Preparation and properties of hierarchical structural alumina/mullite composites

Hierarchical structural alumina/mullite composites constructed by alumina platelets inter-locked porous matrices and mullite whiskers secondary structures had been designed and prepared based on the fluorine-catalyzed gas-phase process. In the composites, mullite whiskers grew on the alumina platelets of the matrices to form cactus-like structures, before that, topaz rods as transitional secondary structures formed at lower temperature. The fluorine-etching effects on secondary structures’ nucleation were discussed. The alumina/mullite composites (1300 °C) had low bulk density (1.10 g/cm 3 ), high porosity (71.4%), and proper compression strength (∼14.2 MPa), meanwhile, the average filtration efficiencies of PM2.5 and PM10 during the filtration tests were 78% and 76%, respectively. The introduced mullite whiskers with length of ∼1 µm had not induced obvious changes on the structural parameters, hence, the alumina/mullite composites (1300 °C) possessed similar particle filtration performances compared with the alumina porous matrices, and both of the two species materials could be applied for hot gas filtration.