Si3N4 Hollow Microsphere Toughened Porous Ceramics from Direct Coagulation Method via Dispersant Reaction

In order to realize the toughening effect of Si 3 N 4 hollow microsphere, direct coagulation casting method via dispersant reaction is utilized to form porous green bodies of Si 3 N 4 ceramics for the first time. It is found that the combination state between Si 3 N 4 hollow microsphere and ceramic matrix is enhanced due to its superiority on the coagulation mechanism. This novel colloidal forming method efficiently contributes to the close contact between hollow microspheres and ceramic particles, leading to the improvement of interface strength between the pore‐former and ceramic matrix. More importantly, it is proved that ceramic hollow microspheres could well perform as both pore‐former and toughening phase. The porosity regulation of porous ceramics is realized by tailoring ludox and carbon amount through carbothermal reduction method. This method turns out to regulate the performance of porous ceramics better especially through the sintering parameters. Porous Si 3 N 4 ceramics prepared with 5 wt% ludox addition which are treated in argon at 1400 °C possesses the optimal performance. They possess the fracture toughness of 2.45 MPa · m 1/2 , dielectric constant of 3.49, and thermal conductivity of 2.57 W/(m · K), which have promising applications in radome materials.