Computer Coupling of Phase Diagrams and Thermochemistry 32 (2008) 43–48 www.elsevier.com/locate/calphad Thermodynamic investigation of the KBr–TbBr 3 system Weiping Gong a,∗ , Slobodan Gadzuric b , Jean Pierre Bros c , Marcelle Gaune-Escard c , Yong Du a a State Key Laboratory of Powder Metallurgy, Central South University, Changsha 410083, Hunan, PR China b Faculty of Natural Science, Department of Chemistry, University of Novi Sad, Trg. D. Obradovia 3, 21000 Nov Sad, Serbia c Ecole polytechnique, Mecanique Energetique, Technopole de Chateau-Gombert, 5 rue Enrico Fermi, 13453 Marseille cedex 13, France Received 11 January 2007; received in revised form 2 December 2007; accepted 8 December 2007 Available online 3 January 2008 Abstract Experimental data for the system KBr–TbBr 3 were subjected to a critical thermodynamic assessment using the CALPHAD approach. The thermodynamic parameters of the KBr and TbBr 3 compounds were taken from the SGTE recommended database and the authors’ previous assessment, respectively. To reach a self-consistent thermodynamic description for the constituent phases in the system, the experimental heat capacity data for the intermediate compound K 3 TbBr 6 were reassessed. A two-sublattice ionic solution model for the liquid, denoted as (K + ) P : (Br − , TbBr −3 6 , TbBr 3 ) Q , was employed to represent phase diagram and enthalpy of mixing data. To make our investigation on K 3 TbBr 6 more accurate, a new and complementary experimental DSC determination regarding the compound was carried out. Our thermodynamic description, compatible with ones for other lanthanide–alkali halide systems, resulted in a good agreement between the calculated and experimental data. c  2007 Elsevier Ltd. All rights reserved. Keywords: Two-sublattice ionic solution model; Excess Gibbs energy; KBr–TbBr 3 ;K 3 TbBr 6 1. Introduction Lanthanide halide–alkali metal halide systems play a significant role in everyday life and in many industrial applications. They are extracted and processed into metals, magnetic alloys, oxides and other forms. Extraction and processing of lanthanides are largely based on molten salt technologies. Many processes, particularly those dealing with reprocessing of spent nuclear fuel or nuclear waste processing [1], are still under development. Lanthanides are also attractive components in high intensity discharge lamps [2,3], highly efficient light sources with energy saving features [4–6] and optical devices [7–10]. Whatever the targeted technological application, basic knowledge such as the thermodynamic and transport properties of lanthanide compounds and their mixtures with alkali metal halides is required for process development and optimization. However these data are scarce and not easily accessible in the literature. As a consequence, intensive efforts are being made at an ∗ Corresponding author. Tel.: +86 731 8877824. E-mail address: weiping gong@mail.csu.edu.cn (W. Gong). international level both on research and development aspects and also on data bank development [11]. The present work is part of our wide and systematic research program performed on the physicochemical properties of lanthanide halide–alkali metal halide systems. 2. Evaluation of experimental data in the literature 2.1. Phase diagram data From differential scanning calorimetry (DSC) combined with electrical conductivity and spectroscopic measurements, Rycerz and Gaune-Escard [12] established the KBr–TbBr 3 phase diagram over the whole composition range for the first time. They reported three intermediate compounds K 3 TbBr 6 , K 2 TbBr 5 and KTb 2 Br 7 , and two eutectics located at about x TbBr 3 = 0.163 (mole fraction), T = 885 K, and x TbBr 3 = 0.433, T = 697 K, respectively. K 3 TbBr 6 was reported to undergo a solid phase transition at 691 K and to melt congruently at 983 K with the corresponding enthalpies 0.8 and 4.8 kJ/mol. K 2 TbBr 5 showed a solid phase transition at 658 K and melted incongruently at 725 K. KTb 2 Br 7 formed from 0364-5916/$ - see front matter c  2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.calphad.2007.12.001