1.How acid-resistant is zinc?
Acid Resistance: Poor
Reaction: Zinc reacts violently with acids, forming zinc salts and releasing hydrogen gas.
Consequences: In an acidic environment, the zinc coating will rapidly corrode and consume, losing its protective effect on the underlying steel base. Once the zinc layer is completely corroded, the underlying steel is exposed and begins to rust.
Common Scenarios:
Acid rain (pH < 5.6): This is the most common acidic threat to galvanized materials outdoors. Acid rain in industrialized areas can slowly and continuously corrode the zinc coating.
Industrial Environments: The air contains acidic gases such as sulfur dioxide (SO₂) and hydrogen chloride (HCl). These dissolve in the water film to form acids, accelerating corrosion.
Coastal Areas: Although seawater is slightly alkaline, salt (sodium chloride) can damage the zinc passivation film and form an electrolyte on the surface, promoting electrochemical corrosion. Tidal areas may also produce acidic substances due to the decomposition of organic matter.
Direct Contact with Acidic Substances: Examples include the chemical industry and battery factories.
Conclusion: Galvanized coils should absolutely avoid contact with acidic solutions or highly acidic atmospheres.
2.How is zinc resistant to alkali?
Zinc has good corrosion resistance to alkaline solutions at room temperature, especially when the pH value is between 8 and 12, and it can form a stable protective film. However, when it encounters concentrated, hot alkaline solutions, zinc will also be corroded and form soluble zincates.
Consequences: In typical mildly alkaline environments (such as concrete and limewater), the zinc coating is very stable and even provides long-term protection. This is why galvanized rebar and brackets can be used in direct contact with concrete.
Common Scenarios:
Concrete Environment: Fresh concrete is highly alkaline (pH can reach 12-13), but the zinc coating quickly forms an inert, insoluble protective film on its surface, preventing further reactions. This is a key reason for the widespread use of galvanized materials in construction.
Weakly alkaline soil or water.
3.How does the zinc coating perform in a neutral environment?
Excellent: A dense basic zinc carbonate protective film is formed on the zinc surface, and the corrosion rate is extremely slow.
4.What is the corrosion resistance of zinc coating in alkaline environment (pH 8-12)?
Good to excellent. Able to form a stable passive film with good corrosion resistance. Especially suitable for concrete environment
5.What are the implications for the application of photovoltaic brackets?
In normal atmospheric environments: The corrosion resistance of galvanized brackets (typically requiring a zinc coating thickness of ≥60-80μm) can fully meet design requirements for over 25 years.
Acid Rain/Industrial Areas: In these areas, the lifespan of galvanized brackets is shortened. It is necessary to choose a thicker zinc coating (e.g., 100g/m² or greater) or a zinc-aluminum-magnesium coating, as the latter offers better resistance to cut-edge corrosion and a slower uniform corrosion rate.
Coastal Areas: Although seawater is alkaline, chloride ion corrosion is the primary concern. A thick zinc coating or zinc-aluminum-magnesium coating is also recommended. Re-zinc treatment may be required for cuts and scratches during processing and installation.
Special Circumstances: Brackets should be protected from direct contact with acidic wastewater and chemicals discharged from factories.