A Troublesome Theory in Materials Science

The shuttle experiments, however, ran for only 10 hours. And perhaps that's the problem. Computer simulations suggest that when coarsening is allowed to continue somewhat longer, the theory redeems itself.

With longer trials in mind, Voorhees and his colleagues designed CSLM-2, a 2nd-generation coarsening experiment for the International Space Station. The device will heat a mixture of lead and tin until it melts. Because pure tin has a higher melting temperature than the lead-tin mixture, tiny embedded crystals of tin will remain solid at the experiment's temperature: about 185°C, or 365°F. (Tin melts at 232°C, or 449°F.) Scientists use lead and tin because the basic physical properties of this mixture are well understood, making the analysis of the results more fruitful.

Many applications employing alloys will benefit from improved theories for coarsening.

As the furnaces keep the samples melted, the tiny tin crystals will coarsen for times ranging from 1.5 to 48 hours. After the larger crystals have grown and the smaller ones shrunk, the samples will be cooled and solidified to preserve them, then returned to Earth where Voorhees and his team of scientists will slice them open and examine them to see if the theory held true for the longer experiment runs.

Although there's still much to learn about coarsening, some of the results from the first CSLM experiment are already being used by industry. For example, Voorhees helped an Evanston, Illinois, company called QuesTek to integrate the findings of the first experiment into the computer software they use to make material design recommendations. QuesTek's clients - which include major manufacturing companies - then use those materials to build a wide range of products.

This means the physics revealed by CSLM may already be finding its way to a jet engine, or an aluminium car chassis, or a suspension bridge near you. CSLM-2 will teach us even more....