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To say aluminum doesn’t rust – will never rust – is a bit of a stretch, but there’s a reason why so much stuff is made of aluminum, and it’s not just because it’s affordable.
Aluminum really can withstand corrosion better than many other elements on the Periodic Table, and knowing how it works can help when you're deciding on the best material for things like outdoor furniture, hardware or kitchen and bath items.
Iron Oxide = Bad
Of course, water and dampness are the chief troublemakers where rust is involved, and some materials don’t fare well in wet conditions. This is because of an electrochemical reaction between water, oxygen and metal surfaces.
When rain falls on iron, for example, the water mixes with carbon dioxide to form carbonic acid, an electrolyte that dissolves the metal. When the water breaks down, the free oxygen combines with the dissolving metal to form iron oxide.
And, iron oxide is what we identify as rust, although there are more processes that actually break the metal down further.
But, aluminum doesn’t respond to water in the same way.
Aluminum Oxide = Good
When aluminum is exposed to oxygen in the air it instantly bonds to form aluminum oxide which, unlike iron oxide, resists any reaction to water. Aluminum oxide acts like an invisible shield between the aluminum surface and the environment.
This is really cool, because aluminum itself is highly reactive to water. When exposed to water absent the oxygenated barrier, aluminum starts dissolving immediately – and sometimes violently.
If the aluminum oxide barrier is penetrated, the dissolving aluminum releases highly flammable hydrogen gas, which can easily ignite.
Anodizing, Powder Coating & Painting
So, if aluminum creates a natural barrier to rust in the open air, why do we bother anodizing it, painting it or powder coating it?
The answer is the same for all three – to add more protection and add color variety.
Paint and powder coating are similar, and only really differ in application. They offer the same benefits, although those benefits can be compromised depending on the quality of the application.
Anodizing, though, is something different. The process of anodizing, which involves running an electric current through the metal, improves its anticorrosive properties and helps coatings and paint adhere by increasing the oxide layer.
So, keep an eye out for these kinds of treated aluminum and you’ll enjoy even more durability when it’s exposed to the elements.