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Mechanism of Reduced Sintering Temperature of Al2O3–ZrO2 Nanocomposites Obtained by Microwave Hydrothermal Synthesis

1
Institute of High Pressure Physics, Polish Academy of Sciences, Sokolowska 29/37, 01-142 Warsaw, Poland
2
Faculty of Applied Physics and Mathematics, Gdansk University of Technology, Narutowicza 11/12, 80-233 Gdansk, Poland
3
Department of Nuclear Engineering, Ben-Gurion University of the Negev, Beer Sheva 8410501, Israel
4
WestCHEM, School of Chemistry, University of Glasgow, University Avenue, Glasgow G12 8QQ, UK
*
Author to whom correspondence should be addressed.
Materials 2018, 11(5), 829; https://doi.org/10.3390/ma11050829
Received: 10 April 2018 / Revised: 1 May 2018 / Accepted: 14 May 2018 / Published: 17 May 2018
A novel method to obtain Al2O3–ZrO2 nanocomposites is presented. It consists of the co-precipitation step of boehmite (AlO(OH)) and ZrO2, followed by microwave hydrothermal treatment at 270 °C and 60 MPa, and by calcination at 600 °C. Using this method, we obtained two nanocomposites: Al2O3–20 wt % ZrO2 and Al2O3–40 wt % ZrO2. Nanocomposites were characterized by Fourier transformed infrared spectroscopy, Raman spectroscopy, X-ray diffraction, and transmission electron microscopy. Sintering behavior and thermal expansion coefficients were investigated during dilatometric tests. The sintering temperatures of the nanocomposites were 1209 °C and 1231 °C, respectively—approximately 100 °C lower than reported for such composites. We attribute the decrease of the sintering temperature to the specific nanostructure obtained using microwave hydrothermal treatment instead of conventional calcination. Microwave hydrothermal treatment resulted in a fine distribution of intermixed highly crystalline nanoparticles of boehmite and zirconia. Such intermixing prevented particle growth, which is a factor reducing sintering temperature. Further, due to reduced grain growth, stability of the θ-Al2O3 phase was extended up to 1200 °C, which enhances the sintering process as well. For the Al2O3–20 wt % ZrO2 composition, we observed stability of the zirconia tetragonal phase up to 1400 °C. We associate this stability with the mutual separation of zirconia nanoparticles in the alumina matrix. View Full-Text
Keywords: microwave hydrothermal synthesis; Al2O3–ZrO2 nanocomposites; shrinkage temperature; grain boundaries; isolation effect of t-ZrO2; phase composition microwave hydrothermal synthesis; Al2O3–ZrO2 nanocomposites; shrinkage temperature; grain boundaries; isolation effect of t-ZrO2; phase composition
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Koltsov, I.; Smalc-Koziorowska, J.; Prześniak-Welenc, M.; Małysa, M.; Kimmel, G.; McGlynn, J.; Ganin, A.; Stelmakh, S. Mechanism of Reduced Sintering Temperature of Al2O3–ZrO2 Nanocomposites Obtained by Microwave Hydrothermal Synthesis. Materials 2018, 11, 829.

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