is still among the highest of any known material.
Graphene is considered an excellent heat conductor, and several studies have found it to have unlimited potential for heat conduction based on the size of the sample, contradicting the law of thermal conduction (Fourier’s law) in the micrometer scale. In both computer simulations and experiments, the researchers found that the larger the segment of graphene, the more heat it could transfer. Theoretically, graphene could absorb an unlimited amount of heat.
The thermal conductivity increases logarithmically, and researchers believe that this might be due to the stable bonding pattern as well as being a 2D material. As graphene is considerably more resistant to tearing than steel and is also lightweight and flexible, its conductivity could have some attractive real-world applications.
But what exactly is thermal conductivity?
Heat conduction (or thermal conduction) is the movement of heat from one object to another, that has a different temperature, through physical contact. Heat can be transferred in three ways: conduction, convection and radiation. Heat conduction is very common and can easily be found in our everyday activities - like warming a person’s hand on a hot-water bottle, and more. Heat flows from the object with the higher temperature to the colder one.
Thermal transfer takes place at the molecular level, when heat energy is absorbed by a surface and causes microscopic collisions of particles and movement of electrons within that body. In the process, they collide with each other and transfer the energy to their “neighbor”, a process that will go on as long as heat is being added.
The process of heat conduction mainly depends on the temperature gradient (the temperature difference between the bodies), the path length and the properties of the materials involved. Not all substances are good heat conductors - metals, for example, are considered good conductors as they quickly transfer heat, but materials like wood or paper are viewed as poor conductors of heat. Materials that are poor conductors of heat are referred to as insulators.
How can graphene’s exciting thermal conduction properties be put to use?
Some of the potential applications for graphene-enabled thermal management include electronics, which could greatly benefit from graphene's ability to dissipate heat and optimize electronic function. In micro- and nano-electronics, heat is often a limiting factor for smaller and more efficient components. Therefore, graphene and similar materials with exceptional thermal conductivity may hold an enormous potential for this kind of applications.
Graphene’s heat conductivity can be used in many ways, including thermal interface materials (TIM), heat spreaders, thermal greases (thin layers usually between a heat source such as a microprocessor and a heat sink), graphene-based nanocomposites, and more.
The latest graphene thermal news:
Graphene foam assists in building a "thermal switch" that dynamically moderates heat of electronic devices
lithium ion batteries used in extreme heat or cold can be prone to malfunctions and low performance. Purdue University engineers have developed a solution: a "thermal switch" made of compressible graphene foam, that dynamically adjusts to temperatures both inside and outside the device to maintain consistent thermal management.
“As electronic devices get smaller and more powerful, managing heat becomes a more crucial issue,” said Xiulin Ruan, professor of mechanical engineering, who studies nanoscale heat transfer and sustainable energy. “Most devices use passive thermal management, such as conduction and convection, to move excess heat. But this system isn’t tunable or adjustable, and doesn’t help at all in cold conditions.”
ZTE recently launched the Axon 30, which reportedly uses a graphene-based cooling system. To be exact, the phone is said to have a “triple ice cooling system” comprising a large VC cooling plate, high power thermal gel, and graphene copper-based composite material.
The Axon 30 is launching first in China, but ZTE says “the global version is coming soon.”
Korea-based Charmgraphene has started to mass produce CVD graphene, using its proprietary roll-to-roll process.
CharmGraphene's R2R production system can produce 2 meters of CVD graphene per minute (maximum width 300 mm). According to CharmGraphene, its current CVD graphene capacity is about 8,000 sqm per month. The company says it uses use 6 um thick copper foil which reduces copper foil etching time dramatically compare to 35 um thickness copper foil used by other companies.
South Korea-based Graphene Square, developer and distributor of graphene materials and films, has announced that it is preparing for an IPO to fuel global expansion. It will select the underwriter this year and plans its Kosdaq listing in 2022 through the Technology Special Listing program, a system introduced in 2005 to allow promising startups to list the local bourse based on a technology evaluation conducted by Korea Exchange-designated institutions.
Graphene Square’s competitive edge is said to be found in its proprietary chemical vapor deposition (CVD) method used for the production of graphene. The method is based on the research of Professor Hong Byung-hee of Seoul National University on the synthesis of large-area graphene. In fact, Graphene Square itself was established in 2012 as a spin-off of chemistry professor Hong Byung-hee’s lab at Seoul National University.
Our friend Dr. Khasha Ghaffarzadeh, a well respected graphene market analyst, is launching a new service called TechBlick that is a subscription-based online and all-year round event focused on advanced materials such as graphene, 2D materials, CNTs, boron nitrides, QDs, and more.
Graphene-Info partnered with TechBlick, to provide our readers an exclusive 25% discount on the TechBlick subscription. We took advantage of this launch to discuss the graphene market and industry with Dr. Ghaffarzadeh and also discuss the new service.
Hello Kasha. How do you see the graphene market shaping up in 2021?
I have closely followed and examined the graphene industry for a full decade. The landscape has certainly changed. Many companies have come and gone, and many once considered revolutionary applications are now ruled out, but overall, the industry is now at a tipping point.
We think 2021/2022 will be a turning point, setting the industry on its growth path, despite the delays caused these past 12 months due to Covid. For some, these delays have been painful as projects were pushed back or partners or customers dropped graphene to focus on other core areas. Many undershot their growth expectations, and some had difficult cash flow situations.