The effect of monovalent cation addition on the γ-Al2O3-to-α-Al2O3 phase transition was investigated by differential thermal analysis, powder X-ray diffractometry, and specific-surface-area measurements. The cations Li+, Na+, Ag+, K+, Rb+, and Cs+ were added by an impregnation method, using the appropriate nitrate solution. β-Al2O3 was the crystalline aluminate phase that formed by reaction between these additives and Al2O3 in the vicinity of the γ-to-α-Al2O3 transition temperature, with the exception of Li+. The transition temperature increased as the ionic radii of the additive increased. The change in specific surface area of these samples after heat treatment showed a trend similar to that of the phase-transition temperature. Thus, Cs+ was concluded to be the most effective of the present monovalent additives for enhancing the thermal stability of γ-Al2O3. Because the order of the phase-transition temperature coincided with that of the formation temperature of β-Al2O3 in these samples, suppression of ionic diffusion in γ-Al2O3 by the amorphous phase containing the added cations must have played an important role in retarding the transition to α-Al2O3. Larger cations suppressed the diffusion reaction more effectively.
|Number of pages||4|
|Journal||Journal of the American Ceramic Society|
|Publication status||Published - Jan 1 2000|
ASJC Scopus subject areas
- Ceramics and Composites
- Materials Chemistry