Influence of pore-forming agents on permeability coefficient of porous Si3N4 ceramics.

To improve their permeability,porous Si₃N₄ ceramics were prepared using Si powder as the raw material,Y₂O₃ and CaF₂ as sintering aids,and polymethyl methacrylate microspheres (5 and 20 μm) as pore-forming agents, gel-casting, binder-removing, and finally reaction sintering at 1 650 °C for 3 h in a nitrogen atmosphere. The effects of the particle sizes and additions (volume fractions of 0,15%, 30%, 45%, and 60%) of the pore-forming agents on the apparent porosity,pore size distribution,pore structure and permeability coefficient of the porous Si₃N₄ ceramics were studied. The results show that: (1) the samples with pore agents exhibit dual pore structures, which are composed of stacking-derived pores and spherical evolution pores, with bimodal pore size distribution; (2) with the same particle size,as the pore-forming agent addition increases,the apparent porosity and permeability coefficient of the samples increase,while the bulk density, bending strength, and fracture toughness decrease; (3) at the same addition, the samples with the smaller-sized agents (5 μm) have higher apparent porosity,permeability coefficient,and bending strength;using smaller-sized pore-forming agents can reduce the thickness of the pore walls and enlarge the pore sizes of the stacking-derived pores within the pore walls,thus enhancing the permeability of the pore walls; (4) the sample with 60% pore-forming agents of 5 μm has the best comprehensive performance,with the apparent porosity of 55.1%,permeability coefficient of 11.62x10^-14 m² and bending strength of 35.3 MPa. [ABSTRACT FROM AUTHOR]