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

•An improved fabrication method of porous Si3N4 ceramics was reported.•Spherical pore-forming agent, spray-dried and CIP method were utilized together.•The porous ceramics possessed uniformly distributed micron-sized spherical pores.•The effect of sizes of spherical pore-forming agent was discussed.•The optimal size of spherical pore-forming agent was given in the article.