SYNTHESIS OF FINELY DISPERSED VANADIUM CARBIDE (VC<sub>0.88</sub>) USING NANOFIBROUS CARBON

Abstract

The paper presents the experimental data on the synthesis of finely dispersed powder of vanadium carbide (VC 0.88 ). Vanadium carbide was prepared by the reduction of vanadium oxide (III) with nanofibrous carbon (NFC) in the induction furnace under an argon atmosphere. NFC is a product of catalytic decomposition of light hydrocarbons. The main characteristic of a NFC is a high specific surface area (~150 000 m 2 /kg), which is significantly higher than that of soot (~50 000 m 2 /kg). The content of impurities in the NFC is at the level of 1 % wt. Based on the analysis of the state diagram of the V – C system, the composition of the charge and the upper temperature limit of the carbide formation reaction for obtaining vanadium carbide in the powder state are determined. Based on the thermodynamic analysis, the temperature of the onset of the carbothermic reduction reaction of vanadium oxide (III) at various CO pressures was determined. The characteristics of vanadium carbide were studied using X-ray and elemental analyzes, pycnometric analysis, scanning electron microscopy using local energy dispersive X-ray microanalysis (EDX), low-temperature adsorption of nitrogen, followed by determination of the BET specific surface area, sedimentation analysis, synchronous thermogravimetry and differential scanning calorimetry (TG/DSC). The material obtained at optimal parameters is represented by a single phase – vanadium carbide VC 0.88 . The powder particles were predominantly aggregated. The average size of the particles and the aggregates equaled 9.2 – 9.4 μm within a wide range of size distribution. The specific surface value of the obtained samples was 1800 – 2400 m 2 /g. Oxidation of vanadium carbide began from the temperature of ~430 °C and practically ends at ~830 °C. Optimum parameters of synthesis are the ratio of reagents according to stoichiometry to obtain carbide of composition VC 0.88 at a temperature of 1500 – 1600 °С and a holding time of 20 minutes. It is shown that for this process nanofibrous carbon is an effective reducing agent and that vanadium oxide (III) is almost completely reduced to carbide VC 0.88