Publication Date:
2015-07-29
Description:
The kinetics of oxygen grain-boundary diffusion in alumina was studied as a function of HfO 2 concentration. The oxidation of Ni marker particles to NiAl 2 O 4 spinel was utilized to delineate the position of the oxidation front. The HfO 2 doping levels spanned the solubility limit, ranging from 100 to 2000 ppm (Hf:Al concentration). For each dopant level, the parabolic rate constant ( k ) was determined for oxidation anneals carried out at 1400°C. Relative to undoped alumina, HfO 2 doping slowed the oxygen transport kinetics by a factor of approximately 3–8, depending on the dopant concentration. At 1400°C, the solubility limit of HfO 2 was found to be between 100 and 200 ppm. The results showed that the level of benefit saturated at the dopant level corresponding to the solubility limit (sol lim ), where 100 ppm 〈 sol lim 〈 200 ppm. The results of the transport experiments were also examined with respect to the fractional grain-boundary coverage ( f ), as opposed to overall HfO 2 content. An approximate linear relationship between the rate of oxygen transport and f was observed, which can be rationalized in terms of a site-blocking model.
Print ISSN:
0002-7820
Electronic ISSN:
1551-2916
Topics:
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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