ATMP·Na4 (Tetra Sodium Salt of Amino Trimethylene Phosphonic Acid) is a highly effective, neutral-pH organophosphonic acid salt used as a scale and corrosion inhibitor. By neutralizing the aggressive acidity of standard ATMP acid with sodium ($\text{Na}^+$) ions, this formulation provides a much safer handling profile and outstanding compatibility in specific water treatment systems.
1. Chemical Structure & Identification
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CAS Number: 20592-85-2
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Molecular Formula: C3H7NO9P3Na4
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Molecular Weight: 387.0 g/mol
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Chemical Nature: It is the partial sodium salt of ATMP. While full neutralization yields a hexasodium salt (Na6), the tetrasodium variant hits a sweet spot, balancing a completely neutral pH with high chemical activity.
2. Standard Technical Specifications
Commercial ATMP·Na4 is typically supplied as an aqueous liquid or a concentrated solid powder.
| Parameter | Liquid Specification | Solid Powder Specification |
| Appearance | Colorless to pale-yellow liquid | White crystalline or granular powder |
| Active Component (as acid) | 20.3% – 21.7% | 50.0% – 54.0% |
| Active Component (as salt) | 31.0% – 36.0% | 78.0% |
| Total Phosphorus (PO43-) | 15.7% | 38.0% |
| pH (1% water solution) | 6.5 – 7.5 | 6.5 – 7.5 |
| Density (20°C) | 1.20 – 1.30g/cm3 | N/A |
3. Key Performance Properties
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Superb Calcium Carbonate (CaCO3) Inhibition: Like its parent acid, ATMP·Na4 excels at preventing calcium carbonate scaling. It works via threshold inhibition, meaning even small, sub-stoichiometric concentrations can distort growing crystal lattices and prevent them from baking onto pipes.
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Neutral pH Edge: Raw ATMP acid is highly corrosive to equipment and skin. ATMP·Na4 dissolves at a neutral pH (6.5–7.5), completely eliminating the need to pre-neutralize or handle hazardous acids at the blending facility.
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Excellent Lattice Distortion & Dispersion: It adsorbs directly onto micro-crystallites of scale, creating a negative surface charge that forces particles to repel each other. This keeps minerals safely suspended in water flow rather than forming dense deposits.
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Zinc Compatibility: Unlike highly acidic phosphonates that can destabilize or aggressively react with zinc salts, the neutral nature of ATMP·Na4 makes it excellent for blending directly with zinc-based corrosion inhibitors.
4. Industrial Applications
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Circulating Cooling Water Systems: Extensively used in industrial cooling towers, power plants, and oil refineries to control scaling in high-hardness water loops.
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Textile Dyeing & Printing Auxiliaries: Functions as an effective chelating agent, stabilizer, and metal-ion scavenger in dyeing baths, preventing trace minerals from throwing off fabric shades.
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Industrial Cleaners & Detergents: Added to metal surface cleaners, bottle-washing compounds, and industrial detergents to soften water and enhance soil removal.
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Oilfield Water Injection: Injected into downhole oilfield systems to stabilize calcium ions and prevent heavy mineral encrustations in pipelines.
5. Formulation & Synergy
In practical industrial applications, ATMP·Na4 is rarely used alone. It is usually combined with other water treatment agents to create a synergistic, multi-functional composite:
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With Polycarboxylic Dispersants: Mixed with PAAS (Polyacrylic Acid Sodium), HPMA, or MA/AA to handle both crystalline scale and amorphous suspended solids (like silt or clay).
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With Corrosion Inhibitors: Combined with zinc sulfate or azoles (like BTA/TTA) to provide robust, dual-action scale and corrosion protection for steel and copper metallurgy.