Transformaciones térmicas de una arcilla kaolinítica modelo: uso de Al-K XANES para la caracterización de las fases y sus transformaciones.

L. ANDRINI; M.R. GAUNA; M.S. CONCONI; G. SUÁREZ; F.G. REQUEJO; E.E. AGLIETTI; N.M. RENDTORFF

Santa Fe

Congreso; XIV IBEROMAT-SAM-CONAMET; 2014

SAM-Asociación Argentina de Materiales

The thermal transformations of kaolinite (K: Al2O3·2SiO2·2H2O) in kaolin clays are dehydroxylation to Metakaolin (MK) at temperatures around 600 °C, followed by a transformation to a phase of low crystallinity: a silico-aluminate spinel (SAS) at temperatures around 980 °C. Finally mullite (M) is formed at temperatures between 1220 and 1300 °C. The temperature at which these changes occur can be assessed by various thermal analysis techniques, also consist of different properties of natural materials, and are a function of the geochemical properties and the heating rate. K, MK, SAS and M have various technological applications in various industries like ceramics, cement, paper, etc. Structural characterization of these phases is usually made by X-ray Diffraction (XRD). M and K have well-defined diffraction patterns, while MK and SAS are low crystallinity phases and the DRX characterization is difficult. In this article, X-ray Absorption characterization (Al K X-ray Absorption Near Edge Structure) is presented for the four materials mentioned. It were obtained from an Argentine kaolinitic clay, obtained from different heat treatment (500, 800, 1000 and 1250 ° C) with 15 minute hold and 5 ° C / min heating rate. Additionally, the results of a series of ceramic characterizations are presented. These include chemical analysis, thermogravimetric and differential thermal analysis (TG-DTA), particle size distribution, and identification and characterization based on DRX and Rietveld method of the structure refinement. The local structure of the Al atoms in the materials is studied in comparison with standards structure. These results demonstrate the potential of the XANES technique for characterization of natural materials with low crystallinity, and could complement traditional use of DRX techniques.