This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).
A team of scientists and students from Washington University in St. Louis, Iowa State University in Ames, Iowa, the University of Tennessee in Knoxville, Tennessee, and the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory, will develop a novel facility for neutron scattering studies of high temperature liquids (NESL, Neutron ElectroStatic Levitation). The liquids will be levitated in high vacuum using electrostatic levitation, thus avoiding container contamination. Liquids and glasses are probably the least understood phases of matter, with many outstanding questions concerning their physical properties and atomic structures. An understanding of how they crystallize and, in some cases, become glasses with cooling is incomplete. Furthermore, novel phase behavior and phase transitions in liquids at temperatures below their melting temperatures (supercooled) are largely unexplored. Since most elements are liquids only at elevated temperatures and react strongly with container materials, experimental studies of their structures and properties are difficult or impossible to accomplish. NESL will allow structural and dynamical studies of high-temperature liquids, both above and below their equilibrium melting temperatures. NESL will be optimized for elastic and inelastic neutron scattering studies, and used on the recently completed SNS, the world's most intense pulsed accelerator-based neutron source. NESL will have a tremendous impact on fundamental and basic research, and will serve as a catalyst for expanded national and international collaborations. It will allow pioneering studies of evolving short and medium range order in and liquid dynamics, addressing fundamental questions that have profound applied as well as basic interest. When coupled with specialized ESL chambers at Washington University and Iowa State University, NESL will create a unique opportunity for coordinated structural and property studies of solids, liquids and metastable phases, for sample temperatures up to 3000K.
Layman Abstract: This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).
While liquids and glasses have been subjects of study for millennia, they are probably the least understood states of matter. Key questions center on their structure at an atomic level, and how this structure determines their properties and their ability to change to other states. For example, in 1721, Fahrenheit discovered that under proper conditions liquids can be held at temperatures below their melting temperature without crystallizing (a common example of crystallization is when liquid water turns into ice). Surprisingly, almost 300 years later we still don't completely understand the origin of this resistance to form the crystal phase, nor do we understand the atomic processes that occur during crystallization and their relations to the liquid atomic structure. In addition to discontinuous transformations like crystallization, if they are cooled fast enough, liquids can also solidify by a continuous process to become a glass, where the atoms are frozen into the structure of the liquid. While cooling through the glass transition has been a technique commonly used by glassblowers for centuries to make intricate and beautiful glass objects, the process is poorly understood, claimed to be the most challenging unsolved problem in the physics of materials. Neutron scattering studies of liquids offer a unique way to unravel these and related questions. However, a key problem is that the liquid cannot be held in a container, since contact with the container will induce crystallization before measurements of the supercooled liquid (i.e. liquid below its melting temperature) can be made. Building on their successes in the development of techniques for x-ray scattering studies of liquids, a team of scientists at Washington University in St. Louis, Iowa State University in Ames, Iowa, the University of Tennessee in Knoxville, Tennessee, and the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory, will develop a facility that is unique in the world, to be used at the SNS for neutron scattering studies of levitated liquids, thus avoiding the need for a container. In addition to their importance to basic understanding, the capabilities that this facility offers will have profound practical technological importance, leading to refined methods for materials development.
While liquids and glasses are extremely common, they are probably the least understood phases of matter. Our understanding of how they crystallize, and in some cases become glasses, is far from complete. It is common knowledge that liquids flow more easily when they become warm, yet why the rate of flow (the viscosity) changes so much with small changes in temperature near the point where they become glasses (the glass transition) and what this tells us about changing atomic structures in the liquids are unclear. Since most materials become liquid only at high temperatures, and since they often react strongly with containers, it is difficult to design experiments that can gain insight into these questions. To address these and related questions, we have designed, constructed and tested a novel facility that enables studies of high-temperature liquids in an evacuated chamber without using a container. An electrostatic levitation (ESL) method is used to contain the samples. While levitated, the samples are melted with high-power lasers. This new ESL facility (Neutron ESL, or NESL) is designed for neutron scattering studies at the Spallation Neutron Source, the most intense pulsed neutron source on earth, located in Oak Ridge National Laboratory in Eastern Tennessee. NESL’s capabilities are complemented by those of an ESL that we have previously constructed for X-ray scattering studies at the Advanced Photon Source synchrotron, located in Argonne National Laboratory near Chicago, Illinois. From quantum physics, even though neutrons are particles they also have a wavelength that is related to their kinetic energy. They will, therefore, scatter from atomic structures (diffract) in much the same way that X-rays do. Because they interact with the spin of the atomic nucleus and with magnetic fields, however, they provide additional information to what is obtained from X-rays, which interact with the atomic electrons. By combining X-ray and neutron scattering studies, both topological and chemical information can be obtained, providing a more detailed description of the atomic structure. Further, inelastic scattering studies, in which the neutrons change energy due to their interaction with the atoms, can provide information on how the atoms are moving. This allows structural information to be linked with dynamical information, necessary to address such questions as the one of flow raised earlier. In addition to increasing fundamental insight, NESL will provide technologically important information. For example, understanding the links between structure and properties can lead to improved predictive ability for glass formation. Knowing the relation between liquid structure and crystallization can lead to better-optimized materials. Finally, NESL can provide information about which crystal phases form and are stable at high temperatures, important for the design of new materials that can be used in demanding applications, such as in engines. As a further part of its broader impact, the design, construction and testing of NESL was executed by undergraduate and graduate students and post-doctoral scientists from a range of backgrounds including chemistry, mechanical engineering and physics. This has provided educational experiences not normally found in an academic program, working with scientists and engineers at a major national facility to develop something new. NESL has successfully demonstrated the ability to maintain levitation of liquid samples while obtaining neutron data, giving structural information on supercooled (i.e. below the melting temperature) Ni-Zr and Ti-Zr-Ni liquids and providing information on the equilibrium crystal phases that form at high temperature in Zr-Rh alloys. On October 1, 2013, the SNS assumed ownership of the NESL facility. The SNS will operate and maintain it as a new user facility. The students and post-docs who have participated in the design and construction of NESL and in the first NESL studies on the VULCAN and NOMAD are in a unique position to continue and expand on their scientific careers using this new facility. For illustration, a figure showing a diagram of the NESL and a photograph of a levitated metallic liquid sample is included. Also included are photographs showing the NESL at the SNS on the VULCAN and NOMAD beam-lines, with the investigators involved in its design, construction and testing.
