Thermal transformations metakaolin ? spinel type aluminosilicate: Al and Si k-xanes characterization

F.G. REQUEJO; L. ANDRINI; N.M. RENDTORFF

Campinas

Otro; 25th Annual users meeting, LNLS; 2015

CNPEM LNLS

Thermal transformations metakaolin ? spinel type aluminosilicate: Al andSi k-xanes characterizationRequejo F. G.; Andrini L.; Rendtorff N.Since the pioneering work of G.W. Brindley and M. Nakahira it is known that one of theopen problems concerning the metakaolin phase, the manner in which it transforms into aspinel-type phase and mullite, and the relation of this spinel-type phase to mullite, becausethe series of reactions by which kaolinite transforms to mullite is perhaps the most importantin the entire field of ceramic technology [1]. The thermal transformations of kaolinite (K) inmetakaolin (MK) and the metakaolin in a spinel type aluminosilicate (SAS) were studied byAl and Si K-XANES to correlate the information obtained with this technique with thatobtained by conventional X-ray Diffraction, and clarify and assign the structural changes.Simultaneously with XANES technique is possible to observe changes in the electronicstructure of the system. For K à MK transformation, by Al K-XANES it was obtained resultsconsistently with reported Aluminium coordination changes occurred in the kaolinitedehidroxylation process [2]. In general, Al K-XANES spectra of aluminum-containing oxidesshowed three distinguishable peaks: one at 1566.0 eV assignable to tetrahedral AlO4 and twoassigned to AlO6 characteristic at 1568.0 and 1572.0 eV [3]. In the case of SAS there areseveral features, particularly there is a shoulder at 1566 eV and two AlO6-peaks one at1567.8 and other at 1571.4 eV. No major changes in the Si K-XANES were observed, i.e. theenvironments of Si it is not primarily affected for thermal transformations, except for a slightvariation in the 3p-holes density. This leads to the conclusion that the structural changes areattributable to changes in the Al environment.