Title : Computer modeling of the Li,La,K||Cl phase diagram: Digital twins for pd variants, cross-validation of horizontal and vertical material balances, electrical conductivity & DTA spectra simulation
Abstract:
Chloride ternary systems based on LiCl–KCl are widely used as catalytic materials and as electrolytes in spent nuclear fuel reprocessing, where accumulation of lanthanides and actinides’ fission products occurs. However, traditional experimental determination of phase diagrams is resource-intensive, and published diagrams often contain graphical errors or inconsistencies due to the complexity of 3D spatial structures. To address these challenges, a comprehensive 3D computer modeling methodology has been developed. Within this approach, 3D computer model reproduces the geometric structure of a phase diagram according to a specific literature source. When conflicting data exist for the same ternary system, multiple digital twins are constructed, each representing one possible variant of its phase diagram structure. This enables direct visual comparison, detection of inconsistencies, and identification of which variant better corresponds to the fundamental laws of phase equilibria.
In the present work, this methodology is applied to the LiCl–LaCl3–KCl system, for which two substantially different versions of the phase diagram have been reported in the literature. The first version, based on thermodynamic optimization [Hao et al., J. Mol. Liq. 400 (2024) 124516], considers the formation of two compounds: K2LaCl5 (congruently melting) and K3La5Cl18 (incongruently melting). According to this source, the ternary system is characterized by two eutectic reactions (E₁ and E₂) and one quasi‑peritectic transformation (Q). The second version, based on direct experimental data [Song & Zheng, Acta Chim. Sinica 53 (1995) 978–984], also includes two compounds—K2LaCl5 and KLa3Cl10—but with different stoichiometry of the incongruently melting phase. Both models share the same topological prototype but differ fundamentally in the compound stoichiometry, coordinate systems (mole fractions vs. weight fractions; Kelvin vs. Celsius).
Beyond resolving inconsistencies between conflicting literature sources, 3D models of phase diagrams can enable cross‑validation of horizontal and vertical material balances, as demonstrated for the analogous Li,M,K||Cl (M=Nd,Pr,La) systems, providing coherence analysis of polythermal sections at fixed temperatures and for specific compositions. The methodology is equally applicable to catalytic materials design, where precise knowledge of phase equilibria guides synthesis and processing. Furthermore, the 3D models facilitate education by providing intuitive visualizations of complex phase relationships, allowing students to understand the family of eutectic‑type diagrams with different degrees of phase region degeneration and to recognize graphical errors in erroneous interpretations of experimental or computational data.
