Effect of Aging on Alumina Gels Rheology and Aerogels Surface Area
- 113 Downloads
Alumina gels were synthesized by catalyzed gelation of aluminum sec-butoxide (ASB) via the Yoldas process. The gels were aged for up to 6 months and then supercritically dried (SCD) with CO2. The molar ratio of acid to ASB was in the range of 0.01–0.6. Viscosity measurements of the gels showed a shear thinning and plastic behavior with no response up to a limiting yield stress. The gel rheology obeys the Casson model. Analysis of the viscosity as a function of the acid to alkoxide molar ratio, showed that the average molecular weight of the gels is inversely proportional to the acid to alkoxide molar ratio.
The viscosity of all the gels increased with aging time for a period of about 6 months reaching an asymptotic value after 1–2 weeks. The viscosity is shown to correlate with the microstructure of these nanomaterials during aging. Aging gives rise to a nearly constant surface area of ∼350 m2/g regardless of acid to alkoxide ratio in an aging period of about 6 months.
Unable to display preview. Download preview PDF.
- 1.C. Gonza'lez, J. Gutie'rrez, J. Llorens, M.I. Gala'n, and C. Mans, J. Non-Cryst. Sol. 147/148, 690 (1992).Google Scholar
- 2.J.Y. Chane-Ching and L.C. Klein, J. Am. Ceram. Soc. 71(1), 83 (1988).Google Scholar
- 3.J.K. Bailey, T. Nagase, S.M. Broberg, and M.L. Mecartney, J. Non-Cryst. Sol. 109, 198 (1989).Google Scholar
- 4.W.H. Shih and L. Pwu, J. Mater. Res. 10(11), 2808 (1995).Google Scholar
- 5.S. Sakka and K. Kamiya, J. Non-Cryst. Sol. 48, 31 (1982).Google Scholar
- 6.M.D. Sacks and R.S. Sheu, J. Non-Cryst. Sol. 92, 383 (1987).Google Scholar
- 7.G.C. Bye and K.S.W. Sing, in Particle Growth in Suspension, edited by A.L. Smith (Academic Press, NY, 1973), p. 29.Google Scholar
- 8.C.J. Brinker and G.W. Scherer, Sol-Gel Science: The Physics and Chemistry of Sol-Gel Processing (Academic Press, NY, 1990), pp. 48, 207, 359.Google Scholar
- 9.B.E. Yoldas, J. Appl. Chem. Biotech. 23, 803 (1973).Google Scholar
- 10.G.S. Grader, Y. Rifkin, Y. Cohen, and S. Keysar, J. Sol-Gel Sci. Tech. 1/3, 825 (1997).Google Scholar
- 11.S. Keysar, Y. De Hazan, Y. Cohen, T. Aboud, and G.S. Grader, J. Mater. Res. 12, 430 (1997).Google Scholar
- 12.B.E. Yoldas, J. Mater. Sci. 10, 1856 (1975).Google Scholar
- 13.F.F. Lange, B.V. Velamakanni, J.C. Chang, and D.S. Pearson, in Structural Ceramics Processing, Microstructure and Properties: Proceedings of the 11th Riso International Symposium on d Materials Science, edited by J.J. Bentzen, J.B. Bilde-Sorensen, N. Christiansen, A. Horsewell, and B. Ralph (Riso National Laboratory, 1990), p. 57.Google Scholar
- 14.C.J. Brinker and G.W. Scherer, J. Non-Cryst. Sol. 70, 301 (1985).Google Scholar
- 15.M. Doi and S.F. Edwards, The Theory of Polymer Dynamics (Oxford University Press, NY, 1994), p. 227.Google Scholar
- 16.E.J.A. Pope and J.D. Mackenzie, J. Non-Cryst. Sol. 101, 198 (1988).Google Scholar
- 17.R. Xu, E.J.A. Pope, and J.D. Mackenzie, J. Non-Cryst. Sol. 106, 242 (1988).Google Scholar
- 18.S. Sakka, K. Kamiya, K. Makita, and Y. Yamamoto, J. Non-Cryst. Sol. 63, 242 (1984).Google Scholar
- 19.R.J. Pugh and L. Bergstrom, Surface and Colloid Chemistry in Advanced Ceramics Processing: Surfactant Science Series, Vol. 51 (Dekker, NY, 1994), p. 197.Google Scholar