Browsing by Author "Filonenko, Vladimir P."

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    Magnetic Nanoparticles with Fe-N and Fe-C Cores and Carbon Shells Synthesized at High Pressures
    (MDPI, 2023) Bagramov, Rustem H.; Filonenko, Vladimir P.; Zibrov, Igor P.; Skryleva, Elena A.; Kulnitskiy, Boris A.; Blank, Vladimir D.; Khabashesku, Valery N.
    Nanoparticles of iron carbides and nitrides enclosed in graphite shells were obtained at 2 ÷ 8 GPa pressures and temperatures of around 800 °C from ferrocene and ferrocene–melamine mixture. The average core–shell particle size was below 60 nm. The graphite-like shells over the iron nitride cores were built of concentric graphene layers packed in a rhombohedral shape. It was found that at a pressure of 4 GPa and temperature of 800 °C, the stability of the nanoscale phases increases in a Fe7C3 > Fe3C > Fe3N1+x sequence and at 8 GPa in a Fe3C > Fe7C3 > Fe3N1+x sequence. At pressures of 2 ÷ 8 GPa and temperatures up to 1600 °C, iron nitride Fe3N1+x is more stable than iron carbides. At 8 GPa and 1600 °C, the average particle size of iron nitride increased to 0.5 ÷ 1 μm, while simultaneously formed free carbon particles had the shape of graphite discs with a size of 1 ÷ 2 μm. Structural refinement of the iron nitride using the Rietveld method gave the best result for the space group P6322. The refined composition of the samples obtained from a mixture of ferrocene and melamine at 8 GPa/800 °C corresponded to Fe3N1.208, and at 8 GPa/1650 °C to Fe3N1.259. The iron nitride core–shell nanoparticles exhibited magnetic behavior. Specific magnetization at 7.5 kOe of pure Fe3N1.208 was estimated to be 70 emu/g. Compared to other methods, the high-pressure method allows easy synthesis of the iron nitride cores inside pure carbon shells and control of the particle size. And in general, pressure is a good tool for modifying the phase and chemical composition of the iron-containing cores.
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    Method for preparation of new superhard B-C-N material and material made therefrom
    (2013-05-28) Khabashesku, Valery N.; Filonenko, Vladimir P.; Davydov, Valery Aleksandrovich; Rice University; United States Patent and Trademark Office
    According to some embodiments, a method of preparing a superhard material involves using mixtures of boron with carbon nitride of C3N4 stoichiometry as precursors. The C3N4 may be nanospherical. The result of chemical interaction of these components is the formation of new ternary compound B—C—N compound with a cubic structure. According to some embodiments, the composition is BCxN, where x is about 0.5. According to some embodiments, the composition is BCxN, where x is about 0.2. According to some embodiments, the compound has a unit cell parameter a=3.645±0.005 Å. According to some embodiments, the unit cell parameter a is about 3.655 Å. Synthesis is carried out under the conditions of thermodynamic stability of diamond at pressures higher that 6.0 GPa and temperatures above 1000° C. The starting components are taken according to the following ratio: boron—20-60 wt. %, C3N4—40-80 wt. %.