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.

Preparation and hydrothermal corrosion behavior of Cf/SiCN and Cf/SiHfBCN ceramic matrix composites

“…Polysilazane (HTT1800, AZ-EM, Wiesbaden, Germany) and a polysilazane-based SiHfBCN precursor (which was prepared as described in 21 ) were considered as preceramic precursors for the PIP fabrication of the composites. The carbon fabric was cut into rectangular pieces with dimension of 44 mm × 16 mm.…”

“…65 and 80 wt.%, respectively, as reported previously. 21 Consequently, the residual open porosity of SiHfBCN was expected to be lower than that of SiCN. Indeed, the C f /SiHfBCN obtained from applying three PIP cycles showed a residual porosity of ca.…”

Synthesis and characteristic of SiBCN/HfN ceramics with high temperature oxidation resistance

“…The c-HfN nano-grains are well-crystallized in SiBCN matrix. It is well known that SiBCN and HfN ceramics are materials that can withstand ultrahigh temperatures beyond 2000 C [9]. Therefore, the SiBCN/HfN ceramic is considered to have promising resistance behavior at high temperatures.…”

“…Recently, metal-modified polymer-derived ceramics have been studied to improve the high-temperature stability for Si-based ceramics [9,10]. That is, multiple elements (such as Zr, Mg, Fe, Al and Cu) were introduced in the bonding network of Si-based ceramics [11e13].…”

“…SiBCN/HfN/Si 3 N 4 nanocomposite ceramics are prepared from polysilazane at 1700 C under nitrogen, which are nanostructured ultrahigh-temperature stable materials. The HfN-rich regions are significantly more stable concerning their carbothermal decomposition than the SiN x regions [9]. The examples using low annealing temperature are seldom reported.…”