We demonstrate a simple experiment in vertical Bridgman growth which can be performed easily and safely by students at all levels. Inspired by an experiment by M. A. Azouni, J. Crystal Growth, 42, 405-410 (1977), we use water for melt and ice for crystal. This system mimics semiconductors which have high conductivity melts (e.g. Si, GaAs, Te, HgCdTe). All material is non toxic and temperatures are easily accessible. We use a clear plastics tube for the crucible, mounted on an aluminum cold finger secured in a Styrofoam plug in the top of a 20 liter LN2 dewar. Since crucible, solid, and melt are all transparent, the solidification is easily viewed live. The interface tends to be flat. The segregation of dyes or colored salts makes a dramatic show. In a research setting, we have used the system to model the effect on interface shape of a conducting crucible wall (The solid will "climb" a conductor placed in the melt). By adding a set of thermocouples, we can study the effects of convection. As a lecture demonstration, the apparatus can be set up ten minutes prior to starting the lecture, and thirty to forty minutes later the show is at its height. As a lab experiment, it is an open ended challenge to the students.
L.R. Holland, J. Cryst. Growth,96 (1989) 577-583.
M.A. Azouni, J. Cryst. Growth,42 (1977) 405-410.
T. Jasinski and A.F. Witt, J. Cryst. Growth, 71 (1985) 295.
W. Kurz and D. J. Fisher, Fundamentals of Solidification, 3rd. ed., Trans Tech Publications, 1989.
for the Irradiation of Materials
NSF/MRCE NSF-HRB 9353548 Dr. Alton Williams, NSF/MRCE principle investigator
Nichols Research Corporation.
Send your comments to jon_fisher@netqm.nichols.com