X-ray Diffraction Analysis of the Pyrolytic Conversion of Perhydropolysilazane into Silicon Nitride

A detailed investigation using X‐ray diffraction and other supportive techniques was performed on a preceramic polysilazane to study its pyrolytic conversion to silicon nitride (Si3N4). Analytical techniques were developed to determine the volumetric degree of crystallinity with respect to pyrolysis temperature. Quantitative data for crystallite size, phase composition, and degree of crystallinity versus pyrolysis temperature and atmosphere (nitrogen and ammonia) are presented. Pyrolytic products produced under nitrogen and ammonia atmospheres consist of microcrystals of silicon, α‐Si3N4, and β‐Si3N4. Under both atmospheres, a majority of the char is crystalline at ≅1270°C, and the entire char is crystallized at 1400°C. Pyrolysis under an ammonia atmosphere produces nearly stoichiometric Si3N4, while pyrolysis under nitrogen produces silicon‐rich material.