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 Si 3 N 4 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‐Si 3 N 4 −5 wt% Y 2 O 3 powders. SiC nanoparticles formed through reaction of the added carbon with SiO 2 on the Si 3 N 4 surface or with the Si 3 N 4 particles themselves. Such reaction‐formed SiC nanoparticles apparently had an effective reinforcing effect, as in nanocomposites. Sintered Si 3 N 4 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.