Low-temperature densification and mechanical properties of monolithic mullite ceramic

Dense mullite ceramics with excellent mechanical properties were produced using three kinds of mullite powders, namely micro-, submicro-, and nano-powders. The influence of sintering temperature on the microstructural and mechanical properties of the produced mullite ceramics was investigated. As the sintering temperature increased from 1200 to 1500 °C, the relative density of the mullite ceramic produced using micro-powder varied from 65.3 to 99.2%, leading to an increase in the flexural strength and fracture toughness from 87.6 to 245.7 MPa, and 1.4 to 2.5 MPa m^1/2, respectively. The densification temperature of mullite ceramics significantly reduced when submicro- and nano-powders were used as raw materials. The relative density and mechanical properties of mullite ceramics fabricated using submicro- or nano-powders increased at first, then decreased following an increase in the sintering temperature. The mullite ceramic produced using submicro-powder became compact after being sintered at 1200 °C, and exhibited a high flexural strength of 254.7 MPa and fracture toughness of 2.9 MPa m^1/2, indicating that low-temperature densification of mullite ceramics can be realised by enhancing the sintering activity of the mullite powder.