The reduction of tungsten oxides by carbon or carbon-containing compounds can be easily performed. Statements about the starting temperature for the reaction between WO3 and solid carbon (carbon blacks, graphite) vary in the current literature between 655℃ and 783℃. Differences in WO3 and C properties (particle size of the powders, preparation history, crystallinity, etc.) as well as in atmospheres may be responsible for that. The temperature range coincides with the beginning of self-conductivity and sublimation of W03: Carbon monoxide starts to react with W03 at 535℃.
The reduction/carburization sequence can be assessed from so-called predominance area diagrams (Kellogg diagram s), which can be derived from free energy of formation data of the compounds occurring in the W-C-O system (WO3, WO2.9, WO2.72, WO2, W, W2C, WC, CO, CO2). It predicts that at 1100℃ the reduction/carburization proceeds via the oxide phases（WO2.9→ WO2.72→WO2→W→W(2)C）, with the possibility of a direct carburization of WO2.72 and WO2.
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