Crystallinity of boehmite and its effect on the phase transition temperature of alumina

Abstract

The effect of the crystallinity of boehmite powders on the temperatures of γ-Al₂O₃ formation and the θ- to α-Al₂O₃ transformation was investigated using boehmite powders of varying crystallite size prepared under various hydrothermal conditions. With increasing crystallite size of the boehmite powders, the specific surface area decreased and the expanded (020) d-spacing approached the reported value. Thermogravimetric (TG) profiles of more poorly crystalline boehmite indicated the presence of excess water molecules of different binding energy located on the surface or in the interlayer. The crystallite size of boehmite also showed a strong correlation with the formation temperature of γ-Al₂O₃ and the phase transition temperature of θ- to α-Al₂O₃. Since both these temperatures are increased with increasing the crystallite size of boehmite, this is an important factor in determining the conditions for obtaining γ-, θ- and α-Al₂O₃ from boehmite. By relating the TG weight loss to the water and OH contents in boehmite and γ-Al₂O₃, respectively, the crystallite size of boehmite can be related to the water content. This indicates that the γ-Al₂O₃ transformed from boehmite of smaller crystallite size contains larger amounts of OH groups, implying more poorly crystalline γ-Al₂O₃. The reported topotactic transformation of boehmite via γ- to θ-Al₂O₃ indicates a relationship between the crystallite size of the boehmite and that of the resulting transition alumina, which could explain the change of the phase transition temperature from θ- to α-Al₂O₃.

References

1. J. H. DeBoer and B. C. Lippens, J. Catal., 1964, 3, 38.
2. H. Knozinger and P. Ratnasamy, Catal. Rev.-Sci. Eng., 1978, 17, 31.
3. A. B. Stiles, Catalyst Supports and Supported Catalysts, Butterworths, London, 1987.
4. F. W. Dynys and J. W. Halloran, in Ultrastructure Processing Ceramics, Glasses, and Composites, ed. L. L. Hench and D. R. Ulrich, John Wiley and Sons, New York, 1984, p. 142.
5. D. L. Clark and J. J. Lannutti, in Ultrastructure Processing Ceramics, Glasses, and Composites, ed. L. L. Hench and D. R. Ulrich, John Wiley and Sons, New York, 1984, p. 126.
6. K. Wefers and C. Misra, Oxide and Hydroxide of Aluminum, Alcoa Technical Paper No.19, Alcoa Laboratories, Pittsburgh, PA, 1987.
7. R. D. Tottenhorst and D. A. Hofmann, Clays Clay Miner., 1980, 28, 373.
8. B. E. Yoldas, J. Am. Ceram. Soc., 1982, 65, 387.
9. S. J. Wilson, J. Br. Ceram. Soc., 1979, 28, 281.
10. B. C. Lippens and J. H. D. Boer, Acta. Crystallogr., 1964, 17, 1312.
11. C. F. J. Baes and R. E. Mesmer, The Hydrolysis of Cations, John Wiley and Sons, New York, London, Sydney, Toronto, 1976.
12. T. Tsukada, T. Saito, H. Segawa, A. Yasumori and K. Okada, J. Ceram. Soc. Jpn., submitted.
13. S. Castet, J. Dandurand, J. Schotte and R. Gout, Geochim. Cosmochim. Acta, 1993, 57, 4869.
14. H. Yanagida and G. Yamaguchi, Bull. Chem. Soc. Jpn., 1964, 37, 1229.
15. H. Yanagida, G. Yamaguchi and J. Kubota, Bull. Chem. Soc. Jpn., 1965, 38, 2194.
16. R. Zhou and R. L. Snyder, Acta Crystallogr., Sect. B, 1991, 47, 617.
17. S. Soled, J. Catal., 1983, 81, 252.
18. P. Burtin, J. P. Brunelle, M. Pijolat and M. Soustelle, Appl. Catal., 1987, 34, 239.
19. T. Tsuchida, R. Furuich and T. Ishii, Thermochim. Acta, 1980, 39, 103.
20. H. Schaper and L. L. Van Reijen, Thermochim. Acta, 1984, 77, 383.
21. B. E. Yoldas, J. Mater. Sci., 1976, 11, 465.
22. M. Pijolat, M. Dauzat and M. Soustelle, Thermochim. Acta, 1987, 122, 71.
23. Y. Saito, T. Takei, S. Hayashi, A. Yasumori and K. Okada, J. Am. Ceram. Soc., 1998, 81, 2197.
24. M. Kumagai and G. L. Messing, J. Am. Ceram. Soc., 1984, 67, C230.
25. J. L. McArdle and G. L. Messing, Adv. Ceram. Mater., 1988, 3, 387.
26. R. A. Shellmann and G. L. Messing, J. Am. Ceram. Soc., 1988, 71, 317.
27. J. L. McArdle and G. L. Messing, J. Am. Ceram. Soc., 1989, 72, 864.
28. S. Jagota and R. Raj, J. Mater. Sci., 1992, 27, 2251.
29. T. Horiuchi, T. Osaki, T. Sugiyama, H. Masuda, M. Horio, K. Suzuki, T. Mori and T. Sago, J. Chem. Soc., Faraday Trans., 1994, 90, 2573.