Polyacrylate-HEDP

Early antisealants used sodium hexametaphosphate (SHMP) as a threshold agent to inhibit the growth of calcium carbonate and sulfate-based scales.6 Most antisealants on the market today contain sulfonate, phosphate, or carboxylic acid functional groups. Perhaps the most effective antisealants today contain and blend of polyacrylic acid (PAA) and phosphoric acid or polyacrylate and a hydroyethylidene diphosphonate (HEDP).12 The polyacrylate-HEDP blends also claim to have good dispersion qualities toward silts and clays.12 Some new inhibitors include a chelant and disper-ant to keep suspended solids such as iron and manganese oxides in solution. These newer antisealants are generally more effective than SHMP for a variety of potential scales.6... 

In the 1960s organic phosphates (phosphonates) were introduced, such as ATMP and HEDP, which proved to be superior to phosphates in many ways, including their thermal stability and sequestering power. Although the corrosion inhibition of carbon steel, derived solely from phosphonates, remains a weak feature, this can be enhanced by syneigizing with other inhibitors, such as zinc. Like the polyacrylates, phosphonate chemistry has endured and remains a second basic DCA constituent of almost all modern formulations. 

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