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High-temperature creep behavior of a SiOC glass ceramic free of segregated carbon
Stabler, Christina,Roth, Felix,Narisawa, Masaki,Schliephake, Daniel,Heilmaier, Martin,Lauterbach, Stefan,Kleebe, Hans-Joachim,Riedel, Ralf,Ionescu, Emanuel Elsevier 2016 Journal of the European Ceramic Society Vol.36 No.15
<P><B>Abstract</B></P> <P>In this study we present the high-temperature creep behavior of a dense SiOC glass ceramic free of segregated carbon. Solid-state NMR spectroscopy, XRD and TEM investigations indicate that the sample consists of β-SiC nanoparticles homogeneously dispersed in an amorphous silica matrix. Compression creep experiments were performed at 1100–1300°C and stresses of 50–100MPa. The calculated creep viscosity of SiOC is two orders of magnitude higher than that of pure silica. Whereas the activation energy for creep (696kJ/mol) is close to that determined in pure silica glass. However, a stress exponent of 1.7 was calculated, suggesting that other mechanisms might contribute to the creep in addition to the Newtonian viscous flow. The strong difference in the creep rates and creep mechanism of the SiOC glass ceramic and amorphous silica is discussed in terms of possible contributions of the interface between the silica matrix and the β-SiC nanoparticles.</P>
Yuan, Jia,Hapis, Stefania,Breitzke, Hergen,Xu, Yeping,Fasel, Claudia,Kleebe, Hans-Joachim,Buntkowsky, Gerd,Riedel, Ralf,Ionescu, Emanuel American Chemical Society 2014 Inorganic chemistry Vol.53 No.19
<P>Amorphous SiHfBCN ceramics were prepared from a commercial polysilazane (HTT 1800, AZ-EM), which was modified upon reactions with Hf(NEt<SUB>2</SUB>)<SUB>4</SUB> and BH<SUB>3</SUB>·SMe<SUB>2</SUB>, 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, N<SUB>2</SUB>) 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/HfB<SUB>2</SUB>/SiC (annealing in argon) and HfN/Si<SUB>3</SUB>N<SUB>4</SUB>/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.</P><P>Amorphous SiHfBCN ceramics were prepared from a suitable single-source precursor. Annealing experiments of the SiHfBCN samples in an inert gas atmosphere at temperatures of 1300−1700 °C led to their conversion nanostructured UHTC-NCs, such as HfC/HfB<SUB>2</SUB>/SiC nanocomposites (in argon) and HfN/Si<SUB>3</SUB>N<SUB>4</SUB>/SiBCN nanocomposites (in nitrogen), thus revealing a convenient preparative approach to nanostructured ultrahigh-temperature stable materials starting from a greatly flexible single-source precursor.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/inocaj/2014/inocaj.2014.53.issue-19/ic501512p/production/images/medium/ic-2014-01512p_0016.gif'></P>