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Nanocrystalline HfB2 powders were successfully synthesized by molten salt synthesis technique at 1373 K using B and HfO2 as precursors within KCl/NaCl molten salts. The results showed that the as-synthesized powders exhibited an irregular polyhedral morphology with the average particle size of 155 nm and possessed a single-crystalline structure. From a fundamental aspect, we demonstrated the molten-salt assisted formation mechanism that the molten salts could accelerate the diffusion rate of the reactants and improve the chemical reaction rate of the reactants in the system to induce the synthesis of the high-purity nanocrystalline powders. Thermogravimetric analysis showed that the oxidation of the as-synthesized HfB2 powders at 773–1073 K in air was the weight gain process and the corresponding oxidation behavior followed parabolic kinetics governed by the diffusion of oxygen in the oxide layer.


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Molten salt synthesis, formation mechanism, and oxidation behavior of nanocrystalline HfB2 powders

Show Author's information Da LIUaQiangang FUbYanhui CHUa( )
School of Materials Science and Engineering, South China University of Technology, Guangzhou 510641, China
State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi’an 710072, China

Abstract

Nanocrystalline HfB2 powders were successfully synthesized by molten salt synthesis technique at 1373 K using B and HfO2 as precursors within KCl/NaCl molten salts. The results showed that the as-synthesized powders exhibited an irregular polyhedral morphology with the average particle size of 155 nm and possessed a single-crystalline structure. From a fundamental aspect, we demonstrated the molten-salt assisted formation mechanism that the molten salts could accelerate the diffusion rate of the reactants and improve the chemical reaction rate of the reactants in the system to induce the synthesis of the high-purity nanocrystalline powders. Thermogravimetric analysis showed that the oxidation of the as-synthesized HfB2 powders at 773–1073 K in air was the weight gain process and the corresponding oxidation behavior followed parabolic kinetics governed by the diffusion of oxygen in the oxide layer.

Keywords:

ultra-high temperature ceramics, powders, molten salt synthesis, oxidation behavior
Received: 01 April 2019 Revised: 19 June 2019 Accepted: 20 July 2019 Published: 05 February 2020 Issue date: February 2020
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Publication history
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Acknowledgements
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Publication history

Received: 01 April 2019
Revised: 19 June 2019
Accepted: 20 July 2019
Published: 05 February 2020
Issue date: February 2020

Copyright

© The author(s) 2019

Acknowledgements

We acknowledge financial support from the National Key R&D Program of China (No. 2017YFB0703200), National Natural Science Foundation of China (Nos. 51802100 and 51972116), Young Elite Scientists Sponsorship Program by CAST (No. 2017QNRC001), and the fund of the State Key Laboratory of Solidification Processing in NWPU (No. SKLSP201820).

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