Spotless arc activated high‐rate deposition using dual crucible technology for titanium dioxide coatings
Spotless arc Activated Deposition (SAD) combines electron beam high-rate evaporation using an axial gun and a spotless arc discharge burning in the metal vapor of a hot evaporating cathode. The SAD process is suitable for the evaporation of high-melting metals such as titanium, zirconium or tantalum, provides a high deposition rate of up to 2000 nm/s and enables a reactive mode of operation for the deposition of oxides, nitrides or other compounds with a deposition rate between20 and 100 nm/s. The limitation of the long-term stability of the SAD process that was caused by coatings deposited at the anode equipment could be overcome by introducing a dual crucible technology. Whereas evaporating metal in the first crucible acts as cathode, evaporating material in the second crucible forms the anode of the arc discharge. Both plasma electrodes evaporate and are in contact with vapor and reactive gas so that the plasma process is no longer disturbed by the coating of electrodes. The main process parameters and discharge characteristics were studied for the evaporation of pure titanium and reactive processing in oxygen atmosphere in order to deposit titanium dioxide coatings on steel strip. Transparent titanium dioxide coatings with a refractive index of between 2.3 and 2.5 were deposited. Photocatalytic and super-hydrophilic effects were obtained for coatings of anatase modification.