MAGNETIC-RESONANCE CHARACTERIZATION OF SOLID-STATE INTERMEDIATES IN THE GENERATION OF CERAMICS BY PYROLYSIS OF HYDRIDOPOLYSILAZANE

Chemical intermediates produced from the pyrolysis of hydridopolysilaz ane (HPZ) were studied in the solid state by multinuclear nuclear magn etic resonance and electron spin resonance. When pyrolysed at temperat ures of 1200 degrees C, uncured HPZ forms a ceramic material with a co mposition of Si2.2N2.2C1.0, A series of HPZ-derived ceramics was produ ced using a number of different heat-treatment temperatures, varying b etween 300 a nd 1200 degrees C. Solid-state magnetic resonance data ge nerated from this set of HPZ-derived ceramics elucidate important feat ures of this complex transformation. Silicon atoms initially exist in two types of sites in the polymer, drop NSi(Me)(3) and (drop N)(3)SiH sites. Upon pyrolysis between 300 and 400 degrees C, the silazane cycl izes and cross-links, forming an intractable, insoluble solid. Increas ing the pyrolysis temperature to between 400 and 600 degrees 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 cleav ed. Elevating the heat-treatment temperature to between 600 and 1200 d egrees C generates a series of chemical structures with silicon in a t etrahedral 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 pr epared at even the highest heat-treatment temperature of 1200 degrees C.