A new method for preparing ultrafine Mo2C by the CVD reaction of CO and gaseous MoO3: Parameter optimization and its formation mechanism

In the work, the method of chemical vapor deposition reaction of CO and gaseous MoO 3 was proposed to prepare ultrafine Mo 2 C. Different technologies, such as XRD, FESEM, TEM, laser particle size analysis and Brunauer-Emmett-Teller method, as well as thermodynamic software FactSage 8.3, were adopted to analyze the experimental data. The results revealed that increasing the flow-rate of reduction‑carbonization regent CO ( V outer (CO)) was beneficial for the formation of Mo 2 C; while when V outer (CO) exceeded the threshold value, single-phase Mo 2 C cannot be prepared. The optimal conditions for preparing ultrafine Mo 2 C were given as T  = 1223–1323 K, V outer (CO) = 900 mL/min, and V inner (Ar) = 100 mL/min; herein, V inner (Ar) means the flow-rate of carrier gas Ar. Under these conditions, the preparation procedures of Mo 2 C followed the pathways of MoO 3  → (MoO 3 ) n ( n  = 2, 3, 4, and 5) → MoO 2  → Mo 2 C. The study also discovered that the as-prepared Mo 2 C kept the overall morphology as the intermediate product MoO 2 with a hexagonal-platelet structure; however, due to the removal of oxygen and the decrease of products' molar volume, the prepared Mo 2 C exhibited a rougher and more porous micro-structure with a specific surface area up to 36.7 m 2 /g. This work may provide an important methodical guidance for the scale-preparation of ultrafine Mo 2 C.