Properties of ceramic materials

In addition to size, shape, and distribution and etchability of the phases, light reflectivity is a criterion for distinguishing and identifying the phases in a ceramic material. The reflectivity of ceramics is considerably lower than the reflectivity of metals. As an aid to microstructural examination, Figs. 53 and 54 plot the reflectivity 

R (as a percentage) of the phases of ceramic materials and refractory construction materials over the index of refraction n. 

The index of refraction n was calculated from the reflectivity R, disregarding the low amount of light absorbed by ceramics, and using the Fresnel formula  

The scatter range plotted on the graph occurs because the optical properties are anisotropic, reflectivity is dependent on wavelength, and the chemical composition of the phases varies. 

The brightness contrast K of two phases 1 and 2 occurring next to one another in the polished section is represented by the value  

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While mechanical properties of ceramic materials are usually quite adequate for the duties which they have to perform, it is essential to realise the limitations of the material, and to design and install any articles made from it in such a way as to minimise any weakness. Table 18.12 gives typical values for the mechanical properties of the different materials which are available. 

Ceramic materials are typically noncrystalline inorganic oxides prepared by heat-treatment of a powder and have a network structure. They include many silicate minerals, such as quartz (silicon dioxide, which has the empirical formula SiO,), and high-temperature superconductors (Box 5.2). Ceramic materials have great strength and stability, because covalent bonds must be broken to cause any deformation in the crystal. As a result, ceramic materials under physical stress tend to shatter rather than bend. Section 14.22 contains further information on the properties of ceramic materials. 

With the following example, we illustrate how in a sequence of activities the students intuitive notions about the influence of particle size and the sintering temperature of the clay on the properties of ceramic materials have productively been used (Klaassen Lijnse, 1996 Mortimer Scott, 2003 Duit Treagust, 2003 ... 

Common ancient ceramic materials often found 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 unique 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. 

The properties of ceramic materials depend on their structures and will be discussed separately for every branch of industry in chapter 11. In this paragraph some properties will be discussed which are measured in most branches of industry.Because the properties of ceramics differ in many aspects from those of metals and plastics and also because some knowledge of the last two is required, chapter 10 is devoted a comparison of these three material groups. In this paragraph they are only compared without going into the the structures of metals and plastics more deeply. 

Atkinson, A. and Selquk, A., Mechanical properties of ceramic materials for solid oxide fuel cells, in Proceedings of Solid Oxide Fuel Cells V, U. Stimming, S.C. Singhal, H. Tagawa and W. Lehnet (Eds.), The Electrochemical Society, Pennington, NJ, 1997, p. 671. 

Rigby, G.R., The effect of expansion mismatch on the mechanical properties of ceramic materials , Trans. Indian. Ceram. Soc., 1972 31(1) 18-30. 

Hampshire, S. (1994), Nitride ceramics , in Swain, M.V. (ed.) Structure and Properties of Ceramics, Materials Science and Technology Series, Vol. 11, Weinheim, VCH, Chapter 3, 119. 

The properties of ceramic materials are influenced not only by their chemical and mineralogical compositions, but also critically by their manufacture-dependent microstructure. Under the terms microstructure or structure is meant the spatial distribution of the individual phases as well as the shape, size and orientation of the particles, pores and glassy phases. 

Ceramic powder characteristics are important because the purity of the powder sets the maximum purity level of the final processed ceramic part, and the particle size and size distribution play major roles in defining the microstructure and properties of the final parts. Both the purity and the microstructure of sintered ceramics influence the properties of ceramic materials, including mechanical, thermal, electrical, and magnetic properties and chemical corrosion resistance. 

Macroscopic properties of ceramic materials are often dominated by localized imperfections such as defects, impurities, surfaces and interfaces. Systematically-doped polycrystalline materials exhibit wider variety of properties as compared with monolithic single crystals. Some of them serve key roles in high-tech society and they are referred to as fine ceramics or advanced ceramics. An ultimate objective of the ceramic science and technology is to understand the nature and functions of the localized imperfections in order to achieve desired performances of materials intellectually without too much accumulation of empirical knowledge. 

Data on atmospheric carbon dioxide Mechanical, thermal, and other properties of ceramic materials... 

In this chapter we examine four key properties of ceramic materials all of which we can classify as optical. (1) Ceramics can be transparent, translucent, or opaque for one particular composition. (2) The color of many ceramics can be changed by small additions additives, dopants, or point defects. (3) Ceramics can emit light in response to an electric field or illumination by light of another wavelength. (4) Ceramics can reflect and/or refract light. We will discuss why these effects are special for ceramics and how we make use of them. 

Rico, A., Garrido, M. A., Otero, E. Rodriguez, J. Roughness Effect on the Mechanical Properties of Ceramic Materials Measured from Nanoindentation Tests. Key Engineering Materials 333, 247-250 (2007). 

The objective of this task Is to develop a comprehensive computer data base containing the experimental data on properties of ceramic materials generated In the overall effort, This computer system is intended to provide a convenient and efficient mechanism for the compilation and dissemination of the large amounts of data involved. The data base will be made available In electronic form to all project participants. In addition, periodic hard copy summaries of the data, Including graphical representation and tabulation of raw data, will be Issued to provide convenient information sources for project participants. 

Garter, G. Barry, and M. Grant Norton. Ceramic Materials Science and Engineering. New York Springer, 2007. Covers ceramic science, defects, and the mechanical properties of ceramic materials and how these materials are processed. Provides many examples and illustrations relating theory to practical applications suitable for advanced undergraduate and graduate study. 

Amey, D.I. and CuriUa, J.E., Microwave properties of ceramic materials. Proceedings of ilst ECTC, IEEE, Eiscataway, NJ, 1991, pp. 267-272. 

Thermal Properties of Ceramic Materials 4.4.1 Thermal Conductivity... 

The mechanical properties of ceramic materials are strongly influenced by the strong interatomic bonds that prevail. Dislocation mechanisms, which create slip mechanisms in softer metals, are relatively scarce in ceramics, and failure may occur with very little plastic deformation. Ceramics also tend to fracture with little resistance. 

As shown in Table 8.1, the piezoelectric effect causes the creation of charges in a dielectric and ferroic materiaL respectively, in response to an applied stress field. The opposite effect-that is, the induction of strain (deformation) by applying an outside electric field-is called the inverse piezoelectric effect. Piezoelectricity requires that no symmetry center exists in the crystal structure. The piezoelectric properties of ceramic materials are described by four parameters (i) the dielectric displacement D (ii) the electric field strength E (iii) the applied stress X and (iv) the strain (deformation) x. These are related by two equations that apply to the (direct) piezoelectric effect D = e x and E = h x, and two equations that apply to the inverse piezoelectric effect x = g D and x = d E. The four coefficients e, h, g, and d are termed the piezoelectric coefficients. 

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