Structural ceramics system

Composite structures in ceramics have been developed for two major reasons. First, they provide a means to enhance dramatically the performance of the so-called functional ceramics these are systems where electrical, dielectrical, piezoelectric or sensitizing properties are greatly amplified by appropriate composite design. Secondly, they are used to avoid or diminish the brittle behaviour of structural ceramic systems. 

Ceramic materials that retain structural integrity to temperatures in the 2100 to 2400°F range have been the subject of research and development for many years. Researchers have in fact created small radial inflow turbines from structural ceramic material for possible use in automotive gas turbines. These experimental units have shown favorable properties in laboratory tests. However, several practical considerations pose potential stumbling blocks to their use in commercial systems, such as coefficients of expansion that are substantially different from those of the metals used in gas turbine construction. One may expect to find ceramic materials in use in industrial gas turbines in the future, first on... 

E. Yu. Batyan, S. V. Matveichuk, and G. A. Branitskii, Structural phase transformations in silver-ceramic systems and their relation to catalytic properties in the process of methanol partial oxidation, Kinet. Catal. 136, 816-820 (1995). 

Common approaches for the tailoring of nonmetallic (ceramic) materials properties involve topochemical methods (those where the crystal structure remains largely unaffected) and the preparation of phases in which one or more sublattices are alloyed. In principle, such materials are within the realm of CALPHAD. On the other hand, as has already been stated, extrapolation does not really aid the discovery of new or novel phases, with unique crystal structures. Furthermore, assessed thermochemical data for the vast majority of ceramic systems, particularly transition metal compounds, are presently not available in commercial databases for use with phase diagram software. This does not necessarily preclude the use of the CALPHAD method on these systems However, it does require the user to carry out their own thermodynamic assessments of the (n — 1 )th-order subsystems and to import that data into a database for extrapolation to nth-order systems, which is not a trivial task. 

The methods of preparing inorganic membranes with tortuous pores vary enormously. Some use rigid dense solids as the templates for creating porous structures while many others involve the deposition of one or more layers of smaller pores on a premanufactured microporous support with larger pores. Since ceramic membranes have been studied, produced and commercialized more extensively than any other inorganic membrane materials, more references will be made to the ceramic systems. 

Generally speaking, in ceramic systems more is known about point defects than about the structure of dislocations, grain boundaries, or free surfaces — a fact that is reflected in the coverage of this chapter in which the lion s share is devoted to point defects. 

Recognizing that polymer-polymer systems exhibit phase behavior similar to - that of other condensed phase systems, it should be possible to prepare multiphase polymeric materials of unique structure by phase transition. The purpose of this work is to show that much of the theoretical and experimental analysis of phase transitions in metallurgical and ceramic systems can provide an interpretation of the behavior of polymeric systems. In addition, there are several features of polymeric systems which distinguish them from low molecular weight systems. 

The class of oxide materials has greatly benefited from the chemical exploration of multinary systems, virtually right from the beginning. Thus, besides a number of binary compounds, mainly in use as structural ceramics, there is an impressive pleAora of multinary oxide materials being applied as functional, as well as structural ceramics. In some instances these are even... 

In addition to their possible use as high temperature structural ceramics, materials in the system SiC-AIN have potential as wide band-gap semiconductors and for opto-electronic applications [166]. 

IV. EXPERIMENTAL RESULTS STRUCTURES AND SUBSTRUCTURES IN DIFFERENT CERAMIC SYSTEMS... 

Therefore, the identification of the most suitable electrolyte media, where the passivation rates remain confined to a limited extent, is essential for the development of long-life LPBs. The answer may again be provided by replacing the simple PEO-LiX system with the composite membranes of the type of those previously described. By finely dispersing in the polymer structure ceramic additives which have high affinity for the electrolyte impurities, and in particular for water impurities, a network of trapping centres for the impurities themselves can be provided and thus ensure their removal from the interface with the final result of controlling the corrosion rate of the electrode. 

In addition to their possible use as high-temperature structural ceramics, materials in the SiC-AiN system have demonstrated potential as wide band-gap semiconductors and for opto-electronic applications [322]. The band gap can be easily adjusted in the range from 3.3 eV (pure SiC) to 6.0 eV (pure AlN) [327, 335, 336]. Likewise, the thermal and electric conductivities can be modulated over a wide range [318, 328]. 

The CSL model was elaborated initially for pure metallic crystals where lattice points can be considered as individual atoms, such that the coincidence in lattice points is equivalent to the formation of atomic bonds. However, it is interesting to note that the CSL model also holds tme in ceramic systems. The energies and structures of various... 

---