Thermophysical properties and atomic structure of liquid Zr-Nb alloys investigated by electrostatic levitation and molecular dynamics simulation

The investigation of the thermophysical properties of liquid Zr-Nb alloys holds great significance for theoretical research and technical application in liquid physics. However, the high temperatures involved make their experimental measurement challenging. In this study, the densities of liquid Zr-x wt.% Nb (x= 1.0, 2.5, 6.0) alloys were examined by electrostatic levitation and molecular dynamics calculation. Remarkably, the alloys achieved maximum undercooling of 335 K, 311 K and 326 K, respectively. Correspondingly, the densities are 6.20, 6.22 and 6.26 g·cm⁻³ at the liquidus temperatures (T _L), respectively. The corresponding temperature coefficients are 2.61 × 10⁻⁴, 2.75 × 10⁻⁴ and 2.84 × 10⁻⁴ g·cm⁻³·K⁻¹, respectively. Notably, the experimental density results align well with the simulated results. Moreover, the molar volume (V _m), thermal expansion coefficient (α) and diffusion coefficient (D) were derived based on the experimental data and simulations. The thermal expansion coefficients reduce linearly with decreasing temperature. The analysis of the pair distribution function, coordination number (CN) and the radial distribution function reveals the temperature-dependent evolution of the atomic structure. The CN _total and CN _Zr-Zr initially increase and then decrease with decreasing temperature, while the change trends for CN _Zr-Nb and CN _Nb-Nb varied among the three alloys. The radial distribution function of three liquid alloys reveals that the atomic number density increases as the temperature drops. Additionally, the total diffusion coefficients decrease with the reduction of temperature and the rise of Nb content from 1.0 wt.% Nb to 6.0 wt.% Nb.