Final answer:
Internal CO₂ corrosion occurs when iron reacts with CO₂, leading to the formation of rust. It can be indicated by the presence of rust on iron surfaces, particularly in areas with scratches or imperfections in protective coatings.
Step-by-step explanation:
Internal CO₂ corrosion can be indicated by the formation of rust on iron surfaces. The presence of CO₂ in the environment, such as atmospheric CO₂ or carbon dioxide dissolved in water, can react with iron to form iron(II) ions (Fe²+). This oxidation process leads to the formation of rust.
For example, when small scratches or imperfections occur in protective coatings on iron surfaces, oxygen can be reduced at these spots (cathode), while iron is oxidized to Fe²+ at other areas (anode). The Fe²+ ions can then react with atmospheric oxygen, remote from the anode, resulting in the formation of rust.
This corrosion process can lead to significant structural damage and mechanical failure if left untreated.