8/27/2023 0 Comments Does zinc corrodeZinc may also exhibit a type of corrosion known as white rust. ![]() According to the ASTM B633 Standard Specification for Electrodeposited Coatings of Zinc on Iron and Steel, the maximum plating thickness is about 25µm. When current is passed through the cell, zinc is plated onto the part. The article to be plated is made the anode in an electrolytic cell containing a zinc salt or electrode. ![]() Zinc is often electroplated onto steel screws, nuts and other small parts. (For more on ASTM standards, read: 6 Tests to Assess Intergranular Corrosion Using ASTM A262. Requirements for galvanizing iron and steel products along with pertinent ASTM standards can be found in ASTM Standard Specification for Zinc (Hot-Dip Galvanized) Coatings on Iron and Steel Products A123 and ASTM A525 Standard Specification for General Requirements for Steel Sheet, Zinc-coated (Galvanized) by the Hot-Dip Process. The inner layers of iron-zinc provide some additional corrosion protection once the outer zinc layer has been corroded away. Service life is a linear function of zinc's thickness. A thin, adherent coating of zinc is accomplished by electrodeposition. Electrogalvanizing usually produces a thinner coating with less corrosion protection. Other common zinc coating processes include electrogalvanizing and zinc plating. Zinc-bearing paints can also be used as a coating on galvanized steel structures in marine environments or for those immersed in seawater for added corrosion protection. Thus, they make repairs fairly straightforward. This type of coating provides the least long-term corrosion protection but is the easiest to apply in the field. Zinc-bearing paints can be used as a primer or finish coating. (For more about galvanizing, read: Hot-dip vs Cold Galvanizing: What’s the Difference?) The outer layer is relatively thin and thus the corrosion resistance is limited.Ĭold galvanizing involves applying zinc paint, either by brushing it on or by spraying zinc dust/oxide mixed with a binder. The coating's structure consists of successive layers that are enriched in zinc until the outer layer is pure zinc. Hot-dip galvanizing of steel is accomplished by immersing the part continuously, or in batches, in a bath of molten zinc. Zinc-rich coatings are used in a processes known as hot-dip or cold galvanizing to prevent corrosion. Therefore, zinc metals and components coated with zinc-based products can have a significantly longer service life than other metals when exposed to the atmosphere. (For more on corrosion rate, read: Corrosion Rate Conversion: Simple Ways to Convert Data Between Common Corrosion Units. The amount of pollutants present will impact the corrosion rate. In these cases, the corrosion rate can be as much as four times greater than in coastal environments without such pollutants. However, when sulfur-type pollutants are present, they will react with the zinc carbonate and moisture to form a water-soluble zinc sulfate. Zinc's corrosion rate is 1/30 that of steel. While the carbonate layer has protective properties, zinc is a reactive metal and will slowly corrode over time. This layer acts as a protective barrier that prevents air and moisture from contacting the underlying substrate and prevents further corrosion and deterioration. Unlike iron oxides, which flake off easily, zinc carbonate is resilient, chemically stable, and adheres firmly to the metal's surface. This layer then reacts with moisture to produce zinc hydroxide, which further reacts with carbon dioxide to create zinc carbonate. Zinc, on the other hand, reacts with oxygen to form a thin oxide layer. This cycle repeats itself until the iron is fully consumed by the corrosion process. Hydrated iron oxides are brittle and flake away easily, thus exposing more of the underlying metal to the atmosphere for further corrosion. This corrosion product, commonly called "rust," is known for its reddish-brown color and its damaging effects. Iron, for example, reacts with water and oxygen in the atmosphere to form hydrated iron (III) oxide on the metal's surface. However, this element does not rust like most other metals. Like all metals, zinc corrodes when exposed to air and moisture.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |