Galvanized steel galvanized steel chromate passivation, corrosion resistance can be increased 6--8 times. Therefore galvanized passivation is an essential step. Organic dyeings on passivating films for protection of low-profile products - decorative coatings.
Zinc is susceptible to corrosion when exposed to volatiles of non-metallic materials (low molecular weight carboxylic acids, aldehydes, phenols, ammonia, etc.) under airtight or poorly aerated, air-humid conditions and produces white, loose corrosion products commonly known as " Hoar frost. " Galvanized steel zinc in high temperature, high humidity, closed conditions, with bakelite, paint, wood contact with volatiles released, zinc filaments tend to grow, commonly known as "long hair."
The standard zinc potential is less than iron, anodic coating for steel, which provides reliable electrochemical protection. In the industrial atmosphere, rural atmosphere and the marine atmosphere of steel products can choose zinc as a protective layer, the protective life is almost proportional to the thickness of the zinc layer. In the atmosphere with industrial exhaust gas pollution, galvanized steel pipe zinc coating corrosion resistance is better than the cadmium coating, the sea or sea water is the opposite.
Galvanized steel coating appearance was blue-white, the standard electrode potential of -0.76V, soluble in acid, soluble in alkali, is the song of amphoteric metals. Zinc dry almost unchanged in the air, the critical humidity of zinc corrosion is greater than 70%, so in the humid atmosphere with carbon dioxide and oxygen to generate a layer mainly composed of zinc carbonate film, this film has some corrosion The role of zinc and hydrogen sulfide and other sulfur compounds react to generate zinc sulfide; zinc susceptible to chloride ion erosion, it is unstable in seawater.