α‐Alumina and spinel react into single‐phase high‐alumina spinel in <3 seconds during flash sintering
Abstract
In situ X‐ray diffraction measurements at the Advanced Photon Source show that α‐Al2O3 and MgAl2O4 react nearly instantaneously and completely, and nearly completely to form single‐phase high‐alumina spinel during voltage‐to‐current type of flash sintering experiments. The initial sample was constituted from powders of α‐Al2O3, MgAl2O4 spinel, and cubic 8 mol% Y2O3‐stabilized ZrO2 (8YSZ) mixed in equal volume fractions, the spinel to alumina molar ratio being 1:1.5. Specimen temperature was measured by thermal expansion of the platinum standard. These measurements correlated well with a black‐body radiation model, using appropriate values for the emissivity of the constituents. Temperatures of 1600‐1736°C were reached during the flash, which promoted the formation of alumina‐rich spinel. In a second set of experiments, the flash was induced in a current‐rate method where the current flowing through the specimen is controlled and increased at a constant rate. In these experiments, we observed the formation of two different compositions of spinel, MgO•3Al2O3 and MgO•1.5Al2O3, which evolved into a single composition of MgO•2.5Al2O3 as the current continued to increase. In summary, flash sintering is an expedient way to create single‐phase, alumina‐rich spinel.
Document Details
- Document Type
- Pub Defense Publication
- Publication Date
- Jul 26, 2018
- Source ID
- 10.1111/jace.15927
Entities
People
- David Kok
- Devinder Yadav
- Emanuele Sortino
- K.-P. Tseng
- Martha L. Mecartney
- Rishi Raj
- Scott J McCormack
- Waltraud M. Kriven
Organizations
- Argonne National Laboratory
- Army Research Office
- United States Department of Energy
- University of California, Irvine
- University of Colorado Boulder
- University of Illinois Urbana–Champaign