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 FTIR and MS. The resultant polyaluminasilazanes were then pyrolysized to form amorphous SiAlCN ceramics at 1000 oC in flowing N2. The structural evolution during pyrolysis was studied using solid-sate 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 relative amount of these units strongly depended on Al-content.