Silicon carbide ceramics and

Silicon nitride (SN) ceramics po.s.sess similar properties to silicon carbide ceramics and can be utilized in the same application sectors. 

K. Ando, K. Hurusawa, M. C. Chu, T. Hanagata, K. Tuji and S. Sato, Crack-healing behavior under stress of mullite silicon carbide ceramics and the resultant fatigue strength, J. Am. Ceram. Soc., 84, 2073-2078 (2001). 

Y. I toh, L. Snead, T. Cheng, C. Shih, W. Lewis, T. Koyanagi, T. Hinoki, C. H. Henager Jr, and M. Ferraris, "Radiation-Tolerant Joining Technologies for Silicon Carbide Ceramics and Composites," J. Nucl. Mater., in press (2013). 

Interest in polysilane polymers has been reawakened because they have appeared as new potential industrial raw materials for production of conducting and semi-conducting electronic devices, photomemories, photoresists, UV-absorbing and thermochromic materials, radical photoinitiators for polymerization, precursors for silicon carbide ceramics and fibers, organic glasses and m cal drugs [7-12]. 

As described above, PDMS is used as a precursor of polycarbosilanes in the industrial production of silicon carbide ceramics and fibers. We confirmed that our PDMS samples could be pyrolytically converted into the corresponding polycarbosilanes [33a] (Equation 19). 

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. 

The history and development of polysilane chemistry is described. The polysilanes (polysilylenes) are linear polymers based on chains of silicon atoms, which show unique properties resulting from easy delocalization of sigma electrons in the silicon-silicon bonds. Polysilanes may be useful as precursors to silicon carbide ceramics, as photoresists in microelectronics, as photoinitiators for radical reactions, and as photoconductors. 

Possible ways in which polysilanes may be useful include, 1. As precursors to silicon carbide ceramics 2. As photoinitiators in radical reactions 3. As photoconductive materials, and 4. As photoresists in microelectronics. The last of these uses will be treated in the chapter by Miller,(31) and so will not be covered here. 

A great potential for new compounds is provided by structures with two carbon and two silicon atoms around the central silicon. These polysilanes with organic groups lead to silicon-carbide ceramics. A wide field of application would be opened up if one could make a polysilane as a plastic mass which could be extruded and modeled and if after pyrolysis silicon-carbide is formed without a strong contraction (this means a high ceramic yield). Polysilane fibers are only one product in a range of many... 

Polysilanes can be regarded as one-dimensional analogues to elemental silicon, on which nearly all of modern electronics is based. They have enormous potential for technological uses [1-3]. Nonlinear optical and semiconductive properties, such as high hole mobility, photoconductivity, and electrical conductivity, have been investigated in some detail. However, their most important commercial use, at present, is as precursors to silicon carbide ceramics, an application which takes no advantage of their electronic properties. 

Many researchers have used glass and glass-ceramic matrices for reinforcing with high-modulus graphite fibres [1, 2], silicon carbide fibres and silicon carbide mono-filaments [3-7], Very strong, tough and refractory composites were obtained from these efforts. 

Wang, C.M., Mitomo, M., and Emoto, H., Microstructure of liquid phase sintered superplastic silicon carbide ceramics , J. Mater. Res. 1997, 12, 3266-70. 

There are several reports of the condensation of bis-silanes of the type H3Si-X-SiH3 (primary silanes) and H2RSi-X-SiR H2 (secondary silanes) principally with the aim of producing polymers that would be precursors to silicon carbide ceramic material. The polymers would, in principle,... 

Ersoy, D.A., McNallan, M.J., and Gogotsi, Y. Carbon coatings produced by high temperature chlorination of silicon carbide ceramics. Mater. Res. Innov. 5, 2001 55-62. 

C. R. Blanchard and R. A. Page, Effect of Silicon Carbide Whisker and Titanium Carbide Particulate Additions on the Friction and Wear Behavior of Silicon Nitride, J. Am. Ceram. Soc., 73[11], 3442-3452 (1990). 

Based on this approach, families of silicon carbide fiber and silicon ceramic composites are now being routinely produced based on polycarbosilane precursors [22] These new materials are finding a wide range of new applications, for example, as a hot zone component in the next generation turbojets where silicon carbide composite components now routinely service at operating temperatures well in excess of 1000°C under high static thrusts (up to 50,000 psi) and high sonic pressure (up to 800 DB). No metallic components survive under these conditions. 

Silicon carbide Manufacture and applications in the nonoxide ceramics sector, see Section 5.5.5.4. 

Compare oxide ceramics such as alumina (AI2O3) and magnesia (MgO), which have significant ionic character with covalently bonded nonoxide ceramics such as silicon carbide (SiC) and boron carbide (B4C see Problems 19 and 20) with respect to thermodynamic stability at ordinary conditions. 

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