Posted by HEDP 4 sodium, i.e., tetrasodium hydroxyethylidene diphosphonate (HEDP-Na4), is an organophosphonate scale and corrosion inhibitor, and its scale inhibition principle is mainly based on the following aspects:
1. Complexation
HEDP-Na4 can form stable complexes with many metal ions in water (such as iron, copper, zinc, etc.). This complexation reduces the opportunity for metal ions to combine with anions in water (such as carbonate, sulfate, etc.) to form scale, thus effectively inhibiting the generation of scale.
2. Dissolve metal surface oxides
HEDP-Na4 also has the ability to dissolve metal surface oxides. Oxides formed on metal surfaces are often precursors to scale formation, and by dissolving these oxides, HEDP-Na4 further reduces scale generation.
3. Dispersing effect
HEDP-Na4 can be dissociated into negatively charged ions in water, which can be adsorbed on the micro grains of microsoluble inorganic salts, or connect several micro grains into loose particle clusters with a considerable distance from each other. This dispersion prevents the particles from contacting each other and growing up, thus avoiding the formation of scale.
4. Lattice distortion or twisting
The molecular structure of HEDP-Na4 allows it to be embedded inside the crystal, resulting in distortion or twisting of the crystal structure. This mechanism of action makes the crystal growth process disturbed and difficult to form a complete and dense scale layer, thus achieving the effect of scale inhibition.
5. Stability
HEDP-Na4 is stable under strong alkaline conditions, which enables it to maintain its scale inhibition effect in many industrial applications (e.g., circulating cooling water systems, low-pressure boilers, etc.). In contrast, some other types of scale inhibitors may gradually hydrolyse or lose activity under strong alkaline conditions.
In summary, HEDP-Na4 achieves its scale inhibition effect in water treatment through a combination of mechanisms, such as complexation, dissolution of metal surface oxides, dispersion, lattice distortion or twisting and good stability. This makes HEDP-Na4 one of the widely used scale and corrosion inhibitors in electric power, chemical industry, metallurgy and other industries.