AlF3-assisted flux growth of mullite whiskers and their application in fabrication of porous mullite-alumina monoliths

Abstract

Mullite is a promising material with its competitive thermochemical and mechanical properties. Although mullite could be obtained by several synthesis methods, the flux method emerges with its advantages over other methods. However, obtaining mullite whiskers with a high aspect ratio and length for ceramic reinforcements is still challenging. In this work, mullite whiskers were grown from AlF3-assisted flux. The addition of AlF3 to flux salt not only decreases the formation temperature of mullite to as low as 700 ​°C and suppresses the formation of corundum side phase, but also increases the length and aspect ratio of the whiskers. The obtained mullite whiskers were used as reinforcement for porous alumina monoliths prepared by the freeze casting route and subsequent sintering at 1500 ​°C. The fabricated mullite-alumina monoliths show competitive compressive strength of 25.7 ​MPa while having as high as 70.6% porosity, which makes them a potential candidate for membrane applications.