Pre-reduction of WO3–Co3O4 by H2–C2H4 in a fluidized bed

ABSTRACT In order to avoid the formation of η phase (W 6 Co 6 C or W 3 Co 3 C) that adversely affects the sintering process and its products in the preparation process of ultra-fine WC-Co powder, a technical route of pre-reduction of WO 3 –Co 3 O 4 to WO 2 –Co and then deep reduction carbonization to WC-Co powder has been proposed. This study mainly investigates the influence of gas partial pressure on the pre-reduction process of WO 3 –Co 3 O 4 under a mixed atmosphere of H 2 –C 2 H 4 –Ar at 600 °C and establishes the kinetic equations of pre-reduction and carbon evolution. The results indicate that increasing the partial pressure of hydrogen is conducive to the rapid and complete conversion of WO 3 to WO 2 . High carbon content can be generated by the deposition of C 2 H 4 , and it hinders the diffusion of the reducing gas; WO 3 still cannot be completely reduced to WO 2 as the partial pressure of C 2 H 4 increases to 60%. For the carbon evolution of C 2 H 4 , the carbon amount is positively related to the H 2 partial pressure, but it shows the highest amount and evolution rate when the ethylene partial pressure is 20%. Based on the reduction rate curves of WO 3 and carbon evolution rate curves of C 2 H 4 , the rate equations of pre-reduction and carbon evolution of WO 3 –Co 3 O 4 system at 600 °C are established. The pre-reduction reaction belongs to the first-order reaction, and its equation is expressed as follows: r = − d w WO 3 d t = 9 ± 0.15 × 1 0 − 2 P H 2 0.44 P C 2 H 4 0.57 The carbon deposition rate equation of C 2 H 4 can be expressed as follows: r ' = d c C d t = r f − r b ≅ 7.35 × 1 0 − 2 × P C 2 H 4 0.31