Kinetics Analysis of Reaction between Molybdenum and Nitrogen Trifluoride

The fluorination behavior of molybdenum (Mo) powder with NF3, such as temperature dependence of reactivity, reaction mechanism and kinetics were investigated on a homemade fluoride volatility process (FVP) research device. The in-situ Fourier transform infrared (FTIR) spectroscopy was applied to determine the beginning and the end of reaction. The research demonstrated that near 500 K or lower, the reaction between Mo power and NF3 occurred, meanwhile, the temperature had an important influence on the average reaction rate and the utilization of NF3. When the temperature increased from 500 K to 700 K, the average rate increased from 1.04 × 10–2 mol/h to 2.40 × 10–2 mol/h and the utilization of NF3 increased from 21.2% to 49.0%. The in-situ FTIR and XRD analysis assisted by thermodynamic calculation indicated that Mo power was converted to MoF6 through an intermediate product MoF3: 2NF3 (g) + 2Mo (s) = 2MoF3 (s) + N2 (g), then 2MoF3 (s) + 2NF3 (g) = 2MoF6 (g) + N2 (g). Based on a mathematical model with unreacted shrinking core, the calculated reaction rate constant increased from 1.77 × 10–2 min–1 to 3.48 × 10–2 min–1 in the temperature range of 500–700 K, and the activation energy was 10.13 kJ/mol.