new tech

Finding superconductors that can take the heat

By studying how superconductors interact with magnetic fields, Pitt researchers advance quest for higher-temperature superconducting materials

Superconductors are materials with no electrical resistance that are used to make strong magnets and must be kept extremely cold--otherwise, they lose their superconducting abilities. Even the "high-temperature" superconductors discovered in the 1980s must be kept at around -300°F.

The search for superconductors that function at higher temperatures has taken a step forward with new findings from University of Pittsburgh professor of physics and astronomy Yadin Y. Goldschmidt and former Pitt postdoctoral associate Eduardo Cuansing that were published in the Oct. 21 issue of the journal Physical Review Letters.

When a superconductor is exposed to a magnetic field, the field penetrates it in the form of thin tubes, called vortices. Around each tube circulates an electric current. These vortices arrange themselves into patterns and melt when the temperature of the material is raised.

"This melting transition of the vortices is important, because it usually causes superconductivity to disappear," said Goldschmidt. "It is thus beneficial to delay the full melting as much as possible."

In addition to confirming previous experimental results, Goldschmidt and Cuansing used computer simulations of the vortex melting process to find, for the first time, direct evidence of new vortex patterns.

"Experimentalists can hardly see individual vortices," said Goldschmidt. "But with our simulations, we can actually see a picture of what's going on inside the material."

Since the vortices tend to attach to long, thin holes in the material, called columnar defects, the Pitt researchers suspected that the vortices would behave differently in the presence of such defects. And they did: When there were more vortices than holes, the vortex matter melted in two stages instead of one as the temperature was raised.

"Once physicists understand these melting mechanisms, they may be able to design materials that remain superconductors at higher temperatures," Goldschmidt said.

http://tinyurl.com/8tr9w

Super high temperature, high wear SiAlON coatings made using innovative production methods

Structural and chemical compositions of Si-Al Oxy-Nitride coatings altered through the use of reactive DC magnetron sputtering

Sialons are ceramics possessing chemical inertness, good thermal shock resistance, and excellent mechanical properties that are retained up to high temperatures. These properties mean sialon systems have found considerable applications in engineering.

Sialons are almost never found as natural minerals and sialon powders must be synthesized. They are commonly synthesized by sintering or a carbothermal reduction process. This study looks at using reactive dc magnetron sputtering to produce Sialon coatings.

The work, published in AZojomo, by Ramón Álvaro Vargas-Ortiz and Francisco Javier Espinoza-Beltrán from Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional (IPN), studies changes in structure and chemical composition of coatings produced using variations of the dc magnetron sputtering technique.

The alterations made were oxygen flux, nitrogen flux and substrate bias potential. The researchers found they were able to produce coatings that ranged from pure alumina, through AlN to (Si,Al)O and (Si,Al)(O,N).

This research opens up a whole range of possibilities for using Sialons in engineering practice as coatings for high temperature and high wear applications.

http://tinyurl.com/9bdog

MIT closes in on bionic speed

Theory could result in faster artificial muscles

CAMBRIDGE, Mass.--Robots, both large and micro, can potentially go wherever it's too hot, cold, dangerous, small or remote for people to perform any number of important tasks, from repairing leaking water mains to stitching blood vessels together.

Now MIT researchers, led by Professor Sidney Yip, have proposed a new theory that might eliminate one obstacle to those goals - the limited speed and control of the "artificial muscles" that perform such tasks. Currently, robotic muscles move 100 times slower than ours. But engineers using the Yip lab's new theory could boost those speeds - making robotic muscles 1,000 times faster than human muscles - with virtually no extra energy demands and the added bonus of a simpler design. This study appears in the Nov. 4 issue of the journal Physical Review Letters.

In this case, a robotic muscle refers to a device that can be activated to perform a task, like a sprinkler activated by pulling a fire alarm lever, explains Yip, a professor of nuclear engineering and materials science and engineering.

In the past few years, engineers have made the artificial muscles that actuate, or drive, robotic devices from conjugated polymers. "Conjugated polymers are also called conducting polymers because they can carry an electric current, just like a metal wire," says Xi Lin, a postdoctoral associate in Yip's lab. (Conventional polymers like rubber and plastic are insulators and do not conduct electricity.)

Conjugated polymers can actuate on command if charges can be sent to specific locations in the polymer chain in the form of "solitons" (charge density waves). A soliton, short for solitary wave, is "like an ocean wave that can travel long distances without breaking up," Yip adds. (See figures.) Solitons are highly mobile charge carriers that exist because of the special nature (the one-dimensional chain character) of the polymer.

Scientists already knew that solitons enabled the conducting polymers to conduct electricity. Lin's work attempts to explain how these materials can activate devices. This study is useful because until now, scientists, hampered by not knowing the mechanism, have been making conducting polymers in a roundabout way, by bathing (doping) the materials with ions that expand the volume of the polymer. That expansion was thought to give the polymers their strength, but it also makes them heavy and slow.

Lin discovered that adding the ions is unnecessary, because theoretically, shining a light of a particular frequency on the conducting polymer can activate the soliton. Without the extra weight of the added ions, the polymers could bend and flex much more quickly. And that rapid-fire motion gives rise to the high-speed actuation, that is, the ability to activate a device.

To arrive at these conclusions, Lin worked from fundamental principles to understand the physical mechanisms governing conjugated polymers, rather than using experimental data to develop hypotheses about how they worked. He started with Schrödinger's equation, a hallmark of quantum mechanics that describes how a single electron behaves (its wave function). But solving the problem of how a long chain of electrons behaves was another matter, requiring long and complex analyses.

http://tinyurl.com/9f23c