Microstructure and fracture toughness of Al2O3 composite ceramics toughened by lignin precursor at different sintering temperatures

In order to improve the fracture toughness of alumina ceramics, nano-lignin with good dispersibility was innovatively added to the alumina matrix as a precursor in this study. Alumina composite with the addition of lignin (with the content of 2 wt%) were prepared by hot pressing sintering at different temperatures. The results showed that, the alumina grains were overcoated with the derived multilayer graphene from lignin. At the sintering temperature of 1600 degrees C, the multilayer graphene overlayer with lower defects and higher strength effectively improved the fracture toughness of the alumina-based ceramic. The fracture toughness increased from 4.66 MPa m1/2 of the single-phase alumina ceramic to 6.31 MPa m1/2 of the alumina-based composite. The graphene overlayer dominated the toughening mechanisms of crack deflection and crack bridging, which effectively inhibited crack propagation and improved the fracture toughness of composite ceramics. This study provided a new way of toughening alumina ceramics and even ceramic materials.