The HVOF Process is a combustion process and uses oxygen — and one of several fuel gases including propane, propylene, hydrogen, or natural gas. The coating material in powdered form, is fed axially through the gun, generally using nitrogen as a carrier gas. The fuel is mixed with oxygen inside the gun and then ejected from a nozzle and ignited outside the gun. The ignited gases surround and heat the powdered spray material as it exits the gun and generates supersonic gas and particle velocities as it propels the molten particles toward the substrate. Due to the high kinetic energy generated and transferred to the particles they flatten plastically as they impact the substrate.