Magnetic Nanoparticles with Fe-N and Fe-C Cores and Carbon Shells Synthesized at High Pressures

Nanoparticles of iron carbides and nitrides enclosed in graphite shells were obtained at 2 divided by 8 GPa pressures and temperatures of around 800 degrees 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 degrees 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 divided by 8 GPa and temperatures up to 1600 degrees C, iron nitride Fe3N1+x is more stable than iron carbides. At 8 GPa and 1600 degrees C, the average particle size of iron nitride increased to 0.5 divided by 1 mu m, while simultaneously formed free carbon particles had the shape of graphite discs with a size of 1 divided by 2 mu m. Structural refinement of the iron nitride using the Rietveld method gave the best result for the space group P6(3)22. The refined composition of the samples obtained from a mixture of ferrocene and melamine at 8 GPa/800 degrees C corresponded to Fe3N1.208, and at 8 GPa/1650 degrees 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.

Automated summary

Under high pressure conditions, nanoparticles of iron carbides and nitrides enclosed in graphite shells were synthesized using specific reactant mixtures. This method allows control over the particle size and core phase.