Self‐propagating mechanosynthesis of HfB₂ nanoparticles by a magnesiothermic reaction

Abstract

A mechanically induced self-sustaining reaction (MSR) was used to synthesize hafnium diboride nanoparticles. Along this route, magnesium was selected as a robust reducing agent for co-reduction in boron and hafnium oxides in a combustive manner. Combustion occurred after a short milling period of 12 minutes. The hafnium diboride nanoparticles had a polygonal faceted morphology and were 50-250 nm in diameter. The assessment of the processing mechanism revealed that the initial combustive reduction in B 2 O 3 to elemental B by Mg was the major step for progressing the overall reaction. After that, HfO 2 can be reduced to elemental Hf, followed by the synthesis of HfB 2 phase.combustion, Hafnium diboride (HfB 2 ), Mechanosynthesis, Nanoparticles

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

“…In addition, there is seldom report so far on the oxidation behavior of TMB 2 nanopowders, which is a critical property for high-temperature applications. HfB 2 ceramics, as a member of TMB 2 ceramics, have recently attracted extensive attentions because they exhibit potential applications in high-temperature electrodes and thermal protection systems for hypersonic aerospace vehicles [17][18][19][20]. In this work, we successfully synthesized the nanocrystalline HfB 2 powders by the molten salt synthesis technique at a relatively low temperature of 1373 K using the inexpensive HfO 2 and B powders as reaction precursors within the inexpensive KCl/NaCl molten salts.…”

Silicothermic synthesis of phase‐pure HfB2 fine powder

“…Magnesiothermic reduction syntheses of HfB 2 have also been explored 23−25 . Magnesiothermic reduction is featured by low processing cost, fast reaction speed, small energy consumption and high yield.…”

“…However, the synthesized products from magnesiothermic processes usually have poor purity due to the remaining of byproducts MgO, Mg 3 B 2 O 6 , Mg 2 B 2 O 5 , MgB 4 O 7 , etc in the final products. To eliminate the byproducts, a ‘‘post reduction’’ HCl leaching process has to be carried out, 23−25 which may cause some environmental concerns.…”

Effects of TaB2 and TiB2 on the grain growth behavior and kinetics of HfB2 ceramics during pressureless sintering

“…Hafnium diboride powders could be mainly prepared by the following routes: (a) self‐propagating high‐temperature synthesis; (b) polymer‐precursor route; (c) the sol‐gel process; (d) borothermal and boro/carbothermal reduction . Refinement of the starting HfB 2 powders could enhance the surface energy, thereby increasing the driving force of sintering and improving the mechanical properties.…”

“…Reaping benefits from excellent mechanical properties and oxidation resistance versus adverse conditions, hafnium diboride (HfB 2 ) is critically regarded as one of the most promising candidates to be applied in extreme conditions, such as supersonic aircraft tip, reusable trans-atmosphere aircraft, etc. [1][2][3][4] Hafnium diboride powders could be mainly prepared by the following routes: (a) self-propagating high-temperature synthesis; 5,6 (b) polymer-precursor route; 7,8 (c) the sol-gel process; 9,10 (d) borothermal and boro/carbothermal reduction. 11,12 Refinement of the starting HfB 2 powders could enhance the surface energy, thereby increasing the driving force of sintering and improving the mechanical properties.…”