Coupled Experimental Study and Thermodynamic Modeling of GeO 2 and GeO 2 –CaO and GeO 2 –SiO 2 Binary Systems

ABSTRACT The phase diagram of the GeO 2 –CaO system was investigated using differential thermal–thermogravimetric analysis and the equilibration–quenching technique, followed by electron probe microanalysis and X‐ray diffraction. The Ca 2 Ge 7 O 16 compound was confirmed to be stable, and a eutectic reaction of L → GeO 2 (hex) + Ca 2 Ge 7 O 16 was identified in the GeO 2 ‐rich region. Based on the previous and present experimental data for the GeO 2 –CaO system and reliable literature data for the GeO 2 –SiO 2 system, thermodynamic optimization of both binaries was carried out. The GeO 2 –SiO 2 system was reoptimized to ensure internal consistency and improved agreement with experimental data relative to the previous assessment, based on refinements to the heat capacity of GeO 2 and the quartz solid‐solution model. The liquid phase was modeled using the Modified Quasichemical Model, and the quartz solid solution in the GeO 2 –SiO 2 system, in which Si 4+ and Ge 4+ cations are mixed over a single sublattice, was described using the Compound Energy Formalism. A single set of self‐consistent Gibbs energy functions for all phases in the GeO 2 –CaO and GeO 2 –SiO 2 systems was obtained, reproducing phase equilibria and thermodynamic properties over wide composition and temperature ranges. The optimized database provides a reliable foundation for thermodynamic modeling of GeO 2 –CaO–SiO 2 ternary and multicomponent oxide systems relevant to metallurgical recycling as well as ceramic‐glass design and processing.