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Silicates are sometimes used in open cooling tower systems for corrosion control, particularly for mild steel and galvanized surfaces, but they’re not always the first choice and come with some trade-offs.

1. What Are Silicates in Water Treatment?

1. 1. Typically added as sodium silicate (Na₂SiO₃)
   2. Acts as an anodic corrosion inhibitor
   3. Forms a passivating film of silica (SiO₂) on metal surfaces

2. How Silicates Help With Corrosion Control
   1. Anodic Protection

1. 1. Silicate promotes the formation of a thin, glassy film of silica on the metal surface.
   2. This film:

1. Reduces metal ion dissolution
2. Slows the anodic corrosion reaction

• Can inhibit localized pitting on mild steel and galvanized steel

3. pH Buffering

1. 1. Silicate has a mild alkaline buffering effect, which helps keep pH in a corrosion-resistant range (usually around 8–9).
   2. This helps maintain passivation, especially when dealing with acidic influences like CO₂ or biological activity.

4. Typical Use in Open Cooling Systems

5. Limitations and Considerations

1. 1. Soft and inconsistent film: Silicate films are not as robust as phosphate/zinc/PBTC films
   2. Precipitation risk: At high pH or with calcium, silicates can precipitate as calcium silicate scale
   3. Lower corrosion protection than zinc or phosphonates under high TDS or high temp
   4. Not effective for copper/brass — doesn’t form protective films on those metals
   5. May interfere with clarity in systems (can cause turbidity/cloudiness)

6. When Are Silicates a Good Choice?

1. 1. When phosphorus discharge limits are strict (phosphate- and zinc-free programs)
   2. In mild steel-dominant systems
   3. In soft or moderate hardness waters
   4. When biostability is important (silicates don’t feed bacteria like phosphates might)

7. Often Used In:

1. 1. Some municipal systems with tight P-discharge limits
   2. HVAC systems with low temperature, low cycles, or reclaimed water
2. Galvanized towers (in startup phases to prevent white rust)