Synthesis and properties of porous Si3N4/SiC nanocomposites by carbothermal reaction between Si3N4 and carbon

Abstract Porous Si 3 N 4 /SiC nanocomposites with 20 and 50 vol% SiC have been fabricated by two-step sintering of powder mixture of α-Si 3 N 4 , carbon powder with a mean size of 13 nm and 5 wt% Y 2 O 3 . Nano-sized SiC particles were formed through reactions: (1) carbon and surface SiO 2 on the Si 3 N 4 particles, and (2) carbon and Si 3 N 4 particles. A bonding between Si 3 N 4 grains was formed by the reactions so the original dimensions of the compact remained unchanged after sintering, and high porosity of 50–70% was obtained. This method of fabricating porous ceramics can be referred to as restrained sintering by reaction bonding (RSRB). It was shown that, with the variation of porosity, the samples has flexural strength of 20–100 MPa, and compressive strength of twice as much as the flexural strength. The composites with high porosity exhibited good permeability, a large strain to failure and ‘pseudo-plastic’ deformation behavior during the compressive test.