MatSE Special Seminar - "Flash-Sintering+: Anomalous Defect Concentrations and Rates of Solid-State Diffusion"
- Sponsor
- Materials Science and Engineering Department
- Speaker
- Prof. Rishi Raj, Materials Science and Engineering, University of Colorado Boulder
- Contact
- Bailey Peters
- bnpeters@illinois.edu
- Views
- 1
- Originating Calendar
- MatSE Colloquium Calendar
In 2010 it was discovered that application of modest electrical fields could induce full sintering in zirconia in a matter of seconds below 1000 oC. Arrhenius extrapolation of data from conventional sintering suggested that flash was five to seven orders of magnitude faster. In the last three years there have been further significant developments:
i. Metals (W, Ni, Re and Cu) show flash behavior very similar to ceramics
ii. In-situ calorimetric measurements show Frenkel defect concentrations of up to 35 mol%
iii. The activation energy for diffusion (for example measured in creep experiments and in diffusion couple experiments) are less than one half of the conventional values, explained by preponderance of defects, that leaves only the activation energy for atom jumps to remain (about 200 kJ mol–1 instead of about 450-500 kJ mol–1 for yttria stabilized zirconia).The ultrafast diffusion kinetics has broad implications in materials science not only in creep but also in phase transformations. Rapid chemical reactions are broadening its applications to Solid State Chemistry. For example, ZnS has been shown to convert into ZnO in a few seconds at low temperature. Graphene infused copper has been produced from copper wires coated with carbon.
A classical mechanics pathway is proposed: that defects are induced by amplification of standing-wave phonons created at the edge of the Brillouin zone, caused by non-linearity in the elastic constants, leading up to Lindemann’s criterion for “melting”, a great interest of Andy Granato of this university.