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When the zinc layer is seriously damaged and endangers the iron matrix, the zinc will produce electrochemical protection on the matrix, the standard potential of zinc is -0.76V and the standard potential of iron is -0.44V. When zinc and iron form microbatteries, the zinc will be dissolved as the anode, and the iron will be protected as the cathode. Obviously, the atmospheric corrosion resistance of hot dip galvanizing is better than that of electric galvanizing.

If the zinc coating is good, but in 3% nitric acid when the light, the coating has dark shadow, passivation occurs when the film is brown, may be caused by foreign metal impurities such as copper or lead in the galvanizing liquid. When problems occur in the process of galvanizing large coil galvanized wire, the temperature and current density are checked first, and then the content of zinc and sodium hydroxide in the plating solution is measured and adjusted through the analysis of the plating solution. Whether DPE content is low can be determined by hull cell test.