Phase Equilibrium in the System RbCl-NdCl3-HCl(13.26 %)-H2O at 298.15 K and Standard Molar Enthalpy of Formation of New Solid Phase Compound

摘要

The solubility of the quaternary system RbCl-NdCl3-HCl(13.26 %)-H2O at 298.15 K was determined, and the corresponding equilibrium diagram was constructed. The quaternary system consists of three equilibrium solid phases, RbCl, RbNdCl4·4H2O (1:1 type), and NdCl3·6H2O. The new solid phase compound RbNdCl4·4H2O was found to be congruently soluble in the system. The compound RbNdCl4·4H2O was characterized by X-ray diffraction, X-ray diffraction single crystal structure analysis, thermogravimetry, and differential thermogravimetry. It belongs to an orthorhombic system, with space group P21212, a = 0.6986(6) nm, b = 1.1319(1) nm, c = 0.6665(6) nm, Dc = 2.795 g·cm~(-3), and Z = 2. The compound loses its crystal water by one step at (370 to 474) K. The standard molar enthalpy of solution of RbNdCl4·4H2O in deionized water was measured to be -(26.97 ± 0.24) kJ·mol~(-1) by heat conduction microcalorimetry. Its standard molar enthalpy of formation was calculated to be -(2732.3 ± 1.0) kJ·mol~(-1).