High temperature single crystal properties of mullite

Interphase Debonding in High Temperature Ceramic Composites

“…*Values in this table are intended only as rough guide for relative stresses. They were calculated using a coaxial cylinder analysis, assuming a temperature change of AT = 1000°C, coating thickness 2 jam, zero volume fraction of fibers, and the following Young's moduli and thermal expansion coefficients (nominal isotropic, temperature-independent values): polycrystalline A1 2 0 3 (400 GPa, 8 x 10" 6 °C _1 ); sapphire (400 GPa, 8 x 10 _s "C" 1 ); mullite (200 GPa, 4 x 10" 6 "C" 1 ); 46 Al 2 0 3 /Zr0 2 (300 GPa, 9 x 10 -6 °C 1 ); and A1 2 0 3 /YAG (350 GPa, 8.5 x 10" 6 "C 1 ). 16 ' 17 The hot-pressed disk was cut into slices (thickness -0.3 to 2mm) normal to the fibers.…”

High temperature elasticity measurements on oxides by Brillouin spectroscopy with resistive and IR laser heating

“…ω ω c 2n sin(θ/2) = ωλ 2n sin(θ/2) (1) where V is the velocity of an acoustic wave, ω is frequency shift of scattered light, ω is the frequency and λ is the wavelength of the incident light, c is the speed of light in vacuum, n is the index of refraction of the sample, and θ is the scattering angle, or the angle between the incident laser ray and scattered ray inside the sample. Among the advantages of this technique are that it requires only very small samples, and that acoustic velocities can be measured along numerous crystallographic directions in a single sample, which makes it highly suitable for measurements on low-symmetry crystals.…”

“…The high-temperature elastic moduli were measured on fibers of mullite (∼2.5Al 2 O 3 ·SiO 2 ), a common ceramic material, to 1475 K. 1,34 Even though the samples consisted of highly-textured polycrystalline fibers, 35 with crystallites having different rotation about their c axis by up to 5 • , it was possible to extract all nine single crystal elastic constants (orthorhombic symmetry). That study 34 revealed substantial differences between bulk elastic properties calculated from "single crystal" measurements and the properties reported in the literature for polycrystalline-sintered mullite.…”

Single crystalline mullite fibres obtained by the internal crystallisation method: Microstructure and creep resistance

“…1,2 An important obstacle on a way to use both these forms of mullite as structural materials for high temperature applications is its inherent brittleness. Hence, fibrous composites of a special structure are needed to make mullite-based materials to be sufficiently tough.…”