Nitrites

Nitrites are used as corrosion inhibitors most frequently in closed recirculating cooling water systems. As anodic inhibitors, they induce the metal to form its own impervious film for passivation. In the presence of high concentrations of chlorides or sulfates, it is necessary to maintain a higher nitrite concentration so as to minimize the detrimental effect of film penetration caused by these anions.

Nitrites inhibit corrosion of aluminum, tin and ferrous materials at pH levels of 9 to 10. For this reason, such pH buffers as borates are normally included in nitrite formulations. To properly protect systems containing copper or copper alloys, specific copper corrosion inhibitors are required.

Nitrite acts as a nutrient for various microorganisms; it can be oxidized to nitrate or reduced to ammonia by certain bacteriological species. It has been proposed that nitrite may be reduced to nitrogen under certain bacteriological conditions.

Nitrates

Sodium nitrate has been used to protect solder and aluminum. It also increases the corrosion inhibition of steel when used with other corrosion inhibitors such as nitrites. Its use in cooling water treatment is primarily in closed recirculating systems.