Silicon Nitride Solid Solution in the Ternary System, Si₃N₄-AlN-SiO₂

Abstract

On the basis of the solid solution in the system, Si₃N₄-AlN-Al₂O₃, the presence of silicon nitride solid solution in the system, Si₃N₄-AlN-SiO₂, is expected from the consideration of their composition. The range of the solid solution expected on this basis covers the compo sitional triangle made by connecting the three points, A (57mol% AIN-43mol% SiO₂), B (67mol% AIN-33mol% SiO₂), and C (100mol% Si₃N₄). An experimental study of the solid solution proved the expectation valid. In addition to this, the actual range of the solid solution was found to be wider than the triangle mentioned above. This excess range agrees rather well with the expected range on the basis of the vacancy concentration, with the exception of the range near Si₂ON₂.
The points, A and B, lie on the binary system, AlN-SiO₂. The triangle, ABC, is intercepted by the line connecting the two points, AlN and Si₂ON₂. In other words, the two binary systems, AlN-SiO₂ and AlN-Si₂ON₂, contain the solid solution which is distinguished from the end members in the cystral structure. Thus the presence of two new compounds to represent the solid solution, SiAl₂N₂O₂ and Si₂AlN₃O is exected for the systems, AlN-SiO₂ and AlN-Si₂ON₂, respectively.
Experimental examinations by X-ray diffraction method, however, failed to confirm the presence of the compounds, may be due to the order-disorder transformation in the compounds, as in some of spinel structure.
The presence of silicon nitride solid solution in the system, Si₃N₄-AlN-SiO₂, shows that the addition of AlN to silicon nitride would be effective to eliminate the glassy phase which is considered to reduce the high temperature strength.