The Thermodynamics of Melts and the State Diagram of the Nickel–Calcium System

• Published in: Russian Journal of Physical Chemistry A Vol. 94; no. 8; pp. 1526 - 1531
• Main Authors: Volodin, V. N., Tuleushev, Yu. G.
• Format: Journal Article
• Language: English
• Published: Moscow Pleiades Publishing 01-08-2020; Springer Nature B.V
• Subjects: Boiling points; Calcium; Chemical Thermodynamics and Thermochemistry; Chemistry; Chemistry and Materials Science; Distillation; Endothermic reactions; Liquid-vapor equilibrium; Melts; Nickel; Numerical integration; Physical Chemistry; Vapor pressure; nickel; alloy; calcium; boiling; distillation; state diagram; condensation; phase boundaries; vapor pressure
• ISSN: 0036-0244; 1531-863X
• DOI: 10.1134/S0036024420080312

Partial and integral thermodynamic functions of the mixing and evaporation of nickel–calcium melts are calculated from the values of calcium vapor pressure at 900–1300°C (1173–1573 K), determined using the boiling points approach (isothermal version), and those of nickel, found via numerical integration of the Gibbs–Duhem equation. It is established that the formation of alloys containing up to 65.5 mol % calcium (the rest is nickel) is exothermic, while at higher Ca content the process is endothermic. The excess entropy of mixing is negative up to a Ca content of ∼64 mol %, testifying to a certain ordering in the melts due to the existence of associates. Using data on the pressure of a saturated vapor of calcium and nickel, the state diagram is supplemented by the fields of the coexistence of melts and vapor at atmospheric pressure and in vacuums of 1.33 and 0.7 kPa. The location of the boundaries of the fields of vapor–liquid equilibrium confirms the possibility of separation of the Ni–Ca melts by distillation in a vacuum.