Structures silicon carbon nitrides

This chapter examines some potential structures that have been proposed for different phases of carbon-nitride and also the tertiary material silicon-carbon-nitride. First we briefly examine some basic modeling procedures that have been employed to date when investigating these materials and then discuss properties of the predicted structures. 

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). 

This chapter describes the preparation and examination of ceramic matrix composites realized by the addition of different carbon polymorphs (carbon black nanograins, graphite micrograins, carbon fibers and carbon nanotubes) to silicon nitride matrices. In the following sections, structural, morphological and mechanical characteristics of carbon-containing silicon nitride ceramics are presented. 

Some ceramic materials are not found widely or at all in nature, and thus are synthesized for use. To prepare more complex ceramic compositions such as perovskites of general structural formula ABO3, and ferrites, of formula MFc204, the individual oxides or salts of the cations A, B, and M are often combined as powders and then reacted at high temperature by a solid-state diffusion mechanism. Silicon nitride (Si3N4) can be manufactured from either the nitridation of silicon metal or from the reaction of silicon tetrachloride with ammonia. Silicon carbide (SiC) is obtained from the reduction of silica with a carbon containing source. 

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. 

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