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:
Huawei has launched its Huawei P40 flagship phone family, that includes three different devices: the Huawei P40, Huawei P40 Pro and, a new addition to the line-up for 2020, the Huawei P40 Pro Plus.
After many rumors about this line sporting a graphene battery - which were later disproved - it appears that Huawei's new P40 phones are using a graphene film cooling technology for heat management purposes (Huawei's SuperCool system), much like the Mate 20X and P30 line that preceded the P40.
Researchers from Swinburne University developed a graphene-based highly efficient solar absorbing film that absorbs sunlight with minimal heat loss. The film rapidly heats up in an open environment and has great potential in solar thermal energy harvesting systems - in addition to other applications such as thermophotovoltaics (directly converting heat to electricity), solar seawater desalination, light emitters and photodetectors.
This is the 2nd-generation material developed by the same group - now with a thickness of only 30 nm and improved performance and longer lifetime. The researchers have now created a first prototype and also suggest a scalable low-cost manufacturing process.
When speaking of graphene in terms of commercialization, the general impression is that "a killer application has not yet been found". While this is not a false concept, it does not do justice with the now-budding graphene world. It can easily be stated that many graphene applications are being developed. This has been true for years, but various commercial products are starting to pop up, hopefully heralding the beginning of a more steady stream of commercialization.
Among these applications, one can point to cooling technology like Cryorig's CPU cooling system or Huawei's Mate 30 X smartphone, which sports a graphene film cooling technology. Various footwear and sports equipment products have also been launched, along with more technical products like oil additives and coatings. The list goes on and on, and there are even graphene-enhanced sanitary napkins on the market!
PC gear company Cryorig has introduced its low-profile CPU graphene-enhanced cooling system for small form-factor PCs that can dissipate up to 125 W. The Cryorig C7 G is among the smallest coolers for higher-end processors available today. To make C7 G's high performance possible, Cryorig applied graphene coating on the heatsink.
As demands arise for higher-performance components, cooling designers are creating low-profile coolers rated for TDP levels of 95 W of higher. To maximize efficiency of such devices, manufacturers use copper for heatsinks, many heat pipes, and large fans. Cryorig decided to go one step further and applied graphene coating to the radiator’s fins. Thermal conductivity of graphene is considerably higher than thermal conductivity of aluminum or copper, so applying it on the fins could theoretically improve cooling performance.
Applied Graphene Materials recently added new adhesive materials to their portfolio, aimed at the Space and Defense sectors. These are said to be two unique graphene-enhanced thermally conductive epoxy paste adhesive systems, called AGM TP300 and AGM TP400
These novel epoxy adhesive systems reportedly exhibit high levels of thermal conductivity (between 3 and 6 W/mK), combined with excellent mechanical, adhesive and outgassing performance. Most significantly these properties are achieved with cured resin densities as low as 40% that of competitive conductive adhesives on the market. AGM’s TP 300/400 products are therefore highly versatile, while providing end users with significant savings in both mass and cost.