Mechanochemical synthesis of Co3C carbide with carbon nanotubes

O I Nakonechna,N M Bilyavyna,M M Dashevski,A M Kurylyuk

doi:10.15330/pcss.20.1.17

Abstract

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 hcp-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 a = 0.4982(3) nm, b = 0.6715(6) nm, c = 0.4457(7) nm, Pnma space group. The reliability factor RB 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.

Highlights

Nanomaterials are increasingly used to modify the structure of metals and alloys in order to obtain their higher physical and mechanical characteristics, which will reduce the weight of products from them while maintaining the necessary complex of properties
According to the results of XRD phase analysis the sample selected after 60 min of processing contains the reflections of hexagonal cobalt with a = 0.2508(5) nm, c = 0.4076(4) nm
The diffraction patterns of the test samples selected after of 120 min of the initial charge processing already contain reflections of the Co3C phase in addition to the reflections of hexagonal cobalt. Amount of this carbide is gradually increased and after 180 min of processing the Co3C carbide becomes the main phase of test samples

Summary

Introduction

Nanomaterials are increasingly used to modify the structure of metals and alloys in order to obtain their higher physical and mechanical characteristics, which will reduce the weight of products from them while maintaining the necessary complex of properties. For the first time the metastable Co3C (Fe3C-type structure) and Co2C (CaCl2) carbides were synthesized in thin films, which are formed on a heated up to 550 °C substrate under cobalt evaporation in CO + H2 gas mixture [1]. These carbides were obtained mainly by cobalt carbidation, which was carried out either at the precipitation in thin films, or by the direct Fischer-Tropsch synthesis in a CO + H2 gas atmosphere [2,3,4,5,6]

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