Silazane derived ceramics and related materials

This review highlights the synthesis, processing and properties of non-oxid e silicon-based ceramic materials derived from silazanes and polysilazanes. A comprehensive summary of the preparation of precursor compounds containi ng Si-N-Si units, including commercially available materials, is followed b y the discussion of various processing techniques. The fabrication of dense bulk ceramics in the Si/E/C/N systems is reported which involves cross-lin king of the polymeric ceramic precursor followed by a polymer-to-ceramic tr ansformation step. The crosslinked precursor can be milled, compacted and p yrolysed to form dense, additive-free, amorphous silicon carbonitride monol iths or polycrystalline composites which withstand oxidation in air at 1600 degrees C. Furthermore, an overview is given on the fabrication of silazan e derived powders and coatings involving chemical vapour deposition (CVD) m ethods utilising volatile precursors. Fibre spinning and fibre properties, as well as other processing techniques like infiltration of preforms, the p reparation of porous ceramics and joining are briefly discussed. A state of the art of the mechanical properties of polymer derived amorphous Si/C/N a nd Si/B/C/N ceramics with respect to hardness as well as high-temperature c reep and oxidation resistance is summarised. Finally, some important aspect s of industrial applications will be considered. The review is in part base d on our own work related to the polysilazane derived ceramics, but will al so cover a comprehensive state of the art including the published literatur e in this field. (C) 2000 Elsevier Science S.A. All rights reserved.