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Living in a "Nano" World

July 24, 2009


When people hear the term nanotechnology, they either think of a brighter future helped along through the introduction of new materials or a gloomy one in which molecular manufacturing (MM) destroys the world. Worries about the latter scenario are expressed on the website of the Center for Responsible Nanotechnology:

“Molecular manufacturing (MM) will be a significant breakthrough, comparable perhaps to the Industrial Revolution—but compressed into a few years. This has the potential to disrupt many aspects of society and politics. The power of the technology may cause two competing nations to enter a disruptive and unstable arms race. Weapons and surveillance devices could be made small, cheap, powerful, and very numerous. Cheap manufacturing and duplication of designs could lead to economic upheaval. Overuse of inexpensive products could cause widespread damage. Attempts to control these and other risks may lead to abusive restrictions, or create demand for a black market that would be very risky and almost impossible to stop; small nanofactories will be very easy to smuggle, and fully dangerous. There are numerous severe risks—including several different kinds of risk—that cannot all be prevented with the same approach. Simple, one-track solutions cannot work. The right answer is unlikely to evolve without careful planning.”

The Center also admits that “the potential benefits of molecular manufacturing are immense.” Not all nanotechnology involves the creation of machines. As noted above, some nanotechnology involves the creation of new materials that could help solve some of the vexing problems currently facing society [“The power of being made very small,” The Economist, 4 July 2009 print issue].

“Big improvements in the production of energy, especially from renewable sources, are expected over the coming years. Safer nuclear-power stations, highly efficient solar cells and the ability to extract more energy from the wind and the sea are among the things promised. But important breakthroughs will be needed for these advances to happen, mostly because they require extraordinary new materials. The way researchers will construct these materials is now becoming clear. They will engineer them at the nanoscale, where things are measured in billionths of a metre. At such a small size materials can have unique properties. And sometimes these properties can be used to provide desirable features, especially when substances are formed into a composite structure that combines a number of abilities. A series of recent developments shows how great that potential might be.”

The article goes on to discuss the work of Michael Demkowicz of the Massachusetts Institute of Technology, whose approach to nanotechnology involves specifying “a set of desired properties and then trying to predict the nanostructures needed to deliver them.” He is currently working with the Los Alamos National Laboratory to develop a material that could replace the stainless steel liners currently used in nuclear reactors.

“[The new material] would extend the reactor’s working life and allow it to be operated more efficiently by burning a higher percentage of nuclear fuel. At present, says Dr Demkowicz, reactors burn only around 1% of their fuel, so even a modest increase in fuel burn would leave less radioactive waste. The reason why the linings of nuclear reactors degrade is that metals can become brittle and weak when they are exposed to radiation. This weakness is caused by defects forming in their crystal-lattice structure, which in turn are caused by high-energy particles such as neutrons bumping into individual atoms and knocking them out of place. When these displaced atoms collide with other atoms, the damage spreads. The result is holes, or ‘vacancies’, and ‘interstitials’, where additional atoms have squeezed into the structure. Dr Demkowicz says it is possible to design nanocomposites with a structure that resists radiation damage. This is because they can be made to exhibit a sort of healing effect in the areas between their different layers. The thinner these layers are, the more important these interfaces become because they make up more of the total volume of the material. Depending on how the nanocomposites are constructed, both the vacancies and the interstitials get trapped at the interfaces. This means there is a greater chance of their meeting one another, allowing an extra atom to fill a hole and restore the crystal structure. In some conditions the effect can appear to show no radiation damage at all, he adds. The ideal nanocomposite would not only resist radiation damage. It would also not itself become radioactive by absorbing neutrons.”

Material for nuclear reactors is not the only way that new materials could help improve the energy sector. The article notes that “nano-engineered materials will also play an important role in a more efficient generation of solar cells.”

