Structural transformations of Muscovite at high temperature by X-ray and neutron diffraction

Structural transformations of Muscovite at temperature up to 1095 degrees C were determined using powder X-ray and neutron diffraction. Data were collected at room temperature from preliminary heated and quenched samples at 650 degrees C, 980 degrees C and 1095 degrees C. X-ray data were interpreted by either Rietveld method and neutron data, which complete the structural information by a better assignation of oxygen positions. With neutron data atom position was refined by fitting Pair Distribution Functions. It was found to be a progressive but continuous microstructural change, with the formation of an increasingly disorganized structure, but the layered organization of muscovite is maintained up to 1095 degrees C. Rietveld refinements from X-ray confirm the 6 to 5 coordination of Al atoms above 650 degrees C. It induces some structural changes as the orientation and mutual position of tetrahedrons in silicate layers. Pair Distribution Function refinements show the weakening of the long range structural organization, above 5 angstrom. At lower distance, a local order is maintained and the preferential alignments of both alumina unit pairs and silica tetrahedron were observed. This residual structural order of high-temperature muscovite is favorable to the achievement of textured ceramics. (C) 2007 Elsevier B.V. All rights reserved.