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

Composites are, in general, a rapidly evolving and growing technical field with a very wide range of applications across the aerospace, defence, energy, medical and transport sectors as a result of...

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Selection, processing, properties and applications of ultra-high temperature ceramic matrix composites, UHTCMCs – a review

Carbon fabric (CF) was modified with strong HNO3 etching, plasma bombardment, and anodic oxidation, respectively. The modified carbon fabric was then used to prepare carbon fabric composites (CFC) by dip-coating in a phenolic resin and the relative mass content of carbon fabric in the carbon fabric composites is 65%. The friction and wear behaviors of the carbon fabric composites were evaluated with a Xuanwu-III high temperature friction and wear tester, and their mechanical properties were evaluated on a Shimadzu™ universal materials testing machine, respectively. The changes in the chemical compositions of the unmodified and modified carbon fabrics were analyzed by means of X-ray photoelectron spectroscopy. The morphologies of the worn surfaces of the unmodified and modified carbon fabric composites were analyzed by means of scanning electron microscopy. It was found that the friction-reduction and anti-wear properties of the carbon fabric composites were improved by anodic oxidation, plasma bombardment, and strong HNO3 etching, so were the mechanical properties and load-carrying capacity. The composite made of the carbon fabric modified with anodic oxidation showed the best tribological and mechanical properties, and the one made of the carbon fabric etched with HNO3 had the poorest tribological and mechanical properties among the three kinds of the tested composites. The active groups were produced during the oxidation process, which contributed to strengthen the bonding strength between the carbon fabric and the adhesive and hence to improve the tribological and mechanical properties of the composites made of the modified carbon fabric. The friction and wear properties of the carbon fabric composites were closely dependent on the environmental temperature. Namely, the wear rates of the composites at elevated temperature above 180 °C were much larger than that below 180 °C, which was attributed to the degradation and decomposition of the adhesive resin at excessively elevated temperature. Moreover, the composite made of the carbon fabric modified with anodic oxidation had better thermal stability than the one made of the unmodified carbon fabrics.

Tribological and mechanical properties of the composites made of carbon fabrics modified with various methods

Processing and properties of C/Si-B-C-N fiber-reinforced ceramic matrix composites prepared by precursor impregnation and pyrolysis

Carbon and SiC fiber-reinforced ceramic matrix composites were prepared via infiltration of fiber preforms using the polymer infiltration technique and polymer pyrolysis. Suitable silazane (SiCN) precursors with appropriate thermosetting behavior, viscosity and ceramic yield were synthesized, starting from functionalized chlorosilanes. Microstructural development and fracture behavior was studied after various infiltration and pyrolysis cycles. Residual stresses induced during processing were evaluated. Mechanical and thermo-physical properties of the composites with polymer-derived matrix, i.e. 3-pt bending strength and thermal expansion coefficients (CTE), were measured dependent on reinfiltration cycles and fiber orientation. The oxidation resistance was investigated. Specific pyrolyzed samples were infiltrated via silicon melts in order to enhance corrosion and wear resistance.

I. Richter

Papers

Fiber-reinforced composites with polymer-derived matrix: processing, matrix formation and properties

C-Fibre Reinforced Composites with Polymer-Derived Matrix: Microstructure, Thermal Properties, Strength