Chalk up another valuable use of carbon nanotubes -- creating the darkest material on Earth. Last month researchers at Rice College and Rensselaer Polytechnic Institute in New York used the handy carbon molecular structures to set an unusual world record -- the record for the most light-absorbing material known to man.
The key to the technology is atom-thick nanotubes. The tubes are arranged vertically on the surface, widely-spaced and standing on end, like the bristles of a paint brush. The key is the spacing. By widely spacing the tubes, light is able to enter the material, but then ends up trapped within the collection of thin tubes.
Project leader and Rensselaer physics professor Shawn-Yu Lin explains, "The loosely packed forest of carbon nanotubes, which is full of nanoscale gaps and holes to collect and trap light, is what gives this material its unique properties. Such a nanotube array not only reflects light weakly, but also absorbs light strongly. These combined features make it an ideal candidate for one day realizing a super black object."
To give an idea of exactly how black the result is, black paint reflects approximately 5 percent of the visible light that strikes it. The previous darkest material was a nickel-phosphorous compound, which only reflected 0.35 percent of visible light. The new nanotube compound blows away these previous competitors, reflecting a bare 0.045 percent of the visible light that hits it. This is almost nine times less than the previous record holder and over a hundred times less than black paint.
Scientist Richard Massey, a dark matter expert at the California Institute of Technology in Pasadena calls the material "very clever", but warns the public not to confuse it with dark matter. He explains that dark matter absorbs no light and somehow behaves as if transparent, allowing all light to pass through it. He contrasts this with the new material which "absorbs all light without reemitting/reflecting any—hence no light reaches us from it, and it appears dark."
The work was featured in the journal Nano Letters. The team also applied for a Guinness World Record for the blackest material.
The first possible business application considered by Rice and RPI was solar power. Despite the recognition, though, the solar industry remains relatively lukewarm to the new material. While a few companies such as SolFocus contacted the team, others like Marc Cortez, executive vice president of sales and marketing at Soliant Energy were skeptical about the technology. Mr. Cortez stated doubts about whether the technology could make an impact, stating, "The ultimate challenge will be to take it from the lab into a high-volume manufacturing environment. It’s only then you’ll know whether or not it will be a 'game-changing' technology."
With the solar power industry not warming up enough to the new technology, a new group has jumped in to court Rice and RPI -- the U.S. Military. The Military, according to Popular Science, approached the researchers with interest in using the technology. The Military, which is investigating a number of nanotube applications, expressed hopes for employing the technology to make its B-2 stealth bombers even stealthier. By using the material, the B-2s would be capable of absorbing even more radar, making them more difficult to spot. The military is excited about how the new material could revolutionize its stealth efforts, making its arsenal deadlier and more efficient than ever.
Meanwhile, Professor Yu-Lin is quick to remind people of the technology's more peaceful applications such as improving the efficiency of solar panels, which are typically coated in more reflective black paint. Another valuable application, he believes is using the material to line telescope barrels to provide a darker background to provide less interference with the focused celestial light.
One thing's for sure, whether it be for war or for peace, someone is certain to be interested in a commercial application of this exciting new nanotube material.
quote: How do the risks from exposure to different kinds of asbestos differ? Though chrysotile (white asbestos) has been used most widely, the greater potency of amphibole (blue and brown) asbestos to cause illness is generally recognised. Hodgson and Darnton in their scientific paper (2000) estimated the risk of mesothelioma and lung cancer by asbestos fibre type for a range of different exposure scenarios . This analysis suggests that on average blue asbestos has a risk about 500 times that of white asbestos for mesothelioma and 10-50 times as high for lung cancer. The equivalent risk ratio for brown asbestos is 100 for mesothelioma and the same as blue (10-50) for lung cancer.
quote: Is there a safe level of exposure below which there is no risk? Mesothelioma There is a lack of scientific consensus as to whether there exists a threshold of exposure to asbestos below which a person is at zero risk of developing mesothelioma. However, there is evidence from epidemiological studies of asbestos exposed groups that any threshold for mesothelioma must be at a very low level – and it is fairly widely agreed that if a threshold does exists then it cannot currently be quantified. For practical purposes HSE does not assume that such a threshold exists. Asbestosis and lung cancer The situation for lung cancer and asbestosis is uncertain. Arguments for a threshold for lung cancer are based on the notion of the carcinogenic process being an extension of the chronic inflammatory processes producing fibrosis. It is generally recognised that heavy doses of white asbestos are required to produce clinically significant lung fibrosis. However, the situation for blue and brown asbestos is more uncertain and fibrosis has been observed at much lower exposures. This also suggests that if a threshold for lung cancer does exist for blue and brown asbestos it must be at a very low level indeed.