Investigation of the oxidation resistance of ZrB2-based monoliths using polymer-derived Si(Zr,B)CN as sintering aid

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Oxidation resistance of ZrB₂‐based monoliths using polymer‐derived Si(Zr,B)CN as sintering aid

The focus of the present work is the investigation of the influence of polymer‐derived ceramics, used as sintering aids for preparing ZrB₂‐based monoliths, on their high‐temperature oxidation behavior. For the preparation of the monoliths, ZrB₂ powder was coated with polymer‐derived SiCN, SiZrCN, or SiZrBCN and subsequently densified via hot‐pressing at temperatures as low as 1800°C. To investigate the oxidation kinetics, thermogravimetric analysis (TGA) was performed at 1300°C in synthetic air with exposure times of 50 and 100 h. A detailed study of the materials oxide scale and subsurface microstructure was conducted using optical microscopy, electron probe microanalysis, scanning electron microscopy, and X‐ray diffraction. The experimental findings were compared to thermodynamic equilibrium calculations using the CALPHAD method, which led to a better understanding of the oxidation mechanism. In comparison to the literature data of ZrB₂–SiC, the results show improved oxidation resistance for all three investigated materials. The formation of gaseous species during oxidation, in particular CO, CO₂, B₂O₃, and SiO, within the oxide scale of the monoliths was rationalized via CALPHAD calculations and used to explain the oxidation behavior and kinetics and also the formation of bubbles in the subsurface region of the oxidized specimens

Oxidationsverhalten von polymerabgeleiteten keramischen Nanokompositen

In dieser Arbeit wurde das Oxidationsverhalten von polymerabgeleiteten keramischen Nanokompositen (PDC-NCs) im Hinblick auf potenzielle Hochtemperaturanwendungen untersucht. Ziel war es den Einfluss der chemischen Zusammensetzung und der daraus resultierenden Mikrostruktur der PDC-NCs auf das Hochtemperaturoxidationsverhalten zu analysieren. Die Arbeit gliedert sich in drei Abschnitte, wobei im ersten Abschnitt (Hf,Ta)C/SiC-Nanokomposite bei 1200 °C bzw. 1400 °C für bis zu 100 h in synthetischer Luft ausgelagert wurden. Im zweiten Abschnitt wird das Oxidationsverhalten einer SiAlOC-Beschichtung und deren Einfluss auf das Korrosionsverhalten von Chromsubstraten bei Auslagerungstemperaturen von 950 °C und 1050 °C untersucht. Der letzte Abschnitt beinhaltet die Untersuchung von ZrB₂/Si(Zr,B)CN-Proben bei 1300 °C, wobei die PDC-NC Si(Zr,B)CN als Sinteradditiv verwendet wurde. In allen drei Abschnitten konnte der Zusammenhang zwischen der chemischen Zusammensetzung und der Mikrostruktur der PDC-NCs und dem resultierenden Oxidationsverhalten aufgeklärt werden. Insgesamt liefert die Arbeit wichtige Erkenntnisse im Hinblick auf die Anwendung von PDC-NCs im Hochtemperaturbereich, wobei mögliche Anwendungsfelder als Hochtemperatur-Schutzschichten und Sinteradditive für Ultra-Hochtemperatur-Keramiken aufgezeigt werden

Oxidation resistance of ZrB₂-based monoliths using polymer-derived Si(Zr,B)CN as sintering aid

The focus of the present work is the investigation of the influence of polymer-derived ceramics, used as sintering aids for preparing ZrB₂-based monoliths, on their high-temperature oxidation behavior. For the preparation of the monoliths, ZrB₂ powder was coated with polymer-derived SiCN, SiZrCN, or SiZrBCN and subsequently densified via hot-pressing at temperatures as low as 1800°C. To investigate the oxidation kinetics, thermogravimetric analysis (TGA) was performed at 1300°C in synthetic air with exposure times of 50 and 100 h. A detailed study of the materials oxide scale and subsurface microstructure was conducted using optical microscopy, electron probe microanalysis, scanning electron microscopy, and X-ray diffraction. The experimental findings were compared to thermodynamic equilibrium calculations using the CALPHAD method, which led to a better understanding of the oxidation mechanism. In comparison to the literature data of ZrB₂–SiC, the results show improved oxidation resistance for all three investigated materials. The formation of gaseous species during oxidation, in particular CO, CO₂, B₂O₃, and SiO, within the oxide scale of the monoliths was rationalized via CALPHAD calculations and used to explain the oxidation behavior and kinetics and also the formation of bubbles in the subsurface region of the oxidized specimens

Oxidation resistance of ZrB 2 ‐based monoliths using polymer‐derived Si(Zr,B)CN as sintering aid

The focus of the present work is the investigation of the influence of polymer-derived ceramics, used as sintering aids for preparing ZrB2-based monoliths, on their high-temperature oxidation behavior. For the preparation of the monoliths, ZrB2 powder was coated with polymer-derived SiCN, SiZrCN, or SiZrBCN and subsequently densified via hot-pressing at temperatures as low as 1800 degrees C. To investigate the oxidation kinetics, thermogravimetric analysis (TGA) was performed at 1300 degrees C in synthetic air with exposure times of 50 and 100 h. A detailed study of the materials oxide scale and subsurface microstructure was conducted using optical microscopy, electron probe microanalysis, scanning electron microscopy, and X-ray diffraction. The experimental findings were compared to thermodynamic equilibrium calculations using the CALPHAD method, which led to a better understanding of the oxidation mechanism. In comparison to the literature data of ZrB2-SiC, the results show improved oxidation resistance for all three investigated materials. The formation of gaseous species during oxidation, in particular CO, CO2, B2O3, and SiO, within the oxide scale of the monoliths was rationalized via CALPHAD calculations and used to explain the oxidation behavior and kinetics and also the formation of bubbles in the subsurface region of the oxidized specimens

Microstructural evolution of Si(HfxTa1−x)(C)N polymer-derived ceramics upon high-temperature anneal

Ultra-high temperature ceramic nanocomposites (UHTC-NC) within the Si(HfxTa1_x)(C)N system were synthe-sized via the polymer-derived ceramics (PDC) synthesis route. The microstructure evolution of the materials was investigated upon pyrolysis and subsequent heat treatment. The crystallization behavior and phase composition were studied utilizing X-ray diffraction, scanning-and transmission electron microscopy. Single-source -precursors were converted into amorphous single-phase ceramics, with the exception of surface crystallization effects, at 1000 degrees C in NH3. Annealing in N2 at 1600 degrees C resulted in fully crystalline UHTCs. The powder samples revealed microstructures consisting of two characteristic regions, bulk and surface; displaying intrinsic micro-structure and phase composition differences. Instead of the expected nitrides, transition metal carbides (TMC) were detected upon high-temperature anneal. The residual carbon available in the system triggered a decom-position reaction, resulting in the formation of TMCs plus gaseous nitrogen and SiC. Experimental data underline that N-containing PDCs are prone to phase separation accompanied by thermal decomposition and diffusion -controlled coarsening