Characteristics of Arc Spray Zinc Coatings

       Zinc is a commonly used non-ferrous metal material with a bluish white color. The melting point is 419°C, the density is 7.14g/cm3, the standard potential is -76OmV, and it is one of the more active metals. The appearance of zinc coating is dark white, the potential in artificial seawater is about -1050mV (SCE), and the coating density is generally 6.2g/cm3. In humid atmosphere or water, the surface of pure zinc often produces white basic zinc carbonate [Zn(OH)·ZnCO3], which has certain protective properties. The advantages of zinc lie in its pronounced anodic properties and the reliability of protection even in very thin conditions. The passivation effect of zinc is very small, but it can be obviously passivated in chromate solution to form a protective film of zinc chromate. The corrosion resistance of zinc is related to its purity. If the impurity iron content in pure zinc is more than 0.0014%, high-resistance, hard and not easy to fall off corrosion products will be formed on the surface of the anode during use, making the pure zinc anode lose its effectiveness. Protective efficacy, this is because the increase of iron content in zinc will form Fe-Zn phase, and its electrochemical performance will be significantly deteriorated. The purity of zinc wire for thermal spraying is 99.99%. Under atmospheric conditions (such as dry atmosphere and rural atmosphere), the requirements can be reduced, and the purity is 99.95%.



The corrosion resistance of zinc is related to the pH value of the environmental medium, and it has good corrosion resistance at pH 5-12. Zinc is very resistant to corrosion in dry atmosphere and rural atmosphere, and the corrosion rate is only 0.001-0.0001mm/a. In industrial atmosphere and humid atmosphere, its corrosion resistance is reduced, and in polluted industrial atmosphere, its corrosion rate is greater than 0.006mm/a.



Zinc is fairly stable in water. In demineralized water, zinc corrodes more rapidly than in hard water. Drinking water has little effect on the corrosion of zinc. With the increase of oxygen, carbon dioxide, hydrogen sulfide and sulfur dioxide in the water, the corrosion rate increases from 0.03mm/year to 0.3mm/year. Chloride ions also increase the corrosion rate of zinc. Increase. If the content of Pb, Cd, Sn and other impurities in zinc increases, the corrosion rate in hot water and steam is significantly accelerated.



The corrosion rate of zinc in seawater is about 0.05mm/year, and about 0.025mm/year in the tidal zone. As the flow rate of seawater increases, the corrosion rate increases.



When spraying zinc, odorous zinc vapor will be produced, which is harmful to human body. Therefore, ventilation and labor protection must be strengthened when spraying zinc