The Si-B-N System

Experimental work on the phase diagram of this system is meager. Some information on selected phase equilibria can be derived indirectly from work on the development of commercial materials in the Si-B-N system. Gugel et al. (1972) [223] suggested a tentative phase equilibrium diagram. Equilibria between silicon Sorides and silicon nitride were assumed. According to this result, silicon does not show an equilibrium with BN. Kato et al. [227] 

The Si-B-N system was calculated in this work by extrapolation from the binary subsystems. The isothermal section at 1273 K is shown in Fig. 15. 

In agreement with experimental information at a pressure of 1 bar the tieline Si3N4-BN exists up to the Si3N4 decomposition temperature of 2114 K. The Scheil reaction scheme as derived from the calculation is given in Fig. 16. Six invariant ternary reactions are calculated. All of them are of a degenerated type because boron nitride, formed at 2767 K, does not participate in the ternary reactions. At room temperature six three-phase equilibria are detected. 

---

Another route to polyborosilazanes, suitable for the synthesis of ceramics in the Si/B/N system, consists of an adaptation of the well-known oxo-sol-gel process to the ammonia system. Metal alkoxides are replaced by metal alkylamides, and ammonia instead of water serves as the solvolysing agent. 

Jansen M, Jaschke B, Jaschke X (2002) Amorphous Multinary Ceramics in the Si-B-N-C System. 101 137-192... 

M. Jansen, T. Jaeschke, B. Jaeschke, Amorphous multinary ceramics in the Si-B-N-C system in Structure and Bonding, Vol. 101 (Ed. M. Jansen), Springer-Verlag, Berlin, Heidelberg, 2002, p. 137. 

Up to now the single source precursor route is mainly used for preparing polymers in the quaternary Si/B/N/C system, and only to a minor degree in the Si/B/N and Si/B/C systems. A synopsis of the reactions of the single source precursors with respective crosslinking reagents is included in Table 2. The most commonly used, and most versatile, procedure for synthesizing prece-... 

During their genesis all precursor derived ceramics pass through an amorphous state which in certain cases is stable up to the respective decomposition temperature. The propensity to crystaUize is strongest for the binary silicon and boron nitrides and carbides, while in particular quaternary materials out of the Si/B/N/C system show the strongest resistance towards crystallization. It is interesting to note that in any case investigated, so far, the amorphous multinary ceramics decompose into the binary border phases upon crystallization - crystalline ternary silicon boron nitrides or carbides are not known to date cf. [9]. 

---