Low-temperature preparation of porous diatomite ceramics via direct-gelcasting using melamine and boric acid as cross-linker and sintering agent

Abstract Porous diatomite ceramics with high porosity, low thermal conductivity and reasonably high compressive strength were prepared at relatively low temperatures (773–923 K) by the direct-gelcasting method using diatomite powder as the main starting material, and melamine and boric acid respectively as a crosslinker and a sintering agent. The sample with solid loading of 20 wt%, after being fired at 923 K, showed the highest compressive strength of 1.3 MPa, though its porosity still remained as high as 80.7%. When the firing temperature was reduced to 873 K, the fired sample exhibited porosity of 82.5%, compressive strength of 0.87 MPa and thermal conductivity of 0.163 W/(m·K) (at 473 K). Upon reducing the solid loading to 10 wt%, the thermal conductivity (at 298 K) of the sample fired at 873 K, was further reduced to as low as 0.154 W/(m·K).