Synthesis of nanosized group IV borides in ionic melts of anhydrous sodium tetraborate

Metal Borides: From Industrial Classics to Versatile Colloidal Nanocrystals for Energy, Catalysis, and Hard Coatings Applications

“…The authors reported two different morphologies of 49 nm spheres, like LaB 6 at 600 °C and a cubic morphology of 94.7 nm at 800 °C reaction temperature. 105 The diborides that were successfully synthesized in molten salt and ionothermal conditions (NbB 2 , HfB 2 ) at 800 °C lead to spherical particles of 7−10 nm of crystallite size, 112 and group IV borides VB 2 in an ionic melt of Na 2 B 4 O 7 and KCl lead to ∼90 nm sized crystallites; 113,114 borohydride reduction with metal hydroxides, metal oxides, and metal chlorides leads to highly aggregated crystalline TiB 2 of ∼20 nm and HfB 2 micrometer sized platelets with 200 nm thickness. 115,116 Molten salt can also be used for MR-M x B y .…”

Low temperature controllable synthesis of transition metal and rare earth borides mediated by molten salt

“…By using MSM-ERS, several transition metal borides, including ZrB 2 , HfB 2 , TiB 2 , NbB 2 and VB 2 were synthesised. [79][80][81][82][83][84][85][86][87][88][89][90][91] In these syntheses, Na 2 B 4 O 7 was more commonly used to form the required molten salt medium, probably owing to its low melting point and reasonably high solubility of B in it. Table 3 summarises synthesis conditions and characteristics of raw materials and boride powders resultant from MSM-ERS, [79][80][81][82][83][84][85][86][87][88][89][90][91] revealing the relatively low synthesis temperatures (750-850 °C) in all the cases, and the high effectiveness of Na 2 B 4 O 7 in facilitating the overall synthesis process.…”

“…A 'common' mechanism for the MSM-ERS in Na 2 B 4 O 7 was suggested as follows [79][80][81][82][83][84][85][86] : B atoms first change to B 2+ ions via interacting with B 3+ ions from the molten Na 2 B 4 O 7 according to Reaction (2):…”

“…However, as revealed by Table 3, the product boride particles did not appear to retain shapes/sizes of the original metal particles. For example, in the syntheses of TiB 2 , ZrB 2 , HfB 2 , VB 2 and NbB 2 , despite the use of micrometer-sized (10-20 μm) metal and boron powders, nanosized product particles (<100 nm) were formed, [79][80][81][82][83][84][85][86] and in the synthesis of Fe-B, despite the use of much coarser Fe particles (∼45 μm/5 μm), the resultant boride particles remained much smaller, and exhibited different morphologies (short-rods of FeB and platelets/nanoflakes of Fe 2 B). 87,88 On the other hand, in the WB 2 synthesis, a 'template growth' mechanism was proposed.…”

“…A ‘common’ mechanism for the MSM-ERS in Na 2 B 4 O 7 was suggested as follows 79–86 : B atoms first change to B 2+ ions via interacting with B 3+ ions from the molten Na 2 B 4 O 7 according to Reaction (2): Then, the formed B 2+ ions diffuse through the molten salt and arrive at the surface of the metal M, and subsequently react with the latter to form the desirable boride according to Reaction (3): Such a mechanism seems to suggest that the boride formation in Na 2 B 4 O 7 is dominated by the ‘template growth’ on the metal M which acts as the template. However, as revealed by Table 3, the product boride particles did not appear to retain shapes/sizes of the original metal particles.…”