Synthesis of bulk nanocrystalline HfB2 from HfCl4–NaBH4–Mg ternary system

A different chemical route to prepare hafnium diboride‐based nanofibers: Effect of chemical composition

“…[33][34][35] Chen et al 12 have synthesized HfB 2 nanopowders by the reaction of HfCl 4 with NaBH 4 at 600°C in an autoclave. Akçamlı et al 9 investigated the synthesis of pure HfB 2 powders with an average particle size of 145 nm using the HfCl 4 -NaBH 4 -Mg blends via autoclave processing at 500°C followed by annealing at 1000°C for 3 hours. Kidchob et al 36 reported the synthesis of thin sol-gel hafnia films with high transparency in the UV-visible range from HfCl 4 .…”

“…However, a high temperature (>1500°C) as well as a long production period are required for above‐mentioned methods to achieve complete reduction, which may result in a large particle size and a relatively poor sinterability 7 . In order to obtain HfB 2 powders with better properties at moderate temperatures, many researchers prefer to use mechanochemical synthesis, 8 mechanically activated borothermal reduction, 2 chemical rout with autoclave processing, 9 solution‐based processing combined with spark plasma sintering (SPS), 10 sol‐gel, 11 hydrothermal synthesis, 12 and preceramic polymer methods 13 . The solution‐derived precursor indicates a homogeneous atomic or molecular distribution among different components, which is beneficial for the conversion from precursor to ceramic with superior purity and compositional homogeneity at a low temperature in a relatively short time 14 .…”

Silicothermic synthesis of phase‐pure HfB2 fine powder

“…1−5 Potential applications of HfB 2 include hypersonic flight and atmospheric re-entry, rocket propulsion systems, cutting tools, wear resistance coatings, molten metal crucibles, plasma arc electrode and neutron absorber in nuclear reactors. 6−11 A variety of investigations on synthesis of HfB 2 have been reported, such as direct reaction between elemental boron and hafnium, 12 self-propagating synthesis, 13−16 boron thermal reduction, 17−19 carbo/borothermal reduction, 20 solgel assistant method, 21 sodium borohydride reduction 22,23 and molten salt-assisted synthesis, 19 among other reactions. However, the above reported techniques for preparing HfB 2 powders suffer from several drawbacks, such as high synthesis temperatures, expensive reaction precursors, flammable and explosive, and so on.…”

“…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.…”