Abstract
Intensive phase transformations of alumina are known to occur at temperatures above 1000 °C. In the present work, high temperature behaviour of pure Al2O3 and the carbon coated Al2O3@C sample with core-shell structure was comparatively studied using low-temperature nitrogen adsorption, transmission electron microscopy, powder X-ray diffraction (XRD) analysis and solid-state nuclear magnetic resonance (NMR). The solid-state NMR 27Al method has allowed us to identify and estimate the concentration of all phases appeared during the transformation of pseudoboehmite γ-Al2O3 into corundum α-Al2O3. The data obtained correlate well with the results of XRD analysis and low-temperature nitrogen adsorption. It is shown that the deposition of carbon coating with formation of core-shell Al2O3@C system stabilizes the size of oxide core and prevents the formation of corundum phase until the temperatures of 1350–1400 °C, which are close to the temperature of carbothermal reduction of alumina. The stabilization of the size of the oxide core nanoparticles was considered as a main factor preventing the formation of corundum phase at high temperatures. At the same time, the carbon coating does not affect the phase transformation of γ-Al2O3 to δ-Al2O3.
Original language | English |
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Pages (from-to) | 4801-4806 |
Number of pages | 6 |
Journal | Ceramics International |
Volume | 44 |
Issue number | 5 |
DOIs | |
Publication status | Published - 1 Apr 2018 |
Keywords
- Alumina
- Carbon coating
- Core-shell structure
- Phase transformations
- Solid-state NMR
- Stabilization effect
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Ceramics and Composites
- Process Chemistry and Technology
- Surfaces, Coatings and Films
- Materials Chemistry