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Characteristics and application of the galvanized coating
Characteristics and application of the galvanized coating
Zinc in GI steel coil with spangles made in China is a lively amphoteric metal. It has a grayish appearance and is soluble in acids and bases. Its standard electrode potential is -0.76v. The zinc layer changes almost nothing in dry air, but in high humidity air or water containing carbon dioxide and oxygen, a film of corrosion resistance forms on the zinc surface. When there are other metal impurities with positive potential in the zinc coating, the electrochemical dissolution rate of the zinc coating will be very fast. In the medium containing chloride ion, the corrosion resistance of galvanized layer is poor. In seawater, the stability of the galvanized layer is not high, corrosion resistance than the pot layer. In the high-temperature humid climate or the presence of the organic acid atmosphere, galvanized layer easy to corrosion, at the same time, the coating will lose luster. Its protection will be greatly reduced.

Galvanizing is a kind of plating with good protection ability, low price, simple operation and easy realization of the electroplating process. The proportion of plating black metal is very high. The zinc layer is a typical anode coating for steel substrates because the standard electrode potential for iron is -0.44V. When exposed to corrosive medium, zinc layer is more likely to lose electrons than iron, so the zinc layer can play an electrochemical protection role on the steel matrix; And in the coating has gaps or because of damage exposed to the matrix. The zinc layer also ACTS as an anode to protect the steel matrix from corrosion. The protection ability of the galvanized layer and coating thickness has a great relationship, generally speaking. The thicker the coating, the stronger its protection ability.

The galvanized solution can be divided into cyanide galvanized and cyanide-free galvanized two categories. Cyanidation zinc can be divided into three categories: high cyanidation, medium cyanidation, and low cyanidation. The main characteristic of cyanidation galvanizing is the high cathode polarization. The dispersing ability and covering ability are very good, and the adhesion between coating and substrate is better than other galvanized processes. Cyanidation zinc coating crystallization is meticulous. The bath is very stable. High tolerance for impurities. Plating solution has little corrosion to production workshop. So for a long time, cyanidation galvanizing technology has been in the main position of galvanizing technology. However, the main disadvantage of the process is that the bath contains highly toxic cyanide, production will also produce harmful gases. It is harmful to the workers' health. In the production process must have good ventilation equipment; In addition, cyanide galvanized wastewater treatment requirements are very strict, so cyanide galvanized is gradually replaced by cyanide-free plating. Cyanide-free galvanizing can be divided into alkaline galvanizing and acid galvanizing. Alkaline galvanized appearance is bright and meticulous. The passivation film is bright in color. Excellent corrosion resistance. The disadvantage of this process is a low current efficiency. The caustic effect of alkali fog on electroplating equipment is great. At present, the application of non - scratch galvanizing in the acid galvanizing process has been widely popularized. The bath is stable and easy to operate. The current efficiency is high, can obtain the full bright coating, the dispersing ability, and the covering ability is also very good, and the wastewater treatment is simple.
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