Effect of reaction time on phase composition and microstructure of chromium carbide nanopowders

Chromium carbide (Cr3C2) nanopowders can be synthesized by carbon thermal reduction of nanometer chromic oxide (Cr2O3) and with nanometer carbon black. Effect of reaction time on phase composition and microstructure of chromium carbide nanopowders was researched under the conditions of 28 wt% C and 1100 degrees C. The products were characterized by X-ray diffractomety (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric and differential scanning calorimetry (TG-DSC) and X-ray photoelectron spectroscopy (XPS) techniques. The results show that the product is mainly composed of Cr2O3 when the reaction time is 0.5 h, and the diffraction peaks of carbon are not observable. Some powders show a spherical morphology, others appear as fused mass. The powders with the single phase of Cr3C2 can be synthesized at 1 h, and an average crystallite size of 26 nm. The powders show good dispersion and are mainly composed of spherical or nearly spherical particles with a mean diameter of about 30 nm. Compared with those of 1 h, the diffraction lines of Cr3C2 synthesized at 1.5 h and 2 h shift toward smaller angles, and the powders exhibit a lot of agglomerated particles. (C) 2013 Elsevier Ltd. All rights reserved.