For additional information:
Dr. Franz Rosenberger, (205) 890-6050
Phillip Gentry, (205) 890-6414
[email protected]
A golden chance to understand diffusion
A small gold oven sent to Russia's MIR space station may give scientists valuable insights into diffusive transport in liquids, a fundamental physical process that is so little understood that there are a half dozen conflicting theories about how the process actually works.
"One cannot measure diffusivity in liquids on Earth to any high accuracy, so it is not possible to identify the correct theory," explained Dr. Franz Rosenberger, director of the Center for Microgravity and Materials Research (CMMR) at The University of Alabama in Huntsville. "Buoyancy-driven convective mixing (cool liquids settling, warm liquids rising) almost always dramatically overpowers diffusion."
"Convective contamination on Earth is so strong, even a one one-hundredth of a degree temperature nonuniformity causes convection to overpower diffusion," said Dr. R. Michael Banish, a CMMR senior research scientist.In the free-falling (microgravity) environment of an orbiting space station, however, buoyancy-driven convection is weak.
A UAH experiment that takes advantage of convection's "absence" is scheduled to be sent to MIR in early 1997. Five tiny samples of indium, each with a small disk of a radioactive indium isotope on one end, will be melted one by one inside the little gold oven. (Gold was chosen because it conducts heat, but blocks radiation.)
There are two tiny holes in the oven, opposite radiation detectors. As the isotope diffuses through the sample and past the holes, escaping gamma rays will tell scientists on the ground how rapidly diffusion has occured.Indium was chosen for its low melting point (156 degrees C, about 312 degrees Fahrenheit), its simple liquid structure, and because the isotope emits low energy gamma photons, which allow safe operation in the space station. The accuracy of the data expected from the experiment will illuminate the molecular processes in self-diffusion.
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