The oxidation of copper

In order to work better with copper, the typical chemical processes associated with non-ferrous metals are important to understand. Significantly, this is about the oxidation of copper. This can be desired, but also absolutely undesirable. What has happened with the oxidation of copper, we have described here for you.

Oxidation and corrosion of metals in general

Most metals have the property of oxidizing due to their chemical composition. This oxidation can be completely different. In iron and ferrous steels, this oxidation process is widely known as rust. It decomposes the metal slowly and evenly from outside to inside in iron oxide - rust just.

The protective oxide layer

For some metals, however, something happens during oxidation. It forms an oxide layer on the actual metal. Thus, neither water nor oxygen reaches the metal and it is protected against further corrosion. This process is also referred to as passivation or the resulting oxide layer as a passive layer.

Conditions for the oxidation of copper

However, with each metal, special circumstances must match each other so that such an oxide layer can form well and optimally. The corrosion of copper pipes to form a passive layer is influenced, for example, by the pH of the water, the carbon and oxygen content.

Under a pH value of 6 and at low or poor oxygen saturation can not form a sufficient oxide layer (copper I oxide). Instead, it comes to a very specific form of corrosion - on, or better said, in the copper pipe uses insidious pitting.

Without passivation it comes to pitting

Due to a sufficient oxidation, in which a good passive layer is formed, the corrosion can not continue. Especially fatal in pitting is the fact that the punctiform holes are so small that hardly or no oxygen can get into them. As a result, the pitting in the copper is again significantly accelerated. Seen from the outside, the copper surface looks almost intact.

After the formation of the oxide layer, a patina forms

But if a good oxidation layer has formed, the process is not yet complete. Copper carbonates are now deposited on this deep brown oxide layer (copper without passive layer is light brown metallic shiny, copper with an oxide layer against it deep brown matt). This is noticeable by the typical intense green color, often referred to as verdigris.

Especially on facades such as churches or other structures, this effect may well be desirable. This natural copper patina protects the underlying copper very well against further, destructive corrosion such as pitting. You can patinate copper artificially, so the copper age.

This oxidation layer can also be removed

However, it may just as well happen that this passive layer is undesirable, for example, if you want to paint the copper. By etching copper, you can completely remove the oxidation layer. A mechanical solution would be grinding the copper or copper sheet.

Tips & Tricks

As a protective layer Zaponlacke be used if the copper effect is to be retained. In addition, you can also galvanize the copper. With electrolysis, the copper can first be nickel-plated and then chrome-plated, especially if the mechanical properties such as the softness of the metal are in the foreground of your requirements.

Video Board: Oxidation of Copper