| Summary: | The tungsten oxides with uniformly grain growth inhibitor elements can significantly improve the distribution of inhibitors in the subsequent WC powders, and finally enhanced the properties of ultra-fine grained cemented carbides. Thus, a new liquid-liquid doping method was used to prepare the tungsten oxide composite powders with grain growth inhibitor elements by spray drying-calcining process. The microstructure and phase transition of Cr-doped and undoped tungsten oxide composite powders were studied by TG/DSC, XRD, SEM, and XPS. The results showed that Cr doping has little effect on the morphology of the precursor powders after spray drying. However, the existence of ammonium chromate had a significant effect on the properties of the calcined tungsten oxide. The volume expansion of ammonium chromate could reduce the decomposition temperature of ammonium tungstate precursor powders. Additionally, the formation of thermodynamic instability Cr-O-W compound could be the reason for the exothermic peak appeared at 486.3 °C. Moreover, the ‘liquid-liquid’ doping method guaranteed the uniform distribution of Cr _2 O _3 , which was favourable for the stable existence of hexagonal metastable h-WO _3 . The tungsten oxide powders calcined at 600 °C have a flaky morphology due to the uniform distribution of Cr _2 O _3 , and the uniform distribution of Cr _2 O _3 in the powder can also prevent the grain growth of WO _3 .
|
|---|