A comprehensive evaluation of non-isothermal simultaneous reduction and carburization kinetics of W-Ni oxide nano-composite powder

Abstract Chemical co-precipitation of NiO-WO3, followed by reduction and carburization in CO-CO2 were carried out non-isothermally in a thermogravimetric analyzer at different heating rates of 5–15 °C/min to yield a Ni-WC composite with 12 wt% Ni. The kinetics of the thermochemical process was evaluated by Kisinger-Akarira-Sunese (KAS) method. It was found that the process is completed through four steps with distinctly dominant reduction/carburization reaction in each step, in the following order NiO→Ni, WO3→WO2, WO2→W and W→WC. The apparent activation energies (Ea) corresponding to these steps were 173, 146, 123 and 60 kJ/mol, respectively. The mechanism prevailing each step were elucidated using the master plot fittings method for various kinetic models, showing that the Avrami-Erofeev models of various order explained all the reaction steps with an exception of an interface-controlled reaction taking over a small portion of the WO3→WO2 step. The effect of heating rate on kinetic model was evaluated as well. The study presents a comprehensive picture of the reaction scheme and kinetics for the system, allowing for controlled design and synthesis of Ni-WC nano-composite powders.