USE OF CARBON MATERIAL WITH DEVELOPED SURFACE FOR SYNTHESIS OF HIGHER CHROMIUM CARBIDE

The paper presents experimental data on synthesis of finely dispersed powder of chromium carbide Cr₃C₂ . Chromium carbide was prepared by reduction of chromium oxide Cr₂O₃ with nanofibrous carbon (NFC) in induction furnace in argon atmosphere. NFC is a product of catalytic decomposition of light hydrocarbons. The main characteristic of NFC is high specific surface area (~150,000  m² /kg), which is significantly higher than that of carbon black (~50,000  m² /kg). Content of impurities in NFC is at the level of 1  wt  %. Based on analysis of state diagram of Cr – C system, composition of charge and the upper temperature limit of carbide formation reaction for obtaining chromium carbide in powder state are determined. Based on thermodynamic analysis, temperature of the onset of carbothermic reduction reaction of chromium oxide Cr₂O₃ was determined at various CO pressures. Characteristics of chromium carbide were studied using X-ray diffraction analysis, pycnometric analysis, scanning electron microscopy using local energy dispersive X-ray microanalysis (EDX), lowtemperature nitrogen adsorption followed by determination of specific surface area by means of BET method, sedimentation analysis, synchronous thermogravimetry and differential scanning calorimetry (TG/DSC). The material obtained at optimal parameters is represented by a single phase – chromium carbide Cr₃C₂ . Powder particles were predominantly aggregated. Average size of particles and aggregates equaled 6.5  μm within a wide range of size distribution. Specific surface value of the obtained samples was 2200  m² /kg. Oxidation of chromium carbide began at temperature of ~640  °C and practically ends at ~1000  °C. Optimum parameters of synthesis are provided by ratio of reagents according to carbide of Cr₃C₂ composition stoichiometry at temperature of 1300  °С and holding time of 20 minutes. It is shown that for this process nanofibrous carbon is an effective reducing agent and that chromium oxide Cr₂O₃ is almost completely reduced to carbide Cr₃C₂ .

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