Water Treatment Chemicals

Corrosion inhibitors are chemical products that, when added to water or any other process fluid, slow down the rate of corrosion. They are typically classified based on their mode of action:

• Anodic Inhibitors: Form a protective film over anodic surfaces by blocking the electrochemical reaction that causes the metal to dissolve.
  • Examples of oxidizing anodic inhibitors: chromates (CrO₄^2-), nitrites (NO₂^-).
  • Examples of non-oxidizing anodic inhibitors: phosphates (PO₄^3-), benzoates (C₇H₅O₂^-), molybdates (MoO₄^2-).
• Cathodic Inhibitors: Soluble at average water pH but form a protective layer over cathodic surfaces. Examples include zinc ions (Zn²⁺), polyphosphates (with Ca²⁺), and phosphonates (with Ca²⁺).
• Combined Anodic/Cathodic Inhibitors: Commercial formulations often combine both types to reduce the overall amount required. Zinc-chromates, for instance, use zinc (purely cathodic) and chromates (anodic inhibitors).

The effectiveness of corrosion inhibitors depends on water chemistry and physical conditions such as temperature and flow velocity.