Preparation of nano mullite from activated kaolin and gibbsite at a low temperature

Nanomullite powders were successfully prepared from activated kaolin and gibbsite. Kaolin activation was performed by the thermal treatment at 800 degrees C and sulfuric acid treatment. The activation process has changed kaolin structure to produce alumina, silica, and aluminosilicate phases, as given by XRD result. The XRD result was corroborated and was proved by the result of electron diffraction TEM analysis, the activated kaolin consisted of alpha-Al2O3, quartz, and mullite phases. Nanomullite was prepared from the activated kaolin, gibbsit, and sulfuric acid and was calcined at 400 degrees, 600 degrees, 800 degrees, and 1200 degrees C. Crystallization of the as-prepared mullite in the temperature range of 400 degrees-1200 degrees C produced mullite, alpha-Al2O3, and spinel phases at 400 degrees C. A further phase transformation of the mullite sample maintained mullite and alpha-Al2O3 phases at 1200 degrees C. The grain sizes of mullite powders are found to be less than 100 nm at a calcination temperature of 1200 degrees C. The electron diffraction (ED) patterns of the calcined mullite are indexed to the mullite phase with the crystal plane orientations of (310), (030), (101), (001), (201), (040) and (121). These results are in agreement with the XRD result for the calcined mullite at 1200 degrees C.