A Study of the Thermodynamic Characteristics of Silicon and Germanium Oxynitrides

The study of any set of compounds proceeds in many diffuse directions influenced by what is already known, what needs to known, and whether any of the properties found can be of use to the rest of the community at large. Ceramics have always attracted those individuals whose interests included better high temperature materials; better in the chemical sense of having good corrosion resistance and structural stability at temperatures comparable to or higher than the materials now in use can withstand. To aid the search for more durable ceramics one can employ that area of chemical knowledge dealing directly with thermal properties, that is thermodynamics. With this tool one is able to gather information regarding the formation, stability, and the decomposition of any probable compound. This information enables one to better predict whether a compound will interact with any of the various chemical environments chosen for its employment. Using thermodynamics it is possible to undertake a study of a substance that will either lead to further experimentation or the search for and study of another substance. Recently, a study of the chemical system Si-N-O has been initiated by many high temperature scientists as a possible candidate for the fabrication of gas turbines, M.H.D. combustion chambers, and general use refractories. Some knowledge of the SiC and Si3N4 systems has been amassed, leading to deeper interest in their companion compounds, particularly Si 2N20. A Study of this substance was initiated to gain information on heats of formation, entropies of reaction, constants of equilibrium, and free energies of formation in a high temperature, high vacuum environment via mass spectrometric and differential scanning calorimetric methods. In connection with M. Billy\u27s research group at the University of Limoges, France, these two compounds have been studied with a view to their application as high temperature refractory materials . Three techniques were employed to study their thermal decomposition and their thermodynamic characteristics, the three techniques being thermogravimetric analysis, done by M. Billy\u27s group in France, molecular beam effusion cell mass spectrometry, and differential scanning calorimetry, with X-ray powder diffractometry used to help identify the final residues of the mass spectral studies