Archive for the ‘materials science’ Category

Fractal structure produces fractal electrons with fractal energies

December 2nd, 2018

Fractals are a source of endless fascination to me. Life itself relies on many of the concepts of fractals: trees are fractal, as are feathers, coast lines, and many other things in nature. Indeed, it was the realization that landscapes are fractal that made modern animated films possible.

But, what about fractional dimensions in quantum mechanics? It turns out that electrons in a Sierpiński gasket are also fractal, and that has some pretty cool consequences.

A fractal is a weird beast. A line is 1D, a square is 2D, and a cube is 3D: dimensions come in integer quantities. Except they don't. For instance, it is possible to create a shape that has a finite area, but a perimeter that is infinitely long (the construction of such a shape is pictured below). A shape with these properties does not behave like a 2D object, but it's not a 3D object. Instead, it is a two-and-a-bit-D object. That is a fractal.

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Posted in electron wave function, fractals, materials science, Physics, science | Comments (0)

High-density lithium in graphene: An intriguing battery possibility

November 29th, 2018
High-density lithium in graphene: An intriguing battery possibility

Enlarge (credit: Getty Images)

Discussions about batteries often revolve around energy density. What we want is a battery that stores a whole lot of energy in a very tiny volume, preferably in a manner that doesn't involve explosions or fire. At the cutting edge of research, what we get are batteries that are a mix of amazing and amazingly bad.

Modern batteries are, quite frankly, a miracle compared to ye olde lead acid battery. Yet they still contain less energy per unit mass than the equivalent mass of wood. Essentially, we simply don’t pack enough atoms into a small enough volume to compete with hydrocarbons. But, now it seems that graphene—it’s always graphene—might help pack lithium in.

The invisible metal

Although there are many ways to make a lithium-ion battery, the chemistry boils down to the following: lithium is stored in some form at one electrode. The lithium is released as an ion, where it travels to another electrode and reacts. At the same time, the electrons that complete the reaction travel out into the world via one electrode, do some work, and end up at the other electrode, where they complete the reaction.

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Posted in graphene, lithium-ion batteries, materials science, science, transmission electron microscope | Comments (0)

Ion drive meets drone, as small plane flies with no moving parts

November 21st, 2018
Ion drive meets drone, as small plane flies with no moving parts

Enlarge (credit: Nature)

The Johnson Indoor Track at MIT probably won't go down in history in the same way as Kitty Hawk has, but it was the scene of a first in powered flight. A team of researchers has managed to build the first aircraft powered by an ionic wind, a propulsion system that requires no moving parts. While the flight took place using a small drone, the researchers' calculations suggest that the efficiency of the design would double simply by building a larger craft.

Ionic wind

In conventional aircraft, air is pushed around by moving parts, either propellers or the turbines within jet engines. But we've known for a while that it's also possible to use electrical fields to push air around.

The challenge is that air is largely made of uncharged molecules that don't respond to electric fields. But at sufficiently high voltages, it's possible to ionize the nitrogen and oxygen that make up our atmosphere, just as lightning does all the time. The electrons that are liberated speed away, collide with other molecules, and ionize some of them as well. If this takes place in an electric field, all those ions will start moving to the appropriate electrode. In the process, they'll collide with neutral molecules and push them along. The resulting bulk movement of atmospheric molecules is called an ionic wind.

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Posted in engineering, FLIGHT, ion drive, ionic wind, materials science, science | Comments (0)

Memristors built with 2-nanometer-thick parts

November 14th, 2018
Image of the crossbar array.

When two blocks are set down on top of each other, they're oriented so that they have nine intersections. (credit: Pi et al.)

Phase-change memory seems to offer the best of both worlds: the speed of current RAM with the permanence of a hard disk. While current implementations are too expensive for widespread use, researchers have been doing interesting things with test hardware. Its distinct properties have allowed people to perform calculations and train neural networks, all in memory. So finding out how to make phase-change memory more efficient could open some new approaches to computing.

This week, a collaboration between scientists at the University of Massachusetts, Amherst and Brookhaven National Lab is publishing a paper describing how it made a tiny set of memristors that acts similarly to phase-change memory. The features of the memory are only two nanometers across, and they can be separated by as little as 12nm—below the cutting edge of processor manufacturing. The down sides? So far, the team has only made nine bits at a time, and they're made using platinum.

On the grid

Key to this new work are tiny sheets of platinum only two nanometers thick—that's just over 11 atoms of the element. While platinum is rather pricey, the thin sheets provide extremely low resistance. The researchers measured each sheet at about 10,000 times less than the expected resistance of a similar-thickness carbon nanotube. And the authors say they can manufacture the sheets in the appropriate dimensions with a 100 percent efficiency.

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Posted in materials science, memory, Memristor, science | Comments (0)

New material could up efficiency of concentrated solar power

October 19th, 2018
New material could up efficiency of concentrated solar power

Enlarge (credit: OPIC)

With the price of photovoltaics having plunged dramatically, solar is likely to become a major contributor to the electrical generating mix in many countries. But the intermittent nature of photovoltaics could put a limit on how much they contribute to future grids or force us to develop massive storage capabilities.

