D. Suttor

Structural characterisation of silicon carbonitride ceramics derived from polymeric precursors

Abstract Polymeric precursors with tailored structures were prepared from functionalised chlorosilanes. Pyrolysis under inert atmospheres led to amorphous Si–C–N–(H) ceramics at 1000°C. Further heat treatment caused the transformation into the thermodynamically stable crystalline phase assemblage. The structural changes associated with crosslinking, pyrolysis and crystallisation were studied by characterising the solid intermediates between 300 and 1600°C applying 29 Si and 13 C solid state nuclear magnetic resonance (NMR) spectroscopy. In addition, Fourier transformed infrared (FTIR) spectroscopy, X-ray diffraction (XRD), thermoanalytical techniques and density measurements were employed. The combination of these methods and the use of polymeric precursors with tailored structures pointed to a correlation of the polymer architecture with the structure of the amorphous ceramic material.

High temperature stability of sol-gel-derived SiOC glasses

The high temperature stability of sol-gel-derived SiOC glasses has been investigated in order to understand the role played by the presence of a free-carbon phase in the amorphous oxycarbide network. Therefore, pure and excess free-carbon containing SiOC glasses have been prepared from hybrid gels and used for the high temperature stability experiments. Moreover, the possible effects of the sample size with respect to local kinetics and thermodynamics and of the testing environment have also been investigated. Results show that all these parameters play a crucial role in defining the high temperature behavior of SiOC glasses.

Non-Oxide and Oxide Ceramics from Preceramic Polymers for Composite Components

Non-oxide and oxide ceramics based on unfilled and filled preceramic polymers were synthesized for applications as matrices (and fibers) for ceramic matrix composites. Two examples are given. Silazane precursors with tailored properties (i.e. ceramic yield, viscosity, setting behavior) were prepared, starting from functionalized chlorosilanes. Thermoanalytical analysis was used to investigate the organic/inorganic transition. Emphasis was put on TEM-studies to reveal aspects of the complex crystallization behavior of the polymer derived amorphous glasses, which is especially important with respect to fiber degradation processes. Monolithic synthetic mullite with low shrinkage, potentially serving as a polymer derived oxide matrix for fiber reinforced composites, was prepared from siloxane/Al2O3- and siloxane/Al-mixtures by reaction bonding processes, thus demonstrating the usefulness of filled polysiloxane systems for the synthesis of stoichiometric silicates.