1.What is the principle by which white rust on galvanized coil affects its conductivity?
Conductivity of the zinc coating: Pure metallic zinc is a good electrical conductor. While its conductivity is not as good as silver and copper, it is worse than most metals. Freshly plated zinc coatings are composed of this metallic zinc, giving them excellent electrical conductivity.
Nature of white rust: White rust is primarily composed of basic zinc carbonate and zinc hydroxide. It forms as a result of electrochemical corrosion between zinc and moisture and carbon dioxide in the air.
The chemical formula is roughly: Zn + H₂O + O₂ + CO₂ → Zn₅(CO₃)₂(OH)₆ or Zn(OH)₂
Conductivity comparison: Metals are conductors because they have freely moving electrons. In contrast, white rust (metal oxides/hydroxides/carbonates) is a typical semiconductor or even an insulator. Its resistivity is much higher than that of metallic zinc.
2.To what extent does white rust on galvanized coil affect its electrical conductivity?
Light White Rust (small grayish-white spots on the surface):
Impact: Minor. Because the rust products haven't formed a continuous, dense, thick film, current can still flow through uncorroded zinc spots or thinner areas. Electrical conductivity will be reduced, but this may still be acceptable in some applications where conductivity isn't critical.
Analogy: It's like a few small potholes on a wide road. Vehicles can still circumvent them, but at a slower speed.
Severe White Rust (large areas of white or gray powdery coating):
Impact: Very significant. A continuous, loose layer of corrosion products with extremely high resistivity forms on the surface. This layer blocks the direct flow of electrons.
Analogy: It's like covering the entire road with a thick layer of sand, making traffic extremely difficult or even impossible.
3.What are the specific impacts of application scenarios?
Grounding systems: This is the most typical application. Galvanized steel is often used as a grounding electrode. If severe white rust forms on the surface, it can significantly increase grounding resistance. This can hinder the rapid conduction of current to the ground in the event of a ground fault or lightning strike, seriously endangering personnel and equipment. In such cases, white rust removal is essential.
Electrical connection points: If two pieces of galvanized material are bolted together to create a current path, white rust between the connecting surfaces can significantly increase contact resistance. According to Joule's law (P = I²R), this can cause abnormal heating at this point when power is applied, posing a fire risk.
Electromagnetic shielding chassis: Some equipment chassis utilize the inherent conductivity of metal to shield against electromagnetic interference. White rust on the surface can reduce the shielding effectiveness.
4.How to deal with white rust that has already occurred?
Mechanical Method: For light white rust, use a stiff brush, scouring pad, or fine sandpaper to polish away, revealing the underlying, shiny zinc layer.
Chemical Method: Wipe with a diluted acetic acid solution (household white vinegar is sufficient) or ammonia. White rust is alkaline and will react with acids to dissolve it. After treatment, rinse thoroughly with clean water and allow to dry thoroughly.
Note: Strong acids or strong steel wool are not recommended, as they may damage the intact zinc layer.
5.How to prevent white rust?
Storage conditions: This is the most critical aspect. Galvanized coils should be stored in a dry, well-ventilated indoor environment, avoiding direct contact with damp floors or walls.
Avoid airtight packaging: Avoid tightly wrapping with airtight plastic film for extended periods, as this can trap condensation and create a "damp box" effect.
Chromate passivation: Many galvanized coils are factory-passivated, forming a dense, passive film (typically iridescent, blue, or pale yellow). This film significantly slows the development of white rust. Passivation can be specified when ordering.