But photovoltaics aren't the only solar technology out there. Concentrated solar power uses mirrors to focus the Sun's light, providing heat that can be used to drive turbines. Advances in heat storage mean that the technology can now generate power around the clock, essentially integrating storage into the process of producing energy. Unfortunately, the price of concentrated solar hasn't budged much, and photovoltaics have left it in the dust. But some materials scientists may have figured out a way to boost concentrated solar's efficiency considerably, clawing back some of photovoltaics' advantage.

Feel the heat

Solar thermal revolves around transfers of heat. Sunlight is used to heat up a working fluid at the mirrors' focus. That then transfers the heat either to a storage system or directly to another fluid that is used to drive a turbine—typically steam. Higher temperatures typically mean more work can be extracted, making the efficiency of these transfers critical.

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Posted in concentrated solar, materials science, renewable energy, science, Solar energy | Comments (0)

Conditions like those inside Neptune cause diamond formation

August 27th, 2017

Enlarge / That lovely blue exterior could be hiding a heart of diamond. (credit: NASA)

Carbon, oxygen, and nitrogen are some of the easiest heavier elements to form through fusion. As a result, they’re common in our Solar System, typically found combined with hydrogen to make ammonia, water, and methane. In the gas and ice giants of the outer Solar System, however, these chemicals are placed under extreme pressures, where chemistry starts to get a bit weird. Do these chemicals survive the crushing interiors of these planets?

One intriguing idea is that methane doesn’t survive. As pressure and temperature increase, methane should start condensing into more complex hydrocarbons. Then, as pressures increase further, calculations indicate the hydrogen and carbon should separate out, leaving pure carbon to sink to the depths of these planets. As a result, it’s been hypothesized that, close to their core, planets like Neptune and Uranus have a layer of pure diamond.

While some evidence supporting this theory has surfaced over the years, it’s been hard to precisely replicate the temperatures and pressures found inside the planets. Now, new work done at the SLAC X-ray laser facility supports the idea that these planets are full of diamonds. But the work indicates the diamonds only form at greater depths than we’d previously thought.

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Posted in astronomy, chemistry, diamonds, laser, materials science, planetary science, science | Comments (0)

Carbon nanotube “yarn” generates electricity when stretched

August 24th, 2017

Enlarge / When the yarn is stretched, the LED lights up. (credit: AAAS/Science)

Spare energy is all around us, from the pressure exerted by every footfall to the heat given off by heavy machinery. In some cases, like regenerative braking in cars, it’s easy to harvest, and the equipment needed to do so is simple and economic. In many others, however, we’re not there yet.

It’s not that we don’t have the materials to do so. Piezoelectric generators can harvest stresses and strains, while triboelectric generators can harvest friction, to give two examples. The problem is that their efficiency is low and the cost of the materials is currently high, making them bad fits for any applications.

But a study in today’s issue of Science describes a “yarn” made of carbon nanotubes that can produce electricity when stretched. Its developers go on to demonstrate its use in everything from wearable fabrics to ocean-based wave power generators. Given that the raw material for carbon nanotubes is cheap and there are lots of people trying to bring their price down, this seems to have the potential to find some economic applications.

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Posted in carbon nanotubes, Energy, materials science, science | Comments (0)

New surface is so slippery, shellfish can’t get a grip

August 19th, 2017

Enlarge / A sticky situation. (credit: University of Washington)

When engineers look at mussels, they’re typically looking in awe at how they anchor themselves to nearly every surface imaginable, all while under water. The fibers they use to attach themselves are incredibly strong, and the adhesive works wet or dry on all sorts of materials. For the most part, engineers are looking to create a substance with similar properties.

This week, however, brings an exception: engineers who want to try to keep mussels from sticking to everything. Zebra mussels, a species that has invaded the Great Lakes, is estimated to cost utilities hundreds of millions of dollars each year due to clogged pipes and intakes. Ships, buoys, and pretty much anything else we put in the water also ends up needing to have mussels cleared off.

The international team behind the new work has designed a material that mussels can’t seem to get a grip on. It’s not because the mussel’s adhesive fail; instead, the mussel itself doesn’t seem to know what it’s touching when it’s set down on the material.

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Posted in adhesives, Biology, materials science, science | Comments (0)

Researchers use lasers to weld spider silk to kevlar

August 16th, 2017

Enlarge (credit: National Park Service/J Schmidt)

Spider silk has some amazing material properties, so there’s lots of enthusiasm for the prospect of using it to make something useful. Unfortunately, spiders aren’t domesticated, and attempts to make the silk proteins in other organisms haven’t been entirely successful. And then there’s the matter of what to do with silk once you have it. It doesn’t always cooperate with modern manufacturing techniques.

But some researchers in India figured out a way to get spider silk to play nicely with lasers. Under the right conditions, the silk itself helps amplify a laser’s power, to the point where it can either cut the silk in specific locations, or soften it to the point where it can be bent or welded.

The work relies on a physics effect termed “nonlinear multiphoton interactions.” In the simplest terms, the effect allows two photons of a given energy to act as a single photon of twice the energy (higher combinations are also possible). It’s a nonlinear effect, since it involves a sudden jump in energy; you don’t end up with any photons in between, at 1.5x the original energy.

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Posted in Biology, lasers, materials science, science, spider silk | Comments (0)