Silicon carbides/nitrides

In some instances, subtle changes in the precursor architecture can change the composition and microstructure of the final pyrolysis product. For example, pyrolysis of —[MeHSiNH] — leads to amorphous, silicon carbide nitride (SiCN) solid solutions at >1000°C (see SiCN section). At ca 1500 °C, these material transform to SisN SiC nanocomposites, of interest because they undergo superplastic deformation20. In contrast, chemically identical but isostructural — [F SiNMe] — transforms to Si3N4/carbon nanocomposites on heating, as discussed in more detail below21. 

Type of Active Sites. - In heterogeneous catalysis the following type of actives sites can be distinguished (i) metallic, (ii) acid-base, (iii) red-ox type, and (iv) anchored metal-complex. The catalytic sites may contain one of the above types of active sites or can include several types of sites. In case of different type of sites the catalysts are bifunctional or multifunctional. For instance, Pt/Al203 and Pt/mordenite are typical bifunctional catalysts containing both metallic and acidic types of active sites. On the other hand, Pt or Pd supported on silicon carbide, nitride, or Pt/L-zeolite are mono-functional catalysts. There are important industrial reactions, such as isomerization and aromatization of linear hydrocarbons, which requires bifunctional catalysts, such as chlorinated... 

Nonoxides such as silicon carbides, nitrides, metal sulfides, and so on, possess unique chemical, thermal, and mechanical properties and can be used as catalysts and catalyst carriers. The properties can be further enhanced by the confined-space effect in nanospace, high surface areas, and large pore volumes. 

Mechanical properties Symbol Units Silicon carbide, sintered Silicon carbide, silicon- infiltrated Silicon carbide, recrystallized Silicon carbide, nitride-bonded Boron carbide... 

The covalently-bonded silicon carbide, silicon nitride, and sialons (alloys of Si3N4 and AI2O3) seem to be the best bet for high-temperature structural use. Their creep resistance... 

Ceramics themselves are sometimes protected in this way. Silicon carbide, SiC, and silicon nitride, Si3N4 both have large negative energies of oxidation (meaning that they oxidise easily). But when they do, the silicon in them turns to Si02 which quickly forms a protective skin and prevents further attack. 

High -performance engineering ceramics Diamond Dense alumina Silicon carbide Silicon nitride Zirconia Sialons... 

Zirconia, ZrOj, is made from the natural hydrated mineral, or from zircon, a silicate. Silicon carbide and silicon nitride are made by reacting silicon with carbon or nitrogen. Although the basic chemistry is very simple, the processes are complicated by the need for careful quality control, and the goal of producing fine (<1 jiva) powders which, almost always, lead to a better final product. 

Turning now to other types of ceramic fibre, the most important material made by pyrolysis of organic polymer precursors is silicon carbide fibre. This is commonly made from a poly(diorgano)silane precursor, as described in detail by Riedel (1996) and more concisely by Chawla (1998). Silicon nitride fibres are also made by this sort of approach. Much of this work originates in Japan, where Yajima (1976) was a notable pioneer. 

Seeding technique, procedure 130, 131 Sequential addition of monomers 164, 167 Silicon-carbide fibers 8 Silicon-nitride fibers 8 Silicone rubber, crosslinked 4, 7-9, 31, 67 Siloxane, definition of 5 Siloxane-acrylate copolymers 27, 29, 56, 57, 64, 70, 71, 73, 74... 

Also noted is the rapid expansion of a number of materials produced by CVD, which include copper, tungsten, diamond, silicon carbide, silicon nitride, titanium nitride, and others. The coverage of the chemistry and deposition techniques of these materials has been greatly expanded. 

Chemical vapor deposition (C VD) is a versatile process suitable for the manufacturing of coatings, powders, fibers, and monolithic components. With CVD, it is possible to produce most metals, many nonmetallic elements such as carbon and silicon as well as a large number of compounds including carbides, nitrides, oxides, intermetallics, and many others. This technology is now an essential factor in the manufacture of semiconductors and other electronic components, in the coating of tools, bearings, and other wear-resistant parts and in many optical, optoelectronic and corrosion applications. The market for CVD products in the U.S. and abroad is expected to reach several billions dollars by the end of the century. 

Other ceramic cutting-tool materials include alumina, Si-Al-0-N, alumina-carbide composites and, more recently, a composite of silicon nitride reinforced with silicon carbide whiskers. This last material can be produced by chemical-vapor infiltration (CVI) and has high strength and toughness as shown in Table 18.3.Cl... 

Foulds, W., LeCostaouec, J., Landry, C., and DiPietro, S., Tough Silicon Nitride Matrix Composites Using Textron Silicon Carbide Monofilaments, Ceram. Eng. Sci. Proc., 10(9-10) 1083-1099(1989)... 

Conventional ceramics are made from natural raw materials such as clay or silica advanced ceramics require extremely pure manmade starting materials such as silicon carbide, silicon nitride, zirconium oxide, or aluminum oxide and may also incorporate sophisticated additives to produce specific microstractures. 

Soluble polysilane polymers can also be used as precursors to silicon carbide. The first such application, using (PhMeSi)n-(Me2Si)m copolymers ("Polysilastyrene"), was to strengthen silicon nitride ceramics. The Si3N4 ceramic body was soaked in polysilane and refired, leading to the formation of silicon carbide whiskers in the pore spaces and a consequent increase in strength. (U)... 

Non-oxide ceramics such as silicon carbide (SiC), silicon nitride (SijN ), and boron nitride (BN) offer a wide variety of unique physical properties such as high hardness and high structural stability under environmental extremes, as well as varied electronic and optical properties. These advantageous properties provide the driving force for intense research efforts directed toward developing new practical applications for these materials. These efforts occur despite the considerable expense often associated with their initial preparation and subsequent transformation into finished products. 

Silicon-containing ceramics include the oxide materials, silica and the silicates the binary compounds of silicon with non-metals, principally silicon carbide and silicon nitride silicon oxynitride and the sialons main group and transition metal silicides, and, finally, elemental silicon itself. There is a vigorous research activity throughout the world on the preparation of all of these classes of solid silicon compounds by the newer preparative techniques. In this report, we will focus on silicon carbide and silicon nitride. 

Silicon carbide, SiC [1] and silicon nitride, Si3N4 [2], have been known for some time. Their properties, especially high thermal and chemical stability, hardness, high strength, and a variety of other properties have led to useful applications for both of these materials. 

Refractories such as boron nitride, silicon nitride, silicon carbide, and boron carbide are of great importance for the production or protection of systems which can be operated in very high... 

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