Materials Ceramics

9 Ceramic Materials An example of a sufficiently conductive metal oxide is magnetite Fe304, which has been used, for example, in the past as corrosion resistant anode material for industrial chlorine evolution (it can be smelted and casted at 1500 °C, but it is a very brittle material). 

The modern material Ebonex is a mixture of substoichiometric titanium oxides Ti40y, TisOg. .. Tin02n-i ( Magneli phases [32]). It offers a unique combination of electrical conductivity and corrosion resistance. Primarily, Ebonex is produced as a powder. As is usual for ceramics, the ready-formed material is hard and brittle, the possibilities of machining are restricted (diamond tools). 

TABLE 57 Linear Shrinkage of Ciays on Drying and Strength of Dry Ciays  

500- 600 Dehydration loss of chemically combined water and modification of clay structure 

Pottery, one of the earliest human-made ceramic materials, is actually an artificial form of stone, made by combining the four basic elements recognized by the ancient Greeks earth (clay), water, air, and fire. In fact pottery is made from a circumstantial or deliberately prepared mixture of clay, other solid materials known by the generic name of fillers, and water. When a wet mixture of clay and fillers is formed into a desired shape, then dried and finally heated to high temperature (above 600°C), it becomes consolidated 

Common ancient ceramic materials often foxmd in archaeological excavations, such as fired brick and pottery, were made mostly from a mixture of a secondary clay and fillers. The nature, composition, and properties of clay have been already discussed the nature of the fillers, the changes undergone by the clay as well as by the fillers during their conversion to ceramics, and the xmique properties of ceramic materials, are reviewed in the following pages. Attention is drawn also to studies that provide information on the composition and characteristics of ancient ceramic materials. 

Some of these studies contribute to the understanding of ancient potterymaking techniques, others to learning about the provenance of pottery. The craft aspects of potterymaking, fascinating as they may be in themselves, are, however, outside the scope of this book (Rice 1982). 

---

CT was applied to various types of samples, such as a) concrete, b) asphalt c) wood and trees d) soil samples e) ceramic materials f) works of art. 

Fabrication technologies for ah electronic ceramic materials have the same basic process steps, regardless of the appHcation powder preparation, powder processing, green forming, and densiftcation. 

R. C. Buchanan, ed.. Ceramic Materials forElectronics, Marcel Dekker, Inc., New York, 1986. 

W. Bunk and H. Hausner, eds., Proc. oJ2ndInt. Sjmp. on Ceramic Materials and Componentsfor Engines, Vedag Deutsche Keramische GeseUschaft, Bad Honeff, 1986. 

P. F. Becher, M. V. Swain, and S. Somiya, eds., MdrancedStructural Ceramics, Materials Kesearch Society Sjmp. Proc. Vol. 78, Materials Research Society, Pittsburgh, Pa., 1987. 

G. Bandyopadhyay and co-workers in J. Tennery, ed., Proc. 3rd. Int. Sjmp. on Ceramics Materials and Components for Engines, American Ceramic Society, Westerville, Ohio, 1989, p. 1397. 

Mixing. The most widely used mixing method is wet ball milling, which is a slow process, but it can be left unattended for the whole procedure. A ball mill is a barrel that rotates on its axis and is partially filled with a grinding medium (usually of ceramic material) in the form of spheres, cylinders, or rods. It mixes the raw oxides, eliminates aggregates, and can reduce the particle size. 

Unlike conventional ceramic materials, glass-ceramics are fully densifted with zero porosity. They generally are at least 50% crystalline by volume and often are greater than 90% crystalline Other types of glass-based materials that possess low amounts of crystallinity, such as opals and mby glasses, are classified as glasses and are discussed elsewhere (see Glass). 

Fig. 1. Heat treatment cycle for a glass-ceramic material.

Certain glass-ceramic materials also exhibit potentially useful electro-optic effects. These include glasses with microcrystaUites of Cd-sulfoselenides, which show a strong nonlinear response to an electric field (9), as well as glass-ceramics based on ferroelectric perovskite crystals such as niobates, titanates, or zkconates (10—12). Such crystals permit electric control of scattering and other optical properties. 

R. Morrek, Handbook of Properties of Technical and Engineering Ceramics, Part 1 An Introduction for the Engineer and Designer, HMSO, London, 1985. Z. Stmad, Glass-Ceramic Materials, Glass Science and Technology, Vol. 8, Elsevier, Amsterdam, 1986. 

Tetraethylene glycol may be used direcdy as a plasticizer or modified by esterification with fatty acids to produce plasticizers (qv). Tetraethylene glycol is used directly to plasticize separation membranes, such as siHcone mbber, poly(vinyl acetate), and ceUulose triacetate. Ceramic materials utilize tetraethylene glycol as plasticizing agents in resistant refractory plastics and molded ceramics. It is also employed to improve the physical properties of cyanoacrylate and polyacrylonitrile adhesives, and is chemically modified to form polyisocyanate, polymethacrylate, and to contain siHcone compounds used for adhesives. 

The U.S. Bureau of Mines has employed glass for forming ceramic materials at high temperatures (75). The viscosity curve for a soda—lime—siUca glass in Figure 19 indicates the high viscosity available at hot forming temperatures. 

W. H. Git2en, ed.,Hlumina as a Ceramic Material, The American Ceramic Society, Columbus, Ohio, 1970, pp. 1—253. 

Refractories, Glass, Ceramic Materials Carbon and Graphite Products," ASTM Annual Book ofASTM Standards, Vol. 15.01, ASTM, Philadelphia, Pa., 1992. 

R. C. Bradt and R. E. Tressler, eds.. Deformation of Ceramic Materials, Proceedings of the 1974 Symposium, Plenum Press, New York, 1975. 

D. Kolar, iu R. J. Brook, ed.. Concise Enyclopedia of Advanced Ceramic Materials, Pergamon, Oxford, 1991, p. 484. 

---