Hydroxyethylidene Diphosphonic Acid CAS#2809-21-4 - Product Characteristics and Usuage of HEDP

HEDP (Hydroxyethylidene Diphosphonic Acid) is an organic phosphonic acid with strong corrosion-inhibiting properties. It forms stable complexes with metal ions such as iron, copper, and zinc, and is capable of dissolving oxides from metal surfaces. Even at temperatures up to 250 °C, HEDP maintains effective corrosion and scale inhibition. It remains stable under high pH conditions, resists hydrolysis, and does not easily decompose under light or heat. Compared with other organic phosphonic acids (or salts), HEDP offers superior resistance to acids, alkalis, and chlorine oxidation. In aqueous systems, it can form a six-membered chelate ring with metal ions, particularly calcium, giving it strong scale-inhibiting effects and a clear solubility threshold. When combined with other water treatment agents, it demonstrates excellent synergistic performance.

HEDP in solid form is a high-purity grade product, well-suited for use in extremely cold climates, and is particularly suitable for cleaning formulations and daily chemical additives in the electronics industry.

Applications of Hydroxyethylidene Diphosphonic Acid
HEDP serves as a scale and corrosion inhibitor in boilers, heat exchangers, and water treatment systems, as well as a complexing agent in non-cyanide electroplating, a chelating agent in soap production, and a cleaning additive for metals and non-metals.

It is widely used in boiler water, circulating cooling water, and oilfield water injection treatment. Often formulated with polyhydroxy acid-based scale inhibitors and dispersants, HEDP enhances overall efficiency. In electroplating, it acts as a complexing agent for non-cyanide systems, providing strong adhesion of copper plating directly onto steel, with smooth coatings and good color quality. A typical plating bath formulation includes 100–120 ml/L of HEDP (60% solution) and 15–20 g/L of copper sulfate. Pre-treatment by immersing components in a 1–2% HEDP solution activates surfaces, improving plating results.

HEDP is also applied as a new chlorine-free electroplating complexing agent, a main stabilizer for circulating cooling water systems, and an effective corrosion and scale inhibitor. It is considered a non-phosphoric, environmentally friendly water treatment option. Similar compounds include ATMP (Amino Trimethylene Phosphonic Acid) and EDTMP (Ethylene Diamine Tetramethylene Phosphonic Acid). Since their development in the late 1960s and validation in the 1970s, organic polyphosphonic acids have significantly advanced water treatment technology. Compared to organic polyphosphates, these compounds exhibit greater chemical stability, resistance to hydrolysis, high-temperature tolerance, and strong anti-fouling efficiency, even at low dosages. They function both as cathodic corrosion inhibitors and non-stoichiometric scale inhibitors.

Recommended Usage

As a scale inhibitor: 1–10 mg/L

As a corrosion inhibitor: 10–50 mg/L

As a cleaning agent: 1000–2000 mg/L
It is often used in conjunction with polycarboxylic acid scale inhibitors and dispersants for optimal results.