What products are included in copper corrosion inhibitors?

Copper corrosion inhibitors are a specialized class of chemicals designed to protect copper and its alloys (like brass and bronze) from degradation in various environments, primarily in aqueous systems.

Here is a breakdown of the products included in copper corrosion inhibitors, categorized by their chemical nature and primary application:

1. Organic Corrosion Inhibitors (Most Common in Water Treatment)

These form a protective film on the metal surface and are widely used in cooling water systems, HVAC, and closed loops.

Azoles (Heterocyclic Nitrogen Compounds): This is the gold standard and most important group for copper protection.

Benzotriazole (BTA): The most widely used, effective across a broad pH range (6-11). Forms a very stable, persistent chemisorbed film.

Tolyltriazole (TTA): Similar to BTA but with methyl groups, offering slightly better solubility and comparable performance. Often used interchangeably.

Mercaptobenzothiazole (MBT): Highly effective, especially in alkaline conditions. However, it is sensitive to oxidizing biocides (like chlorine) and can degrade.

Phosphonates: While primarily used for calcium scale inhibition, some also provide auxiliary corrosion protection.

1-Hydroxyethylidene-1,1-diphosphonic Acid (HEDP): Offers mild corrosion inhibition for copper in addition to its excellent scale inhibition properties.

Other Organic Compounds:

Imidazole and its derivatives.

Fatty amines and amines salts (used in steam condensate systems).

2. Inorganic Corrosion Inhibitors

These work by passivating the metal surface or forming a protective layer.

Ortho- and Polyphosphates: Sodium hexametaphosphate, tripolyphosphate, etc. They form a thin protective film of calcium phosphate/cupric phosphate on the metal. Often used in potable water systems.

Silicates (Sodium Silicate/Meta-silicate): Used in potable water and some cooling systems. They form a glass-like protective layer.

Molybdates (Sodium Molybdate): Environmentally friendly, oxidizing inhibitors that promote the formation of a protective ferric oxide/molybdate complex layer. Also protects copper alloys.

Nitrites (Sodium Nitrite): Primarily for ferrous metals in closed loops, but can be used in multi-metal systems with azoles for copper protection. Note: Their use is declining due to environmental and health concerns (nitrosamines formation).

3. Mixed/Multi-Functional Products & Formulations

In practice, copper inhibitors are rarely used alone. They are components of comprehensive treatment programs.

All-in-One Formulations: Commercial water treatment products often combine:

A primary copper inhibitor (e.g., Tolyltriazole).

A scale inhibitor (e.g., Phosphinopolycarboxylate, HEDP).

A general steel corrosion inhibitor (e.g., a phosphonate, polymer).

pH buffers and dispersants.

Synergistic Blends: For example, Azole + Phosphonate blends are common, as the phosphonate can help stabilize the protective film and inhibit scale under the film.

Primary Applications & Selection Factors

Cooling Water Systems (Open & Closed): Azoles (BTA/TTA) are dominant, often fed alongside scale and dispersant programs. They are compatible with common biocides (though sensitive to high chlorine).

HVAC & Chiller Systems: Critical systems with copper tubes always require a dedicated copper inhibitor like BTA/TTA.

Potable Water Systems: Regulations are strict. Common inhibitors include orthophosphates and silicates, which are approved for use in drinking water.

Metalworking Fluids & Automotive Coolants: BTA and other organic inhibitors are standard components to protect radiators (brass/copper/solder).

Key Factors for Choosing a Copper Corrosion Inhibitor:

System pH: BTA/TTA work in neutral to alkaline pH. MBT works best in alkaline conditions.

Presence of Oxidizing Biocides: Chlorine/bromine can degrade some inhibitors like MBT. "Chlorine-stable" or "bromine-stable" azole formulations are available.

Water Chemistry: High hardness or suspended solids can interfere with film formation.

Environmental & Regulatory Requirements: This dictates the use of phosphates, heavy metals (like zinc), or nitrites.

Multi-Metal Compatibility: The program must also protect steel, aluminum, and other metals present in the system.

In summary, while Benzotriazole (BTA) and Tolyltriazole (TTA) are the cornerstone products for dedicated copper protection, effective corrosion control in real-world systems typically involves formulated blends that address scaling and corrosion of all metals in the system.