Oxygen grain-boundary transport in polycrystalline alumina using wedge-geometry bilayer samples: Effect of Y-doping

✍ Scribed by H. Cheng; H.S. Caram; W.E. Schiesser; J.M. Rickman; H.M. Chan; M.P. Harmer

• Book ID: 103999035
• Publisher: Elsevier Science
• Year: 2010
• Tongue: English
• Weight: 979 KB
• Volume: 58
• Category: Article
• ISSN: 1359-6454
• DOI: 10.1016/j.actamat.2009.12.030

✦ Synopsis

Novel wedge-geometry, dual-layer alumina samples, both undoped and 500 ppm Y 3+ -doped, were studied in the temperature regime 1250-1400 °C to determine the effect of Y 3+ on oxygen grain-boundary transport in alumina. The samples consisted of a wedge-shaped, single-phase alumina top layer, diffusion bonded to an alumina/Ni substrate containing a fine, uniform dispersion of Ni marker particles (0.5 vol.%). The extent of the alumina spinel oxidation layer was measured as a function of the wedge thickness for a series of heat-treatment conditions. Models of the transport behavior were used to derive values for the rate constants (k) in both the alumina top layer and the alumina/Ni substrate. It was found that the presence of yttrium slows oxygen grain-boundary diffusion in alumina by a factor of $5 (at 1300 °C), and increases the corresponding activation enthalpy for oxidation from 407 ± 20 to 486 ± 34 kJ mol À1 . Microstructural observations suggested that yttrium also slows Ni outward diffusion. A comparison of the different k values revealed that, at 1300 °C, the presence of Ni alone enhances transport by a factor of $2 relative to undoped alumina.