Microstructure and mechanical properties of low-carbon MgO–C refractories bonded by an Fe nanosheet-modified phenol resin

The effect of adding Fe nanosheets on the microstructure of phenol resin and low-carbon MgO–C refractories was investigated. The results indicate that well-crystallised carbon nanotubes (CNTs) of 50–100 nm in diameter and of micrometre scale in length could be generated at 1000 °C. The yield of CNTs decreases and the diameter of CNTs increases significantly as the coking temperature increases. The growth mechanism of vapour–solid (V–S) is transformed into the vapour–liquid–solid (V–L–S) mechanism at 1200 °C for CNTs in low-carbon MgO–C refractories. The mechanical properties and thermal shock resistance at 1000–1400 °C of the specimens with 0.5 wt% Fe nanosheets are greatly improved compared with specimens without Fe nanosheets. The largest magnitudes in the cold crushing strength (CCS), the cold modulus of rupture (CMOR), the hot modulus of rupture (HMOR), and the residual cold modulus of rupture (CMORst) are 25%, 44%, 24%, and 30%, respectively. The results are attributed to in situ formation of CNTs and the subsequent generation of bridging and crack deflection mechanisms in the matrix. However, as the coking temperature increases, the yield of the CNTs becomes lower and their diameter becomes larger. Thus, the favourable contribution on the thermal shock resistance decreases gradually.