Rust is the colloquial term for a coating that occurs on the surface of iron, and many of its alloys. This happens as a response to the presence of oxygen and moisture, and eventually converts the material to iron oxide. Aluminum, on the other hand is often praised as the metal that cannot rust. But is this actually true?
Aluminum Does Rust But It Stops There
The ‘wonder material’ does not break down in the presence of oxygen and moisture. To the contrary, it actually cloaks itself with a protective layer of aluminum oxide. But there any similarity ends.
- The protective aluminum oxide coating is actually quite hard.
- It does not flake off like iron oxide, exposing fresh material.
- It thereby stops the rust continuing, neutralizing the process.
The aluminum oxide is moreover a pleasant, light-grey colour similar to its host and therefore to all intents invisible.
Where Does Anodized Aluminum Fit Into This?
Anodizing is a process whereby a factory immerses aluminum in a chemical acid bath, and then passes an electric circuit through it. This oxidizes (‘rusts’) the surface adding an extremely hard protective film. This process – which can add a color tint – works equally well on other non-ferrous metals such as tantalum, titanium, zinc, and magnesium.
Anodized aluminum therefore ‘seals in a color’ while stopping oxidation in its tracks. But it does more than that. It makes the material more attractive, while making it react better with dyes, adhesives, and paints. This often makes it the choice for exposed metals, furniture, and casings for items such as computers, phones, and appliances.
The ‘Acid Test’ – Is Un-Anodised or Anodised Better?
Scientists at Christchurch, New Zealand studied the effect of atmospheric corrosion on an architectural grade of aluminum alloy. Their samples included run-of-the-mill ones, and three thicknesses of anodized coatings. They exposed samples at five different sites for twelve years. And then weighed them to gauge the extent of decomposition.
This confirmed other findings that anodized aluminum films improve with aging, compared to other protective coatings. Although both natural and anodized surfaces show excellent resistance to atmospheric corrosion. However, the anodized product looks better for longer, because it repels soiling and dirt more effectively.
How to Make Your Exterior Finishes Last Longer
Yet another reason to speak to Calgary’s acknowledged experts, if you want to know the real truth. They carefully select their roof shingles, eavestroughs, and sidings in terms of durability and low maintenance. This care extends to the metallic fittings behind them that you may never see.
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Anodised and Natural Aluminum Cooking Pots (R Taras BY CC 2.0)