PORTLAND, Ore. —Light-emitting-diodes (LEDs), once quoted to have 100,000-hour lifetimes, are still working today in some front-panel indicators after 30 years of service. But the advent of high-intensity LEDs for solid-state lighting sacrifices longevity by operating at temperatures too high for lifetimes much longer than a few years.
Now Oak Ridge National Laboratory (ORNL) claims to have rolled back the calendar on LEDs with a graphite foam material that keeps even high-intensity LEDs as cool as those used for front-panel indicators, thereby reclaiming their long lifetimes. ORNL recently granted an exclusive license for their graphite foam technology to LED North America (Oak Ridge, Tenn.) an ORNL-spinoff located in the adjacent Technology 2020 "incubator" park.
According to ORNL, decreasing the operating temperature by 10 degrees can double the lifetime of LEDs. As a result, municipalities can change over their existing mercury-vapor lamps for LEDs to save millions on their electricity bill without suffering premature failures due to overheating. As a result of their cool-running graphite foam heat sinks, LED N.A. aims to offer retrofits for street lights and parking garage lighting with warrantees that are longer than its competitors.
ORNL researcher James Klett developed a graphite foam technology that can help cool LED light fixtures and extend their lifespan.
Graphite foam is light and porous like Styrofoam—with 25 percent density—making it easy to machine into heat sinks, but with the vastly superior thermal conductivity afforded by the pure-carbon material compared to conventional metal heat sinks. Ligaments in the foam "wick" heat away from its source, according to ORNL, rather than just heat up with the LED like a conventional heat sink.
[" which have been estimated to exhibit thermal conductivity greater than 1700 W/mK (2300 W/mK at cryogenic temperatures) as compared to copper at 398W/mK."]
Copper is now far too costly, and Al is also energy intensive.
[" A finned heat sink made from graphitic foam can be up to 3 times more efficient than one made of Al "]
I see Carbon Foams are electrically conductive, which is a problem, but maybe they can manage a large area insulation step ?
The holy grail would be high thermal conductivity _and_ electrical insulation.
I suppose this is the next best thing compared to CVD Diamond as for heatsinking. I would like to know more about reworking and (also pointed by @hm) physical behaviour over time.
@RoboticDeveloper, the ThetaJ(x) numbers can be estimated from the thermal conductivity numbers already published. Are you looking for the JEDEC-defined (1ft cube) numbers?
@Kinnar, the industry has used graphite's superior properties before, though not to the scale I would like to see. StableCor is one such material that is used in PCB cores and a number of power electronics companies use it.
Dr. MP Divakar
Graphite Ligament Thermal Conductivity 1700 W/mK Apparent bulk conductivity 180 W/mK Low CTE -~2 -4 µin/in/°C Excellent thermal management material
This is 3 to 5 times more efficient compared to Aluminium
More technical information available at poco graphite website www.poco.com
Many applications can take advantage of this material. Is this material RoHS compliant? If it is employed in product, will product be green and can be exported to EU market? What is the maximum operating temperature for this material? If it is exceeded in normal operation, will it permanently damage and change its heat sink property drastically?
I am thinking that this will be great for the energy savings and lowered maintenance costs. The early failures of LEDs due to heat my explain why the almost brand new LED street lights in my town have failed LEDs at less than a year old. It would be nice if the article gave a little more detail like the ThetaJ numbers of the material. Thanks for an interesting bit of hot news.
The world has got a new heat sink, this can be used for other applications as well. Simultaneously it is a very good news for domestic and industrial lighting as well as for energy conversation. Going towards green earth..
Yeah! It is great to know about this graphite foam heat sinking technology. I understand from this article how this could be very useful for heat sinking the high-intensity LEDs. Can this also be used for heat-sinking the chips on board, as an alternative solution to the aluminium/copper heat-sinking? It is mentioned in this article that the conductivity provided by graphite foam is superior to that provided by the metal heat-sinks. What are the other advantages / drawbacks of graphite foam vs. aluminium/copper heat sinking methods?
January 2016 Cartoon Caption ContestBob's punishment for missing his deadline was to be tied to his chair tantalizingly close to a disconnected cable, with one hand superglued to his desk and another to his chin, while the pages from his wall calendar were slowly torn away.122 comments