Ceramic Characterization

The quality of a ceramic sample is a function of the degree to which it consists of the desired product. An essential tool for the characterization of a polycrystalline sample is powder X-ray diffraction. The powder pattern is a fingerprint of the sample. For a sample to be declared single phase, all low angle peaks (below 60 20 for CuKq radiation) which are above the noise must be accounted for. Powder X-ray diffraction is often unable to see impurity phases present below the 5% level. Visual inspection (using a microscope) 

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Because geochemically different clay sources may have been used by potters to produce ceramics for both domestic and trade purposes, neutron activation analysis (NAA) has been used as an independent means of ceramic characterization. Because of the relatively good analytical precision possible with NAA, statistical patterning of NAA data for major, minor, and trace element concentrations may be used as a powerful provenancing tool. 

Research in the preceramic polymer area, if it is to come to fruition, must be an interdisciplinary endeavor. After the chemistry has been developed, there are important ceramics issues to be addressed. Good chemistry does not guarantee good ceramics However, there is the possibility that the chemistry can still be modified to give good ceramics. Either the chemist must learn a good bit about ceramics characterization and processing... 

Ewsuk K G 1993 Consolidation of bulk ceramics Characterization of Ceramics ed R E Loehman (Greenwich, CT Butterworth-Fleinemann) pp 77-101... 

The most commonly adopted filtering media is a high-density ceramic characterized by an asymmetric structure, a support material covered with a thin membrane layer containing very small pores. The membrane collects the fine particles and by making it thin the differential pressure of the filter element is kept low. The ideal solution is to have a very thin layer without defects that just covers the support material, so that purely surface filtration takes place. Experimental evidence at industrial scale shows that this ideal solution can be achieved in practice, penetration of particles into the support structure of the filter element being prevented, and that the element can be effectively regenerated by the clean gas back-pulsing procedure described by Cocco et al. [56]. It has also been confirmed at... 

Ceramic characterization 30-32 range from a process as simple as determining the bulk density of a green powder compact from its mass and dimensions, to a process as complicated as identifying the composition and structure of a submicron size crystal in a dense ceramic matrix using analytical electron microscopy (AEM). Some of the important characteristics evaluated during ceramic consolidation are outlined in Figure 5.2. 

Germany, produced two types of this glass-ceramic, characterized by different optical transmission (Pannhorst 1992 and Nass et al., 1995). The products are called Ceran Color and Ceran Hightrans . 

Silicon Carbides. Silicon carbide is a widely used ceramic characterized by high hardness, high strength at elevated temperatures, good thermal shock resistance resulting from its good thermal conductivity, and relatively low thermal expansion. In recent years it... 

Refractories represent a broad classification of ceramics characterized by the ability of the materials to withstand high temperatures. These materials are used for steel making, glass melting, and in various chemical processing industries. They are used as containment materials, insulation, and heat and chemical barriers of all kinds. 

In addition to the XRPD data (Fig. 6) available for the ceramic characterization, SEM (Figs. 4 - 5) data confirmed the distinction of "closed and "open" structures for the highly crosslinked, and non-crosslinked materials, respectively. It was not possible to determine fully the structure of either the original polymeric compositions, or the resultant ceramics, by diffraction techniques or solution-based analyses alone, or in combination. Attention was turned, therefore, to solid state NMR. 

Based upon a piezoelectric 1-3-composite material, air-bome ultrasonic probes for frequencies up to 2 MHz were developped. These probes are characterized by a bandwidth larger than 50 % as well as a signal-to-noise ratio higher than 100 dB. Applications are the thickness measurement of thin powder layers, the inspection of sandwich structures, the detection of surface near cracks in metals or ceramics by generation/reception of Rayleigh waves and the inspection of plates by Lamb waves. 

Characterization of Germanium PhosphosUicate Films Prepared by MCVD," presentation, at the faU meeting of the American Ceramic Society, 1981, Bedford, Pa, 1981. 

