Solid–liquid phase equilibria of Ca(H2PO2)2–CaCl2–H2O and Ca(H2PO2)2–NaH2PO2–H2O ternary systems at 298.15 K

Calcium hypophosphite has been widely used as an anti-corrosive agent, flame retardant, fertilizer, assistant for Ni electroless plating, and animal nutrition supplements. High purity calcium hypophosphite can be synthesized via the replacement reaction of sodium hypophosphite and calcium chloride. In this work, the solid–liquid phase equilibria of Ca(H2PO2)2–CaCl2–H2O and Ca(H2PO2)2 –NaH2PO2–H2O ternary systems at 298.15 K were studied experimentally via the classical isothermal solubility equilibrium method, and the phase diagrams for these two systems were obtained. It was found that two solid salts of Ca(H2PO2)2 and CaCl2∙6H2O, and three solid salts of Ca(H2PO2)2, NaCa(H2PO2)3, and NaH2PO2∙H2O can form in the corresponding systems under phase-equilibrium conditions. Ca(H2PO2)2 has low solubility in the Ca(H2PO2)2–CaCl2–H2O system. NaCa(H2PO2)3 occupies a large solid field in the ternary system of Ca(H2PO2)2 –NaH2PO2–H2O.