Polymer-ceramic conversion of liquid polyaluminasilazanes for SiAlCN ceramics

Liquid-phased polyaluminasilazanes were synthesized by simply reacting a liquid polyureasilazane with aluminum isopropoxide. The reaction was studied by Fourier-transform infrared spectrometry (FTIR) and mass spectroscopy. The resultant polyaluminasilazanes were then pyrolysized to form amorphous SiAlCN ceramics at 1000 degrees C in flowing N-2. The structural evolution during pyrolysis was studied using solid-state NMR and FTIR. Spectral analysis revealed that the amorphous structures of the ceramics consisted Of SiC2N2 and SiCN3 as major building units, small amounts Of SiC3N and SiN4 units, and penta- or hexa-coordinated aluminum with nitrogen. Such units were connected with each other through C-C/C = C bonds or by shearing N to form network structures. The results also revealed that the relative amount of these units strongly depended on the Al content.