Chonggao Bao

Porous Silicon Nitride Ceramics Fabricated by Carbothermal Reduction-Reaction Bonding

Porous Si3N4 ceramics with a fibrous interlocking microstructure were synthesized directly by carbothermal reduction between SiO2 and carbon and reaction bonding of Si, in the N2 atmosphere. X-ray diffractometry analysis demonstrated that β-Si3N4 was the major phase. The influences of content and powder size of the Si on the microstructure and properties of the samples were investigated. Scanning electron microscope (SEM) analysis exhibited that rod-like β-Si3N4 grains were formed in the samples prepared by using the fine Si powder. With an increase in the Si content, the porosity decreased, and the flexural strength increased accordingly.

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 β-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 β-Si3N4 grains became smaller accordingly. The sample with addition of 1wt% Y2O3 showed finer β-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 β-Si3N4 at a drastically reduced processing cost.