High temperature single crystal properties of mullite
Journal of the European Ceramic Society 19(13-14): 2529-2541
Extensive neutron diffraction and Rietveld studies of dense, hot pressed mullite (3Al(2)O(3). 2SiO(2)) have been conducted up to 1650 degrees C in air, yielding a complete set of lattice parameters and axial thermal expansion coefficients. Unconstrained powders of the same stoichiometric composition were also analyzed by X-ray diffraction and Rietveld techniques up to 900 degrees C in air, from which lattice parameters and thermal expansion coefficients were obtained. An earlier reported structural discontinuity was confirmed by XRD to lie in the temperature range 425 to 450 degrees C. Single-crystalline mullite fibers of composition 2.5Al(2)O(3). SiO2 were grown from the melt by a laser-heated, float zone method. A partial set of the single-crystal elastic moduli were determined from various sections of fiber, by Brillouin spectroscopy, from room temperature up to 1400 degrees C. They indicated a roughly 10% reduction in stiffness over that temperature range. (C) 1999 Elsevier Science Ltd. All rights reserved.