Inhibitor Compounds

Inhibitors may be inorganic or organic materials. Inorganic inhibitors are usually crystalline salts including sodium chromates, phosphates and molybdates. The negative ions of these materials are responsible for reducing corrosion. Organic inhibitors include sodium sulfonates, phosphonates, mercaptobenzotriazole (MBT), and aliphatic or aromatic compounds containing positively charged amine groups. Inhibitors may be produced into liquids, solids including hard and soft materials, or vapors to be used in numerous applications. Their greatest use comes in systems involved with liquid heating or cooling systems. Inhibitors are introduced into the liquid media and the concentration and/or the corrosion rate of the system monitored to maintain an optimal concentration level. Vapor phase inhibitors including morpholine and hydrazine are introduced into steam environments such as boilers, to increase the pH level in the system. The selection of inhibitors will depend upon the metal requiring protection, as well as the operating environment. Various inhibitors used to protect metals in some environments are listed in Table 50.