Preparation and properties of porous silicon nitride ceramics with uniform spherical pores by improved pore-forming agent method

Microsphere powder containing monodisperse polymethylmethacrylate (PMMA) microspheres and Si₃N₄ particles was prepared by spray-dried method. The homogeneous green body was obtained by using the microsphere powder and Cold Isostatic Pressing (CIP) method. The porous Si₃N₄ ceramics with uniformly-distributed micron-sized spherical pores were fabricated after sintering under N₂ atmosphere. The properties of the samples with differential additions and various sizes of the PMMA microspheres as pore-forming agent respectively were compared. The results showed that the optimal properties of the materials were achieved when the PMMA microspheres with a diameter of 5 μm were used as the pore-forming agent. The average bending strength of the samples was 122 MPa with a dielectric constant of 3.46, when the porosity was about 51%. The fabrication method is promising for the industrial applications of the porous Si₃N₄ ceramics with excellent properties.