An anode is a metallic node through which electric current passes and eventually meets with a cathode. Oxidation occurs at an anode. For a copper anode, this means that electrons leave the copper atoms and eventually join with other atoms at the cathode. Passivation is a process by which materials become inert, or inactive; in this case the copper anodes lose their oxidation potential, stopping the flow of electrons.
Slime Layer
Sulfuric acid acts to dissolve the copper at the anode, sending electrons to the cathode and leaving copper ions behind. As the anode loses electrons and dissolves, a slime layer of sulfur bonded with copper ions forms on the anode surface. This layer of copper sulfate grows with time, slowly passivizing the anode.
Chromate Conversion Coating
Sometimes, electrochemists intentionally passivate a material so that it doesn't oxidize when exposed to the elements. This can inhibit corrosion and make the substance more durable. A common passivation technique called chromate conversion coating is commonly used with copper. The chemist places the material to be coated in a chromium-based bath until its surface has been effectively passivated.
Impurities in the Copper
Impurities in the copper, released during the oxidization process, can also contribute to the slime-like film on the anode's surface. Some common copper impurities include selenium and tellurium. Copper selenide forms a ring-like structure on the anode that contributes to passivation.
Tags: anode surface, copper anode, copper ions, with copper
