Enhancing the mechanical properties of Al2O3‐C refractory: Carbonized coconut shell as a substitution for graphite

At present, graphite is commonly used as the carbon source in Al2O3‐C refractory. However, graphite resources are limited and belong to the category of nonrenewable resources. Coconut shell is a biomass material with low cost, low impurity, and high reactivity, and also belongs to renewable resources. Therefore, the research for using coconut shell carbon as a substitution for graphite in Al2O3‐C refractory has great significance. In this work, the coconut shell was firstly carbonized at 200–1000°C in flowing argon, and the microstructure of the carbonized coconut shells was investigated. Then the carbonized coconut shell powder was introduced into Al2O3‐C refractory instead of graphite, and the effect of carbonized coconut shell on mechanical properties and microstructure evolution of materials was investigated. The results show that the carbonized coconut shell has porous structures, composed of amorphous carbon and disordered micro‐graphite with many defects, endowing its high reactivity. Compared with graphite, the carbonized coconut shell promotes the Si and Al to in situ formation of nonoxide ceramic whiskers (SiC, Al4C3, and AlN), which play a strengthening and toughening role in the materials. When graphite is replaced by 1 wt% carbonized coconut shell, the residual strength ratio of samples increased from 81.8% to 90.2%, and that of the hot modulus of rupture increased from 17.53 MPa to 18.47 MPa.