Heats of solution/substitution in TlNO 3 and CsNO 3 crystals and in RbNO 3 and CsNO 3 crystals from heats of transition: the complete phase diagrams of TlNO 3–CsNO 3 and RbNO 3–CsNO 3 systems

Abstract

From measurements of the decrease in the heat (enthalpy) of transition in the solid phase using differential scanning calorimetry, the apparent molar heats of solution, slope Δ H t/ x, the partial molar heats of solution at infinite dilution, χ, and the heats of solution, Δ H s °, of Tl + in CsNO 3 crystal and Cs + in TlNO 3 crystal and Rb + in CsNO 3 crystal and Cs + in RbNO 3 crystal along with their recovered lattice energies, Δ H L °, are reported. Δ H s ° of Tl + and Rb + in CsNO 3 crystal are each found to be negligible or zero representing an ideal solid solution, i.e. Δ H mix=0. The complete phase diagrams of the TlNO 3–CsNO 3 and RbNO 3–CsNO 3 systems with details of the sub-solidus regions are included. The properties of Tl (1− x) Cs x NO 3 and Rb (1− x) Cs x NO 3 compositions are discussed in terms of a ‘mixed crystal’ or ‘crystalline solid solution’ in relation to parallel compositions of Tl (1− x) Rb x NO 3.