FACTORS CONTROLLING NITRIDE FORMATION

Three general and interrelated atomic characteristics play an essential part in the formation of nitrides the difference in electron ativity between the element nitrogen and the other element forming the nitride, the size of the respective atoms, and the electronic bonding characteristics of these atoms. 

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The second factor controlling the formation of nitrides is the atomic radius of the constituent elements. The radii of these elements are listed in Table 9.2 (see discussion on atomic radius in Sec. 4.1 of Ch. 2). One should note that nitrogen is one of the smallest atoms, and smaller than carbon. Table 9.2 also shows the type of nitride formed, i.e., interstitial (IS) or covalent (C), or intermediate (IM). 

Osborne Reynolds was the first to show that tightly packed granular solids expand their volume when deformed.84 This phenomenon is called dilatancy. It is well understood and is discussed in some detail in the literature on soil mechanics.85-87 In vitreous-bonded structural materials such as silicon nitride, dilatancy has been suggested as a contributing factor in the formation of cavities,88 and may be an important factor in the cavitation of ceramic matrix composites.64 Dilatancy has also been suggested as an important factor in controlling the creep and creep relaxation of glass-ceramics.89... 

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