Brunauer, G.; Frey, Friedrich; Boysen, Hans; Schneider, H.
High temperature thermal expansion of mullite: An in situ neutron diffraction study up to 1600°C.
In: Journal of the European Ceramic Society, Vol. 21, No. 14: pp. 2563-2567
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Structural thermal expansions of undoped and Cr-doped 3/2 mullites (10.8 wt.\% Cr2O3) were measured with in situ neutron (25-1600°C) and X-ray synchrotron (25-1000°C) diffraction techniques. Heat treatments between 25 and 300°C cause little and non-linear structural expansions. Above 300°C and up to 1000°C the mullites display linear and low increase of the lattice constants. The mean values of undoped mullite are slightly higher (aav ≈ 5.45 × 10-6) than those of Cr-doped mullite (aav ≈ 4.95x10-6), thus confirming earlier in situ high-temperature diffraction data. Above about 1000°C the expansion behaves discontinuously. Structural expansions of undoped and Cr-doped mullite strongly increase yielding similar mean expansion coefficients (aav ≈ 7.50x10-6) for both materials. The highest increase of lattice constants has been determined in b axis direction throughout 1600°C in undoped and Cr-doped mullite. High temperature diffraction studies under heating-up and cooling-down conditions yielded reversible expansion effects, including the anomalous behaviour at about 1000°C.