Ceramic materials characterization data

The main point to be emphasized here Is that the feasibility of these approaches In assuring the reliability of ceramic materials depends on basic crack growth or strength data that characterize failure mechanisms In these materials. Without these basic data, these techniques of lifetime assurance could not be usefully employed on ceramic materials. 

In the original treatment, also called the microscopic approach, the Hamaker constant was calculated from the polarizabilities and number densities of the atoms in the two interacting bodies. Lifshitz presented an alternative, more rigorous approach where each body is treated as a continuum with certain dielectric properties. This approach automatically incorporates many-body effects, which are neglected in the microscopic approach. The Hamaker constants for a number of ceramic materials have been calculated from the Lifshitz theory using optical data of both the material and the media (Table 9.1) (9). Clearly, all ceramic materials are characterized by large unretarded Hamaker constants in air. When the materials interact across a liquid, their Hamaker constants are reduced, but still remain rather high, except for silica. 

A substantial amount of work on fracture toughness testing methodologies and materials characterization was performed in the 1970 s, much of it motivated by potential ceramic heat engine applications. Nevertheless, there was considerable confusion and conflicting fracture toughness data in the 1980 s. A 1981 report associated with a project to prepare a handbook of ceramic property data stated ... 

Literature reports on interfaces are mainly limited to metallic solids while little is known on ceramic materials, which are mainly ionic solids of nonstoichiometric compounds. The reason for the scarcity of literature reports on ceramic interfaces results from the substantial experimental difficulties in studies of these compounds. Even the most advanced surface-sensitive techniques have experimental limitations in the surface studies of materials. Most of these techniques are based on ion and electron spectroscopy, such as XPS, SIMS, LEED, AFM, and LETS, and are still not adequate to characterize the complex nature of compounds. Namely, these surface techniques require an ultra-high vacuum and therefore may not be applied to determine surface properties during the processing of materials which takes place at elevated temperatures and under controlled gas phase composition. Consequently, the resultant experimental data allow one to derive only an approximate picture of the interface layer of compounds. 

The ramp of pressure to about 3 GPa observed in shock-loaded fused quartz has been used very effectively in acceleration-pulse loading studies of viscoelastic responses of polymers by Schuler and co-workers. The loading rates obtained at various thicknesses of fused quartz have been accurately characterized and data are summarized in Fig. 3.6. At higher peak pressures there are no precise standard materials to produce ramp loadings, but materials such as the ceramic pyroceram have been effectively employed. (See the description of the piezoelectric polymer in Chap. 5.)... 

With electro-osmosis data, on the other hand, interpretation is not subject to the complexities of the electrophoretic measurement. Analysis of zeta potential is straightforward, and a wide range of pH can be employed. In this light it would be promising to characterize ceramic and mineral materials of a wide variety of compositions and forms, e.g., powders and processed plates. 

This review of physical, bulk chemical, surface chemical, and spectroscopic techniques for the characterization of powders shows that no one or two techniques can provide all the necessary details regarding powder properties. In fact, each method reveals a distinctly different characteristic of the powder. Often, a choice must be made in terms of the selection and measurement of relevant properties of a powder. When one is faced with this question of which specific properties to measure, the relationships between powder properties and their effect on the final microstructure and properties of the ceramic should be explored. Currently, the quality and reproducibility of data are significantly affected by the unavailability of standard methods and standard reference materials. Efforts are underway in different organizations around the world to alleviate this problem. 

Powder XRD is one of the most widely used techniques to characterize ceramics. The material is in the form of a powder so that the grains will be present in all possible orientations so that all d spacings, or 0 values, will appear in one pattern. The classical powder pattern was recorded on photographic film. Now the data are in the form of a plot (known as a diffractogram) of counts or intensity versus scattering angle (20) as shown in Figure 10.30. A computer that contains the entire PDF is usually used for peak identification. In many examples you will see in the literature phase identihcation is the extent to which powder XRD is used. This ability alone makes it a powerful and indispensable tool for the ceramist. In a multiphase material the relative amounts of each phase can be determined from the peak areas. 

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