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Phase selection in electrohydrodynamic atomization of alumina

  • C. G. Levi (a1), V. Jayaram (a1), J. J. Valencia (a1) and R. Mehrabian (a1)


Electrohydrodynamic atomization'has been adapted to produce Al2O3 powders ranging in size from 10 nm to 300 μm. Microstructural characterization using x-ray diffraction, scanning, and transmission electron microscopy reveals changes in phase selection as a function of particle size, hence supercooling. Amorphous powders are common below 100 nm in diameter. Cubic spinel γ is found in single phase form between 100 nm and 2μm, and partially transformed to δ between 2 and 20 μm. There is also evidence of σ and θ or a precursor of θ forming directly from the liquid above 5 μm. The stable corundum structure is consistently found above 20 μm but exhibits three different morphologies: faceted, dendritic, and cellular. Phase selection is examined on the basis of fundamental thermodynamic and kinetic considerations and results from computer models predicting the thermal history of the powders. It is concluded that metastable phases require the elimination of catalytic sites for the nucleation of a and are thus more likely to form in the smaller powders. Furthermore, submicron powders achieve sufficiently high cooling rates to preserve the metastable phases formed (γ), but those higher than ∼ 1 μm experience a thermal excursion long enough to transform γ to more stable forms of Al2O3.



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1Levi, C. G. and Mehrabian, R., Metall. Trans. A 13, 221 (1982).
2Levi, C. G. and Mehrabian, R., in Undercooled Alloy Phases, edited by Collings, E. W. and Koch, C. C. (The Metallurgical Society, Warrendale, PA, 1987), pp. 345374.
3Brockway, M. C. and Wills, R. R., “Rapid Solidification of Ceramics, A Technology Assessment,” Metals and Ceramics Information Center Report MCIC-84-49 (1984).
4Kronberg, M. L., Acta Metall. 5, 507 (1957).
5Lippens, B. C. and Boer, J. H. de, Acta Cryst. 17, 1312 (1964).
6Wafers, K. and Bell, G. M., Oxides and Hydroxides of Aluminum, Technical Paper No. 19 (Alcoa Research Laboratories, Alcoa Center, PA, 1972).
7Ervin, G., Acta Cryst. 5, 103 (1952).
8Saalfeld, H., Clay Min. Bull. 3, 249 (1958).
9Brindley, G. W. and Choe, J. O., J. Min. Soc. Am. 46(7/8), 771 (1961).
10Yamaguchi, G., Yasui, I., and Chiu, W., Bull. Chem. Soc. Jpn. 43, 2478 (1970).
11Lejus, A. M., Rev. Int. Hautes Temp. Refract. 1, 53 (1964).
12Rooksby, H. P. and Rooymans, C. J. M., Clay Min. Bull. 4, 234 (1961).
13Jayaram, V. and Levi, C. G., “The Structure of δ-Alumina Evolved from the Melt and the γ←δ Transformation,” submitted to Acta Metall.
14Geller, S., J. Chem. Phys. 33(3), 676 (1960).
15Ault, N. N., J. Am. Ceram. Soc. 40(3), 69 (1957).
16Plummer, M., J. Appl. Chem. 8, 35 (1958).
17Das, A. R. and Fulrath, R. M., in Reactivity of Solids, edited by Schwab, G. M. (Elsevier, New York, 1965), pp. 3144.
18McPherson, R., J. Mater. Sci. 8, 851 (1973).
19Wilms, V. and Herman, H., Thin Solid Films 39, 251 (1976).
20Hurley, G. F. and Gac, F. D., Ceram. Bull. 58, 509 (1979).
21McPherson, R., J. Mater. Sci. 15, 3141 (1980).
22Fargeot, D., Lortholary, P., and Dauger, A., in Ceramic Powders, edited by Vincenzini, P. (Elsevier, Amsterdam, 1983), pp. 977985.
23Dauger, A., Fargeot, D., and Laval, J. P., Mater. Res. Soc. Symp. Proc. 21, 207 (1984).
24Matthiesen, D. H. and Petuskey, W. T., J. Am. Ceram. Soc. 68(5), C114 (1985).
25Topol, L. E., Hengstenberg, D. H., and Blander, M., J. Non-Cryst. Solids 12, 377 (1973).
26Herman, H., “Properties of Materials Quenched from the Liquid State,” Final Report AR08571. 11-MC (1977).
27Jantzen, C. M., Krepski, R. P., and Herman, H., Mater. Res. Bull. 15, 1313 (1980).
28Dragoo, A. L. and Diamond, J. J., J. Am. Ceram. Soc. 50(11), 568 (1967).
29Goranchev, B. and Orlinov, V., Thin Solid Films 70, 111 (1980).
30Roy, D. M., Roy, R., and O'Holleran, T. P., “Innovative Technology for Fabrication of Ceramics: EDS Rapid Solidification Process Application to Specialized Materials,” Final Report Bureau of Mines OFR66-81, 53 (1980).
31Levi, C. G. and Mehrabian, R., Metall. Trans. A 13, 13 (1982).
32Shechtman, D., Ridder, S. D., and Mehrabian, R., in Rapid Solidification Processing, Principles and Technologies III, edited by Mehrabian, R. (National Bureau of Standards, Gaithersburg, MD, 1983), pp. 96104.
33Salas, O. and Levi, C. G., “Solute Redistribution and Interfacial Stability in Ultrafine Al-Fe-Ce powders,” accepted for publication in Int. J. Rapid Solidification.
34Kaufman, M. J. and Fraser, H. L., Int. J. Rapid Solidification 1, 27 (1984-1985).
35Mahoney, J. F., Taylor, S., and Perel, J., in Proceedings of the 1984 IEEE/IAS Annual Conference, Session on Electrostatic Processes (IEEE, Chicago, IL, 1984).
36Kingery, W. D., Bowen, H. K., and Uhlmann, D. R., Introduction to Ceramics (Wiley, New York, 1976), 2nd ed., p. 905.
37Levi, C. G., Valencia, J. J., and Mehrabian, R., in Processing of Structural Metals by Rapid Solidification, edited by Froes, F. H. and S. Savage, J. (ASM International, Metals Park, OH, 1987), pp. 112.
38JANAF Thermochemical Tables, J. Phys. Chem. Ref. Data 14, Suppl. 1, 156 (1985).
39Flemings, M. C., Solidification Processing (McGraw-Hill, New York, 1970), Chap. 9.
40Christian, J. W., The Theory of Transformations in Metals and Alloys, (Pergamon, Oxford, 1975), 2nd ed., P. I, Chap. 10.
41Levi, C. G., Metall. Trans. A 19, 699 (1988).
42Skapski, A. S., Acta Met. 4, 576 (1956).
43Kingery, W. D., J. Am. Ceram. Soc. 37(2), 42 (1954).
44Steiner, C. J. P., Hasselman, D. H. P., and Spriggs, R. M., J. Am. Ceram. Soc. 54(8), 412 (1971).
45Turnbull, D., in Ref. 2, pp. 322.
46Perepezko, H. J., Mueller, B. A., and Ohsaka, K., in Ref. 2, pp. 289320.

Phase selection in electrohydrodynamic atomization of alumina

  • C. G. Levi (a1), V. Jayaram (a1), J. J. Valencia (a1) and R. Mehrabian (a1)


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