Mechanistic study of solid-state reaction between kaolinite and ferrous oxide at high temperatures

A mechanistic investigation of the solid-state reaction occurring in the mi xture of kaolinite and ferric oxide heated in a mildly reducing atmosphere at 900-1300 degreesC was performed, and the following reaction scheme was p ostulated, Above 950 degreesC, FeO reacted with Al2O3 in both the spinel ph ase (SiO2 . 6Al(2)O(3)) and the amorphous phase (6SiO(2) . Al2O3) which wer e formed as the result of phase separation of metakaolin to produce hercyni te (FeAl2O4), This extraction of Al2O3 from the amorphous phase should decr ease the Al content. The mineralizing action of FeO caused the crystallizat ion of quartz solid solution from the SiO2-enriched amorphous phase. On the other hand, the spinel phase which lost a considerable amount of Al2O3, al so due to the formation of hercynite, yielded mullite, Concentration analys es by electron spectroscopy for chemical analysis (ESCA) combined with the Ar etching treatment for Al, Si and Fe revealed that, during the above soli d-state reaction, migration of Al toward FeO grains occurred.