Alpha-Alumina And Spinel React Into Single-Phase High-Alumina Spinel In < 3 Seconds During Flash Sintering

In situ X-ray diffraction measurements at the Advanced Photon Source show that alpha-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 alpha-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 degrees 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 center dot 3Al(2)O(3) and MgO center dot 1.5Al(2)O(3), which evolved into a single composition of MgO center dot 2.5Al(2)O(3) as the current continued to increase. In summary, flash sintering is an expedient way to create single-phase, alumina-rich spinel.