Synthesis of Porous Silicon Nitride Ceramics from Diatomite

Porous Si3N4 were fabricated by carbothermal reduction between carbon black and diatomite. Diatomite is a non-metallic mineral composed of skeletal remains of single-cell water plants (algae). The main ingredient of diatomite is the amorphous active SiO2. The influence of sintering additives on the microstructure and mechanical properties of porous Si3N4 was analyzed. X-ray diffraction (XRD) analysis demonstrated the formation of Si3N4 except for minor of glass phase. Scanning electron microscope (SEM) analysis showed that porous beta-Si3N4 occupied fine microstructure and uniform pore structure. The addition of Y2O3 accelerated the densification of porous Si3N4 ceramics. With an increase in the content of Y2O3, the porosity decreased, the flexural strength increased, and the aspect ratio of beta-Si3N4 grains became smaller accordingly. The sample with addition of 1 wt% Y2O3 showed finer beta-Si3N4 grains with higher aspect ratio. Porous Si3N4 ceramics with the porosity of 70.1-79.5% and the flexural strength of 2.3-14.5 MPa were obtained by this technique. This technique would provide an innovatory approach to the synthesis of porous beta-Si3N4 at a drastically reduced processing cost.