75-DEGREES-C ISOTHERM OF THE RECIPROCAL QUATERNARY SYSTEM H3PO4-K2SO4-H2SO4-K3PO4-H2O - STUDY OF LIQUIDUS CURVES

The liquidus curves at 75 degrees C, 1 atm, of the system under consideration have been studied systematically by means of solubilities determined conductimetrically, and lines of constant water content have been deduced. The study used isoplethic sections chosen to complete data on previous measurements of limiting ternary systems and lines of double saturation. Four isoplethic sections: K2SO4-KH2PO4, K2SO4-K2HPO4, KHSO4-K2HPO4, and KHSO4-KH2PO4 were determined, the first two of which are quasi-ternary systems. A total of nine portions of the curves were measured to extend knowledge of the liquidus. The limiting curves in the field of KHSO4 and K-8(H2PO4)(1-X)(HSO4)(7-X) show curvature, which reveals retrograde solubility as a function of water content.