Preparation and Anisotropic Lattice Thermal Expansion of Hexagonal Cordierite

The hexagonal cordierite was synthesized by the reverse coprecipitation-calcination method and characterized by powder X-ray diffraction. The lattice thermal expansion behavior of hexagonal cordierite was investigated by high temperature X-ray diffraction in the temperature range 298-1273 K. The lattice parameters of the hexagonal cordierite at different temperature were calculated by a least squares method. The hexagonal cordierite expressed anisotropic thermal expansion behavior with the average lattice thermal expansion coefficient were 2.13×10 -6 K -1 along a or b axis and-1.03×10 -6 K -1 along c axis from room temperature to 1273 K. The crystal structure of hexagonal cordierite at 298 K and 1273 K were refined by Rietveld method. The thermal expansion coefficient of the height of the [MgO 6 ]-[AlO 4 ] polyhedral layer is-1.8×10 -6 K -1 . Although the six-member ring expressed the normal positive thermal expansion along arbitrary direction, the height thermal expansion coefficient of the six-member ring is just 0.6×10 -6 K -1 .