Novel class of precursor-derived Zr–La–B–C(O) based ceramics containing nano-crystalline ultra-high temperature phases stable beyond 1600 °C |
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Affiliation: | 1. Laboratory for High Performance Ceramics, Department of Metallurgical and Materials Engineering, Indian Institute of Technology Madras (IIT Madras), Chennai, 600036, India;2. Ceramic Technologies Group - Center of Excellence in Materials and Manufacturing for Futuristic Mobility, Indian Institute of Technology-Madras (IIT Madras), Chennai, 600036, India;3. CALPHAD Lab, Department of Metallurgical and Materials Engineering, Indian Institute of Technology Madras (IIT Madras), Chennai, 600036, India;4. Ceramic Matrix Products Division, Analytical Spectroscopy and Ceramics Group, PCM Entity, Vikram Sarabhai Space Center (VSSC), ISRO, Thiruvananthapuram, 695022, India |
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Abstract: | In this work, a novel ultra-high temperature resistant precursor-derived ceramic containing Zr, La, B, and C was synthesized through precursor modification of phenol formaldehyde resin. The thermal stability and resistance to crystallization of the ceramic at a temperature of 1600 °C was investigated and was found to be profoundly influenced by the boron content in the starting precursors. The ceramics remained amorphous at 1600 °C for 2 h in argon and upon sustained heat-treatment for up to 16 h resulted in nano-crystalline ultra-high temperature phases such as ZrB2, ZrC, LaB6 and La2Zr2O7. Thermodynamic equilibrium phase calculations show that even longer durations of heat treatment may be required to achieve thermodynamic equilibrium. High-resolution transmission electron microscopy revealed encapsulation of nanocrystals (<5 nm) in an amorphous matrix surrounded by turbostratic layers of carbon inhibiting its growth. Spectrochemical techniques confirmed the presence of boron substituted carbon in the amorphous matrix of the ceramic. The unique nature of the amorphous matrix lends the ceramic resistance to crystallization and chemical degradation that can surpass the likes of classical silicon-based precursor-derived ceramics. |
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Keywords: | Precursor-derived ceramics Ultra-high temperature ceramics Thermal stability Transition metal carbides and borides Rare earth borides |
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