Enhanced thermal shock resistance of low‐carbon Al₂O₃‐C refractories via CNTs/MgAl₂O₄ whiskers composite reinforcement

Abstract

The CNTs/MgAl2O4 whiskers composite reinforcement was prepared by catalytic carbon‐bed sintering and added to low‐carbon Al2O3‐C refractories to enhance the thermal shock resistance of refractories. The effects of Ni(NO3)2·6H2O content on the phase and microstructure of CNTs/MgAl2O4 were investigated. The nano‐indentation technology was used to quantitatively evaluate the effect of CNTs/MgAl2O4 on the thermal shock resistance of low‐carbon Al2O3‐C refractories, and the toughening mechanism of CNTs/MgAl2O4 on refractories was further investigated. The results revealed that the inner and outer diameters of the CNTs were approximately 5.69 and 16.26 nm, respectively. The CNTs winded around interlocking structural MgAl2O4 whiskers with a high aspect ratio (>100), which was beneficial to the dispersion of CNTs in the refractory matrix. The thermal shock resistance of low‐carbon Al2O3‐C refractories was significantly improved by adding 3.0 wt.% of CNTs/MgAl2O4 (named C3). The specific fracture energy of refractory matrix and residual strength ratio of C3 reached 141 N·m−1 and 39.2%, which were 29.4% and 97.0% higher than those of the blank sample (109 N·m−1 and 19.9%), respectively. This is because the refractory matrix was significantly reinforced by CNTs and MgAl2O4 whiskers, promoting the occurrence of “bridging” and “crack deflection” and the generation of microcracks in the refractory matrix.

Aluminum nitride‐based ceramics with excellent thermal shock resistances

“…5 Introducing a suitable amount of second phases in the ceramic matrix is an effective approach to improve the thermal shock resistance of ceramics by refining their microstructure and increasing the resistance of a fracture to propagation. 6,7 Second phases can be introduced in the form of particles, 2,8,9 whiskers, 10,11 fibers, 12,13 etc. The most successful method to mitigate thermal shock damage to ceramics has been to incorporate continuous fibers into the ceramic matrix, [14][15][16] but the process of making ceramic matrix composites is too complex and the cost is very high, continuous fibers also reduce the hardness of ceramics.…”