So much of our modern world is made up from iron and steel, that we’ve become completely accepting of the use of certain words that specifically relate to iron-based metals but are often used on other products. The biggest example by far is when we refer to ‘rusty’ metals when in reality, we mean something entirely different.
Rust only happens to iron-based metals. The most common type of rust is, surprise surprise, common rust. It’s a form of iron oxide, which relies on a chemical reaction where energy is transferred between atoms; namely the iron in the metal and moisture from the air. The reaction is due to a form of electrolysis and happens much faster when near salts or chlorides, which is why metals rust much faster at the seaside than away from salty, damp air.
Even though rust is a specific thing, you’ll hear people talk about rust on all sorts of metals; it’s now commonly thought of as the name for corrosion, tarnishing and reactions with all metals, not just iron-based ones.
Almost every town centre in the UK has a statue that appears to be an odd colour – the only way to describe it is as a kind of milky shade of blue-green. This isn’t rust, as the statues are likely to be made from copper, brass or bronze. Bronze is a copper alloyed with tin, while brass is copper and zinc. There’s no recognisable iron content in there, but the copper-based metals still react with the air to form what’s called ‘patina’, which is just the aged look of the piece. Interestingly, this kind of reaction is to all intents and purposes superficial, as it only takes place on the surface, not at any deeper level in the material.
Aluminium is also a metal that can lose its initial shiny, silver lustre and dull over time. Aluminium oxide forms in the same kind of way as iron oxide, but what’s truly fascinating is that aluminium oxide is a more stable compound, which is less likely to continue corroding or reacting than the aluminium it sits on top of! Iron based metals will not form a protective layer, which means that given enough time, moisture and catalyst, iron will disappear away to nothing.
While there are some types of steel that are thought of as ‘rust-proof’, in truth items such as stainless steel and galvanised steel are more ‘rust-resistant’ than anything else. Exposure to hygroscopic compounds such as salt – that will suck moisture from the air and hold it in contact with the metal to be a catalyst for electrolysis – will eventually cause the steel to react and succumb.
Stainless steel uses chromium or nickel almost as a ‘sacrificial’ metal. The oxygen reacts with these elements first, instead of the iron and the resulting oxide compounds then act as a way to prevent corrosion of the iron, in the same way aluminium oxide does. Galvanised steel does a similar thing, but the steel is coated with zinc to form a resistant layer of zinc oxide.
While almost all metals on the Periodic Table will corrode, tarnish and react with their surroundings, it’s worth remembering that while all rust is corrosion, not all corrosion is rust!
FAQs
Only iron can rust. That means other metals that do not contain iron are not susceptible to rusting. This makes them ideal for outdoor placement, as they'll last much longer in natural conditions. Learn about which metals don't rust, as well as which metals do rust.
Why is rust a problem at the coast? ›
Rusting takes place with the presence of iron and water together. Near the coast, there is a lot of water. In addition, sodium chloride, salt, ionizes and is hydroscopic, both of which add to the problem. Hydroscopic means it absorbs moisture from the air, and the salt can then dissolve in the moisture.
Why is rusting problematic for people? ›
Rust and corrosion can release harmful chemicals and pollutants into the environment, causing environmental damage, whilst causing health hazards for workers and the public.
What is the problem with objects that have rusted? ›
Weakened Structure Probably the biggest problem from rust in metal items is structural weakness. As metal increasingly corrodes, it becomes weaker. Rust replaces strong, pure metal with a flaky powder. Rust is dangerous in metal components needed to support structures.
Do any metals not rust? ›
Copper, brass, and bronze do not rust for the same reason as aluminum. All three have a negligible amount of iron in them. Therefore no iron oxide, or rust, can form. However, copper can form a blue-green patina on its surface when exposed to oxygen over time.
Which metals will never rust? ›
10 Metals That Don't Rust
- Aluminum. Aluminum is one of the most commonly used metals on the planet, and it's arguably the most famous for not rusting. ...
- Brass. Brass does not rust for the same reason as aluminum. ...
- Bronze. ...
- Copper. ...
- Corten or Weathering Steel. ...
- Galvanized Steel. ...
- Gold. ...
- Platinum.
California Clean
A generally low amount of snow and ice means no salt on the roads. Coastal mountains prevent salty ocean air from reaching inland. However, even cars found by the coast would require consistent contact with ocean water to develop rust.
Do cars rust on the West Coast? ›
Ocean air and paint damage
According to the Colorado Department of Transportation, the combination of the sun and salt air near a coast can destroy a car's finish. That's because the hot sun increases the pores in the paint, which results in greater absorption of salty moisture — and ultimately, more corrosion.
Should I be worried about rust? ›
If scale rust is left untreated, it eventually evolves into the most destructive stage of rusting—rust holes. At this stage, the rust has eaten through the metal, leading to holes. Rust holes, especially on body panels near the suspension components or battery terminal, can cause severe damage and safety concerns.
Why does stainless steel not rust? ›
Stainless steel is a steel alloy that contains a minimum chromium content of 10.5%. The chromium reacts with the oxygen in the air and forms a protective layer that makes stainless steel highly resistant to corrosion and rust. At the moment, there are over 150 varieties of stainless steel in the market.
Rusty objects are a contributor to HAIs because of its irregular surfaces that are more likely to harbor dangerous bacteria. Each year, about 1 in 25 U.S. hospital patients are diagnosed with at least one infection related to hospital care alone, according to the Centers for Disease and Control Prevention (CDC).
How long does steel last outside? ›
The zinc coating of hot-dipped galvanized steel will last in the harshest soil is 35 to 50 years and in less corrosive soil 75 years or more. Although humidity affects corrosion, temperature itself has less of an impact.
Can rust infect other metals? ›
The short answer to this is No. Rust will not spread from one component to another and generally the reason that components that are close together will both rust is that they are both in the same conditions.
Can rust cause other metal to rust? ›
This can be a tricky question for some, but what it comes down to is no, rust is not contagious. If you have a flake or two of rust on an unaffected metal part, this does not mean it will soon start to rust. The issue does not lie with rust itself, but rather the reason rust occurred in the first place.
Does rust weaken metal? ›
Rust weakens the metal structure over time, compromising its strength and durability. This is mainly due to the loss of material from the metal surface. Rusty metal is more prone to deformation and load failure points.
How does rust affect different metals? ›
It makes them weaker, by replacing the strong iron or steel with flaky powder. Some oxides on some metals such as aluminum form just a thin layer on top which slows down further corrosion, but rust can slowly eat away at even the biggest piece of iron.
