Isothermal kinetics of reduction and carburization of WO3–NiO nanocomposite powder by CO/CO2

Reduction and carburization behavior of composite oxide powder of WO3–NiO by CO/CO2 was studied. And also for these reactions, the kinetics was investigated using isothermal thermogravimetric analysis technique under various CO/CO2 ratios and temperatures. The reaction products were analyzed by XRD, TEM and SEM. The effect of CO fraction was investigated at constant temperature (950 °C), to obtain an optimum value that results in complete reduction of the oxides and carburization of W, while avoiding deposition of excess carbon. An atmosphere containing 93 % CO yielded the best results above which deposition of carbon on particles was observed. The effect of temperature at constant CO content (80 %), was studied in the range of 775–1100 °C. At higher temperatures carburization did not happen because of thermodynamic reasons, whereas at the lowest temperature the reduction was incomplete due to the slower kinetics. The optimum temperature was found to be 850 °C for complete reduction and carburization along with limited agglomeration and carbon deposition. The kinetics of reduction and carburization reactions was evaluated using isoconversional method. The calculated activation energy for different stages of reduction and carburization was 25.2, 92.8, 171.5 and 112.6 kJ mol−1.Graphical Abstract