Processing methods sintering

Eor processing after sintering, in the least expensive method for sintered PTEE tape or sheet, a large billet is skived on a lathe after it has been sintered and cooled. High precision articles are machined from ram-extmded rods. 

Sihcon carbide is also a prime candidate material for high temperature fibers (qv). These fibers are produced by three main approaches polymer pyrolysis, chemical vapor deposition (CVD), and sintering. Whereas fiber from the former two approaches are already available as commercial products, the sintered SiC fiber is still under development. Because of its relatively simple process, the sintered a-SiC fiber approach offers the potential of high performance and extreme temperature stabiUty at a relatively low cost. A comparison of the manufacturing methods and properties of various SiC fibers is presented in Table 4 (121,122). 

In addition to the use of composite anodes and cathodes, another commonly used approach to increase the total reaction surface area in SOFC electrodes is to manipulate the particle size distribution of the feedstock materials used to produce the electrodes to create a finer structure in the resulting electrode after consolidation. Various powder production and processing methods have been examined to manipulate the feedstock particle size distribution for the fabrication of SOFCs and their effects on fuel cell performance have also been studied. The effects of other process parameters, such as sintering temperature, on the final microstructural size features in the electrodes have also been examined extensively. 

The main processing methods for addition polyimides are machining compression, transfer and injection moulding encapsulation, impregnation, stratification, filament winding, varnishing, sintering. 

Alternative processing methods also offer the potential to control the microstructure and final properties of nanocomposites. Both self-propagating high-temperature sintering and spark plasma sintering offer means to obtain metastable yet dense nanocomposites. Subsequent heat treatments can then be used to approach equilibrium microstructures, where the properties will be a function of the heat treatment temperature and time. In this way a variety of microstructures, and thus variations of the composite properties, can become available. 

Important processing methods vapor phase deposition, spin coating, injection molding, casting, ex-trusion, drawing of oriented films, compression molding, sintering... 

Table 20.1 lists the desirable powder characteristics for advanced ceramics. For most processing methods we want a small particle size. The small size helps shape the product and during densi-fication (sintering) at high temperature, allows higher density bodies at lower firing temperatures. 

PZT ceramics can be made by normal powder processing methods. The main difficulty is the high volatility of PbO. To retain as much PbO as possible sintering may be performed with the component surrounded by a lead-rich powder such as PZ and enclosed in a lidded crucible. Even with these precautions there is usually some (typically 2-3%) loss of PbO, which is compensated for by adding additional PbO to the starting batch. A note about safety lead is toxic and exposure to lead compounds has a cumulative effect. It is therefore necessary that evaporation is controlled. 

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