Micro-Raman and FT-IR spectroscopy study of the thermal transformations ofSt. Claire dickite

The thermal transformations of St. Claire dickite up to 1300 degreesC were studied by micro-Raman and FT-IR spectroscopy methods. Spectra recorded aft er the thermal treatment at 700 degreesC show drastic changes from those re corded at 600 degreesC, which are compatible with the dehydroxylation and f ormation of a pseudo-amorphous phase of meta-dickite. Some silica is expell ed together with the beginning of Al/Si ordering at 1000 degreesC, as obser ved by FT-IR spectroscopy through the splitting of the combined Al-O and Si -O deformation band into two modes at 553 and 465 cm(-1). A separate phase of amorphous silica is detected by micro-Raman spectroscopy at 1100 degrees C, as observed by the appearance of characteristic Raman bands at 432, 489 and 601 cm(-1). Presence of minor amounts of corundum is detected through l uminescence spectroscopy at 1100 degreesC, and is indicated by the appearan ce of R-lines of Cr+3 impurity at 692 and 694 nm. Crystallization of some m ullite is observed at 1200-1300 degreesC by the appearance of characteristi c Raman bands at 308, 413, 960, 1035 and 1127 cm(-1) and by the appearance of IR band at 815 and 906 cm(-1). (C) 2001 Elsevier Science B.V. All rights reserved.