Techniques standard ceramic

The use of a prereacted precursor is the typical approach to the preparation of ceramics of the Tl-containing superconductors (S). For example, to prepare the 120K T1 phase, H2Ba2Ca2CusO10, or 2223-T1, an alkaline earth cuprate precursor which is a mixed phase sample of overall stoichiometry, Ba2Ca2CusOx is prepared by standard ceramic techniques. An intimate mixture of the precursor and a stoichiometric... 

In the past, most solids were prepared on a large scale by standard ceramic techniques, in which accurate control of the composition, as well as uniform homogeneity of the product, were not readily achieved. Unfortunately, this has sometimes led to uncertainty in the interpretation of the physical measurements. In recent years more novel methods have been developed to facilitate the reaction between solids. This is particularly true for the preparation of polycrystalline samples, on which the most measurements have been made. It is of utmost importance to prepare pure single-phase compounds, and this may be very difficult to attain. Even for a well-established reaction, careful control of the exact conditions is essential to ensure reproducible results. For any particular experiment, it is essential to devise a set of analytical criteria to which each specimen must be subjected. It will be seen from the solid-state syntheses included in this volume that one or more of the following common tests of purity are used to characterize a product. 

Further development of standard ceramic kilns is aimed at faster firing, improved insulations and increased thermal efficiency. No principal changes in the firing techniques or in the conception of ceramic kilns are expected in the near future. 

The industrially most important refractory products are supplemented by specialty products for particular applications. The most important of these is zirconia bricks. They are produced from natural zircon (ZrSi04) with optional addition of quartz or alumina using standard ceramic techniques. They are used in tank furnaces in the glass industry, aluminum melting furnaces and high temperature furnaces. 

Refractory oxides are an important class of materials that enable processes to exploit extreme environments. A wide variety of unary, binary, and ternary oxides can be considered refractory, based on their melting temperatures. Refractory oxides are generally prepared from powdered precursors using standard ceramic forming techniques such as casting, pressing, or extrusion, and subsequently sintered to achieve final density. In addition to chemical compatibility, the physical properties of refractory oxides such as thermal expansion coefficient, thermal conductivity, modulus of elasticity, and heat capacity must be considered when selecting an oxide for a specific application. 

The corrosion resistance of CVD layers and solids that are made out of (nominally) the same products fabricated with standard ceramic techniques is quite different. Glasses also are often more resistant against chemical attack than the polycrystalline modification of the same compound. Why ... 

The characterization of ceramic thick films requires the use of special techniques in addition to those normally used to characterize bulk ceramics. This chapter has focused on these special techniques. The reader is referred to the following chapter for more information on the standard characterization techniques for ceramics, since many of them are also applicable to thick films. 

Powder Preparation. The goal in powder preparation is to achieve a ceramic powder which yields a product satisfying specified performance standards. Examples of the most important powder preparation methods for electronic ceramics include mixing/calcination, coprecipitation from solvents, hydrothermal processing, and metal organic decomposition. The trend in powder synthesis is toward powders having particle sizes less than 1 p.m and Httie or no hard agglomerates for enhanced reactivity and uniformity. Examples of the four basic methods are presented in Table 2 for the preparation of BaTiO powder. Reviews of these synthesis techniques can be found in the Hterature (2,5). 

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. 

Typically, the sample or object to be activated is placed in a container for irradiation. This may be aluminium foil (as aluminium cannot easily be measured by this technique) or silica glass tubes. Several samples and standards are placed in the same container for irradiation, to ensure the same conditions for samples and standards. For example, in the case of ceramics measured at the British Museum laboratories (Hughes et al. 1991), powdered... 

In the analysis of solid samples (e.g., LA-ICP-MS, SEM), synthetic standards cannot easily be prepared to the required concentrations, and accurate calibration of such techniques is often challenging. In some cases (e.g., SEM) pure element or single mineral standards are used, ideally with an appropriate standard for each element to be quantified. (It is possible in SEM, within limits, to use fewer standards than the number of elements to be determined, with the calibration for other elements being predicted from the response of the nearest element.) More often, however, multielement primary standards are used as the means of calibrating the instrument, e.g., for LA-ICP-MS of glasses, volcanics, and ceramics, two glass standards, NIST 610 and 612 (Pearce et al. 1996), are often used. It is always advisable to use more than one multielement standard in order to cover as wide a range of concentrations as possible, and to use at least one additional independent reference material as an unknown, for quality assurance purposes (see below). 

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