Glass-ceramics and realization of the unobtainable: Property combinations that push the envelope
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uction Materials undergo some type of fundamental change during preparation from the raw materials to their final state. Prepared metals and ceramics date back nearly 12,000 years. Glassmaking dates back about one-half of that timespan, 4500 to 6000 years, whereas polymers, semiconductors, and graphene, for instance, are more recent additions, less than a century or even recent decades. The use of natural materials (e.g., wood, bone, and stone) dates further back than any of these materials, tied to the development of rudimentary tools of our distant ancestors. As civilization developed, so has the complexity with which materials are designed, prepared, and characterized. Some 65 years ago, an alert and innovative researcher, S.D. Stookey, at Corning Glass, in Corning, N.Y., realized he had discovered something quite useful in what was an otherwise failed experiment—a highly crystallized glass with mechanical properties superior to those of the precursor glass.1 Thus began intentional and focused research toward expanding knowledge and realizing specific applications with this unique “new” material. Of course, to geologists, a glass— or more correctly, a supercooled liquid at the temperatures required for crystallization—that crystallizes to one or more crystalline phases is a well-known material: an igneous rock,
with granite, a classic example. However, to the glass-ceramic researcher, either academic or industrial, the chemistry and realized crystal phases are far less constrained than they are in the natural world. So too are the resulting physical, chemical, and optical properties. Figure 12 shows an optical micrograph of a glass-ceramic containing one crystal phase dispersed in a residual glass matrix. Figure 2 shows a typical example in which a glass-ceramic combines two properties in a way not easily accessible in any other material. The application considered here is for a substrate material, highly transparent at 1.5 microns, used to produce an extremely narrow passband filter for telecommunications purposes (dense wavelength division multiplexing). For a sufficiently small temperature dependence of the passband, as demanded by the application, optical coating companies found out in the 1990s that a specific and difficult to achieve combination of Young’s modulus and thermal expansion was required (“target” region). Unfortunately, no known optical glass material could meet this specific combination (symbols in figure represent the entire SCHOTT optical glass catalog, 20003). However, both SCHOTT AG4 and Ohara Corp.5 were able to develop glass-ceramics that could meet this unique and challenging combination of properties.
Mark J. Davis, Department of Research and Development, SCHOTT North America, Inc., USA; [email protected] Edgar D. Zanotto, Center for Research, Technology, and Education in Vitreous Materials, Universidade Federal de São Carlos, Brazil; [email protected] doi:10.1557/mrs.2017.27
• VOLUME 2017 Materials Research Society MRSCambridge BULLETIN Core 42of• use, MARCH 2017 • at www.mrs.org/bulleti
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