Manufacturing Bits: June 23

Diamond shock waves; X-ray record; recycling rare earths.


Diamond shock waves
For years, the industry has been exploring the use of diamonds for electronics applications. Diamonds could be used to reduce heat in electronic systems. In addition, diamond FETs are also intriguing. Diamond has a wide bandgap (5.45 eV), a high breakdown field (10MV/cm), and high thermal conductivity (22W/cmK).

But it could take years before diamond FETs reach the mainstream. Still, researchers are looking to understand the properties of diamond.

For example, using X-ray imaging, the Deutsches Elektronen-Synchrotron (DESY) organization has filmed the shock waves in diamonds. The research was conducted using an X-ray free-electron laser at the SLAC National Accelerator Laboratory. The laser is called the Linac Coherent Light Source (LCLS).

In the experiment, researchers devised a diamond strip. The strip was three centimeters long and 0.3 millimeters thick. In a specimen holder, the laser hit the edge of the diamond. The pulse lasted 150 picoseconds and reached a power level of up to 12 terawatts per square centimeter. The resulting shock wave was measured at about 72,000 kilometers per hour. All told, the shock wave compressed the diamond by almost 10% percent.

Snapshot of a shock wave racing through a diamond. (Source: DESY)

Snapshot of a shock wave racing through a diamond. (Source: DESY)

Researchers were able to follow the changes with at high spatial and temporal resolution. The X-ray pulses from the LCLS lasted 50 femtoseconds, but researchers were able to capture the images.

But the diamond sample was destroyed with every shot. So the experiment was repeated several times. Researchers assembled the images to create a film. “In view of the remarkable physical properties of diamond it continues to be important both scientifically and technologically,” said Jerome Hastings, a professor from SLAC, on DESY’s Web site. “We have for the first time directly imaged shock waves in diamond using X-rays, and this opens up new perspectives on the dynamic behavior of diamond under high pressure.”

X-ray record
In a separate event, SLAC’s LCLS achieved a new world’s record for X-ray energy. The LCLS hit 12.8 kiloelectronvolts (keV) in X-ray energy. This is 54% higher than the original design limit for LCLS and almost 8% higher than a previous record.

LCLS is the world’s first hard X-ray free-electron laser (Source: SLAC)

LCLS is the world’s first hard X-ray free-electron laser (Source: SLAC)

This, in turn, has pushed the LCLS laser to a new high-energy threshold for X-rays. The threshold, known as the selenium K-edge, could be used to study biological structures and other technologies. “The other advantage is that these higher-energy X-rays will provide access to higher resolution for many types of samples,” said Sebastien Boutet, who oversees the Coherent X-ray Imaging End Station at LCLS, on SLAC’s Web site.

Still, this type of energy level is not ready for prime time. Researchers must still test the klystrons, which amplify and tune the microwave energy that drives the electron beams.

Recycling rare earths
Rare earths are chemical elements found in the Earth’s crust. They are used in cars, consumer electronics, computers, communications, clean energy and defense systems. The big market for rare earths is magnets.

China has a monopoly in rare earths, accounting for 85% of the world’s total production of these elements. Europe, Japan and the United States have been looking for ways to develop more rare earths.

The University of Pennsylvania has found a way to recycle two rare earths–neodymium and dysprosium. These elements are used to make the world’s most powerful magnets.

Powerful magnets are made by combining neodymium, dysprosium and other elements. Before they can be recycled, these rare earths must be separated and remixed, according to researchers.

One way is a technique called liquid-liquid extraction, but this method must be repeated thousands of times and is expensive.

Researchers from the University of Pennsylvania devised a different approach. First, neodymium and dysprosium are combined into a mixed powder. Then, a molecule known as a ligand is applied. The molecule converges on the metal atoms. This, in turn, holds the metal atoms in the aperture between the tips.

As a result, the neodymium complex encapsulates the ions. This, in turn, enables it to dissolve. The dysprosium complex does not dissolve, allowing the two metals to be separated. Once apart, an acid bath can strip the ligand off.

The technology is still in R&D. Researchers must improve the stability of the ligand. “It’s, in principle, easier to get the neodymium and dysprosium out of technology than it is to go back and mine more of the minerals they are originally found in,” said Eric Schelter, assistant professor in the Department of Chemistry at Penn, on the university’s Web site. “Those minerals have five elements to separate, whereas the neodymium magnet in a wind turbine generator only has two.

“If you have the right ligand, you can do this separation in five minutes, whereas the liquid-liquid extraction method takes weeks,” Schelter said. “A potential magnet recycler probably doesn’t have the capital to invest in an entire liquid-liquid separations plant, so having a chemical technology that can instantaneously separate these elements enables smaller scale recyclers to get value out of their materials.”

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