1.What is the principle of electrochemical corrosion protection?
Electrode potential difference: The electrode potential of zinc (-0.76V) is lower than that of iron (-0.037V). When the zinc layer contacts the steel substrate, if the surface is damaged or exposed to an electrolyte environment (such as humid air, water), zinc will preferentially undergo oxidation reaction as a "sacrificial anode", while the steel will become the cathode and be protected.
Corrosion transfer: Even if the zinc layer is partially damaged, the surrounding zinc will continue to protect the steel through electrochemical action to prevent direct rusting of the substrate.
2.What is the principle of physical barrier?
Dense coating structure: The hot-dip galvanized layer is a composite structure of zinc-iron alloy and pure zinc, forming a uniform and dense coating on the surface, which can directly prevent oxygen, moisture, salt spray and other corrosive media from contacting steel.
Corrosion-resistant product film: Zinc reacts with oxygen, carbon dioxide and moisture in the air to generate stable corrosion products such as basic zinc carbonate, which adheres to the surface of the zinc layer to form a gray-white passivation film, further slowing down the corrosion rate.
3.How is the "self-healing" ability of the zinc layer manifested?
Electrochemical repair: When the surface of the zinc layer is scratched or worn, the exposed zinc will form a micro-battery with the surrounding undamaged zinc layer, and continue to generate corrosion products through electrochemical action, filling the tiny defects and partially restoring the barrier effect.
Zinc salt dissolution and re-deposition: In a humid environment, the corrosion products of zinc may partially dissolve in water, diffuse with water to the defects and re-deposit to form a new protective layer.
4.What are the protective characteristics of different galvanizing processes?
Hot-dip galvanizing: The coating has strong bonding with the substrate, and has excellent electrochemical protection and physical barrier effects, which is suitable for long-term outdoor or harsh environments.
Electrogalvanizing: The coating has good uniformity, but the thickness is thin, mainly relying on physical barrier, and the electrochemical protection effect is weak.
Zinc-nickel alloy coating: The corrosion resistance is better than that of pure zinc layer, and the electrochemical performance can be optimized by adjusting the composition, which is suitable for harsh scenes such as high salt spray.
5.What is the protection effect in actual application?
Relationship between life and thickness: The thicker the zinc layer, the longer it takes for corrosion to consume. For example, a 50-micron thick hot-dip galvanized layer can protect steel for up to 10-15 years in a neutral atmosphere, while 40-micron thick bolts and nuts can also meet long-term use requirements in indoor environments.
Environmental impact: In industrial pollution areas (containing sulfides) or marine climates (high salt spray), the corrosion rate of the zinc layer will accelerate, and protection needs to be enhanced by increasing the coating thickness or combining other protective measures (such as painting).