Preparation of ceramic composites

Zirconium oxide, partially stabilized widi MgO and S1O2  

Prepared in accordance with recommend procedure III for zirconium oxide (see Table 43). 

These composite materials are formed by combining ceramics with metals and certain plastics. These composites combine the most favorable properties of the various component materials. The ceramic components (consisting of oxides, nitrides, and 

The following ceramic composites are used most often in industrial technology  

When brittle materials or phases are combined with materials or phases displaying ductility and some degree of wear resistance, certain special factors must be considered in the preparation of the polished section. This is especially important when the ceramic component also exhibits a certain degree of porosity and/or when the ceramic material has been apphed as a coating on a metallic substrate. 

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The conventional production method for SiC - the reaction of coke and sand (Acheson process) -does not involve soluble or fusible intermediates. For many applications of silicon carbide this fact is not necessarily a disadvantage, but for the preparation of ceramic composites such intermediates are required. 

In this section the preparation of ceramic composites by the directed metal oxidation process is described. First, in Section II.A, the aluminum oxide system is used as an example to explain the nature of the process, and a further example, a ZrB2 reinforced ZrC composite, is discussed in Section II.B. 

Electrical and Electronic Applications. Silver neodecanoate [62804-19-7] has been used in the preparation of a capacitor-end termination composition (110), lead and stannous neodecanoate have been used in circuit-board fabrication (111), and stannous neodecanoate has been used to form patterned semiconductive tin oxide films (112). The silver salt has also been used in the preparation of ceramic superconductors (113). Neodecanoate salts of barium, copper, yttrium, and europium have been used to prepare superconducting films and patterned thin-fHm superconductors. To prepare these materials, the metal salts are deposited on a substrate, then decomposed by heat to give the thin film (114—116) or by a focused beam (electron, ion, or laser) to give the patterned thin film (117,118). The resulting films exhibit superconductivity above Hquid nitrogen temperatures. 

One of the main advantages of the polymer route to ceramics is the preparation of ceramic fibers, a shape difficult to achieve by other methods. Ceramic fiber-based composites are becoming an increasingly important group of structural materials (12, 13). 

Sols arc dispersions of colloidal particles in a liquid. Colloids arc nanoscaled entities dispersed in a fluid. Gels are viscoelastic bodies that have interconnected pores of submicrometric dimensions. A gel typically consists of at Icasl two phases, a solid network that entraps a liquid phase. Sol-gel technology is the preparation of ceramic, glass, or composite materials by the preparation of a sol, gelation of the sol. and removal of the solvent. 

Sol-gel processing involves the use of a hydrolysis reaction to obtain a cross-linked network, which results in the formation of a gel. When preparing metal-ceramic composites, both components may be obtained in this way, or alternatively the metal reinforcement can be introduced by adding, for example, metal nitrates.1718 The gel properties may be controlled by adjusting the pH level, water to metal ratio, and temperature. 

The third way to prepare CNT-ceramic composite powders is via the synthesis of CNT by a CCVD process, in situ in the ceramic powder. A ceramic powder which contains catalytic metal particles at a nanometric size, appropriate to the formation of CNTs, is treated at a high temperature (600-1100°C), in an atmosphere containing a hydrocarbon or CO. In the method reported in 1997 by the present authors,27 iron nanoparticles are generated in the reactor itself, at a high temperature (>800°C), by the selective reduction in H2/CH4 (18% CH4) of an a-Al203 based oxide solid solution ... 

Although colloids may be undesirable components in industrial systems, particularly as waste or by-products and, in nature, in the forms of fog and mist, they are desirable in many technologically important processes such as mineral beneficiation and the preparation of ceramics, polymers, composite materials, paper, foods, textiles, photographic materials, drugs, cosmetics, and detergents. The remainder of this chapter specifies some applications for colloidal solids, liquids, and gases and illustrates how colloids can affect many technologically important systems. 

Silicon-containing preceramic polymers are useful precursors for the preparation of ceramic powders and fibers and for ceramic binder applications (i). Ceramic fibers are increasingly important for the reinforcement of ceramic, plastic, and metal matrix composites (2, 3). This chapter will emphasize those polymer systems that have been used to prepare ceramic fibers. An overview of polymer and fiber processing, as well as polymer and fiber characterization, will be described to illustrate the current status of this field. Finally, some key issues will be presented that must be addressed if this area is to continue to advance. 

The methods for preparation of nonporous composite membrane catalyst are discussed in Ref. 10. The porous stainless steel sheets were covered with a dense palladium alloy film by magnetron sputtering [113] or by corolling of palladium alloy foil and porous steel sheet. The electroless plating of palladium or palladium alloy on stainless steel [114] or on porous alumina ceramic [115,116] gives the composite membranes with an ultrathin, dense palladium top layer. 

To reduce the porosity of ceramic composites based on the NZP system, a matrix of single phase (Cao.6.Mgo.4)Zr4(P04)6 (CMZP) was prepared using sol-gel Process 1. The amorphous CMZP formed had a mean particle size of 20 nm. After calcining the amorphous powder, a single phase crystalline CMZP was obtained which is stable to 1500°C. To quantify.the porosity present, it was necessary to determine the theoretical density. The calculated theoretical densities of CMZP and CBZP were 3.177 g/cm3 and 3.264 g/cm3, respectively, based on the theoretical density of CaZr4(P04)e (3.20 g/cm3) calculated by Limaye et al.3... 

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