Mechanochemical synthesis of Co3C carbide with carbon nanotubes

Nanoscaled (about 15 nm of size) metastable carbide Co₃C was synthesized in a high-energy planetary ball mill by mechanical alloying of a mixture of powder cobalt (75 at. %) and multiwalled carbon nanotubes (CNT, 25 at. %). Phase transformation takes place at reaction milling according to the reaction <em>hcp</em>-Co + CNT ® Co₃C (reaction time is 120 - 220 min). The crystal structure of the Co₃C carbide formed in the milling products was studied by X-ray diffraction method. It has revealed that the Co₃C phase crystallizes in a Fe₃C-type structure with <em>a</em> = 0.4982(3) nm, <em>b</em> = 0.6715(6) nm, <em>c</em> = 0.4457(7) nm, <em>Pnma</em> space group. The reliability factor <em>R_B</em> is equal to 0.065 for 48 reflections presented at diffraction pattern. It is found that the crystal structure of the Co₃C carbide obtained by reaction milling of the Co-CNT charge is significantly internally deformed (distortion degree of the CCo₆ octahedron is 3.67 %) and contains the reduced interatomic Co-C distances (up to 0.188 nm). It was shown that the use of carbon nanotubes instead of graphite substantially reduces the duration of the Co₃C carbide synthesis.