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Platinum Metals Rev., 1987, 31, (2), 62

Solidification in Microgravity

  • I.R.M.

Gravity induces significant disturbances in gaseous and liquid systems. These disturbances are manifested in the form of buoyancy, sedimentation, thermal convection and hydrostatic pressure. All these phenomena affect the solidification characteristics of liquid metals and alloys. By carrying out a solidification process in a microgravity environment, gravity-induced disturbances are virtually eliminated and the solid structures produced are unique in uniformity of composition and properties.

Undercooling experiments have been carried out on a number of refractory elements, including platinum, rhodium, iridium and ruthenium, in the free-fall microgravity (10−6g0; 1×10−5 Torr) environment of the drop-tube facility of the Marshall Space Flight Center by W. H. Hofmeister, H. B. Robinson and R. J. Bayuzick (Appl. Phys. Lett., 1986, 49, (20), 1342–1344).

Both platinum and rhodium achieved an expected cooling rate of between 17 and 20 per cent of their melting temperatures whereas iridium and ruthenium undercooled between 10 and 13 per cent. The latter effect was associated with heterogeneous nucleation caused by impurities. A high degree of undercooling on solidification is an important phenomenon in the production of amorphous, single crystal and metastable phase structures.

Clearly microgravity research is providing an understanding of material behaviour which will lead ultimately to new Earth- and Space-based products and processes.