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Synthesis and oxidation behavior of HFB2 nano-powders by molten salt method


Ultra-high temperature ceramics are a kind of materials with high melting point above 3000and excellent oxidation resistance, ablation resistance and thermal shock resistance at high temperature, mainly including transition metal borides, carbides and nitride compounds. Among them, HFB2 material with its strong covalent bond characteristics and high melting point, high modulus, high hardness, low saturated vapor pressure, high thermal conductivity and good oxidation resistance and other comprehensive properties, is considered to be the most potential candidate material for new space vehicle thermal protection system, nose cone and wing leading edge components. However, how to synthesize HFB2 nanometer powder efficiently, rapidly, low-cost and on a large scale to meet the development of high-performance HFB2 materials is still one of the main problems it faces.

Recently, the research group of Zhu Yan-hui, from the School of Materials Science and Engineering, South China University of Technology, used B powder and HfO2 as precursors, and KCl/NaCl as molten salt, using low temperature molten salt method successfully synthesized HfB2 nanocrystalline powder at 1100. The average particle size of the synthesized powder is 150 nm, with good single crystal structure. It was found that the presence of liquid molten salt at high temperature could not only effectively increase the diffusion rate of the reactants, but also increase the reaction rate between them, and finally induce the synthesis of high purity HFB2 nano-powder. Thermogravimetric experiments show that the synthesis of HfB2 nano powder in 500 ~ 800 in air showed good antioxidant properties, namely the powder of the oxidation process is a process of weight gain, the increase trend of obvious oxidation behavior of parabola, showed that the oxidation of powder rate is the rate of diffusion of oxygen in the generated oxide layer. The synthesized HFB2 nano-powders laid a good foundation for the development and application of high-performance HFB2 materials in the future. This method has the advantages of simple process, rapid reaction (minute grade) and low temperature, and has the potential of large-scale synthesis of ultra-high temperature ceramic nano powders.

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