Directional Melting of Alumina via Polarized Microwave Heating
Department of Astronautical Engineering, University of Southern California,USA
A recent development of millimeter-wave thermal rocket has proposed α-alumina as a promising candidate material for the absorbing heat exchanger of the millimeter-wave thermal launch system. Successful design of microwave thermal propulsion systems requires fundamental understanding of the dielectric and thermal properties of heat-exchanger materials under high frequency microwaves at high temperature (> 1,000 K). Using molecular dynamics simulations, we found that drastically different melting temperatures and behaviors can be achieved for α-alumina using microwave heating, where the electric field is aligned with different crystallographic orientations. Namely, alumina melts much earlier at lower temperatures when the electric field is parallel to the c-axis. The atomistic mechanism was identified as selective liberation of the Al sublattice due to the shear instability along the c-axis. This directional melting concept may be used for triggering distinct dynamical instabilities and melting of dielectric crystals using polarized microwave fields.
Yuan Hu is currently working toward the Ph.D. degree in Astronautical Engineering at the University of Southern California, Los Angeles. He received the B.Eng. degree in Thermal Energy and Power Engineering from the Huazhong University of Science and Technology, Wuhan, in 2009 and the M.S. degree in Fluid Mechanics from the Institute of Mechanics, Chinese Academy of Sciences, Beijing, in 2012. His research interests include advanced propulsion technologies, molecular dynamics simulations of materials, kinetic simulation methods of gases and plasmas, and high-performance computing