Text: Detached Bridgman Growth How Does it Work? Scientists have considered several theories to explain why the crystal forms a small distance away from the container wall. All agree that the gas pressure in the gap is important, but they differ on other points. [see caption] Some scientists think gases produced from volatile substances within the material can provide enough pressure to cause the separation. But others believe this source of gas is inconsequential and the needed pressure difference between p1 and p2 (see illustration) has to be provided by other means. Szofran and his colleagues hope to answer this question. They will do experiments where the necessary gas is sealed into the container and others where no gas is added to see if enough comes out of the material to cause detachment. Szofran explains the value of doing such experiments in space: "You'd like to have the pressure in the gap between the solid and the container [p2 in the illustration] to be higher than the pressure above the liquid [p1]. And you're limited on the ground as to how high that difference can be, because if it gets to be very large, a bubble will form and release the pressure in the gap. In space that won't happen because there's no buoyancy to move the bubble through the liquid." http://science.nasa.gov/headlines/y2001/ast11dec_1.htm?aol495287

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