<![CDATA[This review aims to comprehensively evaluate the thermodynamic properties and phase stability of ultra-high-temperature ceramics (UHTCs) using the CALPHAD (CALculation of PHAse Diagrams) approach. UHTCs exhibit exceptional properties, including high melting points, superior hardness, and thermal shock resistance, making them promising materials for aerospace applications and high-temperature scientific instrumentation. The study focuses on phase equilibria in binary systems, including Zr–B, Hf–B, Ta–B, Mo–B, Zr–C, Hf–C, Ta–C, and Mo–C, as well as multicomponent Zr–Hf–(Ta,Mo)–C systems. Despite their technological importance, comprehensive thermodynamic assessments remain limited, particularly due to insufficient experimental data and incomplete coverage in existing thermodynamic databases. The primary objective is to assess thermodynamic properties, including Gibbs energy of formation, enthalpy of formation, heat capacity, and phase stability, through computational thermodynamic modeling. The CALPHAD methodology is employed to calculate component activities, construct phase diagrams, and map phase equilibria across different compositions and temperatures. Temperature-dependent Gibbs energy functions are used to predict equilibrium phase relationships, phase transformations, and critical equilibrium points. The analysis integrates available experimental information with computational models to establish consistent thermodynamic descriptions of relevant ceramic systems. Furthermore, the review identifies knowledge gaps and highlights the need for additional experimental investigations to improve thermodynamic databases and validate predicted phase equilibria. Ultimately, this assessment provides a theoretical foundation for optimizing UHTC compositions, understanding high-temperature phase behavior, and supporting the development of advanced ceramic materials with enhanced thermal and mechanical performance for extreme operating environments, particularly in aerospace engineering.]]>
