Effect of the reactivity and porous structure of expanded graphite (EG) on microstructure and properties of Al2O3-C refractories

Al2O3-C refractories with Al, Si and SiO2 as additives were prepared in the coke bed in the temperature ranging from 800 degrees C to 1400 degrees C when expanded graphite (EG) was used as carbon source to partially or totally replace the graphite flake. The results showed that the EG accelerated in-situ formed ceramic phases in specimens fired at different temperature due to its higher reactivity than that of graphite flake. At 1000 degrees C, much more Al4C3 whiskers and AlN whiskers or lamellas formed in the matrix. At 1200 degrees C and 1400 degrees C, much more SiC whiskers with high aspect ratio were distributed in matrix of specimens. So, the mechanical properties such as modulus of rupture (CMOR), modulus of elasticity (E), force and displacement of Al2O3-C refractories with 0.2-0.5 wt% EG were improved in comparison with those without EG. Furthermore, the thermal shock resistance of Al2O3-C refractories was remarkably promoted with the addition of the EG, which was attributed to the absorption and release of the stress from porous structure of EG during thermal cycles. (C) 2015 Elsevier B.V. All rights reserved.