Pure copper is not easy to rust. However, as long as it is exposed to the air in a humid environment, it will still rust and form basic copper carbonate, the chemical formula is Cu2(OH)2CO3, which is a substance produced by the reaction of copper with oxygen, carbon dioxide, water and other substances in the air. Called patina (patina). Heating in air will decompose to copper oxide, water and carbon dioxide. Copper reacts with O2, CO2, H2O in the air to rust to produce copper green Cu2(OH)2CO3. Heating can generate CuO, CO2, H2O. Chemical equation: Cu2(OH)2CO3→2CuO+CO2↑+H2O
The patina can be removed by soaking in dilute hydrochloric acid or selenium nitric acid, and then apply a protective film, such as paint or oil (edible oil), and place it in a dry place, paying attention to waterproofing.