Ceramics techniques

Once the structural support layers have been fabricated by extrusion or EPD for tubular cells or by tape casting or powder pressing for planar cells, the subsequent cell layers must be deposited to complete the cell. A wide variety of fabrication methods have been utilized for this purpose, with the choice of method or methods depending on the cell geometry (tubular or planar, and overall size) materials to be deposited and support layer material, both in terms of compatibility of the process with the layer to be deposited and with the previously deposited layers, and desired microstructure of the layer being deposited. In general, the methods can be classified into two very broad categories wet-ceramic techniques and direct-deposition techniques. 

Both wet-ceramic techniques and direct-deposition techniques require preparation of the feedstock, which can consist of dry powders, suspensions of powders in liquid, or solution precursors for the desired phases, such as nitrates of the cations from which the oxides are formed. Section 6.1.3 presented some processing methods utilized to prepare the powder precursors for use in SOFC fabrication. The component fabrication methods are presented here. An overview of the major wet-ceramic and direct-deposition techniques utilized to deposit the thinner fuel cell components onto the thicker structural support layer are presented below. 

REDEX process, 3 606 Red-figures ceramic techniques, 5 745 Red fuming nitric acid, 17 188 Redingtonite, 6 4 7 It Red iron oxide(s), 19 397, 398-399 wet preparation of, 19 399 Redistribution technology, 19 816 Red Lake C... 

Na3Sc2V30j2, NaCa2Mn2V30i2< and NaCd2Mg2V30j2 have been synthesized using conventional ceramic techniques. ... 

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. 

The increasing use of light ceramic composites for high temperature and space applications has stimulated the development and optimization of the Chemical Vapour Infiltration technique. The use of conventional ceramic techniques for the fabrication of fibre-reinforced composites damages the fibres both mechanically as chemically. Also, the high process temperature causes a thermal degradation of the fibres. 

Different methods have been used to deposit microporous thin films, including solgel, pyrolysis, and deposition techniques [20], Porous inorganic membranes are made of alumina, silica, carbon, zeolites, and other materials [8], They are generally prepared by the slip coating method, the ceramic technique, or the solgel method (Section 3.7). In addition, dense membranes are prepared with metals, oxides, and other materials (Chapter 2). 

In spite of such limitations, ceramic techniques have been widely used for the synthesis of solid materials. Mention must be made, among others, of the use of this technique for the synthesis of rare earth mono-chalcogenides such as SmS and SmSe. The method involves heating the elements, first at lower temperatures (870-1170 K) in evacuated silica tubes the contents are then homogenized, sealed in tantalum tubes and heated to around 2300 K by passing a high current through the tube [15]. 

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. 

Typically, the support thickness is about 1-2 mm, the MF layer is 10-30 pm thick, UF membranes are a few microns thick and NF membranes are less than 1 pm thick. The support and the MF layer are elaborated by classical ceramic techniques the top layers (UF or NF) are formed using the sol-gel process (Fig. 5.1). 

Attempted Preparation of Ba YCu Oy from BaCO, Y2O3 and CuO. Samples were prepared by the usual ceramic techniques using predried BaCOj (400°C), Y2O3 heated at 800°C for 6 hours and analyzed CuO. The mixture of the carbonate and oxides was heated at 900°C for 24 hours. 

The processing of high Tc ceramic superconductors by traditional ceramic techniques is reviewed. All high Tc ceramic superconductors are layered Cu-0 compounds that are closely related to each other. In each, Cu-0 coordination polyhedra are typical of Cu+2 compounds. A critical step in processing these compounds is the intercalation of oxygen which changes the coordination polyhedra at a few atomic sites and causes a dramatic effect on the superconducting properties. 

The compounds of the spinel system Cuj xZnxMnCr04 (0crystallographic studies were carried out to study influence of... 

Spinel, Ceramic technique. Electrical resistiivity. Thermoelectric power. Catalytic decomposition. 

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