Mullite whiskers derived from kaolin

Short mullite whiskers prepared by firing compacts of kaolin and NH4Al(SO4)(2)center dot 12H(2)O powders, with a small addition (0.8, 1.5 wt%) of NaH2PO4 center dot 2H(2)O, in air 1300 and 1400 degrees 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 (similar to 0.5 mu m in diameter). The mullite whiskers had a composition of 51.06 mol% Al2O3 and 48.94 mol% SiO2, with an orthorhombic crystallographic structure. (C) 2008 Elsevier Ltd and Techna Group S.r.l. All rights reserved.