Microstructure and Mechanical Properties of Al 2 O 3 -C Refractories Using Carbon Black and Multi- Walled Carbon Nanotubes as Carbon Sources

Low-carbon Al2O3-C refractories were prepared using tabular alumina and reactive alumina powder as the main raw materials and silicon powder as an additive, while nano carbon black and multi-walled carbon nanotubes (MWCNTs) were added as nano carbon sources. The low-carbon Al2O3-C refractories were first fired at 800 °C, 1000 °C, 1200 °C and 1400 °C in a coke bed. Then the phase compositions and microstructures of the samples coked at the above temperatures were analyzed by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM). Finally, the mechanical properties and thermal shock resistance of the samples were evaluated using three-point bending methods. The results showed that: 1) The mechanical properties of MWCNTs-containing Al2O3-C refractories coked above 1000 °C were significantly improved, which is attributed to the strengthening effects of MWCNTs and the formation of a large quantity of SiC whiskers via transformation of MWCNTs based on the Vapor-Solid model. 2) Thanks to the thermal stress absorption effect of nano carbon black, strengthening effects of MWCNTs and SiC whiskers, the low-carbon Al2O3-C refractories containing 1 wt% mixture of nano-carbon-black and MWCNTs achieved a similar residual strength ratio to those containing a 2 wt% mixture of nano carbon black and flaky graphite, exhibiting a higher residual strength.