Heating-rate-dependent Oxidation Kinetics and Mechanism of Waste Tungsten Carbide

This study investigates the effect of heating rate on the oxidation behavior of waste tungsten carbide (WC) using non-isothermal thermogravimetric analysis (TGA). Tungsten oxide formation through high-temperature oxidation was systematically analyzed at different heating rates (5, 10, 20, and 40 °C min−1) under an air atmosphere. The kinetic parameters were evaluated using four model-free iso-conversional methods—Flynn–Wall–Ozawa (FWO), Kissinger–Akahira–Sunose (KAS), and Starink together with the model-fitting Coats–Redfern (CR) approach. The calculated average activation energy values were found to be 231.1, 229.1, and 229.5 kJ mol−1 for FWO, KAS, and Starink methods, respectively, showing good agreement among the models. Reaction mechanism analysis revealed a transition from reaction-controlled kinetics at low heating rates (5 °C min−1) to diffusion-controlled behavior at higher heating rates (20–40 °C min−1). Structural and morphological characterization was performed using XRD, Raman spectroscopy, SEM, and EDS analyses. The results confirmed the formation of tungsten oxide phases after oxidation. The positive activation enthalpy indicates that energy input is required to reach the transition state, confirming the kinetically controlled nature of the oxidation process. The findings provide useful insights for the recycling and thermal processing of waste tungsten carbide materials.