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Shock wave gun promotes advanced materials research.

Insight into advanced materials, including buckyballs and superconducting bearing ceramics, is being gained with a new shock wave facility at Lawrence Livermore (CA) National Laboratory.

At 20 ft Long, the two-state, lightgas gun directs small plastic projectiles toward sample targets at speeds up to 4 km/sec (about 9,000 mph).

The gun was installed to allow academic and industry groups to perform unclassified experiments with potential commercial uses. A 60-ft version is used mostly for U.S. Dept. of Defense tests in a classified section of the lab.

"This method allows us to expose samples in the lab to very high pressures and temperatures under carefully controlled conditions with a very closely monitored process," says Bill Nellis, head of the Shock Wave Physics Group in LLNL's H Division and the High Pressure Center in the Univ. of California's Institute of Geophysics and Planetary Physics.

"We want to get data for very thin sample layers," he adds. "We can take films as thin as one micron, subject them to severe conditions, and recover them to study their properties and microstructure. That distinguishes us from previous explosive techniques."

In one test series, coworker C.S. Yoo subjected 0.1-mm-thick layers of buckyballs to pressures ranging from 100,000 to million times atmospheric pressure to determine the material's mechanical properties. "The data showed buckyballs are surprisingly strong," Nellis reports. "Below 150,000 bar, buckyballs survive. Each one supports a force 100 trillion times its own weight. Above 170,000 bar they transform to graphite. At higher pressures, a very fine grained diamond film is made.

"The process can be applied to other materials to take an existing form and put it into a new crystal structure, or to see if we achieve a new material from a mixture after exposing it to severe pressures and temperatures."

Superconducting tests, he says, now involve yttrium 1-2-3 compounds. "Shock waves create a lot of defects that act to hold little superconducting loops in place, and that improves the intragranular current densities. This can lead to improved superconducting bearings that can be used to levitate objects ranging from maglev trains to computer disks."

The researchers also are doing consolidation tests with structural oxide ceramic powders. The goal is to provide better substrates, optimized microstructures for ferromagnets, and other ceramic advances.

The 60-ft gun still has advantages over the 20-ft model. "The big gun can make measurements telling the history of pressure, temperature, and density," Nellis says. "The small gun is less expensive to use, however, and it's set up for much more rapid turnaround. Ultimately we want to build up the diagnostic capabilities of the little gun so they approach those of the large one."

Japanese scientists have used shock wave techniques developed in the U.S. for military research and to develop commercial materials, such as ceramic oxides for high-temperature engines and hard materials for cutting tools, Nellis says.

Researchers Create Organic Asbestos Replacement

An operator uses an optical gauging device to measure a part machined out of a new asbestos replacement called Celazole.

Engineers at Hoechst Celanese Corp., Houston, created such substitutes for use in hot glass handling and the automotive, electronics, and petroleum industries.

Unlike some asbestos replacements, the products are fully organic and extend the performance of plastics, metals, and ceramics in high-stress and high-temperature settings.

The products are pseudo-thermoplastics formed from polybenzimidazole (PBI), a polymer resin that does not burn in air.

"With our product, the PBI synergizes with the thermoplastic, resulting in thermal properties far beyond those found in a filled system," says Larry DiSano of Hoechst Celanese.

While Teflon materials begin to creep at 450 F, Celazole U-60 is designed to handle 650 F to 800 F with spikes of up to 1,400 F.

The material has a glass transition temperature that allows it to soften at about 810 F, DiSano says.
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Publication:R & D
Date:Apr 1, 1992
Words:644
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