Flash Sintering of Ceramics
Abstract
Abstract Flash sintering, first discovered at UC-Boulder in 2010, refers to sintering ofceramics in a rather simple experiment where a modest electric field is applied directly to the specimen, with a pair of wires, in an open manner, in a conventional furnace. Sintering occurs in just a few seconds at low furnace temperatures. For example, yttria stabilized zirconia which normally requires several hours to sinter at ~1400 oC, can reach full density in just a couple of seconds at ~800 oC, with an electric field of just 100 V cm~1.The experiment is distinct from spark plasma sintering (SPS) where electricallyheated graphite dies and pressure are used to promote densification of powders.More recently, the experiment has been shown to apply to a wide range of (oxide)ceramics, including those that are semiconductors, electronic and ionic conductors as well as insulators. Flash is characterized by three events that occur simultaneously: sintering which is evidence for massive rates of chemical diffusion, electroluminescence, and a non-linear rise in electrical conductivity; the latter two suggest the evolution of an unusual electronic structure.The flash phenomenon occurs in dense polycrystals as well as in single crystals. Insitu experiments at synchrotrons (APS at Argonne and NSLS-II at Brookhaven) continue to provide new insights into the physics of this new phenomenon. Specimen temperatures, measured in such live experiments with a platinum-standard have shown that the temperature of the specimens remains too low to explain sintering in just a few seconds. These in-situ studies are providing new insights into dynamic changes in structure during flash, such aresidual lattice expansion which has been related to the generation of unusual concentrations of Frenkel pairs of oxygen and zirconium atoms in yttria stabilized zirconia. The objective of the present proposal is to further develop and employ in-situ methods for gaining scientific insights into the underlying physics of flash sintering. The Xray diffraction and scattering experiments at APS and NSLS-II will be expanded into pairdistribution-function (PDF) analysis to obtain atom displacements. We further propose to expand the in-situ methods to mechanical spectroscopy for live measurements of the changes in elastic modulus during the flash, which is embedded in the idea of non-linear lattice vibrations being the precursor to the onset of the flash. A third in-situ method being proposed is the measurement of the optical absorption spectra during the flash in order to determine changes in the electronic structure, which is manifested in the form of electroluminescence in such experiments. Ab-initio calculations will be performed in parallel to determine whether or not the formation of polar-nonpolar interfaces may be a significant event in the onset of flash. The polar phase is assumed to form by the clustering of Frenkel Dipoles within a parent matrix, which is nonpolar. This interface is projected to have novel electronic structure.The incubation time for the onset of flash is postulated to be associated with the growth of the polar embryos.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jul 10, 2018
- Source ID
- N000141812270
Entities
People
- Rishi Raj
Organizations
- Office of Naval Research
- Regents of the University of Colorado
- United States Navy