Thermodynamic Analysis and Synthesis of Fine WC Powder in the WO3-CH4-H-2 System Using Excessive CH4

Abstract

This study aims to investigate reaction behavior of WO3 powder in H-2-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 H-2 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 mu m at 900 K to 1 mu m at 1300 K.