Materials Science Research Lecture
How structural changes in liquids correlate with changes in the dynamnical properties, and what role these processes play in glass formation and the glass transition remain outstanding questions. Although it is widely (but not universally) believed that the dynamical behavior is linked to the atomic structure of the liquid, this has been difficult to demonstrate experimentally. While the viscosity of the liquid changes by orders of magnitude with temperature, changes in the structure static structure factor, S(q), or pair correlation function, g(r), are almost negligible. However, the recent development of containerless processing methods and the introduction of intense X-ray and neutron sources have now enabled these changes to be accurately measured in deeply supercooled liquids.
Molecular dynamics (MD) and experimental studies of the viscosity in liquid metals have identified a crossover temperature near the liquidus temperature. The MD studies suggest that this marks the onset of cooperative atomic behavior in shear flow. Inelastic neutron scattering data are presented that partially support this. Additional results are presented that confirm a general correlation between dynamics and structure in metallic liquids. They also point to a microscopic origin for liquid fragility, with the atomic potentials for stronger liquids having a steeper repulsive part and less anharmonicity. Fragility and the reduced glass transition temperature are widely believed to correlate with glass formability. It will be shown that both quantities can be accurately calculated from properties of the high temperature liquid. The role of the structure of the liquid for crystal glass formation will also be discussed.
More about the Speaker:
Kenneth Kelton is Professor of Physics and the Arthur Holly Compton Professor in Arts & Sciences at Washington University in St. Louis. He received his Ph.D. in Applied Physics from Harvard University in 1983 and after a two year postdoctoral position at Harvard joined the Physics faculty at Washington University. In 2005, he was elected as a Fellow of the American Physical Society. He has been a visiting fellow at several Colleges within Cambridge University, most recently as an Overseas Visiting Scholar in St. John's College in 2003, and was visiting scientist in the Joint Institute of Neutron Sciences at Oak Ridge National Laboratory in 2012/2013. He served as the Chair of the Physics Department at Washington University from 2007 – 2012 and was the inaugural director of the Institute of Materials Science and Engineering at Washington University from July 2013 to July 2016.
He has published almost 300 scientific articles, one book, "Nucleation in Condensed Matter," and is on the editorial advisory board for the Journal of Non-Crystalline Solids and Philosophical Magazine Letters. Kelton's current research interests include nucleation processes in condensed phase, in particular precipitation and crystallization of metallic and silicate glasses, metallic glass formation, structural, dynamical and thermophysical properties of supercooled liquids and the origin of liquid fragility and it's relation to glass formation.