Chemical Properties of Tungsten Carbide

There are two well characterized compounds of tungsten and carbon, WC and tungsten semicarbide, W₂C. Both compounds may be present in coatings and the proportions can depend on the coating method.

WC can be prepared by reaction of tungsten metal and carbon at 1400–2000 °C. Other methods include a patented fluid bed process that reacts either tungsten metal or blue WO3 with CO/CO₂ mixture and H₂ between 900 and 1200 °C. Chemical vapor deposition methods that have been investigated include:

• Tungsten hexachloride with hydrogen, as reducing agent and methane as the source of carbon at 670 °C (1,238 °F)

WCl₆ + H₂ + CH₄ → WC + 6 HCl

Tungsten hexachloride

• reacting tungsten hexafluoride with hydrogen as reducing agent and methanol as source of carbon at 350 °C (662 °F)

WF₆ + H₂ + CH₃OH → WC + 6 HF + H₂O

• At high temperatures WC decomposes to tungsten and carbon and this can occur during high temperature thermal spray, e.g. high velocity oxygen fuel (HVOF) and high energy plasma (HEP) methods.

• Oxidation of WC starts at 500–600 °C. It is resistant to acids and is only attacked by hydrofluoric acid/nitric acid (HF/HNO₃) mixtures above room temperature. It reacts with fluorine gas at room temperature and chlorine above 400 °C (752 °F) and is unreactive to dry H₂ up to its melting point.

WC has been investigated for its potential use as a catalyst and it has been found to resemble platinum in its catalysis of the production of water from hydrogen and oxygen at room temperature, the reduction of tungsten trioxide by hydrogen in the presence of water, and the Isomerisation of 2,2-dimethylpropane to 2-methylbutane. It has been proposed as a replacement for the iridium catalyst in hydrazine powered satellite thrusters.