Design of High Thermal Expansion Glass-Ceramics Through Microstructural Control
High thermal expansion glass-ceramics can be made from lithium silicate glasses that contain small amounts of P2O5. The essential step involves heating the glass to a temperature near 1000°C to grow well-faceted 0.1–0.5 μm Li3PO4 crystallites in the molten glass matrix. When the temperature is lowered to the 750°–850°C range, a mixture of high expansion SiO2 polymorphs and lithium silicate phases crystallize. TEM observations on one composition reveal the crystallization is by epitaxial growth on specific faces of the Li3PO4 crystallites. Heat treatments that do not form faceted Li3PO4 crystallites give glass-ceramics with much lower expansion coefficients. Our understanding and control of this epitaxial crystallization and growth mechanism has led to the development of a family of high thermal expansion glass ceramics useful for making hermetic seals with a number of stainless steels and superalloys.
KeywordsEpitaxial Growth Glass Composition High Expansion Lithium Disilicate Lithium Silicate
Unable to display preview. Download preview PDF.
- 1.P. W. McMillan, Glass Ceramics. 2nd edition, Academic Press, New York (1979) pp. 245–266.Google Scholar
- 2.R. D. Watkins and R. E. Loehman, “Interfacial Reactions Between A Complex Lithium Silicate Glass-Ceramic and Inconel 718,” Adv. Ceramic Materials 1  77–80 (1986).Google Scholar
- 3.T. J. Headley, R. E. Loehman, R. D. Watkins, and M. C. Madden, “Study of the Interfacial Reaction Zone in a Glass-Ceramic to Metal Seal by Analytical Electron Microscopy,” Proc. 44th Annual Meeting, Electron Microscopy Society of America, ed., G. W. Bailey, (San Francisco Press, San Francisco, CA) pp. 856–7.Google Scholar
- 4.S. C. Kunz and R. E. Loehman, “Thermal Expansion Mismatch Produced by Interfacial Reactions in Glass-Ceramic to Metal Seals,” accepted for publication in Adv. Ceramic Materials.Google Scholar
- 6.H. L. McCollister and S. T. Reed, “Glass-Ceramic Seals to Inconel,” U.S. Patent 4,414,282, November 8, 1983.Google Scholar
- 7.P. W. McMillan, Op cit., p. 102.Google Scholar
- 9.H. P. Klug and Leroy E. Alexander, X-Ray Diffraction Procedures. ( Wiley, New York, 1954 ), pp. 162–585.Google Scholar