Synthesis of nanocrystalline tungsten and tungsten carbide powders in a single step via thermal plasma technique

• The capability of thermal plasma technique to produce nano size W and WC in a single step process was studied.
• The amount of W and WC formed showed strong dependency on the H2 flow and power
• Due to short exposure time to plasma, complete reduction or carburization was not achieved.
• Near complete carburization was achieved after heating the plasma treated powders at 1000 °C for 1 h in H2.

The capability of thermal plasma technique to produce nanocrystalline tungsten powder from tungsten oxide and tungsten carbide powder form a mixture of tungsten oxide and carbon in a single step process was investigated. The amount of tungsten and tungsten carbide powders formed strongly depended on the hydrogen flow and power. Due to short exposure time of tungsten oxide and carbon to plasma, complete reduction or carburization was not achieved. The crystallite size of the reduced W and the resulting W2C was under 70 nm. The free carbon, total carbon and surface area of the powders decreased with increase in hydrogen flow rate and power. The results from the study highlight the challenges involved in obtaining successful reduction and carburization of the tungsten oxide in a one step process. Near complete carburization was achieved after heating the plasma treated powders at significantly lower temperature of 1000 °C for 1 h in hydrogen atmosphere. The results from the study introduce a potential two-step process to economically manufacture nano size tungsten carbide powder.