本帖最后由 shsihen869 于 2010-12-15 16:58 编辑

号称使用寿命可达1万小时的 LED ,在一些汽车的前仪表板做为指示灯已经服务超过30年；但后来出现的固态照明应用高亮度LED （high-intensity LEDs），却因为运作在温度太高的环境而牺牲了好几年的使用寿命。　　美国橡树岭国家实验室（Oak Ridge NATIONal Laboratory,ORNL）的研究人员最近宣布，他们已经利用一种石墨泡沫（graphite foam）材料，让LED的寿命能更进一步延长，甚至能让高亮度LED的运作温度降到像仪表板LED指示灯那样的水准，使它们用得更久。ORNL最近已将该石墨泡沫技术独家授权给由该实验室独立而出的公司──LED North America.
　　ORNL表示，将LED运作温度降十度，就能让其使用寿命延长一倍；如此各地方zheng fu 就能够将现有的水银路灯换成LED灯，以节省高达数百万美元的电费，又不须负担LED灯可能过热的技术不成熟风险。未来LED North America则打算利用低温运作的石墨泡沫散热片，提供新一代的路灯、车库灯解决方案，而且使用寿命又比其他竞争产品来得更长。
　　石墨泡沫类似发泡塑胶（Styrofoam），重量轻且多孔，密度为25%;这使得该种材料很容易制作成散热片。这种纯碳材料制成的散热片，导热性能据说远优於传统的金属散热片；ORNL表示，该种泡沫「芯（wick）」的韧带（ligament），原本就是绝热的，而不是像传统散热片那样会跟LED一起升高温度。

The technique for fabricating high thermal conductivity pitch-based graphitized carbon foams was developed and patented at ORNL under the direction of the U.S. Department of Energy (DOE) Office of Transportation Technologies. This technique produces an open-celled material. The cell or pore walls consist of highly oriented graphite planes, similar to high performance carbon fibers, 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. The open porous structure yields a relatively large specific surface area (>20 m2/g), 100 times greater surface area than typical heat exchangers. This leads to extremely efficient and lightweight heat exchangers. A finned heat sink made from graphitic foam can be up to 3 times more efficient than one made of Al, with 1/5th the weight. This is effectively 5 times more efficient per gram of heat sink High chemically stability, small pore size (60 µm), high surface area (>20,000 m2/m3), and high thermal conductivity with porosities of up to 90% make graphitic foams ideal for use in advanced cooling and heat storage applications. Graphitic foam is dimensionally stable and can be readily machined. The material is an excellent electromagnetic shield as it effectively reflects RF energy. It can also be used to control acoustic signature as the foam absorbs sound efficiently, even in the non-thermally conductive form. The technology to manufacture pitch-based carbon foam as developed at ORNL is currently licensed by Poco Graphite, Inc and Koppers Inc.

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