Carbon/silicon nitride, properties

Table 2.71 Properties of silicon nitride and carbon/silicon nitride (4) Property Si N C/SijN4...

A. Y. Liu and M. L. Cohen, Structural Properties and Electronic Structure of Low-Compressibility Materials P-silicon Nitride and Hypothetical Carbon Nitride (P-C3N4), Phys. Rev. B, 41(15), 10727-34 (1990). 

Concerning carbon nanotube-reinforced silicon nitride matrices, only a few reports have so far been published [19]. In this case, hot isostatic pressing has been used for composite processing. The carbon nanotubes remained in the microstructure only under low pressures (2 MPa) they connect the silicon nitride grains and produce a 15-37% improvement of the mechanical properties as compared with other carbon-filled samples (Fig. 19.11). Increase of pressure... 

The thermodynamics of the above-elucidated SiC/C and SijN Si composites are determined by the decomposition of silicon carbide and silicon nitride, respectively, into their elements. The chemistry of ternary Si-C-N composites is more complex. If producing Si-C-N ceramics for applications at elevated temperature, reactions between carbon and silicon nitride have to be considered. Figure 18.2, which exhibits a ternary phase diagram valid up to 1484°C (1 bar N2) displays the situation. The only stable crystalline phases under these conditions are silicon carbide and silicon nitride. Ceramics with compositions in the three-phase field SiC/Si3N4/N are unknown (this is a consequence of the thermal instability of C-N bonds). Although composites within the three-phase field SiC/Si3N4/Si are thermodynamically stable even above 1500°C, such materials are rare. The reasons are difficulties in the synthesis of the required precursors and silicon melting above 1414°C. The latter aspect is of relevance, since liquid silicon dramatically worsens the mechanical properties of the derived ceramics. 

Roels N, Platon F, Aubreton J, Desmaison J (1990) Chemical vapour deposition of silicon nitride study of the interrelationships of experimental parameters, carbon content, oxidation and wear properties. In Spear KE, Cullen GW (eds) Proceedings of the 11th international conference on chemical vapor deposition. Electrochemical Society, Pennington, NJ, pp717-723... 

The extraordinary mechanical, thermal and electrical properties of carbon nanotubes (CNT) have prompted intense research into a wide range of applications in structural materials, electronics, and chemical processing.Attempts have been made to develop advanced engineering materials with improved or novel properties through the incorporation of carbon nanotubes in selected matrices (polymers, metals and ceramics). But the use of carbon nanotubes to reinforce ceramic composites has not been very successful. So far, only modest improvements of properties were reported in CNTs reinforced silicon carbide and silicon nitride matrix composites, while a noticeable increase of the fracture toughness and of electrical conductivity has been achieved in CNTs reinforced alumina matrix composites. ... 

The experimental and theoretical research activities in the field of materials with hardness comparable to or higher than diamond have been stimulated in recent years by the discovery and postulation of novel carbon aUotropes and novel carbon- and boron-based materials. Comparison of the experimental and theoretical results obtained in the past shows that first principles quantum mechanical and semi-empirical calculations are very useful for the screening of the structural and electronic properties of new materials. The fascinating variety of new possible carbon aUotropes which have been calculated to be stable relative to diamond or can be stabilized for kinetic reasons refiects the high potential and the topicality of modem carbon chemistry. Novel carbon aUotropes and carbon and silicon nitrides are subjects of discussion in Part I in the chapter written by G. Jungnickel et al. and J. E. Lowther. 

Superhard compounds are obviously formed by a combination of the low atomic number elements boron, carbon, silicon, and nitrogen. Carbon-carbon as diamond, boron-nitrogen as cubic boron nitride, boron-carbon as boron carbide, and silicon-carbon as silicon carbide, belong to the hardest materials hitherto known. Because of their extreme properties and the variety of present and potential commercial applications, silicon carbide (SiC) and boron carbide (B4C) are, besides tungsten carbide-based hard metals, considered by many as the most important carbide materials. 

H. Iwanaga, M. Kawaguchi and S. Motojima. Growth mechanisms and properties of coiled whiskers of silicon nitride and carbon. J. J. Appl. Phys., 32 [1], 105-115 (1993). 

The common commercially available fibers used in composites are fiberglass, graphite (carbon), aramid, polyethylene, boron, silicon carbide, and other ceramics such as silicon nitride, alumina, and alumina silica. Many matrix choices are available, both thermosetting and thermoplastic. Each type has an impact on the processing technique, physical properties, and environmental resistance of the finished composite. The most common resin matrices include polyester, vinyl esters, epoxy, bismaleimides, polyimides, cyanate ester, and triazine. 

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