Sodium Molybdate Corrosion Inhibitor Supplier

What Is Sodium Molybdate?

Sodium molybdate (Na₂MoO₄·2H₂O) is the sodium salt of molybdic acid — a white crystalline solid highly soluble in water. In water treatment chemistry, it is used as an anodic corrosion inhibitor for ferrous metals (carbon steel) in closed recirculating water systems and cooling water. Molybdate inhibitor mechanism: MoO₄²⁻ ions migrate to anodic sites on the steel surface where iron dissolution is occurring, react with Fe²⁺ ions to form an insoluble iron molybdate (FeMoO₄) passivation film, blocking further metal dissolution. This anodic passivation mechanism works best in combination with cathodic inhibitors (zinc, benzotriazole) in formulated corrosion inhibitor blends. Sodium molybdate is the most widely used non-toxic, non-chromate corrosion inhibitor for steel in closed loop water systems.

Application in Closed Loop and Cooling Water Systems

Sodium molybdate is the preferred corrosion inhibitor in closed loop chilled water and hot water systems because it does not biodegrade, does not form scale precipitates at high concentration, and offers very low mammalian toxicity (LD₅₀ > 4 g/kg oral). In closed systems (HVAC chilled water, heating circuits), molybdate is maintained at 50–200 mg/L MoO₄²⁻ combined with an azole (for copper protection) — this combination provides comprehensive corrosion protection for both mild steel and copper alloy components. Molybdate is compatible with azoles, HEDP, and zinc but incompatible with calcium ions at high concentration (calcium molybdate scale risk in hard water above ~150 mg/L Mo). In open recirculating cooling systems, molybdate is used where molybdate concentration can be maintained at cycles of concentration.

Environmental Advantages Over Chromate

A key advantage of sodium molybdate over conventional inhibitors (chromate, nitrite, zinc) is its environmental and health profile. Chromate inhibitors (historically the most effective) are acutely toxic, carcinogenic, and heavily regulated under environmental legislation — they have been replaced by molybdate in most new systems. Nitrite inhibitors are unstable under chlorine dosing and support bacterial activity. Molybdate is non-toxic, non-carcinogenic, and generally accepted in effluent discharge streams. Molybdate is listed as an acceptable corrosion inhibitor under many environmental and occupational health regulatory frameworks, making it the green inhibitor of choice for steel in closed water systems. Terracore Chemicals supplies sodium molybdate dihydrate in 25 kg bags across Southern Africa.