Common Ceramic Materials

The electrical characteristics of ceramic materials vary gteady, since the atomic processes ate different for the various conduction modes. The transport of current may be because of the motion of electrons, electron holes, or ions. Electrical ceramics ate commonly used in special situations where reftactoriness or chemical resistance ate needed, or where other environmental effects ate severe (see Refractories). Thus it is also important to understand the effects of temperature, chemical additives, gas-phase equilibration, and interfacial reactions. 

These lead-based materials (PZT, PLZT, PMN) form a class of ceramics with either important dielectric, relaxor, pie2oelectric, or electrooptic properties, and are thus used for appHcations ia actuator and sensor devices. Resistive properties of these materials ia film form mirror the conduction processes ia the bulk material. Common problems associated with their use are low dielectric breakdown, iacreased aging, and electrode iajection, decreasiag the resistivity and degrading the properties. 

All ceramic materials are elastic, and hence show very little bending under load. They do not exhibit any creep under load. The modulus of rupture type of test is the routine test most commonly used in the ceramic industry, and gives the figure generally quoted for the strength of the material. It must be remembered that the value obtained for any particular body depends on the cross-sectional area of the test piece thus figures quoted from test results may be higher than those obtained on actual articles, which usually have a thicker section than the test piece. 

Ceramics and minerals present many common problems, but ceramics warrant special treatment because elements of low atomic number predominate in them and they consequently offer x-ray emission spectrog-raphy of the light elements an excellent opportunity to prove its usefulness. Scott,8 in making this clear, emphasized the absorption and enhancement effects to be expected, and pointed out the need for careful sample preparation. By use of a General Electric XRD-5 spectrograph and associated equipment, he set up working curves for alumina, silica, potash, lime, phosphate, titania, and iron oxide in clays, refractories, and other ceramic materials. 

The reaction is carried out under an inert atmosphere in an open crucible at approximately 830°C. Figure 1 shows typical equipment used for direct oxide reduction. Vitrified magnesium oxide ceramic is commonly used as a container material, but tungsten and tantalum can also be used(3). If the latter are used, CaF2 is added to lower the temperature needed to liquify... 

Network solids are typically hard and rigid they have high melting and boiling points. Ceramic materials are commonly network solids. 

The deposition of a binary compound can be achieved by a coreduction reaction. In this manner, ceramic materials such as oxides, carbides, nitrides, borides, and silicides can be produced readily and usually more readily than the parent metal. A common example is the deposition of titanium diboride ... 

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 above methods represent the most commonly employed methods for inorganic electronic thin film preparation. A variety of other methods, including Pechini,21 citrate,86 nitrate,23 and aqueous processes87 have also been used. For a discussion of these methods, the reader is referred to Refs. 5 through 12, which highlight these methods for the preparation of various electronic ceramic materials. 

Here again certain trends were observed, and the most influential factor was the crystal structure which the superconducting material adopted. The most fruitful system was the NaCl-type structure (also referred to as the B1 structure by metallurgists). Many of the important superconductors in this ceramic class are based on this common structure, or one derived from it. Other crystal structures of importance for these ceramic materials include the Pu2C3 and MoB2 (or ThSi2) prototypes. A plot of transition temperature versus the number of valence electrons for binary and ternary carbides shows a broad maximum at 5 electrons per atom, with a Tc maximum at 13 K. 

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