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Detached Solidification Normally, when melts are slowly frozen in a vertical ampoule the surface of the resulting crystal replicates the surface of the ampoule with which it was in contact. However, many experiments performed in space gave a surprising result - the resulting crystal had a somewhat smaller diameter than the ampoule, with a wavy surface sometimes including miniature walls of China that contacted the ampoule wall. When the "detached solidification" was obtained, the crystal had significantly fewer dislocations, grain boundaries, and twins. This phenomenon remained a puzzling mystery from its discovery in 1975 until 1995 when Professors Regel and Wilcox conceived their Moving Meniscus Model, which is shown in Figure 13.
Figure 13. Schematic diagram of the Moving Meniscus Model for Detached Solidification. Phase-Field Modeling of Eutectic Solidification Metal eutectic alloys solidified in space frequently showed a different microstructure than when solidified on earth. In an attempt to explain this, students of Professors Regel and Wilcox have developed many numerical models over the years. Most recently, the influence of an oscillatory freezing rate was modeled using a phase-field method. Most fascinating was the view this provided of the composition field during eutectic solidification, as illustrated in Figure 14.
Figure 14. Example of phase-field calculation for eutectic solidification. The
white and black strips on the left are the two phases solidifying
out as pure white component and pure black component. The gray portion
on the right is the melt, with the shading indicating the relative
amounts of black and white components. Note that the white component
is concentrated in front of the freezing black phase, and vice versa.
This is the first pictorial view of the composition field generated
in eutectic solidification. Video clips of the variation in microstructure
due to a changing freezing rate can be downloaded from
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CAMP Professor Yuzhuo Li, of Clarkson University's Department of Chemistry, has been promoted to Full Professor. He began his career at Clarkson in 1990 as an Assistant Professor in the Department of Chemistry. He was promoted to Associate Professor and received tenure in 1996. Prior to his appointment to Clarkson, he was a Visiting Professor at SUNY Potsdam and a postdoctoral Research Associate at the University of Illinois at Urbana-Champaign. In 1999, he held guest professorships at China's Tianjin University of Light Industry and Yangzhou University. Professor Li's research focuses on the synthesis, characterization, and applications of nanomaterials such as emulsions, microemulsions, liposomes, and semiconductor particles. The scope of his work extends to other areas including chemical - mechanical planarization (CMP), a critical process for the manufacturing of advanced computer and microelectronic devices. His research has been published in scientific journals, including the Journal of Organic Chemistry, Langmuir, Macromolecules, and the Journal of the Electrochemical Society. During his
time at Clarkson, Professor Li has been recognized with several
awards, including Outstanding New Teacher Award, Outstanding Advisor
Award, a J. W. Graham Jr. Faculty Research Award and an Award in
Recognition of Scholarly Excellence. He is a member of the American
Institute of Chemical Engineers, the American Chemical Society,
the American Center for Photobiology, and the Chinese American Chemical
Society. CAMP Professor Raymond Mackay Honored in France CAMP Professor Raymond Mackay, of Clarkson University's Department of Chemistry, was honored at a dinner and Symposium "Atelier des Matériaux Mésoscopiques et Nanométriques: Soft Matter" held on June 7, 2002 at the Institut Universitaire de France in Paris. The event was organized by Professor Marie-Paule Pileni from the University of Pierre & Marie Curie-Paris VI. Professor Mackay has had connections to France for many years. He had a sabbatical at CNRS in Strasbourg and was involved in NATO collaborations at Paris VI. Professor Mackay serves as the Director of Research and Technology of the U.S. Army Edgewood Chemical Biological Center at Aberdeen Proving Ground, Maryland. |
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