Reduction and carburization behavior of NiO–WO3 mixtures by carbon monoxide

• Simultaneous reduction and carburization of NiO–WO3 mixtures was performed in CO.
• The reaction path was found to be NiWO4→CONi, WO3→COWO2→CW→C/COWC.
• The reduction of NiO and WO3 to WO2 by CO and W carburization took place exothermally around 550 °C, 650 °C, and 800 °C respectively.
• The endothermic reduction of WO2 to W took place with the deposited C as reductant before 780 °C.
• Ni played a catalytic role in C deposition from CO leading to mass gain at temperatures above 800 °C.

The reduction and carburization behavior of NiO–WO3 mixtures by CO was studied using thermogravimetric and differential thermal analysis techniques (TGA–DTA) with the aim of preparing homogenous Ni–WC composite powders. Based on the TGA–DTA results and characterization of the reaction products using XRD and SEM, the following reaction path is suggested. Reduction of NiO with CO begins at 550 °C, followed by reduction of WO3 to first WO2 by CO, and then to W by carbon. The generation of W was accompanied by its carburization through C and CO. The reactions were near completion at 850 °C, producing clusters of Ni–WC in the few micrometer range. Increasing the Ni content of the mixture resulted in greater carbon deposition, also appeared to widen the temperature range for the reactions.