Mechanical properties of in situ synthesized mullite‐based composite ceramics with three‐dimensional network structure

Abstract Needle‐like nanocrystalline mullite powders were prepared through the molten salt process at the temperature of 900°C using coal gangue as raw material. Then, mullite‐based composite ceramics were prepared by a conventional solid‐state reaction between in situ synthesized mullite and Al 2 O 3 powders. Effects of Al 2 O 3 content and sintering temperatures on phase compositions, microstructure, and mechanical properties of the mullite‐based composite ceramics were also studied. The results show that mullite content productivity increase from 72% to 95%, as the sintering temperature increased from 1480°C to 1580°C, which led to the improvement in the bulk density and flexural strength of the samples. The three‐dimensional interlocking structure for mullite‐based composite ceramics was obtained by the in situ solid‐state reaction process. The maximum bulk density, flexural strength, and fracture toughness for the sample with 15 wt% Al 2 O 3 content are 2.48 g/cm 3 , 139.79 MPa, and 5.62 MPa··m 1/2 , respectively, as it was sintered at the temperature of 1560°C for 3 h. The improved mechanical properties of mullite‐based composite ceramics maybe ascribed to good densification and increased mullite phase content, as well as to the in situ three‐dimensional network structure. Therefore, the results would provide new ideas for high‐value utilization of coal gangue.