Development of a low-temperature novel porous Si3N4–Al2O3 composite with excellent specific mechanical properties

Abstract

Porous composites of Si3N4 and Al2O3 have potential applications for various engineering applications. Fabrication of porous ceramic composites is generally expensive due to the requirement of high sintering temperatures and expensive raw materials. A relatively simple, cost-effective, versatile, and novel processing technique with phosphoric acid performing the dual roles of binder and pore-former has been proposed in this work. Porous Si3N4–Al2O3 composites with up to 20 vol% Al2O3 content and porosities in the range of 37–54 vol% were fabricated at only 1200 °C. Young's modulus, flexural strength, and compressive strength of the porous composites were found to be in the range of 21–54 GPa, 31–110 MPa, and 39–103 MPa, respectively. The best combination of mechanical properties was achieved at 10 vol% Al2O3 content, which corresponded to 39 % total porosity. The combination of low density and good mechanical properties yielded outstanding specific properties, which are significantly higher than monolithic porous Si3N4. The excellent combination of a low processing cost, tunable porosity and pore morphology, outstanding mechanical properties, as well as the inherent chemical and thermal stability of these porous composites render them potentially very attractive as chemical filters, porous membranes, as well as porous preforms for interpenetrating metal/ceramic composites.