Does Copper Rust? Why Does Copper Turn Green?

Copper is a widely used material across various industries. Its excellent electrical conductivity makes it stand out for making wires. Moreover, manufacturers consider it suitable for CNC machining. However, many still seem skeptical of its selection, fearing it will rust. This forced me to answer the question: Does copper rust?

 

Products made of such materials that are prone to rusting are not long-lasting. So manufacturers and even customers don’t like such materials. Therefore, knowing if copper rusts or not is crucial. It will help you know if this material is suitable for you or not. In this article, we will discuss the rusting or corrosion of copper. So, let’s get started!

 

What is Rust?

It might seem like a straightforward term, but almost everyone misinterprets it. Generally, rusting and corrosion are often considered the same, but this is incorrect. 

 

Rusting is a type of corrosion that occurs specifically with iron or iron-based materials. When iron reacts with oxygen, it makes reddish-brown flakes known as iron oxide (Fe₂O₃). This oxide layer, commonly known as rust, can deteriorate the quality of the materials. Materials without iron do not rust.

 

As you know, copper does not have iron in any proportion. So, it does not make an iron oxide layer. So the copper does not rust. Generally, people confuse rusting with corrosion. Corrosion is the deterioration of materials that happens due to chemical reactions. For example, if material remains in salty water, it starts to deteriorate and corrode. 

 

But this material is corroded but not rusted. Remember, every material can corrode, but rusting is specific to iron-containing materials. Corrosion is a broad category that induces material deterioration through any means. Conversely, rusting itself is a type of corrosion that happens in iron-containing materials, such as steel.

 

Does Copper Corrode?

Yes, copper materials can corrode. However, corrosion is not quick and can take years to start. For example, a copper-made product generally remains in good condition for the first 4 to 5 years. After that, corrosion begins to occur gradually due to moisture, salty water, and other factors.

 

When copper is exposed to air or moisture, it does not corrode immediately. Copper reacts with oxygen, resulting in a chemical reaction. As a result of this chemical reaction, a layer of copper oxide is formed. This copper oxide, CuO, remains on the surface of copper when exposed to carbon dioxide and other carbonates. 

 

Due to its exposure, the copper oxide layer becomes greenish. This green layer of copper oxide is called patina. Interestingly, this patina plays a key role in protecting the copper from corrosion. The patina on copper prevents any further moisture or oxygen from contacting it. 

 

Copper cannot react with oxygen and corrode, so these patina layers remain in good shape for many years. However, due to external factors such as heat and UV exposure, this thin patina layer begins to degrade over time. When this layer depletes, oxygen makes contact with copper. Copper reacts with it, and an oxidation reaction starts. 

 

The copper deteriorates before the second patine layer is formed. Before the layer is remade, some portion of the copper becomes corroded. However, this corrosion process in copper is very slow, and it takes many years for the material to deteriorate completely. Generally, copper-made products last in good condition for 7 to 25 years.

 

Why Does Copper Turn Green?

 

Copper turns green due to the formation of a patina layer. Actually, the copper color remains the same as before, i.e., an orange-green hue. An additional thin patina layer is formed on the surface of copper. This layer is green, and it is present on the copper. So, the copper looks more greenish.

 

The color of pure copper is generally a reddish-orange hue. When it comes into contact with oxygen, it forms layers of copper oxide. The color of copper oxide (CuO) is dark brown. However, this copper oxide layer remains exposed to carbon dioxide and sulfur compounds. Due to this, the color of copper oxide changes from dark brown to a greenish hue. 

 

This layer, known as patina, protects the copper surface from corrosion. The copper underneath the patina remains the same, i.e., a reddish-orange color. However, the patina on the surface of copper is greenish. Due to this, copper materials look more attractive.

 

With time, the patina layers start to weaken and deteriorate. Once this layer is destroyed, the original copper, which is reddish-orange in color, is revealed. This means the color of copper itself does not change. Instead, copper looks greenish due to a patina on its surface. However, the deterioration of the patina layer is not rapid and takes many years.

