Synergic effects of nano carbon sources on thermal shock resistance of Al₂O₃-C refractories

The fracture behavior and thermal shock resistance of low-carbon containing Al₂O₃-C refractories with various nano carbon sources were comparatively investigated by means of three-point bending test and wedge splitting test. The results show that synergic enhancing mechanisms, including “pull-out”, “crack bridging”, “crack deflection” and “crack branching”, can be developed with the application of multiple nano carbon sources. Therefore, the carbon black, expanded graphite, in-situ multi-walled carbon nanotubes and SiC whiskers containing Al₂O₃-C refractories have the highest residual strengths of 11.16 MPa. Furthermore, the wedge splitting test results suggest that the improvement of thermal shock resistance is mainly associated with an increase of crack propagation resistance, which can be fulfilled through decreasing the brittleness and inducing tortuous crack propagation along grain/matrix. Additionally, it is demonstrated that the wedge splitting test after thermal shock treatment should be a feasible way to evaluate the thermal shock cycling resistance of Al₂O₃-C refractories.