Preparation of nano-scale Cr_3C_2 particles dispersed on alumina particles by MOCVD in fluidized reactor and carbothermal treatment

摘要

Nano-scale Cr_3C_2 powder with an average particle size of 50-80 nm, uniformly coated on alumina particles, has been prepared by metal organic chemical vapor deposition (MOCVD) in the fluidized chamber, using the pyrolysis of Cr(CO)_6 precursor, and carbothermal treatment in the CH_4 and H_2 gas mixtures. The Cr(CO)_6 precursor was characterized by differential scanning calorimetry (DSC) to understand the decomposition temperature of the precursor, which was determined to be 163 deg C. The precursor decomposed and formed the mixture of CrC_(1-x_, Cr_2O_3 and free carbon on the surface of the Al_2O_3 particles when pyrolyzed in fluidized bed at 300 and 400 deg C. The resultant powders were examined by X-ray diffractometer (XRD) and transmission electron microscopy (TEM) equipped with energy dispersion spectrometer (EDS), for investigating phase composition and microstructures. The as-deposited particles fabricated at 300 and 400 deg C in fluidized chamber were amorphous and crystalline, respectively. The thermal behaviour investigated by TG/DTA indicates that the amorphous powder had a exothermic peak in the DTA curve at ~400 deg C, which crystallized at this temperature. In order to prepare the nano-particle reinforced composites, the powder fabricated in the fluidized bed was carbonized in the mixed atmosphere of CH_4 and H_2. Both CrC_(1-x) and Cr_2O_3 phase were transferred into Cr_3C_2 phase after the carbothermal treatment.