Project 1: Single-source precursor synthesis of ceramic nanocomposites for (ultra) high-temperature applications

M.Sc. Jan Bernauer

Supervisors: Prof. Ralf Riedel, Prof. Hans-Joachim Kleebe

Ultra-high-temperature ceramics (UHTCs) are a class of materials with a melting point of 3000°C and beyond. Therefore, they are mainly used in applications where high temperatures (T > 2000°C) are required e.g. thermal barrier coatings. Borides, carbides and nitrides of the early transition metals (Zr, Hf, Nb, Ta) are suitable for this purpose. However, various studies revealed that single-phase bulk UHTCs have rather poor oxidation resistance under extreme and aggressive environment. Ceramic composites can be an alternative solution for applications in such environment.

The PDC (polymer derived ceramics) method is particularly suitable for the synthesis of ceramic composites. Pre-ceramic polymer precursors are thermally decomposed and thus offer simple and inexpensive access to various ceramic systems. Project 1 of GRK 2561 deals with the synthesis of ceramic composite systems for high-temperature applications by the PDC route. To produce suitable precursors, various polysilazanes [R1R2Si-NR3] are used in this project. The ternary system SiCN and modified systems with the composition Si(M, B)CN (M = Ti, Zr, Hf) are manufactured by thermal treatment of the precursors. Organometallic compounds are used to modify the polysilazanes. Spectroscopic and thermogravimetric analyzes are used for the intensive investigation of the precursors and the ceramization process.

Subsequently, various processes are used to produce monoliths of the ternary and multinary systems namely: warm pressing followed by thermal treatment, hot pressing at temperatures from 1600°C - 1800°C, as well as FAST / SPS techniques (Field Assisted Sintering Technology / Spark Plasma Sintering) at 1600°C - 1800 ° C. The monoliths produced in this way are structurally characterized using the common methods.