This review highlights the synthesis, processing and properties of non-oxide silicon-based ceramic materials derived from silazanes and polysilazanes. A comprehensive summary of the preparation of precursor compounds containing Si–N–Si units, including commercially available materials, is followed by the discussion of various processing techniques. The fabrication of dense bulk ceramics in the Si/E/C/N systems is reported which involves cross-linking of the polymeric ceramic precursor followed by a polymer-to-ceramic transformation step. The cross-linked precursor can be milled, compacted and pyrolysed to form dense, additive-free, amorphous silicon carbonitride monoliths or polycrystalline composites which withstand oxidation in air at 1600°C. Furthermore, an overview is given on the fabrication of silazane derived powders and coatings involving chemical vapour deposition (CVD) methods utilising volatile precursors. Fibre spinning and fibre properties, as well as other processing techniques like infiltration of preforms, the preparation of porous ceramics and joining are briefly discussed. A state of the art of the mechanical properties of polymer derived amorphous Si/C/N and Si/B/C/N ceramics with respect to hardness as well as high-temperature creep and oxidation resistance is summarised. Finally, some important aspects of industrial applications will be considered. The review is in part based on our own work related to the polysilazane derived ceramics, but will also cover a comprehensive state of the art including the published literature in this field.

Silazane derived ceramics and related materials

The purpose of this paper is to review some recent developments inthe field of the synthseis of covalent ceramics such as carbides and nitrides by pyrolysis of preceramic compounds and to demonstrate how several different fields of research like organoelement chemistry materialss processing and charcaterization can be combined for the development of novel advanced materials.

Precursor‐derived Covalent Ceramics*

Ordered mesoporous inorganic non-oxide materials attract increasing interest due to their plenty of unique properties and functionalities and potential applications. Lots of achievements have been made on their synthesis and structural characterization, especially in the last five years. In this critical review, the ordered mesoporous non-oxide materials are categorized by compositions, including non-oxide ceramics, metal chalcogenides, metal nitrides, carbides and fluorides, and systematically summarized on the basis of their synthesis approaches and mechanisms, as well as properties. Two synthesis routes such as hard-templating (nanocasting) and soft-templating (surfactant assembly) routes are demonstrated. The principal issues in the nanocasting synthesis including the template composition and mesostructure, pore surface chemistry, precursor selection, processing and template removal are emphatically described. A great number of successful cases from the soft-templating method are focused on the surfactant liquid-crystal mesophases to synthesize mesostructured metal chalcogenide composites and the inorganic-block-organic copolymer self-assembly to obtain non-oxide ceramics (296 references).

Ordered mesoporous non-oxide materials.

The fate and role of in situ formed carbon in polymer-derived ceramics

Preparation of moisture curable polysilazane coatings: Part I. Elucidation of low temperature curing kinetics by FT-IR spectroscopy

The pyrolysis of perhydropolysilazane in anhydrous ammonia has been studied up to 1000 °C through the analysis of the gas phase and the characterization of the solid residue by thermogravimetric analysis, Fourier transform-infrared analysis. X-ray photoelectron spectroscopy, X-ray diffraction and 29Si cross-polarization magic angle spinning-nuclear magnetic resonance. The pyrolysis mechanism involves three main steps: (1) below 400 °C, evaporation of residual solvent; (2) from 400–600 °C, reaction with ammonia leading to an increase of nitrogen content and formation of preceramic polymer-ceramics intermediate solid with a three-dimensional network; (3) from 600–1000 °C, completion of the formation of an amorphous hydrogenated solid with composition close to silicon nitride.

A. Kamo

Papers

Conversion mechanism of perhydropolysilazane into silicon nitride-based ceramics