Microscopists in every technical field use the microscope to characterize, compare, and identify a wide variety of substances, eg, protozoa, bacteria, vimses, and plant and animal tissue, as well as minerals, building materials, ceramics, metals, abrasives, pigments, foods, dmgs, explosives, fibers, hairs, and even single atoms. In addition, microscopists help to solve production and process problems, control quaUty, and handle trouble-shooting problems and customer complaints. Microscopists also do basic research in instmmentation, new techniques, specimen preparation, and appHcations of microscopy. The areas of appHcation include forensic trace evidence, contamination analysis, art conservation and authentication, and asbestos control, among others. 

Performance assessments are predictions of radioactivity releases, the rate of transfer of contaminants through various media, and the potential for hazard to the pubHc. These are based on a combination of experimental data obtained in the process called site characterization and detaded computations about radionuchdes and their effects. The progressive attack on the metal or ceramic waste container, the diffusion of water into the waste form, the leaching of the radioactive compounds, diffusion out, and washing away of radionuchdes are all considered. 

The processes employed in manufacturing a ceramic are defined and controlled to produce a product with properties suited to a specific appHcation. Processing—microstmcture—property relationships are deterrnined by characterizing the ceramic raw materials, mixes, and the formed ceramic body intermittently during processing and after final thermal consoHdation. It is possible to modify and optimize processes to optimize properties and to identify and correct processing deficiencies when less than optimal properties are obtained. Examples of some process—microstmcture—property relations in advanced ceramics are outlined in Figure 4. 

Characterization. Ceramic bodies are characterized by density, mass, and physical dimensions. Other common techniques employed in characterizing include x-ray diffraction (XRD) and electron or petrographic microscopy to determine crystal species, stmcture, and size (100). Microscopy (qv) can be used to determine chemical constitution, crystal morphology, and pore size and morphology as well. Mercury porosknetry and gas adsorption are used to characterize pore size, pore size distribution, and surface area (100). A variety of techniques can be employed to characterize bulk chemical composition and the physical characteristics of a powder (100,101). 

Hardness is determined by measuring the penetration (depth or area) when a harder material, such as diamond, is pushed into the surface of the material of interest under a specified load. Tme hardness is defined as the force divided by the projected area. Vickers hardness tests, which employ a pyramid-shaped indentor, are frequently used to characterize ceramics however, Vickers hardness calculations normally employ total surface area rather than projected area (43). Measurements are made on the diamond impression shown in Figure 6. Vickers hardness is calculated using... 

Ceramic bond formation and grain growth by diffusion are the two prominent reactions for bonding at the high temperature (1100 to 1370°C, or 2000 to 2500°F, for iron ore) employed. The minimum temperature required for sintering may be measured by modern dilatometry techniques, as well as by differential scanning calorimetry. See Compo et al. [Powder Tech., 51(1), 87 (1987) Paiticle Characterization, 1, 171 (1984)] for reviews. 

Stress in crystalline solids produces small shifts, typically a few wavenumbers, in the Raman lines that sometimes are accompanied by a small amount of line broadening. Measurement of a series of Raman spectra in high-pressure equipment under static or uniaxial pressure allows the line shifts to be calibrated in terms of stress level. This information can be used to characterize built-in stress in thin films, along grain boundaries, and in thermally stressed materials. Microfocus spectra can be obtained from crack tips in ceramic material and by a careful spatial mapping along and across the crack estimates can be obtained of the stress fields around the crack. ... 

SIMS is one of the most powerful surface and microanalytical techniques for materials characterization. It is primarily used in the analysis of semiconductors, as well as for metallurgical, and geological materials. The advent of a growing number of standards for SIMS has gready enhanced the quantitative accuracy and reliability of the technique in these areas. Future development is expected in the area of small spot analysis, implementation of post-sputtering ionization to SIMS (see the articles on SALI and SNMS), and newer areas of application, such as ceramics, polymers, and biological and pharmaceutical materials. 

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