title: Single-source-precursor synthesis of hafnium-containing ultrahigh-temperature ceramic nanocomposites (UHTC-NCs).
abstract: Amorphous SiHfBCN ceramics were prepared from a commercial polysilazane (HTT 1800, AZ-EM), which was modified upon reactions with Hf(NEt2)4 and BH3·SMe2, and subsequently cross-linked and pyrolyzed. The prepared materials were investigated with respect to their chemical and phase composition, by means of spectroscopy techniques (Fourier transform infrared (FTIR), Raman, magic-angle spinning nuclear magnetic resonance (MAS NMR)), as well as X-ray diffraction (XRD) and transmission electron microscopy (TEM). Annealing experiments of the SiHfBCN samples in an inert gas atmosphere (Ar, N2) at temperatures in the range of 1300-1700 °C showed the conversion of the amorphous materials into nanostructured UHTC-NCs. Depending on the annealing atmosphere, HfC/HfB2/SiC (annealing in argon) and HfN/Si3N4/SiBCN (annealing in nitrogen) nanocomposites were obtained. The results emphasize that the conversion of the single-phase SiHfBCN into UHTC-NCs is thermodynamically controlled, thus allowing for a knowledge-based preparative path toward nanostructured ultrahigh-temperature stable materials with adjusted compositions.
authors.affiliation: Technische Universität Darmstadt , Institut für Materialwissenschaft, Jovanka-Bontschits-Strasse 2, D-64287, Darmstadt, Germany.
authors.forename: Jia
authors.initials: J
authors.lastname: Yuan
authors.forename: Stefania
authors.initials: S
authors.lastname: Hapis
authors.forename: Hergen
authors.initials: H
authors.lastname: Breitzke
authors.forename: Yeping
authors.initials: Y
authors.lastname: Xu
authors.forename: Claudia
authors.initials: C
authors.lastname: Fasel
authors.forename: Hans-Joachim
authors.initials: HJ
authors.lastname: Kleebe
authors.forename: Gerd
authors.initials: G
authors.lastname: Buntkowsky
authors.forename: Ralf
authors.initials: R
authors.lastname: Riedel
authors.forename: Emanuel
authors.initials: E
authors.lastname: Ionescu