Spectroscopic Investigations of the Kaolinite‐Mullite Reaction Sequence

The changes of Al coordination in the kaolinite‐mullite thermal sequence in the presence of mineralizers were investigated. Small amounts of mineralizers added to kaolinite promoted, selectively (9007deg;), either (a) direct mullite formation or (b) spinel. X‐ray fluorescence measurements of the Al Kα aL shift showed that, in case (a), the Al(IV) content decreases from the metakaolinite level to values found in 3:2 mullite (without intermediary spinel formation); in case (b) A1(IV) content decreases to values corresponding to pure γ‐Al 2 O 3 (lower than in mullite). The formation of a mixed Al‐Si spinel as a major product is excluded. Results are discussed in the light of complementary ESCA measurements.