Structure of Silicon Nitride

Silicon nitride crystallizes in two hexagonal forms (a- and fl-SisN and also a cubic y-modification with spinel structure that is stable at high pressure and temperature ( 15GPa, 2000 K Zerr et al, 1999 Leitch et al, 2004). The a-phase occurs in nature as a rare mineral (nierite) in ordinary and enstatite chondritic meteorites (Lee et al, 1995). 

The structure refinement of a-Si3N4, using synchrotron radiation powder diffraction, was more recently accomplished by Toraya (2000), yielding a = 775.193 (3) pm, c = 561.949 (4) pm, and Z = 4. 

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Hardie, D., and K. H. Jack Crystal structures of silicon nitride. Nature [London] 180, 332-333 (1957). 

FIGURE 22.16 Structure of silicon nitride (Si3N4). Each Si atom is bonded to four N atoms, and each N atom is bonded to three Si atoms. The result is a strong network. 

Hardie, D. and Jack, K.H. (1957) Crystal structures of silicon nitride . Nature 180, 332. Initial report of the structures of Si3N4. 

The measures of solid state reactivity to be described include experiments on solid-gas, solid-liquid, and solid-solid chemical reaction, solid-solid structural transitions, and hot pressing-sintering in the solid state. These conditions are achieved in catalytic activity measurements of rutile and zinc oxide, in studies of the dissolution of silicon nitride and rutile, the reaction of lead oxide and zirconia to form lead zirconate, the monoclinic to tetragonal transformation in zirconia, the theta-to-alpha transformation in alumina, and the hot pressing of aluminum nitride and aluminum oxide. 

Materials are three-dimensionally arranged. Thus, the two-dimensional information which is gained from the examination of microsections or thin foils, the types of specimen usually used for materialographic investigations, does not truly reflect the whole structure of a material. This becomes clear from the photomontage (Fig. 25a). It shows a cube of silicon nitride ceramic in... 

Klemm H, Herrmann M, Schubert C (1996) The Influence of the Grain Boundary Phase Composition on the High Temperature Properties of Silicon Nitride Materials. In Parilak L, Danninger H, Dusza J, Weiss B (eds) Proc Int Conf Deformation and Fracture in Structural PM Materials, IMR SAS Kosice 2 75... 

Trice, R.W., and Halloran, J.W. (1999), Influence of micro structure and temperature on the fracture energy of silicon nitride/boron nitride fibrous monolithic ceramics , J. Am. Ceram. Soc., 82(9) 2502-2508. 

This approach was successfully used in modeling the CVD of silicon nitride (Si3N4) films [18, 19, 22, 23]. Alternatively, molecular dynamics (MD) simulations can be used instead of or in combination with the MC approach to simulate kinetic steps of film evolution during the growth process (see, for example, a study of Zr02 deposition on the Si(100) surface [24]). Finally, the results of these simulations (overall reaction constants and film characteristics) can be used in the subsequent reactor modeling and the detailed calculations of film structure and properties, including defects and impurities. 

Structure of the nitrides of silicon and germanium. Nature [London]... 

In fact Van Wyk ° used something similar to a composite structure for the lubrication of silicon nitride and alumina in plain spherical bearings. He incorporated a 90% molybdenum disulphide/8% molybdenum/2% tantalum compact in holes drilled in the surface of the alumina outer ring, and the details have been described in Chapter 8. The system was very successful, giving a forty times increase in wear life. 

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