Effect of Platinum Elements Additions on the Active Dissolution of Plastic Chromium in Sulfuric Acid

Alloys based on plastic chromium with 0.1 to 0.4 mass % Ru, Pd, Ir, or Pt were investigated in 40% sulfuric acid in active state under cathodic polarization (–0.175 V). All of the studied additions of alloying elements are responsible for the reduced anodic dissolution of chromium. The corrosion resistance of alloys depends on the concentration and nature of the alloying additions. Two mechanisms decelerating the active dissolution of the cathode-modified chromium have been established, i.e., blocking mechanism (cathodic component atoms block the active points in the lattice) and screening mechanism (cathodic component, while getting crystallized on the surface, partly screens the latter).