Mullite whiskers derived from kaolin

Short mullite whiskers prepared by firing compacts of kaolin and NH4Al(SO4)2·12H2O powders, with a small addition (0.8, 1.5 wt%) of NaH2PO4·2H2O, in air 1300 and 1400 °C for 15 h have been characterized in terms of whisker morphology, composition and structure. Relatively uniform whisker shaped crystals grew within the silicate glass matrix. After chemically leaching the glass matrix with HF solution using a microwave heating source, the resulting whiskers were exposed as isolated crystals and exhibited an aspect ratio of >17 (∼0.5 μm in diameter). The mullite whiskers had a composition of 51.06 mol% Al2O3 and 48.94 mol% SiO2, with an orthorhombic crystallographic structure.