Thermodynamic Analysis and Synthesis of Fine WC Powder in the WO3-CH4-H2 System Using Excessive CH4

Abstract

This study aims to investigate reaction behavior of WO3 powder in H2-CH4 flow using excessive CH4 with respect to the oxide at 900–1300 K for 60 min and 120 min. Mass measurement, x-ray diffraction and scanning electron microscopy techniques were used to characterize the products. The oxide reduction occurred prior to the carburization possibly owing to high H2 diffusivity. WC formation significantly increased with temperature, but slightly with time. Incomplete carburization was observed at 900–1100 K, whereas single WC phase was attained at 1200 K and 1300 K for both reaction times. The thermodynamics predicted single WC phase at 900–980 K, and free C phase along with WC at 980–1300 K. The results have been discussed in terms of solid state C diffusivity, CH4 decomposition, CH4 residence time, defects and self-created local atmosphere. The mean particle size increased with temperature from 0.15 µm at 900 K to 1 µm at 1300 K.