Prevention of Metal Rust

Rust is a generic term applied to the metallic oxides that form when oxygen reacts with iron and its alloys. Although many oxides are the same size as their original metal atoms, certain metals, like pure iron, puff up when oxidized, causing a more noticeable layer of rust. Rust damages metal significantly, and can weaken the structural integrity of metal frameworks. As metals are used in a wide variety of home furnishings and appliances, rust prevention strategies will differ based on the application.

Rust

Rust (Fe2O3) is a red metallic stain occurring on the surface layer of a metal. Atmospheric oxygen collides with metal substances, and, depending on the susceptibility of the metal to rust, reacts chemically with the metal. The final product of this reaction is a metal oxide. Exposure to water can also facilitate the oxidation process; iron needs an atmospheric humidity of at least 40 percent to react properly with oxygen, forming rust. Rust compromises the strength of metal, and can weaken the bonds between atoms, causing cracks or larger fractures.

Another form of iron oxide is known as black oxide (Fe3O4), and is used in a wide variety of applications to protect metals from environmental exposure. Other metallic oxides, such as aluminum oxides, are used to protect surfaces from environmental exposure. These oxides protect surfaces because oxidation doesn't cause the metal to puff up; they reduce the reactivity of the surface with the environment while exposing less surface area.

Corrosion

Corrosion refers to a localized formation of rust on a metal surface. Corrosion at the site of a connection between two different metals is referred to as galvanic corrosion. This can occur on a metal door hinge, or at a soldering hinge between two metals. Galvanic corrosion is caused by a difference in the flow of electrons between the two metals, causing increased reactivity. Crevice corrosion occurs when dirt is allowed to infiltrate a crevice or other metal opening. Dirt allows water to accumulate in amounts large enough to facilitate the oxidation of ferrous metals. Exposure of metal to high winds can cause pitting corrosion, where the wind buffets tiny dirt particles against a surface, causing pits where water can accumulate and facilitate rusting.

Depending on the strength of the bond between the metals, galvanic corrosion can be prevented by replacing one metal with a more compatible one, preferably the same type. Crevice corrosion can be reduced by cleaning outdoor metal surfaces, removing the dirt from any inner cracks or openings. If rust is already present, an electric sander can remove the surface rust. If you live near the ocean or an area that receives a lot of wind, you'll need to check your outdoor metal surfaces often for pitting damage. If pitting is noticeable, sand area with an electric sander and repaint surface.

Prevention

The best way to reduce the rusting of ferrous metals is to limit exposure to water and humidity. Placing a tarp over outdoor metal fixtures, especially during bad weather, can help to reduce the chance of rust forming. Lacquering a surface, or providing a coat of paint or wax, significantly reduces the metal's environmental exposure.

Rust that forms on tools can greatly effect their durability and strength. However, lacquers and some waxes can be counterproductive, as they can effect the cutting ability of woodworking tools. Paste wax works best, as it provides a buffer to the environment without containing any water. Spray products offering moisture displacement, like WD-40 or Rust-X, can prevent rust, but the aerosol cans are not environmentally friendly, and they can cause smaller drill bits to become slippery. Different formulas offer different benefits, so make sure to research the chemical makeup of a rust prevention spray before purchasing.

Outfitting your work space with a dehumidifier can help reduce water in the atmosphere that can encourage rust. Storing your tools in a tight fitting wooden box keeps dust, which can attract water, and humidity both away from them.

Zinc Galvanization

Zinc galvanization is a popular commercial protecting strategy for metal. A layer of zinc coats a metal surface, such as a car frame. The zinc is more reactive with oxygen than the ferrous metal it coats, so that the zinc oxidizes instead of the iron molecules. When the zinc oxidizes, the molecules retain their original size, much like the aluminum oxide, so that less surface area is revealed to the environment and the iron stays completely covered.