Excess heat capacity in liquid binary alkali-fluoride mixtures.

Area of Science:

• Physical Chemistry
• Materials Science
• Thermodynamics

Background:

• Understanding thermodynamic properties of molten salt systems is crucial for applications like nuclear reactors and thermal energy storage.
• Accurate heat capacity data is essential for modeling and predicting the behavior of these high-temperature materials.

Purpose of the Study:

• To measure enthalpy increments and determine molar heat capacity functions for LiF-KF, LiF-RbF, and LiF-CsF binary systems.
• To investigate the excess heat capacity and its dependence on composition and cation radius in these molten salt solutions.
• To compare experimental results with ideal behavior predictions.

Main Methods:

• Drop calorimetry was employed to measure enthalpy increments at high temperatures (884 K to 1382 K).
• Ten samples with varying compositions across the three binary systems were prepared and analyzed.
• An encapsulating technique using laser-welded nickel containers protected the calorimeter from corrosive fluoride vapor.

Main Results:

• Molar heat capacity functions were derived from the experimental enthalpy increment data.
• Excess heat capacity functions were determined for the entire composition range of the liquid solutions.
• A clear dependence of excess heat capacity on cation radius was observed, increasing in the order LiF-NaF < LiF-KF < LiF-RbF < LiF-CsF.

Conclusions:

• The study provides valuable thermodynamic data for LiF-based binary molten salt systems.
• Excess heat capacity is a significant factor in these non-ideal solutions and is directly influenced by the size of the alkali metal cation.
• The findings contribute to the fundamental understanding of molten salt behavior and can inform material selection for high-temperature applications.