α‐Alumina and spinel react into single‐phase high‐alumina spinel in <3 seconds during flash sintering

Journal Article · Thu Jul 26 00:00:00 EDT 2018 · Journal of the American Ceramic Society

DOI:https://doi.org/10.1111/jace.15927· OSTI ID:1461713

Kok, David  ^[1]; Yadav, Devinder ^[2]; Sortino, Emanuele ^[2]; McCormack, Scott J. ^[3]; Tseng, Kuo‐Pin ^[3]; Kriven, Waltraud M.  ^[3]; Raj, Rishi  ^[2]; Mecartney, Martha L. ^[1]

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1. Department of Chemical Engineering and Material Science University of California Irvine California
2. Department of Mechanical Engineering University of Colorado at Boulder Boulder Colorado
3. Department of Material Science and Engineering University of Illinois at Urbana‐Champaign Urbana Illinois

Abstract In situ X‐ray diffraction measurements at the Advanced Photon Source show that α‐Al ₂ O ₃ and MgAl ₂ O ₄ 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‐Al ₂ O ₃ , MgAl ₂ O ₄ spinel, and cubic 8 mol% Y ₂ O ₃ ‐stabilized ZrO ₂ (8 YSZ ) 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•3Al ₂ O ₃ and MgO•1.5Al ₂ O ₃ , which evolved into a single composition of MgO•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.

• Sponsoring Organization: USDOE
• OSTI ID: 1461713
• Journal Information: Journal of the American Ceramic Society, Journal Name: Journal of the American Ceramic Society Vol. 102 Journal Issue: 2; ISSN 0002-7820
• Publisher: Wiley-Blackwell
• Country of Publication: United States
• Language: English