Fabrication of Low-Shrinkage, Porous Silicon Nitride Ceramics by Addition of a Small Amount of Carbon

Successful net-shape sintering offers a significant advantage for producing large or complicated products. Porous Si3N4 ceramics with very low shrinkage were developed, in the present investigation, by the addition of a small amount of carbon. Carbon powders (1–5 vol%) of two types, with different mean particle sizes (13 nm and 5 μm), were added to α-Si3N4−5 wt% Y2O3 powders. SiC nanoparticles formed through reaction of the added carbon with SiO2 on the Si3N4 surface or with the Si3N4 particles themselves. Such reaction-formed SiC nanoparticles apparently had an effective reinforcing effect, as in nanocomposites. Sintered Si3N4 porous ceramics with a high porosity of 50%–60%, a very small linear shrinkage of ∼2%–3%, and a strength of ∼100 MPa were obtained.

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