Effect of Monovalent Cation Additives on the γ-Al2O3-to-α-Al2O3 Phase Transition

• Published in: Journal of the American Ceramic Society 2000-05, Vol.83 (5), p.1233-1236
• Main Authors: Okada, Kiyoshi, Hattori, Akiyoshi, Kameshima, Yoshikazu, Yasumori, Atsuo, Das, Rathindra Nath
• Format: Article
• Language: English
• Subjects: additives; alumina; phase transformations
• ISSN: 0002-7820; 1551-2916
• DOI: 10.1111/j.1151-2916.2000.tb01359.x

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.