Fabrication processes sintering

There are two further processes. Silicon-based ceramics can be fabricated by sintering or by hot-pressing. But a new route, reaetion bonding (Fig. 19.6), is cheaper and gives good precision. If pure silicon powder is heated in nitrogen gas, or a mixture of silicon and carbon powders is sintered together, then the reactions... 

Another important point regarding the fabrication process of MPLs is the fact that, typically, when carbon fiber paper is used as the DL, the MPL is coated just on one surface of the CLP. However, when a carbon cloth is used, a homogeneous water suspension of carbon powder and PTFE is filtered under vacuum onto both faces of the carbon cloth material to form the MPLs [153,158,161,171], followed by drying and sintering as mentioned earlier. Antolini et al. [161] were able to demonstrate that carbon cloth with double MPLs, for both the anode and the cathode sides, showed better performance than when a CFP was used as the cathode DL with one MPL. At low current densities, the difference between the two DLs was not as obvious, but it became more evident at higher current densities because the limiting current densities for each case are quite different ( 1.6 A cm for CFP vs. 2.7 A cm for CC) (see Figure 4.20 for more details). 

In addition to utilization of monoliths as a column material, two reports describing respectively silicate and synthetic organic polymer based monolithic frits were published recently [85,86], The conventional method of frit fabrication for a particle packed column usually involves thermal sintering of a section of the packing material, such as bare or octadecyl silica, using a heating device. This approach has several weaknesses such as the lack of control of the temperature and porous properties of the frit that decreases reproducibly of the fabrication process. 

In order to extend applications of cBN to include machining of medium-hardness steels, modifications of the cBN were introduced. An example is the fabrication of sintered cBN tools by the same HP—HT process, but using binder and second phase (either metallic or nonmetallic) such as TiN or TiC to increase toughness (171). In regard to phase distribution, cBN tools resemble cemented-carbide or alumina—TiC ceramic tools, but are tougher and have greater chemical stability. 

Because of their strong chemical bonds, bulk ceramics are most efficiently fabricated by means of densification of powders. The fabrication process involves two main stages (1) consolidation of the powder to form a porous, shaped article (the green body), also referred to as forming, and (2) heating of the shaped powder form to produce a dense article, referred to as firing or sintering. The final product commonly consists of a relatively dense polycrystal with some residual porosity (Fig. 1). The microstructure, which... 

A ceramic support is formed by shaping a powder and then consolidation of the green body by sintering. The fabrication process consists of four main stages the choice of inorganic material, paste preparation, shaping, and firing (Fig. 5.2). 

Some researchers attempted to crystallize IrSbs from a Sb-rich melt[3J. In this method, the IrSb3 ingot contains many Sb inclusions. On the other hand, an attempt was made to form IrSb3 via liquid-solid phase sintering (LSPS) with an Ir and Sb powder mixture. However, the relationship between the fabrication process and the IrSbs thermoelectric properties was not clear. 

Another area in which preceramic polymers can be utilized effectively is as binders for ceramic powders in near net shaping fabrication processes, such as compression or injection molding with subsequent sintering. Alternatively, an active filler and a polymer [67,68], as reported by Greil and Seibold, can be used in such fabrication. Other potential applications of preceramic polymers is in the general area of coatings, especially for carbon-carbon composites [69], and in the synthesis of nanostructured ceramic particles and composites [70-73]. 

A key point regarding electrochemical sensors is the fabrication process. These devices are usually obtained by means of sintering techniques to achieve pellet structures (Kida et al., 2000), and some authors even combine thin- or thick-film techniques to fabricate some elements such as electrodes (Salam et al., 1998). But the great potential of the use of planar configurations has made them more usual in the literature (Ramfrez-Salgado and Fabry, 2003, Fergus, 2008). Planar devices ease the fabrication process so... 

Figure 31. Microstructures of functional-gradient cemented carbonitrides based on the system (Ti, W)(C, N)-Co which are surface modified by applying a reactive gas phase during sintering in a one step fabrication process [146].

Ceramic processing typically consists of three main steps (i) synthesis or preparation of precursor powders, (ii) consolidation or packing of the powders into green bodies, and (iii) sintering [44]. Every step has a significant effect on the microstructure and optical performance of the final transparent ceramics. There are a number of parameters relevant to the quality of the powders, facility, and way of consolidation and techniques of sintering, which can be used to optimize the fabrication process as a whole. 

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