Materials Research

In the materials-processing arena, major focal points for the STS-94 crew were again the Japanese-built LIF and German-provided TEMPUS facilities, both of which were activated shortly after Columbia entered orbit. After switching on LIF early on 2 July, Thomas kicked off a series of investigations to analyse diffusion in liquid tin telluride, developed by Misako Uchida of Ishikawajima-Harima Heavy Industries in Tokyo. Diffusion - whereby liquid metals mix without the need for stirring - of liquid tin telluride in microgravity was expected to lead to advances in making improved infrared detectors and lasers for terrestrial applications.

Minor teething troubles hit the facility on 6 July, when it was found that LIF was using up helium from its built-in purge - used to rapidly cool samples after heating -faster than predicted, but this was not expected to impact its ability to gather data. Diffusion of liquid metals is an imperfect procedure on Earth, because gravity-driven movements in the fluids cause complications. As on the original MSL-1 mission in April, Tsutomu Yamamura's study of the ideal conditions needed for electrolysis of molten salts was again conducted as part of research into refining basic science and engineering processes.

Other experiments included the Liquid Phase Sintering study, initiated by Crouch during his 3 July shift. This subjected tungsten, nickel, iron and copper to intense 1,500 Celsius heating to create solid-liquid mixtures. ''Sintering is thermal heating that causes particles to bond together,'' said Randall German of Pennsylvania State University. ''On Earth, sintering distorts the material. We are trying to learn the rules of why things distort on Earth. And we are!" In industry, sintering is routinely employed to form very hard, very dense solids, which can then be used to make cutting tools, car transmission gears and radiation shields.

Sintering normally involves heating metallic or ceramic 'powders' which, when placed under high pressures and temperatures, liquefy and bond to form strong materials. However, on Earth, gravity affects the dispersal of the powders and causes the resultant solid to be considerably less 'uniform' in nature. ''How to make materials of the right shape and size'', said German, ''with no distortion is fundamental to powder metallurgy, so we are learning why distortion occurs on Earth.''

Although technically a member of the three-person 'orbiter' crew, and responsible for monitoring Columbia's systems during his shift, Mike Gernhardt participated in numerous experiment sessions with LIF, performing an experiment on 8 July to explore the diffusion characteristics of 'dopants' - or impurities - in samples of melted germanium, which is often used as a semiconductor, as well as an alloying agent. ''It's a fundamental scientific study,'' said David Matthiesen of Case Western Reserve University in Ohio. ''We're trying to measure the fundamental thermo-physical properties of this semiconductor.'' Such experiments could eventually lead to faster-performing electronic components, including transistors and integrated circuits.

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