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The most commonly used method to protect cooling systems from corrosion of copper alloys is the use of azoles. Azoles are a class of organic compounds that possess the ability to form a protective film on copper surfaces, which serves as a barrier against corrosion. This protective layer significantly reduces the rate of electrochemical reactions that lead to metal deterioration, particularly in environments where oxygen and other corrosive agents may be present.

Azoles are especially effective for copper alloys due to their specific chemical structure, which allows them to adsorb onto the metal surface and inhibit corrosion without significantly impacting the overall chemistry of the cooling water. They are often used in combination with other corrosion inhibitors to provide a more comprehensive protective strategy.

While molybdate, orthophosphate, and phosphonate are also used as corrosion inhibitors in various contexts, they do not offer the same level of targeted protection for copper alloys as azoles do. Molybdate is more effective for ferrous metals and might not provide the same benefits for copper, whereas orthophosphate and phosphonate can influence the scale formation and phosphate precipitation but are not specifically tailored for copper corrosion protection. Therefore, azoles stand out as the optimal choice for safeguarding copper alloys in cooling systems.