Kinetics of alumina segregation in mullite ceramics

✍ Scribed by P. Fielitz; G. Borchardt; P. Mechnich; M. Schmücker

• Publisher: Elsevier Science
• Year: 2008
• Tongue: English
• Weight: 393 KB
• Volume: 28
• Category: Article
• ISSN: 0955-2219
• DOI: 10.1016/j.jeurceramsoc.2007.03.014

✦ Synopsis

Dense polycrystalline mullite was equilibrated for 6 h in air at 1800 • C and then quenched to room temperature. During subsequent annealing at 1600 • C a gradual decrease of the Al 2 O 3 concentration in the grains occurs which approaches an equilibrium concentration after about 100 h annealing time. A simplified model of spherical grains of uniform size is applied to describe the observed kinetics of the Al 2 O 3 concentration decrease in the mullite grains. This model allows to determine a chemical diffusion coefficient of Al 2 O 3 from the measured kinetics data. This chemical diffusion coefficient of Al 2 O 3 is compared to the ambipolar diffusion coefficient of Al 2 O 3 calculated from our tracer diffusivity data in single crystalline 2/1-mullite. The resulting thermodynamic factor is in reasonable agreement with the value calculated from literature data for mullite formation in a solid state reaction.