Hydrothermal silicon nitrides

Silicon nitride-based ceramics are promising engineering materials for application under corrosive and wear conditions [135-142]. However, the use of silicon nitride materials in hot acids under hydrothermal conditions and in bases is often limited by degradation of the materials. This is the impetus for current efforts for better understanding of the influence of the microstructure on the corrosion behaviour of silicon nitride materials and to improve the materials behaviour on its basis. Up to now, only a small amount of data about the mechanisms of corrosion and pitting formation exists. 

The corrosion resistance of selected Si3N4 materials in NaOH is given in Fig. 32. The silicon nitride materials are less attacked by bases than by acids. The extent of corrosion increases with increasing temperature and concentration of the bases [150]. Materials which are less stable in acids are more stable in bases and under hydrothermal conditions. 

Figure 33. Weight loss of silicon nitride materials under hydrothermal conditions at 210°C.

T. Sato, T. Murakami, E. Shimada, K. Komeya, T. Komeda and M. Komatsu, Corrosion of Silicon nitride ceramics under hydrothermal conditions J. Mat. Science, 26,1991,1749-1754. 

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