Role of mechanical activation of precursors in solid state processing of nano-structured mullite phase

Effects of precursor milling on phase evolution and morphology of mullite (3Al(2)O(3)-2SiO(2)) processed by solid-state reaction have been investigated. Alumina and silica powders were used as starting materials and milling was taken place in a medium energy conventional ball mill and a high-energy planetary ball mill. Milling in a conventional ball mill although decreases mullite formation temperature by 200 degrees C, but does not considerably change mullite phase morphology. Use of a planetary ball mill after 40 h of milling showed to be much more effective in activating the oxide precursors, and mullitization temperature was reduced to below 900 degrees C. Whisker like mullite was formed after sintering at 1450 degrees C for 2 h and volume fraction of this structure was increased by increasing the milling time. XRD results showed that samples mechanically activated for 20 h in the planetary ball mill were fully transformed to mullite after sintering at 1450 degrees C, whereas Al2O3 and SiO2 phases were still detected in the samples milled in the conventional ball mill for 20 h and then sintered at the same conditions. (C) 2006 Elsevier B.V. All rights reserved.