Characterisation of porous silicon nitride materials produced with starch

Porous silicon nitride is gaining interest for a number of applications including metal-ceramic thermal engineering components, biomaterials and catalyst supports. This paper describes the fabrication of porous silicon nitride ceramic materials using a fugitive additive, corn starch, which allows samples to be produced with different volume fractions of porosity from ∼0 to 0.25. The initial composition consisted of 92 wt.% Si₃N₄, 6 wt.% Y₂O₃ and 2 wt.% Al₂O₃. Sintering was carried out at 1800 °C for 2 h under nitrogen. Relative density as a function of the fugitive additive content has been measured. Microstructural analysis reveals a dense matrix of elongated β-Si₃N₄ grains surrounded by intergranular glass phase and containing large pores and cavities. Pore size, geometry and grain size have been measured for certain compositions. Young's modulus and modulus of rupture have been determined as a function of the volume fraction of porosity. The Young's modulus-porosity relationship has been compared with previous work in the literature and it was found that this dependency is close to that for a model for spherical pores in cubic stacking arrangement.