“The desired effects are obtained by using combinations of material produced at extremely small sizes. In this case, they are used to make ‘multi-junction’ solar cells, in which each layer captures energy from a particular colour in the spectrum of sunlight. Overall, this is more efficient than a conventional solar cell which converts energy from only part of the spectrum. Whereas conventional solar cells might turn 20% or so of the energy in sunlight into electricity, multi-junction solar cells already have an efficiency of just over 40% and within a decade that could reach 50%.”

Like many cutting-edge technologies, however, the cost of producing some of these new materials is currently too high to make them commercially feasible. In some cases, the strength and durability of some new materials will help offset some of their initial costs but probably not all of them. The article continues:

“The nanostructure of composites can also provide great mechanical strength in relatively light materials. Composites such as fibreglass and carbon fibre bonded in a plastic resin are already widely used to replace metal in making, for instance, cars and aircraft. But by controlling the direction and the tension of the fibres during their construction it is possible to produce a morphing composite, which adjusts its shape under certain conditions. The change can be instigated by an external control or it can be automatic, for instance in response to variations in heat, pressure or velocity. These morphing composites could be used to produce more efficient turbine blades in wind and tidal generators.”

In an accompanying article, The Economist noted that sometimes it’s difficult to do better than nature [“Plumage power“]. Scientists, for example, have been researching ways to create a material that will efficiently store hydrogen, which will be critical if we ever move to a hydrogen economy.

“Hydrogen is difficult to store because it is the lightest element. Filling a typical fuel tank of 75 litres—about 20 American gallons—with hydrogen at room temperature and pressure will take a hydrogen-powered car only about a kilometre or so. The gas can be compressed to take up less space, but that can be dangerous. It also uses energy, which removes some of the benefits. … [One solution to this problem is] to put something inside the tank which increases the total internal surface area to which the molecules of the gas can cling. This means more hydrogen can then be packed into a smaller volume. There has been some progress with materials that can do this, including specially engineered carbon nanotubes. But carbon nanotubes are very expensive to make, especially in large quantities. Richard Wool, a chemical engineer at the University of Delaware, estimates the cost of fitting a single car with a tank full of carbon nanotubes to be $5.5m. Other materials might do, but they could still end up costing over $20,000 a car.”

Enter the lowly chicken. Dr. Wool believes that the cost of creating an automobile hydrogen storage tank could be reduced to about $200 by stuffing the tank with chicken feathers.

“The fibres in feathers are almost entirely composed of keratin, a protein also found in hair and nails. When heated in the absence of oxygen (a process called pyrolysis), keratin forms hollow tubular structures six millionths of a metre across and riddled with microscopic pores, much like carbon nanotubes.”

Because the feathers need to be strengthened and heated, you just can’t pluck a chicken and then stuff untreated feathers in a tank. Besides having to use treated chicken feathers, a feather-filled tank has other challenges as well — one of which is size.

“[A treated feather is] capable of holding 1.5% of its weight in hydrogen. Since about 4.5kg of the gas is needed to cover 480km (about 300 miles), the typical range of a petrol-powered car, this would translate into a rather large 284-litre tank stuffed with some 300kg of carbonised chicken feathers, according to Mr Senöz. This still falls short of the 6% hydrogen-storage target which has been set by America’s Department of Energy to encourage innovation with alternative fuels. But the researchers think they can improve their material further by making it even more porous. And unlike rival technologies theirs is well on the way to meeting the department’s cost criteria of a hydrogen system that costs $4 per kilowatt hour stored and less than $700 for installing it. Moreover, it could also help with another environmental problem: reducing the mountains of chicken feathers that the poultry industry has to dispose of every year.”

Treated chicken feathers, of course, aren’t the answer to every challenge that could be solved using new materials created by nanotechnology. Whether you welcome or fear the future nanotechnology, new materials are going to emerge. Like other technologies, we won’t really know how they will be used until they get into the hands of creative people. New materials will be put to uses that their creators never dreamed of. There has to be continued research on the potential environmental effects of nanoparticles. We really don’t know what having new nanoparticles floating around in the air could do plants, animals, or us. On the whole, however, I suspect that new materials will be a good thing.

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