Microstructure and mechanical properties of Lu₂O ₃-doped porous silicon nitride ceramics using phenolic resin as pore-forming agent

The joint process consisting of pressureless sintering and chemical vapor infiltration (CVI) was developed to prepare porous Si₃N₄ ceramics with controlled microstructure. Lu₂O₃ and phenolic resin acted as sintering aid and pore-forming agent, respectively. The 5 wt% Lu₂O₃-doped ceramics using 12-57 vol% phenolic resin attained a porosity ranging from 46% to 53%. With increasing the resin content, the average pore size increased from 1 to 2 μm. The porous ceramic infiltrated with CVI Si₃N₄ had an improved microstructure. The decreased pore size and porosity led to an increase in flexural strength, and the densified surface led to an improved surface hardness.