Magnetic resonance characterization of solid-state intermediates in the generation of ceramics by pyrolysis of hydridopolysilazane
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Chemical intermediates produced from the pyrolysis of hydridopolysilazane (HPZ) were studied in the solid state by multinuclear nuclear magnetic resonance and electron spin resonance. When pyrolysed at temperatures of 1200°C, uncured HPZ forms a ceramic material with a composition of Si2.2N2.2C1.0. A series of HPZ-derived ceramics was produced using a number of different heat-treatment temperatures, varying between 300 and 1200°C. Solid-state magnetic resonance data generated from this set of HPZ-derived ceramics elucidate important features of this complex transformation. Silicon atoms initially exist in two types of sites in the polymer,Si(Me)3 and ()3SiH sites. Upon pyrolysis between 300 and 400°C, the silazane cyclizes and cross-links, forming an intractable, insoluble solid. Increasing the pyrolysis temperature to between 400 and 600°C creates a matrix that is partially inorganic; at heat-treatment temperatures in this range, many of the C-H bonds of the starting polymer are cleaved. Elevating the heat-treatment temperature to between 600 and 1200°C generates a series of chemical structures with silicon in a tetrahedral site of the general form SiN4−xCx, where x=0, 1, 2, 3, 4. No crystalline forms of Si3N4 or SiC were detected in the material prepared at even the highest heat-treatment temperature of 1200 °C.
KeywordsSilicon Nuclear Magnetic Resonance Pyrolysis Electron Spin Resonance Electron Spin
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