There are two well characterized compounds of tungsten and carbon, WC and tungsten semi-carbide, W2C. Both compounds may be present in coatings and the proportions can depend on the coating method. At high temperatures WC decomposes to tungsten and carbon and this can occur during high-temperature thermal spray, e.g., in high velocity oxygen fuel (HVOF) and high energy plasma (HEP) methods. Oxidation of WC starts at 500–600 °C (932–1,112 °F). 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. Finely powdered WC oxidizes readily in hydrogen peroxide aqueous solutions.