Unusual Stability of Amorphous Polymer Derived Ceramics at High Temperatures
Zusammenfassung der Projektergebnisse
Solid-state NMR spectroscopy was used for structural characterization of various types of PDC materials. The structural characteristics and alteration during the preparation of carbon-rich SiCN PDCs was studied by 13C, 29Si and 1H NMR spectroscopy, covering the whole range from the precursor polymers to the final ceramic materials. Significant structural differences were observed, depending on the molecular composition of the precursor materials. Similar studies were performed for polymer-derived SiCO/HfO2 ceramic nanocomposites, from which again the structural features of the pyrolysis intermediates up to the final ceramics were examined. The residual hydrogen content in various types of SiCN and SiCNO PDCs was determined for the first time by 1H MAS NMR spectroscopy. It was demonstrated that 1H NMR spectroscopy – after careful calibration – is very reliable for quantitative measurements, can detect very small proton contents, and can even identify different proton containing species. Surprisingly, for the present materials it was possible to detect residual hydrogen even after exposure to temperatures above 1300 °C, which was completely unexpected, but which is important for the description of the phase behavior of such materials. Single and double resonance solid-state NMR experiments were performed on SiBCN ceramic samples. The analysis of such experiments provided homonuclear and heteronuclear dipolar interactions, and in turn internuclear distances. From these studies it was demonstrated that the structure of BNCx phase in the SiBCN ceramics resembles that of hexagonal boron nitride. However, due to the incorporation of carbon, the hexagonal phase is disordered. Hence, the boron-boron and boron-nitrogen distances change with the actual pyrolysis temperature, and are in general larger than in hexagonal boron nitride.
Projektbezogene Publikationen (Auswahl)
- 11B{15N} REDOR and 11B spin echo studies for structural characterization of Si-B-C-N precursor ceramics. Soft Materials, 4 (2006), 207 -225
Emmler, T., Tsetsgee O., Buntkowsky G., Weinmann M., Aldinger F., Müller K.
- Thermodynamically Stable SixOyCz Polymer-Like Amorphous Ceramics, J. Am. Ceram. Soc. 90 (2007) 3213-3219
Varga T., Navrotsky A., Moats J. L., Morcos R. M., Poli F., Müller K., Sahay A., Raj R.
- Energetics of SixOyCz Polymer-Derived Ceramics Prepared Under Varying Conditions, J. Am. Ceram. Soc. Society 91 (2008) 2969-2974
Morcos R.M., Navrotsky A., Varga T., Blum Y., Ahn D., Poli F., Müller K., Raj R.
- Enthalpy of Formation of Carbon-Rich Polymer-Derived Amorphous SiCN Ceramics, J. Am. Ceram. Soc. Society 91 (2008) 3349-3354
Morcos R. M., Mera G., Navrotsky A., Varga T., Riedel. R., Poli F., Müller K.
- Influence of the Precursor Cross-Linking Route on the Thermal Stability of Si-B-C-O Ceramics, Chem. Mater. 20 (2008) 7148-7156
Ischenko V., Pippel E., Woltersdorf J., Ngoumeni Yappi B.R., Hauser R., Fasel C., Riedel R., Poli F., Müller K.
- Thermodynamically Stable SiwCxNyOz Polymer-Like, Amorphous Ceramics Made from Organic Precursors, J. Am. Ceram. Soc. 91 (2008) 2391-2393
Morcos R.M., Navrotsky A., Varga T., Ahn D., Saha A., Poli F., Müller K., Raj R.
- Carbon-Rich SiCN Ceramics Derived from Phenyl- Containing Poly(silylcarbodiimides), J. Am. Ceram. Soc. Society 29 (2009) 2873-2883
Mera G., Riedel R., Poli F., Müller K.
- Solid-State NMR Studies on Precursor-Derived Si-B-C-N and B-C-N Ceramics, PhD Thesis, University of Stuttgart, Stuttgart 2009
Tsetsgee O.
- Polymer-Derived Silicon Oxycarbide/Hafnia Ceramic Nanocomposites. Part I: Phase and Microstructure Evolution during the Ceramization Process, J. Amer. Ceram. Soc., 93(6) (2010) 1774-1782
Ionescu E., Papendorf B., Kleebe H-J., Poli F., Müller K., Riedel R.
- Solid-State NMR Studies on Precursor-Derived Si-B-C-N Ceramics in Advances in Polymer Derived Ceramics and Composites: Ceramic Transactions, Vol. 213 (Eds.: P. Colombo, R. Raj, M. Singh), p. 13- 32, 2010
Tsetsgee O. and Müller K.
