Unformatted text preview: 422 ● Chapter 13 / Types and Applications of Materials ber of common environments and, therefore, susceptible to corrosion. Galvanized steel is just plain carbon steel that has been coated with a thin zinc layer; the zinc preferentially corrodes and protects the steel (Section 16.9). Typical applications of galvanized steel are familiar (sheet metal, fences, screen, screws, etc.). Common applications of zinc alloys include padlocks, automotive parts (door handles and grilles), and ofﬁce equipment. Although zirconium is relatively abundant in the earth’s crust, it was not until quite recent times that commercial reﬁning techniques were developed. Zirconium and its alloys are ductile and have other mechanical characteristics that are comparable to those of titanium alloys and the austenitic stainless steels. However, the primary asset of these alloys is their resistance to corrosion in a host of corrosive media, including superheated water. Furthermore, zirconium is transparent to thermal neutrons, so that its alloys have been used as cladding for uranium fuel in water-cooled nuclear reactors. In terms of cost, these alloys are also often the materials of choice for heat exchangers, reactor vessels, and piping systems for the chemical-processing and nuclear industries. They are also used in incendiary ordnance and in sealing devices for vacuum tubes. In Appendix B is tabulated a wide variety of properties (e.g., density, elastic modulus, yield and tensile strengths, electrical conductivity, coefﬁcient of thermal expansion, etc.) for a large number of metals and alloys. TYPES OF CERAMICS
The preceding discussions of the properties of materials have demonstrated that there is a signiﬁcant disparity between the physical characteristics of metals and ceramics. Consequently, these materials are utilized in totally different kinds of applications and, in this regard, tend to complement each other, and also the polymers. Most ceramic materials fall into an application–classiﬁcation scheme that includes the following groups: glasses, structural clay products, whitewares, refractories, abrasives, cements, and the newly developed advanced ceramics. Figure 13.6 presents a taxonomy of these several types; some discussion is devoted to each. We have also chosen to discuss the characteristics and applications of diamond and graphite in this section. Ceramic materials Glasses Clay products Refractories Abrasives Cements Advanced ceramics Glasses Glassceramics Structural Whitewares clay products Fireclay Silica Basic Special FIGURE 13.6 Classiﬁcation of ceramic materials on the basis of application. ...
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- Spring '08
- Accounting, nuclear reactors, Ceramic materials, Austenitic Stainless Steels, water-cooled nuclear reactors, Clay Products