In this paper, novel Al₂O₃-based poly-hollow microsphere (PHM) ceramics were prepared using Si₃N₄ and Al₂O₃ PHMs as pore-forming agents. The effect of Si₃N₄ and Al₂O₃ PHMs with different percentages on properties of Al₂O₃-based PHM ceramics was investigated. Through adjusting percentage of Al₂O₃ PHMs, Al₂O₃-based PHM ceramics with enhanced properties are achieved. X-ray diffraction (XRD) results show that main phases of Al₂O₃-based PHM ceramics vary from β-SiAlON (z value increases from 2.9 to 4) to Al₂O₃ with the increase of percentage of Al₂O₃ PHMs from 10% to 100%. The different phase compositions result in different properties of Al₂O₃-based PHM ceramics. With the increase of percentage of Al₂O₃ PHMs, porosity of Al₂O₃-based PHM ceramics gradually decreases, while their shrinkage, flexural strength, and fracture toughness firstly decrease and then increase. Using different kinds of ceramic PHMs as pore-forming agents, various novel and high-performance porous ceramics could be prepared via optimizing percentage of ceramic PHMs in the future.

Porous Si₃N₄ ceramics were prepared by aqueous gelcasting using Si₃N₄ poly-hollow microspheres (PHMs) as pore-forming agent. The effects of solid loading of Si₃N₄ slurry and Si₃N₄ PHM content on the properties of porous Si₃N₄ ceramics were investigated. Only β-Si₃N₄ phase is observed in porous Si₃N₄ ceramics, and Si₃N₄ PHMs distribute uniformly both in Si₃N₄ green samples and porous Si₃N₄ ceramics. Results show that solid loading of Si₃N₄ slurry and Si₃N₄ PHM content could considerably influence the properties of porous Si₃N₄ ceramics. With the increase of solid loading of Si₃N₄ slurry (decrease of Si₃N₄ PHM content), the distributing state of Si₃N₄ PHMs changes from contacting with each other to just embedding in the matrix, thus their porosity decreases, while their shrinkage, flexural strength, and fracture toughness increase.