Synthesis and formation mechanisms of nanocomposite WC–MgO powders by high-energy reactive milling

Abstract

The nanocomposite WC–MgO powders were prepared at room temperature by reactive milling of low-cost WO 3, Mg and graphite powders under argon gas atmosphere in a planetary ball milling. Powder samples were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The milling energy was calculated using a collision model and the milling energy maps were attained. The effects of milling parameters (including milling speed, ball-to-powder weight ratio and milling time) on the formation mechanism have been illuminated by the obtained milling energy maps. Results show that WC–MgO can be formed via Self-propagation High-temperature Synthesis (SHS) when the effective extensive factor E b is above 38.24 kJ g −1 s −1, and it also can be formed from gradual reaction when E b is between 22.12 kJ g −1 s −1 and 38.24 kJ g −1 s −1. As the energy map demonstrates, the total energy E t required for fabricating WC–MgO through SHS ranges from 25.61 × 10 6 kJ g −1 to 61.82 × 10 6 kJ g −1, while more than 112.83 × 10 6 kJ g −1 is necessary for gradual reaction one. These milling energy maps are proposed as a tool for better understanding of the synthesis and formation of WC–MgO by high-energy reactive milling.