 

How Long Does It Take for Copper to Rust?

There is no fixed answer to the question regarding the lifespan of copper materials. It can last as short as 3 years or as long as 30 years. The lasting of copper materials depends on the care you take. Moreover, if the copper remains exposed to salty water or chemicals, it will corrode faster and vice versa.

 

As I said earlier, copper reacts with oxygen when it comes into contact with it. As a result of this reaction, the copper oxide layer is formed. Later, the color of this layer changes to green, which is called patina. It plays a key role in protecting the copper from corrosion. Moreover, other chemicals and salty water also cannot directly contact copper. 

 

The reason is that the patina covers the copper surface. As a result, it remains safe and lasts longer. However, you should care for copper and ensure the patina layer does not deteriorate. Moreover, you should not expose the copper-made product to heat or UV rays. Generally, copper lasts between 5 and 25 years with proper care and maintenance.

 

Relation of Patina (Corrosion) & CNC Machining of Copper

 

Copper is a popular metal for CNC machining. It has multiple good characteristics, which make it easy to cut and shape. However, its brittle patina layer can pose some challenges. Generally speaking, CNC machining of copper is a smooth and straightforward process.

 

Let’s drill down and discuss how corrosion affects copper’s CNC machining:

 

1- Surface Contamination Causes Tool Wear

As mentioned above, copper reacts with oxygen to form a patina layer. This layer is thin but very durable and strong. Moreover, it is also abrasive and more complex. Breaking and cutting this layer is not easy.

Therefore, CNC machining can be a bit more challenging when using copper with a patina layer. The tools that cut the materials can get damaged due to the hardness of the patina layer present on the surface of copper. Moreover, the precision of CNC machining is affected when tools first cut the patina layer and then cut copper material.

 

2- Inconsistent Cutting Behavior

If the material is smooth, the CNC machines can easily cut and shape it. However, cutting can be very challenging if the material is hard. The patine present on the copper surface is very hard. 

During cutting, cutters can misbehave and create the wrong cut. Remember, copper itself is soft, and patina is hard. So when cutters put more force on patina cutting, it cuts it. However, it cannot control it and may also create a wrong cut on the copper. This may result in inconsistent cutting quality.

 

3- Copper’s Non-Magnetic Nature Affects Chip Collection

This point isn’t about corrosion or patina but is essential for machining copper. As you know, copper is a non-magnetic metal that does not stick to magnets. The CNC machines have a chip evacuation system. 

When the material is cut, its pieces are attracted to the chip collection center, which is a magnet. However, when copper is cut, its pieces or chips do not collect at a single point. They don’t get attracted to the magnet present in chip evacuation centers. Therefore, the operator will need to remove those chips from the machines manually.

 

4- Friction Isn’t a Major Issue

Copper’s melting point is 1,085°C, which is considered a very high temperature. During CNC machining, cutting tools generate heat as they cut and shape copper materials. As copper’s melting point is very high, it is not affected by the heat produced by the cutters. Instead, copper has excellent thermal conductivity. So it dissipates the heat quickly and supports CNC machining.

 

Frequently Asked Questions

 

What Happens to Copper Instead of Rusting?

Copper does not rust, as it does not contain iron. However, it corrodes when exposed to salty water or other chemical reactions.

 

Is patina harmful to copper?

No! The patina layer is not harmful to copper materials. Instead, it is very beneficial for protecting and shielding copper against corrosion.

 

Will copper rust if it gets wet?

No, copper does not rust even if it gets wet. Instead, if copper remains in salty water for an extended period, it will undergo corrosion. However, this copper corrosion will be a very slow and time-consuming process.

 

Conclusion

 

Copper is a vital material in the manufacturing industry. Its usage is wide across various industries. Copper’s good conductivity makes it a top pick for wires and electronics. Despite its popularity, many seem confused by its rusting and corroding. 

 

It is generally believed that copper does not rust. Instead, copper metal undergoes corrosion over time. In this article, I also explained the formation of a patina layer, which protects copper from corrosion. You’ll also learn how corrosion affects CNC machining.