pyrophosphate

Also known as polyphosphate, a polymer made from an orthophosphate by dehydration with heat. Orthophosphates are phosphoric acid (H3PO4) salts, where 1, 2 or 3 of the hydrogen ions are neutralized. Sodium acid pyrophosphate (SAPP) is a clay deflocculant and treatment for cement contamination. For clay deflocculation, polyphosphates are limited by the temperature at which they hydrolyze back to orthophosphates, although several that performed up to 280°F [138°C] have been documented in the literature (see reference).

Reference: Sikorski CF and Weintritt DJ: "Polyphosphate Drilling-Mud Thinners Deserve Second Look," Oil & Gas Journal 81, no. 27 (July 4, 1983): 71-78.