Carbothermal reduction process for synthesis of nanosized chromium carbide via metal-organic vapor deposition

Abstract

Nanosized chromium carbide was synthesized by metal-organic chemical vapor deposition method in a fluidized bed using mixtures of methane/hydrogen ambient as carburization source in the temperature range 700–850 °C. The microstructure and the phase evolution were deciphered by XRD, TEM and XPS analysis. The carburization process involved the sequential deposition of carbon on the outer surface of the Cr 2O 3 powder followed by carbon diffusion into the powder, leading to the formation of metastable Cr 3C 2 − x phase and stable Cr 3C 2. STEM line scan mode was utilized to delineate the resultant composition gradient within the interlayer of the metastable intermediates and the final stable powder species, that were generated during the course of the carburization process. The formation of carbon nanofilms surrounding the carbide crystallites provides the stress and assists the phase transformation from metastable Cr 3C 2 − x to stable Cr 3C 2. XPS spectral analysis revealed that, the chromium ion in stable chromium carbide carries higher valance than that in metastable chromium carbide.