Functional properties, ceramic materials

Keywords Functional properties Multifunctional materials Nanohybrid materials Polymer-ceramic interface Polymer-ceramic nanohybrids Structural properties Synthesis methods... 

FIGURE 5.3 The myriad functions, properties, and applications of advanced ceramics. Reprinted from High-Technology Ceramics in Japan, National Materials Advisory Board, National Research Council, 1984. 

The ultimate goal of assemblies of nanoscale MBBs is to create nanostructures with improved properties and functionality heretofore unavailable to conventional materials and devices. As a result, one should be able to alter and engineer materials with desired properties. For example, ceramics and metals produced through controlled consolidation of their MBBs are shown to possess properties substantially improved and different from materials with coarse microstmctures. Such different and improved properties include greater hardness and higher yield strength in the case of metals and better ductility in the case of ceramic materials [102]. 

Improved characterization of the morphological/microstructural properties of porous solids, and the associated transport properties of fluids imbibed into these materials, is crucial to the development of new porous materials, such as ceramics. Of particular interest is the fabrication of so-called functionalized ceramics, which contain a pore structure tailored to a specific biomedical or industrial application (e.g., molecular filters, catalysts, gas storage cells, drug delivery devices, tissue scaffolds) [1-3]. Functionalization of ceramics can involve the use of graded or layered pore microstructure, morphology or chemical composition. 

We have described new routes to useful preceramic organosilicon polymers and have demonstrated that their design is an exercise in functional group chemistry. Furthermore, we have shown that an organosilicon polymer which seemed quite unpromising as far as application is concerned could, through further chemistry, be incorporated into new polymers whose properties in terms of ceramic yield and elemental composition were quite acceptable for use as precursors for ceramic materials. It is obvious that the chemist can make a significant impact on this area of ceramics. However, it should be stressed that the useful applications of this chemistry can only be developed by close collaboration between the chemist and the ceramist. 

Baddeleyite has a monocHnic structure with space group Plljc. The Zr + ion has seven-fold coordination, while the idealized ZrOz polyhedron is close to tetrahedral orientation, where one angle in the structure is different significantly from the tetrahedral value. Natural baddeleyite is a raw material for zirconium. In industry ZrOz, named usually zirconia, is important in areas such as surface chemistry, where its activity as a red ox material and its acid-based functions are important. As a ceramic material, zirconia can resist very high temperatures and its stabihzed form, yttrium-stabihzed zirconiiun, shows remarkable mechanical properties. 

Functionally graded materials (FGMs) are multifunctional materials, which contain a spatial variation in composition and/or microstructure for the specific purpose of controlling variations in thermal, structural or functional properties. Also in the ceramics composites field, a wide range of functionally graded (FG) ceramics are available. Hence, a possible classification of the different classes is made in this chapter. 

In an SOFC, the electrochemical reactions take place in the electrodes in the functional layer, that is, a zone within a distance of less than 10-20 pm from the electrolyte surface [5,136-138], The portion of the electrode beyond this width is principally a current collector structure, which has to be porous to permit the admission of gas to the functional layer where the oxidation and reduction reactions occur. Besides, the electrolyte has to be gas impermeable to avoid direct combination and combustion of the gases [137], The essential parts of the SOFC, that is, the electrolyte, the anode, and the cathode, are made of ceramic materials produced with appropriate electrical conducting properties, chemical and structural stabilities, similar expansion coefficients, and negligible reactivity properties [135],... 

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. 

The dissipation of microwave power by ceramics is a function of the material properties s and s, which are the real (storage) and imaginary (loss) parts of the dielectric constant, respectively. In addition to the frequency dependence of pabs [Eq. (la)], s and s are themselves functions of the microwave frequency, the ambient temperature, T, as well as material properties, including a number of microstructural and chemical variables. Thus, to emphasize the range of parameters that impact the local power dissipation, we define the following symbols M denotes the microstructural variables, especially volume fraction porosity (VFP), as well as the size, shape, and the distribution of size... 

The ceramic industry has developed various highly sophisticated manufacturing methods to meet the material requirements of homogeneous microstructure and phase distribution of the sintered ceramic. These are the key factors for predictable mechanical and functional properties. 

In Chapter 1, we observed that plastics have experienced a phenomenal growth since World War n, when they assumed enhanced commercial importance. This explosive growth in polymer applications derives from their competitive costs and versatile properties. Polymers vary from liquids and soft rubbers to hard and rigid solids. The unique properties of polymers coupled with their light weight make them preferable alternatives to metallic and ceramic materials in many applications. In the selection of a polymer for a specific end use, careful consideration must be given to its mechanical properties. This consideration is important not only in those applications where the mechanical properties play a primary role, but also in other applications where other characteristics of the polymer sueh as eleetrical, optical, or thermal properties are of crucial importance. In the latter cases, mechanical stability and durability of the polymer may be required for the part to perform its function satisfactorily. 

Using the definition given in Section 1.1 you can see that large numbers of materials are ceramics. The applications for these materials are diverse, from bricks and tiles to electronic and magnetic components. These applications use the wide range of properties exhibited by ceramics. Some of these properties are listed in Table 1.1 together with examples of specific ceramics and applications. Each of these areas will be covered in more detail later. The functions of ceramic products are dependent on their chemical composition and microstructure, which determines their properties. It is the interrelationship between... 

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