Silicon nitride Subject

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. 

Historically, the development of nitrides proceeded slowly until the emergence of silicon nitride during the late 1950s. From that time onwards, the intricacies of the relationship between the two forms of silicon nitride, combined with the observation that, when hot-pressed or sintered into dense products, silicon nitride displayed excellent mechanical properties at temperatures in excess of 1000 °C, propelled silicon nitride into a subject area of intense interest. As a result, it now resides in a well-defined niche as a stmctural material for wear parts and related applications. At the same time, this provided a catalyst for the development of other nitrides, both of a binary and ternary character. Increasing complexity was provided by the observation that, just as with mineral silicates, aluminum could replace silicon in... 

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