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Kaolinite–Mullite Reaction Series: The Development and Significance of a Binary Aluminosilicate Phase

1991; Wiley; Volume: 74; Issue: 6 Linguagem: Inglês

10.1111/j.1151-2916.1991.tb04119.x

1551-2916

A. K. Chakravorty, Dilip K. Ghosh,

Recycling and utilization of industrial and municipal waste in materials production

The semiquantitative estimations of 980°C exothermic reaction products of kaolinite by quantitative X‐ray diffraction (QXRD) and chemical leaching techniques show the formation of a significant amount of amorphous aluminosilicate phase (∼ 30 to 40 wt%). The theoretically expected AlO 4 /AlO 6 ratio in the 980°C reaction is in close agreement with the value measured by the X‐ray fluorescence (XRF) technique and the experimental radial electron distribution (RED) profile agrees with the suggested 980°C formation of Si‐Al spinel with mullite‐like composition. Mullitization of kaolinite has been compared with a synthetic Al 2 O 3 —SiO 2 mixture. In synthetic mixtures development of an intermediate amorphous aluminosilicate phase is an essential step prior to mullitization. Kaolinite forms mullite in two ways: (i) by polymorphic transformation of cubic mullite at 1150° to 1250°C and (ii) by nucleation of mullite in the amorphous aluminosilicate phase and its subsequent growth above 1250°C. Thus chemical continuity is maintained throughout the reaction series and the intermediate spinel phase is silicon bearing and its subsequent transformation to mullite confirms the topotactic concept in the kaolinite transformation.