Nano-sized Tungsten Carbide Fabricated Using Violet Tungsten Oxide

Cemented carbide is a kind of composite material prepared with tungsten carbide (WC) powder, which is widely used in cutting tools, drilling, and other technical fields due to its high hardness, high wear resistance, high strength and good toughness. In recent years, nano tungsten carbide powder is more required than ever due to the development of nanocrystalline cemented carbide.

Therefore, researchers have prepared nano-sized tungsten carbide by using violet tungsten oxide (WO2.72) as the raw material, a fluidized bed as the reactor, and CO as the carbonization gas. The preparation process of nano-sized tungsten carbide is as below:

Violet tungsten oxide (WO2.72) with irregular shapes and particle size of 30-100μm is used as precursor material. It can be found that micron-sized particles are agglomerated by nano-needle crystals. These WO2.72 powders have a high aspect ratio (length/diameter) of 10 to 50. High-purity carbon monoxide (CO) and nitrogen (N2) were used as experimental gases.

Vertically placed quartz tubes with a diameter of 20 mm (internal) and a length of 700 mm are used for the reduction and carbonization experiment. A quartz distributor (0.04mm hole) is installed in the middle of the reactor to move N2 and CO upward from the compressor. Flow meters and valves are used to control the gas velocity. For the carbonization experiment, the violet tungsten oxide powder was added to the fluidized bed reactor, first fluidized with nitrogen, and then the reactor was directly moved to the hot zone of the furnace. When the sample reaches the desired temperature measured by the inserted thermocouple, high purity carbon monoxide is introduced into the reactor. After the required reaction time, the reactor was removed from the hot zone of the furnace, and water was sprayed directly on its outer surface for quenching, and then the reacted samples were collected and subjected to various characterizations.

In conclusion, nano-sized tungsten carbide is fabricated by using violet tungsten oxide (WO2.72) as the raw material, a fluidized bed as the reactor, and CO as the carbonization gas. The results show that the particle size of WC increases as the temperature increases from 800°C to 950°C. As the residence time increases, the particle size gradually decreases, and then increases due to slight sintering. The successful preparation of nano-sized tungsten carbide has laid a good foundation for large-scale fluidization production.

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