Thermal transformations metakaolin ? spinel type aluminosilicate: Al and Si K-XANES characterization

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

Campinas

Otro; Annual Users Meeting LNLS/CNPEM; 2015

LNLS/CNPEM

Since the pioneering work of G.W. Brindley and M. Nakahira it is knownthat one of the open problems concerning the metakaolin phase, the manner inwhich it transforms into a spinel-type phase and mullite, and the relation ofthis spinel-type phase to mullite, because the series of reactions by whichkaolinite transforms to mullite is perhaps the most important in the entirefield of ceramic technology [1].The thermal transformations of kaolinite (K) in metakaolin (MK) and themetakaolin in a spinel type aluminosilicate (SAS) were studied by Al and Si K-XANESto correlate the information obtained with this technique with that obtained byconventional X-ray Diffraction, and clarify and assign the structural changes. Simultaneouslywith XANES technique is possible to observe changes in the electronic structureof the system.For K à MK transformation, by Al K-XANESit was obtained results consistently with reported Aluminium coordinationchanges occurred in the kaolinite dehidroxylation process [2]. In general, AlK-XANES spectra of aluminum-containing oxides showed three distinguishablepeaks: one at 1566.0 eV assignable to tetrahedral AlO4 and twoassigned to AlO6 characteristic at 1568.0 and 1572.0 eV [3]. In thecase of SAS there are several features, particularly there is a shoulder at1566 eV and two AlO6-peaks one at 1567.8 and other at 1571.4 eV. Nomajor changes in the Si K-XANES were observed, i.e. the environments of Si it is not primarily affected forthermal transformations, except for a slight variation in the 3p-holes density.This leads to the conclusion that the structural changes are attributable tochanges in the Al environment. [1] G.W. Brindley and M. Nakahira, J.Am. Ceram. Soc., 42, 311-314 (1959).