Fabrication porous Si3N4 ceramics via starch consolidation-freeze drying process

Si3N4 ceramics with porosity of similar to 72% were prepared via starch consolidation-freeze drying process. Pre-gelled method was used to reduce the granular size of starch which acted as consolidator/binder and pore forming agent. Polyvinyl alcohol (PVA) was added to control ice crystal growth. The results indicated that the porosities of Si3N4 ceramics were mainly controlled by slurry concentrations, starch/PVA contents had slight influence on the porosities. With higher PVA content, large pores around 35 mu m were decreased, the microstructure turned more uniform. Typical trimodal pore size distributions were obtained with 0 and 2.5% PVA addition, the sample with 5% PVA only showed bimodal pore size distribution without large pores. The flexural strength was increased from 6.7 to 42.3 MPa with increasing PVA content. (C) 2011 Elsevier B.V. All rights reserved.