Preparation of low thermal conductivity hierarchically porous diatomite ceramics by doped with ZrSiO 4 opacifier-based foam-gelcasting method

Hierarchically porous diatomite ceramics (HPDCs) doped with ZrSiO 4 as the opacifier were successfully prepared by means of foam-gelcasting with diatomite powder as original material. The effects of the opacifier, ZrSiO 4 , on the microstructure, mechanical properties, and thermal conductivity of the HPDCs were studied. The HPDCs doped with ZrSiO 4 showed a typical porous structure with excellent properties such as high porosity (84.5–89.1%) and high compressive strength (0.66–1.99 MPa). The added ZrSiO 4 hardly influenced the porosity, bulk density, and compressive strength, but decreased the thermal conductivity, especially at high temperatures. When 5 wt% ZrSiO 4 was added to HPDC, its thermal conductivity at 298 and 1073 K decreased to 0.068 and 0.132 W/(m K), respectively. This decrease in the thermal conductivity could be attributed to the outstanding scattering and absorption of the infrared electromagnetic waves by the added opacifier. The results indicated that the addition of ZrSiO 4 as an opacifier is a promising approach for enhancing the properties of porous ceramics at high temperatures.